Near-Infrared Mass-to-Light Ratios in Galaxies: Stellar Mass and Star Formation in the Heart of the Whirlpool
Abstract
We use the observed stellar population in the solar neighborhood to derive a relationship between the local stellar mass density and the visual and near-infrared brightness, which we then extend to apply to a wide range of galaxies. Use of the solar neighborhood as a model for the infrared light from a variety of galaxies is justified by evidence that the emission at λ ~ 1-2.5 microns is dominated by low- to moderate-mass red giants. For many objects, these stars should be produced in proportion to the number of older main-sequence stars, which will dominate the total stellar mass. We compare our results with dynamical masses determined for a number of galaxies. The agreement is good. To apply our technique, we present and discuss near-infrared (J, H, and K) images of the central 2.3 kpc (50") of the Whirlpool Galaxy (M51, NGC 5194). This object has an elliptical brightness distribution at these wavelengths similar to that reported at longer visual wavelengths. Over the region that we map in the near-infrared, we find a total stellar mass of M_*,old_~1.2x10^10^ M_sun_. From far-infrared photometric data, we find that over the same region, stars are presently being born at a rate of ~4 M_sun_ yr^-1^, which is about a factor of 5 greater than the rate averaged over a Hubble time. Therefore, the center part of M51 appears to be undergoing a period of enhanced star formation. However, the present efficiency of star formation, defined as the ratio of the mass of new stars to the mass of star-forming gas, is only ~1%, quite comparable to the global value for the Milky Way and other galaxies. We estimate that the current high rate of star formation can last no more than another 10^8^ yr or so and, if a large fraction of the stars in the nucleus of M51 was created in periods of enhanced formation, the duty cycle for such events is roughly 5%. In the Appendix, we compare the three different definitions of blue luminosity that are widely used at present.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- April 1988
- DOI:
- 10.1086/166224
- Bibcode:
- 1988ApJ...327..671T
- Keywords:
-
- Galactic Nuclei;
- Mass To Light Ratios;
- Near Infrared Radiation;
- Photometry;
- Solar Neighborhood;
- Star Formation Rate;
- Cosmic Gases;
- Early Stars;
- Milky Way Galaxy;
- Red Giant Stars;
- Stellar Mass;
- Astrophysics;
- GALAXIES: INDIVIDUAL MESSIER NUMBER: M51;
- GALAXIES: NUCLEI;
- PHOTOMETRY;
- GALAXIES: STELLAR CONTENT;
- STARS: FORMATION