Probing turbulence in ISM of galaxies with 21 cm line!

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1 Probing turbulence in ISM of galaxies with 21 cm line! Bharadwaj and Ali (2005) Leonardo da Vinci Prasun Dutta! IISER Bhopal

2 Collaborators: Somnath Bharadwaj Jayaram N Chengalur Ayesha Begum Nirupam Roy Bharadwaj and Ali (2005)

3 Plan for today Turbulence in the ISM What do we need to know How do we try to know Neil Fleming

the MW (Kalberla 2009) LAB survey: Karberla et al (2005) Star

4 Turbulence in the ISM High velocity dispersion of HI in our galaxy and external galaxies (Agertz 2009) Scale height of the MW (Kalberla 2009) LAB survey: Karberla et al (2005) Star formation (Klessen 2001) Coherent structures Walter et al (2008)

5 Compressible Turbulence Compressible Solinoidal Energy :: [density, velocity] Injection scale Federrath et al (2010)

6 What do we observe?

7 What do we observe?

8 NHI power spectrum : MW

9 NHI power spectrum : MW Crovisior and Dickey (1983) Green (1993) : [ ] Elmegreen (2001)

10 NHI power spectrum : MW Solinoidal Compressive 3D : [ ] Elmegreen (2001)

11 NHI power spectrum : MW Compressive 3D 2D : [ ] Elmegreen (2001)

12 NHI power spectrum : MW Compressive 3D 2D : [ ] Elmegreen (2001)

13 NHI power spectrum : MW Observation suggests that there are scale free structures over length scales ranging 200 pc to sub parsecs. It is found that the slope of the density spectra is about -2.6, consistent with a supersonic turbulence driven by compressive forcing. It is believed that the energy input (forcing) into the turbulence is from supernovae shocks and self gravity.

NHI power spectrum : MW Observation suggests that there are scale free structures over length scales ranging 200 pc to sub parsecs. It is found that the slope of the density spectra is about -2.

14 NHI power spectrum : MW Observation suggests that there are scale free structures over length scales ranging 200 pc to sub parsecs. It is found that the slope of the density spectra is about -2.6, consistent with a supersonic turbulence driven by compressive forcing. What at the larger length scales? It is believed that the energy input (forcing) into the turbulence is from supernovae shocks and self gravity. Begum et al. (2006) and Dutta et al. (2009) for dwarf galaxies.

15 NHI power spectrum : THINGS 18 spiral galaxies from THINGS survey Power spectra follow power law at scales [ 600 pc to 16 kpc] Amplitude of the NHI fluctuations are of the order of 1/10th of the mean NHI density Dutta et al. (2009, 10, 13, 14)

16 NHI power spectrum : SPIRALS 2D 3D NGC 1058 HI Scale height ~ 500 pc Dutta et al. (2009)

17 Vturb power spectrum : MW Milky Way

18 Vturb power spectrum : MW Statistics of centroid of velocities (Lazarian and Esquivel 2003) Spectral Correlation function (Padoan et al. 1998) Velocity channel analysis! (Lazarian and Pogosyan 2000) Velocity coordinate spectrum (Lazarian and Pogosyan 2006)

19 Vturb power spectrum : MW Velocity channel analysis (3D)!! Lazarian and Pogosyan (2000)

20 Vturb power spectrum : MW Velocity channel analysis (3D)!! Slope of the velocity spectra is about -2 along the galactic plane and about in vertical directions. Energy input estimated from the amplitude of the spectra is what expected from supernovae.

21 Vturb power spectrum : SPIRALS Dutta (2015) External Galaxies Walter et al (2008)

22 Vturb power spectrum : SPIRALS Ensemble averaging of can not be done as we do not have statistical isotropy here. We can estimate the quantity without any bias.

23 Vturb power spectrum : SPIRALS

24 Vturb power spectrum : SPIRALS We do not need to use a mapping between line of sight velocity and distance. Estimator works (almost) entirely in the visibility plane. Challenge is to estimate the rotational velocity with sufficient accuracy. Effective for only galaxies with inclination angle < 45 degrees. Dutta (2015)

25 Summary At scales to 200 pc in our galaxy density power spectra is consistent with compressive forcing by supernovae. At larger scales of 10 kpc, observations from external galaxies suggest supersonic turbulence with compressive forcing operational at those scales. Key questions: Are the observed fluctuations at these two different scales result of a same physics or different. What gives energy input to the turbulence at large scales.

Investigating the structure and dynamics of the Interstellar Medium! from radio interferometric observations

Investigating the structure and dynamics of the Interstellar Medium! from radio interferometric observations Prasun Dutta IIT (BHU), Varanasi Collaborators: Somnath Bharadwaj Ayesha Begum Jayaram Chengalur