Morphological Demographics of Galaxies at <i>z</i> ∼ 10–16: Log-normal Size Distribution and Exponential Profiles Consistent with the Disk Formation Scenario
Yoshiaki Ono, Masami Ouchi, Yuichi Harikane, Hidenobu Yajima, Kimihiko Nakajima, Seiji Fujimoto, Minami Nakane, Yi Xu
Abstract
Abstract We homogeneously investigate the morphological properties of 169 galaxies at z ∼ 10–16 with deep JWST NIRCam images employing our established techniques of GALFIT modeling and uncertainty evaluation (systematics+statistics). We obtain effective radii r e ranging 20–500 pc, with a distribution significantly broader than the scatter made by the uncertainties. We find that the r e distribution is well described by a log-normal distribution with a mean of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>r</mml:mi> <mml:mi mathvariant="normal">e</mml:mi> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>13</mml:mn> <mml:msubsup> <mml:mn>3</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>12</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>13</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> pc and a standard deviation of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>σ</mml:mi> <mml:mrow> <mml:mi>ln</mml:mi> <mml:msub> <mml:mi>r</mml:mi> <mml:mi mathvariant="normal">e</mml:mi> </mml:msub> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>0.52</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.08</mml:mn> </mml:math> . The standard deviation is comparable to that of local galaxies, indicating no significant evolution over z ∼ 0–10. We also find that the axis ratio distribution is nearly uniform, statistically similar to that of local spirals. We estimate the virial radius r vir from the stellar masses via the star formation main sequence and stellar-to-halo mass relation, obtaining a stellar-to-halo size ratio <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>r</mml:mi> <mml:mi mathvariant="normal">e</mml:mi> </mml:msub> <mml:mo>/</mml:mo> <mml:msub> <mml:mi>r</mml:mi> <mml:mi>vir</mml:mi> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>0.01</mml:mn> <mml:msubsup> <mml:mn>5</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.005</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.015</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> , which is comparable to those of star-forming galaxies in the local and low- z Universe. Our results of (1) the log-normal r e distribution, (2) the uniform axis ratio distribution, and (3) a mean radial profile consistent with an exponential profile ( n = 1.3 ± 0.6) suggest that galaxies at z ∼ 10–16 generally follow the classical galaxy disk formation scenario with a specific disk angular momentum fraction of j d / m d ∼ 0.5–1. Interestingly, we identify two remarkable outliers GN-z11 ( z spec = 10.60) and GHZ2 ( z spec = 12.34) with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>r</mml:mi> <mml:mi mathvariant="normal">e</mml:mi> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>5</mml:mn> <mml:msubsup> <mml:mn>5</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>6</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>5</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> pc and 39 ± 11 pc, respectively, that may not be explained by disk structures but by active galactic nucleus or compact star-forming galaxies merging underway in short periods of time, as reproduced in numerical simulations.