Early results from GLASS-JWST XIV: A first morphological atlas of the 1 < z < 5 Universe in the rest-frame optical

TL;DR

This study presents the first morphological atlas of galaxies at 0.8<z<5.4 using JWST NIRCam data, revealing higher incidences of disks and bulges than previously observed with HST, and showing morphological features more similar to local galaxies.

Contribution

It provides the first rest-frame optical morphological analysis of high-redshift galaxies with JWST, highlighting the prevalence of disks and bulges and comparing these features to earlier ultraviolet observations.

Findings

Higher incidence of disks and bulges at z>1.5 compared to HST data.

No significant evolution in bulge fraction with redshift.

Galaxies are more asymmetric and have more regular morphologies than UV-based high-z observations.

Abstract

We present a rest-frame optical morphological analysis of galaxies observed with the NIRCam imager on the James Webb Space Telescope (JWST) as part of the GLASS-JWST Early Release Science program. We select 388 sources at redshifts \(0.8 < z < 5.4\) and use the seven 0.9--5\micron\ NIRCam filters to generate rest-frame $gri$ composite color images, and conduct visual morphological classification. Compared to HST-based work we find a higher incidence of disks and bulges than expected at $z>1.5$, revealed by rest frame optical imaging. We detect 123 clear disks (58 at $z>1.5$) of which 76 have bulges. No evolution of bulge fraction with redshift is evident: 61\% at \(z<2\) (\(N=110\)) versus 60\% at \(z\geq2\) (\(N=13\)). A stellar mass dependence is evident, with bulges visible in 80\% of all disk galaxies with mass \(> 10^{9.5}\, {\rm M}_{\odot}\) (\(N=41\)) but only 52\% at \(M < 10^{9.5}\, {\rm M}_{\odot}\) (\(N=82\)). We supplement visual morphologies with non-parametric measurements of Gini and Asymmetry coefficients in the rest-frame $i$-band. Our sources are more asymmetric than local galaxies, with slightly higher Gini values. When compared to high-z rest-frame ultraviolet measurements with Hubble Space Telescope, JWST shows more regular morphological types such as disks, bulges and spiral arms at $z>1.5$, with smoother (i.e. lower Gini) and more symmetrical light distributions.