Dark matter in the Milky Way, II. the HI gas distribution as a tracer of the gravitational potential

Abstract

Context. Gas within a galaxy is forced to establish pressure balance against gravitational forces. The shape of an unperturbed gaseous disk can be used to constrain dark matter models. Aims. We derive the 3-D HI volume density distribution for the Milky Way out to a galactocentric radius of 40 kpc and a height of 20 kpc to constrain the Galactic mass distribution. Methods. We used the Leiden/Argentine/Bonn all sky 21-cm line survey. The transformation from brightness temperatures to densities depends on the rotation curve. We explored several models, reflecting different dark matter distributions. Each of these models was set up to solve the combined Poisson-Boltzmann equation in a self-consistent way and optimized to reproduce the observed flaring. Results. Besides a massive extended halo of M ~ 1.8 10^{12} Msun, we find a self-gravitating dark matter disk with M=2 to 3 10^{11} Msun, including a dark matter ring at 13 < R < 18.5 kpc with M = 2.2 to 2.8 10^{10} Msun. The existence of the ring was previously postulated from EGRET data and coincides with a giant stellar structure that surrounds the Galaxy. The resulting Milky Way rotation curve is flat up to R~27 kpc and slowly decreases outwards. The \hi gas layer is strongly flaring. The HWHM scale height is 60 pc at R = 4 kpc and increases to ~2700$pcatR=40kpc.Spiralarmscauseanoticeableimprintonthegravitationalfield,atleastouttoR=30kpc.Conclusions.Ourmassmodelsupportspreviousproposalsthatthegiantstellarringstructureisduetoamergingdwarfgalaxy.ThefactthatthemajorityofthedarkmatterintheMilkyWayfor$R \la 40$ kpc can be successfully modeled by a self-gravitating isothermal disk raises the question of whether this massive disk may have been caused by similar merger events in the past.

19 pages, 21 figures, accepted for publication by A&A

References in corpus (1)

• Cats and Dogs, Hair and A Hero: A Quintet of New Milky Way Companions

Cited by in corpus (8)

• Thin, thick and dark discs in LCDM
• The Flattened Dark Matter Halo of M31 as Deduced from the Observed HI Scale Heights
• Marriage à-la-MOND: Baryonic dark matter in galaxy clusters and the cooling flow puzzle
• Dark matter dominance at all radii in the superthin galaxy UGC 7321
• HI Clouds in the Lower Halo: I. The Galactic All-Sky Survey Pilot Region
• The thickness of HI in galactic discs under MOND: theory and application to the Galaxy
• Azimuthal dependence of the density distribution in outer galactic discs accreting intergalactic flows
• A new Determination of the Extragalactic Background of Diffuse Gamma Rays taking into account Dark Matter Annihilation