Towards Understanding the Mass-Metallicity relation of Quasar Absorbers: Evidence for bimodality and consequences

Details Towards Understanding the Mass-Metallicity relation of Quasar Absorbers: Evidence for bimodality and consequences Towards Understanding the Mass-Metallicity relation of Quasar Absorbers: Evidence for bimodality and consequences

2008-03-27

arxiv.org/abs/0803.3944v3

Astronomy and Astrophysics

Astrophysics

6 pages, 4 figures, accepted for publication in MNRAS

Scientific paper

10.1111/j.1745-3933.2008.00513.x

One way to characterize and understand HI-selected galaxies is to study their metallicity properties. In particular, we show that the metallicity of absorbers is a bivariate function of the HI column density (NHI) and the MgII equivalent width (Wr(2796)). Thus, a selection upon Wr(2796) is not equivalent to a HI selection for intervening absorbers. A direct consequence for damped absorbers with NHI>20.3 from the bivariate metallicity distribution is that any correlation between the metallicity [X/H] and velocity width (or Wr(2796)) arises from the HI cut and therefore can not be interpreted as a signature of the mass-metallicity relation akin to normal field galaxies. Thus DLA samples are intrinsically heterogeneous. On the other hand, a sample of MgII-selected absorbers, which are statistically dominated by lowest NHI systems (sub-DLAs), are found to have a more uniform metallicity distribution. We postulate that the bivariate metallicity distribution can be explained by two different physical origins of absorbers, namely sight-lines through the ISM of small galaxies and sight-lines through out-flowing material. Several published results follow from this bivariate [X/H] distribution such as (a) the two classes of DLAs, reported by Wolfe et al., and (b) the constant dust-to-gas ratio for MgII-absorbers.

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