Newly discovered Ca II absorbers in the early universe: statistics, element abundances and dust

TL;DR

This study identifies new Ca II absorbers in the early universe, analyzes their dust properties and element abundances, and reveals their association with different galactic environments and dust extinction laws over cosmic time.

Contribution

It presents a large sample of newly discovered Ca II absorbers, characterizes their dust depletion and extinction features, and compares their properties with other known absorbers, highlighting their environmental diversity.

Findings

Weak and strong Ca II absorbers show distinct dust depletion patterns.

12 new 2175{ A} dust absorbers (2DAs) discovered, some following LMC extinction law.

Dust bump strength increases as redshift decreases, indicating dust growth over time.

Abstract

We report discoveries of 165 new quasar Ca II absorbers from the Sloan Digital Sky Survey (SDSS) Data Release 7 and 12. Our Ca II rest frame equivalent width distribution supports the weak and strong subpopulations, split at ${W}^{\lambda3934}_{0}=0.7${\AA}. Comparison of both populations' dust depletion shows clear consistency for weak absorber association with halo-type gas in the Milky Way (MW) while strong absorbers have environments consistent with halo and disc-type gas. We probed our high redshift Ca II absorbers for 2175{\AA} dust bumps, discovering 12 2175{\AA} dust absorbers (2DAs). This clearly shows that some Ca II absorbers follow the Large Magellanic Cloud (LMC) extinction law rather than the Small Magellanic Cloud extinction law. About 33% of our strong Ca II absorbers exhibit the 2175{\AA} dust bump while only 6% of weak Ca II absorbers show this bump. 2DA detection further supports the theory that strong Ca II absorbers are associated with disk components and are dustier than the weak population. Comparing average Ca II absorber dust depletion patterns to that of Damped Ly{\alpha} Absorbers (DLAs), Mg II absorbers, and 2DAs shows that Ca II absorbers generally have environments with more dust than DLAs and Mg II absorbers, but less dust than 2DAs. Comparing 2175{\AA} dust bump strengths from different samples and also the MW and LMC, the bump strength appears to grow stronger as the redshift decreases, indicating dust growth and the global chemical enrichment of galaxies in the universe over time.