Dust and Star Formation in the Extreme Outer Disks of Spiral Galaxies
Abstract
The discovery by GALEX of extended UV emission in the extreme outskirts of local star-forming galaxies challenges our current understanding of star formation, of the modality for polluting the intergalactic medium, and of the long-term impact of interactions. The nature of the outer disk UV light is unclear with possible origins including in-situ star formation as well as dust-scattered photons originating in the galaxy disk. Spitzer, with its wavelength windows sensitive to both the low mass stars and the dust emission, has a unique capability to address some of these fundamental questions. Building on the success of our Cycle 2 pilot program on the UV-emitting outer regions of M83, we propose IRAC imaging of regions in the extreme outer disks (> 1.5 R_{opt}) of five nearby star-forming spirals. The five galaxies are a subsample of all the galaxies with extended UV emission discovered by GALEX, selected to cover the full range of UV morphologies and properties, including arm-interarm contrast and extended emission in the presence/absence of H-alpha edges. With this varied sample we plan to: (1) investigate whether a fraction of the UV light in those regions is due to dust scattering, and obtain a census of the UV leakage from galaxy disks; (2) derive masses for the UV-emitting knots associated with star formation and compare this mass range with those of disk clusters; (3) investigate variations in the properties of those extreme regions as a function of the parent galaxy's characteristics. With a modest committment of time, Spitzer will provide a milestone for unraveling the properties of these regions at the boundary between galaxies and the intergalactic medium.
- Publication:
-
Spitzer Proposal
- Pub Date:
- May 2006
- Bibcode:
- 2006sptz.prop30753C