High-z Radio Galaxy Survey
with Subaru HSC
Takuji Yamashita (NAOJ)
and the WERGS collaboration1

High-z radio galaxies in early universe
Negative feedback on SF• SF Suppression• Key effect to reproduce
the massive end of MF↓ feedback
McNamara+05

Evolution of massive galaxies• The most massive galaxies
have been formed at z > 3• A half of local stellar mass
was assembled at 1 < z < 4Croton+06← log M*/Msun> 12

Perez-Gonzalez+08

Beacon for proto-clusters• RGs are often associated with overdense regions
Constrain theory on the black hole growth• RGs tend to have massive stellar mass (>1011 Msun).

2High-z Radio galaxies (HzRGs)
Number density evolution of HzRGs

z > 4 HzRGs• Only 13 HzRGs have been
discovered to date.
• All known z > 4 RGs were found with
an ultra-steep spectrum technique,except for two HzRG(s).

low-Lhigh-L
0.1z

1

2 34

Redshifts of spectroscopically identified RGs
Khabibullina & Verkhodanov 09

Num. of RGs

Evolution of radio galaxies• Number density (ND) moderatelyincreases up to z = 1 — 2• Abruptly decline at z ~ 2 — 3• At z > 3, ND is not well constrained
due to a dearth of HzRG samples

Dunlop & Peacock 90; Rigby+15

redshift

3

HzRG Search with the ultra-steep spectral tech.
Search for HzRGs• It’s not easy to find HzRGs because of‣ the low surface densities (<1/z/deg2)‣ much more optical faintness than quasars
Ultra-steep spectra (USS)• Empirical relation: z - α (radio spectral index)• HzRGs are believed to have an ultra-steep
radio spectrum• α < —1.3(Sν ∝ ν α)
• Based on an idea: ideal spectra steepen withfrequency

325MHz-1.4GHz spectral index vs. redshift(De Breuck et al. 2000)

USSBias toward USS• A sample bias of HzRGs from USS could impact on the number density
evolutions (Jarvis+01; Yuan+17)• There are two objects (z~4-5) without USS (Jarvis+09; Waddington+99)• Known z > 4 HzRGs must be the tip of the iceberg!
4Approach not relying on USS
Subaru HSC-SSP: wide & deep optical imaging• Hyper-Suprime Cam (HSC)• 5 BBs & 4 NBs• 1400 deg2 & r~26 in the Wide layer• On-going survey

Apply “Lyman break technique” to HzRG search• HSC-SSP enables us to use Lyman breaktechnique for HzRGs• The best way for high-z surveys

Ono+18(e.g., Ono+18; Akiyama+18; Matsuoka+18)• z = 3.5 - 7.0 HzRGs will be found• Not relying on USS• no bias of radio SED

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WERGSWERGS: Wide and Deep Exploration of Radio Galaxies with Subaru HSC
Exploration of high-z or optically faint radio galaxies with Subaru HSC in order totackle the issues on the galaxy/AGN evolution.
‣ T. Nagao, Y. Matsuoka, M. Kajisawa, M Niida, A. Noboriguchi, A. Ishida, K. Matsuoka(Ehime U.), M. Akiyama, W. He, K. Ichikawa (Tohoku U.), Y. Toba, Y. Ueda (Kyoto U.),
H. Ikeda, M. Tanaka, M. Schramm, I. Tanaka, T. Kawamuro, H. Uchiyama (NAOJ), T.
Morokuma, Kianhong Lee (IoA, U. of Tokyo), T. Kawaguchi (Onomichi), C.-H. Lee(NOAO), Li-Ting Hsu (ASIAA), Y. Ono, Y. Harikane (ICRR, U. of Tokyo), M. Onoue(MPIA), K. Ogura (Bunkyo), N. Kawakatu (Kure), K. Inayoshi (KIAA)‣ Optical spectroscopy (T. Yamashita)‣ X-ray (eROSITA, XMM) follow-up(K. Ichikawa, Y. Ueda, T. Kawamuro, L.T. Hsu)
‣ SED fitting (Y. Toba)‣ HzRGs (H. Uchiyama, K. Lee, T. Yamashita)‣ IR counterparts (K. Ichikawa)

HSC-SSPVLA FIRST 1.4GHz surveyX• Early-release data (S16A)• grizy
Wide

Ultra-DeepLimiting mag i [mag]

26.4

27.0

Area [deg2]1542••••

1.4 GHz (20 cm) imaging
Area = 10,575 deg2; ~ SDSS
Detection limit = 1 mJy(SF gals are not detected at z>0.5)
Resolution = 5” , Accuracy < 0.5”

