Volume 524, December 2010
|Number of page(s)||9|
|Section||Galactic structure, stellar clusters and populations|
|Published online||24 November 2010|
The inner halo of M 87: a first direct view of the red-giant population
Tuorla Observatory, University of Turku,
e-mail: email@example.com; firstname.lastname@example.org
2 Department of Physics and Astronomy, McMaster University, Hamilton L8S 4M1, Canada
3 Herzberg Institute of Astrophysics, National Research Council of Canada, Victoria BC V9E 2E7, Canada
4 Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Väsiäläntie 20, 21500 Piikkiö, Finland
5 Department of Physics and Astronomy, University of Sydney, Sydney, Australia
Accepted: 15 September 2010
An unusually deep (V,I) imaging dataset for the Virgo supergiant M 87 with the Hubble Space Telescope ACS successfully resolves its brightest red-giant stars, reaching MI(lim) = −2.5. After assessing the photometric completeness and biasses, we use this material to estimate the metallicity distribution for the inner halo of M 87, finding that the distribution is very broad and likely to peak near [m/H] ≃ −0.4 and perhaps higher. The shape of the MDF strongly resembles that of the inner halo for the nearby giant E galaxy NGC 5128. As a byproduct of our study, we also obtain a preliminary measurement of the distance to M 87 with the TRGB (red-giant branch tip) method; the result is (m − M)0 = 31.12±0.14 (d = 16.7±0.9 Mpc). Averaging this result with three other recent techniques give a weighted mean d(M87) = (16.4 ± 0.5) Mpc.
Key words: galaxies: stellar content / galaxies: halos / galaxies: individual: M 87
© ESO, 2010
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