Oral Presentation

Diverse Origins of Broad Hα Lines in Heavily Obscured AGNs Revealed by Optical Multi-epoch Spectroscopy

Author(s): Shoichiro Mizukoshi (ASIAA)

Presenter: Shoichiro Mizukoshi (ASIAA)

According to the classical AGN model, the broad emission lines originate from the broad line region (BLR) near the center of the AGN, and they can be observed only when the dust extinction due to the obscuring structure, or the dusty torus, is small enough. However, we previously found several heavily-obscured AGNs with optical broad-line detections. To understand their origins, we performed optical multi-epoch spectroscopic observations of three heavily obscured broad-line AGNs to investigate the time variation of the broad Halpha line using the 3.8-m Seimei Telescope, which is one of the largest optical telescopes in East Asia. As a result, one object (Mrk 268) showed the broad Halpha flux variation with a significance of 4.3 sigma. This result implies that the broad Halpha line in Mrk 268 directly comes from the BLR through the clump gaps in the dusty torus. On the other hand, the rest two objects (UGC 5101 and MCG -3-34-64) did not show clear Halpha flux variations. This suggests that the broad Halpha line observed in these AGNs is not the direct emission from the BLR, but rather it comes from extended outflows or polar scattering. This result suggests that we should be careful to use the broad Halpha line as a BH mass tracer, especially for obscured AGNs that have often been observed in the distant universe.