6WERGSWERGS: Wide and Deep Exploration of Radio Galaxies with Subaru HSC
Exploration of high-z or optically faint radio galaxies with Subaru HSC in order totackle the issues on the galaxy/AGN evolution.
‣ T. Nagao, Y. Matsuoka, M. Kajisawa, M Niida, A. Noboriguchi, A. Ishida, K. Matsuoka(Ehime U.), M. Akiyama, W. He, K. Ichikawa (Tohoku U.), Y. Toba, Y. Ueda (Kyoto U.),H. Ikeda, M. Tanaka, M. Schramm, I. Tanaka, T. Kawamuro, H. Uchiyama (NAOJ), T.
Morokuma (IoA, U. of Tokyo), T. Kawaguchi (Onomichi), C.-H. Lee (NOAO), Li-Ting
2 (ASIAA),
samplesHsu
Y. Ono, Y. Harikane (ICRR, U. of Tokyo), M. Onoue (MPIA), K. Ogura(Bunkyo),N. Kawakatu(Kure),(Yamashita+18,K. Inayoshi (KIAA)Toba+2019)‣ Photo-z(z<2) Sample‣ Optical spectroscopy‣ X-ray (eROSITA, XMM) follow-upYamashita)• ~ 3600 (T.
RGs
in the early-release
HSC-SSP region (~150deg2)(K. Ichikawa, Y. Ueda, T. Kawamuro, L.T. Hsu)
‣ SED fitting (Y. Toba)• SED fitting (e.g., SFR, M*, LAGN)‣
Environments(H. Uchiyama)‣ IR counterparts (K. Ichikawa)‣ Dropout sample (Yamashita+ in prep.)• g/r-dropouts with VLA FIRST detections
HSC-SSPVLA FIRST 1.4GHz survey

X• Early-release data (S16A)• grizy
Wide

Ultra-Deep

Limiting mag i [mag]

26.4

27.0

Area [deg2]1542••••

1.4 GHz (20 cm) imaging
Area = 10,575 deg2; ~ SDSSDetection limit = 1 mJy(SF gals are not detected at z>0.5)
Resolution = 5” , Accuracy < 0.5”

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P9: Toba et al.

Photo-z sample•~ 3600 RGs at z <~ 2 in 150deg2•

SED fitting (u-band — radio)• z ~ 1 RGs have• higher SFR• larger extinction• less-massive stellar massi < 21.3

i > 21.3

Yamashita+2018

Toba, TY+ 20198

z~5 HzRGs: Lyman break selection
Color selection

1. Dropouts• Lyman break for FIRST radio sources‣ riz color selection for z ~ 5 radio sources

HzRG candidates(ref. the COLDRUSH project, Ono et al. 2018)‣16 r-band dropouts (z ~ 5 candidates)in the HSC-SSP region.

2. Follow-up spectroscopy• Gemini-FT/GMOS spectroscopy in Feb 2018
for a z~5 candidate‣ z_AB = 23.5 mag‣ 2 hours exposuresr-dropout targetgr
HSC g

HSC ri
HSC iz
HSC zyHSC y

1.4GHzFIRST 1.4GHz

9z = 4.7 HzRG: our first discovery
z=4.72 HSC HzRG

Redshift• Asymmetric line profile & r-dropout → Lyα line
• Lyα emission line at 6959 A• Redshift: z = 4.7210

The host galaxy• log M*/M⊙ = 11.4 at the cosmic age of 1.3 Gyr• The Ks magnitude is consistent with the K - z relation for RGs• As massive as other HzRGs• The massive end of MF of z~5 Lyman break galaxies (e.g., Yabe et al. 2009)• E(B-V) = 0.4, large extinction → abundant gas/dust?

11Not Ultra-Steep Spectrum
Radio spectral index• α(325MHz-1.4GHz) = —1.1
• α(150MHz-1.4GHz) = —0.97‣ Non USS
✴ USS definition: α < —1.3

(De Breuck et al. 2000, Saxena et al. 2018)• This discovery show a variety of α

at high-z universe

325MHz-1.4GHz spectral index vs. redshift(De Breuck et al. 2000)

USSHSC HzRG

• It demonstrates the advantage ofour survey over the USS technique!

• Higher-z dropout radio galaxies!

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PFS-SSP study
The Large spectroscopic survey with Subaru/PFS• 1400 deg2 sky will be observed• 380-1260 nm in optical & NIR is covered

Radio galaxies census

200k RGs expected in the PFS-SSP field (~500 z>4 HzRGs)• Number density evolution of RGs from z = 0 to >4to examine the role of RGs in the Universe.
• SF activity and stellar age of host galaxies

as functions of z and radio-AGN power
to reveal the feedback effect• Environments as a function of z andradio-AGN power

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Summary• Lyman break technique is now applied to the HzRG survey by taking

advantage of Subaru HSC-SSP• z = 4.7 HzRG was found out of the pre-selected g-dropouts with radiodetections• The z = 4.7 HzRG are‣ not USS (α = —1.1)‣ massive (log M*/M⊙ = 11.4)• This discovery demonstrates the feasibility of our HzRG search• Future:• Large RG survey with PFS• Draw the number density evolution of RGs from local to high-z !
• Reveal the effect and evolution of the radio-AGN feedback !

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