Challenge to the Most Distant Evolved Galaxies:
Hint on Star-Formation Activity during the First
500 Million Years of the Cosmic History

Ken Mawatari（Univ. of Tsukuba）
2023/6/27
TCHoU2023前期

Credit: National Astronomical Observatory of Japan1

About myself
宇宙観測・理論合同BBQ

Birthplace: Abiko, Chiba
2006-2015 Tohoku Univ.（B.Sci, phD）
2012-2014 Harvard-Smithsonian CfA（during phD course）
2015-2018 Osaka-Sangyo Univ.（posdoc）
2018-2021 UTokyo, ICRR（ICRR Fellow）
2021-2023 NAOJ, Subaru（posdoc）
2023- U.Tsukuba, （posdoc）

Research Topic: Obs of high-z galaxiesMulti-wavelength study
Proto-clusters, Inter-galactim Medium
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Ultimage
Goal
Understanding of thefirst galaxy formation
process

Immediate
Goal
Observationally reveal
how active star-formation
was in earlier era

Approaches
1. Direct obs (w/ high sensitivityinstruments)
2. Archaelogical method (w/"fossil record")
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宇宙史研究センターウェブサイトより

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Passive and Star-Forming Galaies
Active StarFormation

Ellipticals

IrregularSpirals

Star-Forming Galaxy (SFG)• Active Star Formation• Blue color (young hot stars)• Easy to observe• Turbulent morphology

https://itu.physics.uiowa.edu/labs/advanced/classifying-galaxies/part-1-hubbles-tuning-fork

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Passive Galaxy• No (little) Star Formation• Red color (old cool stars)• Passively evolving(受動的進化)• Settled morphology• Featureless in spectra

Star-Formation
Makes the galaxy easily observed, butDrowns out the past info,,,
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Key Spectral Feature of Passive Galaxies
Balmer BreakOrigin: Hydrogen Balmer Break of Atype stars.
This feature becomes prominent atage = 200Myr ~ 1Gyr.
Lifetime of O,B stars4000Å BreakOrigin: Metal absorptions of G-type
or cooler stars.
This feature becomes prominent atage > 1Gyr.

Balmer Break strength indicates
how long the galaxy is stopping Star-Formation,(and metallicity).

Balmer Break Galaxy (BBG) = Passive galaxy
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Potential Power of High-z Passive Galaxies(Mawatari+20)

Stellar Mass
Density (SMD)

Star-FormingStar Formation
Rate Density (SFRD)

ivessPa?

?
@z>10(Madau & Dickinson 2014)

Passive galaxies at z>5 can open a new window on star-formation at z>10”Passive galaxy” in this work:
Galaxy with strong Balmer-break (Balmer-break galaxy; BBG) experiencing >200Myr after stopping star-formation
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Our Previous Works• Mawatari et al. 2016, PASJ, 68, 46• Mawatari et al. 2020, ApJ, 889, 137• Wide-area photometric search for z~6 Balmer Break Galaxies• First Step is always photometric obs!
• Difficulty in spectroscopy: faintness, rarity of the targets

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Colors of z~6 BBG (Mawatari+16,20)
Faint in FIR
Faint in optical

Red K-[3.6]Blue [3.6] – [4.5]2023/6/27

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COSMOS Field
RA = 10h 00m 28.6s Dec = +02° 12’ 21.0”
しし座
COSMOS

コップ座 ろくぶんぎ座

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4xMoon
Area!

うみへび座

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Rich observations in COSMOS Field
Keck

VLT

VISTA

Subaru
（Opt）

（Opt）

（Opt）

GALEX （UV）

（NIR）
VLA（radio）
JCMT（X-ray）
Hubble（Opt）

XMM-Newton

Herschel

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Chandra （X-ray） （FIR）

TCHoU2023前期（submm）

Spitzer（NIR~MIR）

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Atacama Large Millimeter/submillimeter Array:
アタカマ⼤型ミリ波サブミリ波⼲渉計

アルマ望遠鏡••••••The largest Radio telescope at Chille, altitude 5000m.
International collaboration of America, Euro, Japan+Taiwan+Korea
Our own observations
Cycle5 #2017.1.01259.S (PI: K. Mawatari)
Wavelength ~ 1mm
40min exposure per target

Credit: Clem & Adri Bacri-Normier (wingsforscience.com)/ESO
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Data (Mawatari+20)
K〜25 & [3.6]〜24 depth
ó z~6 passive galaxy down
to M* ~ 4x1010 Msun.

