Emission Line Modeling of Galaxies
at Cosmic Dawn
Yuma Sugahara
National Astronomical Observatory of Japan
Waseda University1

History of Universe and Galaxies
Cosmic Dawn

Cosmic Noon

Redshift evolution
NAOJ

ESO/M. Kornmesser

Harikane, …, YS, et al. (2022) Wang, et al. (2020)

Elmegreen, et al. (2009) NASA, ESA, CXC, SSC, and STScI 2

Metallicity — Chemical Abundances◯ Abundance of elements heavier than H and He.

◯ Gas-phase metallicity□ Oxygen□ Solar values• 12 + log (O/H) = 8.67
• Zgas = 0.02 = 1Z

◯ Stellar metallicity□ Iron□ Solar value:• Z* = 0.02 =1Z• [Fe/H] = 1

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Cosmic and Galaxy Ecosystem

OReserve of metallicity
FeRelease of metallicity

FeOO
Fe

Production of metallicity

Meixner et al. 2021

4How we observe the metallicity?
Ionized gas
H+O2+

N+

Neutral gas
C+

H+ dust[OIII], [NII], Ha

dust
HMolecular gas
H[CII] (, HI)

dust

H2

H2

CO(CO, H2)

Stellar continuum

NASA, ESA, CSA, and STScI

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Panchromatic Spectrum of Star-forming Galaxy

H+O2+

N+H+ dust

C+dustHHdustH2

H2COGalliano, Galametz, and Jones 20186

BPT diagram—Optical Emission-line Diagram

Star-formingGalaxies
Kauffmann et al. 2003

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BPT diagram—Optical Emission-line Diagram
Stronger ionization
log[OIII]5007/Hβz~2Strom+17

Higher-energy
Ionizing phtons

SDSS
(z~0)

log[NII]6585/HαHigher electrondensity

Kewley et al. 2013

◯ z ~ 2 galaxies have higher [OIII]5007/Hb than local galaxies
8Redshift of Galaxy Spectra caused by expansion of the universe

scikit-learn

9Redshift of Galaxy Spectra … requiring New Window
z~0At redshift z > 4,it becomes difficult
to detect optical
opticalGalliano, Galametz, and Jones 2018

emission lines.
10Redshift of Galaxy Spectra … requiring New Windowz~4

At redshift z > 4,
it becomes difficult
to detect optical
opticalGalliano, Galametz, and Jones 2018

emission lines.
11Redshift of Galaxy Spectra … requiring New Windowz~4

At redshift z > 4,
we need anotherwindow to observe
opticalGalliano, Galametz, and Jones 2018

FIR

emission lines.
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ALMA—Atacama Large Millimeter/submillimeter Array◯aFIRNAOJ

13

[CII] 158 μm emission lines◯ C+ Fine-structure emission line

□ Strongest at far-infrared□ Important coolant in neutral gas
Maiolino et al. (2015)

Carniani et al. (2018)

Tadaki et al. (2019)◯ Detected in many galaxies□ ALMA large programs• ALPINE: 75 gals at 4<z<6• REBELS: >18 gals at 6.5<zPentericci et al. (2016)

Le Fevre et al. (2020)[ALPINE]

Bouwens et al. (2018)[REBELS]14

[OIII] 88 μm emission lines◯ O2+ Fine-structure line

□ Coolant in ionized gas◯ Scientific Highlights□ Prediction (Inoue+14)□ Detection (Inoue+16)□ Highest-z (Hashimoto+18)□ [CII]&[OIII]&dust

Inoue et al. (2016)[First detection]

Marrone et al. (2018) Harikane, …, YS, et al. (2020)(Hashimoto+19)□ Large dust mass (Tamura+19)

Hashimoto et al. (2018)
Tamura et al. (2019)[z=9.1096, which was highest]

Witstok et al. (2022)15

High [OIII]88/[CII]158 Ratios at z > 6

Hashimoto et al. (2019)

Harikane, …, YS et al. (2020)◯ Intense ionization at high redshift?
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Short summary: To the next steplog[OIII]5007/Hβ◯ NIR obs. of rest-opt. lines at z~2z~2

hard ionizing spectra,
high ionization param.,high electron density,
high N/O, …

Strom+17◯ ALMA [OIII]88μm & [CII]158μm

high ionization param.,
low PDR covering frac.,
bursty star-formation,
low C/O, …

SDSS
(z~0)

log[NII]6585/HαHarikane, …, YS+20

We would like to bridge optical and FIR diagrams from local to z > 6.
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Observational Data
◯ FIR diagram◯ BPT diagramz~2z>6

DwarfsDwarfsz~0
U/LIRGs

U/LIRGs

dwarfs: Cormier+15; U/LIRGs: Diaz-Santos+17, Herrera-Camus+18; z~2: Strom+17, Shivaei+18; z > 6: Harikane+20, Carniani+20

