Abstract

We present a new set of deep H I observations of member galaxies of the Fornax cluster. We detected 35 cluster galaxies in H I. The resulting sample, the most comprehensive to date, is used to investigate the distribution of neutral hydrogen in the cluster galaxies. We compare the H I content of the detected cluster galaxies with that of field galaxies by measuring H I mass-to-light ratios and the H I deficiency parameter of Solanes et al. (1996). The mean H I mass-to-light ratio of the cluster galaxies is 0.68 +/- 0.15, significantly lower than for a sample of H I-selected field galaxies (1.15 +/- 0.10), although not as low as in the Virgo cluster (0.45 +/- 0.03). In addition, the H I content of two cluster galaxies (NGC1316C and NGC1326B) appears to have been affected by interactions. The mean H I deficiency for the cluster is 0.38 +/- 0.09 (for galaxy types T = 1-6), significantly greater than for the field sample (0.05 +/- 0.03). Both these tests show that Fornax cluster galaxies are H I-deficient compared to field galaxies. The kinematics of the cluster galaxies suggests that the H I 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 Tully-Fisher 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 0.50 mag, which is slightly larger than the intrinsic scatter of 0.4 mag. We use the Tully-Fisher relation to derive a distance modulus of Fornax relative to the Virgo cluster of -0.38 +/- 0.14 mag. The galaxies in the subcluster are (1.0 +/- 0.5) mag brighter than the galaxies of the main cluster, indicating that they are situated in the foreground. With their mean velocity 95 km s(-1) higher than that of the main cluster we conclude that the subcluster is falling into the main Fornax cluster.

Highlights

  • The nearby Fornax cluster has a high central surface density of galaxies (Ferguson 1989b) it is not a rich cluster in Abell’s (1956) sense

  • We present a new set of deep H i observations of member galaxies of the Fornax cluster

  • We compare the H i content of the detected cluster galaxies with that of field galaxies by measuring H i mass-to-light ratios and the H i deficiency parameter of Solanes et al

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Summary

Introduction

The nearby Fornax cluster has a high central surface density of galaxies (Ferguson 1989b) it is not a rich cluster in Abell’s (1956) sense. It forms an intermediate sample suitable for comparison with richer clusters like. Hydra I (McMahon et al 1992), as well as smaller groups and nearby field galaxies Fornax lies almost opposite in the sky from the well-studied Virgo cluster but at a distance just about equal to it (e.g., Pierce 1989; Bridges et al 1991; Hamuy et al 1991; McMillan et al 1993; see Table 6.1 in Schröder 1995). More recent H i surveys of the cluster galaxies include Horellou et al (1995) and Bureau et al (1996)

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