Superdense and normal early-type galaxies at 1<z<2

04/2010; DOI: 10.1063/1.3458529
Source: arXiv

ABSTRACT We combined proprietary and archival HST observations to collect a sample of 62 early-type galaxies (ETGs) at 0.9<z<2 with spectroscopic confirmation of their redshift and spectral type. The whole sample is covered by ACS or NICMOS observations and partially by Spitzer and AKARI observations. We derived morphological parameters by fitting their HST light profiles and physical parameters by fitting their spectral energy distributions. The study of the size-mass and the size-luminosity relations of these early-types shows that a large fraction of them (~50) follows the local relations. These 'normal' ETGs are not smaller than local counterparts with comparable mass. The remaining half of the sample is composed of compact ETGs with sizes (densities) 2.5-3 (15-30) times smaller (higher) than local counterparts and, most importantly, than the other normal ETGs at the same redshift and with the same stellar mass. This suggests that normal and superdense ETGs at z~2 come from different histories of mass assembly. Comment: 4 pages, 3 figures. To appear in "Hunting for the Dark: The Hidden Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P. Debattista and C.C. Popescu, AIP Conf. (in press)

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    ABSTRACT: We measure the sizes of 82 massive (M>10^11 M_sun) galaxies at 1.7<z<3 utilizing deep HST NICMOS data taken in the GOODS North and South fields. Our sample is almost an order of magnitude larger than previous studies at these redshifts, providing the first statistical study of massive galaxy sizes at z>2, confirming the extreme compactness of these galaxies. We split our sample into disk-like (n<2) and spheroid-like (n>2) galaxies based on their Sersic indices, and find that at a given stellar mass disk-like galaxies at z~2.3 are a factor of 2.6+/-0.3 smaller than present day equal mass systems, and spheroid-like galaxies at the same redshifts are 4.3+/-0.7 smaller than comparatively massive elliptical galaxies today. At z>2 our results are compatible with both a leveling off, or a mild evolution in size. Furthermore, the high density (~2x10^10 M_sun kpc^-3) of massive galaxies at these redshifts, which are similar to present day globular clusters, possibly makes any further evolution in sizes beyond z=3 unlikely. Comment: 5 pages, 2 figures, 2 tables, accepted by ApJ Letters, minor changes added to match the accepted version
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