TY - THES A1 - Klar, Jochen T1 - A detailed view of filaments and sheets of the warm-hot intergalactic medium T1 - Eine detaillierte Ansicht der Filamente und Ebenen des warm-heißen intergalaktischen Mediums N2 - In the context of cosmological structure formation sheets, filaments and eventually halos form due to gravitational instabilities. It is noteworthy, that at all times, the majority of the baryons in the universe does not reside in the dense halos but in the filaments and the sheets of the intergalactic medium. While at higher redshifts of z > 2, these baryons can be detected via the absorption of light (originating from more distant sources) by neutral hydrogen at temperatures of T ~ 10^4 K (the Lyman-alpha forest), at lower redshifts only about 20 % can be found in this state. The remain (about 50 to 70 % of the total baryons mass) is unaccounted for by observational means. Numerical simulations predict that these missing baryons could reside in the filaments and sheets of the cosmic web at high temperatures of T = 10^4.5 - 10^7 K, but only at low to intermediate densities, and constitutes the warm-hot intergalactic medium (WHIM). The high temperatures of the WHIM are caused by the formation of shocks and the subsequent shock-heating of the gas. This results in a high degree of ionization and renders the reliable detection of the WHIM a challenging task. Recent high-resolution hydrodynamical simulations indicate that, at redshifts of z ~ 2, filaments are able to provide very massive galaxies with a significant amount of cool gas at temperatures of T ~ 10^4 K. This could have an important impact on the star-formation in those galaxies. It is therefore of principle importance to investigate the particular hydro- and thermodynamical conditions of these large filament structures. Density and temperature profiles, and velocity fields, are expected to leave their special imprint on spectroscopic observations. A potential multiphase structure may act as tracer in observational studies of the WHIM. In the context of cold streams, it is important to explore the processes, which regulate the amount of gas transported by the streams. This includes the time evolution of filaments, as well as possible quenching mechanisms. In this context, the halo mass range in which cold stream accretion occurs is of particular interest. In order to address these questions, we perform particular hydrodynamical simulations of very high resolution, and investigate the formation and evolution of prototype structures representing the typical filaments and sheets of the WHIM. We start with a comprehensive study of the one-dimensional collapse of a sinusoidal density perturbation (pancake formation) and examine the influence of radiative cooling, heating due to an UV background, thermal conduction, and the effect of small-scale perturbations given by the cosmological power spectrum. We use a set of simulations, parametrized by the wave length of the initial perturbation L. For L ~ 2 Mpc/h the collapse leads to shock-confined structures. As a result of radiative cooling and of heating due to an UV background, a relatively cold and dense core forms. With increasing L the core becomes denser and more concentrated. Thermal conduction enhances this trend and may lead to an evaporation of the core at very large L ~ 30 Mpc/h. When extending our simulations into three dimensions, instead of a pancake structure, we obtain a configuration consisting of well-defined sheets, filaments, and a gaseous halo. For L > 4 Mpc/h filaments form, which are fully confined by an accretion shock. As with the one-dimensional pancakes, they exhibit an isothermal core. Thus, our results confirm a multiphase structure, which may generate particular spectral tracers. We find that, after its formation, the core becomes shielded against further infall of gas onto the filament, and its mass content decreases with time. In the vicinity of the halo, the filament's core can be attributed to the cold streams found in other studies. We show, that the basic structure of these cold streams exists from the very beginning of the collapse process. Further on, the cross section of the streams is constricted by the outwards moving accretion shock of the halo. Thermal conduction leads to a complete evaporation of the cold stream for L > 6 Mpc/h. This corresponds to halos with a total mass higher than M_halo = 10^13 M_sun, and predicts that in more massive halos star-formation can not be sustained by cold streams. Far away from the gaseous halo, the temperature gradients in the filament are not sufficiently strong for thermal conduction to be effective. N2 - Im Rahmen der kosmologischen Strukturbildung entstehen durch Gravitationsinstabilitäten Flächen, Filamente und schließlich Halos. Interessanterweise befinden sich zu jedem Zeitpunkt der kosmologischen Entwicklung der Großteil der Baryonen nicht in den Halos, sondern in den Filamenten und Ebenen des intergalaktischen Mediums. Während diese Baryonen bei höheren Rotverschiebungen (z ~ 2) noch in Form durch die Absorbtion von Licht (von weit entfernteren Quellen) durch neutralen Wasserstoff bei einer Temperatur von T ~ 10^4 K beobachtbar sind (Lyman-Alpha Wald), gilt dies bei niedrigeren Rotverschiebungen für nur noch ca. 20 % der Baryonen. Der überwiegende Teil (ca. 50-70 % der gesamten baryonischen Masse) sind bisher noch nicht direkt beobachtbar. Numerische Simulationen sagen jedoch voraus, das sich diese Baryonen in den Filamenten und Flächen des kosmischen Netzes befinden. Die entsprechende Gasverteilung zeichnet sich durch hohe Temperaturen T = 10^5 - 10^7 K und geringe bis mittlere Dichten aus und wird als warm-heißes intergalaktisches Medium (WHIM) bezeichnet. Die hohen Temperaturen entstehen in Folge der Bildung von Stoßwellen und der darauf folgenden Erhitzung des Gases (shock-heating). Das WHIM ist daher hochgradig ionisiert und sein verlässlicher Nachweis stellt eine große Herausforderung für die beobachtende Kosmologie dar. Neuere hydrodynamische Simulationen zeigen, dass sich bei höheren Rotverschiebungen von z ~ 2 Gasströmungen entlang der Filamente bilden, die massive Galaxien mit erheblichen Mengen an relativ kaltem Gas (T ~ 10^4 K) versorgen können. Dies hätte einen erheblichen Einfluss auf die Sternentstehung in diesen Galaxien. Es ist daher von grundsätzlichem Interesse, die spezifischen hydro- und thermodynamischen Bedingungen in den Strukturen des WHIM zu untersuchen. Sowohl Dichte- und Temperaturprofile als auch Geschwindigkeitsfelder prägen spektroskopische Beobachtungen. Eine mögliche Mehrphasenstruktur des WHIM könnte daher als Indikator in beobachtenden Studien dienen. Im Zusammenhang mit den kalten Strömen ist es besonders interessant, Prozesse zu untersuchen die den Zufluss von kaltem Gas zu den Galaxien regulieren. Dies umfasst die Zeitentwicklung des Anteils an kaltem Gas in den Filamenten, sowie mögliche Mechanismen, die zum Versiegen des Zuflusses von kaltem Gas auf die Galaxienscheibe führen. Um diese Zusammenhänge zu erforschen, führen wir spezielle hydrodynamische Simulationen mit sehr hoher Auflösung durch, die zu ausgewählten, wohldefinierten Strukturen führen, die das WHIM charakterisieren. Wir beginnen mit einer ausführlichen Untersuchung des eindimensionalen Kollaps einer sinusförmigen Störung (pancake formation). Hierbei untersuchen wir den Einfluss von Strahlungkühlung, Heizung durch den intergalaktischen UV Hintergrund, Wärmeleitung, sowie von kleinskaligen Störungen, welche dem kosmologischen Störungsspektrum folgen. Wir benutzen hierbei eine Reihe von Simulationen, welche die Längenskala der anfänglichen Störung L als Parameter verwenden. Für L ~ 2 Mpc/h führt der Kollaps zur Ausbildung einer Stoßwelle. Zusätzlich entsteht als Folge der Strahlungskühlung und der Heizung durch den UV Hintergrund ein relativ dichter und kalter isothermer Kern. Mit ansteigendem L wird dieser Kern dichter und kompakter. Durch Wärmeleitung reduziert sich die räumliche Ausdehnung des Kerns. Für L ~ 30 Mpc/h führt dies zu einem Verschwinden des Kerns. Mit der Erweiterung unserer Methodik auf dreidimensionale Simulationen, entsteht nun eine Konfiguration, welche aus wohldefinierten Flächen, Filamenten und einem gasförmigen Halo besteht. Für L > 4 Mpc/h, erhalten wir Filamente, die vollständig durch Akkretionsschocks begrenzt sind. Wie in unseren eindimensionalen Simulationen weisen auch sie einen isothermen Kern auf. Dies legt nahe, dass das WHIM eine Mehrphasenstruktur besitzt und mögliche Spektralsignaturen erzeugen kann. Nach seiner Entstehung ist der Kern gegen weiteren Zufluss von Gas abgeschirmt und seine Masse reduziert sich mit der Zeit. In der direkten Umgebung des Halos entspricht der Kern des Filamentes den oben angesprochenen kalten Strömen. Unsere Untersuchung zeigt, dass diese während der gesamten Entwicklung des Halos existent sind. In der weiteren Entwicklung werden sie durch den expandierenden Akkretionsschock des Halos verengt. Ab einer Skala von L > 6 Mpc/h kann Wärmeleitung zu einem Verschwinden des Zustroms von kaltem Gas führen. Diese Skala entspricht Halos mit einer Gesamtmasse von M_halo = 10^13 M_sun. Galaxien, die sich in noch massiveren Halos bilden, können daher nicht durch kalte Ströme mit Gas für die Sternentstehung versorgt werden. Im Filament, weit außerhalb des gasförmigen Halos, sind die Temperaturgradienten zu klein, um effiziente Wärmeleitung zu ermöglichen. KW - Kosmologie KW - Hydrodynamik KW - Intergalaktisches Medium KW - cosmology KW - hydrodynamics KW - intergalactic medium Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-58038 ER - TY - JOUR A1 - Tepper-Garcia, Thor A1 - Richter, Philipp A1 - Schaye, Joop T1 - Absorption signatures of warm-hot gas at low redshift - ne viii JF - Monthly notices of the Royal Astronomical Society N2 - At z < 1 a large fraction of the baryons is thought to reside in diffuse gas that has been shock-heated to high temperatures (10 (5)-10 (6) K). Absorption by the 770.41, 780.32 A doublet of Ne viii in quasar spectra represents a unique tool to study this elusive warm-hot phase. We have developed an analytic model for the properties of Ne viii absorbers that allows for an inhomogeneous metal distribution. Our model agrees with the predictions of a simulation from the OverWhelmingly Large Simulations project indicating that the average line-of-sight metal-filling fraction within the absorbing gas is low (c(L) similar to 0.1). Most of the Ne viii in our model is produced in low-density, collisionally ionized gas (n(H) = 10(-6)-10(-4) cm(-3), T = 10 (5)-10 (6) K). Strong Ne viii absorbers (log(10)(N-NeVIII/cm(-2))14), like those recently detected by Hubble Space Telescope/Cosmic Origins Spectrograph, are found to arise in higher density gas (n(H) greater than or similar to 10(-4) cm(-3), T approximate to 5 x 10 (5) K). Ne viii cloudlets harbour only 1 per cent of the cosmic baryon budget. The baryon content of the surrounding gas (which has similar densities and temperatures as the Ne viii cloudlets) is a factor c(-1)L higher. We conclude that Ne viii absorbers are robust probes of shock-heated diffuse gas, but that spectra with signal-to-noise ratios S/N > 100 would be required to detect the bulk of the baryons in warm-hot gas. KW - methods: analytical KW - methods: numerical KW - galaxies: formation KW - intergalactic medium KW - quasars: absorption lines KW - cosmology: theory Y1 - 2013 U6 - https://doi.org/10.1093/mnras/stt1712 SN - 0035-8711 SN - 1365-2966 VL - 436 IS - 3 SP - 2063 EP - 2081 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Tepper-Garcia, Thorsten A1 - Richter, Philipp A1 - Schaye, Joop A1 - Booth, C. M. A1 - Vecchia, Claudio Dalla A1 - Theuns, Tom A1 - Wiersma, Robert P. C. T1 - Absorption signatures of warm-hot gas at low redshift o vi JF - Monthly notices of the Royal Astronomical Society N2 - We investigate the origin and physical properties of O vi absorbers at low redshift (z = 0.25) using a subset of cosmological, hydrodynamical simulations from the OverWhelmingly Large Simulations (OWLS) project. Intervening O vi absorbers are believed to trace shock-heated gas in the warm-hot intergalactic medium (WHIM) and may thus play a key role in the search for the missing baryons in the present-day Universe. When compared to observations, the predicted distributions of the different O vi line parameters (column density, Doppler parameter, rest equivalent width W-r) from our simulations exhibit a lack of strong O vi absorbers, a discrepancy that has also been found by Oppenheimer & Dave. This suggests that physical processes on subgrid scales (e.g. turbulence) may strongly influence the observed properties of O vi systems. We find that the intervening O vi absorption arises mainly in highly metal enriched (10-1 < Z/Z(circle dot) less than or similar to 1) gas at typical overdensities of 1 < /<<>> less than or similar to 102. One-third of the O vi absorbers in our simulation are found to trace gas at temperatures T < 105 K, while the rest arises in gas at higher temperatures, most of them around T = 105.3 +/- 0.5 K. These temperatures are much higher than inferred by Oppenheimer & Dave, probably because that work did not take the suppression of metal-line cooling by the photoionizing background radiation into account. While the