Dark matter dominance at all radii in the superthin galaxy UGC 7321

TL;DR

This study models the dark matter halo of the superthin galaxy UGC 7321, revealing that dark matter dominates its dynamics at all radii, with a spherical isothermal halo fitting the observed rotation and HI data.

Contribution

It provides the first detailed modeling of the dark matter halo in a superthin galaxy, showing dominance at all radii and comparing halo core size to stellar disc scale length.

Findings

Dark matter halo dominates at all radii in UGC 7321.

Best-fit halo has a core radius slightly larger than the stellar disc scale length.

Halo parameters are consistent with an isothermal spherical model.

Abstract

We model the shape and density profile of the dark matter halo of the low surface brightness, superthin galaxy UGC 7321, using the observed rotation curve and the HI scale height data as simultaneous constraints. We treat the galaxy as a gravitationally coupled system of stars and gas, responding to the gravitational potential of the dark matter halo. An isothermal halo of spherical shape with a core density in the range of 0.039 - 0.057 M_sun/pc^3 and a core radius between 2.5 - 2.9 kpc, gives the best fit to the observations for a range of realistic gas parameters assumed. We find that the best-fit core radius is only slightly higher than the stellar disc scale length (2.1 kpc), unlike the case of the high surface brightness galaxies where the halo core radius is typically 3-4 times the disc scale length of the stars. Thus our model shows that the dark matter halo dominates the dynamics of the low surface brightness, superthin galaxy UGC 7321 at all radii, including the inner parts of the galaxy.