Understanding Ultra Massive Galaxies at Z~1.6
Abstract
Using an adaptation of the BzKs technique, we select and distinguish between star-forming and passive galaxies at high redshift in order to focus our attention on the most massive (Mstar > 1011 Msun), passive galaxies at high redshift (z~1.5-2). We will refer to these objects as Ultra-Massive Passive Galaxies or UMPEGs.It is of great interest trying to understand how massive passive galaxies can exist in large numbers by z~2, when the age of the Universe is just ~3 Gyr. Since they are already quenched by the time we observe them at the peak epoch of cosmic star formation, they must have attained very high rates of star formation to assemble their stellar masses in the short time available to them. Their SFRs at the time of quenching must have been several hundred Msun/yr. UMPEGs are also believed to reside in high-density environments, and due to their extremely large stellar masses are guaranteed to be the central galaxies of their host dark matter haloes.We use the CFHTLS Wide Fields and matching Ks-band observations (Arnouts et al. (in prep.)) covering an effective area of ~20 deg2 to select and study a large sample of UMPEGs at z~1.5--2. This large area provides us with a unique opportunity to detect these very rare and bright objects in large numbers and to effectively constrain the bright end of their luminosity and mass functions. Given how steep the stellar mass function is at its massive end (where we expect UMPEGS with stellar masses of Mstar > 1011 Msun), it is important to constrain it by building a representative sample. Thereby allowing us to understand their evolution from a very hight redshift of z=2 down to z=0 (for instance the contribution of dry mergers).We we will present a summary of properties of these rare but important objects based on our large sample of ~150 UMPEGS, including their luminosity and mass functions as well as general morphologies and SED-fitting results.
- Publication:
-
IAU General Assembly
- Pub Date:
- August 2015
- Bibcode:
- 2015IAUGA..2257954A