The constraints on dark matter distribution in the isolated spiral NGC 4414

The purpose of our work is to strongly constrain the mass to light ratio in the disk of the flocculent isolated Sc type spiral NGC 4414 using a combined high resolution interferometric CO(1-0) and HI rotation curve, and deep HST B-V-I images of the galaxy. To identify the mass contributions of the visible – stellar and gaseous – components, we observed the rotation curve with high resolution in the optical disk. The M/L ratios we derive are low, about 1.5 in I band and 0.5 in K' band. The B and V band M/L ratios vary greatly due to absorption by dust, reaching 4 in the molecular ring and decreasing to about 1.6 –1.8 at larger radii. This unequivocally shows that models, like most maximum disk models, assuming constant M/L ratios in an optical waveband, simply are not appropriate. We illustrate this by making mock maximum disk models with a constant V band M/L ratio. The key is having the central light distribution unobscured such that it can be used to trace the mass. The K' band M/L ratio is virtually constant over the disk, suggesting that the intrinsic (unobscured) stellar M/L ratio is roughly constant. We use our knowledge of the visible mass distribution to test disk and halo dark matter models. Fitting an NFW (Navarro et al., 1996) halo to the rotation curve suggests that NGC 4414 is in a low mass concentrated halo typical of small galaxies and early halo formation times. This revised version was published online in August 2006 with corrections to the Cover Date.