Journal Article

The association between gas and galaxies – III. The cross-correlation of galaxies* and Lyα absorbers† at <i>z</i>∼ 1

Allen M. Shone, Simon L. Morris, Neil Crighton and Richard J. Wilman

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 402, issue 4, pages 2520-2538
Published in print March 2010 | ISSN: 0035-8711
Published online March 2010 | e-ISSN: 1365-2966 | DOI:
The association between gas and galaxies – III. The cross-correlation of galaxies* and Lyα absorbers† at z∼ 1

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We have measured the two-dimensional two-point correlation function, ξAG, between low-column-density Lyα absorbers and galaxies at a redshift z∼ 1. We measured Lyα absorbers between redshifts z= 0.68 and 1.51 over a total redshift path length of Δz= 1.08 from Hubble Space Telescope Space Telescope Imaging Spectrograph E230M absorption spectra towards the quasars HE 1122−1648 (z= 2.4) and PKS 1127−145 (z= 1.187). The column density of the Lyα absorbers ranged from 13.2 ≤ log10 [NH I(cm−2)] ≤ 17.4, with a median column density of log10 [NH I(cm−2)] = 14.0. A total of 193 galaxy redshifts within the surrounding 6.8 × 5.7 arcmin2 field of view of both quasars were identified in a R-magnitude-limited survey (21.5 ≤RVega≤ 24.5) using the Focal Reducer and Low Dispersion Spectrograph (FORS2) at the Very Large Telescope, of which 95 were higher than the minimum redshift of z= 0.68 to be used in the correlation function. A 3σ upper limit of ξAG= 2.8 was found when 145 Lyα absorber–galaxy pairs were binned in redshift space, in a bin of size Δσ= 1.0, Δπ= 2.0 h−170 Mpc along the projected separation and line-of-sight distances, respectively.

The upper limit in the cross-correlation was found to be 5.4σ lower than the central peak in the galaxy autocorrelation within the same redshift range, ξGG, which was in our data equal to 10.7 ± 1.4. Thus, we have shown for the first time that the clustering between low-column-density absorbers and galaxies at a redshift of 1 is weaker than that between galaxies at the same redshift.

Keywords: galaxies: haloes; intergalactic medium; quasars: absorption lines

Journal Article.  15319 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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