Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Photometry and the Metallicity Distribution of the Outer Halo of M31.
  II. The 30 Kpc Field   We present the results of a wide-field (V,I) photometric study of the
red-giant branch (RGB) stars in the outer halo of M31, in a field located 30 to
35 kpc from the center of the galaxy along the southeast minor axis. At this
remote location, we find that RGB stars belonging to M31 are sparsely but
definitely present, after statistical subtraction of field contamination. We
derive the metallicity distribution (MDF) for the halo stars using
interpolation within a standard (I,V-I) grid of RGB evolutionary tracks. The
halo MDF is quite broad but dominated by a moderately high-metallicity
population peaking at [m/H] ~ -0.5, strikingly different from the [m/H] ~ -1.3
level which characterizes the outer halo of the Milky Way. However,the shape
and peak metallicity for this region are entirely similar to those found in
other studies for the inner regions of the M31 halo, particularly our previous
study of a 20-kpc region (Durrell, Harris, & Pritchet 2001) employing similar
data. In summary, we find no evidence for a metallicity gradient or systematic
change in the MDF out to quite large distances in the M31 halo: it appears to
be a homogeneous and moderately metal-rich subsystem of the galaxy at all
locations. The star counts in the 30-kpc field are also consistent with the
r^1/4 law that fits the interior regions of the M31 spheroid surface brightness
profile. The metal-rich MDF and the r^1/4 spheroid suggests M31 more strongly
resembles a giant elliptical galaxy than other, Milky-Way-like, spirals.

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The categories of this paper are: atom-ph
2
The categories of this paper are: math
30
The categories of this paper are: q-alg
0
The categories of this paper are: hep-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: supr-con
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The categories of this paper are: dg-ga
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The categories of this paper are: eess
1
The categories of this paper are: cs
4
The categories of this paper are: cond-mat
16
The categories of this paper are: stat
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The categories of this paper are: chem-ph
18
The categories of this paper are: econ
25
The categories of this paper are: patt-sol
22
The categories of this paper are: chao-dyn
12
The categories of this paper are: nucl-th