Nonuniversal interstellar density spectra probed by pulsars

TL;DR

This paper introduces a novel method using pulsar dispersion measures to measure interstellar turbulence spectra across multiple phases and scales, revealing nonuniversal density spectra in the interstellar medium.

Contribution

The study presents a new approach to measure interstellar turbulent density spectra directly from pulsar DMs without relying on multiple tracers, uncovering different spectral behaviors across phases.

Findings

Shallow density spectrum from supersonic turbulence in cold phases

Kolmogorov-like spectrum in warm ionized medium

Steep spectrum in diffuse WIM extending to several kpc

Abstract

The Galactic interstellar turbulence affects the density distribution and star formation. We introduce a new method of measuring interstellar turbulent density spectra by using the dispersion measures (DMs) of a large sample of pulsars. Without the need of invoking multiple tracers, we obtain nonuniversal density spectra in the multi-phase interstellar medium over different ranges of length scales. By comparing the analytical structure function of DMs with the observationally measured one in different areas of sky, we find a shallow density spectrum arising from the supersonic turbulence in cold interstellar phases, and a Kolmogorov-like density spectrum in the diffuse warm ionized medium (WIM). Both spectra extend up to hundreds of pc. On larger scales, we for the first time identify a steep density spectrum in the diffuse WIM extending up to several kpc. Our results show that the DMs of pulsars can provide unique new information on the interstellar turbulence.