THE ULTRAVIOLET DETECTION OF DIFFUSE GAS IN GALAXY GROUPS

John T. Stocke, Brian A. Keeney, Charles W. Danforth, Benjamin D. Oppenheimer, Cameron T. Pratt, Andreas A. Berlind, Chris Impey, Buell Jannuzi

Research output: Contribution to journalArticlepeer-review

Abstract

A small survey of the UV-absorbing gas in 12 low-z galaxy groups has been conducted using the Cosmic Origins Spectrograph (COS) on-board the Hubble Space Telescope (HST). Targets were selected from a large, homogeneously-selected sample of groups found in the Sloan Digital Sky Survey (SDSS). A critical selection criterion excluded sight lines that pass close (< 1.5 virial radii) to a group galaxy, to ensure absorber association with the group as a whole. to characterize these 1013.5 to 1014.5 M groups, the most massive of which are highly-virialized with numerous early-type galaxies (ETGs). This sample also includes two spiral-rich groups, not yet fully-virialized. At group-centric impact parameters of 0.3-2 Mpc, these S/N = 15-30 spectra detected H I absorption in 7 of 12 groups; high (O VI) and low (Si III) ion metal lines are present in 2/3 of the absorption components. None of the three most highly-virialized, ETG-dominated groups are detected in absorption. Covering fractions & 50% are seen at all impact parameters probed, but do not require large filling factors despite an enormous extent. Unlike halo clouds in individual galaxies, group absorbers have radial velocities which are too low to escape the group potential well without doubt. This suggests that these groups are “closed boxes” for galactic evolution in the current epoch. Evidence is presented that the cool and warm group absorbers are not a pervasive intra-group medium (IGrM), requiring a hotter (T ∼ 106 to 107 K) IGrM to be present to close the baryon accounting.

Original languageEnglish (US)
JournalUnknown Journal
StatePublished - Nov 29 2018

Keywords

  • Galaxies: evolution
  • Galaxies: groups
  • Galaxies: halos
  • Intergalactic medium
  • Quasars: absorption lines

ASJC Scopus subject areas

  • General

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