SMOOTH(ER) STELLAR MASS MAPS IN CANDELS: CONSTRAINTS ON THE LONGEVITY OF CLUMPS IN HIGH-REDSHIFT STAR-FORMING GALAXIES

Abstract

We perform a detailed analysis of the resolved colors and stellar populations\nof a complete sample of 323 star-forming galaxies at 0.5 < z < 1.5, and 326\nstar-forming galaxies at 1.5 < z < 2.5 in the ERS and CANDELS-Deep region of\nGOODS-South. Galaxies were selected to be more massive than 10^10 Msun and have\nspecific star formation rates above 1/t_H. We model the 7-band optical ACS +\nnear-IR WFC3 spectral energy distributions of individual bins of pixels,\naccounting simultaneously for the galaxy-integrated photometric constraints\navailable over a longer wavelength range. We analyze variations in rest-frame\ncolor, stellar surface mass density, age, and extinction as a function of\ngalactocentric radius and local surface brightness/density, and measure\nstructural parameters on luminosity and stellar mass maps. We find evidence for\nredder colors, older stellar ages, and increased dust extinction in the nuclei\nof galaxies. Big star-forming clumps seen in star formation tracers are less\nprominent or even invisible on the inferred stellar mass distributions.\nOff-center clumps contribute up to ~20% to the integrated SFR, but only 7% or\nless to the integrated mass of all massive star-forming galaxies at z ~ 1 and z\n~ 2, with the fractional contributions being a decreasing function of\nwavelength used to select the clumps. The stellar mass profiles tend to have\nsmaller sizes and M20 coefficients, and higher concentration and Gini\ncoefficients than the light distribution. Our results are consistent with an\ninside-out disk growth scenario with brief (100 - 200 Myr) episodic local\nenhancements in star formation superposed on the underlying disk.\nAlternatively, the young ages of off-center clumps may signal inward clump\nmigration, provided this happens efficiently on the order of an orbital\ntimescale.\n