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   We have conducted a wide-field CCD-mosaic study of the resolved red-giant
branch (RGB) stars of M31, in a field located 20 kpc from the nucleus along the
SE minor axis. In our (I, V-I) color-magnitude diagram, RGB stars in the top
three magnitudes of the M31 halo are strongly present. Photometry of a more
distant control field to subtract field contamination is used to derive the
`cleaned' luminosity function and metallicity distribution function (MDF) of
the M31 halo field. From the color distribution of the foreground Milky Way
halo stars, we find a reddening E(V-I)= 0.10 +/- 0.02 for this field, and from
the luminosity of the RGB tip, we determine a distance modulus (m-M)_o = 24.47
+/- 0.12 (= 783 +/- 43 kpc). The MDF is derived from interpolation within an
extensive new grid of RGB models (Vandenberg et al. 2000). The MDF is dominated
by a moderately high-metallicity population ([m/H]~ -0.5) found previously in
more interior M31 halo/bulge fields, and is much more metal-rich than the
[m/H]~ -1.5 level in the Milky Way halo. A significant (~30% - 40%, depending
on AGB star contribution) metal-poor population is also present. To first
order, the shape of the MDF resembles that predicted by a simple,
single-component model of chemical evolution starting from primordial gas with
an effective yield y=0.0055. It strongly resembles the MDF recently found for
the outer halo of the giant elliptical NGC 5128 (Harris et al. 2000), though
NGC 5128 has an even lower fraction of low-metallicity stars. Intriguingly, in
both NGC 5128 and M31, the metallicity distribution of the globular clusters in
M31 does not match the halo stars; the clusters are far more heavily weighted
to metal-poor objects. We suggest similarities in the formation and early
evolution of massive, spheroidal stellar systems.

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The categories of this paper are: nucl-ex
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The categories of this paper are: bayes-an
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The categories of this paper are: cs
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The categories of this paper are: math-ph
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The categories of this paper are: q-fin
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The categories of this paper are: stat
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The categories of this paper are: funct-an
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The categories of this paper are: hep-lat
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The categories of this paper are: nlin
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The categories of this paper are: hep-th
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The categories of this paper are: mtrl-th
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The categories of this paper are: q-bio
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The categories of this paper are: cond-mat
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The categories of this paper are: alg-geom
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The categories of this paper are: physics
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The categories of this paper are: plasm-ph