James Webb Space Telescope Feed Post

Harvard ADS: JWST PRIMER: A lack of outshining in four normal z =4-6 galaxies from the ALMA-CRISTAL Survey

Paper abstract: We present a spatially resolved analysis of four star-forming galaxies at z = 4.44-5.64 using data from the JWST PRIMER and ALMA-CRISTAL surveys to probe the stellar and inter-stellar medium properties on the sub-kpc scale. In the 1-5\,\mu{\rm m} JWST NIRCam imaging we find that the galaxies are composed of multiple clumps (between 2 and ~ 8) separated by ~eq 5\,{\rm kpc}, with comparable morphologies and sizes in the rest-frame UV and optical. Using BAGPIPES to perform pixel-by-pixel SED fitting to the JWST data we show that the SFR (~eq 25\,{\rm M}_{\odot}/{\rm yr}) and stellar mass ({\rm log}_{10}(M_{*}/{\rm M}_{\odot}) ~eq 9.5) derived from the resolved analysis are in close ( <~ 0.3\,{\rm dex}) agreement with those obtained by fitting the integrated photometry. In contrast to studies of lower-mass sources, we thus find a reduced impact of outshining of the older (more massive) stellar populations in these normal z ~eq 5 galaxies. Our JWST analysis recovers bluer rest-frame UV slopes (\beta ~eq -2.1) and younger ages (~eq 100\,{\rm Myr}) than archival values. We find that the dust continuum from ALMA-CRISTAL seen in two of these galaxies correlates, as expected, with regions of redder rest-frame UV slopes and the SED-derived A_{\rm V}, as well as the peak in the stellar mass map. We compute the resolved IRX-\beta relation, showing that the IRX is consistent with the local starburst attenuation curve and further demonstrating the presence of an inhomogeneous dust distribution within the galaxies. A comparison of the CRISTAL sources to those from the FirstLight zoom-in simulation of galaxies with the same M_{*} and SFR reveals similar age and colour gradients, suggesting that major mergers may be important in the formation of clumpy galaxies at this epoch.