Cold gas and a Milky Way-type 2175-Å bump in a metal-rich and highly depleted absorption system

Jingzhe Ma, Paul Caucal, Pasquier Noterdaeme, Jian Ge, J. Xavier Prochaska, Tuo Ji, Shaohua Zhang, Hadi Rahmani, Peng Jiang, Donald P. Schneider, Britt Lundgren, Isabelle Pâris

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Abstract

We report the detection of a strong MilkyWay-type 2175-Å extinction bump at z = 2.1166 in the quasar spectrum towards SDSS J121143.42+083349.7 from the Sloan Digital Sky Survey Data Release 10.We conduct followup observations with the Echelle Spectrograph and Imager on-board the Keck II telescope and the Ultraviolet and Visual Echelle Spectrograph on the Very Large Telescope. This 2175-Å absorber is remarkable in that we simultaneously detect neutral carbon (C I), neutral chlorine (Cl I), and carbon monoxide (CO). It also qualifies as a damped Lyman α system. The J1211+0833 absorber is found to be metal rich and has a dust depletion pattern resembling that of the Milky Way disc clouds. We use the column densities of the CI fine structure states and the CII/C I ratio (under the assumption of ionization equilibrium) to derive the temperature and volume density in the absorbing gas. A CLOUDY photoionization model is constructed, which utilizes additional atoms/ions to constrain the physical conditions. The inferred physical conditions are consistent with a canonical cold (T ~ 100 K) neutral medium with a high density (n(H I) ~ 100 cm-3) and a slightly higher pressure than the local interstellar medium. Given the simultaneous presence of C I, CO, and the 2175-Å bump, combined with the high metallicity, high dust depletion level, and overall low ionization state of the gas, the absorber towards J1211+0833 supports the scenario that the presence of the bump requires an evolved stellar population.

Original languageEnglish (US)
Pages (from-to)1751-1766
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Volume454
Issue number2
DOIs
StatePublished - Jan 1 2015

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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