Satoshi Yamamoto and Nobuyuki Kuboi

Department of Physics The University of Tokyo

Submillimeter-wave CI Line Survey in Molecular Clouds

Why Atomic Carbon?

• The fourth abundant element after H, He, and O • Two fine structure lines at submm band

3P1-3P0 492 GHz, 3P2-3P1 809 GHz

• Low ionization potential

HII region PDR MC

C+ C CO

Tracer of an interface between PDR and MC

→ 　 Formation and Evolution of Molecular Clouds

[CI] Observations with Mt. Fuji Submillimeter-wave Telescope

• [CI] 3P1-3P0 (492 GHz) Large-scale Mapping (> 50 deg2) GMC: Orion A, Orion B, M17, W51, DR15, DR21, W3, W44 etc. Dark Cloud: Taurus, NGC1333, rho Oph, L134 , Bright Rimmed Clouds, etc. Translucent Cloud: G216-2.5, MBM12, Draco

• [CI] 3P2-3P1 (809 GHz) Mapping toward representative sources Orion A, Orion B, DR21, NGC1333 etc.

Taurus Dark Cloud

• Distance ～ 140 pc• Active formation site of low-mass stars　　　 (Extensive studies with molecular

lines)• No OB stars associated• No SNR associated　　　　　　　　　　　↓Spontaneous formation and evolution of

molecular clouds

CI Integrated Intensity

CI rich cloud

Translucent Cloud

Dense Cores

CI/13CO(1-0) Integrated IntensityRatio

Late

Early

Hirahara et al. 1992TMC-1

CI Rich Cloud in HCL2

• High C/CO ratio > 0.8 Av > 6

H2 density ～ 5 x 103 cm-3

No enhancement in IRAS color Early stage of chemical evolution?• Interface between translucent part and dense

part• Consistent with chemical evolution scheme in the TMC-1 ridge

→ 　 Formation site of molecular cloud cores

CI PeakAv=6, C/CO=0.6

CI Integrated Intensity

CI/C18O(1-0)Integrated IntensityRatio

CI/13CO(1-0)Integrated IntensityRatio

CI Peak of L1495

Early Stage of Chemical Evolution?

CI/13CO(1-0) Integrated IntensityRatio

CI/C18O(1-0) Integrated IntensityRatio

No translucent part Is associated.

Relatively low C/CO ratio (0.2)

B18 is more evolved than HCL2 and L1495 ?

A lack of translucent part in B18

Summary

• CI/13CO(1-0) intensity ratio is a good indicator of a translucent part of a molecular cloud.• HCL2 and L1495 regions contain an interface between a translucent part and a dense part. >>> Formation site of molecular cloud cores?• B18 does not contain a clear interface. >>> More evolved than HCL2 and L1495

• CI line >>>Unique probe of cloud core formation and evolution

Diffuse part is not Associated.