The Herschel Virgo Cluster Survey - XIX. Physical properties of low luminosity FIR sources at z & 0.5

摘要

Context. The star formation rate is a crucial parameter for the investigation galaxy evolution. At low redshift the cosmic star formation rate density declines smoothly, and massive active galaxies become passive, reducing their star formation activity. This implies that the bulk of the star formation rate density at low redshift is mainly driven by low mass objects. Aims. We investigate the properties of a sample of low luminosity far-infrared sources selected at 250 μ m. We have collected data from ultraviolet to far-infrared in order to perform a multiwavelengths analysis. The main goal is to investigate the correlation between star formation rate, stellar mass, and dust mass for a galaxy population with a wide range in dust content and stellar mass, including the low mass regime that most probably dominates the star formation rate density at low redshift. Methods. We define a main sample of ~ 800 sources with full spectral energy distribution coverage between 0.15 & λ & 500 μ m and an extended sample with ~ 5000 sources in which we remove the constraints on the ultraviolet and near-infrared bands. We analyze both samples with two different spectral energy distribution fitting methods: MAGPHYS and CIGALE, which interpret a galaxy spectral energy distribution as a combination of different simple stellar population libraries and dust emission templates. Results. In the star formation rate versus stellar mass plane our samples occupy a region included between local spirals and higher redshift star forming galaxies. These galaxies represent the population that at z & 0.5 quenches their star formation activity and reduces their contribution to the cosmic star formation rate density. The subsample of galaxies with the higher masses ( M _(?)& 3 × 10 ~(10) M _(⊙) ) do not lie on the main sequence, but show a small offset as a consequence of the decreased star formation. Low mass galaxies ( M _(?)& 1 × 10 ~(10) M _(⊙) ) settle in the main sequence with star formation rate and stellar mass consistent with local spirals. Conclusions. Deep Herschel data allow the identification of a mixed galaxy population with galaxies still in an assembly phase or galaxies at the beginning of their passive evolution. We find that the dust luminosity is the parameter that allow us to discriminate between these two galaxy populations. The median spectral energy distribution shows that even at low star formation rate our galaxy sample has a higher mid-infrared emission than previously predicted.