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NGC 0253 and M82

In a study of the complex of ultraviolet filaments in the starburst-driven halos of NGC 0253 and M82 Hoopes et al. [5] concluded that the UV luminosities in the halo are too high to be provided by continuum and line emission from shock-heated or photoionized gas except perhaps in the brightest filaments in M82. This suggests that most of the UV light is the stellar continuum of the starburst scattered into our line of sight by dust in the outflow. This interpretation agrees with previous results from optical imaging polarimetry in M82. The observed luminosity of the halo UV light is leq 0.1% of the bolometric luminosity of the starburst. The morphology of the UV filaments in both galaxies shows a high degree of spatial correlation with Halpha and X-ray emission, which indicates that these outflows contain cold gas and dust, some of which may be vented into the intergalactic medium (IGM). UV light is seen in the "Halpha cap" 11 kpc north of M82. If this cap is a result of the wind fluid running into a pre-existing gas cloud, the gas cloud contains dust and is not primordial in nature but was probably stripped from M82 or M81 (Figure 2). If starburst winds efficiently expel dust into the IGM, this could have significant consequences for the observation of cosmologically distant objects.

Figure 2

Figure 2. GALEX Montage of M31. As large as the field of view of GALEX is, it still requires many pointings (in this case 9 images) to cover the main body of the galaxy and part of its halo. Both M32 and NGC 205 are visible in this image, but because of their intrinsically red population they are not as conspicuous as they are in the visible.

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