名古屋大学学部4年 山田梨加

The 3.3 μ m PAH emission of the mid-infrared excess galaxies in the

mid-infrared all-sky survey

CONTENTS

About star-forming galaxy

About PAH

Targets

Results

2.5-5 um spectroscopy of star-forming galaxy

fitting

Discussion

3.3umPAH emission and infrared luminosity

Star-forming galaxy

SFR=101−2M⊙yr−1

Indicators

・UV light from OB stars

・optical hydrogen recombination lines

→affected by the dust extinction

・Infrared luminosity reradiation from dust

grains(several 10K) warmed by absorbing UV light

・PAH emission lines

PAH

Polycyclic aromatic hydrocarbons

Emitted at 3.29, 6.2, 7.7, 8.6, 11.3 μ m

Ubiquity: Present in post-AGB stars, planetary nebulae, HII region, reflection nebulae, diffuse interstellar medium

3.3um emission feature is relatively weak, but…

Small PAHs are warmed to a high temperature when high energy photon hits them, and emit at 3.29um by thermal vibration of C-H.

→Reflect UV light very well

3.3𝜇𝑚PAH emission

Imanishi & Dudley (2000) detected 3.3umPAH emission from 6 out of 9 LIRGs , using ground based L-band spectroscopy.

Rodriguez-Ardila & Viegas (2003): AGN have the 3.3umPAH luminosity levels similar to those of starburst and LIRGs.

→the arrow indicates 3.3umPAH feature

10−15erg cm

−2s−

1Å−1

Wavelength[𝜇m]

10−15 W m

−2μm−1

Watabe et al.(2008), Oi et al.(2010): there is a strong correlation between nuclear starburst activity and AGN activity.

→・𝐿3.3𝑃𝐴𝐻 correlats with 𝐿𝑁−𝑏𝑎𝑛𝑑 Oi et al.(2010)

Sample selection

AKARI mid-infrared All-Sky survey catalog sources

Selection criterion flux(9,18um)

flux(2.2um)> 2

→Near-infrared spectra of 94 selected objects are taken.

The 3.3μ mPAH detection(5𝜎) in 2.5-5μ m spectroscopy.

→44 objects

( redshift z=0.01～0.1 )

RESULTS

2.5-5μ m spectroscopy 3.3 umPAH 𝜆𝑟𝑒𝑠𝑡 = 3.29[μ𝑚]

Subfeatures 𝜆𝑟𝑒𝑠𝑡 = 3.42[μ𝑚]

aliphatic hydrocarbon

𝐻2𝑂ice 𝜆𝑟𝑒𝑠𝑡 = 3.05~3.1[μ𝑚](2.75～3.55)

absorbed by ice

Brα 𝜆𝑟𝑒𝑠𝑡 = 4.05[μ𝑚]

typical spectrums→

Wavelength[um]

Flu

x[m

Jy]

Flu

x[m

Jy]

Red continuum

CO2 absorption 𝜆𝑟𝑒𝑠𝑡 = 4.26[μ𝑚]

CO absorption 𝜆𝑟𝑒𝑠𝑡 = 4.67[μ𝑚]

Seem to contain AGN

CO,CO2 absorption present

Wavelength[um]

Wavelength[um]

Flu

x[m

Jy]

Flu

x[m

Jy]

Fitting Drude profile→3.3umPAH

𝐼𝜈 =𝑏𝑟𝛾𝑟

2

(𝜆𝜆𝑟

−𝜆𝑟𝜆)2+𝛾𝑟

2

𝑏𝑟 : the central intensity of the feature

𝜆𝑟 : the central wavelength

𝜆𝑟𝛾𝑟 = 𝐹𝑊𝐻𝑀

・is the theoretical frequency profile for a classical damped harmonic oscillator.

