TY - JOUR A1 - Muzahid, S. A1 - Fonseca, G. A1 - Roberts, A. A1 - Rosenwasser, B. A1 - Richter, Philipp A1 - Narayanan, A. A1 - Churchill, C. A1 - Charlton, J. T1 - COS-Weak: probing the CGM using analogues of weak Mg II absorbers at z < 0.3 JF - Monthly notices of the Royal Astronomical Society N2 - We present a sample of 34 weak metal line absorbers at z < 0.3 selected by the simultaneous >3σ detections of the Si iiλ1260 and C iiλ1334 absorption lines, with Wr(SiII)<0.2 Å and Wr(CII)<0.3 Å, in archival HST/COS spectra. Our sample increases the number of known low-z ‘weak absorbers’ by a factor of >5. The column densities of H i and low-ionization metal lines obtained from Voigt profile fitting are used to build simple photoionization models. The inferred densities and line-of-sight thicknesses of the absorbers are in the ranges of −3.3 < log nH/cm−3 < −2.4 and ∼1 pc–50 kpc (median ≈500 pc), respectively. Most importantly, 85 per cent (50 per cent) of these absorbers show a metallicity of [Si/H]>−1.0(0.0)⁠. The fraction of systems showing near-/supersolar metallicity in our sample is significantly higher than in the H i-selected sample of Wotta et al., and the galaxy-selected sample of Prochaska et al., of absorbers probing the circum-galactic medium at similar redshift. A search for galaxies has revealed a significant galaxy-overdensity around these weak absorbers compared to random positions with a median impact parameter of 166 kpc from the nearest galaxy. Moreover, we find the presence of multiple galaxies in ≈80 per cent of the cases, suggesting group environments. The observed dN/dz of 0.8 ± 0.2 indicates that such metal-enriched, compact, dense structures are ubiquitous in the haloes of low-z group galaxies. We suggest that these are transient structures that are related to galactic outflows and/or stripping of metal-rich gas from galaxies. KW - galaxies: formation KW - galaxies: haloes KW - quasar: absorption line Y1 - 2018 U6 - https://doi.org/10.1093/mnras/sty529 SN - 0035-8711 SN - 1365-2966 VL - 476 IS - 4 SP - 4965 EP - 4986 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 - 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 - 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 - 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 - 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 -