Damped Lyα absorbing galaxies at low redshifts z ≤ 1 from hierarchical galaxy formation models

We investigate damped Ly alpha absorbing galaxies (DLA galaxies) at low redshifts ( z <= 1) in the hierarchical structure formation scenario. In our previous paper, we showed that our model of galaxy formation can explain basic properties of DLA systems such as the metallicity evolution and H I column density distribution. As a subsequent study, we focus on low-redshift DLA systems in detail and compare recent data of many characteristics and their relationships, such as the luminosities, H I column densities, and sizes of galaxies with H I column densities large enough to produce DLA absorptions obtained by optical / radio observations. While there has been debate about what types of galaxies correspond to DLA systems, by using a theoretical model that simultaneously treats both DLA systems and galaxies, we clarify the nature of low-redshift galaxies that produce DLA absorptions, because observational data of such galaxies, mainly at low redshifts, are currently available. We find that our model well reproduces the distributions of fundamental properties of DLA galaxies such as the luminosities, column densities, and impact parameters obtained by optical and near-infrared imagings. Our results suggest that DLA systems primarily consist of low-luminosity galaxies with small impact parameters ( typical radius similar to 3 kpc, surface brightness from 22 to 27 mag arcsec(-2)) similar to those of low surface brightness (LSB) galaxies. In addition, we investigate selection biases arising from the faintness of DLA systems and from the masking effect, which prevents us from identifying a DLA galaxy hidden or contaminated by the point-spread function of a background quasar. We find that the latter affects the distributions of DLA properties more seriously than the former and that the observational data are well reproduced only when the masking effect is taken into account. The rate of DLA galaxies missed because of the masking effect reaches 60% - 90% in the sample at redshifts 0 <= z <= 1 when an angular size limit is as small as 100. Furthermore, we find a tight correlation between H I mass and a cross section of DLA galaxies, and we also find that H I - rich galaxies with MH I similar to 10(9) M-. dominate DLA systems at z similar to 0. These features are entirely consistent with those from the Arecibo Dual-Beam Survey, which is a blind 21 cm survey. Finally, we discuss star formation rates and find that they are typically about 10(-2) M-. yr(-1), as low as those in LSB galaxies.