2) Inoue & Inutsuka, 2008

Without B field

2 pc

with B field

2 pc 0 1 2 3

log # [/cc]

Dense molecular cloud cannot be formed!

Evolutionary Description of Giant Molecular Cloud Mass Functions across Galactic Disks

Observed slopes may put unique constraints on Tf/Td.

1. Introduction

1)  The slope of the observed giant molecular cloud (GMC) mass functions varies between regions in nearby galaxies. (e.g., Colombo+ 2014)

2)  Multiphase magneto hydrodynamics simulations indicate that magnetic fields significantly prevent the molecular cloud formation, thus multiple episodes of supersonic compression of HI gas is essential for GMC formation. (e.g., Inoue & Inutsuka, 2008)

(masato.kobayashi@nagoya-u.jp)

Inutsuka et al., 2015 proposed a scenario of global GMC/subsequent star formation on galactic scales driven by the network of expanding bubbles (expanding HII regions and supernova remnants). This scenario inherently includes multiple episodic compression (i.e. (2)) and CCC (i.e., (3)).

Ø What determines/controls the variation in the GMC mass function slope?

Ø Cloud-Cloud Collisions (CCC) may alter ISM conditions as well? (e.g., Fukui+ 2014) (e.g., modifying GMC mass function?)

Key questions

2. Formulation: Coagulation Equation and the Fate of Dispersed Gas

3. Results With CCC terms

ü  Based on the GMC/subsequent star formation scenario from Inutsuka et al., 2015, we formulate the coagulation equation for the GMC mass function and compute its time evolution.

ü  Although CCC could be important for the formation of massive stars and star clusters, CCC may be effective only in the massive end.

ü  Almost 100% of the dispersed gas accrete onto the pre-existing GMCs in arm regions whereas ~ 55% in inter-arm regions.

ü  Large surveys may put unique constrains on GMC formation/dispersal timescales and resurrecting factor in different environment on galactic disks by slope of GMC mass function.

Observational / Simulation Facts

3) Fukui+ 2014Inutsuka+ 2015

Our goal: Based on the scenario from Inutsuka et al., 2015, develope the evolutionary picture of GMC mass function by formulating the coagulation equation in GMC mass space.

Without CCC terms CCC modifies only the massive end.

Future large surveys (e.g., ALMA) may reveal the variation of GMC formation/dispersal timescales between different regions on galactic disks.

Arm regions (Tf ~4.2 Myr)Small resurrection (1%)

Inter-arm regions (Tf ~22.4 Myr)

Masato I.N. Kobayashi, S.-i. Inutsuka, H. Kobayashi, K. Hasegawa, and R. Okamoto (Nagoya University, Japan)

2

1

0

-1

log

n(>

M)

[/kpc

2 ]

2

1

0

-1

2

1

0

-1

5 6 7 5 6 7 5 6 7

log GMC mass [Msun]

1) Colombo+ 2014

Massive stars seem to be formed where clouds are colliding.

GMC formation and self-growth through compressions (Tf ~ 10 Myr; c.f. Inoue & Inutsuka 2012)

GMC self-dispersaldue to radiation by massive stars

(Td ~ 14 Myr; c.f. line-radiation hydrodynamics simulation: Hosokawa & Inutsuka 2006)

Cloud-Cloud Collisions (CCCs)

Collision Rate:

Column Density:

Relative Velocity:

Cross Section: ~ 7.52 pc2 for collisions between 104 Msun GMCs

If CCCs are ineffective, then a steady state solution without CCC terms can be obtained:

Large resurrection (45%)

: differential number density of GMCs with mass m

Kobayashi et al. 2017a in press Kobayashi et al. 2017a in press

Kobayashi et al. 2017a in press Kobayashi et al. 2017a in press

Investigate what resurrecting factor can support and keep the GMC MF steady.

The fate of dispersed gas: “Resurrecting Factor”

that regenerates the minimum mass GMC

m

Mass budget resurrected For the self-growth of pre-existing GMCs

When the gas becomes dispersed, they contribute to either the mass growth of pre-existing GMCs or regeneration of the minimum mass GMCs.

GMC

Further compressions

4. Summary

Uironkon Symposium 2016, 2017. Feb. 22 – 23, NAOJ

: resurrecting factor (~0.01 - 1) : total mass dispersal rate

: minimum-mass in GMCMF {

4 5 6 7log(GMC Mass [M�])

-8

-6

-4

-2

0

log(n

cl[/

kpc3 /

M�])

Time [Myr]

Tf,fid = 10.0 [Myr]Td = 14.0 [Myr]

20406080120160200

4 5 6 7log(GMC Mass [M�])

-8

-6

-4

-2

0

log(n

cl[/

kpc3 /

M�])

Time [Myr]

Tf,fid = 10.0 [Myr]Td = 14.0 [Myr]

20406080120160200

4 5 6log(GMC Mass [M�])

-5

-4

-3

-2

-1

log(n

cl[/

kpc3 /

M�])

Time [Myr]

Tf,fid = 4.2 [Myr]Td = 14.0 [Myr]"res = 0.0123

20406080120160200

4 5 6log(GMC Mass [M�])

-5

-3

-1

1

log(n

cl[/

kpc3 /

M�])

Time [Myr]

Tf,fid = 22.4 [Myr]Td = 14.0 [Myr]"res = 0.45

20406080120160200

Kobayashi et al. 2017a in ApJ