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6th Galaxy Evolution Workshop@ Kavli IPMU
Jun. 6, 2019

CO(J = 2–1)/CO(J = 1–0) ratio
in nearby galaxies

スクールカラーの定義

プロセスカラー

CyanMagenta

Yoshiyuki YAJIMA (矢島 義之, Hokkaido Univ.)& COMING members

CO transitions and their energy levels• CO J = 1 level: well excited thanks to
low energy

rotational energy of CO∆𝐸/𝑘%• CO(J = 1–0): most used tracer of cold
molecular gas

17 K• CO J = 2 level: higher level by 10 K
than J = 110 K• CO(J = 2–1): traces warmer or denser
molecular gas?

5.5 K

J=2
typical temp.
of mol. gas

J=1J=0

Leroy+ 2009

2.030

1.5
1.0

0.8

0.5
0.0

0.0

0.2

0.4

r/r25

measurements

ICO(J = 2–1) / ICO(J = 1–0)
≡ ℛ '/(CO(J = 2–1) as a proxy of CO(J = 1–0)?

0.6⌃mol = cos i ↵CO ICO(J=1 0)<latexit sha1_base64="GGw4bRGYU0WOPqcgQCOmhHNgmU0=">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</latexit>

ICO(J=2 1)= cos i ↵CO
R2/1<latexit sha1_base64="Z6qqBBydTganRWUFNwy9nBf8x9Q=">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</latexit>

Leroy+ 2013

median 0.67

20

ü median of ℛ'/( :~ 0.7 in several
galaxies

100-1.0-0.5

0.0log ℛ'/(0.5ü when ∑mol is derived from CO(J = 2–1)ℛ'/( is assumed as const. (0.7) !!
ü ℛ'/( depends on excitation of CO…

Data of the CO lines
CO(J = 1–0)
Nobeyama 45-m telescope• COMING (Sorai+ 2019)• Nobeyama CO Atlas of Nearby
Spiral Galaxies (Kuno+ 2007)

CO(J = 2–1)
IRAM 30-m telescope(DiVertiCimes/IRAM)• HERACLES (Leroy+ 2009)SampleCO Atlas ∩ HERACLES:
COMING ∩ HERACLES:HERACLES

8 galaxies(not including COMING samples)

21 galaxies
Nobeyama CO Atlas
COMING
total sample: 29 galaxies

SampleNGC CO2903Atlas ∩ HERACLES:NGC 2798

NGC 337

8 galaxiesNGC 2976

HERACLES (notNGC
includingsamples)
2841 COMINGNGC
NGC 628 NGC 2146
3034
NGC 3351
COMING ∩ HERACLES:NGC 3521
21 galaxies

NGC 3077 NGC 3184
NGC 4736
NGC 4254

NGC 4321
NGC 4569

NGC 3627

NGC 3938 NGC 4214

NGC 5194
Nobeyama CO Atlas

NGC 5055
NGC 5713 NGC 5457 NGC 6946

COMING

total
29NGC
galaxies
4579
NGC sample:
4559

NGC 7331

ℛ'/( maps of the sample

Histogram of ℛ'/(0.57 0.7ü ℛ '/( = 0.7 is rather larger• median = 0.57
• weighted mean = 0.62
• std. dev. = 0.20ℛ'/(

NGC 3351

NGC 5713

w/ CO(J=2–1) &ℛ'/( = 0.7

w/ CO(J=2–1) &ℛ'/( = 0.7

N = 1.3

w/ CO(J=1–0)

N = 1.9∑mol [M⨀ pc-2]∑SFR [M⨀ yr -1 kpc-2]∑SFR [M⨀ yr -1 kpc-2]

Effects on the Kennicutt–Schmidt relation

N = 1.1

w/ CO(J=1–0)

N = 1.4∑mol [M⨀ pc-2]

index by CO(J = 2–1)
and ℛ '/( = 0.7

Effects on the K–S relation
ü the index is underestimated in most ofgalaxies∑SFR∑mol is overestimated∵ ℛ'/( > 0.7
K–S relation
by CO(J=1–0)

K–S relation
by CO(J=2–1)

index by CO(J = 1–0)∑mol is underestimated∵ ℛ'/( < 0.7∑molCorrelations of ℛ '/( and basic quantities – ∑SFR
open red diamonds: global (not resolved)ℛ'/(ρS = 0.19
ρS (glob.) = 0.54

~ 0.8~ 0.45log ∑SFR [M⨀ yr -1 kpc-2]

log ∑SFR [M⨀ yr -1 kpc-2]

Correlations of ℛ '/( and basic quantities – IR color
open red diamonds: global (not resolved)

ρS = 0.27
ρS (glob.) = 0.46

üℛ '/( is affectedby radiation feedback?

ℛ'/(~ 0.8~ 0.55

log I70µm / I160µm

log I70µm / I160µm

Correlations of ℛ '/( and basic quantities – τdep
open red diamonds: global (not resolved)

ρS = -0.55
ρS (glob.) = -0.42ℛ'/(~ 0.9ü high ℛ'/( is related torapid consumptionof mol. gas & active SF~ 0.4

log τdep [Gyr]log τdep [Gyr]Conclusionsl The assumption of the constant ℛ '/( (≡ ICO(J = 2–1) / ICO(J = 1–0) )of 0.7 is no longer validl The index of the K-S relation is underestimated if ℛ '/( isassumed as 0.7
l ℛ '/( would be influenced by radiation feedback from starsü CO(J = 2–1)/CO(J = 1–0) ratio should notbe assumed as a constant!!

Appendix

Why our median is less than 0.7?
Observed regions of Usero+ 2015:
only positions where CO(J = 2–1) is strong
Not the entire disk of galaxies
The obs. points usually
include the center→The obs. position selection
would bias large ℛ'/(

ℛ'/(Radial distribution of ℛ'/(0.70.56

r [kpc]r [kpc]Correlations of ℛ '/( and basic quantities – sSFR
ρS = 0.13
ρS (glob.) = 0.66

ℛ'/( and density, temperature of mol. gasü ℛ'/( is more sensitive to temp.?

(I will increase samples)n(H2) and Tkin are derived from CO(1–0), CO(2–1) & 13CO(1–0)

Variations of ℛ'/( and XCO
𝑋-. ∝𝑛(H' )𝑇678∑mol = ICO(J=1–0) × αCO(e.g., Solomon+ 1987)= ICO(J=2–1) × αCO /R2/1

n(H2)

→ XCO

& R2/1

Tkin

→ XCO

& R2/1effect of high n(H2), large σV and low Z:
variations of XCO and R2/1
will be canceled

metallicity Z→ XCO& R2/1(e.g., Bolatto+ 2013, Penaloza+ 2018)velocity disp. σV→ XCO& R2/1(e.g., Watanabe+ 2011, Sorai+ 2012)

effect of high Tkin :variations of XCO and R2/1
will be amplified→ more underestimatedmol. gas mass