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arXiv · 2108.02781

A Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). IV. Rapidly Growing (Super-)Massive Black Holes in Extremely Radio-Loud Galaxies

Kohei Ichikawa·Takuji Yamashita·Yoshiki Toba·Tohru Nagao·Kohei Inayoshi·Maria Charisi·Wanqiu He·Alexander Y. Wagner·Masayuki Akiyama·Bovornpratch Vijarnwannaluk·Xaioyang Chen·Masaru Kajisawa·Taiki Kawamuro·Chien-Hsiu Lee·Yoshiki Matsuoka·Malte Schramm·Hyewon Suh·Masayuki Tanaka·Hisakazu Uchiyama·Yoshihiro Ueda·Janek Pflugradt·Hikaru Fukuchi
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Abstract

We present the optical and infrared properties of 39 extremely radio-loud galaxies discovered by cross-matching the Subaru/Hyper Suprime-Cam (HSC) deep optical imaging survey and VLA/FIRST 1.4 GHz radio survey. The recent Subaru/HSC strategic survey revealed optically-faint radio galaxies (RG) down to $g_\mathrm{AB} \sim 26$, opening a new parameter space of extremely radio-loud galaxies (ERGs) with radio-loudness parameter of $\log \mathcal{R}_\mathrm{rest} = \log (f_{1.4 \mathrm{GHz,rest}}/f_{g,\mathrm{rest}}) >4$. Because of their optical faintness and small number density of $\sim1~$deg$^{-2}$, such ERGs were difficult to find in the previous wide but shallow, or deep but small area optical surveys. ERGs show intriguing properties that are different from the conventional RGs: (1) most ERGs reside above or on the star-forming main-sequence, and some of them might be low-mass galaxies with $\log (M_\star/M_\odot) < 10$. (2) ERGs exhibit a high specific black hole accretion rate, reaching the order of the Eddington limit. The intrinsic radio-loudness ($\mathcal{R}_\mathrm{int}$), defined by the ratio of jet power over bolometric radiation luminosity, is one order of magnitude higher than that of radio quasars. This suggests that ERGs harbor a unique type of active galactic nuclei (AGN) that show both powerful radiations and jets. Therefore, ERGs are prominent candidates of very rapidly growing black holes reaching Eddington-limited accretion just before the onset of intensive AGN feedback.

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Kohei Ichikawa, Takuji Yamashita, Yoshiki Toba, Tohru Nagao, Kohei Inayoshi, Maria Charisi, Wanqiu He, Alexander Y. Wagner, Masayuki Akiyama, Bovornpratch Vijarnwannaluk, Xaioyang Chen, Masaru Kajisawa, Taiki Kawamuro, Chien-Hsiu Lee, Yoshiki Matsuoka, Malte Schramm, Hyewon Suh, Masayuki Tanaka, Hisakazu Uchiyama, Yoshihiro Ueda, Janek Pflugradt, Hikaru Fukuchi. 2021-08-05. A Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). IV. Rapidly Growing (Super-)Massive Black Holes in Extremely Radio-Loud Galaxies. https://doi.org/10.3847/1538-4357/ac1b26

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