Kavli Affiliate: Masahiro Takada
| First 5 Authors: Daiki Hashimoto, Atsushi J. Nishizawa, Masahiro Takada, Oscar Macias,
| Summary:
A new method to constrain the dark matter annihilation cross section by
taking the cross correlation of gamma-ray diffuse maps and galaxies is
proposed. As a result, the statistical power of constraining the annihilation
cross section is proportional to the galaxy mass and the inverse square of the
distance to the galaxy. Therefore, for analyses using dwarf galaxies, the
measurement of the distance to the dwarf galaxies is crucial for stringent
constraints. However, measuring the distance to galaxies is, in general
observationally expensive, particularly for faint or diffuse galaxies. Under
the situation of stacking N galaxies, we show that the distance to the
individual galaxy measurement is not required, but the overall distance
distribution is sufficient for the cross section constraints. Further, based on
real Large Area Telescope (LAT) data, we show that the effect of covariance
between two galaxies located closely, typically comparable with the point
spread function size of the Fermi-LAT, is negligibly small. We can
independently stack the likelihood for the N galaxies, which dramatically
reduces the computation costs. By using actual datasets of the LAT gamma-ray
sky and about 800 faint objects discovered by Hyper Suprime-Cam, we find that
the upper limit on the annihilation cross-section scales with 1/N. Therefore,
it can be one of the most powerful and robust probe of the annihilation signal
to stack more than 100,000 galaxies readily available with the Legacy Survey of
Space and Time.
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