S21A0002

We propose optical spectroscopic observations of extremely radio-loud AGN residing in the low-mass galaxies. Recent Subaru/HSC strategic survey revealed optically-faint radio galaxies (RG) down to g_AB ∼ 26, opening the new parameter space of extremely radio-loud AGN with radio-loudness parameter of logR_rest = log(f_{1.4\ GHz}/f_{g\ band}) >4. They are called extremely radio-loud galaxies (ERGs). ERGs show completely different properties compared to the conventional RGs: 1) ERGs are located above the SF main-sequence 2) ERGs are prominent candidates in the (super-)Eddington-limited accretion phase, and some low-z ERGs reside in low-mass galaxies with M_⋆ < 10¹⁰ M_⊙). Therefore, ERGs are candidates of very rapidly growing black holes with super-Eddington accretion before the feedback process is in place. However, those results solely rely on our photo-z estimates. Our goal is to obtain the spectroscopic redshift to confirm the above strong cases on the interesting properties of the rapid BH assembly phase for the first time in such a low-z universe.

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