Modeling HI distribution and kinematics in the edge-on dwarf irregular galaxy KK250

TL;DR

This study models the vertical distribution and kinematics of neutral hydrogen in the edge-on dwarf galaxy KK250, revealing a puffier gas disc compared to spiral galaxies and providing insights into its velocity dispersion and vertical structure.

Contribution

It presents a detailed hydrostatic equilibrium model of HI distribution in KK250, incorporating velocity dispersion as a free parameter, and compares the disc thickness with that of the solar neighborhood.

Findings

Best fit velocity dispersion is ~22 km/s at the center, decreasing to ~8 km/s at 1 kpc.

HI disc thickness varies, minimum at ~1 kpc, increasing towards the center and out to 3 kpc.

Vertical HWHM of HI in KK250 is ~350 pc, larger than in the solar neighborhood.

Abstract

We model the observed vertical distribution of the neutral hydrogen (HI) in the faint (M_B ~ -13.7 mag) edge-on dwarf irregular galaxy KK250. Our model assumes that the galaxy consists of axi-symmetric, co-planar gas and stellar discs in the external force-field of a spherical dark matter halo, and in vertical hydrostatic equilibrium. The velocity dispersion of the gas is left as a free parameter in the model. Our best fit model is able to reproduce the observed vertical distribution of the HI gas, as well as the observed velocity profiles. The best fit model has a large velocity dispersion (~ 22 km/s) at the centre of the galaxy, which falls to a value of ~ 8 km/s by a galacto-centric radius of ~ 1 kpc, which is similar to both the scale-length of the stellar disc, as well as the angular resolution of the data along the radial direction. Similarly we find that the thickness of the HI disc is also minimum at ~ 1 kpc, and increases by about a factor of ~ 2 as one goes to the centre of the galaxy or out to ~ 3 kpc. The minimum intrinsic HWHM of the HI vertical distribution in KK250 is ~ 350 pc. For comparison the HWHM of the vertical distribution of the HI in the solar neighbourhood is ~ 70-140 pc. Our results are hence consistent with other observations which indicate that dwarf galaxies have significantly puffier gas discs than spirals.