The Need for Speed: Escape velocity and dynamical mass measurements of the Andromeda galaxy

Abstract

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 $470\pm 40$ 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 $0.8\pm 0.1\times 10^{12}{M}_{\odot }$ and $240\pm 10$ 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 HI constraint on circular velocity between $10\lesssim R/\text{kpc}<35$, 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 $\Lambda \mathrm{CDM}$ 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.

14 pages, 7 figures, 1 table. Accepted for publication in MNRAS

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• Lensing constraints on ultradense dark matter halos
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• A Census of Thermally-Pulsing AGB stars in the Andromeda Galaxy and a First Estimate of their Contribution to the Global Dust Budget
• The imprint of galaxy mergers on satellite planes in a cosmological context
• Galaxy And Mass Assembly (GAMA): The group HI mass as a function of halo mass
• Implications for the hierarchy problem, inflation and geodesic motion from fiber fabric of spacetime
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• Measuring the Mass of Missing Baryons in the Halo of Andromeda Galaxy with Gamma-Ray Observations
• Fast Forward Modelling of Galaxy Spatial and Statistical Distributions
• Cosmological Simulations of Stellar Halos with Gaia Sausage-Enceladus Analogues: Two Sausages, One Bun?
• Dark matter fraction derived from the M31 rotation curve
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• The role of impact parameter in typical close galaxy flybys
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• On Stellar Migration from Andromeda to the Milky Way
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• Timing Mass of the Local Group
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