1分子雲衝突による巨大分子雲質量関数の進化
Masato I.N. Kobayashi (Nagoya U)

第二回銀河進化研究会 2015. Jun. 3 at Nagoya U
Collaborators; Shu-ichiro Inutsuka,Kenji Hasegawa,
Hiroshi Kobayashi (Nagoya U)

Contents2 Backgrounds--- Observed Giant Molecular Cloud (GMC) Mass Functions (MF)--- Simulations with Turbulence and Magnetic Field--- Multiple Episodes of Compression

 GMC Formation on Galactic Scales--- Network of Expanding Shells--- Formulation of GMC Evolution with Cloud-Cloud Collsions(CCCs)

 Results--- Variation of Mass Functions with/without CCCs
with various timescales Summary3Backgrounds
 Observed GMC MF
 Multiphase Simulations
 Multiple Episodes of Compression

Observed Mass Functions
PAWS program observed M51

Colombo et al., 2014, MNRAS

4Observed Mass Functions
Variation of GMC Mass Functions (GMCMF)

Colombo et al., 2014, MNRAS

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Observed Mass Functions
Variation of GMC Mass Functions (GMCMF)

Colombo et al., 2014, MNRAS
Bar regions

6Observed Mass Functions
Variation of GMC Mass Functions (GMCMF)
Arm regions
Colombo et al., 2014, MNRAS

78Observed Mass Functions
Variation of GMC Mass Functions (GMCMF)

Colombo et al., 2014, MNRASInter-armregions

9Observed Mass Functions
Variation of GMC Mass Functions (GMCMF)
Arm regions
Colombo et al., 2014, MNRAS
Bar regions
Inter-armregions

10Observed Mass Functions
Variation of GMC Mass Functions (GMCMF)
Arm regions
Colombo et al., 2014, MNRAS
Bar regions
Inter-armregions
Bar/Arm regions:
Shallow Log-slope()

Inter-arm regions:
Steep Log-slope()

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ISM simulations
Multiphase Turbulent Structure
Audit & Hennebelle, 2008

20 pc

See also;
Koyama & Inutsuka, 2002
Heitsch et al., 2006
Hennebelle & Audit, 2007
etc.

What aboutmagnetic fields?

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ISM simulations
Magnetic Fields Prevent Cloud Formation
Inoue and Inutsuka, 2008
With magnetic field

Without magnetic field

Molecular cloud formation is significantly prevented
unless the shock wave propagates along the magnetic field…
Similar results also obtained in other works, (e.g.,Heitsch 2009)

ISM simulations
Multiple Episodes of Compression
To form molecular clouds from magnetized warm medium,
multiple episodes of compression is essential.

A few 10 Myrse.g., Inoue and Inutsuka, 2012

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GMC Formation
 Network of Expanding Shells
 Mass Continuity Equation with CCC

GMC Formation due to Shells
Inutsuka+ 2015 A&A

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GMC Formation due to Shells
Inutsuka+ 2015 A&A

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Cloud-Cloud Collisions (CCCs)
Fukui+ 2014
Nakamura+ 2012Torii+2015
etcEvolution of GMC Mass Function17Evolution of GMC Mass Function

GMC self-growththrough compressions(i.e. Tf ~10 Myr)

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Evolution of GMC Mass Function

GMC self-dispersal by
dissociating photon andionizing photon due to OB stars(i.e. Td ~14 Myr)

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Evolution of GMC Mass Function

Cloud-Cloud collisions (CCCs)

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Results With/without CCCs
 With Different Timescales

Resultant Mass Functions
Without CCC; only self-growth and self-dispersal

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Resultant Mass Functions
With CCC, self-growth, and self-dispersal

CCC does not alter GMC mass function significantly

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Steady State Solution
Inutsuka et al., 2015

Steady state solution can be obtained as:

Observed Tf/Td may put an unique constraint
on relevant timescales.
e.g.,

forfor longer Tf regions

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Time Scales for GMC Formation

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Long Tf (~ 22.4 Myr)

Inter-arm regions may have longer timescales for formation

Time Scales for GMC Formation
Short Tf (~ 4.2 Myr)

Arm regions may have shorter timescale for formation

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Summary

Background: Multiple episodes of compression--- Variation of GMC MF on galactic scales--- Magnetic fields retard molecular cloud formation

Formulation: Mass continuity eq. with CCC--- CCC does not alter GMC MF significantly--- Cloud formation timescale may vary GMC MF slope

Future Prospects--- Td varying with CCC--- Tracking individual GMC
star formation histories

Without CCC

With CCC