Sunday, June 26, 2011

Two papers relevant to MgII absorption around galaxies

Will need to reference both these papers in passing in our revised paper testing the Tinker & Chen MgII halo model.

arXiv:1106.0616 Bordoloi et al. The radial and azimuthal profiles of Mg II absorption around 0.5 < z < 0.9 zCOSMOS galaxies of different colors masses and environments

They can't say anything about covering fraction using composites, but can constrain strength of absorption with radius.  Need to mention how consistent their results are with Tinker & Chen's.

Fig. 3: absorption quite weak in composites.  Some smearing will have occurred, due to velocity offsets. 

Fig. 5a: abs. detected out to 100 proper kpc at EW~ few 0.01 Ang for non-group galaxies, but need to check what EW threshold Tinker & Chen had; if TC had a threshold of EW=0.1 Ang, they would have detected absorption only out to ~70 kpc.

We should point out that quasar asterisms offer the chance to probe the variation in absorbing EW with azimuth in individual halos, whereas this work's approach can only study statistical azimuthal variations, and then only for inclined disk galaxies.

arXiv:1106.1642 Lundgren et al. The Dark Matter Haloes and Host Galaxies of MgII Absorbers at z~1

Abstract:  They find from a sample of galaxies at 0.7<z<1.45 that the halo mass of MgII absorbers is the same as at z~0.6, which is good news for us because we don't model any redshift evolution in the halo mass distribution of absorbers.  Their f_c=0.5 (based on 1 detection! see section 6) is consistent with our measurement of f_c. 

Note that they have a sample of only 21 strong MgII absorption systems detected in SDSS quasars with which to compare to a large galaxy sample, and they only usefully probe scales of >~1 h^-1 Mpc from those absorbers with those galaxies.  (They detect MgII absorption in 2 of 3 cases of separations < 60 h^-1 kpc.)

Note that their Fig. 5 shows a slight preference for radius evolution of absorbers, despite being consistent with no evolution.  But what they're cross-correlating with their galaxy sample is a random point in an MgII halo (random because the quasar position is randomly placed within the halo), and that will increase the uncertainties a bit... hopefully they've tried to account for that in their uncertainties.

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