1. マゼラン雲中の星形成領域、 分子雲中でのダストの性質
左近　樹、尾中 敬、金田英宏、
加藤大輔、河村晶子、大西利和、福井康雄
AKARI MP/ISMGN team, AKARI IRC team

2. Interstellar dust Composition Carbonaceous Dust
(carbonaceous, silicate, etc.)
Infrared emission from diffuse ISM
Composition
Submicron dust (in thermal equilibrium)
(BGs; ~100nm)
Polycyclic Aromatic Hydrocarbons
(PAHs; ~10Å)
Very Small Grains (graphites, small silicate )
(VSGs; 1~10nm, stochastic heating)
PAH platelet (≡)
　Carbonaceous Dust
PAH cluster (≡)
PAH molecule C H
Amorphous carbon

3. IRAS 12/25 and young star clusters (<10Myr)
SED characteristics of dust emission around young star clusters in the LMC
IRAS 12/25 and young star clusters (<10Myr)
→ enhancement of 25mm emission around young star clusters
(young star clusters catalogue from Bica et al. 1996)

4. SED characteristics of dust emission around young star clusters in the LMC
ISRF distribution; f(U)∝U-b for Umin < U < Umax
U=1 corresponds to solar vicinity value (Mathis, Mezger, and Panagia 1983)
Iexcess/FIR vs. TBGs
12mm
Iexcess/FIR vs. TBGs
25mm
Around the Young Star Clusters ; ( Umin , Umax ) = (1, 105)
Regions without Young Star Clusters; ( Umin , Umax ) = (0.5, 102)
(cf. Sakon et al. 2004, 2006,　Tokura et al. 2006, Hibi et al. 2006)

5. SED characteristics of dust emission in the CO Molecular Clouds in the LMC
NANTEN 12CO(J=1->0) LMC survey data at l=2.7mm
(Fukui 2002; Yamaguchi et al. 2001; Mizuno et al. 2001)
HPBW 2.6’ at 115GHz
Infrared SED;
IRAS Sky Survey Atlas 12mm, 25mm, 60mm, 100mm
beam size ; 4’ x 4’
-> only the data more than 16’
apart from the young (<30Myr)
star clusters in the LMC are used
large scatter in 12/25 color
for I12CO < 5 K km s-1

6. SED characteristics of dust emission in the CO Molecular Clouds in the LMC
ISRF distribution; f(U)∝U-b for Umin < U < Umax
Umin ; CO 分子雲に特徴的な輻射場環境 Umin~0.1; TBGs~13K (Miville-Deschenes et al. 2002)
Umax ; CO 分子雲の外部の輻射場環境によって決まる
IRAS 12mm / 25mm vs. b for various (Umin , Umax )
b 大; CO分子雲領域が
　　　　領域内で支配的
　　　　（ I12CO 大に相当）
b 小; CO分子雲領域
　　　　外側の輻射場
　　　　環境が支配的
　　　　（ I12CO 小に相当）
(Umin , Umax ) = (0.1, 10) ; Arc I, Molecular Ridge South etc.
(Sakon et al. 2006)
(Umin , Umax ) = (0.1, 1000) ; Arc III, Molecular Ridge North etc.

7. Unidentified Infrared Bands
Ubiquitous presence of UIR emission
HII region, Reflection Nebulae, Planetary Nebulae, etc. (Tokunaga et al. 1997)
Diffuse ISM (Onaka et al. 1996; Mattila et al. 1996)
External Galaxies (e.g. Helou et al. 2000) even at z~2 (Yan et al. 2004) H C
CH out-of-plane
bending
CH in-plane
CH stretching
CC stretching C H
trio
duo
quartet
solo
UV photon
energy UV
photon
IR photons

8. Focal plane of AKARI/IRC channels
(Onaka et al. 2007)

9. System spectral response curves
of AKARI/IRC imaging filters

10. System spectral response curves of AKARI/IRC spectroscopic filters
(Ohyama et al. 2007)
NP/NG: UIR 3.3mm
SG1 : UIR 6.2mm, 7.7mm
SG2 : UIR 8.6mm, 11.2mm

