Candidate Massive Galaxies at $z sim 4$ in the Dark Energy Survey

Kavli Affiliate: Rafe Schindler

| First 5 Authors: Pierandrea Guarnieri, Claudia Maraston, Daniel Thomas, Janine Pforr, Violeta Gonzalez-Perez

| Summary:

Using stellar population models, we predicted that the Dark Energy Survey
(DES) – due to its special combination of area (5000 deg. sq.) and depth ($i =
24.3$) – would be in the position to detect massive ($gtrsim 10^{11}$
M$_{odot}$) galaxies at $z sim 4$. We confront those theoretical calculations
with the first $sim 150$ deg. sq. of DES data reaching nominal depth. From a
catalogue containing $sim 5$ million sources, $sim26000$ were found to have
observed-frame $g-r$ vs $r-i$ colours within the locus predicted for $z sim 4$
massive galaxies. We further removed contamination by stars and artefacts,
obtaining 606 galaxies lining up by the model selection box. We obtained their
photometric redshifts and physical properties by fitting model templates
spanning a wide range of star formation histories, reddening and redshift. Key
to constrain the models is the addition, to the optical DES bands $g$, $r$,
$i$, $z$, and $Y$, of near-IR $J$, $H$, $K_{s}$ data from the Vista Hemisphere
Survey. We further applied several quality cuts to the fitting results,
including goodness of fit and a unimodal redshift probability distribution. We
finally select 233 candidates whose photometric redshift probability
distribution function peaks around $zsim4$, have high stellar masses
($log($M$^{*}$/M$_{odot})sim 11.7$ for a Salpeter IMF) and ages around 0.1
Gyr, i.e. formation redshift around 5. These properties match those of the
progenitors of the most massive galaxies in the local universe. This is an
ideal sample for spectroscopic follow-up to select the fraction of galaxies
which is truly at high redshift. These initial results and those at the survey
completion, which we shall push to higher redshifts, will set unprecedented
constraints on galaxy formation, evolution, and the re-ionisation epoch.

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