The Dead Sequence: A Clear Bimodality in Galaxy Colors from z=0 to z=2.5
  We select 25,000 galaxies from the NEWFIRM Medium Band Survey (NMBS) to study
the rest-frame U-V color distribution of galaxies at 0 < z < 2.5. The five
unique NIR filters of the NMBS enable the precise measurement of photometric
redshifts and rest-frame colors for 9,900 galaxies at 1 < z < 2.5. The
rest-frame U-V color distribution at all z<~2.5 is bimodal, with a red peak, a
blue peak, and a population of galaxies in between (the green valley). Model
fits to the optical-NIR SEDs and the distribution of MIPS-detected galaxies
indicate that the colors of galaxies in the green valley are determined largely
by the amount of reddening by dust. This result does not support the simplest
interpretation of green valley objects as a transition from blue star-forming
to red quiescent galaxies. We show that correcting the rest-frame colors for
dust reddening allows a remarkably clean separation between the red and blue
sequences up to z~2.5. Our study confirms that dusty starburst galaxies can
contribute a significant fraction to red sequence samples selected on the basis
of a single rest-frame color (i.e. U-V), so extra care must be taken if samples
of truly "red and dead" galaxies are desired. Interestingly, of galaxies
detected at 24 microns, 14% remain on the red sequence after applying the
reddening correction.
