Abstract
The dark matter halo of the Milky Way is expected to contain an abundance of
smaller subhalos. These subhalos can be dense and produce potentially
observable fluxes of gamma rays. In this paper, we search for dark matter
subhalo candidates among the sources in the Fermi-LAT Second Source Catalog
which are not currently identified or associated with counterparts at other
wavelengths. Of the nine high-significance, high-latitude (|b|>60 degrees),
non-variable, unidentified sources contained in this catalog, only one or two
are compatible with the spectrum of a dark matter particle heavier than
approximately 50-100 GeV. The majority of these nine sources, however, feature
a spectrum that is compatible with that predicted from a lighter (~5-40 GeV)
dark matter particle. This population is consistent with the number of
observable subhalos predicted for a dark matter candidate in this mass range
and with an annihilation cross section of a simple thermal relic (sigma
v~3x10^{-26} cm^3/s). Observations in the direction of these sources at other
wavelengths will be necessary to either reveal their astrophysical nature (as
blazars or other active galactic nuclei, for example), or to further support
the possibility that they are dark matter subhalos by failing to detect any
non-gamma ray counterpart.