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Session 48 - Spiral & Field Galaxies.
Display session, Tuesday, January 16
North Banquet Hall, Convention Center
Data obtained with the Infrared Astronomical Satellite(IRAS) are used to investigate the dependence of the far-infrared luminosity on Hubble type for a complete sample of 1495 galaxies selected from the Nearby Galaxy Catalog(NBG). The sample includes all known spiral and lenticular galaxies within 40 Mpc. Reliable 60 micron fluxes have been determined for 982 galaxies or equivalently 66% of the galaxies in the NBG catalog.
The origin of the far-infrared emission from spiral galaxies is a subject of continuing controversy. However, recent observations illustrating the close correspondence between the H\alpha and far-infrared morphology in spiral galaxies indicate that the far-infrared luminosity is a reliable tracer of high-mass star formation. Our assertion is further supported by the fact that the luminosity measured in the far-infrared is commensurate with that expected from the O and B stars which are required to ionize the Hydrogen gas.
Our results indicate that the 60 micron luminosities of spiral galaxies of types Sa-Scd are very similar while the luminosities of the very early (SO-SO/a) and very late (Sd-Sm) types, are on average one order of magnitude lower. The result implies that the massive star formation rate is independent of Hubble type for Sa-Scd, which is contrary to the widely held perception that the massive star formation rates decrease along the Hubble sequence from Sc through to Sa. Evidently the Hubble sequence is not a sequence in the present day rate of high mass star formation. Collectively our results reveal a remarkable homogeniety in the present-day high mass star forming capabilities of spiral galaxies despite the wide diversity of optical morphology.
