Revealing the host galaxy of a quasar 2175 Å dust absorber at z = 2.12

Abstract

We report the first detection of the host galaxy of a strong 2175 Å dust absorber at z = 2.12 towards the background quasar SDSS J121143.42+083349.7 using HST/WFC3 IR F140W direct imaging and G141 grism spectroscopy. The spectroscopically confirmed host galaxy is located at a small impact parameter of ~ 5.5 kpc (~ 0.65${}^{\prime \prime }$). The F140W image reveals a disk-like morphology with an effective radius of 2.24 $\pm$ 0.08 kpc. The extracted 1D spectrum is dominated by a continuum with weak emission lines ([O\III] and [O\II]). The [O\III]-based unobscured star formation rate (SFR) is 9.4 $\pm$ 2.6 M${}_{\odot }$yr${}^{-1}$ assuming an [O\III]/H$\alpha$ ratio of 1. The moderate 4000 Å break (Dn(4000) index $\sim$ 1.3) and Balmer absorption lines indicate that the host galaxy contains an evolved stellar population with an estimated stellar mass M${}_{\ast }$ of (3 - 7) $\times$ 10${}^{10}$ M${}_{\odot }$. The SFR and M${}_{\ast }$ of the host galaxy are comparable to, though slightly lower than, those of typical emission-selected galaxies at $z$ $\sim$ 2. As inferred from our absorption analysis in Ma et al. (2015, 2017, 2018), the host galaxy is confirmed to be a chemically-enriched, evolved, massive, and star-forming disk-like galaxy that is likely in the transition from a blue star-forming galaxy to a red quiescent galaxy.

7 pages, 4 figures; accepted for publication in ApJL

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• Damped Ly-alpha Absorbers in Star-forming Galaxies at z < 0.15 Detected with the Hubble Space Telescope and Implications for Galaxy Evolution
• Chemical enrichment and host galaxies of extremely-strong intervening DLAs towards quasars
• MUSE-ALMA Haloes IX: Morphologies and Stellar Properties of Gas-rich Galaxies
• Studying Quasar Absorber Host Galaxy Properties Using Image Stacking Technique