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Date and Time of the Query: 2019-08-17 T10:36:49 PDT
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For refcode 1990A&A...238...28D:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
1990A&A...238...28D IR tracers of star formation and the origin of the 25{micron} emission in H II galaxies D. Dultzin-Hacyan, J.Masegosa, and M. Moles Instituto de Astrofisica de Andalucia, Apdo. 2144, F-18080 Granada, Spain Instituto de Astronomia, UNAM, Apdo. 70-264, 04510 Mexico D.F., Mexico Received November 13, 1989; accepted March 21, 1990 Abstract. We present statistical IRAS data for a large sample of H II Galaxies selected from the Spectroscopic Catalogue of H II Galaxies and compiled from the literature. Their IR and optical properties have been compared. The detectability rate was found to be of 18% in good agreement with previous studies for the same kind of galaxies. A detailed analysis of the detected galaxies leads us to the conclusion that the low metallicity, very compact galaxies were not easily detected by IRAS. The physical reason for that appears to be their low dust content. The origin of the (12-100 micron) emission has been investigated. Our main result is that the emission at 25 microns is the one which is more neatly related to recent events of star formation. We have confirmed a previous result (Dultzin-Hacyan, et al., 1988) in the sense that this emission correlates best with the ionizing photons source. Here we show that the best IRAS tracer of recent star formation is the ratio I_25_/I_100_. We discuss two alternatives for the origin of the 25 micron emission: hot dust {T_d_ ~100 K) very near the ionizing cluster or emission of shock heated dust. We also find that L_FIR_ ({lambda} > 40 microns) is mainly due to emission of dust heated by non-ionizing photons. This has been discussed for spiral galaxies (Bothun et al., 1989) the explanation being that the emitting dust is heated by old disk 1-2 M_sun_ stars; we suggest that in H II galaxies L_FIR_ is emitted by dust heated by intermediate mass stars. Key words: H II galaxies - IR radiation - star formation
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