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M83: Extinction and Extended UV Disks

Boissier et al. [3] used FUV and NUV images of M83 to compute the radial profile of the UV spectral slope disk. They briefly present a model of its chemical evolution which allows them to obtain realistic intrinsic properties of the stellar populations. Using corollary data, they also compute the profiles of Halpha / Hbeta and of the total IR (TIR) to FUV ratio. Both data and model are used to estimate and compare the extinction gradients at the FUV wavelength obtained from these various indicators. They discuss the implications for the determination of the star formation rate.

Thilker et al. [14] have discovered an extensive sample of UV-bright stellar complexes in the extreme outer disk of M83 (Figure 6), extending four to five times the radius where the majority of H II regions are detected (RHII = 5.1 arcmin or 6.6 kpc). These sources are typically associated with large-scale filamentary H I structures in the warped outer disk of M83, and are distributed beyond the galactocentric radii at which molecular ISM has yet been detected. It is of interest that only a subset of the outer disk UV sources have corresponding H II regions detected in Halpha imaging, consistent with a sample of mixed age in which a few sources are a few Myr old and the majority is much more evolved (~ 108 yr).

Figure 6

Figure 6. GALEX Imaging of M83. The grey-scale background image of M83 is derived from a combination of the FUV and NUV GALEX data. The contours correspond to the HI distribution published by Tilanus & Allen (1993) extend out to the limits of the image (44 arcmin diameter, which corresponds to a physical extent of about 60 kpc at the distance of M83; the inner disk of M83 as defined by its inner high-surface-brightness disk HII regions is about 5 times smaller (from Thilker et al.[ 14].

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