Star Formation Histories in a Cluster Environment at z~0.84
  We present a spectrophotometric analysis of galaxies belonging to the
dynamically young, massive cluster RX J0152.7-1357 at z~0.84, aimed at
understanding the effects of the cluster environment on the star formation
history (SFH) of cluster galaxies and the assembly of the red-sequence (RS). We
use VLT/FORS spectroscopy, ACS/WFC optical and NTT/SofI near-IR data to
characterize SFHs as a function of color, luminosity, morphology, stellar mass,
and local environment from a sample of 134 spectroscopic members. In order to
increase the signal-to-noise, individual galaxy spectra are stacked according
to these properties. Moreover, the D4000, Balmer, CN3883, Fe4383 and C4668
indices are also quantified. The SFH analysis shows that galaxies in the blue
faint-end of the RS have on average younger stars (Delta t ~ 2 Gyr) than those
in the red bright-end. We also found, for a given luminosity range, differences
in age (Delta t ~ 0.5 - 1.3 Gyr) as a function of color, indicating that the
intrinsic scatter of the RS may be due to age variations. Passive galaxies in
the blue faint-end of the RS are preferentially located in the low density
areas of the cluster, likely being objects entering the RS from the "blue
cloud". It is likely that the quenching of the star formation of these RS
galaxies is due to interaction with the intracluster medium. Furthermore, the
SFH of galaxies in the RS as a function of stellar mass reveals signatures of
"downsizing" in the overall cluster.
