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Title:
Detection of the Tip of the Red Giant Branch in NGC 3379 (M105) in the Leo I Group Using the Hubble Space Telescope
Authors:
Sakai, Shoko; Madore, Barry F.; Freedman, Wendy L.; Lauer, Tod R.; Ajhar, Edward A.; Baum, William A.
Publication:
Astrophysical Journal v.478, p.49 (ApJ Homepage)
Publication Date:
03/1997
Origin:
APJ
ApJ Keywords:
GALAXIES: DISTANCES AND REDSHIFTS, GALAXIES: INDIVIDUAL ALPHANUMERIC: M105, GALAXIES: STELLAR CONTENT, STARS: AGB AND POST-AGB
DOI:
10.1086/303768
Bibliographic Code:
1997ApJ...478...49S

Abstract

We report the detection of individually resolved stars in the elliptical galaxy NGC 3379, a luminous member of the Leo I Group. The bright end of the stellar luminosity function has a logarithmic slope that is consistent with these stars being Population II red giants. An abrupt discontinuity in the apparent luminosity function at I = 26.30 +/- 0.09 mag is identified with the tip of the first-ascent red giant branch (TRGB). Adopting MI(TRGB) = -4.0 +/- 0.1 mag gives a distance modulus of 30.30 mag +/- 0.14 (random errors) +/- 0.23 (systematic errors) corresponding to a linear distance to NGC 3379 of 11.5 +/- 1.6 Mpc. The TRGB distance compares very well with the Cepheid distance of 11.9 +/- 0.9 Mpc (30.37 +/- 0.16 mag) to another group member M96 (=NGC 3368). The distance to NGC 3379 can be used in turn to calibrate the zero points of four other distance indicators: surface brightness fluctuations, planetary nebula luminosity functions, globular cluster luminosity functions and the Dn - sigma method. We apply two approaches to measuring the Hubble constant: (1) using a simple Virgocentric infall model and (2) stepping out from Leo I to the Coma cluster using the previously measured relative distance between the two clusters. These give values of the Hubble constant in the range H0 = 60--68 km s-1 Mpc-1, each having a 20% uncertainty. The largest systematic errors could potentially increase this value to H0 = 74 +/- 14 km s-1 Mpc-1.
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