Related papers: Intergalactic HeII absorption towards QSO 1157+314…
We have detected a broad interstellar absorption band centred close to 7700 \r{A} and with a FWHM of 176.6$\pm$3.9 \r{A}. This is the first such absorption band detected in the optical range and is significantly wider than the numerous…
We observed the quasar PG1211+143 using the Cosmic Origins Spectrograph on the Hubble Space Telescope in April 2015 as part of a joint campaign with the Chandra X-ray Observatory and the Jansky Very Large Array. Our ultraviolet spectra…
We examine the Ly-alpha absorber population at z<0.3 detected in spectra of the QSOs PG0953+415 and H1821+643 taken with the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope. We compare their statistical properties to…
Measuring rest-frame ultraviolet rotational transitions from the Lyman and Werner bands in absorption against a bright background continuum is one of the few ways to directly measure molecular hydrogen (H2). Here we report the detection of…
CaII 3934,3969 absorbers, which are likely to be a subset of damped Lyman alpha systems, are the most dusty quasar absorbers known, with an order of magnitude more extinction in E(B-V) than other absorption systems. There is also evidence…
We have serendipitously detected a strong O VI-bearing Lyman limit system at z_abs = 0.3558 toward the QSO J1009+0713 (z_em = 0.456) in our survey of low-redshift galaxy halos with the Hubble Space Telescope's Cosmic Origins Spectrograph.…
We constrain the spectrum of the cosmic ultraviolet background radiation by fitting the observed abundance ratios carbon ions at $z\sim 2\hbox{--}3$ with those expected from different models of the background radiation. We use the recently…
We have used STIS aboard HST to search for Lyman-alpha (Lya) absorption in the outer regions of nine nearby (cz<6000 km/s) galaxies using background QSOs and AGN as probes. The foreground galaxies are intercepted between 26 and 199 h-1 kpc…
1.02-1.16 micron spectra (R ~ 7,000) of the gravitationally lensed QSO APM 08279+5255 at z_em=3.911 were obtained during the commissioning run of IRCS, the 1-5 micron near-infrared camera and spectrograph for the Subaru 8.2 m Telescope.…
We searched for 21-cm absorption associated with the z_abs = 1.3647 absorption system toward PKS 0237-233 using the GMRT. A high quality UVES spectrum shows that C I and C I* are detected at this redshift together with C II*, Mg I, Mg II,…
The discovery of a z_abs = 0.0912 damped Lyman-alpha absorption-line system in the HST-FOS ultraviolet spectrum of the quasar OI 363 (0738+313) is reported. This is the lowest redshift quasar damped Lyman-alpha system known. Its neutral…
The importance of HST for the study of quasar absorption lines and of the nature of the intergalactic medium is illustrated by reviewing selected results from past HST observations. Topics reviewed include the study of Ly-alpha absorbers at…
We present new observations of the binary Sirius A / Sirius B performed with HST-GHRS. Two interstellar clouds are detected on this sightline, one of them being identified as the Local Interstellar Cloud (LIC). The interstellar structure of…
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…
The reionization epoch of singly ionized helium (He II) is believed to start at redshifts z~3.5--4 and be nearly complete by z~2.7. We explore the post-reionization epoch with far-ultraviolet spectra of the bright, high-redshift quasar…
We have obtained high resolution (FWHM = 4.4 km/s) Keck spectra of images A and C of the gravitationally lensed QSO Q1422+231. The images are separated by 1.3" on the sky. In an absorption system at z = 3.538 gas column density variations…
We examined the sizes of the absorption clouds in a z=1.3911 damped Ly-alpha absorber (DLA) in the double image lensed quasar Q0957+561 A,B (separation 135 pc at the absorber redshift). Using HIRES/Keck spectra, we studied the MgII…
The HeII transverse proximity effect -- enhanced HeII Ly$\alpha$~transmission in a background sightline caused by the ionizing radiation of a foreground quasar -- offers a unique opportunity to probe the morphology of quasar-driven HeII…
We report observations from the Hubble Space Telescope (HST) and the VLA on the galactic environment, metallicity, and D/H in strong low-redshift Lya absorption systems toward the bright BL Lac object PKS 2155-304. GHRS/G160M spectra at 20…
We consider various possible scenarios to explain the recent observation of a claimed broad H$\alpha$ absorption in our Galactic halo with peak optical depth $\tau \simeq 0.01$ and equivalent width $W \simeq 0.17 \, \rm \AA$. We show that…