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We present the first results from our NASA Keck Observatory Database of Ionized Absorbers toward Quasars (KODIAQ) survey which aims to characterize the properties of the highly ionized gas of high redshift galaxies and their circumgalactic…

The distribution of the absorption line broadening observed in the Ly$\alpha$ forest carries information about the temperature and widths of the filaments in the intergalactic medium (IGM). In this work, we present and test a new method for…

We obtained over 90 hours of spectroscopic observations of four exoplanetary systems with the Hobby-Eberly Telescope (HET). Observations were taken in transit and out of transit, and we analyzed the differenced spectra---i.e., the…

We present results of a blind survey of Lyman limit systems (LLSs) detected in absorption against 105 quasars at z~3 using the blue sensitive MagE spectrograph at the Magellan Clay telescope. By searching for Lyman limit absorption in the…

We report on Atacama Large Millimeter/submillimeter Array (ALMA) detections of molecular absorption lines in Bands 3, 6 and 7 toward four radio-loud quasars, which were observed as the bandpass and complex gain calibrators. The absorption…

We present the high-resolution X-ray spectra of Mkn 421 obtained in November 2003 with the RGS aboard the XMM-Newton satellite. This Target of Opportunity observation was triggered because the source was in a high state of activity in the…

Low ionization metal absorption due to OI has been identified as an important probe of the physical state of the inter-/circumgalactic medium at the tail-end of reionization. We use here high-resolution hydrodynamic simulations to interpret…

We investigate interstellar absorption from molecular hydrogen (H_2) and metals in an intermediate-velocity cloud (IVC) in the direction of the LMC star Sk -68 80 (HD 36521), based on data from the Far Ultraviolet Spectroscopic Explorer…

Mapping the intergalactic medium (IGM) in Lyman-$\alpha$ emission would yield unprecedented tomographic information on the large-scale distribution of baryons and potentially provide new constraints on the UV background and various feedback…

X-ray absorption spectroscopy provides a potentially powerful tool in determining the metal abundances in various phases of the interstellar medium (ISM). We present a case study of the sight line toward 4U 1820-303 (Galactic coordinates l,…

Detections and non-detections of Lyman alpha (Ly$\alpha$) emission from $z>6$ galaxies ($<1$ Gyr after the Big Bang) can be used to measure the timeline of cosmic reionization. Of key interest to measuring reionization's mid-stages, but…

Accurate atomic data are essential for opacity calculations and for abundance analyses of the Sun and other stars. The aim of this work is to provide accurate and extensive results of energy levels and transition data for C I - IV. The…

Observations show that the ISM contains sub-structure on scales less than 1 pc, detected in the form of spatial and temporal variations in column densities or optical depth. Despite the number of detections, the nature and ubiquity of the…

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 report on a comparison between 21 cm rotation measure (RM) and the optically-thin atomic hydrogen column density (N_HI) measured towards unresolved extragalactic sources in the Galactic plane of the northern sky. HI column densities…

The metal absorption lines found in association with \lya absorbers of moderate to high HI column density contain valuable information about the metallicity and ionization conditions within the absorbers and offer a stronger test of models…

The circumgalactic medium (CGM) of galaxies serves as a record of the influences of outflows and accretion that drive the evolution of galaxies. Feedback from star formation drives outflows that carry mass and metals away from galaxies to…

We summarize the attempts by our group and others to derive constraints on variations of fundamental constants over cosmic time using quasar absorption lines. Most upper limits reside in the range 0.5-1.5x10-5 at the 3sigma level over a…

Highly ionized, z=0 metal absorption lines detected in the X-ray spectra of background active galactic nuclei (AGNs) provide an effective method to probe the hot ($T\sim10^6$ K) gas and its metal content in and around the Milky Way. We…

We present an ultraviolet spectroscopic survey of strong H I absorbers in the intergalactic medium, probing their evolution over the last 6-7 Gyr at redshifts $0.24 \leq z \leq 0.84$. We measure column densities $N_{\rm HI} \,( {\rm…