Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The impact of spheroid stars for Macho microlensing surveys of the
  Andromeda Galaxy   The Andromeda Galaxy (M31) is an important test case for a number of
microlensing surveys looking for massive compact halo objects (Machos). A
long-standing theoretical prediction is that the high inclination of the M31
disk should induce an asymmetry in the spatial distribution of M31 Macho
events, whilst the distribution of variable stars and microlensing events in
the M31 disk should be symmetric. We examine the role of stars in the M31
visible spheroid as both lenses and sources to microlensing events. We compute
microlensing event number density maps and estimate pixel-lensing rates and
event durations for three-component models of M31 which are consistent with the
observed rotation curve, surface brightness profile and dynamical mass
estimates. Three extreme models are considered: a massive spheroid model; a
massive disk model; and a massive Macho halo model. An important consequence of
the spheroid is that, even if Machos are absent in M31, an asymmetric spatial
signature is still generally expected from stellar lensing alone. The relative
mass-to-light ratio of the spheroid and disk populations controls which of
these signatures dominates the overall stellar spatial distribution. We find
that the inclusion of the spheroid weakens the M31 Macho spatial asymmetry by
about 20-30% over a disk-only asymmetry for the models considered. We also find
for our models that Machos dominate over most of the far disk provided they
contribute at least ~25% of the halo dark matter density. The presence of the
spheroid also has beneficial consequences for M31 lensing surveys. The stellar
asymmetry is likely to be important in distinguishing between a spheroidal
Macho halo or a highly flattened halo or dark matter dominated disk, since
spatial asymmetries of opposing signs are expected in these cases. (Abridged)

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The categories of this paper are: patt-sol
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The categories of this paper are: bayes-an
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The categories of this paper are: math-ph
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The categories of this paper are: hep-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: eess
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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: mtrl-th
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The categories of this paper are: q-fin
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The categories of this paper are: chao-dyn
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The categories of this paper are: nucl-th
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The categories of this paper are: q-alg
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The categories of this paper are: quant-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: alg-geom