Tests of the long and short extragalactic distance scales.

Abstract

Distances on the short and long scales of 12 nearby galaxies, one group, and three clusters are compared with recent estimates by independent methods and researchers. All comparisons show a close agreement [within 0.3 magnitude (mag) in the distance modulus (DM)] between the short-scale moduli and the new estimates by others at all distances from the Large Magellanic Cloud [Delta (distance) = 0.05 megaparsec (Mpc); 1 pc = 3.09 x 10(16) m] to the Coma cluster (Delta = 83 Mpc). The mean systematic difference (short - others) is only -0.04 mag with no evidence for a significant Malmquist bias in the short scale. The long scale differs systematically from all the others by about +0.25 mag within the Local Group (DM < 26) and by +1.1 outside (26 < DM < 35). Accidental errors are also much larger in the long-scale moduli (0.5 mag) than in the other two scales (0.1 mag). The mean value of the Hubble expansion ratio for the test objects is <H> = 86 +/- 1 km.sec-1. Mpc-1.