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 - Wendt, Martin A1 - Molaro, P. T1 - QSO 0347-383 and the invariance of m(p)/m(e) in the course of cosmic time JF - Astronomy and astrophysics : an international weekly journal N2 - Context. The variation of the dimensionless fundamental physical constant mu = m(p)/m(e) - the proton to electron mass ratio - can be constrained via observation of Lyman and Werner lines of molecular hydrogen in the spectra of damped Lyman alpha systems (DLAs) in the line of sight to distant QSOs. Aims. Our intention is to maximize the possible precision of quasar absorption spectroscopy with regard to the investigation of the variation of the proton-to-electron mass-ratio mu. The demand for precision requires an understanding of the errors involved and effective techniques to handle present systematic errors. Methods. An analysis based on UVES high resolution data sets of QSO 0347-383 and its DLA is put forward and new approaches to some of the steps involved in the data analysis are introduced. We apply corrections for the observed offsets between discrete spectra and for the first time we find indications for inter-order distortions. Results. Drawing on VLT-UVES observations of QSO 0347-383 in 2009 our analysis yields Delta mu/mu = (4.3 +/- 7.2) x 10(-6) at z(abs) = 3.025. Conclusions. Current analyzes tend to underestimate the impact of systematic errors. Based on the scatter of the measured redshifts and the corresponding low significance of the redshift-sensitivity correlation we estimate the limit of accuracy of line position measurements to similar to 220 m s (1), consisting of roughly 150 m s (1) due to the uncertainty of the absorption line fit and about 150 m s (1) allocated to systematics related to instrumentation and calibration. KW - cosmology: observations KW - quasars: absorption lines KW - quasars: individual: QSO 0347-383 KW - early Universe Y1 - 2012 U6 - https://doi.org/10.1051/0004-6361/201218862 SN - 0004-6361 VL - 541 IS - 3 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Richter, Philipp T1 - Cold gas accretion by high-velocity clouds and their connection to QSO Absorption-line systems JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We combine H I 21 cm observations of the Milky Way, M31, and the local galaxy population with QSO absorption-line measurements to geometrically model the three-dimensional distribution of infalling neutral-gas clouds ("high-velocity clouds" (HVCs)) in the extended halos of low-redshift galaxies. We demonstrate that the observed distribution of HVCs around the Milky Way and M31 can be modeled by a radial exponential decline of the mean H I volume-filling factor in their halos. Our model suggests a characteristic radial extent of HVCs of R-halo similar to 50 kpc, a total H I mass in HVCs of similar to 10(8) M-circle dot, and a neutral-gas accretion rate of similar to 0.7 M-circle dot yr(-1) for M31/Milky-Way-type galaxies. Using a Holmberg-like luminosity scaling of the halo size of galaxies we estimate R-halo similar to 110 kpc for the most massive galaxies. The total absorption cross-section of HVCs at z approximate to 0 most likely is dominated by galaxies with total H I masses between 10(8.5) and 10(10) M-circle dot. Our model indicates that the H I disks of galaxies and their surrounding HVC population can account for 30%-100% of intervening QSO absorption-line systems with log N(H I) >= 17.5 at z approximate to 0. We estimate that the neutral-gas accretion rate density of galaxies at low redshift from infalling HVCs is dM(H) (I)/dt/dV approximate to 0.022 M-circle dot yr(-1) Mpc(-3), which is close to the measured star formation rate density in the local universe. HVCs thus may play an important role in the ongoing formation and evolution of galaxies. KW - Galaxy: halo KW - ISM: clouds KW - quasars: absorption lines Y1 - 2012 U6 - https://doi.org/10.1088/0004-637X/750/2/165 SN - 0004-637X VL - 750 IS - 2 PB - IOP Publ. Ltd. CY - Bristol 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 -