Calibration of metallicity effects on the integrated colors of globular clusters and early-type galaxies
New infrared observations of globular clusters have been obtained which show that both infrared and optical colors are strongly correlated with metallicity and which provide an empirical calibration of abundance effects in composite stellar systems. Models have been constructed, based on the isochrones of Ciardullo and Demarque, with Z-values between 0.0001 and 0.04, and slope of the initial mass function s between 0 and 4. Metal-poor models with s ≤ 2.35 (the Salpeter function) give good agreement with the empirical calibration. Metal-rich models are compared with observations of the central regions of early-type galaxies, and imply that galaxies which have -19 ≥ M_v ≥ -23 correspond to a range in metallicity of 0.0 ≤ [M/H] ≤ +0.3. Models with s = 2.35 adequately fit the observations; proper accounting of metallicity effects on narrow-band infrared features does not require s < 2, as previously published models have suggested. An upper limit on s of 3.2 is determined.
Additional Information© American Astronomical Society • Provided by the NASA Astrophysics Data System. Received 1977 December 9; accepted 1978 February 8. We thank John Huchra, Bruce Carney, and Phil Marcus for their assistance at the telescope. We also thank Doug Kleinmann, Jay Frogel, Eric Persson, and George Rieke for discussions and encouragement during the course ofthis work. M. A. and M. M. thank the Center for Astrophysics for generous financial support. This research was partially supported with funds from NSF grants AST 76-81874 and AST 76-22991.
Published - 1978ApJ___223__824A.pdf