High-redshift Damped Lyman-alpha Research Articles

A halo model for cosmological neutral hydrogen : abundances and clustering

We extend the results of previous analyses towards constraining the abundance and clustering of post-reionization ($z \sim 0-5$) neutral hydrogen (HI) systems using a halo model framework. We work with a comprehensive HI dataset including the small-scale clustering, column density and mass function of HI galaxies at low redshifts, intensity mapping measurements at intermediate redshifts and the UV/optical observations of Damped Lyman Alpha (DLA) systems at higher redshifts. We use a Markov Chain Monte Carlo (MCMC) approach to constrain the parameters of the best-fitting models, both for the HI-halo mass relation and the HI radial density profile. We find that a radial exponential profile results in a good fit to the low-redshift HI observations, including the clustering and the column density distribution. The form of the profile is also found to match the high-redshift DLA observations, when used in combination with a three-parameter HI-halo mass relation and a redshift evolution in the HI concentration. The halo model predictions are in good agreement with the observed HI surface density profiles of low-redshift galaxies, and the general trends in the the impact parameter and covering fraction observations of high-redshift DLAs. We provide convenient tables summarizing the best-fit halo model predictions.

DETECTION OF NEUTRAL PHOSPHORUS IN THE NEAR-ULTRAVIOLET SPECTRA OF LATE-TYPE STARS

We report the detection of several absorption lines of neutral phosphorus (P, Z=15) in archival near ultraviolet spectra obtained with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. We derive phosphorus abundances or interesting upper limits in 14 late-type stars with metallicities spanning -3.8<[Fe/H]<-0.1. Previously, phosphorus had only been studied in Galactic stars with -1.0<[Fe/H]<+0.3. Iron lines reveal abundance offsets between the optical and ultraviolet regions, and we discuss and apply a correction factor to account for this offset. In stars with [Fe/H]>-1.0, the [P/Fe] ratio decreases toward the solar value with increasing metallicity, in agreement with previous observational studies. In stars with [Fe/H]<-1.0, <[P/Fe]>=+0.04+/-0.10, which overlaps with the [P/Fe] ratios found in several high-redshift damped Lyman-alpha systems. This behavior hints at a primary origin in massive stars.

The nitrogen and oxygen abundances in the neutral gas at high redshift

We study the Oxygen and Nitrogen abundances in the interstellar medium of high-redshift galaxies. We use high resolution and high signal-to-noise ratio spectra of Damped Lyman-alpha (DLA) systems detected along the line-of-sight to quasars to derive robust abundance measurements from unsaturated metal absorption lines. We present results for a sample of 16 high-redshift DLAs and strong sub-DLAs (log N(HI)>19.5, 2.4 -1 and nine systems have [N/O]<-1.15. In the diagram [N/O] versus [O/H], a loose plateau is possibly present at [N/O]=-0.9 that is below the so-called primary plateau as seen in local metal-poor dwarf galaxies ([N/O] in the range -0.57 to -0.74). No system is seen above this primary plateau whereas the majority of the systems lie well below with a large scatter. All this suggests a picture in which DLAs undergo successive star-bursts. During such an episode, the [N/O] ratio decreases sharply because of the rapid release of Oxygen by massive stars whereas inbetween two bursts, Nitrogen is released by low and intermediate-mass stars with a delay and the [N/O] ratio increases.

A molecular probe of dark energy

Many theoretical models of dark energy invoke rolling scaler fields which in turn predict time varying values of the fundamental constants. Establishing the value of the fundamental constants at various times in the universe can probe and test the various dark energy theories. One of the constants that is predicted to vary is the ratio of the electron to proton mass μ. It was established early on that molecular spectra are sensitive to the value of μ and can be used as probes of that value. This article describes the use of the spectrum of molecular hydrogen in high redshift Damped Lyman Alpha systems (DLAs) as a sensitive probe of the time evolution of μ.

Relative abundance pattern along the profile of high redshift Damped Lyman-$\vec \alpha$ systems

We investigated abundance ratios along the profiles of six high-redshift Damped Lyman-alpha systems, three of them associated with H2 absorption, and derived optical depths in each velocity pixel. The variations of the pixel abundance ratios were found to be remarkably small and usually smaller than a factor of two within a profile. This result holds even when considering independent sub-clumps in the same system. The depletion factor is significantly enhanced only in those components where H2 is detected. There is a strong correlation between [Fe/S] and [Si/S] abundances ratios, showing that the abundance ratio patterns are definitely related to the presence of dust. The depletion pattern is usually close to the one seen in the warm halo gas of our Galaxy.

New high-redshift damped Lyman-alpha absorption systems and the redshift evolution of damped absorbers

We have discovered two high-redshift (z abs =3.388 and 2.908) damped Lyα absorption systems and a third possible damped system (z abs =3.080) while obtaining spectra of optical counterparts from a sample of flat spectrum radio sources. These three systems all have higher redshifts than any previously known damped Lyα absorption systems in the spectra of radio-loud quasars, and they are among the highest redshift damped Lyα systems known. It is unlikely that we would have found as many as two or three damped Lyα absorption systems among our sample unless there is a significant increase in the area-weighted comoving density of damped systems for z≥3