http://arxiv.org/abs/1905.08583
Context: The ISM is on all scales full of structures that may be considered as tracers of processes that feed turbulence. Aims: We use HI survey data to derive global properties of the angular power distribution of the local ISM. Methods: HI4PI observations on an nside = 1024 HEALPix grid and Gaussian components representing three phases, the cold, warm and unstable lukewarm medium (CNM, WNM and LNM), are used for velocities $|v_{\mathrm{LSR}}| \leq 25$ \kms. For high latitudes $|b| > 20\deg$ we generate apodized maps. After beam deconvolution we fit angular power spectra. Results: Power spectra for observed column densities are exceptionally well defined and straight in log-log presentation with 3D power law indices $\gamma \geq -3$ for the local gas. For intermediate velocity clouds (IVCs) we derive $\gamma = -2.6$ and for high velocity clouds (HVCs) $\gamma = -2.0$. Single phase power distributions for the CNM, LNM, and WNM are highly correlated and shallow with $ \gamma \sim -2.5$ for multipoles $l \leq 100$. Excess power from cold filamentary structures is observed at larger multipoles. The steepest single channel power spectra for the CNM are found at velocities with large CNM and low WNM phase fractions. Conclusions: The phase space distribution in the local ISM is configured by phase transitions and needs to be described with three distinct different phases, being highly correlated but having distributions with different properties. Phase transitions cause locally hierarchical structures in phase space. The CNM is structured on small scales and is restricted in position-velocity space. The LNM as an interface to the WNM envelops the CNM. It extends to larger scales than CNM and occupies also a larger range in velocity. Correlations between the phases are self similar in velocity.
P. Kalberla and U. Haud
Wed, 22 May 19
42/59
Comments: 23 pages, 33 figures, accepted for publication in A&A
You must be logged in to post a comment.