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Session 13 - Large Scale Structure & Cosmology.
Display session, Monday, January 13
Metropolitan Ballroom,

[13.11] Statistical evidence for extinction in gravitational lenses: Is the Universe old and dusty?

J. E. Rhoads (Kitt Peak National Obs.), S. Malhotra (IPAC), E. L. Turner (Princeton U. Obs.)

Foreground galaxies that amplify the light from background quasars may also dim that light if the galaxies contain enough dust. This reduced optical flux can cause dusty lens systems to be missed by optical lensing searches, but will not affect radio searches. Thus, if dust occurs frequently in lenses, we expect radio-selected lens systems to be redder on average than optical-selected ones.

We apply this test using optical-infrared colors of a large set of lens systems, compiled from Apache Point Observatory data and the literature. We find that radio-selected systems are indeed redder than optical-selected ones. We then compare the colors of the lensed samples to those of unlensed quasars from the literature, and find that radio-selected lensed systems are also redder than radio-selected unlensed quasars. This argues that at least part of the color difference between the two lens samples is due to dust.

Extinction by dust in lenses could hide the large number of lensed systems predicted for a flat universe with a large value of the cosmological constant \Lambda. Thus, the results presented here weaken the best constraint on cosmological scenarios with \Lambda > 0. Such scenarios allow the universe to be older than its apparent expansion age 1/H_0. A nonzero \Lambda can also satisfy predictions of inflationary models of the early universe and play a role in large scale structure formation models.

Finally, we consider the use of gravitational lenses to study the interstellar medium at cosmological distances, and outline further ways of testing the dusty lens hypothesis to see if the Universe might be old and dusty.

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