1997/11/30 by Andrew Gould, Chris Flynn, John N. Bahcall · 4 citations
Environmental Science · Physics and Astronomy · #Astronomy #Astrophysics #Galaxies: Formation, Evolution, Phenomena #Galaxy #Globular cluster #Gravitational microlensing #Hubble Deep Field #Hubble space telescope #Impact of Light on Environment and Health #Luminosity #Luminosity function #Metallicity #Physics #Power law #Spheroid #Star formation #Stars #Stellar mass #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/306023
published as Astrophys.J. 503 (1998) 798 · Clarifications and improvements made in response to referee report
arxiv created 1998/03/03 · openalex publication_date 1998/08/20 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We analyze 166 spheroid subdwarfs (6.5 < M V < 14.5) found in 53 fields observed with the Wide Field Planetary Camera on the Hubble Space Telescope . The fields cover 221 arcmin 2 over a wide range of directions. The spheroid luminosity function (LF) is inconsistent at about the 3 σ 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 difference may reflect 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 ∝ M α , with α = 0.25 ± 0.32 over the mass range 0.71 M ☉ > M > 0.09 M ☉ . The spheroid therefore does not contribute significantly 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 ρ ~ 6.4 × 10 -5 M ☉ pc -3 , with an uncertainty of about 50%. The power-law indices α = 0.25 for the spheroid and α = 0.44 for the disk (both uncorrected for binaries) are similar to those of globular clusters of moderate-to-high metallicity.