Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). III. Star formation properties of the host galaxies at z ≳ 6 studied with ALMA

PASJ: Publications of the Astronomical Society of Japan

Taniguchi, Akio¹  Shirakata, Hikari²  Toba, Yoshiki²  Fujimoto, Seiji²  Ikarashi, Soh²  Schulze, Andreas²  Iono, Daisuke³  Nagao, Tohru⁴  Tang, Ji-Jia⁵  Iwasawa, Kazushi⁶  Tamura, Yoichi⁷  Greene, Jenny E⁷  Minezaki, Takeo⁸  Matsuoka, Yoshiki⁹  Makiya, Ryu⁹  Yamaguchi, Yuki⁹  Lee, Chien-Hsiu⁹  Nakanishi, Kouichiro^1,10  Onoue, Masafusa^1,11  Umehata, Hideki^1,11  Kashikawa, Nobunari^1,11  Izumi, Takuma^1,11  Hashimoto, Yasuhiro^1,11  Harikane, Yuichi^1,11  Silverman, John D^1,11  Kohno, Kotaro^1,12  Strauss, Michael A^1,12  Imanishi, Masatoshi^1,13  Goto, Tomotsugu^1,14 

[1] Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 10617, Taiwan;Department of Astronomical Science, Graduate University for Advanced Studies (SOKENDAI), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan;Department of Astrophysics, Princeton University, 4 Ivy Ln, Princeton, NJ 08544-1001, USA;Department of Cosmosciences, Graduate School of Science, Hokkaido University, N10 W8, Kitaku, Sapporo, Hokkaido 060-0810, Japan;Department of Earth Sciences, National Taiwan Normal University, Taipei 11677, Taiwan;Division of Particle and Astrophysical Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan;Institute for Cosmic Ray Research, The University of Tokyo, 5-1-5 Kashiwa-no-Ha, Kashiwa, Chiba 277-8582, Japan;Institute of Astronomy and Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan;Institute of Astronomy, Graduate School of Science, The University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan;Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo Institutes for Advanced Study, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583, Japan;National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan;Research Center for Space and Cosmic Evolution, Ehime University, 2-5 Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan;Research Center for the Early Universe, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan;The Open University of Japan, 2-11 Wakaba, Mihama-ku, Chiba 261-8586, Japan

关键词: galaxies: high-redshift;    galaxies: ISM;    (galaxies:) quasars: general;    (galaxies:) quasars: individual;    galaxies: starburst;   

DOI  :  10.1093/pasj/psy026

学科分类：天文学(综合)

来源: Oxford University Press

【 摘 要 】

We present our ALMA Cycle 4 measurements of the [C ii] emission line and the underlying far-infrared (FIR) continuum emission from four optically low-luminosity (M1450 > −25) quasars at z ≳ 6 discovered by the Subaru Hyper Suprime Cam (HSC) survey. The [C ii] line and FIR continuum luminosities lie in the ranges |$L_{\rm [C\,{\small {II}}]} = (3.8\mbox{--}10.2)\times 10^{8}\,L_{\odot }$| and LFIR = (1.2–2.0) × 1011 L|$_{\odot}$|⁠, which are at least one order of magnitude smaller than those of optically-luminous quasars at z ≳ 6. We estimate the star formation rates (SFRs) of our targets as ≃ 23–40 M|$_{\odot}$| yr−1. Their line and continuum-emitting regions are marginally resolved, and found to be comparable in size to those of optically-luminous quasars, indicating that their SFR or likely gas mass surface densities (key controlling parameter of mass accretion) are accordingly different. The |$L_{\rm [C\,{\small {II}}]}/L_{\rm FIR}$| ratios of the hosts, ≃ (2.2–8.7) × 10−3, are fully consistent with local star-forming galaxies. Using the [C ii] dynamics, we derived their dynamical masses within a radius of 1.5–2.5 kpc as ≃ (1.4–8.2) × 1010 M|$_{\odot}$|⁠. By interpreting these masses as stellar ones, we suggest that these faint quasar hosts are on or even below the star-forming main sequence at z ∼ 6, i.e., they appear to be transforming into quiescent galaxies. This is in contrast to the optically-luminous quasars at those redshifts, which show starburst-like properties. Finally, we find that the ratios of black hole mass to host galaxy dynamical mass of most of the low-luminosity quasars, including the HSC ones, are consistent with the local value. The mass ratios of the HSC quasars can be reproduced by a semi-analytical model that assumes merger-induced black hole host galaxy evolution.

【 授权许可】

CC BY