1. 12-10-2010 Qualifying Exam Jonathan Carroll-Nellenback Physics & Astronomy University of Rochester Turbulence in Molecular Clouds

2. 2 Talk Outline Molecular Cloud Formation & Lifetime Turbulence in Molecular Clouds Sources of Turbulence Formation Energy Gravitational Collapse Feedback Supernovae Winds Outflows Results Conclusion

3. 3 Molecular Cloud Formation Giant Molecular Clouds are large dense regions within the ISM, with masses generally between 10 4 and 10 6 M ʘ. GMC's are the primary site of star formation. GMC's primarily form in the galactic disk through some combination of the magneto-Jeans instability and the Parker instability

4. 4 Molecular Cloud Formation Molecular clouds are quite cooler than the diffuse ISM with temperatures of only 10-100 K and as such are best seen in rotational transitions of molecules (CO).

5. 5 Molecular Cloud Formation

6. 6 Turbulence Incompressible turbulence can be thought of as a cascade of energy from large scales to small scales. If motions on a given scale have velocity dispersions, then the rate at which kinetic energy cascades to smaller scales should be Since the energy distribution Alternatively, on dimensional grounds For compressible turbulence (or shock dominated turbulence), energy can dissipate from large scales to the smallest scales directly so the cascade argument breaks down. Instead the velocity scales as which happens to coincide with the spectra corresponding to an ensemble of step functions (shocks)

7. 7 Properties of Molecular Clouds Molecular Clouds obey a velocity-linewidth size relation expected for a supersonic turbulence cascade Molecular Clouds tend to be virialized (or gravitationally bound) Combining these implies that either the size or the linewidths of the clouds depend on their density. Incidentally, this implies that molecular clouds of different sizes have the same column density

8. 8 Molecular Cloud Lifetimes Two views on molecular cloud lifetimes Molecular Clouds are quasi-steady state structures supported by internally driven turbulence Formed from large scale gravitional instabilities Explains why clouds are virialized Surface densities set by pressure of the ISM Requires feedback to sustain turbulence and prevent global collapse. Molecular Clouds are transient dynamic entities produced by colliding flows Explains the linewidth size relation Does not require feedback to sustain turbulent motions Does not explain why clouds seem to be gravitationally bound or have uniform column densities

9. 9 Star Formation Efficiencies Molecular clouds are inefficient at turning gas into stars. In the absence of any support, the cloud (assuming that it is gravitationally bound) would collapse and convert nearly all of its gas into stars in a free fall time giving an efficiency per free fall time ε ff = 1 instead of the typically observed values of ~.01 Turbulence is therefore required to reduce the star formation efficiency and prevent global collapse of the cloud. Supersonic turbulence however typically decays in a crossing time (or a free fall time for a virialized cloud) and therefore requires continual driving.

10. 10 Sources of Energy injection in Molecular Clouds External/Initial – Can explain large scale turbulence Magneto-Rotational instabilities in the spiral arms (too weak) Cloud-cloud collisions (too rare) Nearby supernovae (too inefficient) Kinetic energy at formation (dissipates too quickly) Internal – Good at reducing ε ff (self-regulated) HII regions driven by O stars (too infrequent) Protostellar outflows (limited to clump scales) Winds from B stars (just right?) Conversion of gravitional energy during contraction Magnetic fields

11. 11 Outflow Feedback

12. 12 Outflow Driven Turbulence

13. 13 Outflow Driven Turbulence We performed a set of 3 simulations Isotropic Forcing to represent external forcing Outflow Forcing to represent feedback from young stellar objects Both Isotropic and Outflow Forcing

14. 14 Outflow Driven Turbulence Isotropic Both Outflow Movies showing column density for various runs. These simulations ran for 8 outflow times and included 512 randomly placed and oriented outflows.

15. 15 Results Outflows are able to drive supersonic turbulence with parameters consistent with the scaling relations of Matzner. The velocity spectrum produced by outflow driven turbulence is steeper then for isotropically driven turbulence. The density spectrum is flattened by the presence of outflows.

16. 16 Why the steeper velocity spectra? The time required for energy to cascade from the outflow scale to smaller scales is equivalent to the outflow time scale which is the time between successive outflow-interactions. No real cascade... Most of the energy is in coherent velocity structures with hubble type flows Randomly placed outflows also disrupt the large scale coherent velocity and density structures that form due to the large scale driving.

17. 17 Conclusions While outflows do drive supersonic turbulence at levels consistent with observations, the injection scale is in general much smaller than the cloud scale. Outflows can prevent local collapse and could significantly reduce the star formation efficiency but something else is needed to sustain the turbulence on larger scales. Outflows coupled to large scale magnetic fields? Conversion of gravitational energy to kinetic energy? This only works if feedback can reduce the star formation efficiency where stars are forming (ie clumps)