HUBBLE SPACE TELESCOPE OBSERVATIONS OF GLOBULAR CLUSTERS IN M87 AND AN ESTIMATE OF H_0

摘要

Hubble Space Telescope observations of over 1000 globular clusters in the central region of M87 have been made using the Wide Field and Planetary Camera 2. The limiting magnitude in V is 26 mag, more than 2 mag beyond the turnover of the luminosity function. The distribution is well fitted by a Gaussian profile with a mean of < m_v~0 > = 23.72 ± 0.06 mag and a width of 1.40 ± 0.06 mag. Assuming a value of < M_v~0 > = -7.4 ± 0.25 mag for the globular cluster luminosity function results in a distance modulus of (m — M) = 31.12 mag to the Virgo Cluster. Using a value of Δ_(coma-virgo)(m - M) = 3.71 ± 0.10 mag and adopting a velocity for the Coma Cluster of 7188 km s~(-1) result in a value for the Hubble constant of H_0 = 78 ± 11 km s~(-1) Mpc~(-1). The V - I color distribution is bimodal, with peaks at V - I = 0.95 mag and 1.20 mag. The mean size of the clusters is R_(eff) = 3 pc, with a scatter of 1 pc.