Power spectrum of H I intensity fluctuations in DDO 210

Abstract

We measure the power spectrum of H i intensity fluctuations in the extremely faint (M_B~−10.9) dwarf galaxy DDO 210 using a visibility-based estimator that is well suited to very low signal-to-noise ratio regimes. DDO 210's H i power spectrum is well fitted by a power law P_HI(U) =A U^α, with α=−2.75 ± 0.45 over the length-scales 80 pc to 500 pc. We also find that the power spectrum does not change with an increase in the velocity channel width, indicating that the measured fluctuations correspond mainly to density fluctuations. However, Kolmogorov turbulence (with a velocity structure function spectral slope of ⅔) cannot be ruled out from the present observations. The value of the slope α is similar to that obtained in the Milky Way. Compared with the Milky Way, DDO 210 has three orders of magnitude less H i, no spiral arms, and also no measurable ongoing star formation. The fact that the power spectrum slope is nonetheless similar in these two galaxies (and also similar to the values measured for the LMC and SMC) suggests that there is some universal, star-formation-independent phenomenon responsible for producing fine scale structure in the gas.