Early Results From GLASS-JWST. XII: The Morphology of Galaxies at the Epoch of Reionization

TL;DR

This study uses high-resolution JWST observations to analyze galaxy morphologies during the epoch of reionization, finding minimal variation across wavelengths and evidence of mergers in some galaxies, supporting rapid growth scenarios.

Contribution

First detailed morphological analysis of $z>7$ galaxies with JWST across multiple wavelengths, revealing minimal morphological variation and signs of galaxy interactions.

Findings

No dramatic morphological variation with wavelength.

Detection of merger signatures in some galaxies.

Consistent with rapid galaxy growth via star formation and accretion.

Abstract

Star-forming galaxies can exhibit strong morphological differences between the rest-frame far-UV and optical, reflecting inhomogeneities in star-formation and dust attenuation. We exploit deep, high resolution NIRCAM 7-band observations to take a first look at the morphology of galaxies in the epoch of reionization ($z>7$), and its variation in the rest-frame wavelength range between Lyman $\alpha$ and 6000-4000\AA, at $z=7-12$. We find no dramatic variations in morphology with wavelength -- of the kind that would have overturned anything we have learned from the Hubble Space Telescope. No significant trends between morphology and wavelengths are detected using standard quantitative morphology statistics. We detect signatures of mergers/interactions in 4/19 galaxies. Our results are consistent with a scenario in which Lyman Break galaxies -- observed when the universe is only 400-800 Myrs old - are growing via a combination of rapid galaxy-scale star formation supplemented by accretion of star forming clumps and interactions.