A Metal-Strong and Dust-Rich Damped \lya Absorption System toward the Quasar SDSS J115705.52+615521.7

TL;DR

This paper reports the discovery of an extremely dust-rich, metal-strong damped Lyman-alpha system with unprecedented high metallicity and extinction, revealing a potentially significant but rare population of such systems affecting cosmic gas and metal evolution studies.

Contribution

It presents the first detailed characterization of a highly dust-rich, metal-strong DLA with the highest known metal column density and extinction among quasar DLAs, highlighting its implications for cosmic evolution.

Findings

Neutral hydrogen column density among the highest in DLAs

Metal column density exceeds previous records in quasar DLAs

Extinction law similar to Milky Way with a prominent 2175 Å feature

Abstract

(Abridged for arXiv) We report the discovery of an unusual, extremely dust-rich and metal-strong damped \lya absorption system (DLA) at a redshift $z_{a}=2.4596$ toward the quasar SDSS J115705.52+615521.7 (hereafter J1157+6155) with an emission-line redshift $z_{e}=2.5125$. Its neutral hydrogen column density $N_{\hi} = 10^{21.8\pm0.2}$ cm$^{-2}$ is among the highest values measured in quasar DLAs. The measured metal column density is $N_{ZnII}\approx 10^{13.8}$ cm$^{-2}$, which is about 1.5 times larger than the largest value in any previously observed quasar DLAs. The best-fit curve is a MW-like law with a significant broad feature centered around 2175 {\AA} in the rest frame of the absorber. The measured extinction $A_V \approx 0.92$ mag is unprecedentedly high in quasar DLAs. After applying an extinction correction, the $i$ band absolute magnitude of the quasar is as high as $M_{i} \approx -29.4$ mag, placing it one of the most luminous quasars ever known. This discovery is suggestive of the existence of a rare yet important population of dust-rich DLAs with both high metallicities and high column densities, which may have significant impact on the measurement of the cosmic evolution of neutral gas mass density and metallicity.