TY - GEN A1 - Richter, Philipp A1 - Paerels, Frits B. S. A1 - Kaastra, Jelle S. T1 - FUV and X-Ray absorption in the warm-hot intergalactic medium T2 - Postprints der Universität Potsdam : Mathematisch Naturwissenschaftliche Reihe N2 - The Warm-Hot Intergalactic Medium (WHIM) arises from shock-heated gas collapsing in large-scale filaments and probably harbours a substantial fraction of the baryons in the local Universe. Absorption-line measurements in the ultraviolet (UV) and in the X-ray band currently represent the best method to study the WHIM at low redshifts. We here describe the physical properties of the WHIM and the concepts behind WHIM absorption line measurements of Hi and high ions such as Ovi, Ovii, and Oviii in the far-ultraviolet and X-ray band. We review results of recent WHIM absorption line studies carried out with UV and X-ray satellites such as FUSE, HST, Chandra, and XMM-Newton and discuss their implications for our knowledge of the WHIM. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 864 KW - galaxies : intergalactic medium KW - quasars : absorption lines KW - cosmology : large-scale structure of the Universe Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-434226 SN - 1866-8372 IS - 864 SP - 25 EP - 49 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 - Nuza, S. E. A1 - Fox, Andrew J. A1 - Wakker, Bart P. A1 - Lehner, N. A1 - Ben Bekhti, Nadya A1 - Fechner, Cora A1 - Wendt, Martin A1 - Howk, J. Christopher A1 - Muzahid, S. A1 - Ganguly, R. A1 - Charlton, Jane C. T1 - An HST/COS legacy survey of high-velocity ultraviolet absorption in the JF - Astronomy and astrophysics : an international weekly journal N2 - Context. The Milky Way is surrounded by large amounts of diffuse gaseous matter that connects the stellar body of our Galaxy with its large-scale Local Group (LG) environment. Aims. To characterize the absorption properties of this circumgalactic medium (CGM) and its relation to the LG we present the so-far largest survey of metal absorption in Galactic high-velocity clouds (HVCs) using archival ultraviolet (UV) spectra of extragalactic background sources. The UV data are obtained with the Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope (HST) and are supplemented by 21 cm radio observations of neutral hydrogen. Methods. Along 270 sightlines we measure metal absorption in the lines of Si II, Si III, C II, and C IV and associated H I 21 cm emission in HVCs in the velocity range vertical bar v(LSR)vertical bar = 100-500 km s(-1). With this unprecedented large HVC sample we were able to improve the statistics on HVC covering fractions, ionization conditions, small-scale structure, CGM mass, and inflow rate. For the first time, we determine robustly the angular two point correlation function of the high-velocity absorbers, systematically analyze antipodal sightlines on the celestial sphere, and compare the HVC absorption characteristics with that of damped Lyman alpha absorbers (DLAs) and constrained cosmological simulations of the LG (CLUES project). KW - Galaxy: halo KW - Galaxy: structure KW - Galaxy: evolution KW - ISM: kinematics and dynamics KW - techniques: spectroscopic KW - ultraviolet: ISM Y1 - 2017 U6 - https://doi.org/10.1051/0004-6361/201630081 SN - 1432-0746 VL - 607 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 - TY - JOUR A1 - Fox, Andrew J. A1 - Richter, Philipp A1 - Ashley, Trisha A1 - Heckman, Timothy M. A1 - Lehner, Nicolas A1 - Werk, Jessica K. A1 - Bordoloi, Rongmon A1 - Peeples, Molly S. T1 - The Mass Inflow and Outflow Rates of the Milky Way JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We present new calculations of the mass inflow and outflow rates around the Milky Way (MW), derived from a catalog of ultraviolet metal-line high-velocity clouds (HVCs). These calculations are conducted by transforming the HVC velocities into the Galactic standard of rest (GSR) reference frame, identifying inflowing (vGSR.