Red Disc and Blue Bulge Galaxies Across Different Environments

Wednesday, 01 June 2016 8 a.m. — 9 a.m. MST

AURA Lecture Hall

NOIRLab South Colloquia
PAULO LOPES (Observatório do Valongo/UFRJ and NOAO South Visiting Astronomer)

We measured the typical environment of two galaxy populations, which we call red discs and blue bulges, as well as their main physical properties, such as age and metallicity. Those were compared to the normal objects in the blue cloud and red sequence. Our sample is composed of cluster members and field galaxies at z < 0.1, so that we can assess the impact of the local and global environment. We find that environment affect galaxy properties, but the most effective parameter is stellar mass. From the metallicity and age differences of red and blue discs, and the analysis of their star formation histories we suggest the quenching process is slow. We estimate a quenching time scale of ~ 2-3 Gyr. We also find from the sSFR-M* plane that red discs gradually change as they move into clusters. We find evidence for a scenario where blue discs are transformed into red discs as they grow in mass and move to the inner parts of clusters. The blue bulges have many similar properties than blue discs, but some of the latter show strong signs of asymmetry. The high asymmetry blue bulges display enhanced recent star formation compared to their regular counterparts. That indicates some of these systems may have increased their star formation due to mergers. Nonetheless, there may not be a single evolutionary path for these blue early-type objects.