The Neutral Hydrogen Content of Fornax Cluster Galaxies

We present a new set of deep HI observations of member galaxies of the Fornax cluster. We detected 35 cluster galaxies in HI. The resulting sample, the most comprehensive to date, is used to investigate the distribution of HI in the cluster galaxies. We compare the HI content of the detected cluster galaxies with that of field galaxies by measuring HI mass-to-light ratios and the HI deficiency parameter of Solanes et al. (1996). The mean HI mass-to-light ratio of the cluster galaxies is 0.68+/-0.15, significantly lower than for a sample of HI-selected field galaxies (1.15+/-0.10), although not as low as in the Virgo cluster (0.45+/-0.03). The mean HI deficiency for the cluster is 0.38+/-0.09 (for T=1-6), significantly greater than for the field sample (0.05+/-0.03). Both these tests show that Fornax cluster galaxies are HI-deficient compared to field galaxies. The kinematics of the cluster galaxies suggests that the HI deficiency may be caused by ram-pressure stripping of galaxies on orbits that pass close to the cluster core. We also derive the most complete B-band TF relation of inclined spiral galaxies in Fornax. A subcluster in the South-West of the main cluster contributes considerably to the scatter. The scatter for galaxies in the main cluster alone is 0.50mag, which is slightly larger than the intrinsic scatter of 0.4mag. We use the TF relation to derive a distance modulus of Fornax relative to the Virgo cluster of -0.38+/-0.14mag. The galaxies in the subcluster are 1.0+/-0.5mag brighter than the galaxies of the main cluster, indicating that they are situated in the foreground. With their mean velocity 95km/s higher than that of the main cluster we conclude that the subcluster is falling into the main Fornax cluster.