Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...211.5202d&link_type=abstract
American Astronomical Society, AAS Meeting #211, #52.02; Bulletin of the American Astronomical Society, Vol. 39, p.819
Astronomy and Astrophysics
Astronomy
Scientific paper
We present a formalism to infer the presence of merging by comparing the change in the galaxy stellar mass function (MF) expected from the star formation rate (SFR) as a function of mass and time with the observed time derivative of the MF. We present the SFR in the Fors Deep Field as a function of stellar mass and time spanning redshift from 0 to 5. We show that at z above 3 the average SFR is a power law of stellar mass. The average SFR in massive objects at this redshift is 100-500 Msun/yr. At z 3, the SFR starts to drop at high masses. As redshift decreases, the SFR drop at progressively lower masses (downsizing). The mass at which the SFR deviates from the power law progresses from log M>13 at z 5 to log M 10.9 at z 0.5. This break mass evolvs as Mb(z)=2.7x1010(1+z)2.1. We directly observe a relationship between SF history (SFH) and galaxy mass. Rise time, peak SFR, peak time, and post-maximum (exponential) decay timescale are all correlated with mass. The SFR observed in high mass galaxies at z 4 is sufficient to observe their rapid increase in number density. At most 0.8 effective major mergers per Gyr are consistent with the data at high z, yet enough to transform most high mass objects into ellipticals contemporaneously with their major star formation episode. In contrast, below redshift 1.5 and at masses above 1011, mergers contribute 0.1-0.2/Gyr to the relative increase in number density. This corresponds to 1 major merger per massive object at z below 1.5. At more oderate masses, we find that galaxies are being preferably destroyed by mergers at early times, while at later times the change in their numbers turns positive. This confirms the top-down buildup of the red sequence suggested by recent observations.
Alvarez Marcelo
Drory Niv
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