Spheroid Luminosity and Mass Functions from Hubbl E Space T El Escope Star Counts

We analyze 166 spheroid subdwarfs found in 53 Ðelds observed with the Wide Field (6.5\ M V \ 14.5) Planetary Camera on the Hubble Space T elescope. The Ðelds cover 221 arcmin2 over a wide range of directions. The spheroid luminosity function (LF) is inconsistent at about the 3 p level with the local spheroid LF of Dahn et al. even when the normalization of the latter is corrected to take account of the latest data on spheroid kinematics. The di†erence may reÑect systematic errors in one of the two studies or features of the spheroid spatial distribution that are not included in the simplest models. The mass function, which shows no obvious structure, can be represented by a power law, dN/d ln M P Ma, with a \ 0.25^ 0.32 over the mass range 0.71 The spheroid therefore does not contribM _ [ M [ 0.09 M _ . ute signiÐcantly to microlensing unless the mass function changes slope dramatically in the substellar range. The total local mass density of spheroid stars (including remnants and unseen binary companions) is o D 6.4] 10~5 pc~3, with an uncertainty of about 50%. The power-law indices a \ 0.25 for the M _ spheroid and a \ 0.44 for the disk (both uncorrected for binaries) are similar to those of globular clusters of moderate-to-high metallicity. Subject headings : stars : luminosity function, mass function È subdwarfs È surveys