Probing the intergalactic medium/galaxy connection. V. on the origin of Lyα and O VI absorption at z < 0.2

J. Xavier Prochaska, B. Weiner, H. W. Chen, J. Mulchaey, K. Cooksey

Research output: Contribution to journalArticlepeer-review

248 Scopus citations


We analyze the association of galaxies with Lyα and O VI absorption, the most commonly detected transitions of the low-z intergalactic medium (IGM), in the fields of 14 quasars with z em = 0.06-0.57. Confirming previous studies, we observe a high covering fraction for Lyα absorption to impact parameter ρ = 300h -1 72kpc: 33/37 of our L > 0.01 L* galaxies show Lyα equivalent width W Lyα ≥ 50m. Galaxies of all luminosity L > 0.01 L* and spectral type are surrounded by a diffuse and ionized circumgalactic medium (CGM), whose baryonic mass is estimated at ∼1010.5±0.3 M for a constant N H = 1019 cm -2. The virialized halos and extended CGM of present-day galaxies are responsible for most strong Lyα absorbers (W Lyα > 300m) but cannot reproduce the majority of observed lines in the Lyα forest. We conclude that the majority of Lyα absorption with W Lyα = 30-300m occurs in the cosmic web predicted by cosmological simulations and estimate a characteristic width for these filaments of 400h -1 72kpc. Regarding O VI, we observe a near unity covering fraction to ρ = 200h -1 72kpc for L > 0.1 L* galaxies and to ρ = 300h -1 72kpc for sub-L* (0.1 L* < L < L*) galaxies. Similar to our Lyα results, stronger O VI systems (W 1031 > 70m) arise in the virialized halos of L > 0.1 L* galaxies. Unlike Lyα, the weaker O VI systems (W 1031 30m) arise in the extended CGM of sub-L* galaxies. The majority of O VI gas observed in the low-z IGM is associated with a diffuse medium surrounding individual galaxies with L 0.3 L* and rarely originates in the so-called warm-hot IGM (predicted by cosmological simulations.

Original languageEnglish (US)
Article number91
JournalAstrophysical Journal
Issue number2
StatePublished - Oct 20 2011


  • galaxies: structure
  • intergalactic medium
  • large-scale structure of universe
  • quasars: absorption lines

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


Dive into the research topics of 'Probing the intergalactic medium/galaxy connection. V. on the origin of Lyα and O VI absorption at z < 0.2'. Together they form a unique fingerprint.

Cite this