Astronomy and Astrophysics – Astronomy
Scientific paper
May 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21641706g&link_type=abstract
American Astronomical Society, AAS Meeting #216, #417.06; Bulletin of the American Astronomical Society, Vol. 41, p.828
Astronomy and Astrophysics
Astronomy
Scientific paper
We report the detection of color gradients in massive (stellar mass M>1010 Msun) galaxies with low specific star formation rate (SSFR<10-11/yr) at redshift z 2. The galaxies are selected by means of SED fitting to spectral population synthesis models using the Great Observatories Origins Deep Survey (GOODS) broad--band photometry, which spans the optical, near--IR and mid--IR windows, augmented by recent ultra--deep near--IR images obtained with HST WFC3. The estimated stellar mass and SSFR would place these galaxies among today's Hubble early types, while their rest--frame optical morphology, as shown by the WFC3 images, is consistent with that of spheroidal systems. The inner regions of these galaxies are found to have redder rest UV--optical colors than their outer parts. To study the physical implications of these color gradients we fit spatially resolved HST seven--bands photometry from ACS and WFC3 images (BVizYJH) in concentric shells across the light profile of each galaxies, sampling the color gradients. The fit shows that the bluer outer regions of the galaxies are up to about 1 Gyr younger than the redder inner regions and have up to 102 times higher SSFR. This can result from a differential mass assembly in these galaxies, in which star formation in the outer regions takes place at a later time or on a longer time scale than in the denser cores. Alternatively, the observed color gradients could result from a mechanism that shuts down star formation more abruptly and effectively in the central regions of the galaxies than in the outskirts.
Cassata Paolo
Giavalisco Mauro
Guo Yicheng
Koekemoer Anton M.
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