Mpc Scale Environments of BL Lac Objects

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Session 4 -- AGNs
Display presentation, Monday, 9:20-6:30, Pauley Room

[4.11] Mpc Scale Environments of BL Lac Objects

E. P. Smith (LASP/GSFC), C. P. O'Dea, S. A. Baum (STScI)

We present preliminary results from a broad--band imaging survey of the large scale clustering environments of BL Lac objects. Deep optical imaging and spectroscopy of nearby BL Lacs has shown that they are found in bright elliptical galaxies. Their radio morphologies and powers are comparable to intermediate radio sources, that is, Fanaroff-Riley Class I (FR I) sources. Current ``unified AGN'' theories postulate that BL Lac objects may be FR I radio galaxies viewed down their doppler--boosted radio jets. If BL Lacs are indeed drawn from the same parent population of objects which manifests itself as FR I radio galaxies then their environments should be similar. To test this theory we have imaged 17 BL Lac Objects and 7 comparison fields (from the Bologna survey) using the KPNO 0.9m telescope, $2048^2$ Tektronics CCD and $V$ and $R$ filters. We have used the Faint Object Classification and Analysis System (FOCAS) to detect and classify objects in our fields. Background galaxy counts were obtained from deep exposures of random fields and subtracted from the data. We further restricted the number of potential cluster members by requiring them to possess plausible $(V-R)$ colors for galaxies at the redshift of the object of interest. We display the galaxy densities as a function of radial distance and compare their clustering strengths (as measured by their spatial cross-correlation amplitudes, $B_{gr}$) and discuss their implications for the unified scheme linking BL Lac objects and FR I radio galaxies.

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