A Significant Population of Red, Near-IR Selected High Redshift Galaxies

Astrophysics, abstract
astro-ph/0303163

From: Marijn Franx <franx@strw.leidenuniv.nl>

Date: Fri, 7 Mar 2003 14:00:03 GMT   (88kb)

Authors:
Marijn Franx,
Ivo Labbe,
Gregory Rudnick,
Pieter G. van Dokkum,
Emanuele Daddi,
Natascha M. Forster Schreiber,
Alan Moorwood,
Hans-Walter Rix,
Huub Rottgering,
Arjen van de Wel,
Paul van der Werf,
Lottie van Starkenburg

Comments: LaTex, 5 pages and 4 figures. Accepted for publication in ApJ
Letters. See also related preprints on astroph today by Daddi et al and van
Dokkum et al

We use very deep near-infrared photometry of the Hubble Deep Field South
taken with ISAAC/VLT to identify a population of high redshift galaxies with
rest- frame optical colors similar to those of nearby galaxies. The galaxies
are chosen by their infrared colors Js-Ks > 2.3, aimed at selecting galaxies
with redshifts above 2. When applied to our dataset, we find 14 galaxies with
Ks < 22.5, corresponding to a surface density of 3+-0.8 /arcmin**2. The
photometric redshifts all lie above 1.9, with a median of 2.6 and a rms of 0.7.
The spectral energy distributions of these galaxies show a wide range: one is
very blue in the rest-frame UV, and satisfies the normal Lyman-break criteria
for high redshift, star-forming galaxies. Others are quite red throughout the
observed spectral range, and are extremely faint in the optical, with a median
V = 26.6. Hence these galaxies would not be included in photometric samples
based on optical ground-based data, and spectroscopic follow-up is difficult.
The spectral energy distributions often show a prominent break, identified as
the Balmer break or 4000 Ang. break. The median age is 1 Gyr when fit with a
constant star formation model with dust, or 0.7 Gyr when fit with a single
burst model. Although significantly younger ages cannot be excluded when a
larger range of models is allowed, the results indicate that these galaxies are
among the oldest at these redshifts. The volume density to Ks=22.5 is half that
of Lyman-break galaxies at z = 3. Since the mass-to-light ratios of the red
galaxies are likely to be higher, the stellar mass density is inferred to be
comparable to that of Lyman-break galaxies. These red galaxies may be the
descendants of galaxies which started to form stars at very high redshifts, and
they may evolve into the most massive galaxies at low redshift.

References and citations for this submission:

SLAC-SPIRES HEP (refers to ,
cited by, arXiv reformatted)