2012/08/27 by Prasun Dutta, Ayesha Begum, Somnath Bharadwaj +1 · 1 citation
Physics and Astronomy · #astro-ph.GA #astro-ph.CO
paper · pdf · doi:10.1016/j.newast.2012.08.008
20 pages, 9 figures, 3 tables. accepted for publication in New Astronomy
arxiv created 2012/08/27 · arxiv updated 2012/08/28
We estimate the \HI intensity fluctuation power spectrum for a sample of 18 spiral galaxies chosen from THINGS. Our analysis spans a large range of length-scales from ∼ 300 \rm pc to ∼ 16 \rm kpc across the entire galaxy sample. We find that the power spectrum of each galaxy can be well fitted by a power law P\rm HI(U) = A Uα, with an index α that varies from galaxy to galaxy. For some of the galaxies the scale-invariant power-law power spectrum extends to length-scales that are comparable to the size of the galaxy's disk. The distribution of α is strongly peaked with 50% of the values in the range α=-1.9 to 1.5, and a mean and standard deviation of -1.3 and 0.5 respectively. We find no significant correlation between α and the star formation rate, dynamical mass, \HI mass or velocity dispersion of the galaxies. Several earlier studies that have measured the power spectrum within our Galaxy on length-scales that are considerably smaller than 500 \rm pc have found a power-law power spectrum with α in the range ≈ -2.8 to -2.5. We propose a picture where we interpret the values in the range ≈ -2.8 to -2.5 as arising from three dimensional (3D) turbulence in the Interstellar Medium (ISM) on length-scales smaller than the galaxy's scale-height, and we interpret the values in the range ≈ -1.9 to -1.5 measured in this paper as arising from two-dimensional ISM turbulence in the plane of the galaxy's disk. It however still remains a difficulty to explain the small galaxy to galaxy variations in the values of α measured here.