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Session 3 - Source Surveys, Galaxy Surveys, Distance Scale I.
Display session, Wednesday, January 07
Exhibit Hall,

[3.07] A HST Cepheid Distance to NGC 4603 and the Peculiar Velocity of the Cen30 Cluster

S. E. Zepf (Yale), J. Newman, M. Davis (UC Berkeley), W. L. Freedman (OCIW), B. F. Madore (NED/IPAC), N. A. Silbermann (IPAC)

We present a determination of the distance to NGC 4603 based on the periods and magnitudes of Cepheid variables observed with the Hubble Space Telescope. NGC 4603 is a spiral galaxy in the ``Cen 30'' portion of the Centaurus cluster that is concentrated around a redshift of 3,000 km/s, the highest redshift yet attempted for Cepheid studies. Previous distance estimates for the Cen 30 cluster suggested a large peculiar motion, but neither optical or IRAS galaxy maps reveal a plausible structure with sufficient mass to generate this motion. Therefore, we obtained images of NGC 4603 with the Hubble Space Telescope at nine epochs (totalling 24 orbits) over 14 months in the F555W filter and 2 epochs (6 orbits) in the F814W filter. Using our WFPC2 observations, we have found a number of Cepheid variable stars with well-determined oscillation periods and mean magnitudes, allowing us to firmly establish the distance of NGC 4603.

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