Star formation rate (SFR) is a crucial parameters to investigate galaxy evolution. At low redshift the cosmic star formation rate density (SFRD) declines smoothly, and massive active galaxies become passive reducing their star formation activity. This imply that the bulk of the SFRD at low redshift is mainly driven by low mass objects.
In this talk I will show the main properties of a sample of low luminosity Far Infra Red sources selected at 250 micron from deep Herschel survey. The data set has been extended with complementary data to perform a multi wavelengths analysis. The main goal is to investigate the correlation between SFR, stellar mass and dust mass for a galaxy population with low dust content and stellar mass, characterizing the bulk of the SFRD at low redshift. We define a main sample of about 800 sources with full Spectral Energy Distribution (SED) coverage between 0.15 and 500 micron and an extended sample with about 5400 sources with the constraints on the Ultra Violet and Near Infra Red bands removed. We analyze both samples with two different SED fitting methods: MAGPHYS and CIGALE, which interpret a galaxy SED as a combination of different simple stellar population libraries and dust emission templates.
In a SFR-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 SFRD. The galaxies subsample with the higher masses does not lie on the main sequence, but shows a small offset, as a consequence of the decreased star formation. Low mass galaxies settle in the main sequence with SFR and stellar masses consistent with local spirals. Deep Herschel data allows 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 discriminates these two galaxy populations. The median SED shows that even at low SFR our galaxy sample have Mid Infra Red emission higher than previously predicted.
2015 September 24, 15:00
Observatório Astronómico de Lisboa (Seminar room)
Tapada da Ajuda, 1349-018 Lisboa