THE GROWTH OF MASSIVE GALAXIES SINCE z = 2
- Department of Astronomy, Yale University, New Haven, CT 06520-8101 (United States)
- Sterrewacht Leiden, Leiden University, NL-2300 RA Leiden (Netherlands)
- Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)
- Carnegie Observatories, Pasadena, CA 91101 (United States)
- Department of Physics and Astronomy, Tufts University, Medford, MA 02155 (United States)
- UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States)
- Department of Physics and Astronomy, University of Kansas, Lawrence, KS 66045 (United States)
We study the growth of massive galaxies from z = 2 to the present using data from the NOAO/Yale NEWFIRM Medium Band Survey. The sample is selected at a constant number density of n = 2 x 10{sup -4} Mpc{sup -3}, so that galaxies at different epochs can be compared in a meaningful way. We show that the stellar mass of galaxies at this number density has increased by a factor of approx2 since z = 2, following the relation log M{sub n} (z) = 11.45 - 0.15z. In order to determine at what physical radii this mass growth occurred, we construct very deep stacked rest-frame R-band images of galaxies with masses near M{sub n} (z), at redshifts (z) = 0.6, 1.1, 1.6, and 2.0. These image stacks of typically 70-80 galaxies enable us to characterize the stellar distribution to surface brightness limits of approx28.5 mag arcsec{sup -2}. We find that massive galaxies gradually built up their outer regions over the past 10 Gyr. The mass within a radius of r = 5 kpc is nearly constant with redshift, whereas the mass at 5 kpc < r < 75 kpc has increased by a factor of approx4 since z = 2. Parameterizing the surface brightness profiles, we find that the effective radius and Sersic n parameter evolve as r{sub e} propor to (1 + z){sup -1.3} and n propor to (1 + z){sup -1.0}, respectively. The data demonstrate that massive galaxies have grown mostly inside-out, assembling their extended stellar halos around compact, dense cores with possibly exponential radial density distributions. Comparing the observed mass evolution to the average star formation rates of the galaxies we find that the growth is likely dominated by mergers, as in situ star formation can only account for approx20% of the mass buildup from z = 2 to z = 0. A direct consequence of these results is that massive galaxies do not evolve in a self-similar way: their structural profiles change as a function of redshift, complicating analyses which (often implicitly) assume self-similarity. The main uncertainties in this study are possible redshift-dependent systematic errors in the total stellar masses and the conversion from light-weighted to mass-weighted radial profiles.
- OSTI ID:
- 21392284
- Journal Information:
- Astrophysical Journal, Vol. 709, Issue 2; Other Information: DOI: 10.1088/0004-637X/709/2/1018; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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