CLEAR: The Morphological Evolution of Galaxies in the Green Valley
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AbstractQuiescent galaxies having more compact morphologies than star-forming galaxies has been a consistent result in the field of galaxy evolution. What is not clear is at what point this divergence happens, i.e., when do quiescent galaxies become compact, and how big of a role does the progenitor effect play in this result? Here we aim to model the morphological and star formation histories of high-redshift (0.8 < z < 1.65) massive galaxies (log(M/M) > 10.2) with stellar population fits using Hubble Space Telescope/WFC3 G102 and G141 grism spectra plus photometry from the CANDELS Ly Emission at Reionization (CLEAR) survey, constraining the star formation histories for a sample of 400 massive galaxies using flexible star formation histories. We develop a novel approach to classifying galaxies by their star formation activity in a way that highlights the green valley population, by modeling the specific star formation rate distributions as a function of redshift and deriving the probability that a galaxy is quiescent (PQ). Using PQ and our flexible star formation histories we outline the evolutionary paths of our galaxies in relation to stellar mass, Srsic index, effective radius Reff, and stellar mass surface density. We find that the galaxies show no appreciable stellar mass growth after entering the green valley (a net decrease of 4%) while their stellar mass surface densities increase by 0.25 dex. Therefore galaxies are becoming compact during the green valley and this is due to an increase in the Srsic index and a decrease in Reff.
