The structures of distant galaxies – V. The evolution of galaxy structure in stellar mass at inline image

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ABSTRACT

The structure and morphology of a galaxy are nearly always studied using the light originating from stars; however, ideally one is interested in measuring structure using the stellar mass distribution. Not only does stellar mass trace out the underlying distribution of matter, it also minimizes the effects of star formation and dust on the appearance and structure of a galaxy. In this paper, we present a study of the stellar mass distributions and structures of galaxies at z < 1 as found within the GOODS fields. We use pixel-by-pixel K-corrections to construct stellar mass and mass-to-light ratio maps of 560 galaxies of known morphology at magnitudes z850 < 24. We measure structural and size parameters using these stellar mass maps, as well as on ACS BViz-band imaging. This includes investigating the structural CAS–Gini–M20 parameters and half-light radius (Re) for each galaxy. We further identify and examine unusual galaxy types with this method, including compact and peculiar ellipticals, and peculiar galaxies in some mode of formation. We compare structural parameters and half-light radii in the ACS z850 band and stellar mass maps, finding no systematic bias introduced by measuring galaxy sizes in z850. We furthermore investigate relations between structural parameters in the ACS BViz bands and stellar mass maps, and compare our result to previous morphological studies. Combinations of various parameters in stellar mass generally reveal clear separations between early- and late-type morphologies, but cannot easily distinguish between star formation and dynamically disturbed systems. We also show that while ellipticals and early-type spirals have fairly constant CAS [the parameters concentration (C), asymmetry (A) and clumpiness (S)] values at z < 1, we find a tendency for late-type spiral and peculiar morphological types to have a higher A(M*) at higher redshift. We argue that this and the large fraction of peculiars that appear spiral-like in stellar mass maps are possible evidence for either an active bulge formation in some late-type discs at z < 1 or the presence of minor merger events.

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