Near-Infrared Color of
Molecular Clouds

Yoichi Itoh(University of Hyogo)

1. Dust growth in a molecular cloud ?
Cloudshine: Clouds emit in NIR
implication of dust growth ?

Nakajima et al. (2003)

a=0.005 0.25μm

a=1μm

Ysard et al. (2016)

2. PAH(Poly-cyclic Aromatic Hydrocarbon)• Many emissions in IR. Molecular bands are broad.
→ Effective coolant of a cloud.
• Strong emission in PDR (E>11.18eV)• Strengths of the PAH features are function of the numberof molecules, degree of ionization, strength of UV radiation.
IR spectrum of Orionbright bar. Red: PAHemissions
Spatial distributionof PAH emission isnot fully investigated.

3. Spatial distribution of dusts
Boersma et al. (2013)• NGC7023(PDR), Spitzer/IRS 5.2 - 14.5 μm scan mode
• Model fitting of PAH emissions• 「Large dusts in PDR」
Large dust: The number of carbon atom: 50 -- 328
70%

thin cloud
molecular
cloud

40%

exciting star PDR
10%

HST optical image of NGC7023

Fraction of large dusts deducedfrom PAH emissions

4. IR color of a protostar L1527• investigate nebula color withSpitzer/IRAC archival data.
• Spatial resolution: 2.0”

Av=300 mag

blackbody(300K～40000K)

thermal emission
near the central star?

PAH(model)

outflow
central starL1527

most stars at (0,0)• Central star of L1527 is lowoutflow
protoplanetary disk 3.6um画像(320” x 410”) mass star.
• No UV, PAH not excited.
NIR 3 color image of L1527

4. IR color of a protostar L1527• large extinction near the central star.
• Av = 100 mag or more at the center.

Extinction map of L1527 nebula. Blue: small, red: large

5. IR color of NGC7023(PDR)
U=105

U=106
small dust:
less abundant

U=104

UV
small dust:abundantsmall dust

molecular cloud•weak UV
•small dust: poorthin cloud•weak UV
•small dust: rich
PDR
•strong UV•small dust: rich

Nebula color of NGC7023
Solid line: dust radius, Dotted line: UV radiation

105

5. IR color of NGC7023(PDR)
Boersma+:large dusts in PDR
number of C
this study: small dusts in PDR
Dusts in Boersma et al. (2013)
small dust：number of C < 50
large dust：50 < number of C < 384384個
50個

ダスト存在度 (Drainモデル)

We used dust distribution of Draine, Li(2007). Small dusts in this study include
large dusts of Boersma et al. (2013).
No conflicts in these two studies.
Different dust models in different paper.
→ Construct own dust model…

6. IR color of BRC13, 14
U=105

U=106
small dust:
less abundant

U=104

UV
small dust:abundantsmall dust

molecular cloud•weak UV
•small dust: poor
B-type BRC•strong UV•small dust: rich
Unusual region•strong UV•small dust: poor

6. IR color of BRC13, 14
Large 4.5μm - 5.8μm
color inside the cloud,indicating poor smalldusts.

Small color at the edgeof the cloud, indicatingrich small dusts.
UV from the exciting stardestroys dusts in themolecular cloud.
4.5μm - 5.8μm。Red: large color.

6. IR color of IC 348
omi Per (B1 III)omi Per

HD 281159 (B5V)
HD 281159
DSS optical image
4.5μm - 5.8μm• Small color around a B-type star, indicating rich small dusts.
• UV from the B-type star destroys dusts→ Dusts are large in a cloud unless destructed by UV.

6. IR color of IC 348
IC348
3MyrNear B star

NGC1333
1MyrinsidecloudUV
small dust

• Small dusts are poor in IC348 (old) than those in NGC 1333
→ Dusts are coagulating inside a cloud ??

8. Dusts in a planetary nebula
Dusts are very small before cloud formation

NGC7027: very young PN.
age: 600 yr.
Mass of the central star is originally
3-4 solar mass

small dust

Poor small dusts even in a planetary nebula……