Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Intrinsic colors and ages of extremely red elliptical galaxies at high
  redshift   In order to know the formation epoch of the oldest elliptical galaxies as a
function of mass and observed redshift, a statistical analysis for 333
extremely red objects (EROs) classified as old galaxies (OGs) at 0.8<z<2.3 is
carried out. Once we get M_V and (B-V) at rest for each galaxy, we calculate
the average variation of this intrinsic color with redshift and derive the
average age through a synthesis model (the code for the calculation of the age
has been made publicly available). The average gradient of the (B-V) color at
rest of EROs/OGs is 0.07-0.10 Gyr^{-1} for a fixed luminosity. The stars in
these extremely red elliptical galaxies were formed when the Universe was ~2
Gyr old on average. We have not found a significant enough dependence on the
observed redshift and stellar mass: dt_{formation}/dt_{observed}=-0.46+/-0.32,
dt_{formation}/(d log_10 M_*)=-0.81+/-0.98 Gyr. This fits a scenario in which
the stellar formation of the objects that we denominate as EROs-OGs is more
intense at higher redshifts, at which the stellar populations of the most
massive galaxies form earlier than or at the same time as less massive
galaxies.

36
The categories of this paper are: cmp-lg
29
The categories of this paper are: funct-an
22
The categories of this paper are: chao-dyn
7
The categories of this paper are: hep-th
8
The categories of this paper are: hep-ex
24
The categories of this paper are: dg-ga
13
The categories of this paper are: quant-ph
31
The categories of this paper are: ao-sci
20
The categories of this paper are: acc-phys
14
The categories of this paper are: math-ph
11
The categories of this paper are: hep-lat
10
The categories of this paper are: q-bio
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The categories of this paper are: supr-con
15
The categories of this paper are: nucl-ex
21
The categories of this paper are: adap-org
12
The categories of this paper are: nucl-th