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16th of January 2017
Evidence for HI replenishment in massive galaxies through gas accretion from the cosmic web
by Dane Kleiner (Monash Uni)
We examine the HI-to-stellar mass ratio (HI fraction) for galaxies near filament backbones within the nearby Universe (d < 181 Mpc). This work uses the 6-degree Field Galaxy Survey (6dFGS) and the Discrete Persistent Structures Extractor (DisPerSE) to define the filamentary structure of the local cosmic web. HI spectral stacking of HI Parkes All Sky Survey (HIPASS) observations yields the HI fraction for filament galaxies and a field control sample. The HI fraction is measured for different stellar masses and 5th nearest neighbour projected densities (Σ5) to disentangle what influences cold gas in galaxies. For galaxies with stellar masses log(M_stellar) < 11 Msun in projected densities 0 < Σ5 < 3 galaxies Mpc-2, all HI fractions of galaxies near filaments are statistically indistinguishable from the control sample. Galaxies with stellar masses log(M_stellar) > 11 Msun have a systematically higher HI fraction near filaments than the control sample. The greatest difference is 0.75 dex with is 5.5σ difference at mean projected densities of 1.45 galaxies Mpc-2. We suggest this is evidence for massive galaxies accreting cold gas from the intra-filament medium which can replenish some HI gas. This supports cold mode accretion where filament galaxies with a large gravitational potential can draw gas from the large-scale structure.

Figure caption: The top row shows the 6dFGS galaxy distribution between 0.0375 < z < 0.0425, the middle panel shows the tessellation that traces the density field of the galaxies and the bottom panel has the filament backbones delineated by DisPerSE overlaid on the tessellation.

Reference: Dane Kleiner, Kevin A. Pimbblet, D. Heath Jones, Bärbel S. Koribalski and Paolo Serra 2017, MNRAS, in press (astro-ph)

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