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

Understand

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.