Turbulent power distribution in the local interstellar medium. (arXiv:1905.08583v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Kalberla_P/0/1/0/all/0/1">P. M. W. Kalberla</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Haud_U/0/1/0/all/0/1">U. Haud</a>
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 $|b| > 20deg$ 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.
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 $|b| > 20deg$ 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.
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