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We analyze the shapes of the HI velocity profiles of The HI Nearby GalaxySurvey (THINGS) to study the phase structure of the neutral interstellar medium(ISM) and its relation to global galaxy properties. We use a method analogousto the stacking method sometimes used in high redshift HI observations toconstruct high signal-to-noise (S/N) profiles. We call these high S/N profilessuper profiles. We analyze and discuss possible systematics that may change theobserved shapes of the super profiles. After quantifying these effects andselecting a sub-sample of unaffected galaxies, we find that the super profilesare best described by a narrow and a broad Gaussian component, which areevidence of the presence of the Cold Neutral Medium (CNM) and the Warm NeutralMedium (WNM). The velocity dispersion of the narrow component range from ~3.4to ~8.6 km/s with an average of 6.5+/-1.5 km/s, whereas that of the broadcomponent range from ~10.1 to ~24.3 km/s with an average of 16.8+/-4.3 km/s. Wefind that the super profile parameters correlate with star formation indicatorssuch as metallicity, FUV-NUV colors and H_alpha luminosities. The flux ratiobetween the narrow and broad components tends to be highest for highmetallicity, high star formation rate (SFR) galaxies. We show that the narrowcomponent identified in the super profiles is associated with the presence ofstar formation, and possibly with molecular hydrogen.

The Shapes of the HI Velocity Profiles of the THINGS Galaxies