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

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

doi:10.3847/1538-4357/ac1b26

Cited by 10 publications

(21 citation statements)

References 166 publications

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“…This means the increase of the population of HERGs in radio galaxies beyond z ∼ 1. In our WERGS radio galaxy sample, the radio galaxies with high sBHAR, that is, HERG-like galaxies are dominantly distributed at z  1 (Toba et al 2019;Ichikawa et al 2021). The stellar masses of the radio galaxies are also found to be significantly anticorrelated with redshift.…”

Section: Redshift Evolution Of Radio Galaxy Environmentsmentioning

confidence: 80%

“…We extract radio galaxies from the HSC-FIRST sources using the rest-frame 1.4 GHz luminosities, L 1.4GHz [W Hz −1 ] according to Ichikawa et al (2021). The L 1.4GHz of the HSC-FIRST sources were calculated to be ∼10 22.0−27.5 W Hz −1 assuming a radio spectral index of α = −0.7 with the form of f ν ∝ ν α (Yamashita et al 2018).…”

Section: Radio Galaxiesmentioning

confidence: 99%

“…The physical quantities we use in this study are obtained by transforming the quantities obtained from the SED fitting. The bolometric AGN luminosity, L AGN [L e ], can be obtained through the bolometric correction for the IR luminosity L IR [L e ] obtained by the SED fitting; L AGN = 3.0 × L IR (Delvecchio et al 2014;Inayoshi et al 2018;Ichikawa et al 2021). The specific black hole mass accretion rate (sBHAR…”

Section: Radio Galaxy With Ir Photometrymentioning

confidence: 99%

“…is defined as L AGN /M * (e.g., Mullaney et al 2012;Ichikawa et al 2021); sBHAR is good indicator of the Eddington ratio λ Edd ( ∝ L AGN /M BH ) according to the M-σ relation (Magorrian et al 1998;Marconi & Hunt 2003). According to Ichikawa et al (2021), sBHAR can be expressed by a function of M * and λ Edd :…”

Section: Radio Galaxy With Ir Photometrymentioning

confidence: 99%

“…The data of a Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS, Yamashita et al 2018;Toba et al 2019;Yamashita et al 2020;Ichikawa et al 2021;Uchiyama et al 2022) can overcome the difficulties. WERGS is the wide optical counterpart survey of radio galaxies with the optical depth down to i ∼ 26.…”

Section: Introductionmentioning

confidence: 99%

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A Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). VII. Redshift Evolution of Radio Galaxy Environments at z = 0.3–1.4

Uchiyama¹,

Yamashita

Nagao³

et al. 2022

ApJ

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We examine the redshift evolution of density environments around 2163 radio galaxies with the stellar masses of ∼109–1012 M ⊙ between redshifts of z = 0.3–1.4, based on the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) and Faint Images of the Radio Sky at Twenty cm. We use the k-nearest neighbor method to measure the local galaxy number density around our radio galaxy sample. We find that the overdensities of the radio galaxies are weakly but significantly anticorrelated with redshift. This is consistent with the known result that the relative abundance of less-massive radio galaxies increases with redshift, because less-massive radio galaxies reside in relatively low-density regions. Massive radio galaxies with stellar masses of M * > 1011 M ⊙ are found in high density environments compared with the control sample galaxies with radio nondetection and matched stellar mass. Less-massive radio galaxies with M * < 1011 M ⊙ reside in average density environments. The fraction of the radio galaxies associated with the neighbors within a typical major merger scale, <70 kpc, is higher than (comparable to) that of the control galaxies at M * > 1011 M ⊙ (M * < 1011 M ⊙). We also find that the local densities around the radio galaxies are anticorrelated with the radio luminosities and black hole mass accretion rates at a fixed stellar mass. These findings suggest that massive radio galaxies have matured through galaxy mergers in the past, and have supermassive black holes whose mass accretion almost ceased at z > 1.4, while less-massive radio galaxies undergo active accretion just at this epoch, as they have avoided such merger events.