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Photoionization Models — CLOUDY v17.02

H+O2+

N+H+ dust

Ionized gas

C+dustH

Neutral gas

Hdust

H2H2COMolecular gas

Encyclepedia of Astrobiology; Tielens and Hollenbach 85

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Photoionization Models — CLOUDY v17.02◯ Fiducial models

Input Ionizing Spectrum□ ionizing spectraU• SB99 300Myr for z ~ 0, U/LIRGs• BPASS 300 Myr, Z* = Zgas for dwarfs□ output SFR ∝ L(Hβ, Z*, age)

□ Ionization parameter U:□ hydrogen density nH□ gas metallicity Zgas
U=Gas StructurenH• BPASS 300 Myr, Z* = 0.2Zgas for z~2, >6Zgas□□□□□
plane-parallel geometry

constant pressure

local N/O–Z abundance relation

Solar C/O abundance ratio

PDR covering fraction (CPDR) = 1◯ Free nebular parameters

1 ṅ
1 ionizing photon number flux/cm 2 s 1=c nHchydrogen density/cm 320

Photoionization Model Grids◯ BPT diagram◯ FIR diagram

Sugahara et al. (2022)

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Photoionization Model Grids◯ BPT diagram

input spectrum: Starburst99 300 Myr model◯ FIR diagram

Sugahara et al. (2022)

22Modeling: z > 6 with FIR lines□ BPT: flat distribution(log[OIII]/Hβ=0.5–0.8)

23Modeling: z > 6 with FIR lines

lowhigh Zgas

□ BPT: flat distribution□ U-Z: negative correlation(log[OIII]/Hβ=0.5–0.8)

Sugahara et al. (2022)

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Graphical Summary of Results

Sugahara+22

1. Continuous shifts at z~0: dwarfs → normal gals. → U/LIRGs

Sugahara et al. (2022)

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Graphical Summary of Resultshigh [OIII]/Hβ

Sugahara+22

high [OIII]88/[CII]158
high U

1. Continuous shifts at z~0: dwarfs → normal gals. → U/LIRGs
2. Continuous evolution from z ~ 0 to z > 6Sugahara et al. (2022)

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Ionizing spectra — high [OIII]88/SFR ratio at z > 6◯ [OIII]88/SFR > 7.5 [L /(M yr-1)]□ cannot be explained by models
w/ BPASS 300 Myr, Z*=Zgas, 1.5 < log nH
BPASS 300 Myr, Z*=Zgas

Zgas/Z* = 510 Myr

10 Myr + Zgas/Z* = 5◯ Solutions

1. high Zgas/Z* (i.e., α/Fe) (fiducial model)• supported by z ≧ 2 studies
Steidel+16, Cullen+19; Day 2 talks

2. bursty/increasing SFH• some galaxies ~5 Myr age from SED fitting
Inoue+16, Hashimoto+18,19, Tamura+19

Sugahara et al. (2022)

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Cosmic and Galaxy Ecosystem

OReserve of metallicity
Fe

Release of metallicity

FeO

OFe

Production of metallicity

Meixner et al. 2021

28

Two types of Supernovae: abundance pattern
Release of metallicity□ Core-collapse supernovae□ Type-Ia supernovae[O/Fe]CCSN
SN Iatime• High O/Fe (i.e., α/Fe)• High Fe• No time delay• Time delay of > 0.1-1 Gyr from SF→ too late at early universe

High [OIII]88/SFR at z > 6 → high α/Fe caused by dominant CCSN
NASA/JPL-Caltech/STScI/CXC/SAO

ESO/M. Kornmesser

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JWST—James Webb
Space Telescope

NASA, ESA, CSA, and STScI

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Comparison with JWST early measurements

Sugahara+22+ JWST measurementsz ~ 7–8Curti+22

Sun+22z~6low

high Zgas

Bright galaxies at z>6:
Similar metallicity to solar
Sugahara et al. (2022)

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History of Universe and Galaxies
Cosmic Dawn

Cosmic Noon

NAOJ

Similar metallicity
Quick enrichment in bright galaxies
Harikane, …, YS, et al. (2022)

NASA, ESA, CXC, SSC, and STScI33

SummarySugahara et al., 2022, ApJ, 935, 2Sugahara et al., 2021, ApJ, 923, 5◯ Continuous distributions on BPT, FIR, and U-Z diagrams predict:□ higher [OIII]/Hb□ higher [OIII]88/[CII]158□ Stronger ionization
at higher redshift◯ High [OIII]88/SFR ratios at z > 6 support:high gaseous-to-stellar metallicity ratio Zgas/Z*→ Less contributions of SN Ia◯ Quick enrichment in bright high-z galaxies
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