AAS 204th Meeting, June 2004
Session 80 Nearby Galaxies
Poster, Thursday, June 3, 2004, 9:20am-4:00pm, Ballroom

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[80.08] A Comparative Study of the Spatial Distribution of Ultraviolet and Far-infrared Fluxes from M101

C. C. Popescu, R. J. Tuffs (Max Planck Institut), B. F. Madore, A. Gil de Paz (Carnegie Obs.), H. J. Voelk (Max Planck Institut), T. Barlow (Caltech), L. Bianchi (Johns Hopkins Univ., Center for Astrophysical Sciences), Y.-I. Byun (Yonsei Univ.), J. Donas (Laboratoire d'Astrophysique de Marseille), K. Forster, P. Friedman (Caltech), T. M. Heckman (Johns Hopkins Univ.), P. Jelinsky (SSL, Univ. of California, Berkeley), Y.-W. Lee (Yonsei Univ.), R. Malina (Laboratoire d'Astrophysique de Marseille), C. Martin (Caltech), B. Milliard (Laboratoire d'Astrophysique de Marseille), P. Morrissey (Caltech), S. Neff (NASA GSFC), R. M. Rich (Univ. of California), D. Schiminovich (Caltech), O. Siegmund (SSL, Univ. of California, Berkeley), T. Small (Caltech), A. Szalay (Johns Hopkins Univ.), B. Welsh (SSL, Univ. of California, Berkeley), T. Wyder (Caltech)

The total ultraviolet (UV) flux (integrated from 1412 to 2718Å) of M~101 is compared on a pixel-to-pixel basis with the total far-infrared (FIR) flux (integrated from 60 to 170 micron), using the maps of the galaxy taken by GALEX in the near-UV and far-UV and by ISOPHOT at 60, 100 and 170 micron. 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. This 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.

The author(s) of this abstract have provided an email address for comments about the abstract: Cristina.Popescu@mpi-hd.mpg.de

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