O vi resides in a similar region of (, T)-space as much of the shock-heated baryonic matter, the vast majority of this gas has a lower metal content and does not give rise to detectable O vi absorption. As a consequence of the patchy metal distribution, O vi absorbers in our simulations trace only a very small fraction of the cosmic baryons (< 2 per cent) and the cosmic metals. Instead, these systems presumably trace previously shock-heated, metal-rich material from galactic winds that is now mixing with the ambient gas and cooling. The common approach of comparing O vi and H i column densities to estimate the physical conditions in intervening absorbers from QSO observations may be misleading, as most of the H i (and most of the gas mass) is not physically connected with the high-metallicity patches that give rise to the O vi absorption. KW - methods: numerical KW - galaxies: formation KW - intergalactic medium KW - quasars: absorption lines KW - cosmology: theory Y1 - 2011 U6 - https://doi.org/10.1111/j.1365-2966.2010.18123.x SN - 0035-8711 VL - 413 IS - 1 SP - 190 EP - 212 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Tepper-Garcia, Thorsten A1 - Richter, Philipp A1 - Schaye, Joop A1 - Booth, C. M. A1 - Dalla Vecchia, Claudio A1 - Theuns, Tom T1 - Absorption signatures of warm-hot gas at low redshift: broad H?i Lya absorbers JF - Monthly notices of the Royal Astronomical Society N2 - We investigate the physical state of H?i absorbing gas at low redshift (z = 0.25) using a subset of cosmological, hydrodynamic simulations from the OverWhelmingly Large Simulations project, focusing in particular on broad (bHI=40 km s-1) H?i Lya absorbers (BLAs), which are believed to originate in shock-heated gas in the warm-hot intergalactic medium (WHIM). Our fiducial model, which includes radiative cooling by heavy elements and feedback by supernovae and active galactic nuclei, predicts that by z = 0.25 nearly 60?per cent of the gas mass ends up at densities and temperatures characteristic of the WHIM and we find that half of this fraction is due to outflows. The standard H?i observables (distribution of H?i column densities NH?I, distribution of Doppler parameters bHI, bHINH?I correlation) and the BLA line number density predicted by our simulations are in remarkably good agreement with observations. BLAs arise in gas that is hotter, more highly ionized and more enriched than the gas giving rise to typical Lya forest absorbers. The majority of the BLAs arise in warm-hot [log?(T/?K) similar to 5] gas at low (log?? < 1.5) overdensities. On average, thermal broadening accounts for at least 60?per cent of the BLA linewidth, which in turn can be used as a rough indicator of the thermal state of the gas. Detectable BLAs account for only a small fraction of the true baryon content of the WHIM at low redshift. In order to detect the bulk of the mass in this gas phase, a sensitivity at least one order of magnitude better than achieved by current ultraviolet spectrographs is required. We argue that BLAs mostly trace gas that has been shock heated and enriched by outflows and that they therefore provide an important window on a poorly understood feedback process. KW - methods: numerical KW - galaxies: formation KW - intergalactic medium KW - quasars: absorption lines KW - cosmology: theory Y1 - 2012 U6 - https://doi.org/10.1111/j.1365-2966.2012.21545.x SN - 0035-8711 VL - 425 IS - 3 SP - 1640 EP - 1663 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Richter, Philipp A1 - Wakker, Bart P. A1 - Fechner, Cora A1 - Herenz, Peter A1 - Tepper-Garcia, T. A1 - Fox, Andrew J. T1 - An HST/COS legacy survey of intervening Si III absorption in the extended gaseous halos of low-redshift galaxies JF - Climate : open access journal N2 - Aims. Doubly ionized silicon (Si III) is a powerful tracer of diffuse ionized gas inside and outside of galaxies. It can be observed in the local Universe in ultraviolet (UV) absorption against bright extragalactic background sources. We here present an extensive study of intervening Si III-selected absorbers and study the properties of the warm circumgalactic medium (CGM) around low-redshift (z <= 0.1) galaxies. Methods. We analyzed the UV absorption spectra of 303 extragalactic background sources, as obtained with the Cosmic Origins Spectrograph (COS) on-board the Hubble Space Telescope (HST). We developed a geometrical model for the absorption-cross section of the CGM around the local galaxy population and compared the observed Si III absorption statistics with predictions provided by the model. We also compared redshifts and positions of the absorbers with those of similar to 64 000 galaxies using archival galaxy-survey data to investigate the relation between intervening Si III absorbers and the CGM. Results. Along a total redshift path of Delta z approximate to 24, we identify 69 intervening Si III systems that all show associated absorption from other low and high ions (e.g., H I, Si II, Si IV, C II, C IV). We derive a bias-corrected number density of dN/dz(Si III) = 2.5 +/- 0.4 for absorbers with column densities log N(Si III) > 12.2, which is similar to 3 times the number density of strong Mg II systems at z = 0. This number density matches the expected cross section of a Si III absorbing CGM around the local galaxy population with a mean covering fraction of < f(c)> = 0.69. For the majority (similar to 60 percent) of the absorbers, we identify possible host galaxies within 300 km s(-1) of the absorbers and derive impact parameters rho < 200 kpc, demonstrating that the spatial distributions of Si III absorbers and galaxies are highly correlated. Conclusions. Our study indicates that the majority of Si III-selected absorbers in our sample trace the CGM of nearby galaxies within their virial radii at a typical covering fraction of similar to 70 percent. We estimate that diffuse gas in the CGM around galaxies, as traced by Si III, contains substantially more (more than twice as much) baryonic mass than their neutral interstellar medium. KW - galaxies: halos KW - galaxies: formation KW - intergalactic medium KW - quasars: absorption lines Y1 - 2016 U6 - https://doi.org/10.1051/0004-6361/201527038 SN - 1432-0746 VL - 590 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Chen, Hsiao-Wen A1 - Johnson, Sean D. A1 - Straka, Lorrie A. A1 - Zahedy, Fakhri S. A1 - Schaye, Joop A1 - Muzahid, Sowgat A1 - Bouche, Nicolas A1 - Cantalupo, Sebastiano A1 - Marino, Raffaella Anna A1 - Wendt, Martin T1 - Characterizing circumgalactic gas around massive ellipticals at z approximate to 0.4-III. BT - the galactic environment of a chemically pristine Lyman limit absorber JF - Monthly notices of the Royal Astronomical Society N2 - This paper presents a study of the galactic environment of a chemically pristine (<0.6 per cent solar metallicity) Lyman Limit system (LLS) discovered along the sightline towards QSO SDSSJ 135726.27+043541.4 (Z(QSO) = 1.233) at projected distance d = 126 physical kpc (pkpc) from a luminous red galaxy (LRG) at z = 0.33. Combining deep Hubble Space Telescope images, MUSE integral field spectroscopic data, and wide-field redshift survey data has enabled an unprecedented, ultradeep view of the environment around this LRG-LLS pair. A total of 12 galaxies, including the LRG, are found at d less than or similar to 400 pkpc and line-of-sight velocity Delta v < 600 km S-1 of the LLS, with intrinsic luminosity ranging from 0.001 L-* to 2 L-* and a corresponding stellar mass range of M-star approximate to 10(7-11) M-circle dot. All 12 galaxies contribute to a total mass of M-star = 1.6 x 10(11) M-circle dot with approximate to 80 per cent contained in the LRG. The line-of-sight velocity dispersion of these galaxies is found to be sigma (group) = 230 km s(-1) with the centre of mass at d(group) = 118 pkpc and line-of-sight velocity offset of Delta v(group) = 181 km s(-1) from the LLS. Three of these are located at d less than or similar to 100 pkpc from the LLS, and they are all faint with intrinsic luminosity less than or similar to 0.02 L-* and gas-phase metallicity of approximate to 10 per cent solar in their interstellar medium. The disparity in the chemical enrichment level between the LLS and the group members suggests that the LLS originates in infalling intergalactic medium and that parts of the intergalactic gas near old and massive galaxies can still remain chemically pristine through the not too distant past. KW - galaxies: elliptical and lenticular, cD KW - galaxies: formation KW - intergalactic medium KW - quasars: absorption lines Y1 - 2019 U6 - https://doi.org/10.1093/mnras/sty3513 SN - 0035-8711 SN - 1365-2966 VL - 484 IS - 1 SP - 431 EP - 441 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Marino, Raffaella Anna A1 - Cantalupo, Sebastiano A1 - Lilly, Simon J. A1 - Gallego, Sofia G. A1 - Straka, Lorrie A. A1 - Borisova, Elena A1 - Pezzulli, Gabriele A1 - Bacon, Roland A1 - Brinchmann, Jarle A1 - Carollo, C. Marcella A1 - Caruana, Joseph A1 - Conseil, Simon A1 - Contini, Thierry A1 - Diener, Catrina A1 - Finley, Hayley A1 - Inami, Hanae A1 - Leclercq, Floriane A1 - Muzahid, Sowgat A1 - Richard, Johan A1 - Schaye, Joop A1 - Wendt, Martin A1 - Wisotzki, Lutz T1 - Dark Galaxy Candidates at Redshift similar to 3.5 Detected with MUSE JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - Recent theoretical models suggest that the early phase of galaxy formation could involve an epoch when galaxies are gas rich but inefficient at forming stars: a "dark galaxy" phase. Here, we report the results of our Multi-Unit Spectroscopic Explorer (MUSE) survey for dark galaxies fluorescently illuminated by quasars at z > 3. Compared to previous studies which are based on deep narrowband (NB) imaging, our integral field survey provides a nearly uniform sensitivity coverage over a large volume in redshift space around the quasars as well as full spectral information at each location. Thanks to these unique features, we are able to build control samples at large redshift distances from the quasars using the same data taken under the same conditions. By comparing the rest-frame equivalent width (EW0) distributions of the Ly alpha sources detected in proximity to the quasars and in control samples, we detect a clear correlation between the locations of high-EW0 objects and the quasars. This correlation is not seen in other properties, such as Ly alpha luminosities or volume overdensities, suggesting the possible fluorescent nature of at least some of these objects. Among these, we find six sources without continuum counterparts and EW0 limits larger than 240 angstrom that are the best candidates for dark galaxies in our survey at z > 3.5. The volume densities and properties, including inferred gas masses and star formation efficiencies, of these dark galaxy candidates are similar to those of previously detected candidates at z approximate to 2.4 in NB surveys. Moreover, if the most distant of these are fluorescently illuminated by the quasar, our results also provide a lower limit of t - 60 Myr on the quasar lifetime. KW - galaxies: formation KW - galaxies: high-redshift KW - galaxies: star formation KW - intergalactic medium KW - quasars: emission lines KW - quasars: general Y1 - 2018 U6 - https://doi.org/10.3847/1538-4357/aab6aa SN - 0004-637X SN - 1538-4357 VL - 859 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Worseck, Gábor A1 - Khrykin, Ilya Sergeevich A1 - Hennawi, Joseph F. A1 - Prochaska, J. Xavier A1 - Farina, Emanuele Paolo T1 - Dating individual quasars with the He II proximity effect JF - Monthly notices of the Royal Astronomical Society N2 - Constraints on the time-scales of quasar activity are key to understanding the formation and growth of supermassive black holes (SMBHs), quasar triggering mechanisms, and possible feedback effects on their host galaxies. However, observational estimates of this so-called quasar lifetime are highly uncertain (t(Q) similar to 10(4)-10(9) yr), because most methods are indirect and involve many model-dependent assumptions. Direct evidence of earlier activity is gained from the higher ionization state of the intergalactic medium (IGM) in the quasar environs, observable as enhanced Ly alpha transmission in the so-called proximity zone. Due to the similar to 30 Myr equilibration time-scale of He II in the z similar to 3 IGM, the size of the He II proximity zone depends on the time the quasar had been active before our observation t(on) <= t(Q), enabling up to +/- 0.2 dex precise measurements of individual quasar on-times that are comparable to the e-folding time-scale t(S) <= 44 Myr of SMBH growth. Here we present the first statistical sample of 13 quasars whose accurate and precise systemic redshifts allow for measurements of sufficiently precise He II quasar proximity zone sizes between similar or equal to 2 and similar or equal to 15 proper Mpc from science-grade Hubble Space Telescope (HST) spectra. Comparing these sizes to predictions from cosmological hydrodynamical simulations post-processed with 1D radiative transfer, we infer a broad range of quasar on-times from t(on) less than or similar to 1Myr to t(on) > 30 Myr that does not depend on quasar luminosity, black hole mass, or Eddington ratio. These results point to episodic quasar activity over a long duty