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Session 78 - Seyfert Galaxies.
Display session, Friday, January 09
Compelling evidence has been presented that some Seyfert 2 galaxies are in fact Seyfert 1s, viewed at an angle such that the Broad Line Region (BLR) is hidden from direct view. Spectropolarimetry observations have shown that in scattered, i.e. polarized\ flux, some of the Seyfert 2s have broad Balmer lines as are seen in the direct flux of Seyfert 1s. But the generalizability of this model to all\ Seyfert 2s is still unproven; perhaps some Seyfert 2s are just obscured Seyfert 1s but others are `real' Seyfert 2s in which no Broad Line Region exists. As part of a spectropolarimetric study of a complete distance limited sample of nearby Seyfert 2s, we observed NGC 788 and found that it too possesses a polarized broad H\alpha line.
This particular hidden BLR Seyfert 2 differs from the others in two respects. Kay (1994) showed that the spectropolarimetrically detected hidden BLR Seyfert 2s had a much lower average galaxy fraction than Seyfert 2s in general and suggested that the lower amount of starlight in the spectra made it easier to observe the scattered light in polarized flux by not diluting the polarization too much. NGC 788 has a higher galaxy fraction than most of the others; even with such dilution the polarization at H\alpha is significant.
Furthermore, it has been previously noted that the hidden BLR Seyfert 2s have a higher than average 20 cm radio power, either because these objects are fundamentally different than `real' Seyfert 2s (Moran et al. 1992) or because the objects with higher luminosities in 20 cm and\ optical continuum are easier to analyze with spectropolarimetry (Kay 1993, Kay et al. 1998). Thus it is noteworthy that NGC 788 has a lower radio power by an order of magnitude, as it suggests that it is indeed possible to detect obscured broad lines in fainter objects.
Program listing for Friday