The need for speed : escape velocity and dynamical mass measurements of the Andromeda galaxy
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Our nearest large cosmological neighbour, the Andromeda galaxy (M31), is a dynamical system, and an accurate measurement of its total mass is central to our understanding of its assembly history, the life-cycles of its satellite galaxies, and its role in shaping the Local Group environment. Here, we apply a novel approach to determine the dynamical mass of M31 using high velocity Planetary Nebulae (PNe), establishing a hierarchical Bayesian model united with a scheme to capture potential outliers and marginalize over tracers unknown distances. With this, we derive the escape velocity run of M31 as a function of galacto-centric distance, with both parametric and non-parametric approaches. We determine the escape velocity of M31 to be 470 ± 40 km s−1 at a galacto-centric distance of 15 kpc, and also, derive the total potential of M31, estimating the virial mass and radius of the galaxy to be 0.8±0.1×1012M⊙ and 240 ± 10 kpc, respectively. Our M31 mass is on the low-side of the measured range, this supports the lower expected mass of the M31-Milky Way system from the timing and momentum arguments, satisfying the H i constraint on circular velocity between 10 ≲ R/ kpc < 35, and agreeing with the stellar mass Tully-Fisher relation. To place these results in a broader context, we compare them to the key predictions of the ΛCDM cosmological paradigm, including the stellar-mass–halo-mass and the dark matter halo concentration–virial mass correlation, and finding it to be an outlier to this relation.
Kafle , P R , Sharma , S , Lewis , G F , Robotham , A S G & Driver , S P 2018 , ' The need for speed : escape velocity and dynamical mass measurements of the Andromeda galaxy ' Monthly Notices of the Royal Astronomical Society . DOI: 10.1093/mnras/sty082
Monthly Notices of the Royal Astronomical Society
© 2018, the Author(s). This work has been made available online in accordance with the publisher’s policies. This is the final published version of the work, which was originally published at https://doi.org/10.1093/mnras/sty082
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