Morphology, sizes, and scatter in a large sample of distant quiescent galaxies

Abstract

After quenching galaxies keep growing in size across time, as established in the literature up to cosmic noon. In this work, we assemble one of the largest and most comprehensive multi-wavelength photometric sample of massive quenched galaxies at z>3, counting 137 quiescent candidates within 825 sq. arcmin and redshift 3<z<7 across the well-studied extragalactic JWST fields. We model their surface brightness distribution across 5 bands mapping their UV-to-NIR rest-frame wavelength with Sersic profiles, and derive their sizes, concentrations, and ellipticities. The size-mass relation is consistent with previous studies. Size decreases with increasing redshift, in agreement with previous studies and extending them up to z_spec=4.9. The intrinsic scatter of the mass-size relation has no relevant dependence on the redshift and the filter used. Our multi-wavelength modeling reveals that size decreases with increasing observed wavelength, and the wavelength gradient decreases with increasing stellar mass. This result proves that in the NIR-bands massive elliptical galaxies appear more compact. The Sersic index does not show significant dependence on wavelength, independently of the stellar mass. Following a forward/backward Bayesian fit analysis to assess the significance of several parameters in predicting the size of our sample, we do not identify any significant secondary dependence of the size on axis ratio q, Sersic index n, UVJ-colors, and environment. The combination of stellar mass and redshift is sufficient to predict the size of quiescent galaxies at z>3, albeit with a large scatter. This suggests that the commonly used parameters of a Sersic distribution cannot explain the large intrinsic scatter around the stellar mass-size relation, suggesting that other physical quantities need to be taken into account to break the degeneracy between evolution paths across the galaxy population.