Kavli Affiliate: Anna Frebel
| First 5 Authors: Xiaowei Ou, Lina Necib, Andrew Wetzel, Anna Frebel, Jeremy Bailin
| Summary:
Recent measurements of the Milky Way rotation curve found a sharp decline at
around $15$-$20$ kpc from the center of the Galaxy, suggesting that the
Galactic dark matter halo is much less massive than predicted by other
dynamical tracers. To address this tension, we study the validity of the
assumptions made in calculating the Milky Way’s rotation curve. To do so, we
apply Jeans’ equation, the current standard approach of measuring rotation
curves, to three cosmological zoom-in simulations of Milky Way-like galaxies
from the FIRE-2 Latte suite. Using synthetic Gaia surveys, we replicate the
sample selection process and calculation employed in measuring the Milky Way
rotation curve. We examine four failure modes of this calculation and find that
the measured curves deviate from the true curve by $5$-$20%$ rather than below
$5%$, as estimated by previous works. Interestingly, there is a large
galaxy-to-galaxy variance, and different systematics dominate different
galaxies. We rederive the Milky Way’s dark matter density profile with the
rotation curve while incorporating systematics from the simulations. The
posterior distribution of the density profiles is consistent with a fiducial
NFW profile when assuming a gNFW profile for dark matter. We find that the
virial mass, $7.32^{+1.98}_{-1.53}times10^{11}~M_{odot}$, consistent with
other probes of the Milky Way’s mass. However, we recommend that the field
moves away from relying solely on the rotation curve when studying the dark
matter profile, and adopts methods that incorporate additional probes and/or do
not heavily depend on assumptions described in this study.
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