Detailed Study of Stars and Gas in a z = 8.3 Massive Merger with Extreme Dust Conditions

TL;DR

This study investigates a high-redshift galaxy undergoing a major merger with extreme dust conditions, revealing star formation bursts, evolved ISM properties, and potential AGN activity at z=8.3, providing insights into early galaxy evolution.

Contribution

It provides a detailed analysis of the physical properties, star formation history, and dust conditions of a z=8.3 galaxy during a merger, highlighting its evolved ISM and possible AGN presence.

Findings

Galaxy undergoing star formation burst in three clumps

ISM properties similar to z~2 star-forming galaxies

Possible AGN activity indicated by emission line diagnostics

Abstract

We present galaxy MACS0416-Y1 at z$_{\rm{spec}} = 8.312$ as observed by the CAnadian NIRISS Unbiased Cluster Survey (CANUCS). MACS0416-Y1 has been shown to have extreme dust properties, thus, we study the physical properties and star formation histories of its resolved components. Overall, we find that MACS0416-Y1 is undergoing a star formation burst in three resolved clumps. The central clump is less massive compared to the other clumps and possibly formed in the merging process of the two larger clumps. Although the star formation history indicates an ongoing star formation burst, this gas-rich galaxy shows comparable star formation efficiency to cosmic noon galaxies. Using NIRSpec prism spectroscopy, we measure metallicity, $12 +\log\rm{(O/H)} = 7.76\pm0.03$ , ionisation parameter, $\log U = -2.48\pm0.03$, and electron temperature $\rm{T}_e = 18000\pm 4000 K $. The emission line ratios of the galaxy indicate an evolved Interstellar medium (ISM) similar to $z\sim2$ star-forming galaxies. Further, we find possible presence of ionisation from an active galactic nuclei (AGN) using emission line diagnostics, however, we do not detect broad line component in H$\beta$ emission line. As this gas-rich galaxy is undergoing a major merger, we hypothesise that the high dust temperature in MACS0416-Y1 is caused by the star formation burst or a possible narrow-line AGN.