We analyze the shapes of the HI velocity profiles of The HI Nearby Galaxy Survey ( THINGS ) to study the phase structure of the neutral interstellar medium ( ISM ) and its relation to global galaxy properties .
We use a method analogous to the stacking method sometimes used in high redshift HI observations to construct high signal-to-noise ( S/N ) profiles .
We call these high S/N profiles super profiles .
We analyze and discuss possible systematics that may change the observed shapes of the super profiles .
After quantifying these effects and selecting a sub-sample of unaffected galaxies , we find that the super profiles are best described by a narrow and a broad Gaussian component , which are evidence of the presence of the Cold Neutral Medium ( CNM ) and the Warm Neutral Medium ( WNM ) .
The velocity dispersion of the narrow component range from \sim 3.4 to \sim 8.6 { km~ { } s ^ { -1 } } with an average of 6.5 \pm 1.5 { km~ { } s ^ { -1 } } , whereas that of the broad component range from \sim 10.1 to \sim 24.3 { km~ { } s ^ { -1 } } with an average of 16.8 \pm 4.3 { km~ { } s ^ { -1 } } .
We find that the super profile parameters correlate with star formation indicators such as metallicity , FUV-NUV colors and H \alpha luminosities .
The flux ratio between the narrow and broad components tends to be highest for high metallicity , high star formation rate ( SFR ) galaxies .
We show that the narrow component identified in the super profiles is associated with the presence of star formation , and possibly with molecular hydrogen .