Near - infrared surface photometry of early - type spiral galaxies : II . M / L ratios and dark halos . ⋆

Abstract. We present mass distributions obtained from near-infrared (NIR) surface brightness decompositions and rotation curve fitting of a sample of early-type spiral galaxies. Bulge and disk mass-to-light (M/L) ratios, dark halo parameters, and the modified Newtonian dynamics (MOND) acceleration parameter are derived. We find that the mean disk NIR M/L is higher than that of the bulge, and comparison with stellar population synthesis models implies that early-type spiral bulges are, on average, younger and more metal rich than disks. NIR disk M/L is found to depend on disk luminosity, consistently with previously reported trends in ellipticals and spirals, and with cold dark matter models for disk formation. Within the optical radius, the mean ratio of stellar to dark matter is 2 and the typical dark halo mass is 10 M⊙. The value of the MOND acceleration parameter that best accommodates the sample as a whole is 1.3 · 10 cm s.