Astronomy and Astrophysics – Astrophysics
Scientific paper
Apr 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...425...91s&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 425, no. 1, p. 91-102
Astronomy and Astrophysics
Astrophysics
37
Astrophysics, Far Infrared Radiation, H Alpha Line, Infrared Astronomy, Ring Galaxies, Spiral Galaxies, Star Formation, Astronomical Spectroscopy, Interstellar Extinction, Kuiper Airborne Observatory, Mass Distribution, Star Distribution, Stellar Evolution, Stellar Luminosity
Scientific paper
We present new high spatial resolution Kuiper Airborne Observatory (KAO) 50 and 100 micrometers measurements of the ringed Sab galaxy NGC 4736 and the Sb galaxy NGC 3627. We detect strong far-infrared emission (approximately 109 solar luminosity) from the bulge areas of these galaxies, regions where there is little observed star formation. This far-infrared radiation is extended over the bulge with spatial distributions similar to that of the old stellar population. The ratio of far-infrared to H-alpha luminosity for these central sources is significantly larger than for the star-forming regions in these galaxies. This ratio is higher than can be accounted for by dust heating due to a population of young stars with a mass distribution similar to the Salpeter initial mass function assuming current estimates of extinction, unless the upper mass limit is unusually low (approximately B1 stars). On the other hand, the bolometric luminosity of the observed bulge stars is sufficient to account for the far-infrared radiation. Thus, older stars are likely to be important in heating dust in these bulges. The dust in the centers of these galaxies is quite warm, approximately 40 K (lambda-1 emissivity), however, the interstellar radiation fields derived from the optical luminosities are consistent with these temperatures without invoking hidden central star formation or a dusty active galactic nucleus.
Colome Cecilia
DiFrancesco James
Harvey Paul Michael
Pogge Richard W.
Smith Beverly J.
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