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Harvard ADS: A First Look at Spatially Resolved Star Formation at 4.8 < z < 6.5 with JWST FRESCO NIRCam Slitless Spectroscopy

Paper abstract: We present the first results on the spatial distribution of star formation in 454 star-forming galaxies at 4.8 < z < 6.5 using H-Alpha emission-line maps and F444W imaging tracing the stellar continuum from the JWST FRESCO NIRCam Slitless Spectroscopy Survey. Star-forming galaxies with stellar masses 6.8<=log(M_{*}/\mathrm{M}_{\odot})<11.1 have positive H-Alpha equivalent width profiles, providing direct evidence for the inside-out growth of galaxies just after the epoch of reionisation. GALFIT is used to calculate half-light radii, R_{\mathrm{eff}} and central surface densities within 1 kiloparsec, \Sigma_{1\mathrm{kpc}} of H-Alpha and the continuum. At a fixed stellar mass of log(M_{*}/\mathrm{M}_{\odot})=9.5, \Sigma_{1\mathrm{kpc, H}\alpha} is 1.3\pm0.1 times higher than \Sigma_{1\mathrm{kpc, C}} with consistent H-Alpha and continuum R_{\mathrm{eff}} that are both less than 1 kpc. These measurements suggest the rapid build up of compact bulges without a significant increase in their radii. By comparing to work done at lower redshifts with HST WFC3 Slitless Spectroscopy as part of the 3D-HST (z=1) and CLEAR (z=0.5) surveys, we find that R_{\mathrm{eff}}(z) and \Sigma_{1\mathrm{kpc}}(z) evolve faster with redshift for H-Alpha. As a function of the Hubble parameter, \frac{R_{\mathrm{eff, H}\alpha}}{R_{\mathrm{eff, C}}}=1.1h(z)^{-0.1} and \frac{\Sigma_{1\mathrm{kpc,H}\alpha}}{\Sigma _{1\mathrm{kpc,C}}}=h(z)^{0.3}. These functions indicate there is a transition point at 2 < z < 4 where the inside-out growth of the disk starts to dominate over the inside-out growth of the bulge towards lower redshifts. This is supported by the redshift evolution in EW(H\alpha) profiles, where there is rapid increase in EW(H\alpha) with radius within the half-light radius at z=5.3 but only significantly increasing EW(H\alpha) with radius in the outer disk at z=0.5.