THE LOW-MASS STELLAR CONTENT OF GALAXIES - CONSTRAINTS THROUGH HYBRID POPULATION SYNTHESIS NEAR-1 MICRON

We present high signal-to-noise observations obtained with the RC spectrograph at the CTIO 4 m telescope of six galaxies and of a variety of dwarfs and galactic bulge giants in the 9800-10200 angstrom spectral range. This spectral region contains gravity-sensitive bands of the FeH molecule. The Wing-Ford band of FeH centered at 9916 angstrom is clearly identified in all galaxies. A variety of modeling procedures employing the stellar library are used to reproduce the observed galactic spectra over this spectral range, and a method is described of scanning the solution space in search of secondary minima in the optimized synthesis procedure. We assume a power-law representation of the mass function with a slope ''x'' and a lower cutoff mass m(low). In order to test for these parameters we introduce a hybrid synthesis method which combines a sub-library of evolutionary-derived populations of known parameters, with a sub-library composed of individual late giants in advanced evolutionary phases. Although strong constraints for the ''x'' and m(low) parameters are not obtained within our limited spectral interval, a valid range of parameters is isolated. On the other hand, no combination of model parameters is capable of producing a luminosity contribution of M dwarfs in the I band larger than 10%-20%. The total luminosity contribution in the I band coming from all dwarfs would rarely exceed 30%-40%. Populations with a Salpeter exponent of the mass function will contribute on average less than 5% of the li ht in the I band from M dwarfs and less than 20% from all dwarfs.