A First Look at Spatially Resolved Star Formation at 4. 8<z<6. 5 with JWST FRESCO NIRCam Slitless Spectroscopy

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 JWST FRESCO NIRCam Slitless Spectroscopy. Star-forming galaxies with stellar masses 6. 8log (M*/M_) <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, R₄₅₅ and central surface densities within 1 kiloparsec, ₁₊₏₂. At a fixed stellar mass of log (M*/M_) =9. 5, ₁₊₏₂, ₇ is 1. 040. 05 times higher than ₁₊₏₂, ₂, R₄₅₅, ₇ is 1. 180. 03 times larger than R₄₅₅, ₂ and both R₄₅₅ measurements are less than 1 kiloparsec. These measurements suggest the rapid build-up of compact bulges just after the epoch of reionisation. 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 R₄₅₅ (z) evolves at the same pace for H and the continuum, but ₁₊₏₂ (z) evolves faster for H. As a function of the Hubble parameter, R₄₅₅, ₇R₄₅₅, ₂=1. 1h (z) and ₁₊₏₂, ₇₁₊₏₂, ₂=h (z) ^1. 3. These functions suggest that the inside-out growth of the disk dominates the inside-out growth of the bulge towards lower redshifts. This is supported by the redshift evolution in EW (H) profiles, where there is rapid increase in EW (H) with radius within the half-light radius at z=5. 3 but only significantly increasing EW (H) with radius in the outer disk at z=0. 5.