Next: Observations and Reductions Up: No Title Previous: No Title

   
Introduction

In the ongoing quest to better understand the luminous quasar population, one of the most fertile areas of study has been the investigation of their galaxy environments. The host galaxy not only must provide fueling for the central engine, but should also display the effects of the strong nuclear ionizing emission and the impact of dynamic activity, such as jets and winds.

Broadband observations of quasar environments suggest a surprising variety of host galaxy morphologies, including spirals and ellipticals, nearby companions, and tidal interactions. While early ground-based work indicated a large percentage of spirals amongst low-redshift quasar hosts ( %; [Hutchings et al. 1984a]) and no concrete evidence for ellipticals, subsequent HST observations find an elliptical fraction of greater than half ([Bahcall et al. 1997]). More recent HST work suggests in fact that nearly all radio-loud and radio-quiet quasars reside in massive ellipticals ([McLure et al. 1999]; see also [Disney et al. 1995]). A substantial fraction of quasar host galaxies exhibit tidal tails and streamers indicative of interactions (e.g., [Hutchings & Campbell 1983]; [Hutchings et al. 1984b]; [Stockton & MacKenty 1987]; [Bahcall et al. 1997]; [Hutchings et al. 1999]). Evidence for extended gas from interactions has also been found at HI 21 cm (e.g., [Lim & Ho 1999]). The presence of companion galaxies is common; the QSO/galaxy correlation function is evidently several times that for galaxies alone ([Fisher et al. 1996]).

Given the strong line emission in the nuclei of active galaxies and quasars, as well as the prevalence of ionized gas in interacting systems, narrowband observations of quasar environments have proved interesting as well. The imaging survey of Stockton & MacKenty (1987), the largest to date, found highly-structured [OIII] emission in a quarter of 47 luminous QSOs, with typical extents of a few tens of kpc. Similar spectroscopic observations have detected extended regions of line emission in half of the objects observed ([Boroson et al. 1985]). The line ratios usually suggest photoionization by the nuclear power-law spectrum (e.g., [Boroson et al. 1985]; [Boisson et al. 1994]), although stellar absorption lines from (presumably in-situ) stars are sometimes seen (e.g., [Miller et al. 1996]). Kinematic studies of the ionized gas component are scarce, but the gas motions generally appear to be complex and chaotic (e.g., [Durret et al. 1994]). The size and luminosity of the ionized component appear to be correlated with both the narrow-line nuclear luminosity and the radio power of the quasar ([Boroson et al. 1985]; [Stockton & MacKenty 1987]; [Véron-Cetty & Woltjer 1990]).

The quasar MR 2251-178 is one of a few radio-quiet quasars which exhibit an extended gaseous envelope (e.g., [Bergeron et al. 1983]). This quasar was first discovered as a strong and variable X-ray source by the Ariel V satellite ([Cooke et al. 1978]). Subsequent observations identified the object as a quasar at a redshift of ([Ricker et al. 1978]; [Canizares et al. 1978]), residing in the outskirts of a small cluster ([Phillips 1980]). In this Letter, we present deep H observations of MR 2251-178 obtained with the TAURUS Tunable Filter (TTF), a new, etalon-based instrument which has been optimized for the detection of faint, extended emission-line gas. These new data allow us to better constrain the extent, velocity field, and origin of the ionized nebula around MR 2251-178.