銀河系外縁部の低金属量分
子雲と星形成齋藤正雄（国立天文台野辺山宇宙電波観測所）

Contents
1. GMC Properties
2. Outer Galaxy
3. Future Observations with Nankyoku
Telescope

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GMC AND STAR FORMATION

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GMC and Star Formation• Most stars form in GMCs
• GMC study important

Kenincutt and Evans+14
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GMC Evolution

Fukui and Kawamura+11
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GMC and Composition• HI and CO wellcorrelated on 40pc scale, but not
well on 10 pc scale• HI and CO peakvelocities agree
well.
Countour CO, grey HI
Fukui+09
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6Galaxy Component• Molecular gas traced byCO
• Molecular gas unseen inCO??
<= argued by Fukui+14• Molecular/Atomic gas
traced by [CII]• Atomic gas traced by HI
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Langer+14

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Key Question• GMC Formation and Evolution• GMC composition, H2 tracer [CI]• Structure of our Galaxy

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8GMCS IN OUTER GALAXY

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9Outer Galaxy• RG>13.5 kpc

Low gas density

Low metallicity

Nakanishi & Sofue 2003

Similar to Dwarf galaxy e.g. LMC
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10Smart+Rolleston
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Our Work• Digel Cloud 1 and 2 (Rg> 18 kpc)
• On-going star formation.
Not contaminatedregion.
• Low Metallicity

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CO(1-0) by Izumi+14 and 15

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HI Shell and Cloud 2• HI bubble – Rg ~ 19 kpc

Stil and Irwin 01

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SN Triggered Formation

Smart+Rolleston 1997
Koyabashi+08
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HI Cloud and Cloud 1• Cloud 1 Rg > 19 kpc
Subaru NIR
Contour: CO(1-0), grey: HI by Izumi+15

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HVC collide with GPHI

2015/11/19• Impact of HVC Complex
H onto the outer part ofthe Galactic disk
• => Cloud 1 formation as
well as star formation inCloud 1.

銀河系外縁部の低金属量分子雲と星形成

15• H2 are really traced by CO?
• [CI] also traces H2?
• <= Offner+14 claimed that [CI] is a better H2column density tracer up to 6 x 1023 cm-3.

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RESEARCH WITH ANTARCTICATELESCOPE
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Specification

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Observable Galactic Plane• l=250-350 deg b=+-10 deg

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Pioneer Work with Nanten

Nakagawa+05
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20Recent Results

Garcia+14
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Proposed Observations• Target: GMCs in Outer Galaxy at 25 kpc• 1” ~ 0.12 pc• Line: CO(3-2)/[CI]• dV = 1 km/s• OTF map covering 100 pc x 100 pc (800”x800”)• Goal– To study Evolution of metal-poor GMCs
– To study Formation of metal-poor GMCs
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C+/C/CO layers

Bolatto+14
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23[CI] is not well understood
Velusamy+14

Shimajiri+14

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Expected Results• GMC formation through shock with [CI] as apotential C-shock tracer– SNR interaction with atomic cloud– HVC collision with GP• GMC Evolution in terms of composition ([CI]/CO).
• Carbon in GMC, HVC, galactic fountain in outer
Galaxy. NII may be also interesting.
• Implication to nearby XUV and LMC/SMC with30m Nankyoku Telescope
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25Summary• GMC evolution and star formation is a key
issue in astrophysics.
• Outer galaxy is a unique and unexplored lab tostudy low-metalliticy clouds.
• [CI] is a potential probe to understand GMC
formation and evolution.
• This study is naturally extended to LMC/SMC,dwarf galaxies, or possibly high-z galaxies.
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