A study of interstellar medium of dwarf galaxies using H i power spectrum analysis |
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Authors: | Prasun Dutta Ayesha Begum Somnath Bharadwaj Jayaram N Chengalur |
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Institution: | Department of Physics and Meteorology &Centre for Theoretical Studies, IIT Kharagpur, Kharagpur 721 302, India;Department of Astronomy, University of Wisconsin, 475 N. Charter Street, Madison, WI 53706, USA;Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge;National Centre For Radio Astrophysics, Post Bag 3, Ganeshkhind, Pune 411 007, India |
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Abstract: | We estimate the power spectrum of H i intensity fluctuations for a sample of eight galaxies (seven dwarf and one spiral). The power spectrum can be fitted to a power-law for six of these galaxies, indicating turbulence is operational. The estimated best-fitting value for the slope ranges from ~?1.5 (AND IV, NGC 628, UGC 4459 and GR 8) to ~?2.6 (DDO 210 and NGC 3741). We interpret this bi-modality as being due to having effectively 2D turbulence on length-scales much larger than the scale-height of the galaxy disc and 3D otherwise. This allows us to use the estimated slope to set bounds on the scale-heights of the face-on galaxies in our sample. We also find that the power-law slope remains constant as we increase the channel thickness for all these galaxies, suggesting that the fluctuations in H i intensity are due to density fluctuations and not velocity fluctuations, or that the slope of the velocity structure function is ~0. Finally, for the four galaxies with '2D turbulence' we find that the slope α correlates with the star formation rate (SFR) per unit area, with larger SFRs leading to steeper power laws. Given our small sample size, this result needs to be confirmed with a larger sample. |
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Keywords: | turbulence Galaxy: disc galaxies: ISM |
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