Statistical Analysis of H i Profile Asymmetry and Shape for Nearby Galaxies

Abstract

We present a uniform analysis of the integrated profile of the H i emission line of 29,958 nearby (z < 0.06) galaxies extracted from the ALFALFA 21 cm survey. We apply the curve-of-growth technique to derive a database of spectral parameters and robust estimates of their associated uncertainties. Besides the central velocity and total flux, the main catalog provides new measures of line width, profile asymmetry, and profile shape. For a subsample of 13,511 galaxies with optical properties available from the Sloan Digital Sky Survey, we compute inclination angle-corrected line widths, rotation velocities empirically calibrated from spatially resolved observations, and dynamical masses based on H i sizes estimated from the H i mass. To facilitate subsequent scientific applications of the database, we also compile a number of ancillary physical properties of the galaxies, including their optical morphology, stellar mass, and various diagnostics of star formation activity. We use the homogeneous catalog of H i parameters to examine the statistical properties of profile asymmetry and shape. Across the full sample, which covers a wide range of stellar masses and environments, statistically significant H i profile asymmetry is detected in ∼20% of the galaxy population. The global H i profiles are 35.2% ± 0.3% single-peaked, 26.9% ± 0.3% flat-topped, and 37.9% ± 0.3% double-horned. At a given inclination angle, double-horned profiles are preferentially associated with galaxies of higher stellar mass or optical concentration, while galaxies of lower mass or concentration tend to have single-peaked profiles.