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02 November 2024
 
  » arxiv » astro-ph/0701042

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The Line-of-Sight Proximity Effect and the Mass of Quasar Host Halos
C.-A. Faucher-Giguere ; A. Lidz ; M. Zaldarriaga ; L. Hernquist ;
Date 3 Jan 2007
AbstractWe show that the Lyman-alpha (Ly-alpha) optical depth statistics in the proximity regions of quasar spectra depend sensitively on the mass of the dark matter halos hosting the quasars. This is owing to both the overdensity around the quasars and the associated infall of gas toward them. For a fiducial quasar host halo mass of (3.0 +/- 1.6) h^-1 x 10^12 M_sun, as inferred by Croom et al. from clustering in the 2dF QSO Redshift Survey, we show that estimates of the ionizing background (Gamma^bkg) from proximity effect measurements that neglect these effects could be biased high by a factor of ~2.5 at z=3. The clustering of galaxies and other active galactic nuclei around the proximity effect quasars enhances the local background, but is not expected to skew measurements by more than a few percent. Assuming the measurements of Gamma^bkg based on the mean flux decrement in the Ly-alpha forest to be free of bias, we demonstrate how the proximity effect analysis can be inverted to measure the mass of the dark matter halos hosting quasars. In ideal conditions, such a measurement could be made with a precision comparable to the best clustering constraints to date from a modest sample of only about 100 spectra. Existing line-of-sight proximity effect measurements of Gamma^bkg (which have assumed that the quasars lie in random locations of the Universe) are a factor of 2-3 higher than the independent flux decrement measurements at z~3. This work thus provides tantalizing evidence for a picture in which proximity effect and flux decrement measurements of Gamma^bkg, as well as clustering measurements of quasar host halo masses, are all consistent with each other when the proximity regions of quasars are realistically modeled as being part of overdense regions and opens the way to proximity effect measurements of dark matter halo masses.
Source arXiv, astro-ph/0701042
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