<.0 km s(-1)) and outflowing (vGSR > 0 km s(-1)) populations, and using observational constraints on the distance, metallicity, dust content, covering fractions, and total silicon column density of each population. After removing HVCs associated with the Magellanic Stream and the Fermi Bubbles, we find inflow and outflow rates in cool (T similar to 10(4) K) ionized gas of dM(in)/dt greater than or similar to.(0.53 +/- 0.23)(d/12 kpc)(Z/0.2Z(circle dot))-1M(circle dot) yr(-1) and dM(out)/dt greater than or similar to (0.16 +/- 0.07)(d/12 kpc)(Z/0.5Z(circle dot))M--1(circle dot) yr(-1). The apparent excess of inflowing over outflowing gas suggests that the MW is currently in an inflow-dominated phase, but the presence of substantial mass flux in both directions supports a Galactic fountain model, in which gas is constantly recycled between the disk and the halo. We also find that the metal flux in both directions (in and out) is indistinguishable. By comparing the outflow rate to the Galactic star formation rate, we present the first estimate of the mass loading factor (eta(HVC)) of the disk-wide MW wind, finding eta(HVC) greater than or similar to (0.10 +/- 0.06)(d/12 kpc)(Z/0.5Z(circle dot))(-1). Including the contributions from low- and intermediatevelocity clouds and from hot gas would increase these inflow and outflow estimates. Y1 - 2019 U6 - https://doi.org/10.3847/1538-4357/ab40ad SN - 0004-637X SN - 1538-4357 VL - 884 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Richter, Philipp A1 - de Boer, Klaas S. A1 - Werner, Klaus A1 - Rauch, Thomas T1 - High-velocity gas toward the LMC resides in the Milky Way halo JF - Astronomy and astrophysics : an international weekly journal N2 - Aims. To explore the origin of high-velocity gas in the direction of the Large Magellanic Cloud, (LMC) we analyze absorption lines in the ultraviolet spectrum of a Galactic halo star that is located in front of the LMC at d = 9.2(-7.2)(+4.1) kpc distance. Methods. We study the velocity-component structure of low and intermediate metal ions (CII, SiII, SiIII) in the spectrum of RXJ0439.8-6809, as obtained with the Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope (HST), and measure equivalent widths and column densities for these ions. We supplement our COS data with a Far-Ultraviolet Spectroscopic Explorer (FUSE) spectrum of the nearby LMC star Sk-69 59 and with Hi 21 cm data from the Leiden-Argentina-Bonn (LAB) survey. Results. Metal absorption toward RXJ0439.8-6809 is unambiguously detected in three different velocity components near v(LSR) = 0, + 60, and + 150 km s(-1). The presence of absorption proves that all three gas components are situated in front of the star, thus located in the disk and inner halo of the Milky Way. For the high-velocity cloud (HVC) at v(LSR) = + 150 km s(-1), we derive an oxygen abundance of [O/H] = -0.63 (similar to 0.2 solar) from the neighboring Sk-69 59 sight line, in accordance with previous abundance measurements for this HVC. From the observed kinematics we infer that the HVC hardly participates in the Galactic rotation. Conclusions. Our study shows that the HVC toward the LMC represents a Milky Way halo cloud that traces low column density gas with relatively low metallicity. We rule out scenarios in which the HVC represents material close to the LMC that stems from a LMC outflow. KW - Galaxy: halo KW - Galaxy: evolution KW - ISM: abundances KW - ISM: structure Y1 - 2015 U6 - https://doi.org/10.1051/0004-6361/201527451 SN - 1432-0746 VL - 584 PB - EDP Sciences CY - Les Ulis ER - 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 - Murray, Claire E. A1 - Stanimirovic, Snezana A1 - McClure-Griffiths, Naomi M. A1 - Putman, Mary E. A1 - Liszt, Harvey S. A1 - Wong, Tony A1 - Richter, Philipp A1 - Dawson, Joanne R. A1 - Dickey, John M. A1 - Lindner, Robert R. A1 - Babler, Brian L. A1 - Allison, James R. T1 - First detection of HCO+ absorption in the magellanic system JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We present the first detection of HCO+ absorption in the Magellanic System. Using the ATCA, we observed nine extragalactic radio continuum sources behind the Magellanic System and detected HCO+ absorption toward one source