Related papers: Can UVB variations reconcile simulated quasar abso…
We present a high resolution (R~500) X-ray spectrum of the bright quasar H1821+643 (z=0.297), obtained in a 470 ksec Chandra observation. We search for X-ray absorption by highly ionized metal species, OVII and OVIII in particular, at the…
Spatial inhomogeneities in the spectral shape of the ultra-violet background (UVB) at the tail-end of HeII reionisation are thought to be the primary cause of the large fluctuations observed in the HeII to HI Ly-a forest optical depth…
We present an analysis of the absorption-line system in the Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph spectrum at a redshift of $z_{\rm a}={3.1448}$ associated with the quasar SDSS J122040.23+092326.96, whose…
Laboratory measurements of unpolarized and polarized absorption spectra of various samples and crystal stuctures of silicon carbide (SiC) are presented from 1200--35,000 cm$^{-1}$ ($\lambda \sim$ 8--0.28 $\mu$m) and used to improve the…
We have obtained spatially resolved spectra of the z=3.911 triply imaged QSO APM08279+5255 using the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope (HST). We study the line of sight equivalent width (EW)…
The neutral intergalactic medium above redshift 6 is opaque to ionizing radiation, therefore one needs indirect measurements of the escape fraction of ionizing photons from galaxies of this epoch. Low-ionization state absorption lines are a…
We present new calculations of the evolving UV background out to the epoch of cosmological reionization and make predictions for the amount of GeV gamma-ray attenuation by electron-positron pair production. Our results are based on recent…
Using Voigt-profile-fitting procedures on Keck HIRES spectra of nine QSOs we identify 1099 CIV absorber components clumped in 201 systems outside the Lyman forest over 1.6 < z < 4.4. With associated SiIV, CII, SiII and NV where available we…
We present a detailed analysis of three metal absorption systems observed in the spectrum of the HDF-South quasar J2233-606 (z_em = 2.238), taking advantage of new VLT-UVES high resolution data (R=45000, S/N = 40-60, \lambda\lambda…
We present an analysis of the complex associated system of the high-redshift QSO HE2347-4342. Absorption features of HI, CIII, CIV, NV, and OVI with up to 16 components occur in the optical spectral range located up to 1500 km/s redwards…
The low density hydrogen and helium in the IGM probed by QSO absorption lines is sensitive to the amplitude and spectral shape of the metagalactic UV background. We use realistic HI and HeII Ly-alpha forest spectra, constructed from…
High resolution optical (HIRES/Keck) and UV (STIS/HST) spectra, covering a large range of chemical transitions, are analyzed for three single-cloud weak MgII absorption systems along the line of sight toward the quasar PG 1634+706. Weak…
We conduct an ultraviolet (HST and FUSE) spectroscopic survey of HI (Lyman lines) and seven metal ions (OVI, NV, CIV, CIII, SiIV, SiIII, FeIII) in the low-redshift intergalactic medium (IGM) at z<0.4. We analyzed 650 Lya absorbers over…
We present the results of a search for variability in the equivalent widths (EWs) of narrow, associated (Delta v < 5,000 km/s) absorption lines found in the UV spectra of z < 1.5 quasars. The goal of this search was to use variability as a…
We have developed a parallel code called "VoIgt profile Parameter Estimation Routine (VIPER)" for automatically fitting the H I Ly-$\alpha$ forest seen in the spectra of QSOs. We obtained the H I column density distribution function (CDDF)…
We present a qualitative analysis of the variability of quasar broad absorption lines using the large multi-epoch spectroscopic dataset of the Sloan Digital Sky Survey Data Release 10. We confirm that variations of absorption lines are…
(Abridged) Aims. To probe the spectral energy distribution (SED) of the ionizing background radiation at z ~ 2 and to specify the sources contributing to the intergalactic radiation field. Methods. The spectrum of a bright quasar…
We present a measurement of the mean intensity of the hydrogen-ionizing background radiation field at low redshift using 906 Ly-alpha absorption lines in 151 quasar spectra from the archives of the Faint Object Spectrograph on the Hubble…
We present further results of a survey for absorption line systems in the spectra of four high redshift quasars (5.79 $\le$ z$_{\textrm{em}}$ $\le$ 6.13) obtained with the ESO Very Large Telescope X-Shooter. We identify 36 $\textrm{CIV}$…
We report on the highly variable SiIV and CIV broad absorption lines in SDSS J113831.4+351725.2 across four observational epochs. Using the SiIV doublet components, we find that the blue component is usually saturated and non-black, with…