Mathematics – Probability
Scientific paper
Jan 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005esasp.577..313p&link_type=abstract
In: Proceedings of the dusty and molecular universe: a prelude to Herschel and ALMA, 27-29 October 2004, Paris, France. Ed. by A
Mathematics
Probability
Galaxies: Individual (M101), Galaxies: Spiral, Ultraviolet: Galaxies, Infrared: Galaxies, Ism: Dust, Extinction, Scattering
Scientific paper
The total ultraviolet (UV) flux (from 1412 to 2718 å) of M101 is compared on a pixel-to-pixel basis with the total far-infrared (FIR) flux (from 60 to 170 μm), using the maps of the galaxy taken by GALEX in the near-UV and far-UV and by ISOPHOT at 60, 100 and 170 μm. The main result of this investigation is the discovery of a tight dependence of the FIR/UV ratio on radius, with values monotonically decreasing from ~4 in the nuclear region to nearly zero towards the edge of the optical disk. Although the tightness of this depencence is in part attributable to resolution effects, the result is consistent with the presence of a large-scale distribution of diffuse dust having a face-on optical depth which decreases with radius and which dominates over the more localized variations in opacity between the arm and interarm regions. We also find a trend for the FIR/UV ratio to take on higher values in the regions of diffuse interarm emission than in the spiral-arm regions, at a given radius. This is interpreted quantitatively in terms of the escape probability of UV photons from spiral arms and their subsequent scattering in the interarm regions, and in terms of the larger relative contribution of optical photons to the heating of the dust in the interarm regions.
GALEX Team
Gil de Paz Amando
Madore Barry F.
Popescu Cristina C.
Tuffs Richard. J.
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