cycle, but do not rule out substantial SMBH growth during phases of radiative inefficiency or obscuration. KW - intergalactic medium KW - quasars: absorption lines KW - quasars: general KW - quasars: supermassive black holes KW - dark ages, reionization, first stars Y1 - 2021 U6 - https://doi.org/10.1093/mnras/stab1685 SN - 0035-8711 SN - 1365-2966 VL - 505 IS - 4 SP - 5084 EP - 5103 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Guber, Christoph R. A1 - Richter, Philipp T1 - Dust depletion of Ca and Ti in QSO absorption-line systems JF - Wiley Interdisciplinary Reviews : Water N2 - Aims. To explore the role of titanium-and calcium-dust depletion in gas in and around galaxies, we systematically study Ti/Ca abundance ratios in intervening absorption-line systems at low and high redshift. Methods. We investigate high-resolution optical spectra obtained by the UVES instrument at the Very Large Telescope (VLT) and spectroscopically analyze 34 absorption-line systems at z <= 0.5 to measure column densities (or limits) for Ca II and Ti II. We complement our UVES data set with previously published absorption-line data on Ti/Ca for redshifts up to z similar to 3.8. Our absorber sample contains 110 absorbers including damped Lyman alpha systems (DLAs), sub-DLAs, and Lyman-Limit systems (LLS). We compare our Ti/Ca findings with results from the MilkyWay and the Magellanic Clouds and discuss the properties of Ti/Ca absorbers in the general context of quasar absorption-line systems. Results. Our analysis indicates that there are two distinct populations of absorbers with either high or low Ti/Ca ratios with a separation at [Ti/Ca] approximate to 1. While the calcium-dust depletion in most of the absorbers appears to be severe, the titanium depletions are mild in systems with high Ti/Ca ratios. The derived trend indicates that absorbers with high Ti/Ca ratios have dust-to-gas ratios that are substantially lower than in the Milky Way. We characterize the overall nature of the absorbers by correlating Ti/Ca with other observables (e.g., metallicity, velocity-component structure) and by modeling the ionization properties of singly-ionized Ca and Ti in different environments. Conclusions. We conclude that Ca II and Ti II bearing absorption-line systems trace predominantly neutral gas in the disks and inner halo regions of galaxies, where the abundance of Ca and Ti reflects the local metal and dust content of the gas. Our study suggests that the Ti/Ca ratio represents a useful measure for the gas-to-dust ratio and overall metallicity in intervening absorption-line systems. KW - quasars: absorption lines KW - dust, extinction KW - galaxies: abundances KW - galaxies: ISM KW - intergalactic medium Y1 - 2016 U6 - https://doi.org/10.1051/0004-6361/201628466 SN - 1432-0746 VL - 591 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Khrykin, Ilya S. A1 - Hennawi, Joseph F. A1 - Worseck, Gabor T1 - Evidence for short similar to 1 Myr lifetimes from the He II proximity zones of z similar to 4 quasars JF - Monthly notices of the Royal Astronomical Society N2 - The duration of quasar accretion episodes is a key quantity for distinguishing between models for the formation and growth of supermassive black holes, the evolution of quasars, and their potential feedback effects on their host galaxies. However, this critical time-scale, often referred to as the quasar lifetime, is still uncertain by orders of magnitude (⁠tQ≃0.01Myr−1Gyr⁠). Absorption spectra of quasars exhibiting transmission in the He  II Ly α forest provide a unique opportunity to make precise measurements of the quasar lifetime. Indeed, the size of a quasar’s He  II proximity zone, the region near the quasar where its own radiation dramatically alters the ionization state of the surrounding intergalactic medium (IGM), depends sensitively on its lifetime for tQ≲30Myr⁠, comparable to the expected e-folding time-scale for SMBH growth tS=45Myr⁠. In this study, we compare the sizes of He  II proximity zones in the Hubble Space Telescope (HST) spectra of six z ∼ 4 quasars to theoretical models generated by post-processing cosmological hydrodynamical simulations with a 1D radiative transfer algorithm. We introduce a Bayesian statistical method to infer the lifetimes of individual quasars which allows us to fully marginalize over the unknown ionization state of the surrounding IGM. We measure lifetimes 0.63+0.82−0.40 Myr and 5.75+4.72−2.74 Myr for two objects. For the other four quasars, large redshift uncertainties undermine our sensitivity allowing us to only place upper or lower limits. However, a joint analysis of these four systems yields a measurement of their average lifetime of ⟨tQ⟩=1.17+1.77−0.84 Myr. We discuss our short ∼1Myr inferred lifetimes in the context of other quasar lifetime constraints and the growth of SMBHs. KW - intergalactic medium KW - quasars: general KW - dark ages KW - reionization KW - first star Y1 - 2019 U6 - https://doi.org/10.1093/mnras/stz135 SN - 0035-8711 SN - 1365-2966 VL - 484 IS - 3 SP - 3897 EP - 3910 PB - Oxford University Press CY - Oxford ER - TY - JOUR A1 - Kulkarni, Girish A1 - Worseck, Gabor A1 - Hennawi, Joseph F. T1 - Evolution of the AGN UV luminosity function from redshift 7.5 JF - Monthly notices of the Royal Astronomical Society N2 - Determinations of the ultraviolet (UV) luminosity function of active galactic nuclei (AGN) at high redshifts are important for constraining the AGN contribution to reionization and understanding the growth of supermassive black holes. Recent inferences of the luminosity function suffer from inconsistencies arising from inhomogeneous selection and analysis of data. We address this problem by constructing a sample of more than 80 000 colour-selected AGN from redshift z= 0 to 7.5 using multiple data sets homogenized to identical cosmologies, intrinsic AGN spectra, and magnitude systems. Using this sample, we derive the AGN UV luminosity function from redshift z= 0 to 7.5. The luminosity function has a double power-law form at all redshifts. The break magnitude M-* shows a steep brightening from M-* similar to -24 at z = 0.7 to M-* similar to -29 at z = 6. The faint-end slope beta significantly steepens from -1.9 at z < 2.2 to -2.4 at z similar or equal to 6. In spite of this steepening, the contribution of AGN to the hydrogen photoionization rate at z similar to 6 is subdominant (< 3 per cent), although it can be non-negligible (similar to 10 per cent) if these luminosity functions hold down to M-1450 = -18. Under reasonable assumptions, AGN can reionize He II by redshift z = 2.9. At low redshifts (z < 0.5), AGN can produce about half of the hydrogen photoionization rate inferred from the statistics of HI absorption lines in the intergalactic medium. Our analysis also reveals important systematic errors in the data, which need to be addressed and incorporated in the AGN selection function in future in order to improve our results. We make various fitting functions, codes, and data publicly available. KW - galaxies: active KW - intergalactic medium KW - quasars: general KW - dark ages, reionization, first stars Y1 - 2019 U6 - https://doi.org/10.1093/mnras/stz1493 SN - 0035-8711 SN - 1365-2966 VL - 488 IS - 1 SP - 1035 EP - 1065 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Wisotzki, Lutz A1 - Bacon, Roland A1 - Blaizot, J. A1 - Brinchmann, Jarle A1 - Herenz, Edmund Christian A1 - Schaye, Joop A1 - Bouche, Nicolas A1 - Cantalupo, Sebastiano A1 - Contini, Thierry A1 - Carollo, C. M. A1 - Caruana, Joseph A1 - Courbot, J. -B. A1 - Emsellem, E. A1 - Kamann, S. A1 - Kerutt, Josephine Victoria A1 - Leclercq, F. A1 - Lilly, S. J. A1 - Patricio, V. A1 - Sandin, C. A1 - Steinmetz, Matthias A1 - Straka, Lorrie A. A1 - Urrutia, Tanya A1 - Verhamme, A. A1 - Weilbacher, Peter Michael A1 - Wendt, Martin T1 - Extended Lyman alpha haloes around individual high-redshift galaxies revealed by MUSE JF - Science N2 - We report the detection of extended Ly alpha emission around individual star-forming galaxies at redshifts z = 3-6 in an ultradeep exposure of the Hubble Deep Field South obtained with MUSE on the ESO-VLT. The data reach a limiting surface brightness (1 sigma) of similar to 1 x 10(-19) erg s(-1) cm(-2) arcsec(-2) in azimuthally averaged radial profiles, an order of magnitude improvement over previous narrowband imaging. Our sample consists of 26 spectroscopically confirmed Ly alpha-emitting, but mostly continuum-faint (m(AB) greater than or similar to 27) galaxies. In most objects the Ly alpha emission is considerably more extended than the UV continuum light. While five of the faintest galaxies in the sample show no significantly detected Ly alpha haloes, the derived upper limits suggest that this is due to insufficient S/N. Ly alpha haloes therefore appear to be ubiquitous even for low-mass (similar to 10(8)-10(9) M-circle dot) star-forming galaxies at z > 3. We decompose the Ly alpha emission of each object into a compact component tracing the UV continuum and an extended halo component, and infer sizes and luminosities of the haloes. The extended Ly alpha emission approximately follows an exponential surface brightness distribution with a scale length of a few kpc. While these haloes are thus quite modest in terms of their absolute sizes, they are larger by a factor of 5-15 than the corresponding rest-frame UV continuum sources as seen by HST. They are also much more extended, by a factor similar to 5, than Ly alpha haloes around low-redshift star-forming galaxies. Between similar to 40% and greater than or similar to 90% of the observed Ly alpha flux comes from the extended halo component, with no obvious correlation of this fraction with either the absolute or the relative size of the Ly alpha halo. Our observations provide direct insights into the spatial distribution of at least partly neutral gas residing in the circumgalactic medium of low to intermediate mass galaxies at z > 3. KW - galaxies: high-redshift KW - galaxies: evolution KW - galaxies: formation KW - cosmology: observations KW - intergalactic medium Y1 - 2016 U6 - https://doi.org/10.1051/0004-6361/201527384 SN - 1432-0746 VL - 587 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Johnson, Sean D. A1 - Chen, Hsiao-Wen A1 - Straka, Lorrie A1 - Schaye, Joop A1 - Cantalupo, Sebastiano A1 - Wendt, Martin A1 - Muzahid, Sowgat A1 - Bouché, Nicolas A1 - Herenz, Edmund Christian A1 - Kollatschny, Wolfram A1 - Mulchaey, John S. A1 - Marino, Raffaella A. A1 - Maseda, Michael A1 - Wisotzki, Lutz T1 - Galaxy and quasar fueling caught in the act from the intragroup to the interstellar medium JF - The astrophysical journal : Part 2, Letters N2 - We report the discovery of six spatially extended (10-100 kpc) line-emitting nebulae in the z approximate to 0.57 galaxy group hosting PKS 0405-123, one of the most luminous quasars at z < 1. The discovery is enabled by the Multi Unit Spectroscopic Explorer and provides tantalizing evidence connecting large-scale gas streams with nuclear activity on scales of <10 proper kpc (pkpc). One of the nebulae exhibits a narrow, filamentary morphology extending over 50 pkpc toward the quasar with narrow internal velocity dispersion (50 km s(-1)) and is not associated with any detected galaxies, consistent with a cool intragroup medium filament. Two of the nebulae are 10 pkpc north and south of the quasar with tidal-arm-like morphologies. These two nebulae, along with a continuum-emitting arm extending 60 pkpc from the quasar, are signatures of interactions that are expected to redistribute angular momentum in the host interstellar medium (ISM) to facilitate star formation and quasar fueling in the nucleus. The three remaining nebulae are among the largest and most luminous [O III] emitting "blobs" known (1400-2400 pkpc(2)) and correspond both kinematically and morphologically to interacting galaxy pairs in the quasar host group, consistent with arising from stripped ISM rather than large-scale quasar outflows. The presence of these large- and small-scale nebulae in the vicinity of a luminous quasar bears significantly on the effect of large-scale environment on galaxy and black hole fueling, providing a natural explanation for the previously known correlation between quasar luminosity and cool circumgalactic medium. KW - galaxies: interactions KW - intergalactic medium KW - quasars: general KW - quasars: individual (PKS 0405-123) Y1 - 2018 U6 - https://doi.org/10.3847/2041-8213/aaf1cf SN - 2041-8205 SN - 2041-8213 VL - 869 IS - 1 PB - IOP Publishing Ltd. (Bristol) CY - Bristol ER - TY - JOUR A1 - Draganova, Nadya A1 - Richter, Philipp A1 - Fechner, Cora T1 - High-resolution observations of two O VI absorbers at z approximate to 2 toward PKS 1448-232 JF - Astronomy and astrophysics : an international weekly journal N2 - To explore the ionization conditions in highly-ionized absorbers at high redshift, we study in detail two intervening O vi absorbers at z approximate to 2 toward the quasar PKS 1448-232, based on high (R approximate to 75 000) and intermediate (R approximate to 45 000) resolution optical VLT/UVES spectra. We find that both absorption systems are composed of several narrow subcomponents with typical Civ/O VI Doppler-parameters of b < 10 km s(-1). This implies that the gas temperatures are T < 10(5) K and