Identification of High-Redshift Galaxy Overdensities in GOODS-N and GOODS-S

Kavli Affiliate: Roberto Maiolino

| First 5 Authors: Jakob M. Helton, Fengwu Sun, Charity Woodrum, Kevin N. Hainline, Christopher N. A. Willmer

| Summary:

We conduct a systematic search for high-redshift galaxy overdensities at $4.9
< z_{,mathrm{spec}} < 8.9$ in both the GOODS-N and GOODS-S fields using
JWST/NIRCam imaging from JADES and JEMS in addition to JWST/NIRCam wide field
slitless spectroscopy from FRESCO. High-redshift galaxy candidates are
identified using HST+JWST photometry spanning $lambda = 0.4-5.0
mumathrm{m}$. We confirmed the redshifts for roughly a third of these
galaxies using JWST/FRESCO spectroscopy over $lambda = 3.9-5.0 mumathrm{m}$
through identification of either $mathrm{H} alpha$ or
$left[mathrm{OIII}right]lambda5008$ around the best-fit photometric
redshift. The rest-UV magnitudes and continuum slopes of these galaxies were
inferred from the photometry: the brightest and reddest objects appear in more
dense environments and thus are surrounded by more galaxy neighbors than their
fainter and bluer counterparts, suggesting accelerated galaxy evolution within
overdense environments. We find $17$ significant ($delta_{mathrm{gal}} geq
3.04$, $N_{mathrm{galaxies}} geq 4$) galaxy overdensities across both fields
($7$ in GOODS-N and $10$ in GOODS-S), including the two highest redshift
spectroscopically confirmed galaxy overdensities to date at $left<
z_{mathrm{,spec}} right> = 7.955$ and $left< z_{mathrm{,spec}} right> =
8.222$ (representing densities around $sim 6$ and $sim 12$ times that of a
random volume). We estimate the total halo mass of these large-scale structures
to be $11.5 leq mathrm{log}_{10}left(M_{mathrm{halo}}/M_{odot}right) leq
13.4$ using an empirical stellar mass to halo mass relation, which are likely
underestimates as a result of incompleteness. These protocluster candidates are
expected to evolve into massive galaxy clusters with
$mathrm{log}_{10}left(M_{mathrm{halo}}/M_{odot}right) gtrsim 14$ by $z =

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