Late bloomers (LBs) are massive (M-* > 10(10) M-circle dot) galaxies at z < 1 that formed the majority of their stars within similar to 2 Gyr of the epoch of observation. Our improved methodology for deriving star formation histories (SFHs) of galaxies at redshifts 0.45 < z < 0.75 from the Carnegie-Spitzer-IMACS Survey includes confidence intervals that robustly distinguish LBs from "old" galaxies. We use simulated SFHs to test for "false positives" and contamination from old galaxies to demonstrate that the late-bloomer population is not an artifact of our template modeling technique. We show that LBs account for similar to 20% of z similar to 0.6 galaxies with masses of the modern Milky Way, with a moderate dependence on mass. We take advantage of a 1% overlap of our sample with HST (CANDELS) imaging to construct a "gold standard" catalog of 74 galaxies with high-confidence SFHs, SEDs, basic data, and HST images to facilitate comparison with future studies by others. This small subset suggests that galaxies with both old and young SFHs cover the full range of morphology and environment (excluding rich groups or clusters), albeit with a mild but suggestive correlation with the local environment. We begin the investigation of whether LBs of sufficient mass and frequency are produced in current-generation.CDM-based semianalytic models of galaxy formation. In terms of halo growth, we find a late-assembling halo fraction within a factor of two of our late bloomer fraction. However, sufficiently delaying star formation in such halos may be a challenge for the baryon component of such models.

In clusters of galaxies, the red sequence is believed to be a consequence of a correlation between stellar mass and chemical abundances, with more massive galaxies being more metal-rich and, as a consequence, redder. However, there is a color scatter around the red sequence that holds even with precision photometry, implying that the galaxy population is more complicated than as described by a mass-metallicity relation. We use precision photometry from the Cluster Lensing and Supernova survey with Hubble (CLASH) to investigate what drives this scatter. In four CLASH clusters at z = 0.355 +/- 0.007, we find that the optical-IR galaxy colors confirm the previously known trend of metallicity along the red sequence but also show a strong connection between stellar age and red sequence offset, with ages ranging from 3 to 8 Gyr. Starting with fixed-age color-magnitude relations motivated by the mass-metallicity correlations of CLASH cluster galaxies, and by adjusting galaxy colors through stellar population models to put them all at the age of our red sequence, we are able to reduce the, e.g., F625W-F814W scatter from 0.051 to 0.026 mag with median photometric errors of 0.029 mag. While we will extend this analysis to the full CLASH sample, in four clusters our technique already provides a color precision in near-total-light apertures to resolve the spread in stellar population formation ages that drives the scatter in the red sequence.

The densities of RNA-seq reads (in reads per kilo-bases per million reads, RPKM) were normalized to the library size and the number of sites in 20bp sliding windows along the genome.