Star Formation at the Epoch of Reionization with CANUCS: The ages of stellar populations in MACS1149-JD1

TL;DR

This study uses JWST observations to analyze the stellar populations of a high-redshift galaxy at z=9.1, revealing multiple components with different star formation histories and challenging previous assumptions about its spectral features.

Contribution

First detailed analysis of a z=9.1 galaxy's stellar populations using JWST, uncovering multiple components with distinct ages and star formation histories.

Findings

Extended component formed stars 50 Myr earlier than others

No strong Balmer break confirmed with JWST data

Galaxy shows multiple unresolved star-forming components

Abstract

We present measurements of stellar populations properties of a z = 9.1 gravitationally lensed galaxy MACS1149-JD1 using deep JWST NIRISS slitless spectroscopy as well as NIRISS and NIRCam imaging from the CAnadian NIRISS Unbiased Cluster Survey (CANUCS). The galaxy is split into four components. Three magnified (${\mu}$ ~ 17) star-forming components are unresolved, giving intrinsic sizes of < 50pc. In addition, the underlying extended component contains the bulk of the stellar mass, formed the majority of its stars ~ 50Myr earlier than the other three components and is not the site of the most active star formation currently. The NIRISS and NIRCam resolved photometry does not confirm a strong Balmer break previously seen in Spitzer. The NIRISS grism spectrum has been extracted for the entire galaxy and shows a clear continuum and Lyman-break, with no Lyman-${\alpha}$ detected.