Are Compact Massive Galaxies at High-z Really Quiescent? A Mid-Infrared to Submillimeter Study of the GOODS NICMOS Survey Sample

We present measurements of the mean mid-infrared-to-submillimeter flux densities of massive (M\ast \approx 2 \times 10^11 Msun) galaxies at redshifts 1.7 < z < 2.9, obtained by stacking positions of known objects taken from the GOODS NICMOS Survey (GNS) catalog on maps: at 24 {\mu}m (Spitzer); 250, 350, 500{\mu}m (BLAST); and 870{\mu}m (LABOCA). A modified black body dust spectrum fit to the stacked flux densities indicates a median [interquartile] star-formation rate of SFR = 148 [110, 189] Msun yr^-1 . Galaxies are grouped according to their Sersic indices, n, dividing the population into disk-like and spheroid-like galaxies. We find evidence that most of the star formation is occurring in n \leq 2 (disk-like) galaxies, with median [interquartile] SFR = 231 [188,288] Msun yr^-1, while the n > 2 (spheroid-like) population is forming stars with median [interquartile] SFR = 57 [36,83] Msun yr^-1. Thus, while the star formation signal in this sample is clearly dominated by disk-like galaxies, on average the red, compact, spheroid-like population do not appear to be dead, and that localized, dust-obscured star formation is a likely mechanism for size evolution in this population, consistent with several models of galaxy growth.