Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21532606d&link_type=abstract
American Astronomical Society, AAS Meeting #215, #326.06; Bulletin of the American Astronomical Society, Vol. 42, p.423
Astronomy and Astrophysics
Astronomy
Scientific paper
We present the stellar mass function (MF) in COSMOS to fainter limits than previously probed at z<1. Neither the total nor the red or blue MF can be fit by a single Schechter function once the mass limit reaches below 3e9Msun. We observe a dip at masses 1e10Msun, just below the traditional M*, and an upturn towards a steep faint-end slope of α=-1.7 at all redshifts. This bimodal nature of the MF is not solely a result of the blue/red dichotomy. The blue mass function itself is bimodal at z=1. This suggests a new dichotomy in that predates the appearance of the red sequence. We propose two interpretations for this bimodal distribution. If the gas fraction increases towards lower mass, galaxies with Mbaryon 1e10Msun would shift to lower stellar masses, creating the observed dip, and indicating a change in star formation efficiency. Therefore, we investigate whether the dip is absent in the baryonic (stars+gas) mass function. Alternatively, the dip could be created by an enhancement of the galaxy assembly rate at M*, a phenomenon that naturally arises if the baryon fraction peaks there. In this scenario we would identify the galaxies occupying the bump with central galaxies and the increasing fraction of satellite galaxies at lower mass with the second, steep component of the MF. The blue and total MFs exhibit a steeper faint-end slope than previously known that may approach the halo MF slope -2. While the dip is apparent in the total MF at all redshifts, it shifts from the blue to the red population, likely as a result of transforming high-mass blue galaxies into red ones. We detect an upturn in teh MF of red galaxies. Their increase with time reflects a decrease in the number of blue systems, hence we tentatively associate them with quenched satellite dSphs.
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