・has more power in the extended wings than a Gaussian. Gaussian →Brα , H2O ice

𝐼𝜈 =𝐴

2𝜋𝜎exp − 𝜆 − 𝜆𝑟

2/2𝜎2

Power low → continuum 𝐼𝜈 ∝ 𝜆

Γ

※Subfeatures’ region is not used for the fitting F

lux[1010m

Jy

cm/s

/um2]

wavelength[um]

Wavelength[um]

Flu

x[m

Jy]

30

0

2.6 4.0

3

0

3.8 4.8

Physical quantity

Flux(PAH, Brα ): integrate fitting function

Flux(subfeatures, ice): trapezoidal integration

→Luminosity (redshift comes from the literature or our optical spectroscopy)

Equivalent Width

→ 𝐸𝑊 = 𝑓𝑙𝑖𝑛𝑒 𝜆 𝑑𝜆∞−∞

𝑓𝑐𝑜𝑛𝑡𝑖𝑛𝑢𝑢𝑚(𝜆𝑐𝑒𝑛𝑡𝑟𝑒)

AGN

EW(3.3PAH)＜40 nm →AGN

Γ > 1 (𝐼𝜈 ∝ 𝑎𝜆Γ) →obscured AGN

(Moorwood 1986;Imanishi & Dudley 2000)

Discussion

Comparison between 3.3umPAH emission and IR Luminosity

Expect L(3.3PAH)/L(IR)～10−3

(Mouri et al.(1990))

L(IR)[1044ergs/s]

L(3

.3P

AH

)[1041er

gs/s

]

0.01 1000

100

0.01

Crosses with error bar : SFG.

Red symbols contain AGN.

Discussion

Comparison between 3.3umPAH emission and IR Luminosity

Expect L(3.3PAH)/L(IR)～10−3

(Mouri et al.(1990))

In higher IR luminosity than ~1045 ergs/s, L(3.3PAH) is relatively weak.

→・3.3umPAH emission is

absorbed? ・PAHs are destroyed? ・IR is stronger?

L(IR)[1044ergs/s]

L(3

.3P

AH

)[1041er

gs/s

]

0.01 1000

100

0.01

Crosses with error bar : SFG.

Red symbols contain AGN.

Diamonds: LIRGs of Imanishi et al.(2010)

Triangles: ULIRGs of Imanishi et al.(2010)

Brα , Aliphatic hydrocarbon

Brα is not attenuated at the high end.

→×extinction effect

? PAHs are destroyed

Need more data at high IR

? 𝐿𝐼𝑅 is stronger

L(IR)[1044ergs/s]

L(IR)[1044ergs/s]

L(B

rα)[1041er

gs/s

]

L(s

ub)/

L(3

.3P

AH

)

0.01 1000

100

1.0

1000 0.01

0.001

0.01

Comparison between 9,18μ m luminosity and 3.3PAH luminosity

1% of 9, 18 μ m monochromatic luminosity converts to 3.3 μ mPAH emission luminosity.

We derived

𝐿 3.3𝑃𝐴𝐻 ~0.01 × 𝐿 9𝜇𝑚

𝐿 3.3𝑃𝐴𝐻 ~0.01 ×𝐿 18𝜇𝑚

L(3

.3P

AH

)[1041

ergs

/s]

L(9𝜇m)[1043ergs/s]

L(3

.3P

AH

)[1041er

gs/s

]

L(18𝜇m)[1043ergs/s]

100

0.01 1000

0.01

100

0.1 1000

0.1

Summary

We study the applicability of 3.3μ mPAH emission as an indicator of star formation

44 Sample galaxies out of 94

: flux(9,18um)

flux(2.2um)> 2

: detected 3.3umPAH emission

We find a linear correlation between 𝐿3.3𝑃𝐴𝐻 and 𝐿𝐼𝑅 ,

Combining data from the literatures, the ratio 𝐿3.3𝑃𝐴𝐻/𝐿𝐼𝑅 at higher IR luminosity than ~10^45 ergs/s seems to be small.

𝐿𝐵𝑟𝛼 has a correlation with 𝐿𝐼𝑅 even in high 𝐿𝐼𝑅 .