# Constraints on the halo density profile using HI flaring in the outer Galaxy

Narayan, CA and Saha, K and Jog, CJ (2005) Constraints on the halo density profile using HI flaring in the outer Galaxy. In: Astronomy and Astrophysics, 440 (2). pp. 523-530.

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## Abstract

The observed flaring of HI disk in the outer region of galaxies has been used in the past to determine the shape of the dark matter halo. Previous studies based on this concept suggest a slightly oblate halo (axis ratio ~0.8) for our Galaxy. We reinvestigate this problem by calculating the HI scaleheight in the outer Galaxy to a larger radial distance, and by studying its dependence on the shape and the density profile of the halo. We find that a simple isothermal infinite halo of any shape- oblate or prolate, is not able to account for the observed flaring. Instead we show that a spherical halo with density falling faster than isothermal halo in the outer region provides a better fit to the observed HI flaring as well as the observed rotation curve of our Galaxy. These halos have about 95% of their mass within a few hundreds of kpc for $R_\cdot$ = 8.5 kpc and $\Theta_o= 220 km s^-^1$, the central density and core radius can be constrained to the range $\rho _\cdot = 0.035-0.06 M_o pc^-^3$ and Rc = 8-10 kpc. Our claim for such "finite-sized" spherical halos is supported by recent literature on numerical simulation studies of halo formation as well as analyses of SDSS data.

Item Type: Journal Article The copyright for this artcle belongs to EDP Sciences SA galaxies: ISM;galaxies: kinematics and dynamics;galaxies: structure;galaxies: halos Division of Physical & Mathematical Sciences > Physics 23 Sep 2005 27 Aug 2008 11:28 http://eprints.iisc.ernet.in/id/eprint/3692