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arXiv · 1603.02302

An Effective Selection Method for Low-Mass Active Black Holes and First Spectroscopic Identification

Tomoki Morokuma·Nozomu Tominaga·Masaomi Tanaka·Naoki Yasuda·Hisanori Furusawa·Yuki Taniguchi·Takahiro Kato·Ji-an Jiang·Tohru Nagao·Hanindyo Kuncarayakti·Kana Morokuma-Matsui·Hiroyuki Ikeda·Sergei Blinnikov·Ken'ichi Nomoto·Mitsuru Kokubo·Mamoru Doi
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Abstract

We present a new method to effectively select objects which may be low-mass active black holes (BHs) at galaxy centers using high-cadence optical imaging data, and our first spectroscopic identification of an active 2.7x10^6 Msun BH at z=0.164. This active BH was originally selected due to its rapid optical variability, from a few hours to a day, based on Subaru Hyper Suprime-Cam~(HSC) g-band imaging data taken with 1-hour cadence. Broad and narrow H-alpha and many other emission lines are detected in our optical spectra taken with Subaru FOCAS, and the BH mass is measured via the broad H-alpha emission line width (1,880 km s^{-1}) and luminosity (4.2x10^{40} erg s^{-1}) after careful correction for the atmospheric absorption around 7,580-7,720A. We measure the Eddington ratio to be as low as 0.05, considerably smaller than those in a previous SDSS sample with similar BH mass and redshift, which indicates one of the strong potentials of our Subaru survey. The g-r color and morphology of the extended component indicate that the host galaxy is a star-forming galaxy. We also show effectiveness of our variability selection for low-mass active BHs.

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Tomoki Morokuma, Nozomu Tominaga, Masaomi Tanaka, Naoki Yasuda, Hisanori Furusawa, Yuki Taniguchi, Takahiro Kato, Ji-an Jiang, Tohru Nagao, Hanindyo Kuncarayakti, Kana Morokuma-Matsui, Hiroyuki Ikeda, Sergei Blinnikov, Ken'ichi Nomoto, Mitsuru Kokubo, Mamoru Doi. 2016-03-07. An Effective Selection Method for Low-Mass Active Black Holes and First Spectroscopic Identification. https://doi.org/10.1093/pasj%2Fpsw033

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