James Webb Space Telescope Feed Post

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

Images of the three clumps and underlying galaxy component in MACS1149-JD1. Shown are different filters, Galfit models and residuals (top panels), RGB (always using F150W, F277W, and F444W filters) model of the clumps and the galaxy (middle panels) and RGB model and RGB NIRCam image (bottom panels). The galaxy consists of at least 3 clumps (all marked in the middle panel), all of which are unresolved and an underlying smooth component. An upper limit to the magnified size (FWHM) of the clumps is 0.05''. The intrinsic (demagnified) size upper limit is < 50pc. 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 (µ ~ 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-a detected.