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E. J. Hooper (McDonald Obs.), R. A. Finn (UMass), C. D. Impey (Steward Obs.)
Supermassive black holes appear to be a ubiquitous component of galaxy bulges, yet only a small fraction of these are strongly accreting. Why? What is responsible for triggering the fueling of the black holes to become quasars? Conventional wisdom holds that agents external to the quasar's host galaxy, such as nearby companions or a large cluster environment, may play a significant role. However, recent results, including our own, indicate that the situation may be more complicated. We find little evidence, based on R-band imaging, for large cluster-scale environments around either radio-loud or radio-quiet quasars.
Our sample consists of 33 quasar fields drawn from the optically selected Large Bright Quasar Survey (LBQS). Most of the quasars in our study lie in the redshift range 0.4 < z < 0.5, though about 1/3 have z > 0.6. In general, the environments are consistent with those of field galaxies. Only two quasars appear to lie in Abell class 0 galaxy clusters, and the error bars on one of these are large. Similar results hold for a subsample of 16 LBQS quasars with z < 0.5 imaged with HST (Finn et al. 2001, ApJ, 557, 578).
Smaller scale environments may exist around the quasar, and in fact there are tantalizing indications of these, including possible galaxy groups and companions to the quasar host galaxies. However, they are statistically undetectable in single-band images against the omnipresent fog of field galaxies. We have begun spectroscopic follow-up on about half of the fields to investigate whether sparse environments are present and what role they play in triggering quasar activity.
The first two authors gratefully acknowledge support of NSF Astronomy & Astrophysics Postdoctoral Fellowships.
The author(s) of this abstract have provided an email address for comments about the abstract: ehooper@astro.as.utexas.edu
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.