Physical properties of molecular clouds for the entire Milky Way disk

Marc-Antoine Miville-DeschênesInstitut d’Astrophysique Spatiale, Orsay, France

and Norman Murray - CITA, Toronto

Eve Lee - UC Berkeley

Why another catalog of molecular clouds ?• The debate on the relative importance of gravity and feedback in feeding the

turbulent motions is partly due to the lack of observational constraints

• Relatively small sample of clouds

• Only a small fraction of the CO emission in catalogs (typically 20%)

• Velocity crowding makes identification difficult

• We propose a new catalog of molecular cloud that includes the totality of the 12CO (J-1) emission in the plane.

• It is by no mean perfect. It relies on some assumptions to isolate structures in PPV space and to disentangle the near-far distance ambiguity.

• It provides a significant increase in statistics that allows to establish large-scale trends in the Galaxy

• Useful until we can do the same in external galaxies.

Miville-Deschênes, Murray & Lee, 2017, ApJ, 834, 57

from Heyer & Dame 2015

12CO survey - Dame et al. (2001)

• Data acquisition over 20 years (New-York, Cambridge, Cerro-Tololo)

• Angular resolution = 8.5’ • Channel width = 1.3 km/s • Noise ~ 0.1 K

- Gaussian decomposition

- Hierarchical identification of structures

•Gaussian decomposition with spatial coherence •Hierarchical cluster identification with a threshold decent

•The parametrisation is set in order to reproduce the radial variation of surface density and the total mass of molecularclouds in the Milky Way.

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• Identification of 8107 molecular clouds • Corresponds to 98% of the total 12CO emission • 2/3 of lines of sight have 0, 1 or 2 clouds • The near-far distance ambiguity is resolved

using the size-linewidth-surface density relation

surface density

inner Galaxyouter Galaxy

Galactic height

Total mass of molecular gas is reproduced : 1.2x109 MSun Radial surface density profile is reproduced

size-linewidth relation

Pearson=0.55 Pearson=0.71

Most clouds are not gravitationally bound

WNM and CNM valueWolfire+03, Saury+14, Hennebelle & Falgarone 12 Leroy et al. 2015

Most clouds are not gravitationally bound

WNM and CNM valueWolfire+03, Saury+14, Hennebelle & Falgarone 12

• GMCs (typical radius of 30pc) are generally above virial equilibrium • not saying that structures within

clouds are not gravitationally collapsing

• only 15% of the clouds are gravitationally bound (they contain 40% of the mass)

Self-gravity can not explain fully the velocity dispersion. • Stellar gravit. potential ? • Feedback E. injection ?

Dynamical time (R/sigma_v) vs Rgal

Pressure

Kinetic energy injection rate

Edissip.rate = Ekinetic / tdynamical = Einjection.rate

Conclusion• First catalog that includes the total 12CO (1-0) emission of Dame et al. (2001)

• Large variation in surface density.

• GMCs (typical radius of 30pc) are generally above virial equilibrium • not saying that structures within clouds are not gravitationally collapsing • only 15% of the clouds are gravitationally bound (they contain 40% of the mass)

• The average virial parameter does not vary much across the MW disk • there is an obvious link between gravitational energy and turbulent energy

• Large number of small non-star forming clouds in the outer Galaxy• can be explained by the accretion of matter in large scale converging flows (Klessen &

Hennebelle 2010)

• The pressure and the turbulent energy injection rate are 100 times higher in the inner Galaxy compared to the outer galaxy

• The velocity dispersion does not increase as much (only a factor of 2-3) indicating that most of the kinetic energy goes into compressive modes.

• Gravitational collapse is a natural source of compression • This must be balanced by feedback from early star formation, otherwise GMCs would get

very dense, something we do not observe • Stellar feedback (SNae, winds, radiation pressure) are also compressive processes

• We favour gravitational collapse because most clouds we observe have little or no sign of massive young stars and that those that do, do now show larger turbulent velocities

www.ias.u-psud.fr/ism3dJuly 3 - 28, 2017

Institut d’Astrophysique Spatiale Orsay, France

the magnetized

ISM

dust as a tracer of structure

interstellar turbulence

the multi-phase ISM