Understanding the UV Alignments of Low and High Redshift Radio Galaxies

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Session 70 -- Active Galaxies and Intergalactic Medium
Oral presentation, Tuesday, 10, 1995, 2:00pm - 3:30pm

[70.06D] Understanding the UV Alignments of Low and High Redshift Radio Galaxies

Arjun Dey, Hyron Spinrad (University of California, Berkeley), Wil van Breugel (IGPP/LLNL)

A spectacular demonstration of the link between galaxy activity and the host galaxy's global properties is the ``alignment effect'': high redshift radio galaxies (z $>$ 1) have complex UV morphologies that are aligned with the major axis of their radio emission. Several explanations have been suggested for the alignment effect, but a detailed study of the continuum light in high redshift radio galaxies which would distinguish between these possibilities has thus far been precluded by the optical faintness of these galaxies. Our research is focused on understanding the alignment effect by (1) identifying low redshift (z$<$0.2) radio galaxies which exhibit the alignment effect; these galaxies lend themselves to a detailed study because of their relative brightness, and (2) directly studying the extended optical continuum in high redshift radio galaxies using W.\ M.\ Keck Telescope and the refurbished Hubble Space Telescope.

We present the results of a continuum imaging survey of a sample of low redshift radio galaxies (0.08$<$z$<$0.2). We have discovered spatially extended UV continuum emission distributed along the radio axis in $\sim$30\% of the radio galaxies in the sample. The alignment effect in these systems has a variety of origins. In most low redshift radio galaxies the aligned continuum light is nonstellar, although there is evidence for jet induced star formation in at least one galaxy.

Using the Keck telescope, we have discovered that the distant radio galaxy 3C265 (z=0.81) contains a buried quasar. The off-nuclear spectrum of the extended continuum of this galaxy shows a broad component of the MgII emission line -- a feature characteristic of quasar spectra. These data both provide critical confirmation that scattering of nuclear AGN light must be responsible for the alignment effect in some galaxies, and also support the AGN unification hypothesis. We also present recent Keck spectroscopic and HST WFPC2 imaging polarimetric observations of the prototypical aligned high redshift radio galaxy 3C368 at z=1.132.

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