New perspectives on strong z=0.5 MgII absorbers: are halo-mass and equivalent width anti-correlated?

Details New perspectives on strong z=0.5 MgII absorbers: are halo-mass and equivalent width anti-correlated? New perspectives on strong z=0.5 MgII absorbers: are halo-mass and equivalent width anti-correlated?

2006-06-13

arxiv.org/abs/astro-ph/0606328v2

Mon.Not.Roy.Astron.Soc.371:495,2006

Astronomy and Astrophysics

Astrophysics

18 pages, 12 EPS figures, Accepted by MNRAS. Full table of MgII absorbers available at http://www.ast.cam.ac.uk/~mim/pub.html,

Scientific paper

10.1111/j.1365-2966.2006.10685.x

We measure the mean halo-mass of z=0.5 MgII absorbers using the cross-correlation (over co-moving scales 0.05-13h^{-1}Mpc) between 1806 MgII quasar absorption systems and ~250,000 Luminous Red Galaxies (LRGs), both selected from the SDSS DR3. The MgII systems have rest-frame equivalent widths W_r(2796)>=0.3A. From the ratio of the MgII-LRG cross-correlation to the LRG-LRG auto-correlation, we find that the bias ratio between MgII absorbers and LRGs is 0.65+/-0.08, which implies that the absorber host-galaxies have a mean halo-mass 20-40 times smaller than that of the LRGs; the MgII absorbers have halos of mean mass =11.94+/-0.31(stat)+/-0.25(sys). We demonstrate that this statistical technique, which does not require any spectroscopic follow-up, does not suffer from contaminants such as stars or foreground and background galaxies. Finally, we find that the absorber halo-mass is anti-correlated with the equivalent width. If MgII absorbers were virialized in galaxy halos a positive M_h-W_r correlation would have been observed since W_r(2796) is a direct measure of the velocity spread of the MgII sub-components. Thus, our results demonstrate that the individual clouds of a MgII system are not virialized in the gaseous halos of the host-galaxies. We review past results in the literature on the statistics of MgII absorbers and find that they too require an M_h-W_r anti-correlation. When combined with measurements of the equivalent width distribution, the M_h-W_r anti-correlation naturally explains why absorbers with W_r(2796)>=2A are not seen at large impact parameters. We interpret the M_h-W_r anti-correlation within the starburst scenario where strong MgII absorbers are produced by supernovae-driven winds.

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