Which Milky Way masses are consistent with the slightly declining 5-25 kpc rotation curve?

Abstract

Discoveries of extended rotation curves have suggested the presence of dark matter in spiral galaxy haloes. It has led to many studies that estimated the galaxy total mass, mostly by using the Navarro Frenk and White (NFW) density profile. We aim at verifying how the choice of the dark-matter profile may affect the predicted values of extrapolated total masses. We have considered the recent Milky Way (MW) rotation curve, firstly because of its unprecedented accuracy, and secondly because the Galactic disk is amongst the least affected by past major mergers having fully reshaped the initial disk. We find that the use of NFW profile (or its generalized form, gNFW) for calculating the dark-matter contribution to the MW rotation curve generates apparently inconsistent results, e.g., an increase of the baryonic mass leads to increase of the dark matter mass. Furthermore we find that NFW and gNFW profile narrow the total mass range, leading to a possible methodological bias particularly against small MW masses. By using the Einasto profile that is more appropriate to represent cold dark matter haloes, we finally find that the Milky Way slightly decreasing rotation curve favors total mass that can be as small as 2.6 $\times 10^{11}$ $M_{\odot }$, disregarding any other dynamical tracers further out in the MW. It is inconsistent with values larger than 18 $\times 10^{11}$ $M_{\odot }$ for any kind of CDM dark-matter halo profiles, under the assumption that stars and gas do not influence the predicted dark matter distribution in the MW. This methodological paper encourages the use of the Einasto profile for characterizing rotation curves with the aim of evaluating their total masses.

10 pages, 6 Figures, 5 Tables including Table A-1 with re-evaluated error bars on the Milky Way rotation curve. After proof editing and to be published in the Astronomy & Astrophysics journal

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Cited by in corpus (6)

• Detection of the Keplerian decline in the Milky Way rotation curve
• The Einasto model for dark matter haloes
• Multiply lensed star forming clumps in the A521-sys1 galaxy at redshift 1
• The accretion history of the Milky Way. I. How it shapes globular clusters and dwarf galaxies
• Dark matter fraction derived from the M31 rotation curve
• An intriguing coincidence between the majority of vast polar structure dwarfs and a recent major merger at the M31 position