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Session 8 - Distance Indicators.
Display session, Monday, January 15
North Banquet Hall, Convention Center

[8.06] Tip of the Red Giant Branch Distances to Nearby Galaxies

S. Sakai (IPAC,JPL,Caltech), W. Freedman (OCIW), B. Madore (NED,IPAC,JPL,Caltech)

We present I vs (V-I) color--magnitude diagrams and I-band luminosity functions for several nearby galaxies including Sextans A, Sextans B and IC 2574, based on CCD photometry obtained with the COSMIC prime--focus camera at Palomar 5m telescope. The tip of the first--ascent red giant branch (TRGB) marks the core--helium flash of low--mass stars, at which point the RBG luminosity function abruptly terminates. In I-band, the TRGB stars resolve at M_I \sim -4.0 \pm 0.1. Using the discontinuity in the TRGB luminosity function as a distance indicator, we have derived Pop II distances to the observed galaxies. Several of the galaxies also have Cepheid (Pop I) distances which can be compared with the TRGB distances. We show that distances derived by two independent distance determinations agree with each other at 0.1 mag level. Our analysis confirms and strengthens the view that the TRGB method is comparable in accuracy and precision to the Cepheid PL relation.

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