The Ks-band Tully–Fisher Relation – A Determination of the Hubble Parameter from 218 ScI Galaxies and 16 Galaxy Clusters

Abstract. The value of Hubble parameter (H0) is determined using the morphologically type dependent Ks-band Tully–Fisher Relation (K-TFR). The slope and zero point are determined using 36 calibrator galaxies with ScI morphology. Calibration distances are adopted from direct Cepheid dis-tances, and group or companion distances derived with the Surface Bright-ness Fluctuation Method or Type Ia Supernova. It is found that a small morphological type effect is present in the K-TFR such that ScI galax-ies are more luminous at a given rotational velocity than Sa/Sb galaxies and Sbc/Sc galaxies of later luminosity classes. Distances are determined to 16 galaxy clusters and 218 ScI galaxies with minimum distances of 40.0 Mpc. From the 16 galaxy clusters a weighted mean Hubble parameter of H0 = 84.2 ± 6 km s−1 Mpc−1 is found. From the 218 ScI galaxies a Hubble parameter of H0 = 83.4 ± 8 km s−1 Mpc−1 is found. When the zero point of K-TFR is corrected to account for recent results that find a Large Magellanic Cloud distance modulus of 18.39±0.05, a Hubble para-meter of 88.0 ± 6 km s−1 Mpc−1 is found. Effects from Malmquist bias are shown to be negligible in this sample as galaxies are restricted to a minimum rotational velocity of 150 km s−1. It is also shown that the results of this study are negligibly affected by the adopted slope for the K-TFR, inclination binning, and distance binning. A comparison with the results of the Hubble Key Project (Freedman et al. 2001) is made. Discrepancies between the K-TFR distances and the HKP I-TFR distances are discussed. Implications for -CDM cosmology are considered with H0 = 84 km s−1 Mpc−1. It is concluded that it is very difficult to reconcile the value of H0 found in this study with ages of the oldest globular clusters and matter den-sity of the universe derived from galaxy clusters in the context of -CDM cosmology. Key words. Distance scale—galaxies: distances and redshifts. 1