that the absorbers are photoionized by the UV background. The system at z = 2.1098 represents a simple, isolated O VI absorber that has only two absorption components and is relatively metal-rich (Z similar to 0.6 solar). Ioinization modeling implies that the system is photoionized with O VI, C IV, and H I coexisting in the same gas phase. The second system at z = 2.1660 represents a complicated, multi-component absorption system with eight O VI components spanning almost 300 km s(-1) in radial velocity. The photoionization modeling implies that the metallicity is non-uniform and relatively low (<= 0.1 solar) and that the O VI absorption must arise in a gas phase that differs from that traced by C IV, C III, and H I. Our detailed study of the two O VI systems towards PKS 1448-232 shows that multi-phase, multi-component high-ion absorbers similar to the one at z = 2.1660 can be described by applying a detailed ionization modeling of the various subcomponents to obtain reliable measurements of the physical conditions and the metal abundances in the gas. KW - intergalactic medium KW - quasars: absorption lines KW - cosmology: observations Y1 - 2012 U6 - https://doi.org/10.1051/0004-6361/201116730 SN - 0004-6361 VL - 538 IS - 1 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Schmidt, Tobias M. A1 - Hennawi, Joseph F. A1 - Worseck, Gabor A1 - Davies, Frederick B. A1 - Lukic, Zarija A1 - Oñorbe, Jose T1 - Modeling the HeII transverse proximity effect BT - constraints on quasar lifetime and obscuration JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - The He II transverse proximity effect-enhanced He II Ly alpha transmission in a background sightline caused by the ionizing radiation of a foreground quasar-offers a unique opportunity to probe the emission properties of quasars, in particular the emission geometry (obscuration, beaming) and the quasar lifetime. Building on the foreground quasar survey published in Schmidt et al., we present a detailed model of the He II transverse proximity effect, specifically designed to include light travel time effects, finite quasar ages, and quasar obscuration. We postprocess outputs from a cosmological hydrodynamical simulation with a fluctuating He II ultraviolet background model, with the added effect of the radiation from a single bright foreground quasar. We vary the age t(age) and obscured sky fractions Omega(obsc) of the foreground quasar, and explore the resulting effect on the He II transverse proximity effect signal. Fluctuations in intergalactic medium density and the ultraviolet background, as well as the unknown orientation of the foreground quasar, result in a large variance of the He II Ly alpha transmission along the background sightline. We develop a fully Bayesian statistical formalism to compare far-ultraviolet He II Ly alpha transmission spectra of the background quasars to our models, and extract joint constraints on t(age) and Omega(obsc) for the six Schmidt et al. foreground quasars with the highest implied He II photoionization rates. Our analysis suggests a bimodal distribution of quasar emission properties, whereby one foreground quasar, associated with a strong He II transmission spike, is relatively old (22 Myr) and unobscured (Omega(obsc) < 35%), whereas three others are either younger than 10 Myr or highly obscured (Omega(obsc) > 70%). KW - dark ages, reionization, first stars KW - intergalactic medium KW - quasars: general Y1 - 2018 U6 - https://doi.org/10.3847/1538-4357/aac8e4 SN - 0004-637X SN - 1538-4357 VL - 861 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Guber, Christoph Rudolf A1 - Richter, Philipp A1 - Wendt, Martin T1 - Multiple origins for the DLA at zabs = 0.313 toward PKS 1127–145 indicated by a complex dust depletion pattern of Ca, Ti, and Mn JF - Astronomy and astrophysics : an international weekly journal N2 - Aims: We aim to investigate the dust depletion properties of optically thick gas in and around galaxies and its origin we study in detail the dust depletion patterns of Ti, Mn, and Ca in the multi-component damped Lyman alpha (DLA) absorber at z(abs) = 0.313 toward the quasar PKS 1127-145. Methods: We performed a detailed spectral analysis of the absorption profiles of Ca II, Mn II, TIII, and Na I associated with the DLA toward PKS 1127-145, based on optical high-resolution data obtained with the UVES instrument at the Very Large Telescope. We obtained column densities and Doppler-parameters for the ions listed above and determine their gas-phase abundances, from which we conclude on their dust depletion properties. We compared the Ca and Ti depletion properties of this DLA with that of other DLAs. Results: One of the six analyzed absorption components (component 3) shows a striking underabundance of Ti and Mn in the gas-phase, indicating the effect of dust depletion for these elements and a locally enhanced dust-to-gas ratio. In this DLA and in other similar absorbers, the Mn II abundance follows that of Ti II very closely, implying that both ions are equally sensitive to the dust depletion effects. Conclusions: Our analysis indicates that the DLA toward PKS 1127 145 has multiple origins. With its narrow line width and its strong dust depletion, component 3 points toward the presence of a neutral gas disk from a faint LSB galaxy in front of PKS 1127 145, while the other, more diffuse and dust-poor, absorption components possibly are related to tidal gas features from the interaction between the various, optically confirmed galaxy-group members. In general, the Mn/Ca II ratio in sub-DLAs and DLAs possibly serves as an important indicator to discriminate between dust-rich and dust-poor in neutral gas in and around galaxies. KW - quasars: absorption lines KW - galaxies: abundances KW - intergalactic medium KW - quasars: individual: PKS1127-145 KW - dust, extinction KW - ISM: kinematics and dynamics Y1 - 2018 U6 - https://doi.org/10.1051/0004-6361/201730984 SN - 1432-0746 VL - 609 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Schroetter, I. A1 - Bouche, Nicolas A1 - Wendt, Martin A1 - Contini, Thierry A1 - Finley, H. A1 - Pello, R. A1 - Bacon, Roland A1 - Cantalupo, Sebastiano A1 - Marino, Raffaella Anna A1 - Richard, J. A1 - Lilly, S. J. A1 - Schaye, Joop A1 - Soto, K. A1 - Steinmetz, Matthias A1 - Straka, Lorrie A. A1 - Wisotzki, Lutz T1 - MUSE GAS FLOW AND WIND (MEGAFLOW). I. FIRST MUSE RESULTS ON BACKGROUND QUASARS JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - The physical properties of galactic winds are one of the keys to understand galaxy formation and evolution. These properties can be constrained thanks to background quasar lines of sight (LOS) passing near star-forming galaxies (SFGs). We present the first results of the MusE GAs FLOw and Wind survey obtained from two quasar fields, which have eight Mg II absorbers of which three have rest equivalent width greater than 0.8 angstrom. With the new Multi Unit Spectroscopic Explorer (MUSE) spectrograph on the Very Large Telescope (VLT), we detect six (75%) Mg II host galaxy candidates within a radius of 30. from the quasar LOS. Out of these six galaxy-quasar pairs, from geometrical argument, one is likely probing galactic outflows, where two are classified as "ambiguous,"two are likely probing extended gaseous disks and one pair seems to be a merger. We focus on the wind-pair and constrain the outflow using a high-resolution quasar spectra from the Ultraviolet and Visual Echelle Spectrograph. Assuming the metal absorption to be due to ga;s flowing out of the detected galaxy through a cone along the minor axis, we find outflow velocities in the order of approximate to 150 km s(-1) (i.e., smaller than the escape velocity) with a loading factor, eta = M-out/SFR, of approximate to 0.7. We see evidence for an open conical flow, with a low-density inner core. In the future, MUSE will provide us with about 80 multiple galaxy-quasar pairs in two dozen fields. KW - galaxies: evolution KW - galaxies: formation KW - intergalactic medium KW - quasars: individual (SDSS J213748+001220, SDSS J215200+062516) Y1 - 2016 U6 - https://doi.org/10.3847/1538-4357/833/1/39 SN - 0004-637X SN - 1538-4357 VL - 833 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Wendt, Martin A1 - Bouche, Nicolas F. A1 - Zabl, Johannes A1 - Schroetter, Ilane A1 - Muzahid, Sowgat T1 - MusE GAs FLOw and Wind V. The dust/metallicity-anisotropy of the circum-galactic medium JF - Monthly notices of the Royal Astronomical Society N2 - We investigate whether the dust content of the circum-galactic medium (CGM) depends on the location of the quasar sightline with respect to the galaxy major-axis using 13 galaxy-Mg II absorber pairs (9-81 kpc distance) from the MusE GAs FLOw and Wind (MEGAFLOW) survey at 0.4 < z < 1.4. The dust content of the CGM is obtained from [Zn/Fe] using ultraviolet and visual echelle spectrograph data. When a direct measurement of [Zn/Fe] is unavailable, we estimate the dust depletion from a method that consists in solving for the depletion from multiple singly ionized ions (e.g. Mn II, Cr II, and Zn II) since each ion depletes on dust grains at different rates. We find a positive correlation between the azimuthal angle and [Zn/Fe] with a Pearson's gamma = 0.70 +/- 0.14. The sightlines along the major axis show [Zn/Fe] < 0.5, whereas the [Zn/Fe] is > 0.8 along the minor axis. These results suggest that the CGM along the minor axis is on average more metal enriched (by approximate to 1 dex) than the gas located along the major axis of galaxies provided that dust depletion is a proxy for metallicity. This anisotropic distribution is consistent with recent results on outflow and accretion in hydro-dynamical simulations. KW - galaxies: evolution KW - galaxies: formation KW - intergalactic medium KW - quasars: KW - absorption lines Y1 - 2021 U6 - https://doi.org/10.1093/mnras/stab049 SN - 0035-8711 SN - 1365-2966 VL - 502 IS - 3 SP - 3733 EP - 3745 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Schroetter, Ilane A1 - Bouche, Nicolas F. A1 - Zabl, Johannes A1 - Contini, Thierry A1 - Wendt, Martin A1 - Schaye, Joop A1 - Mitchell, Peter A1 - Muzahid, Sowgat A1 - Marino, Raffaella Anna A1 - Bacon, Roland A1 - Lilly, Simon J. A1 - Richard, Johan A1 - Wisotzki, Lutz T1 - MusE GAs FLOw andWind (MEGAFLOW) BT - III. Galactic wind properties using background quasars JF - Monthly notices of the Royal Astronomical Society N2 - We present results from our on-going MusE GAs FLOw and Wind (MEGAFLOW) survey, which consists of 22 quasar lines of sight, each observed with the integral field unit MUSE and the UVES spectrograph at the ESO Very Large Telescopes (VLT). The goals of this survey are to study the properties of the circumgalactic medium around z similar to 1 star-forming galaxies. The absorption-line selected survey consists of 79 strong MgII absorbers (with rest-frame equivalent width greater than or similar to 0.3 angstrom) and, currently, 86 associated galaxies within 100 projected kpc of the quasar with stellar masses (M-star) from 109 to 1011 M-circle dot. We find that the cool halo gas traced by MgII is not isotropically distributed around these galaxies from the strong bi-modal distribution in the azimuthal angle of the apparent location of the quasar with respect to the galaxy major axis. This supports a scenario in which outflows are bi-conical in nature and co-exist with a co-planar gaseous structure extending at least up to 60-80 kpc. Assuming that absorbers near the minor axis probe outflows, the current MEGAFLOW sample allowed us to select 26 galaxy-quasar pairs suitable for studying winds. From this sample, using a simple geometrical model, we find that the outflow velocity only exceeds the escape velocity when M-star less than or similar to 4 x 10(9) M-circle dot, implying the cool material is likely to fall back except in the smallest haloes. Finally, we find that the mass loading factor., the ratio between the ejected mass rate and the star formation rate, appears to be roughly constant with respect to the galaxy mass. KW - galaxies: evolution KW - galaxies: formation KW - intergalactic medium KW - quasars: absorption lines Y1 - 2019 U6 - https://doi.org/10.1093/mnras/stz2822 SN - 0035-8711 SN - 1365-2966 VL - 490 IS - 3 SP - 4368 EP - 4381 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Turner, Monica L. A1 - Schaye, Joop A1 - Crain, Robert A. A1 - Theuns, Tom A1 - Wendt, Martin T1 - Observations of metals in the z approximate to 3.5 intergalactic medium and comparison to the EAGLE simulations JF - Monthly notices of the Royal Astronomical Society N2 - We study the z approximate to 3.5 intergalactic medium (IGM) by comparing new, high-quality absorption spectra of eight QSOs with < z(QSO)> = 3.75, to virtual observations of the Evolution and Assembly of Galaxies and their Environments (EAGLE) cosmological hydrodynamical simulations. We employ the pixel optical depth method and uncover strong correlations between various combinations of H I, C III, C IV, Si III, Si IV, and O VI. We find good agreement between many of the simulated and observed correlations, including tau(O) (VI) (tau(H) (I)). However, the observed median optical depths for the tau(C) (IV) (tau(H) (I)) and tau(Si) (IV) (tau(H) (I)) relations are higher than those measured from the mock spectra. The