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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 .