Deep Extragalactic VIsible Legacy Survey (DEVILS): The Size-Mass Relation of Galaxies and their Components in HST-COSMOS over the Last 8 Billion Years

Abstract

We present the evolution of the size-mass relation since z = 1 in the COSMOS region of the Deep Extragalactic VIsible Legacy Survey (DEVILS). We combine structural decomposition measurements with stellar mass estimates from fitting spectral energy distributions to multi-wavelength photometry. We implement a novel technique to fit 2D light profiles to repeated observations, removing the requirement to co-add images, which maximises the effective signal-to-noise ratio and avoids issues arising when averaging point spread functions. The sample is then separated into distinct morphological classifications, which reveals that the size-mass relation of disk-dominated galaxies shows an overall flattened slope with very little redshift evolution over 0.3 < z < 1.0. In contrast, spheroid-dominated morphologies show a much steeper relation and are generally more compact at a given stellar mass. The size-mass relations of bulge and disk components are also examined revealing that diffuse bulges occupy a similar region to disk structures, in stark contrast to the size-mass relation of compact bulges. Furthermore, the size-mass relation of disks becomes steeper in the presence of a compact bulge, whereas the relation for disks hosting a diffuse bulge is identical to that of pure-disks. The lack of evolution in disk-dominated galaxies (i.e. R_eff∝(1 + z)^{−0.13 ± 0.02}) is inherent to their self-similar assembly. In contrast, the size-mass relation of spheroid-dominated morphologies is rapidly evolving despite minimal growth in the individual compact bulge components, with average sizes increasing at a pace of R_eff∝(1 + z)^{−3.0 ± 0.2} and a slope that flattens with time as dlog₁₀(R_eff)/dlog₁₀(M_⋆)∝(1 + z)^{2.8 ± 0.2}.

galaxies: structure, galaxies: evolution, galaxies: photometry

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