Astronomy and Astrophysics – Astrophysics
Scientific paper
Feb 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996a%26a...306...61b&link_type=abstract
Astronomy and Astrophysics, v.306, p.61
Astronomy and Astrophysics
Astrophysics
128
Galaxies: Stellar Content, Ism, Infrared: Galaxies, Ultraviolet: Galaxies
Scientific paper
We have used a radiation transfer model to estimate the extinction in galactic disks considering their ultraviolet, optical and infrared emission and applied this model to a sample of 152 disk galaxies observed both in ultraviolet (UV) (2000A) and far-infrared (FIR) by IRAS. The sample galaxies are found to exhibit a moderate extinction at 2000A: 0.9 and 0.2 magnitude in average for Sa-Scd and Sd-Irr galaxies respectively. Most of the dust heating is due to the UV non-ionizing radiation (912-3650A). The optical depth estimated with our model does not correlate with the atomic hydrogen surface density whereas a positive correlation is found with the molecular and total (HI plus H_2_) surface densities. The presence of a strong selection bias in our sample toward galaxies with a low extinction is dismissed by a comparison between the UV and FIR detections in two selected fields. A calibration of the FIR (40-120μm) luminosity in quantitative star formation rate is performed by a comparison with the intrinsic UV luminosity (i.e. corrected from extinction) at 2000A for Sb-Irr galaxies. Although the mean relation found between the FIR luminosity and the recent star formation rate is in agreement with previous determinations, the dispersion of this calibration amounts a factor ~2 (1σ). The cause for this dispersion is found different when considering the galaxies with low and high UV optical depth: the variation of the optical depth explains most of the dispersion in galaxies optically thin at UV wavelengths whereas the relative contribution to the dust heating by the UV photons compared to that by the optical photons becomes an important factor at large UV optical depths.
Buat Veronique
Xu Cenke
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