High Dust Depletion in Two Intervening Quasar Absorption Line Systems with the 2175-{\AA} Extinction Bump at $z\sim1.4$

TL;DR

This study analyzes two quasar absorption systems at redshift ~1.4 with the 2175-{ ing} extinction feature, revealing exceptionally high dust depletion patterns similar to cold diffuse clouds in the Milky Way.

Contribution

It provides the first detailed dust depletion measurements in these systems, linking the 2175-{ ing} bump to heavy dust depletion characteristic of cold dense clouds.

Findings

High dust depletion levels similar to Milky Way cold clouds.

2175-{ ing} bump associated with heavy dust depletion.

Comparable depletion patterns found in another system at z=1.64.

Abstract

We present the column densities of heavy-elements and dust depletion studies in twostrong Mg~II absorption systems at $z\sim1.4$ displaying the 2175-{\AA} dust extinction feature. Column densities are measured from low-ionization absorption lines using Apparent Optical Depth Method on the Keck/ESI spectra. We find the dust depletion patterns resemble to that of cold diffuse clouds in the Milky Way (MW). The values, [Fe/Zn]$\approx -1.5$ and [Si/Zn]$<-0.67$, are among the highest dust depletion measured for quasar absorption line systems. In another 2175-{\AA} absorber at $z$=1.64 toward the quasar SDSS J160457.50+220300.5, Noterdaeme et al. (2009) reported a similar dust depletion measurement ([Fe/Zn]=$-1.47$ and [Si/Zn]=$-1.07$) and detected C~I and CO absorption lineson its VLT/UVES spectrum. We conclude that heavy dust depletion (i.e. a characteristic of cold dense clouds in MW) is required to produce a pronounced 2175-{\AA} extinction bump.