Rotation curves of Ursa Major galaxies in the context of modified Newtonian dynamics

This is the third in a series of papers in which spiral galaxy rotation cur ves are considered in the context of Milgrom's modified dynamics (MOND). Th e present sample of 30 objects is drawn from a complete sample of galaxies in the Ursa Major cluster, with photometric data from Tully et al. and 21 c m fine data from Verheijen. The galaxies are roughly all at the same distan ce (15 to 16 Mpc). The radio observations are made with the Westerbork Synt hesis Array, which means that the linear resolution of all rotation curves is comparable. The greatest advantage of this sample is the existence of K' -band surface photometry for all galaxies; the near-infrared emission, bein g relatively free of the effects of dust absorption and less sensitive to r ecent star formation, is a more precise tracer of the mean radial distribut ion of the dominant stellar population. The predicted rotation curves are c alculated; from the K'-band surface photometry and the observed distributio n of neutral hydrogen using the simple MOND prescription, in which the one adjustable parameter is the mass of the stellar disk or the implied mass-to -light ratio. The predicted rotation curves generally agree with the observ ed curves, and the mean MIL in the near-infrared is about 0.9 with a small. dispersion. The fitted MIL in the B-band correlates with B-V color in the sense predicted by population synthesis models. Including earlier work, abo ut 80 galaxy rotation curves are now well reproduced from the observed dist ribution of detectable matter using the MOND formula to calculate the gravi tational acceleration; this lends considerable observational support to Mil grom's unconventional hypothesis.