EPOCHS XI: The Structure and Morphology of Galaxies in the Epoch of Reionization to z ~ 12.5

Abstract

We present a structural analysis of 521 galaxy candidates at 6.5 < z < 12.5, with $SNR>10\ddot{I}ƒ$ in the F444W filter, taken from the EPOCHS v1 sample, consisting of uniformly reduced deep JWST NIRCam data, covering the CEERS, JADES GOOD-S, NGDEEP, SMACS0723, GLASS and PEARLS surveys. We use standard software to fit single Sérsic models to each galaxy in the rest-frame optical and extract their parametric structural parameters (Sérsic index, half-light radius and axis-ratio), and \texttt{Morfometryka} to measure their non-parametric concentration and asymmetry parameters. We find a wide range of sizes for these early galaxies, but with a strong galaxy-size mass correlation up to $z\sim 12$ such that galaxy sizes continue to get progressively smaller in the high-redshift regime, following $R_e=2.74\pm 0.49{\left(1+z\right)}^{-0.79\pm 0.08}$ kpc. Using non-parametric methods we find that galaxy merger fractions, classified through asymmetry parameters, at these redshifts remain consistent with those in literature, maintaining a value of $f_m\sim 0.12\pm 0.07$ showing little dependence with redshift when combined with literature at $z>4$. We find that galaxies which are smaller in size also appear rounder, with an excess of high axis-ratio objects. Finally, we artificially redshift a subsample of our objects to determine how robust the observational trends we see are, determining that observed trends are due to real evolutionary effects, rather than being a consequence of redshift effects.

35 pages, 13 figures. Submitted to ApJ on 19/12/2024. Comments to corresponding author welcome at [email protected]