located behind the leading edge of the Magellanic Bridge. The detection is located at an LSR velocity of v = 214.0 +/- 0.4 km s(-1), with an FWHM of Delta v = 4.5 +/- 1.0 km s(-1), and an optical depth of tau (HCO+) = 0.10 +/- 0.02. Although there is abundant neutral hydrogen (H I) surrounding the sight line in position-velocity space, at the exact location of the absorber the H I column density is low, <10(20) cm(-2), and there is little evidence for dust or CO emission from Planck observations. While the origin and survival of molecules in such a diffuse environment remain unclear, dynamical events such as H I flows and cloud collisions in this interacting system likely play an important role. KW - ISM: molecules KW - ISM: structure KW - Magellanic Clouds Y1 - 2015 U6 - https://doi.org/10.1088/0004-637X/808/1/41 SN - 0004-637X SN - 1538-4357 VL - 808 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Wisotzki, Lutz A1 - Bacon, R. A1 - Brinchmann, J. A1 - Cantalupo, S. A1 - Richter, Philipp A1 - Schaye, J. A1 - Schmidt, Kasper Borello A1 - Urrutia, Tanya A1 - Weilbacher, Peter Michael A1 - Akhlaghi, M. A1 - Bouche, N. A1 - Contini, T. A1 - Guiderdoni, B. A1 - Herenz, E. C. A1 - Inami, H. A1 - Kerutt, Josephine Victoria A1 - Leclercq, F. A1 - Marino, R. A. A1 - Maseda, M. A1 - Monreal-Ibero, A. A1 - Nanayakkara, T. A1 - Richard, J. A1 - Saust, R. A1 - Steinmetz, Matthias A1 - Wendt, Martin T1 - Nearly all the sky is covered by Lyman-alpha emission around high-redshift galaxies JF - Nature : the international weekly journal of science N2 - Galaxies are surrounded by large reservoirs of gas, mostly hydrogen, that are fed by inflows from the intergalactic medium and by outflows from galactic winds. Absorption-line measurements along the lines of sight to bright and rare background quasars indicate that this circumgalactic medium extends far beyond the starlight seen in galaxies, but very little is known about its spatial distribution. The Lyman-alpha transition of atomic hydrogen at a wavelength of 121.6 nanometres is an important tracer of warm (about 104 kelvin) gas in and around galaxies, especially at cosmological redshifts greater than about 1.6 at which the spectral line becomes observable from the ground. Tracing cosmic hydrogen through its Lyman-a emission has been a long-standing goal of observational astrophysics(1-3), but the extremely low surface brightness of the spatially extended emission is a formidable obstacle. A new window into circumgalactic environments was recently opened by the discovery of ubiquitous extended Lyman-alpha emission from hydrogen around high-redshift galaxies(4,5). Such measurements were previously limited to especially favourable systems(6-8) or to the use of massive statistical averaging(9,10) because of the faintness of this emission. Here we report observations of low-surface-brightness Lyman-alpha emission surrounding faint galaxies at redshifts between 3 and 6. We find that the projected sky coverage approaches 100 per cent. The corresponding rate of incidence (the mean number of Lyman-alpha emitters penetrated by any arbitrary line of sight) is well above unity and similar to the incidence rate of high-column-density absorbers frequently detected in the spectra of distant quasars(11-14). This similarity suggests that most circumgalactic atomic hydrogen at these redshifts has now been detected in emission. Y1 - 2018 U6 - https://doi.org/10.1038/s41586-018-0564-6 SN - 0028-0836 SN - 1476-4687 VL - 562 IS - 7726 SP - 229 EP - 232 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Richter, Philipp A1 - Fox, Andrew J. A1 - Ben Bekhti, Nadya A1 - Murphy, M. T. A1 - Bomans, Dominik J. A1 - Frank, S. T1 - High-resolution absorption spectroscopy of the circumgalactic medium of the Milky Way JF - Astronomische Nachrichten = Astronomical notes KW - Galaxy: halo KW - Galaxy: structure KW - quasars: absorption lines KW - techniques: spectroscopic Y1 - 2014 U6 - https://doi.org/10.1002/asna.201312013 SN - 0004-6337 SN - 1521-3994 VL - 335 IS - 1 SP - 92 EP - 98 PB - Wiley-VCH CY - Weinheim ER -