Compatibility of the CO and H I linewidths considering the gas distribution and rotation curves

We have found the trend between CO and Hi linewidths by compiling the CO and Hi linewidths of 219 nearby galaxies. The trend is that the CO linewidths of fast rotating galaxies tend to be larger than the Hi linewidths, and that the Hi linewidths of slow rotating galaxies tend to be larger than the CO linewidths, whereas the intermediately rotating galaxies have almost equal values. We have examined the trend using the synthetic rotation curve model given by Persic et al. (1996), which provides the linewidth – absolute magnitude relations at any radii. We conclude that the trend is produced by the differences in CO and HI distributions in a galaxy and the gradient of a rotation curve that depends on the luminosity of the galaxy. We should note that the distribution of the tracer of linewidths (e.g. CO, Hi) and the gradient of rotation curves influence observed linewidths, therefore the exact linewidths should be corrected for them.