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R.D. Cohen (Grossmont Coll. & UCSD), R.R.J. Antonucci, M. Kishimoto (UCSB), T.W. Hurt (Raytheon), L.E. Kay (Barnard Coll.), J.H. Krolik (JHU), R.G. Allen (UA)
We have used the FOS as a broad band polarimeter to measure the polarization of 20 Seyfert 2 galaxies in the near-UV. The unified picture of active galactic nuclei suggests that the polarization of Seyfert 2 nuclei should be high, because the nuclear Seyfert spectrum is scattered into our line-of-sight. However, broad band polarization measured in the optical region of the spectrum is generally low. Our original expectation was that UV observations would show uniformly high polarization in the UV where dilution of the spectrum by starlight in the host galaxies would be minimized. Systematic effects due to interstellar polarization of starlight in the host galaxies would be reduced as well. Since we began this program, evidence has been found for another component of the spectrum in addition to the scattered nuclear continuum plus a normal stellar component. Referred to as FC2, as it is a second featureless continuum component, it is known to be due to hot stars in some cases. FC2 might not decrease significantly in the UV, compared to any scattered nuclear spectrum, and thus the polarization might not be large compared with the optical.
Our results are mixed. Some objects have higher polarization in the UV than in the optical, similar to the prototypical galaxy NGC 1068. Others show no increase over the optical polarization. In a significant fraction of Seyfert 2 galaxies, we detect no polarization in the UV or optical.
This research was supported by grants from STScI.
The author(s) of this abstract have provided an email address for comments about the abstract: rdcohen@ucsd.edu