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

Abstract

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 h 70 −1 Mpc proper) are coincident in the two lines of sight, which are separated by ∼90 h 70 −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.

Searching for the shadows of giants: characterizing protoclusters with line of sight Lyman-α absorption

“…Orientation of structure to the line of sight, rather than association with a protocluster of a given mass or an overdensity, appears to be a critical factor that determines the extended nature of the Ly-α absorption. In this context, we briefly note that Finley et al (2014) argued for the detection of an intergalactic filament based on observations of multiple LLSs and SLLSs with N HI > 10 18 cm −2 along two closely separated quasar sight lines at z = 2.69. The seven strong H I absorption systems observed by Finley et al (2014) span ∼ 1700 km s −1 , corresponding to 16.6h −1 cMpc at z = 2.69.…”

“…In this context, we briefly note that Finley et al (2014) argued for the detection of an intergalactic filament based on observations of multiple LLSs and SLLSs with N HI > 10 18 cm −2 along two closely separated quasar sight lines at z = 2.69. The seven strong H I absorption systems observed by Finley et al (2014) span ∼ 1700 km s −1 , corresponding to 16.6h −1 cMpc at z = 2.69. While Finley et al (2014) could not definitively rule out association of the H I absorbers with a protocluster, their favoured interpretation is broadly consistent with our anal- Table 3.…”

“…The seven strong H I absorption systems observed by Finley et al (2014) span ∼ 1700 km s −1 , corresponding to 16.6h −1 cMpc at z = 2.69. While Finley et al (2014) could not definitively rule out association of the H I absorbers with a protocluster, their favoured interpretation is broadly consistent with our anal- Table 3. From left to right, the maximum H I column density associated with each CoSLA is N HI = 10 16.5 cm −2 , 10 14.9 cm −2 , 10 19.0 cm −2 and 10 14.7 cm −2 .…”

UBIQUITOUS GIANT Lyα NEBULAE AROUND THE BRIGHTEST QUASARS AT z ∼ 3.5 REVEALED WITH MUSE∗

“…Absorption line studies using quasar pairs have found a high covering fraction (∼60%) of optically thick gas at projected distances of 200 pkpc from the quasars (e.g., Prochaska et al 2013;Finley et al 2014), suggesting the presence of large amounts of cold gas around these quasars. Combining the constraints from absorption and emission studies 11 , one might be tempted to interpret the low detection rate of giant emitting nebulae as a consequence of a small opening angle of the quasar radiation "beam" together with an anisotropic distribution of the "cold" gas.…”

Three- and two-point spatial correlations of intergalactic medium at z ∼ 2 using projected quasar triplets

“…Using a group of background quasars, we can probe different physical processes at different scales: (i) The H i density and velocity fields at the scales of few 100 cKpc may have thermal memory of cosmic reionization in the form of pressure broadening (Peeples et al 2010;Rorai et al 2018); (ii) at the scale of ∼ 1 pMpc we can probe matter clustering around massive galaxies (quasar hosts and intervening metal systems) and various feedback processes connecting gas flows between galaxies and the IGM. At present these scales are best probed using quasar pairs (see for example, Prochaska et al 2013); (iii) at the scales of one to few Mpc, one is probing the cosmic structure of filaments and voids and the effect of radiative feed back from bright persistent objects like quasars (e.g Finley et al 2014;Lee et al 2018); and (iv) the Baryon Acoustic Oscillations (BAO) at ∼100 Mpc probes primordial density fluctuations at very large scales (Ata et al 2018).…”