The Interchangeability of CO and H I in the Tully-Fisher Relation

We investigate the viability and precision of using 12CO (J = 1 → 0) emission lines from galaxies in lieu of 21 cm emission in the Tully-Fisher distance indicator (TF). Here we combine CO data gathered specifically for Tully-Fisher analysis with I-band photometry (both new and from the literature) for cluster galaxies between 3500 and 8000 km s-1 and compare the luminosity–line width relation using CO with the results of recent, large TF surveys using H I and Hα. We cull some CO data as suggested by previously published numerical simulations and find that CO line widths, with corrections for turbulence and noise-broadening on the order of 35 km s-1, behave identically to H I and Hα in luminosity–line width analyses. We also examine the relation between CO line shapes and other parameters of the galaxies. Key words: distance scale — galaxies: distances and redshifts — galaxies: spiral