Accurate and Robust Calibration of the Extragalactic Distance Scale with the Maser Galaxy NGC4258

Details Accurate and Robust Calibration of the Extragalactic Distance Scale with the Maser Galaxy NGC4258 Accurate and Robust Calibration of the Extragalactic Distance Scale with the Maser Galaxy NGC4258

Jul 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003hst..prop.9810g&link_type=abstract

HST Proposal ID #9810

Computer Science

Hst Proposal Id #9810 Cosmology

Scientific paper

The extragalactic distance scale {EDS} is defined by a comparison of Cepheid Period-Luminosity {PL} relations for nearby galaxies and the LMC, whose uncertain distance is thereby the SOLE anchor. Studies of maser sources orbiting the central black hole in the galaxy NGC4258 have provided the most accurate extragalactic distance ever {7.2+/- 0.5Mpc}. Since this distance is well determined and based on GEOMETRIC arguments, NGC4258 can provide a much needed new anchor for the EDS. We propose multi-epoch BVIH observations of NGC4258 in order to discover about 100 Cepheids and to characterize their light curves with 2-3 times greater accuracy than was previously possible with WFPC2. At 90 orbits {48 in Cycle 12; 42 in Cycle 13}, this is a relatively large program. However, the result will have a major impact on the EDS, and substantial attention must be paid to characterization and minimization of systematic errors, as from metallicity, crowding, and blending. The resulting dataset will be the most complete for Cepheids in any galaxy yet studied with HST. In an ongoing NASA-funded program {OSS-SARA}, we are using new analysis techniques and radio data to reduce uncertainty in the geometric distance to < 3% {0.07 mag}. With this improved geometric distance and the BVIH data, we will be able to calculate the zero point of the PL relation ROBUSTLY to <4% {0.09 mag}.

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