11. AKARI/IRC spectroscopy of Diffuse ISM in the LMC
Molecular Cloud with Young
star cluster near N159
Molecular Cloud without
young star clusters
IRAS 12mm/25mm

12. AKARI/IRC spectroscopy of Diffuse ISM in the LMC① ② ③
[NeII] ① ② ③
Molecular Cloud with Young
star cluster near N159
[SIV]
[ArIII]
-69
-70
-71
-72 90 89 88 87 86
R.A. (B1950) (deg)
DEC (B1950) (deg)
UIR6.2
UIR7.7
UIR8.6
UIR11.2
UIR12.7
[NeII]
[SIV]
[ArIII]
Molecular Cloud without
young star clusters
Molecular Cloud with Young star cluster (①, ②) :
small 12mm/25mm, large UIR 7.7/11.2
Molecular Cloud without Young star cluster (③) :
large 12mm/25mm, small UIR 7.7/11.2

13. AKARI/IRC Slit-spectroscopy
of diffuse ISM in NGC6946

14. UIR bands in NGC6946
IRC MIR-S/SG1 & SG2 spectra: Arm region, Inter-arm region
※ Zodiacal emission is not subtracted as for (a) and (b)
[ArIII]
[SIV]
Band strengths of UIR 6.2mm and 7.7mm features relative to that of UIR 11.2mm feature become stronger in the arm region than in the inter-arm region :
inter-arm
arm
star forming region
UIR 6.2, 7.7mm
UIR 6.2, 7.7mm
UIR 6.2, 7.7mm
<
<
UIR 11.2mm
UIR 11.2mm
UIR 11.2mm

15. Properties of PAHs in NGC6946
UIR band ratios of 6.2mm/11.2mm, 7.7mm/11.2mm, 8.6mm/11.2mm
UIR band ratio Inter-Arm* Arm* S.F.Region*2
[6.2 / 11.2] ext.corr (±0.14) 1.33(±0.13) (±0.64)
[7.7 / 11.2] ext.corr (±0.32) 3.32(±0.35) (±1.44)
[8.6 / 11.2] ext.corr (±0.14) 0.56(±0.09) (±0.28)
*1 no extinction correction for the extreme case
*2 Taking account of the extinction of Av=3 mag
(Ferguson, Gallagher & Wyse 1998).
- As a valid measure of the on-going star formation
cf. second plateau component
in Peeters et al.2002
UIR band / Plateau Emission in7-9mm
⇒ gas-phase PAHs ( NC) / PAH clusters (~500NC)
UIR band / plateau emission in7-9mm
Feature Inter-Arm Arm S.F.Region
UIR* / plateau (±0.018) (±0.009) (±0.016)
* Total intensity of UIR 6.2mm + 7.7mm + 8.6mm features
More abundant small sized (free-flying) PAHs in Star forming Region
possibly as a result of photo-evaporation of PAH clusters into free-flying PAHs

16. PAHs and PAH clusters (Rapacioli, Joblin and Boissel 2005, A&A, 429, 193)
Peak position of
“7.7mm” complex
UIR7.7/11.2
A : ionized PAHs large mm
B : neutral PAHs small mm
C : PAH clusters mm
-> 7.6mm / 7.8mm ratios: PAHs/PAH clusters

17. PAHs and PAH clusters
Results of the fit mm component mm component ratio
lcenter(fixed) h7.6(free) D7.6(free) lcenter(fixed) h7.8(free) D7.8(free) I(7.6) / I(7.8)
(mm) (W/m2/um/pixel) (mm) (mm) (W/m2/um/pixel) (mm)
Arm region E E
Inter-arm region E E
Larger ratio of I(7.6)/I(7.8) in star forming region
-> More abundant small sized (free-flying) PAHs in Star forming Region
as a result of photo-evaporation of PAH clusters into free-flying PAHs