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Section: Redshift Evolution Of Radio Galaxy Environmentsmentioning

confidence: 80%

Section: Radio Galaxiesmentioning

confidence: 99%

Section: Radio Galaxy With Ir Photometrymentioning

confidence: 99%

Section: Radio Galaxy With Ir Photometrymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). VII. Redshift Evolution of Radio Galaxy Environments at z = 0.3–1.4

Uchiyama¹,

Yamashita

Nagao³

et al. 2022

ApJ

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eROSITA Final Equatorial-Depth Survey (eFEDS)

Ichikawa

Yamashita

Merloni

et al. 2023

A&A

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We constructed the eROSITA X-ray catalog of radio galaxies discovered by the WERGS survey, made by cross-matching the wide area Subaru/Hyper Suprime-Cam (HSC) optical survey and VLA/FIRST 1.4 GHz radio survey. We report finding 393 eROSITA detected radio galaxies in the 0.5−2 keV band in the eFEDS field covering 140 deg2. Thanks to the wide and medium depth eFEDS X-ray survey down to f0.5 − 2 keV = 6.5 × 10−15 erg s−1 cm−2, the sample contains the rare and most X-ray luminous radio galaxies above the knee of the X-ray luminosity function, spanning 44 < log(L0.5−2 keV(abs,corr)/erg s−1) < 46.5 at 1 < z < 4. The sample also contains the sources around and below the knee for the sources 41 < log(L0.5−2 keV(abs,corr)/erg s−1) < 45 at z < 1. Based on the X-ray properties obtained by the spectral fitting, 37 sources show obscured active galactic nucleus (AGN) signatures with log(NH/cm−2) > 22. These obscured and radio AGN reside in 0.4 < z < 3.2, indicating that they are obscured counterparts of the radio-loud quasar, which were missed in the previous optical quasar surveys. By combining radio and X-ray luminosities, we also investigated the jet production efficiency ηjet = ηradPjet/LAGN,bol by utilizing the jet power of Pjet. We find that there are 14 sources with extremely high jet production efficiency at ηjet ≈ 1. This high ηjet value might be a result of the decreased radiation efficiency of ηrad < 0.1, due to the low accretion rate for those sources, and/or of the boosting due to the decline of LAGN,bol by a factor of 10−100 by keeping Pjet constant in the previous Myr, indicating the experience of the AGN feedback. Finally, inferring the BH masses from the stellar mass, we find that X-ray luminous sources show the excess of the radio emission with respect to the value estimated from the fundamental plane. This radio emission excess cannot be explained by the Doppler boosting alone, and therefore the disk–jet connection of X-ray luminous eFEDS-WERGS is fundamentally different from the conventional fundamental plane which mainly covers the low-accretion regime.

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Discovery of 24 radio-bright quasars at 4.9 ≤ z ≤ 6.6 using low-frequency radio observations

Gloudemans

Duncan

Saxena

et al. 2022

A&A

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High-redshift quasars (z > 5) that also shine brightly at radio wavelengths are unique signposts of supermassive black hole activity in the early universe. However, bright radio sources at z ≥ 5 are extremely rare and therefore we have started a campaign to search for new high-z quasars by combining an optical dropout selection driven by the g, r, and z bands from the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys with low-frequency radio observations from the LOFAR Two-metre Sky Survey (LoTSS). Currently, LoTSS covers a large fraction of the northern sky (∼5720 deg 2 ) to such a depth (median noise level ∼ 83 µJy beam −1 ) that about 30% of the general quasar population is detected − which is a factor of 5-10 more than previous large sky radio surveys such as NVSS and FIRST, respectively. In this paper, we present the discovery of 20 new quasars (and the independent confirmation of four) between 4.9 ≤ z ≤ 6.6. Out of the 24 quasars, 21 satisfy the traditional radio-loudness criterion of R = f 5GHz / f 4400Å > 10, with the full sample spanning R ∼6-1000, thereby more than doubling the sample of known radio-loud quasars at z ≥ 5. Our radio detection requirement strongly decreases the contamination of stellar sources and allows one to select these quasars in a broad redshift range. Despite selecting our quasar candidates using fewer and less conservative colour restrictions, both the optical and near-infrared colours, Lyα emission line properties, and dust reddening, E(B − V), measurements of our quasar sample do not deviate from the known radio-quiet quasar population, suggesting similar optical quasar properties of the radio-loud and radio-quiet quasar population at high-z. Our campaign demonstrates the potential for discovering new high-z quasar populations through next generation radio continuum surveys.

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

Cited by 10 publications

References 166 publications

A Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). VII. Redshift Evolution of Radio Galaxy Environments at z = 0.3–1.4

A Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). VII. Redshift Evolution of Radio Galaxy Environments at z = 0.3–1.4

eROSITA Final Equatorial-Depth Survey (eFEDS)

Discovery of 24 radio-bright quasars at 4.9 ≤ z ≤ 6.6 using low-frequency radio observations

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