The I-Band Tully-Fisher Relation for Abell 400

by Jennifer Rebecca Mack

Under the supervision of Professor John Dickey


We present new I-band photometry of twenty galaxies in the cluster A400. When combined with their 21cm emission profiles, we obtain a Tully Fisher relation with very low scatter, sigma = 0.024, and a slope of -8.68±0.67, in excellent agreement with the calibration of Pierce and Tully (1992). The resulting distance modulus is 34.6 mag, corresponding to an average distance of 83 Mpc. Assuming magnitude deviations are due to cluster depth, we show that A400's galaxies no longer participate in smooth Hubble expansion and lie roughly at a common distance. These galaxies appear deficient in HI gas, through this deficiency is not correlated with cluster radius. Beers et al (1992) suggest a two-component model, with a spiral-poor and a spiral-rich group that are currently falling together. When dividing our sample into two velocity groups, our data support the infall model, i.e. the high redshift group is closer and moving away.