Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Halo Stars in NGC 5128. III: An Inner-Halo Field and the Metallicity
  Distribution   We present new HST/WFPC2 (V,I) photometry for the red-giant stars in NGC 5128
at a projected distance of 8 kpc from the galaxy center, which probe a mixture
of its inner halo and outer bulge. The color-magnitude diagram shows an old
red-giant branch which is even broader in color than our two previously studied
outer-halo fields (at 21 and 31 kpc), with significant numbers of stars
extending to Solar metallicity and higher. The peak frequency of the
metallicity distribution function (MDF) is at [m/H] ~ -0.4, with even fewer
metal-poor stars than in the outer-halo fields. We find that the main features
of the halo MDF can be reproduced by a simple chemical evolution model in which
early star formation goes on simultaneously with an initial stage of rapid
infall of very metal-poor gas, after which the infall dies away exponentially.
A comparison with the MDF for the NGC 5128 globular clusters indicates that
there is a clear decrease of specific frequency $S_N$ (number of clusters per
unit halo light) with increasing metallicity, from S_N ~ 4-8 at [Fe/H] < -1.6
down to S_N = 1.5 at [Fe/H] > -1. This trend may indicate that globular cluster
formation efficiency is a strong function of the metallicity of the
protocluster gas.

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The categories of this paper are: supr-con
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The categories of this paper are: q-alg
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The categories of this paper are: atom-ph
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The categories of this paper are: econ
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The categories of this paper are: acc-phys
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The categories of this paper are: math
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The categories of this paper are: hep-lat
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The categories of this paper are: chao-dyn
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The categories of this paper are: cond-mat
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The categories of this paper are: dg-ga
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The categories of this paper are: funct-an
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The categories of this paper are: comp-gas
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The categories of this paper are: hep-th
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The categories of this paper are: plasm-ph
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The categories of this paper are: adap-org
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The categories of this paper are: nucl-ex