A Cepheid Distance to NGC 4603 in Centaurus

摘要

In an attempt to use Cepheid variables to determine the distance to theCentaurus cluster, we have obtained images of NGC 4603 with the Hubble SpaceTelescope on 9 epochs using WFPC2 and the F555W and F814W filters. This galaxyhas been suggested to lie within the ``Cen30'' portion of the cluster and isthe most distant object for which this method has been attempted. Previousdistance estimates for Cen30 have varied significantly and some have presenteddisagreements with the peculiar velocity predicted from redshift surveys,motivating this investigation. Using our observations, we have found 61candidate Cepheid variable stars; however, a significant fraction of thesecandidates are likely to be nonvariable stars whose magnitude measurementerrors happen to fit a Cepheid light curve of significant amplitude for somechoice of period and phase. Through a maximum likelihood technique, wedetermine that we have observed 43 +/- 7 real Cepheids and that NGC 4603 has adistance modulus of 32.61 +0.11/-0.10 (random, 1 sigma) +0.24/-0.25(systematic, adding in quadrature), corresponding to a distance of 33.3 Mpc.This is consistent with a number of recent estimates of the distance to NGC4603 or Cen30 and implies a small peculiar velocity consistent with predictionsfrom the IRAS 1.2 Jy redshift survey if the galaxy lies in the foreground ofthe cluster.