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Session 75 - Dust & PAHs in Galaxies.
Display session, Friday, January 09
Exhibit Hall,

[75.08] Does the 2175 ÅExtinction Bump Exist Outside the Local Group?

G. C. Clayton, K. D. Gordon, K. A. Misselt (Louisiana State U.), M. J. Wolff (Space Science Inst.)

The ultraviolet extinction bump at 2175 Å\ is ubiquitous in the diffuse interstellar medium in the Galaxy. However, the bump is weak or missing in interstellar dust in the LMC, SMC and M31. For many years, it has also been suggested that the bump is weak or non-existent beyond the Local Group. In particular, starburst galaxies seem to have no measurable bump. However, detections of the bump have been suggested in some high redshift objects including QSO's. It has been suggested that environmental processing by radiation and shocks near regions of star formation or variations in galactic metallicity are responsible for the large observed variations in 2175 Å\ bump strength seen from one galaxy to another. We will attempt to relate what we have learned about dust properties and environments in the Local Group to more distant objects such as starburst galaxies, Mg II absorption systems and QSO's.

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