discrepancy increases from up to approximate to 0.1 dex at tau(H) (I) = 1 to approximate to 1 dex at tau(H) (I) = 10(2), where we are likely probing dense regions at small galactocentric distances. As possible solutions, we invoke (a) models of ionizing radiation softened above 4 Ryd to account for delayed completion of He II reionization; (b) simulations run at higher resolution; (c) the inclusion of additional line broadening due to unresolved turbulence; and (d) increased elemental abundances; however, none of these factors can fully explain the observed differences. Enhanced photoionization of H I by local sources, which was not modelled, could offer a solution. However, the much better agreement with the observed O VI(H I) relation, which we find probes a hot and likely collisionally ionized gas phase, indicates that the simulations are not in tension with the hot phase of the IGM, and suggests that the simulated outflows may entrain insufficient cool gas. KW - galaxies: formation KW - intergalactic medium KW - quasars: absorption lines Y1 - 2016 U6 - https://doi.org/10.1093/mnras/stw1816 SN - 0035-8711 SN - 1365-2966 VL - 462 SP - 2440 EP - 2464 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Bouche, Nicolas A1 - Finley, H. A1 - Schroetter, I. A1 - Murphy, M. T. A1 - Richter, Philipp A1 - Bacon, Roland A1 - Contini, Thierry A1 - Richard, J. A1 - Wendt, Martin A1 - Kamann, S. A1 - Epinat, Benoit A1 - Cantalupo, Sebastiano A1 - Straka, Lorrie A. A1 - Schaye, Joop A1 - Martin, C. L. A1 - Peroux, C. A1 - Wisotzki, Lutz A1 - Soto, K. A1 - Lilly, S. A1 - Carollo, C. M. A1 - Brinchmann, Jarle A1 - Kollatschny, W. T1 - POSSIBLE SIGNATURES OF A COLD-FLOW DISK FROM MUSE USING A z similar to 1 GALAXY-QUASAR PAIR TOWARD SDSS J1422-0001 JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We use a background quasar to detect the presence of circumgalactic gas around a z = 0.91 low-mass star-forming galaxy. Data from the new Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope show that the galaxy has a dust-corrected star formation rate (SFR) of 4.7 +/- 2.0. M-circle dot yr(-1), with no companion down to 0.22 M-circle dot yr(-1) (5 sigma) within 240 h(-1) kpc ("30"). Using a high-resolution spectrum of the background quasar, which is fortuitously aligned with the galaxy major axis (with an azimuth angle alpha of only 15 degrees), we find, in the gas kinematics traced by low-ionization lines, distinct signatures consistent with those expected for a "cold-flow disk" extending at least 12 kpc (3 x R-1/2). We estimate the mass accretion rate M-in to be at least two to three times larger than the SFR, using the geometric constraints from the IFU data and the H (I) column density of log N-H (I)/cm(-2) similar or equal to 20.4 obtained from a Hubble Space Telescope/COS near-UV spectrum. From a detailed analysis of the low-ionization lines (e.g., Zn II, Cr II, Ti II, MnII, Si II), the accreting material appears to be enriched to about 0.4 Z(circle dot) (albeit with large uncertainties: log Z/Z(circle dot) = -0.4 +/- 0.4), which is comparable to the galaxy metallicity (12 + log O/H = 8.7 +/- 0.2), implying a large recycling fraction from past outflows. Blueshifted Mg II and Fe II absorptions in the galaxy spectrum from the MUSE data reveal the presence of an outflow. The Mg II and Fe II absorption line ratios indicate emission infilling due to scattering processes, but the MUSE data do not show any signs of fluorescent Fe II* emission. KW - galaxies: evolution KW - galaxies: formation KW - intergalactic medium KW - quasars: individual (SDSS J142253.31-000149) Y1 - 2016 U6 - https://doi.org/10.3847/0004-637X/820/2/121 SN - 0004-637X SN - 1538-4357 VL - 820 SP - 1872 EP - 1882 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Fechner, Cora T1 - Reconstructing the intergalactic UV background with QSO absorption lines JF - Astronomy and astrophysics : an international weekly journal N2 - We present a new approach to observationally constraining the spectral energy distribution of the intergalactic UV background by studying metal absorption systems. We study single-component metal line systems that exhibit various well-measured species. Among the observed transitions, at least two ratios of ionization stages from the same element are required, e. g. C III/C IV and Si III/Si IV. For each system photoionization models are constructed by varying the spectrum of the ionizing radiation. The spectral energy distribution can then be constrained by comparing the models with the observed column density ratios. Extensive tests with artificial absorbers show that the spectrum of the ionizing radiation cannot be reconstructed unambiguously, but it is possible to constrain the main characteristics of the spectrum. Furthermore, the resulting physical parameters of the absorber, such as ionization parameter, metallicity, and relative abundances, may depend strongly on the adopted ionizing spectrum. Even in case of well-fitting models, the uncertainties can be as high as similar to 0.5 dex for the ionization parameter and up to similar to 1.5 dex for the metallicity. Therefore, it is essential to know the hardness of the UV background when estimating the metallicity of the intergalactic medium. Applying the procedure to a small sample of 3 observed single-component metal line systems yields a soft ionizing radiation at z > 2 and a slightly harder spectrum at z < 2. The resulting energy distributions exhibit strong He II Lya re-emission features, suggesting that reprocessing by intergalactic He II is important. Comparing the observed systems to UV background spectra from the literature indicates that a recent model that includes sawtooth modulation due to reprocessing by intergalactic He II with delayed helium reionization fits the investigated systems very well. KW - intergalactic medium KW - quasars: absorption lines KW - diffuse radiation Y1 - 2011 U6 - https://doi.org/10.1051/0004-6361/201117080 SN - 0004-6361 VL - 532 IS - 2 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Abramowski, Attila A1 - Aharonian, Felix A. A1 - Benkhali, Faical Ait A1 - Akhperjanian, A. G. A1 - Angüner, Ekrem Oǧuzhan A1 - Anton, Gisela A1 - Backes, Michael A1 - Balenderan, Shangkari A1 - Balzer, Arnim A1 - Barnacka, Anna A1 - Becherini, Yvonne A1 - Tjus, J. Becker A1 - Bernlöhr, K. A1 - Birsin, E. A1 - Bissaldi, E. A1 - Biteau, Jonathan A1 - Boettcher, Markus A1 - Boisson, Catherine A1 - Bolmont, J. A1 - Bordas, Pol A1 - Brucker, J. A1 - Brun, Francois A1 - Brun, Pierre A1 - Bulik, Tomasz A1 - Carrigan, Svenja A1 - Casanova, Sabrina A1 - Chadwick, Paula M. A1 - Chalme-Calvet, R. A1 - Chaves, Ryan C. G. A1 - Cheesebrough, A. A1 - Chretien, M. A1 - Colafrancesco, Sergio A1 - Cologna, Gabriele A1 - Conrad, Jan A1 - Couturier, C. A1 - Cui, Y. A1 - Djannati-Ataï, A. A1 - Domainko, W. A1 - Dubus, G. A1 - Dutson, K. A1 - Dyks, J. A1 - Dyrda, M. A1 - Edwards, T. A1 - Egberts, Kathrin A1 - Eger, P. A1 - Espigat, P. A1 - Farnier, C. A1 - Fegan, S. A1 - Feinstein, F. A1 - Fernandes, M. V. A1 - Fernandez, D. A1 - Fiasson, A. A1 - Fontaine, G. A1 - Foerster, A. A1 - Fussling, Matthias A1 - Gajdus, M. A1 - Gallant, Y. A. A1 - Garrigoux, T. A1 - Giavitto, G. A1 - Giebels, B. A1 - Glicenstein, J. F. A1 - Grondin, M. -H. A1 - Grudzinska, M. A1 - Haeffner, S. A1 - Hahn, J. A1 - Harris, J. A1 - Heinzelmann, G. A1 - Henri, G. A1 - Hermann, G. A1 - Hervet, O. A1 - Hillert, A. A1 - Hinton, James Anthony A1 - Hofmann, W. A1 - Hofverberg, P. A1 - Holler, M. A1 - Horns, D. A1 - Jacholkowska, A. A1 - Jahn, C. A1 - Jamrozy, M. A1 - Janiak, M. A1 - Jankowsky, F. A1 - Jung, I. A1 - Kastendieck, M. A. A1 - Katarzynski, K. A1 - Katz, U. A1 - Kaufmann, S. A1 - Khelifi, B. A1 - Kieffer, M. A1 - Klepser, S. A1 - Klochkov, D. A1 - Kluzniak, W. A1 - Kneiske, T. A1 - Kolitzus, D. A1 - Komin, Nu. A1 - Kosack, K. A1 - Krakau, S. A1 - Krayzel, F. A1 - Krueger, P. P. A1 - Laffon, H. A1 - Lamanna, G. A1 - Lefaucheur, J. A1 - Lemiere, A. A1 - Lemoine-Goumard, M. A1 - Lenain, J. -P. A1 - Lohse, T. A1 - Lopatin, A. A1 - Lu, C. -C. A1 - Marandon, V. A1 - Marcowith, A. A1 - Marx, R. A1 - Maurin, G. A1 - Maxted, N. A1 - Mayer, M. A1 - McComb, T. J. L. A1 - Mehault, J. A1 - Meintjes, P. J. A1 - Menzler, U. A1 - Meyer, M. A1 - Moderski, R. A1 - Mohamed, M. A1 - Moulin, E. A1 - Murach, T. A1 - Naumann, C. L. A1 - de Naurois, M. A1 - Niemiec, J. A1 - Nolan, S. J. A1 - Oakes, L. A1 - Odaka, H. A1 - Ohm, S. A1 - Wilhelmi, E. de Ona A1 - Opitz, B. A1 - Ostrowski, M. A1 - Oya, I. A1 - Panter, M. A1 - Parsons, R. D. A1 - Arribas, M. Paz A1 - Pekeur, N. W. A1 - Pelletier, G. A1 - Perez, J. A1 - Petrucci, P. -O. A1 - Peyaud, B. A1 - Pita, S. A1 - Poon, H. A1 - Puehlhofer, G. A1 - Punch, M. A1 - Quirrenbach, A. A1 - Raab, S. A1 - Raue, M. A1 - Reichardt, I. A1 - Reimer, A. A1 - Reimer, O. A1 - Renaud, M. A1 - Reyes, R. de los A1 - Rieger, F. A1 - Rob, L. A1 - Romoli, C. A1 - Rosier-Lees, S. A1 - Rowell, G. A1 - Rudak, B. A1 - Rulten, C. B. A1 - Sahakian, V. A1 - Sanchez, David M. A1 - Santangelo, A. A1 - Schlickeiser, R. A1 - Schuessler, F. A1 - Schulz, A. A1 - Schwanke, U. A1 - Schwarzburg, S. A1 - Schwemmer, S. A1 - Sol, H. A1 - Spengler, G. A1 - Spies, F. A1 - Stawarz, L. A1 - Steenkamp, R. A1 - Stegmann, Christian A1 - Stinzing, F. A1 - Stycz, K. A1 - Sushch, Iurii A1 - Tavernet, J. -P. A1 - Tavernier, T. A1 - Taylor, A. M. A1 - Terrier, R. A1 - Tluczykont, M. A1 - Trichard, C. A1 - Valerius, K. A1 - van Eldik, C. A1 - van Soelen, B. A1 - Vasileiadis, G. A1 - Venter, C. A1 - Viana, A. A1 - Vincent, P. A1 - Voelk, H. J. A1 - Volpe, F. A1 - Vorster, M. A1 - Vuillaume, T. A1 - Wagner, S. J. A1 - Wagner, P. A1 - Wagner, R. M. A1 - Ward, M. A1 - Weidinger, M. A1 - Weitzel, Q. A1 - White, R. A1 - Wierzcholska, A. A1 - Willmann, P. A1 - Woernlein, A. A1 - Wouters, D. A1 - Yang, R. A1 - Zabalza, V. A1 - Zacharias, M. A1 - Zdziarski, A. A. A1 - Zech, Alraune A1 - Zechlin, H. -S. A1 - Malyshev, D. T1 - Search for extended gamma-ray emission around AGN with HESS and Fermi-LAT JF - Astronomy and astrophysics : an international weekly journal N2 - Context. Very-high-energy (VHE; E > 100 GeV) gamma-ray emission from blazars inevitably gives rise to electron-positron pair production through the interaction of these gamma-rays with the extragalactic background light (EBL). Depending on the magnetic fields in the proximity of the source, the cascade initiated from pair production can result in either an isotropic halo around an initially- beamed source or a magnetically- broadened cascade :aux. Aims. Both extended pair-halo (PH) and magnetically broadened cascade (MBC) emission from regions surrounding the blazars 1ES 1101-232, IRS 0229+200, and PKS 2155-304 were searched for using VHE y-ray data taken with the High Energy Stereoscopic System (HESS.) and high-energy (HE; 100 MeV < E < 100 GeV) gamma-ray data with the Fermi Large Area Telescope (LAT). Methods. By comparing the angular distributions of the reconstructed gamma-ray events to the angular profiles calculated from detailed theoretical models, the presence of PH and MBC was investigated. Results. Upper limits on the extended emission around lES 1101-232, lES 0229+200, and PKS 2155-304 are found to be at a level of a few per cent of the Crab nebula flux above 1 TeV, depending on the assumed photon index of the cascade emission. Assuming strong extra-Galactic magnetic field (EGME) values, >10(-12) G, this limits the production of pair haloes developing from electromagnetic cascades. For weaker magnetic fields, in which electromagnetic cascades would result in MBCs. EGMF strengths in the range (0.3-3) x 10(-15) G were excluded for PKS 2155-304 at the 99% confidence level, under the assumption of a 1 Mpc coherence length. KW - gamma rays: galaxies KW - galaxies: magnetic fields KW - intergalactic medium KW - BL Lacertae objects: individual: PKS 2155-304 KW - BL Lacertae objects: individual: lES 1101-232 KW - BL Lacertae objects: individual: lES 0229+200 Y1 - 2014 U6 - https://doi.org/10.1051/0004-6361/201322510 SN - 0004-6361 SN - 1432-0746 VL - 562 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Nuza, Sebastian E. A1 - Parisi, Florencia A1 - Scannapieco, Cecilia A1 - Richter, Philipp A1 - Gottloeber, Stefan A1 - Steinmetz, Matthias T1 - The distribution of gas in the Local Group from constrained cosmological simulations: the case for Andromeda and the Milky Way galaxies JF - Monthly notices of the Royal Astronomical Society N2 - We study the gas distribution in the Milky Way and Andromeda using a constrained cosmological simulation of the Local Group (LG) within the context of the CLUES (Constrained Local UniversE Simulations) project. We analyse the properties of gas in the simulated galaxies at z = 0 for three different phases: 'cold', 'hot' and H i, and compare our results with observations. The amount of material in the hot halo (M-hot a parts per thousand 4-5 x 10(10) M-aS (TM)), and the cold (M-cold(r a parts per thousand(2) 10 kpc) a parts per thousand 10(8) M-aS (TM)) and H i components displays reasonable agreement with observations. We also compute the accretion/ejection rates together with the H i (radial and all-sky) covering fractions. The integrated H i accretion rate within r = 50 kpc gives similar to 0.2-0.3 M-aS (TM) yr(-1), i.e. close to that