AAS 196th Meeting, June 2000
Session 50. Active Galaxies
Display, Thursday, June 8, 2000, 9:20am-4:00pm, Empire Hall South

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[50.14] An Optical Polarization Survey of Infrared-Selected QSOs

P.S. Smith, G.D. Schmidt, D.C. Hines (Steward Observatory), R.M. Cutri, B.O. Nelson (Caltech, IPAC)

Observations of some of the most luminous examples of IR-selected (i.e., IRAS) AGN indicate that the optical radiation is not emitted isotropically, and that these objects would be indistinguishable from UV/optically-selected QSOs if their nuclei were viewed from a different vantange point. In addition, the Two-Micron All Sky Survey (2MASS) is uncovering a large population of previously unidentified radio-quiet AGN. The large IR-to-optical flux ratios of these objects also suggest that their optical emission is largely obscured from our view. The existence of a population of obscured active nuclei may increase the space density of AGN by a factor of two or more, and this has major implications for theories of the origin and evolution of these accretion-powered objects.

We present the results of a broad-band optical polarization survey of AGN discovered by 2MASS. The object sample has near-IR luminosities similar to Palomar-Green (PG) QSOs, and is more highly polarized than optically selected samples such as the PG and broad absorption-line QSOs. High polarization (P > 3%) is restricted to objects with large near-IR-to-optical flux ratios (B-K > 5). Spectropolarimetry of some of the QSOs indicates that scattering of nuclear radiation by material near or within the narrow emission-line region is the dominant polarizing mechanism. These results are consistent with the optical emission of 2MASS AGN being hidden from our direct view by dust; leading to higher polarizations than observed for unobscured, optically selected QSOs because the scattered nuclear light is not swamped by the emission seen directly.

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