A ~6 Mpc overdensity at z ≃ 2.7 detected along a pair of quasar sight lines: filament or protocluster?

Hayley Finley (1) , Patrick Petitjean (1) , Pasquier Noterdaeme (1) , Isabelle Pâris

1 IAP - Institut d'Astrophysique de Paris

Simulations predict that gas in the intergalactic medium (IGM) is distributed in filamentary structures that connect dense galaxy clusters and form the cosmic web. These structures of predominantly ionized hydrogen are difficult to observe directly due to their lack of emitting regions. We serendipitously detected an overdensity of log N(H i) > 18.0 absorbers at z ≃ 2.69 along the lines of sight toward a pair of background quasars. Three main absorption regions spanning ~ 2000 km s^-1 (corresponding to 6.4 h₇₀^-1 Mpc proper) are coincident in the two lines of sight, which are separated by ~ 90 h₇₀^-1 kpc transverse proper distance. Two regions have [Fe/H] <-1.9 and correspond to mild overdensities in the IGM gas. The third region is a sub-DLA with [Fe/H] = -1.1 that is probably associated with a galaxy. We discuss the possibility that the lines of sight probe along the length of a filament or intercept a galaxy protocluster.

Based on observations with X-shooter on the Very Large Telescope at the European Southern Observatory under program 089.A-0855.

Keywords: quasars: absorption lines; intergalactic medium; large-scale structure of Universe; Astrophysics - Cosmology and Nongalactic Astrophysics; Astrophysics - Astrophysics of Galaxies

Domains: Sciences of the Universe [physics]; Astrophysics [astro-ph]

Hayley Finley, Patrick Petitjean, Pasquier Noterdaeme, Isabelle Pâris. A ~6 Mpc overdensity at z ≃ 2.7 detected along a pair of quasar sight lines: filament or protocluster?. Astronomy and Astrophysics - A&A, 2014, 572, ⟨10.1051/0004-6361/201423961⟩. ⟨insu-03645241⟩