obtained from high-velocity clouds in the Milky Way. We find that the global accretion rate is dominated by hot material, although ionized gas with T a parts per thousand(2) 10(5) K can contribute significantly too. The net accretion rates of all material at the virial radii are 6-8 M-aS (TM) yr(-1). At z = 0, we find a significant gas excess between the two galaxies, as compared to any other direction, resulting from the overlap of their gaseous haloes. In our simulation, the gas excess first occurs at z similar to 1, as a result of the kinematical evolution of the LG. KW - methods: numerical KW - Galaxy: halo KW - intergalactic medium KW - Local Group KW - large-scale structure of Universe Y1 - 2014 U6 - https://doi.org/10.1093/mnras/stu643 SN - 0035-8711 SN - 1365-2966 VL - 441 IS - 3 SP - 2593 EP - 2612 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Worseck, Gabor A1 - Prochaska, J. Xavier A1 - McQuinn, Matthew A1 - Dall'Aglio, Aldo A1 - Fechner, Cora A1 - Hennawi, Joseph F. A1 - Reimers, Dieter A1 - Richter, Philipp A1 - Wisotzki, Lutz T1 - The end of Helium Reionization at z similar or equal to 2.7 Inferred from cosmic variance in HST/COS He II Ly alpha Absorption spectra JF - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters N2 - We report on the detection of strongly varying intergalactic He II absorption in HST/COS spectra of two z(em) similar or equal to 3 quasars. From our homogeneous analysis of the He II absorption in these and three archival sightlines, we find a marked increase in the mean He II effective optical depth from similar or equal to 1 at z similar or equal to 2.3 to greater than or similar to 5 at z similar or equal to 3.2, but with a large scatter of 2 less than or similar to tau(eff, He II) less than or similar to 5 at 2.7 < z < 3 on scales of similar to 10 proper Mpc. This scatter is primarily due to fluctuations in the He II fraction and the He II-ionizing background, rather than density variations that are probed by the coeval Hi forest. Semianalytic models of He II absorption require a strong decrease in the He II-ionizing background to explain the strong increase of the absorption at z greater than or similar to 2.7, probably indicating He II reionization was incomplete at z(reion) greater than or similar to 2.7. Likewise, recent three-dimensional numerical simulations of He II reionization qualitatively agree with the observed trend only if He II reionization completes at z(reion) similar or equal to 2.7 or even below, as suggested by a large tau(eff, He II) greater than or similar to 3 in two of our five sightlines at z < 2.8. By doubling the sample size at 2.7 less than or similar to z less than or similar to 3, our newly discovered He II sightlines for the first time probe the diversity of the second epoch of reionization when helium became fully ionized. KW - dark ages, reionization, first stars KW - diffuse radiation KW - intergalactic medium KW - quasars: absorption lines KW - quasars: individual (SDSS J092447.36+485242.8, SDSS J110155.74+105302.3) Y1 - 2011 U6 - https://doi.org/10.1088/2041-8205/733/2/L24 SN - 2041-8205 VL - 733 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Worseck, Gabor A1 - Davies, Frederick B. A1 - Hennawi, Joseph F. A1 - Prochaska, J. Xavier T1 - The Evolution of the He II-ionizing Background at Redshifts 2.3 < z < 3.8 Inferred from a Statistical Sample of 24 HST/COS He II Lyα Absorption Spectra JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We present measurements of the large-scale (≈40 comoving Mpc) effective optical depth of He ii Lyα absorption, ${\tau }_{\mathrm{eff}}$, at 2.54 < z < 3.86 toward 16 He ii-transparent quasars observed with the Cosmic Origins Spectrograph on the Hubble Space Telescope, to characterize the ionization state of helium in the intergalactic medium (IGM). We provide the first statistical sample of ${\tau }_{\mathrm{eff}}$ measurements in six signal-to-noise ratio gsim3 He ii sightlines at z > 3.5, and study the redshift evolution and sightline-to-sightline variance of ${\tau }_{\mathrm{eff}}$ in 24 He ii sightlines. We confirm an increase of the median ${\tau }_{\mathrm{eff}}$ from sime2 at z = 2.7 to ${\tau }_{\mathrm{eff}}\gtrsim 5$ at z > 3, and a scatter in ${\tau }_{\mathrm{eff}}$ that increases with redshift. The z > 3.5 He ii absorption is predominantly saturated, but isolated narrow (Δv < 650 km s−1) transmission spikes indicate patches of reionized helium. We compare our measurements to predictions for a range of UV background models applied to outputs of a large-volume (146 comoving Mpc)3 hydrodynamical simulation by forward-modeling our sample's quality and size. At z > 2.74, the variance in ${\tau }_{\mathrm{eff}}$ significantly exceeds expectations for a spatially uniform UV background, but is consistent with a fluctuating radiation field sourced by variations in the quasar number density and the mean free path in the post-reionization IGM. We develop a method to infer the approximate median He ii photoionization rate ${{\rm{\Gamma }}}_{\mathrm{He}{\rm{II}}}$ of a fluctuating UV background from the median ${\tau }_{\mathrm{eff}}$, finding a factor sime5 decrease in ${{\rm{\Gamma }}}_{\mathrm{He}{\rm{II}}}$ between z sime 2.6 and z sime 3.1. At z sime 3.1, ${{\rm{\Gamma }}}_{\mathrm{He}{\rm{II}}}=\left[{9.1}_{-1.2}^{+1.1}\,(\mathrm{stat}.){\,}_{-3.4}^{+2.4}\,(\mathrm{sys}.)\right]\times {10}^{-16}$ s−1 corresponds to a median He ii fraction of sime2.5%, indicating that our data probe the tail end of He ii reionization. KW - dark ages, reionization, first stars KW - diffuse radiation KW - intergalactic medium KW - quasars: absorption lines Y1 - 2019 U6 - https://doi.org/10.3847/1538-4357/ab0fa1 SN - 0004-637X SN - 1538-4357 VL - 875 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER - TY - THES A1 - Hildebrandt, Dominik T1 - The HI Lyman-alpha opacity at redshift 2.7 < z < 3.6 T1 - Die HI-Lyman-α-Opazität im Rotverschiebungsbereich 2.7 < z < 3.6 N2 - Most of the baryonic matter in the Universe resides in a diffuse gaseous phase in-between galaxies consisting mostly of hydrogen and helium. This intergalactic medium (IGM) is distributed in large-scale filaments as part of the overall cosmic web. The luminous extragalactic objects that we can observe today, such as galaxies and quasars, are surrounded by the IGM in the most dense regions within the cosmic web. The radiation of these objects contributes to the so-called ultraviolet background (UVB) which keeps the IGM highly ionized ever since the epoch of reionization. Measuring the amount of absorption due to intergalactic neutral hydrogen (HI) against extragalactic background sources is a very useful tool to constrain the energy input of ionizing sources into the IGM. Observations suggest that the HI Lyman-alpha effective optical depth, τ_eff, decreases with decreasing redshift, which is primarily due to the expansion of the Universe. However, some studies find a smaller value of the effective optical depth than expected at the specific redshift z~3.2, possibly related to the complete reionization of helium in the IGM and a hardening of the UVB. The detection and possible cause of a decrease in τ_eff at z~3.2 is controversially debated in the literature and the observed features need further explanation. To better understand the properties of the mean absorption at high redshift and to provide an answer for whether the detection of a τ_eff feature is real we study 13 high-resolution, high signal-to-noise ratio quasar spectra observed with the Ultraviolet and Visual Echelle Spectrograph (UVES) at the Very Large Telescope (VLT). The redshift evolution of the effective optical depth, τ_eff(z), is measured in the redshift range 2.7≤z≤3.6. The influence of metal absorption features is removed by performing a comprehensive absorption-line-fitting procedure. In the first part of the thesis, a line-parameter analysis of the column density, N, and Doppler parameter, b, of ≈7500 individually fitted absorption lines is performed. The results are in good agreement with findings from previous surveys. The second (main) part of this thesis deals with the analysis of the redshift evolution of the effective optical depth. The τ_eff measurements vary around the empirical power law τ_eff(z)~(1+z)^(γ+1) with γ=2.09±0.52. The same analysis as for the observed spectra is performed on synthetic absorption spectra. From a comparison between observed and synthetic spectral data it can be inferred that the uncertainties of the τ_eff values are likely underestimated and that the scatter is probably caused by high-column-density absorbers with column densities in the range 15≤logN≤17. In the real Universe, such absorbers are rarely observed, however. Hence, the difference in τ_eff from different observational data sets and absorption studies is most likely caused by cosmic variance. If, alternatively, the disagreement between such data is a result of an too optimistic estimate of the (systematic) errors, it is also possible that all τ_eff measurements agree with a smooth evolution within the investigated redshift range. To explore in detail the different analysis techniques of previous studies an extensive literature comparison to the results of this work is presented in this thesis. Although a final explanation for the occurrence of the τ_eff deviation in different studies at z~3.2 cannot be given here, our study, which represents the most detailed line-fitting analysis of its kind performed at the investigated redshifts so far, represents another important benchmark for the characterization of the HI Ly-alpha effective optical depth at high redshift and its indicated unusual behavior at z~3.2. N2 - Der Großteil der baryonischen Materie des Universums, die im Wesentlichen aus Wasserstoff und Helium besteht, befindet sich in Form von diffusem Gas zwischen den Galaxien. Dieses intergalaktische Medium (IGM) bildet großräumige Strukturen aus, dessen Filamente als "kosmisches Netz" bezeichnet werden. Die leuchtkräftigen extragalaktischen Objekte, die man heutzutage beobachten kann (z.B. Galaxien und Quasare), sind von diesem IGM umgeben und befinden sich in den dichtesten Regionen innerhalb des kosmischen Netzes. Die von diesen Objekten ausgehende ultraviolette (UV) Strahlung ist Bestandteil des UV-Strahlungshintergrunds, der seit der Reionisationsphase den hochionisierten Zustand des IGM aufrecht hält. Eine Auswertung des absorbierten Strahlungsanteils durch den noch im IGM vorhandenen neutralen Wasserstoff (HI) entlang der Sichtlinie zu einer beobachteten extragalaktischen Hintergrundquelle lässt auf den Energieeintrag der Strahlungsquellen ins IGM schließen. Aus geeigneten Messdaten lässt sich schlussfolgern, dass sich die effektive optische Tiefe von HI (Ly-alpha Übergang) mit abnehmender Rotverschiebung verringert, was im Wesentlichen auf die Expansion des Universums zurückzuführen ist. Einige Arbeiten finden jedoch bei der ausgewiesenen Rotverschiebung z~3.2 einen kleineren Wert für die effektive optische Tiefe als erwartet, ein Trend der möglicherweise mit der vollständigen Reionisation von Helium im IGM und einem Anstieg der Intensität des UV-Hintergrunds in Verbindung steht. Die Detektion und mögliche Ursache einer Abnahme der effektiven optischen Tiefe bei z~3.2 ist in der Literatur kontrovers diskutiert und die beobachteten Besonderheiten machen eine weitere Untersuchung erforderlich. Um die Eigenschaften der mittleren Absorption bei hoher Rotverschiebung besser zu verstehen und um einen Lösungsansatz für die Debatte zu liefern, untersuchen wir 13 hoch aufgelöste Quasarabsorptionsspektren mit einem hohen Signal-zu-Rauschen Verhältnis, die mit dem Instrument UVES des Very Large Telescope (VLT) aufgenommen wurden. Die Entwicklung der effektiven optischen Tiefe wird im Rotverschiebungsbereich 2.7≤z≤3.6 gemessen. Die Messung wird um den Beitrag von Metallen durch die detaillierte Anpassung von Linienprofilen an die beobachtete Absorption korrigiert. Im ersten Teil der Arbeit wird eine Auswertung der Parameter der ≈7500 einzeln angepassten Absorptionslinien (Säulendichte N und Doppler-Parameter b) vorgenommen. Die entsprechenden Ergebnisse stimmen im Rahmen der Messunsicherheiten mit Literaturwerten überein. Der Hauptteil der Arbeit beschäftigt sich mit der Berechnung der effektiven optischen Tiefe in Abhängigkeit von der Rotverschiebung τ_eff(z). Es stellt sich heraus, dass die τ_eff-Messwerte um ein empirisches Potengesetz der Form τ_eff(z)~(1+z)^(γ+1) mit γ=2.09±0.52 streuen. Die gleiche Auswertung wie für die Beobachtungsdaten wird für synthetische Spektren durchgeführt. Ein Vergleich dieser Daten legt nahe, dass die Größe der Unsicherheiten der τ_eff-Messwerte wahrscheinlich unterschätzt wird und dass die Streuung der Datenpunkte auf Absorber hoher Säulendichte (15≤logN≤17) zurückzuführen ist. Solche Absorber sind im beobachtbaren Universum jedoch selten, sodass der Unterschied in den τ_eff-Messwerten bei verschiedenen Zusammenstellungen von Beobachtungsdaten und Studien zum Absorptionsverhalten höchstwahrscheinlich durch kosmische Varianz bedingt ist. Sollte jedoch die fehlende Übereinstimmung dieser Daten eine Folge zu optimistischer (systematischer) Fehlerabschätzungen sein, so ist es ebenfalls denkbar, dass die τ_eff-Messwerte mit einer gleichmäßigen