Detection of the Polarized Broad Emission Line in the Seyfert 2 Galaxy Markarian 573

Abstract

We report the discovery of the scattered emission from a hidden broad-line region (BLR) in a Seyfert 2 galaxy, Mrk 573, based on our recent spectropolarimetric observation performed at the Subaru Telescope. This object has been regarded as a type 2 active galactic nucleus (AGN) without a hidden BLR by previous observations. However, our high-quality spectrum of the polarized flux of Mrk 573 shows prominent broad (∼3000 km s-1) Hα emission, broad weak Hβ emission, and subtle Fe II multiplet emission. Our new detection of these indications for the presence of the hidden BLR in the nucleus of Mrk 573 is thought to be because of the high signal-to-noise ratio of our data, but the possibility of a time variation of the scattered BLR emission is also mentioned. Some diagnostic quantities such as the IRAS color, the radio power, and the line ratio of the emission from the narrow-line region of Mrk 573 are consistent with the distributions of such quantities of type 2 AGNs with a hidden BLR. Mrk 573 is thought to be an object whose level of the AGN activity is the weakest among the type 2 AGNs with a hidden BLR. In terms of the systematic differences between the type 2 AGNs with and without a hidden BLR, we briefly comment on an interesting Seyfert 2 galaxy, Mrk 266 SW, which may possess a hidden BLR but has been treated as a type 2 AGNs without a hidden BLR.