Red Nuggets at z~1.5: Compact passive galaxies and the formation of the Kormendy Relation

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  • 14 July 2008
Abstract
We present the results of NICMOS imaging of a sample of 16 high mass passively evolving galaxies with 1.32, this is the first time such systems have been detected in a rest-frame optical survey at 1.3<z<2. We refer to these compact galaxies as "red nuggets". Similarly compact massive galaxies are completely absent in the nearby Universe. We introduce a new "stellar mass Kormendy relation" (stellar mass density vs size) which isolates the effects of size evolution from those of luminosity and color evolution. The 1.1 < z < 2 passive galaxies have mass densities that are an order of magnitude larger then early type galaxies today and are comparable to the compact distant red galaxies at 2 < z < 3. We show that size evolution occurs primarily in the 1.1 < z < 1.5 redshift interval, or over a time of only 1.6 Gyr. We briefly consider mechanisms for size evolution in contemporary models focusing on equal-mass mergers and adiabatic expansion driven by stellar mass loss. Neither of these mechanisms appears able to transform the high-redshift Kormendy relation into its local counterpart.

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