All imaging data available in COSMOSUVISTA UD stripes 1〜3 (Area = 0.5deg2)
Subaru VISTA

Spitzer/IRAC

Spitzer/MIPSHerschel

Scuba2

Hubbleustz =6 dAGNsury toz=6 SF galaxy
with SFR=100 Msun/yr

ALMAz =6 Pawith ssive galax
M* =4E + 1 y0M

sun

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z~6 BBG search in COSMOS (Mawatari+20)
・Isolated objects in the Spitzer/IRAC image
N ~ 37000

・NIR Color selection
K - [3.6] > 1.75
K ‒ [3.6] > 2.4([3.6]-[4.5])+1.05
・Non-detection in
optical, MIR(λ>10um), FIR, radio, and X-ray
to remove
N=6strong line emitters,
extremely dusty galaxies, and AGNs.
・Non-detection in ALMA Band7 (1σ~ 30uJy)

N=32023/6/27

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z~6 BBG search in COSMOS (Mawatari+20)

Flux(erg/s/cm2)- Photometric selection of 3 Balmer Break Galaxies at 5<z<8 in COSMOS- SED analysis suggests that they areat z~6（age of Univ ~ 1Gyr）, stellar age > 0.5Gyr, and passive phase (no SF, no Dust).

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Dusty solution
is inconsistent
with non-det inALMA

Best-fit “passive”
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Wavelength(μm)

14z~6 BBG search in COSMOS (Mawatari+20)
Stellar Mass Density
Starforming

Pa
sseiv

NEW

SMD of the BBGs at z ~ 6 is consistent with themeasurements for lower-z passive galaxies.
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15z~6 BBG search in COSMOS (Mawatari+20)
Progenitors of z~6 BBGslDef. of the progenitors: age = τSFH
Progenitorsʼ z and SFR
are sensitive to SFH shape…

lSFRD of the progenitors

Model
SFH

TSF = 2 τSFH
SF phase

0.2Gyr

TBBG: BBG phase

Fraction of observable timescale

Progenitorsʼ SFRD
is less sensitive to SFH assumption!
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16z~6 BBG search in COSMOS (Mawatari+20)
Star Formation Rate Density at z〜20

ivessPaStar-fo 3) < 1.2E-4 at z > 14 (99.7% confidence level)ü 2.4E-5 < SFRD/(Msun/yr/Mpcrmingü Our result supports smooth evolution (Finkelstein+15, Kikuchihara+19)
more than rapidly declining evolution (Oesch+14,18, Harikane+18).
ü Relatively high SFRD indicates higher SF efficiency at z > 10.

NEW
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ダークマターハローの重⼒集積のみによる数密度進化

99.7% CL(3sigma)

17Summary of our previous works• Identification of passive galaxy "candidates" at z ~ 6• They give interesting constraint on SFRD at z>10
https://www.nasa.gov/directorates/heo/scan/s• Many technical concerns,,,• Based on many non-detections• Photometric id of the Balmer breaks• Combination of different instruments

ervices/missions/universe/JWST.html=> Need of Spectroscopic confirmation

Now, it's a new (JWST) age!
James Webb Space Telescope, launched in 2021 Dec
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Recent JWST results• Direct observations of z>10 star-forming galaxiesHarikane+23, arXiv:2304.06658

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Recent JWST results• Spectroscopy of Passive Galaxies（up to z=7.3!?）
z=7.3 quiescent galaxy (Looser+23, arXiv:2302.14155)
Only 10-30Myr after stopping star-formation

z=3.2 quiescent galaxy (Nanayakkara+22, arXiv:2212.11638)
Only 10-30Myr after stopping star-formation

The area JWST observed is NOT enough.
Wider-area imaging survey for the candidates
is needed!
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Our Challenges in Univ. of Tsukuba• RIOJA project (Hashimoto et al. 2023, arXiv:2305.04741)• JWST spec of ALMA 6<z<9 galaxies• z=7.88 overdensity region• Accelerated galaxy evolution• Dust production, quenching2023/6/27

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