Kavli Affiliate: Anna Frebel
| First 5 Authors: Xiaowei Ou, Anna-Christina Eilers, Lina Necib, Anna Frebel,
| Summary:
In this paper, we construct the circular velocity curve of the Milky Way out
to $sim 30$ kpc, providing an updated model of the dark matter density
profile. We derive precise parallaxes for 120,309 stars with a data-driven
model, using APOGEE DR17 spectra combined with Gaia DR3, 2MASS, and WISE
photometry. At outer galactic radii up to 30 kpc, we find a significantly
faster decline in the circular velocity curve compared to the inner parts. This
decline is better fit with a cored Einasto profile with a slope parameter
$0.91^{+0.04}_{-0.05}$ than a generalized Navarro-Frenk-White (NFW) profile.
The virial mass of the best-fit dark matter halo profile is only
$1.81^{+0.06}_{-0.05}times10^{11}$ $M_{odot}$, significantly lower than what
a generalized NFW profile delivers. We present a study of the potential
systematics, affecting mainly large radii. Such a low mass for the Galaxy is
driven by the functional forms tested, given that it probes beyond our
measurements. It is found to be in tension with mass measurements from globular
clusters, dwarf satellites, and streams. Our best-fit profile also lowers the
expected dark matter annihilation signal flux from the galactic centre by more
than an order of magnitude, compared to an NFW profile-fit. In future work, we
will explore profiles with more flexible functional forms to more fully
leverage the circular velocity curve and observationally constrain the
properties of the Milky Way’s dark matter halo.
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