Abstract
We present morphologies of galaxies at $z\sim9-17$ resolved by JWST/NIRCam
$2-5\mu$m imaging. Our sample consists of $25$ galaxy candidates identified by
stringent dropout and photo-$z$ criteria in GLASS, CEERS, SMACS J0723, and
Stephan's Quintet flanking fields. We perform surface brightness (SB) profile
fitting with GALFIT for $6$ bright galaxies with S/N $=10-40$ on an individual
basis and for stacked faint galaxies with secure point-spread functions (PSFs)
of the NIRCam real data, carefully evaluating systematics by Monte-Carlo
simulations. We compare our results with those of previous JWST studies, and
confirm that effective radii $r_e$ of our measurements are consistent
with those of previous measurements at $z9$. We obtain $r_e\simeq
200-300$ pc with the exponential-like profiles, Sérsic indexes of $n\simeq
1-1.5$, for galaxies at $z12-17$, indicating that the relation of $r_\rm
e(1+z)^s$ for $s=-1.19^+0.16_-0.15$ explains cosmic evolution over
$z0-17$ for $L^*_z=3$ galaxies. One bright ($M_UV=-21$ mag)
galaxy at $z12$, GL-z12-1, has an extremely compact size with $r_\rm
e=61 11$ pc that is surely extended over the PSF. Even in the case that
the GL-z12-1 SB is fit by AGN$+$galaxy composite profiles, the best-fit galaxy
component is again compact, $r_e=78^+30_-12$ pc that is significantly
($>5\sigma$) smaller than the typical $r_e$ value at $z12$.
Comparing with numerical simulations, we find that such a compact galaxy
naturally forms at $z10$, and that frequent mergers at the early epoch
produce more extended galaxies following the $r_e(1+z)^s$
relation.
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