Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21733503g&link_type=abstract
American Astronomical Society, AAS Meeting #217, #335.03; Bulletin of the American Astronomical Society, Vol. 43, 2011
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. The slope of the color gradient has no obvious dependence on the redshift and stellar mass of the galaxies. It does depend, however, on the overall dust obscuration and rest-frame U-V color of the galaxies mildly, with more obscured or redder galaxies having steeper color gradient. The slope of the color gradient is generally steeper than that of local early-type galaxies. We find that the gradient of a single parameter (age, extinction or metallicity) cannot fully explain the observed color gradient. 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. Regardless of the assumed metallicity gradient, the redder inner regions always have slightly higher dust obscuration than the bluer outer regions, implying that a dust gradient may partly contribute to the observed color gradients. Because of the age--metallicity degeneracy, the derived age gradient is coupled with the assumed metallicity gradient. We discuss the plausibility and implication of each derived age gradient.
Cassata Paolo
Giavalisco Mauro
Guo Yicheng
Koekemoer Anton
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