S18A0058abst
S18A0058
It is empirically known that masses of supermassive black holes (SMBH) in active galactic nuclei (AGNs) can be estimated from line widths of broad emission lines (BELs) originated from broad line regions. Although this kind of BH mass estimation is generally possible only for type 1 AGNs, deep near-infrared (NIR) spectroscopy and optical spectropolarimetry provide independent ways to reveal the otherwise hidden BELs and consequently to estimate BH masses in type 2 AGNs. However, by comparing literature values of line widths of NIR BELs and of polarized BELs for three type 2 AGNs, we have found tentative evidence that the polarized BELs have at least 2 times larger line widths than the NIR BELs. If this is a general trend among type 2 AGNs, the BH masses estimated from these two independent methods disagree with each other at least by 0.6 dex, which may be introducing a huge systematic bias into studies dealing with differences between the type 1 and type 2 AGNs. To examine whether the offsets between the line widths of NIR BELs and polarized BELs are generally observed in type 2 AGNs, here we propose carrying out optical spectropolarimetry for a sample of type 2 AGNs having NIR BELs to systematically compare the two line widths in the type 2 AGNs.
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