Study of Kinematics and Chemical abundances properties of Damped and Sub-Damped Lyman alpha absorbers from the Sloan Digital Sky Survey

Abstract

Studying the lifecycle of metals and gas in a galaxy is important to understand the formation and development of Galaxies. Galaxies at high redshifts are very faint to study in emission-line technique, but can be observed in absorption. Generally, background quasars are utilized to study the galaxies in the foreground. Quasar absorption lines serve as valuable tools for studying features of gas within and surrounding galaxies. These lines are independent of quasar luminosity and have been widely employed in the study of galaxies, IGM and CGM. However, getting the high- resolution spectroscopic observation of quasars is very expensive, meanwhile, low resolution data from the all-sky survey such as SDSS are publicly available. For this research, we utilize hundreds of spectra from the SDSS with galaxies of high-redshift to identify, study the kinematic and chemical properties of the gas-rich galaxies (Damped Lyman-alpha systems).

The report introduces measurements chemical abundance of DLAs and sub-DLAs quasar absorbers galaxy evolution traced by at cosmological redshift of 3 ≲ zabs ≲ 5. We found 3 new DLAs with neutral hydrogen column densities log NH I (cm−2) = 20.55 ± 0.2, 20.34 ± 0.2, 20.35 ± 0.2 and 3 new sub-DLAs with neutral hydrogen column densities log NH I (cm−2) = 20.1± 0.2, 20.25 ± 0.2, 20.1 ± 0.2 with multiple ions detected at more than 3 σ. These 6 new gas-rich galaxies show strong Lyman α absorption in the background Quasars with 2 sightlines probing metal rich and remining 4 probing metal poor galaxies. We determined H I column density using Voigt profile fitting program VoigtFit. We further estimate the equivalent widths and metal column densities fitting the Gaussian and applying the Apparent Optical Depth (AOD) method with the help of spectra analysis tool called Linetools. We further studied the relative abundance of [C/O] and [Si/O] and found that two out of six systems have solar and other have super-solar ratios which may signify the enrichment from early stars. We also measure the velocity dispersion to study the kinematics. We also detect C IV and Si IV absorption signifying that the collisional ionization may be prevalent in these DLAs/sub-DLAs. The column density ratios of N (C IV)/N (Si IV) in the range of in the range of 1.4 – 6.5, signifying these absorbers may be ionized by both the photoionization and collisional ionization.