Entwicklung über den untersuchten Rotverschiebungsbereich hinweg konsistent sind. Um die wesentlichen Unterschiede in den Untersuchungsmethoden vorheriger Studien zu untersuchen, wird in dieser Arbeit ein umfassender Vergleich der Ergebnisse dieser Arbeit mit entsprechender Literatur vorgenommen. Eine endgültige Erklärung für das Auftreten einer Abweichung in τ_eff(z) vom empirischen Potenzgesetz, wie sie von einigen Studien bei z~3.2 gefunden wurde, kann in dieser Arbeit zwar nicht gegeben werden, dennoch stellt sie die bislang umfassendste Parameterbestimmung von Absorptionslinien ihrer Art im untersuchten Rotverschiebungsbereich dar. Sie ist somit ein weiterer wichtiger Schritt in Richtung des ganzheitlichen Verständnisses der effektiven optischen Tiefe bei hohen Rotverschiebungen und deren möglicherweise ungewöhnlichem Verlauf bei z~3.2. KW - intergalactic medium KW - cosmology: observations KW - methods: data analysis KW - methods: statistical KW - quasars: absorption lines KW - intergalaktisches Medium KW - Kosmologie: Beobachtungen KW - Methoden: Datenauswertung KW - Methoden: statistisch KW - Quasare: Absorptionslinien Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-78355 ER - TY - JOUR A1 - Becker, George D. A1 - D'Aloisio, Anson A1 - Christenson, Holly M. A1 - Zhu, Yongda A1 - Worseck, Gábor A1 - Bolton, James S. T1 - The mean free path of ionizing photons at 5 < z < 6 BT - evidence for rapid evolution near reionization JF - Monthly notices of the Royal Astronomical Society N2 - The mean free path of ionizing photons, lambda(mfp), is a key factor in the photoionization of the intergalactic medium (IGM). At z greater than or similar to 5, however, lambda(mfp) may be short enough that measurements towards QSOs are biased by the QSO proximity effect. We present new direct measurements of lambda(mfp) that address this bias and extend up to z similar to 6 for the first time. Our measurements at z similar to 5 are based on data from the Giant Gemini GMOS survey and new Keck LRIS observations of low-luminosity QSOs. At z similar to 6 we use QSO spectra from Keck ESI and VLT X-Shooter. We measure lambda(mfp) = 9.09(-1.28)(+1.62) proper Mpc and 0.75(-0.45)(+0.65) proper Mpc (68 percent confidence) at z = 5.1 and 6.0, respectively. The results at z = 5.1 are consistent with existing measurements, suggesting that bias from the proximity effect is minor at this redshift. At z = 6.0, however, we find that neglecting the proximity effect biases the result high by a factor of two or more. Our measurement at z = 6.0 falls well below extrapolations from lower redshifts, indicating rapid evolution in lambda(mfp) over 5 < z < 6. This evolution disfavours models in which reionization ended early enough that the IGM had time to fully relax hydrodynamically by z = 6, but is qualitatively consistent with models wherein reionization completed at z = 6 or even significantly later. Our mean free path results are most consistent with late reionization models wherein the IGM is still 20 percent neutral at z = 6, although our measurement at z = 6.0 is even lower than these models prefer. KW - intergalactic medium KW - quasars: absorption lines KW - cosmology: observations KW - dark ages KW - large-scale structure of Universe KW - reionization KW - first stars Y1 - 2021 U6 - https://doi.org/10.1093/mnras/stab2696 SN - 0035-8711 SN - 1365-2966 VL - 508 IS - 2 SP - 1853 EP - 1869 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Richter, Philipp A1 - Krause, F. A1 - Fechner, Cora A1 - Charlton, Jane C. A1 - Murphy, M. T. T1 - The neutral gas extent of galaxies as derived from weak intervening Ca II absorbers JF - Astronomy and astrophysics : an international weekly journal N2 - We present a systematic study of weak intervening CaII absorbers at low redshift (z < 0.5), based on the analysis of archival high-resolution (R >= 45 000) optical spectra of 304 quasars and active galactic nuclei observed with VLT/UVES. Along a total redshift path of Delta z approximate to 100 we detected 23 intervening CaII absorbers in both the CaII H & K lines, with rest frame equivalent widths W-r,W-3934 = 15-799 m angstrom and column densities log N(CaII) = 11.25-13.04 (obtained by fitting Voigt-profile components). We obtain a bias-corrected number density of weak intervening CaII absorbers of dN/dz = 0.117 +/- 0.044 at < z(abs)> = 0.35 for absorbers with log N(CaII) >= 11.65 (W-r,W-3934 >= 32 m angstrom). This is similar to 2.6 times the value obtained for damped Lyman alpha absorbers (DLAs) at low redshift. All CaII absorbers in our sample show associated absorption by other low ions such as MgII and FeII; 45 percent of them have associated NaI absorption. From ionization modelling we conclude that intervening CaII absorption with log N(CaII) >= 11.5 arises in DLAs, sub-DLAs and Lyman-limit systems (LLS) at HI column densities of log N(HI) >= 17.4. Using supplementary HI information for nine of the absorbers we find that the CaII/HI ratio decreases strongly with increasing HI column density, indicating a column-density-dependent dust depletion of Ca. The observed column density distribution function of CaII absorption components follows a relatively steep power law, f(N) proportional to N-beta, with a slope of -beta = -1.68, which again points towards an enhanced dust depletion in high column density systems. The relatively large cross section of these absorbers together with the frequent detection of CaII absorption in high-velocity clouds (HVCs) in the halo of the Milky Way suggests that a considerable fraction of the intervening CaII systems trace (partly) neutral gas structures in the halos and circumgalactic environment of galaxies (i.e., they are HVC analogs). Based on the recently measured detection rate of CaII absorption in the Milky Way HVCs we estimate that the mean (projected) CaII covering fraction of galaxies and their gaseous halos is < f(c,CaII)> = 0.33. Using this value and considering all galaxies with luminosities L >= 0.05 L-star we calculate that the characteristic radial extent of (partly) neutral gas clouds with log N(HI) >= 17.4 around low-redshift galaxies is R-HVC approximate to 55 kpc. KW - galaxies: halos KW - galaxies: formation KW - galaxies: ISM KW - intergalactic medium KW - quasars: absorption lines Y1 - 2011 U6 - https://doi.org/10.1051/0004-6361/201015566 SN - 0004-6361 VL - 528 IS - 4 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Bouma, Sietske Jeltje Deirdre A1 - Richter, Philipp A1 - Wendt, Martin T1 - The relation between Ly alpha absorbers and local galaxy filaments JF - Astronomy and astrophysics : an international weekly journal N2 - Context. The intergalactic medium (IGM) is believed to contain the majority of baryons in the universe and to trace the same dark matter structure as galaxies, forming filaments and sheets. Ly alpha absorbers, which sample the neutral component of the IGM, have been extensively studied at low and high redshift, but the exact relation between Ly alpha absorption, galaxies, and the large-scale structure is observationally not well constrained.Aims. In this study, we aim at characterising the relation between Ly alpha absorbers and nearby over-dense cosmological structures (galaxy filaments) at recession velocities Delta v <= 6700 km s(-1) by using archival observational data from various instruments.Methods. We analyse 587 intervening Ly alpha absorbers in the spectra of 302 extragalactic background sources obtained with the Cosmic Origins Spectrograph (COS) installed on the Hubble Space Telescope (HST). We combine the absorption line information with galaxy data of five local galaxy filaments from the V8k catalogue.Results. Along the 91 sightlines that pass close to a filament, we identify 215 (227) Ly alpha absorption systems (components). Among these, 74 Ly alpha systems are aligned in position and velocity with the galaxy filaments, indicating that these absorbers and the galaxies trace the same large-scale structure. The filament-aligned Ly alpha absorbers have a similar to 90% higher rate of incidence (d?/dz=189 for log N(HI) >= 13.2) and a slightly shallower column density distribution function slope (-beta=-1.47) relative to the general Ly alpha population at z=0, reflecting the filaments' matter over-density. The strongest Ly alpha absorbers are preferentially found near galaxies or close to the axis of a filament, although there is substantial scatter in this relation. Our sample of absorbers clusters more strongly around filament axes than a randomly distributed sample would do (as confirmed by a Kolmogorov-Smirnov test), but the clustering signal is less pronounced than for the galaxies in the filaments. KW - galaxies: halos KW - intergalactic medium KW - quasars: absorption lines KW - large-scale structure of Universe KW - techniques: spectroscopic KW - ultraviolet: general Y1 - 2021 U6 - https://doi.org/10.1051/0004-6361/202039786 SN - 0004-6361 SN - 1432-0746 VL - 647 PB - EDP Sciences CY - Les Ulis ER - TY - THES A1 - Worseck, Gábor T1 - The transverse proximity effect in quasar spectra T1 - Der Transversale Proximity-Effekt in Quasarspektren N2 - The intergalactic medium is kept highly photoionised by the intergalactic UV background radiation field generated by the overall population of quasars and galaxies. In the vicinity of sources of UV photons, such as luminous high-redshift quasars, the UV radiation field is enhanced due to the local source contribution. The higher degree of ionisation is visible as a reduced line density or generally as a decreased level of absorption in the Lyman alpha forest of neutral hydrogen. This so-called proximity effect has been detected with high statistical significance towards luminous quasars. If quasars radiate rather isotropically, background quasar sightlines located near foreground quasars should show a region of decreased Lyman alpha absorption close to the foreground quasar. Despite considerable effort, such a transverse proximity effect has only been detected in a few cases. So far, studies of the transverse proximity effect were mostly limited by the small number of suitable projected pairs or groups of high-redshift quasars. With the aim to substantially increase the number of quasar groups in the vicinity of bright quasars we conduct a targeted survey for faint quasars around 18 well-studied quasars at employing slitless spectroscopy. Among the reduced and calibrated slitless spectra of 29000 objects on a total area of 4.39 square degrees we discover in total 169 previously unknown quasar candidates based on their prominent emission lines. 81 potential z>1.7 quasars are selected for confirmation by slit spectroscopy at the Very Large Telescope (VLT). We are able to confirm 80 of these. 64 of the newly discovered quasars reside at z>1.7. The high success rate of the follow-up observations implies that the majority of the remaining candidates are quasars as well. In 16 of these groups we search for a transverse proximity effect as a systematic underdensity in the HI Lyman alpha absorption. We employ a novel technique to characterise the random absorption fluctuations in the forest in order to estimate the significance of the transverse proximity effect. Neither low-resolution spectra nor high-resolution spectra of background quasars of our groups present evidence for a transverse proximity effect. However, via Monte Carlo simulations the effect should be detectable only at the 1-2sigma level near three of the foreground quasars. Thus, we cannot distinguish between the presence or absence of a weak signature of the transverse proximity effect. The systematic effects of quasar variability, quasar anisotopy and intrinsic overdensities near quasars likely explain the apparent lack of the transverse proximity effect. Even in absence of the systematic effects, we show that a statistically significant detection of the transverse proximity effect requires at least 5 medium-resolution quasar spectra of background quasars near foreground quasars whose UV flux exceeds the UV background by a factor 3. Therefore, statistical studies of the transverse proximity effect require large numbers of suitable pairs. Two sightlines towards the central quasars of our survey fields show intergalactic HeII Lyman alpha absorption. A comparison of the HeII absorption to the corresponding HI absorption yields an estimate of the spectral shape of the intergalactic UV radiation field, typically parameterised by the HeII/HI column density ratio eta. We analyse the fluctuating UV spectral shape on both lines of sight and correlate it with seven foreground quasars. On the line of sight towards Q0302-003 we find a harder radiation field near 4 foreground quasars. In the direct vicinity of the quasars eta is consistent with values of 25-100, whereas at large distances from the quasars eta>200 is required. The second line of sight towards HE2347-4342 probes lower redshifts where eta is directly measurable in the resolved HeII forest. Again we find that the radiation field near the 3 foreground quasars is significantly harder than in general. While eta still shows large fluctuations near the quasars, probably due to radiative transfer, the radiation field is on average harder near the quasars than far away from them. We interpret these discoveries as the