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Date and Time of the Query: 2019-06-17 T23:40:45 PDT
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For refcode 1994ApJ...435...22K:
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Copyright by American Astronomical Society. Reproduced by permission
1994ApJ...435...22K PAST AND FUTURE STAR FORMATION IN DISK GALAXIES ROBERT C. KENNICUTT, JR., AND PETER TAMBLYN Steward Observatory, University of Arizona, Tucson, AZ 85721 AND CHARLES W. CONGDON 1943 SE 113th Ave, Portland, OR 97216 Received 1994 February 17; accepted 1994 May 5 ABSTRACT We have combined H{alpha} and UBV measurements of 210 nearby Sa-Irr galaxies with new photometric synthesis models to reanalyze the past and future star formation timescales in disks. The integrated photoionization rates and colors of disks are best fitted by a stellar initial mass function (IMF) which is enriched in massive stars by a factor of 2-3 relative to the Scalo solar neighborhood IMF. We have used published surface photometry of spiral galaxies to analyze the star formation histories of disks independent of their bulge properties. The ratio of the current star formation rate (SFR) to the average past rate increases from of order 0.01 in Sa galaxies to 1 in Sc-Irr disks. This confirms that the pronounced change in the photometric properties of spiral galaxies along the Hubble sequence is predominantly due to changes in the star formation histories of disks, and only secondarily to changes in the bulge/disk ratio. A comparison of current SFRs and gas masses of the sample yields median timescales for gas consumption of ~3 Gyr, in the absence of stellar recycling. However, a proper time-dependent treatment of the gas return from stars shows that recycling extends the gas lifetimes of disks by factors of 1.5-4 for typical disk parameters. Consequently the current SFRs in many (but not all) disks can be sustained for periods comparable to the Hubble time. Subject headings: galaxies: evolution - galaxies: luminosity function, mass function - galaxies: spiral - galaxies: stellar content - stars: formation
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