NASA/IPAC EXTRAGALACTIC DATABASE
Date and Time of the Query: 2019-08-18 T00:31:21 PDT
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For refcode 1989ApJ...344..135H:
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Copyright by American Astronomical Society. Reproduced by permission
1989ApJ...344..135H EXCESS 10 MICRON EMISSION IN EXTRAGALACTIC NUCLEI PAUL T. P. HO, JEAN L. TURNER, GIOVANNI G. FAZIO, AND S. P. WILLNER Harvard-Smithsonian Center for Astrophysics Received 1988 October 6; accepted 1989 February 1 ABSTRACT Intense 10 micron emission has been mapped with 4" resolution toward the nuclei of four nearby spiral galaxies: NGC 253, Maffei II, NGC 2903, and NGC 6946. In all four cases, the ratio of 10 micron to thermal radio emission is significantly higher than the ratio observed in Galactic H II regions. In addition, the 10 micron emission shows excellent spatial agreement with 6 cm radio continuum emission. This is surprising since the 10 micron emission is due to thermal dust emission, while the radio emission is predominantly nonthermal synchrotron emission. A new process that operates in galactic nuclei, but not in H II regions, may be responsible for much of the 10 micron emission. We propose that a population of small dust grains or large molecules heated by massive stars and supernova remnants (SNRs) may be responsible for an excess of 10 micron emission over the amount expected from radio free-free emission. The presence of an enhanced population of small dust grains in the nuclei of galaxies may result from dust destruction in shocks associated with the SNRs producing the radio emission, and the heating of these small grains may be via collisions with keV electrons associated with the SNRs. Subject headings: galaxies: nuclei - infrared: sources - radiation mechanisms - radio sources: galaxies
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