first detections of the transverse proximity effect as a local hardness fluctuation in the UV spectral shape. No significant HI proximity effect is predicted for the 7 foreground quasars. In fact, the HI absorption near the quasars is close to or slightly above the average, suggesting that the weak signature of the transverse proximity effect is masked by intrinsic overdensities. However, we show that the UV spectral shape traces the transverse proximity effect even in overdense regions or at large distances. Therefore, the spectral hardness is a sensitive physical measure of the transverse proximity effect that is able to break the density degeneracy affecting the traditional searches. N2 - Das intergalaktische Medium wird durch das intergalaktische UV-Hintergrundsstrahlungsfeld in einem hochgradig photoionisierten Zustand gehalten. Der UV-Hintergrund stammt von der gesamten Population von Quasaren und Galaxien. In der Nähe von leuchtkräftigen Quasaren, ist das UV-Strahlungsfeld lokal erhöht durch den Anteil der Quelle. Der höhere Ionisationsgrad ist beobachtbar als eine reduzierte Liniendichte oder allgemein als ein vermindertes Maß an Absorption im Lyman-alpha Wald des neutralen Wasserstoffs. Dieser sogenannte Proximity-Effekt ist bei leuchtkräftigen Quasaren mit hoher statistischer Signifikanz nachgewiesen worden. Falls Quasare fast isotrop strahlen, dann sollten Sichtlinien zu Hintergrundquasaren in der Nähe von Vordergrundquasaren eine Region mit verminderter Absorption zeigen. Trotz beträchtlichen Aufwands wurde solch ein transversaler Proximity-Effekt nur in wenigen Fällen entdeckt. Bisher waren Studien des transversalen Proximity-Effekts meist begrenzt durch die kleine Anzahl von geeigneten projizierten Paaren oder Gruppen von hochrotverschobenen Quasaren. Mit dem Ziel die Zahl der Quasargruppen in der Nähe von hellen Quasaren beträchtlich zu erhöhen, führen wir eine gezielte Suche nach schwachen Quasaren um 18 oft studierte Quasare durch. Unter den reduzierten und kalibrierten spaltlosen Spektren von 29000 Objekten auf einer Gesamtfläche von 4.39 Quadratgrad entdecken wir insgesamt 169 vorher unbekannte Quasarkandidaten anhand ihrer Emissionslinien. 81 potentielle z>1.7 Quasare werden ausgesucht zur Bestätigung mittels Spaltspektroskopie am Very Large Telescope (VLT). Wir können 80 von diesen als Quasare bestätigen. 64 der neu entdeckten Quasare liegen bei z>1.7. Die hohe Erfolgsrate der Nachfolgebeobachtungen deutet an, dass die Mehrzahl der verbleibenden Kandidaten ebenfalls Quasare sind. In 16 dieser Gruppen suchen wir nach dem transversalen Proximity-Effekt als eine systematische Unterdichte in der HI Lyman-alpha-Absorption. Wir nutzen eine neuartige Methode die zufälligen Absorptionsfluktuationen zu charakterisieren, um die Signifikanz des transversalen Proximity-Effekts abschätzen zu können. Weder schwach aufgelöste noch hoch aufgelöste Spektren von Hintergrundquasaren unserer Gruppen zeigen Anzeichen für einen transversalen Proximity-Effekt. Aufgrund von Monte Carlo Simulationen sollte der Effekt jedoch nur schwach in der Nähe von 3 Vordergrundquasaren detektierbar sein. Deshalb können wir nicht zwischen An- oder Abwesenheit des Effekts unterscheiden. Selbst in Abwesenheit von systematischen Effekten zeigen wir, dass eine statistisch signifikante Detektion des transversalen Proximity-Effekts mindestens 5 Hintergrundquasarspektren bei mittlerer Auflösung nahe Vordergrundquasaren erfordert, deren UV-Fluss den UV-Hintergrund um einen Faktor 3 übersteigt. Deshalb erfordern statistische Studien des transversalen Proximity-Effekts große Zahlen von geeigneten Quasaren. Zwei Sichtlinien zeigen HeII-Absorption. Ein Vergleich der HeII-Absorption mit der entsprechenden HI-Absorption liefert eine Abschätzung der Spektralform des UV-Strahlungsfelds, das typischerweise durch das HeII/HI Säulendichteverhältnis eta parameterisiert wird. Wir analysieren die fluktuierende spektrale Form des UV-Strahlungsfelds auf beiden Sichtlinien und korrelieren sie mit 7 Vordergrundquasaren. Auf der Sichtlinie zu Q0302-003 finden wir ein härteres Strahlungsfeld nahe 4 Vordergrundquasaren. In der direkten Umgebung der Quasare ist eta konsistent mit Werten von 25-100, wogegen bei großen Entfernungen zu den Quasaren eta>200 erforderlich ist. Die zweite Sichtlinie zu HE2347-4342 sondiert kleinere Rotverschiebungen. Wieder finden wir, dass das Strahlungsfeld nahe der 3 Vordergrundquasaren signifikant härter ist als im allgemeinen. Während eta trotzdem große Fluktuationen nahe den Quasaren aufweist, die wahrscheinlich von Strahlungstransport herrühren, ist das Strahlungsfeld in der Nähe der Quasare im Mittel härter als in großer Entfernung. Wir interpretieren diese Entdeckungen als die ersten Detektionen des transversalen Proximity-Effekts als eine lokale Fluktuation im spektralen Härtegrad. Kein signifikanter HI Proximity-Effekt ist für die 7 Vordergrundquasare vorhergesagt. Tatsächlich ist die HI-Absorption nahe den Quasaren nahe am oder etwas über dem Mittelwert, was darauf hindeutet, dass die schwache Signatur des transversalen Proximity-Effekts maskiert wird durch intrinsische Überdichten. Jedoch zeigen wir, dass der Härtegrad den transversalen Proximity-Effekt selbst in überdichten Regionen oder auf großen Distanzen sichtbar werden läßt. Deshalb ist der spektrale Härtegrad ein empfindliches physikalisches Maß für den transversalen Proximity-Effekt, der in der Lage ist, die Dichteentartung zu brechen, die die traditionelle Suche behindert. KW - Quasar KW - Proximity-Effekt KW - intergalaktisches Medium KW - quasar KW - proximity effect KW - intergalactic medium Y1 - 2007 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18738 ER - TY - JOUR A1 - Rahmani, H. A1 - Wendt, Martin A1 - Srianand, R. A1 - Noterdaeme, P. A1 - Petitjean, P. A1 - Molaro, P. A1 - Whitmore, J. B. A1 - Murphy, M. T. A1 - Centurion, Martin A1 - Fathivavsari, H. A1 - D'Odorico, S. A1 - Evans, T. M. A1 - Levshakov, S. A. A1 - Lopez, S. A1 - Martins, C. J. A. P. A1 - Reimers, D. A1 - Vladilo, G. T1 - The UVES large program for testing fundamental physics - II. Constraints on a change in mu towards quasar HE 0027-1836 JF - Monthly notices of the Royal Astronomical Society N2 - We present an accurate analysis of the H-2 absorption lines from the z(abs) similar to 2.4018 damped Ly alpha system towards HE 0027-1836 observed with the Very Large Telescope Ultraviolet and Visual Echelle Spectrograph (VLT/UVES) as a part of the European Southern Observatory Large Programme 'The UVES large programme for testing fundamental physics' to constrain the variation of proton-to-electron mass ratio, mu m(p)/m(e). We perform cross-correlation analysis between 19 individual exposures taken over three years and the combined spectrum to check the wavelength calibration stability. We notice the presence of a possible wavelength-dependent velocity drift especially in the data taken in 2012. We use available asteroids spectra taken with UVES close to our observations to confirm and quantify this effect. We consider single-and two-component Voigt profiles to model the observed H-2 absorption profiles. We use both linear regression analysis and Voigt profile fitting where Delta mu/mu is explicitly considered as an additional fitting parameter. The two-component model is marginally favoured by the statistical indicators and we get Delta mu/mu = -2.5 +/- 8.1(stat) +/- 6.2(sys) ppm. When we apply the correction to the wavelength-dependent velocity drift, we find Delta mu/mu = -7.6 +/- 8.1(stat) +/- 6.3(sys) ppm. It will be important to check the extent to which the velocity drift we notice in this study is present in UVES data used for previous Delta mu/mu measurements. KW - intergalactic medium KW - quasars: absorption lines KW - quasars: individual: HE 0027-1836 Y1 - 2013 U6 - https://doi.org/10.1093/mnras/stt1356 SN - 0035-8711 SN - 1365-2966 VL - 435 IS - 1 SP - 861 EP - 878 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Evans, T. M. A1 - Murphy, M. T. A1 - Whitmore, J. B. A1 - Misawa, T. A1 - Centurion, Martin A1 - Lopez, S. A1 - Martins, C. J. A. P. A1 - Molaro, P. A1 - Petitjean, P. A1 - Rahmani, H. A1 - Srianand, R. A1 - Wendt, Martin T1 - The UVES Large Program for testing fundamental physics - III. Constraints on the fine-structure constant from three telescopes JF - Monthly notices of the Royal Astronomical Society KW - intergalactic medium KW - quasars: absorption lines KW - quasars: individual: HS 1549+1919 KW - cosmology: miscellaneous KW - cosmology: observations Y1 - 2014 U6 - https://doi.org/10.1093/mnras/stu1754 SN - 0035-8711 SN - 1365-2966 VL - 445 IS - 1 SP - 128 EP - 150 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Molaro, P. A1 - Centurion, Martin A1 - Whitmore, J. B. A1 - Evans, T. M. A1 - Murphy, M. T. A1 - Agafonova, I. I. A1 - Bonifacio, P. A1 - D'Odorico, S. A1 - Levshakov, S. A. A1 - Lopez, S. A1 - Martins, C. J. A. P. A1 - Petitjean, P. A1 - Rahmani, H. A1 - Reimers, D. A1 - Srianand, R. A1 - Vladilo, G. A1 - Wendt, Martin T1 - The UVES Large Program for testing fundamental physics I. Bounds on a change in alpha towards quasar HE 221-2818 JF - Astronomy and astrophysics : an international weekly journal N2 - Context. Absorption-line systems detected in quasar spectra can be used to compare the value of the fine-structure constant, alpha, measured today on Earth with its value in distant galaxies. In recent years, some evidence has emerged of small temporal and also spatial variations in alpha on cosmological scales. These variations may reach a fractional level of approximate to 10 ppm (parts per million). Aims. To test these claims we are conducting a Large Program of observations with the Very Large Telescope's Ultraviolet and Visual Echelle Spectrograph (UVES), and are obtaining high-resolution (R approximate to 60 000) and high signal-to-noise ratio (S/N approximate to 100) UVES spectra calibrated specifically for this purpose. Here we analyse the first complete quasar spectrum from this programme, that of HE 2217-2818. Methods. We applied the many multiplet method to measure alpha in five absorption systems towards this quasar: z(abs) = 0.7866, 0.9424, 1.5558, 1.6279, and 1.6919. Results. The most precise result is obtained for the absorber at z(abs) = 1.6919 where 3 Fe II transitions and Al II lambda 1670 have high S/N and provide a wide range of sensitivities to alpha. The absorption profile is complex with several very narrow features, and it requires 32 velocity components to be fitted to the data. We also conducted a range of tests to estimate the systematic error budget. Our final result for the relative variation in alpha in this system is Delta alpha/alpha = +1.3 +/- 2.4(stat) +/- 1.0(sys) ppm. This is one of the tightest current bounds on alpha-variation from an individual absorber. A second, separate approach to the data reduction, calibration, and analysis of this system yielded a slightly different result of -3.8 +/- 2.1(stat) ppm, possibly suggesting a larger systematic error component than our tests indicated. This approach used an additional 3 Fe II transitions, parts of which were masked due to contamination by telluric features. Restricting this analysis to the Fe II transitions alone and using a modified absorption profile model gave a result that is consistent with the first approach, Delta alpha/alpha = +1.1 +/- 2.6(stat) ppm. The four other absorbers have simpler absorption profiles, with fewer and broader features, and offer transitions with a narrower range of sensitivities to alpha. They therefore provide looser bounds on Delta alpha/alpha at the greater than or similar to 10 ppm precision level. Conclusions. The absorbers towards quasar HE 2217-2818 reveal no evidence of any variation in alpha at the 3-ppm precision level (1 sigma confidence). If the recently reported 10-ppm dipolar variation in alpha across the sky is correct, the expectation at this sky position is (3.2-5.4) +/- 1.7 ppm depending on dipole model used. Our constraint of Delta alpha/alpha = +1.3 +/- 2.4(stat) +/- 1.0(sys) ppm is not inconsistent with this expectation. KW - quasars: absorption lines KW - quasars: individual: HE 2217-2818 KW - intergalactic medium KW - cosmology: miscellaneous cosmology KW - observations Y1 - 2013 U6 - https://doi.org/10.1051/0004-6361/201321351 SN - 0004-6361 VL - 555 IS - 4 PB - EDP Sciences CY - Les Ulis ER - TY - GEN A1 - Kaastra, Jelle S. A1 - Paerels, Frits B.S. A1 - Durret, Florence A1 - Schindler, Sabine A1 - Richter, Philipp T1 - Thermal radiation processes T2 - Postprints der Universität Potsdam : Mathematisch Naturwissenschaftliche Reihe N2 - We discuss the different physical processes that are important to understand the thermal X-ray emission and absorption spectra of the diffuse gas in clusters of galaxies and the warm-hot intergalactic medium. The ionisation balance, line and continuum emission and absorption properties are reviewed and several practical examples are given that illustrate the most important diagnostic features in the X-ray spectra. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 891 KW - atomic processes KW - radiation mechanisms: thermal KW - intergalactic medium KW - X-rays: general Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-436220 SN - 1866-8372 IS - 891 SP - 155 EP - 190 ER -