Global HI Kinematics in Dwarf Galaxies

TL;DR

This study analyzes the global HI kinematics in dwarf galaxies by creating superprofiles from spectral data, revealing a universal profile shape and correlations with star formation, suggesting supernovae energize the HI gas.

Contribution

It introduces a method of characterizing global HI profiles in dwarf galaxies and links star formation activity to HI kinematic features, highlighting supernovae as a key energy source.

Findings

Superprofiles have a universal shape with a narrow core and high-velocity wings.

Velocity dispersion correlates with HI surface density.

Star formation, via supernovae, supplies enough energy to drive observed HI motions.

Abstract

HI line widths are typically interpreted as a measure of ISM turbulence, which is potentially driven by star formation. In an effort to better understand the possible connections between line widths and star formation, we have characterized \hi{} kinematics in a sample of nearby dwarf galaxies by co-adding line-of-sight spectra after removing the rotational velocity to produce an average, global \hi{} line profile. These "superprofiles" are composed of a central narrow peak (~6-10 km/s) with higher-velocity wings to either side that contain ~10-15% of the total flux. The superprofiles are all very similar, indicating a universal global HI profile for dwarf galaxies. We compare characteristics of the superprofiles to various galaxy properties, such as mass and measures of star formation (SF), with the assumption that the superprofile represents a turbulent peak with energetic wings to either side. We use these quantities to derive average scale heights for the sample galaxies. When comparing to physical properties, we find that the velocity dispersion of the central peak is correlated with $<\Sigma_\mathrm{HI}>$. The fraction of mass and characteristic velocity of the high velocity wings are correlated with measures of SF, consistent with the picture that SF drives surrounding HI to higher velocities. While gravitational instabilities provide too little energy, the SF in the sample galaxies does provide enough energy through supernovae, with realistic estimates of the coupling efficiency, to produce the observed superprofiles.