Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Surface Brightness Fluctuations and Globular Cluster Populations of
  M87 and its Companions   Using the surface brightness fluctuations in HST WFPC-2 images, we determine
that M87, NGC 4486B, and NGC 4478 are all at a distance of ~16 Mpc, while NGC
4476 lies in the background at ~21 Mpc. We also examine the globular clusters
of M87 using archived HST fields. We detect the bimodal color distribution, and
find that the amplitude of the red peak relative to the blue peak is greatest
near the center. This feature is in good agreement with the merger model of
elliptical galaxy formation, where some of the clusters originated in
progenitor galaxies while other formed during mergers.

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The categories of this paper are: quant-ph
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The categories of this paper are: q-alg
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The categories of this paper are: nucl-th
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The categories of this paper are: alg-geom
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The categories of this paper are: acc-phys
2
The categories of this paper are: math
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The categories of this paper are: dg-ga
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The categories of this paper are: gr-qc
34
The categories of this paper are: chem-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: patt-sol
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The categories of this paper are: hep-ex
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The categories of this paper are: cmp-lg
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The categories of this paper are: bayes-an
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The categories of this paper are: supr-con
1
The categories of this paper are: cs