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Arxiv: Galaxy Size and Mass Build-up in the First 2 Gyrs of Cosmic History from Multi-Wavelength JWST NIRCam Imaging Published: 10/21/2024 9:00:00 PM Updated: 10/21/2024 9:00:00 PM

Paper abstract: The evolution of galaxy sizes in different wavelengths provides uniqueinsights on galaxy build-up across cosmic epochs. Such measurements can nowfinally be done at z>3 thanks to the exquisite spatial resolution andmulti-wavelength capability of the JWST. With the public data from the CEERS,PRIMER-UDS, and PRIMER-COSMOS surveys, we measure the sizes of ~ 3500star-forming galaxies at 3 <=slant z<9, in 7 NIRCam bands using themulti-wavelength model fitting code GalfitM. The size-mass relation is measuredin four redshift bins, across all NIRCam bands. We find that, the slope andintrinsic scatter of the rest-optical size-mass relation are constant acrossthis redshift range and consistent with previous HST-based studies at low-z.When comparing the relations across different wavelengths, the averagerest-optical and rest-UV relations are consistent with each other up to z=6,but the intrinsic scatter is largest in rest-UV wavelengths compared torest-optical and redder bands. This behaviour is independent of redshift and wespeculate that it is driven by bursty star-formation in z>4 galaxies.Additionally, for 3<=slant z<4 star-forming galaxies at \rm M_* > 10^{10}M_{\odot}, we find smaller rest-\rm 1\rm\,\mu m sizes in comparison torest-optical (and rest-UV) sizes, suggestive of colour gradients. Whencomparing to simulations, we find agreement over \rm M_* ~ 10^{9} -10^{10} M_{\odot} but beyond this mass, the observed size-mass relation issignificantly steeper. Our results show the power of JWST/NIRCam to provide newconstraints on galaxy formation models.