Sizes and mass profiles of candidate massive galaxies discovered by JWST at $7
appear to have redshifts of $zsim 7-9$ and high masses of $M_*$ $sim$
10$^{10}$ M$_{odot}$ (Labb’e et al. 2023). Here we fit S’ersic profiles to
the F200W NIRCam images of the 13 massive galaxy candidates of Labb’e et al.,
to determine their structural parameters. Satisfactory fits were obtained for
nine galaxies. We find that their effective radii are extremely small, ranging
from $r_{rm e}sim 80$ pc to $r_{rm e} sim 300$ pc, with a mean of $langle
r_{rm e}rangle approx 150$ pc. For their apparent stellar masses, the
galaxies are smaller than any other galaxy population that has been observed at
any other redshift. We use the fits to derive circularized three-dimensional
stellar mass profiles of the galaxies, and compare these to the mass profiles
of massive quiescent galaxies at $zsim$2.3 and nearby elliptical galaxies. We
find that, despite the high redshift galaxies having $10-20$ times smaller
half-light radii, the central stellar densities are comparable to those of
their putative descendants at later times. The most straightforward
interpretation is that the dense compact inner regions of the most massive
ellipticals today were already in place $sim 600$ Myr after the Big Bang. We
caution that the redshifts and masses of the galaxies remain to be confirmed,
and that the complex NIRCam point spread function is not yet fully
characterized.
The first JWST data revealed an unexpected population of red galaxies that
appear to have redshifts of $zsim 7-9$ and high masses of $M_*$ $sim$
10$^{10}$ M$_{odot}$ (Labb’e et al. 2023). Here we fit S’ersic profiles to
the F200W NIRCam images of the 13 massive galaxy candidates of Labb’e et al.,
to determine their structural parameters. Satisfactory fits were obtained for
nine galaxies. We find that their effective radii are extremely small, ranging
from $r_{rm e}sim 80$ pc to $r_{rm e} sim 300$ pc, with a mean of $langle
r_{rm e}rangle approx 150$ pc. For their apparent stellar masses, the
galaxies are smaller than any other galaxy population that has been observed at
any other redshift. We use the fits to derive circularized three-dimensional
stellar mass profiles of the galaxies, and compare these to the mass profiles
of massive quiescent galaxies at $zsim$2.3 and nearby elliptical galaxies. We
find that, despite the high redshift galaxies having $10-20$ times smaller
half-light radii, the central stellar densities are comparable to those of
their putative descendants at later times. The most straightforward
interpretation is that the dense compact inner regions of the most massive
ellipticals today were already in place $sim 600$ Myr after the Big Bang. We
caution that the redshifts and masses of the galaxies remain to be confirmed,
and that the complex NIRCam point spread function is not yet fully
characterized.
http://arxiv.org/icons/sfx.gif
