On the Dearth of Compact, Massive, Red Sequence Galaxies in the Local Universe

Details On the Dearth of Compact, Massive, Red Sequence Galaxies in the Local Universe On the Dearth of Compact, Massive, Red Sequence Galaxies in the Local Universe

2009-07-27

arxiv.org/abs/0907.4766v1

2010ApJ...720..723T

Astronomy and Astrophysics

Astrophysics

Cosmology and Extragalactic Astrophysics

Submitted to ApJ: 18 pages in emulateapj format, 11 figures. Table of galaxy properties available on line from http://www.strw

Scientific paper

10.1088/0004-637X/720/1/723

Using data from the Sloan Digital Sky Survey (SDSS; data release 7), we have conducted a search for local analogs to the extremely compact, massive, quiescent galaxies that have been identified at z > 2. We show that incompleteness is a concern for such compact galaxies, particularly for low redshifts (z < ~0.05) as a result of the SDSS spectroscopic target selection algorithm. We have identified 63 massive red sequence galaxies at 0.066 < z < 0.12 that are smaller than the median size-mass relation by a factor of 2 or more. Consistent with expectations from the virial theorem, the median offset from the mass-velocity dispersion relation for these galaxies is 0.12 dex. We do not find any galaxies with sizes and masses comparable to those observed at z ~ 2, implying a decrease in the comoving number density (at fixed size and mass) by a factor of > 5000. This result cannot be explained by incompleteness: at 0.066 < z <0.12, the SDSS spectroscopic sample should typically be ~75% complete for galaxies with the sizes and masses seen at high redshift, although for the very smallest galaxies it may be as low as ~20%. To confirm that the absence of such compact massive galaxies in SDSS is not a spectroscopic selection effect, we have also looked for such galaxies in the SDSS photometric catalog, using photometric redshifts. While we do find signs of a bias against massive, compact galaxies, this analysis suggests that the SDSS spectroscopic sample is missing at most a few objects in the regime we consider. Accepting the high redshift results, it is clear that massive galaxies must undergo significant structural evolution over z<2 in order to match the population seen in the local universe. Our results suggest that a highly stochastic mechanism like major mergers cannot be the primary driver of this strong size evolution.

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