The 3.3 μm PAH emission of the mid-infrared excess

The 3.3 μm PAH emission of the mid-infrared excess

The 3.3 μ m PAH emission of the
mid-infrared excess galaxies in the
mid-infrared all-sky survey
名古屋大学学部4年 山田梨加
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=101−2 M⊙ 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
10−15 W m−2 μm−1
(2000) detected
3.3umPAH emission
from 6 out of 9 LIRGs ,
using ground based Lband spectroscopy.
 Rodriguez-Ardila &
10−15 erg cm−2 s−1 Å−1
Viegas (2003): AGN
have the 3.3umPAH
luminosity levels similar
to those of starburst
and LIRGs.
→the arrow indicates
3.3umPAH feature
Wavelength[𝜇m]
 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
𝜆𝑟𝑒𝑠𝑡 = 3.42[μ𝑚]
aliphatic hydrocarbon
 Subfeatures
Flux[mJy]
2.5-5μ m spectroscopy
 3.3 umPAH 𝜆𝑟𝑒𝑠𝑡 = 3.29[μ𝑚]
 𝐻2 𝑂ice
Wavelength[um]
 Brα
𝜆𝑟𝑒𝑠𝑡 = 4.05[μ𝑚]
typical spectrums→
Flux[mJy]
𝜆𝑟𝑒𝑠𝑡 = 3.05~3.1[μ𝑚](2.75～3.55)
absorbed by ice
Seem to contain AGN
Flux[mJy]
 Red continuum
Wavelength[um]
𝜆𝑟𝑒𝑠𝑡 = 4.26[μ𝑚]
 CO absorption
𝜆𝑟𝑒𝑠𝑡 = 4.67[μ𝑚]
CO,CO2 absorption
present
Flux[mJy]
 CO2 absorption
Wavelength[um]
Fitting
 Drude profile→3.3umPAH
Flux[mJy]
30
0
2.6
Flux[1010 mJy cm/s/um2 ]
𝑏𝑟 𝛾𝑟 2
𝐼𝜈 =
𝜆 𝜆
( − 𝑟 )2 +𝛾𝑟 2
𝜆𝑟 𝜆
𝑏𝑟 : the central intensity of the feature
𝜆𝑟 : the central wavelength
𝜆𝑟 𝛾𝑟 = 𝐹𝑊𝐻𝑀
・is the theoretical frequency profile
for a classical damped harmonic oscillator.
・has more power in the extended
wings than a Gaussian.
 Gaussian →Brα , H2 O ice
𝐴
𝐼𝜈 =
exp − 𝜆 − 𝜆𝑟 2 /2𝜎 2
2𝜋𝜎
 Power low → continuum
𝐼𝜈 ∝ 𝜆Γ
※Subfeatures’ region is not used for the
fitting
Wavelength[um]
4.0
3
0
3.8
wavelength[um]
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 =
∞
𝑓
−∞ 𝑙𝑖𝑛𝑒
𝜆 𝑑𝜆
𝑓𝑐𝑜𝑛𝑡𝑖𝑛𝑢𝑢𝑚 (𝜆𝑐𝑒𝑛𝑡𝑟𝑒 )
AGN
 EW(3.3PAH)＜40 nm →AGN
 Γ > 1 (𝐼𝜈 ∝ 𝑎𝜆Γ )
→obscured AGN
(Moorwood 1986;Imanishi & Dudley 2000)
Comparison between 3.3umPAH
emission and IR Luminosity
 Expect L(3.3PAH)/L(IR)～10−3
(Mouri et
al.(1990))
L(3.3PAH)[1041 ergs/s]
Discussion
100
0.01
0.01
L(IR)[1044 ergs/s]
1000
 Crosses with error bar :
SFG.
 Red symbols contain AGN.
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(3.3PAH)[1041 ergs/s]
Discussion
100
0.01
0.01
L(IR)[1044 ergs/s]
1000
 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
L(Brα )[1041 ergs/s]
the high end.
→×extinction effect
100
0.001
0.01
L(sub)/L(3.3PAH)
1.0
L(IR)[1044 ergs/s]
1000
? PAHs are destroyed
 Need more data at high IR
? 𝐿𝐼𝑅 is stronger
0.01
0.01
L(IR)[1044 ergs/s]
1000
Comparison between 9,18μ m luminosity and 3.3PAH luminosity
 1% of 9, 18 μ m
𝐿 3.3𝑃𝐴𝐻 ~0.01 × 𝐿 9𝜇𝑚
𝐿 3.3𝑃𝐴𝐻 ~0.01 ×
𝐿 18𝜇𝑚
L(3.3PAH)[1041
ergs/s]
 We derived
0.1
0.01
L(3.3PAH)[1041 ergs/s]
monochromatic luminosity
converts to 3.3 μ mPAH
emission luminosity.
100
L(9𝜇m)[1043 ergs/s]
1000
100
0.1
0.01
L(18𝜇m)[1043 ergs/s] 1000
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 .