Cosmic-ray electron propagation in NGC 3044 from radio continuum observations

TL;DR

This study uses high-sensitivity radio observations of NGC 3044 to analyze cosmic-ray electron transport, revealing advective winds exceeding escape velocity and evidence of a superbubble, advancing understanding of galactic winds in star-forming galaxies.

Contribution

It introduces detailed modeling of cosmic-ray electron propagation and wind dynamics in NGC 3044 using new ASKAP radio data, highlighting the role of cosmic-ray-driven winds.

Findings

CREs are advected with velocity increasing with height

Beyond 3 kpc, wind velocity exceeds escape speed

Identification of a superbubble with hot gas and HI shell

Abstract

Star-forming edge-on galaxies often exhibit extended halo radiation in multiple bands, providing ideal laboratories for studying the transfer of matter from the disk to the halo. We investigate the transport of cosmic-ray electrons (CREs) and the associated galactic wind, and assess their impact on the surrounding medium in NGC 3044. We obtained the NGC 3044 total intensity image at 943 MHz from the Australian SKA Pathfinder (ASKAP) observations with a resolution of 16 arcsec and an rms noise of 20 $\mu$Jy beam$^{-1}$. The sensitivity is higher than the previous observations at similar frequencies. We find that the ASKAP intensity profiles perpendicular to the disk can be fit with two exponential components. The scale heights of the thin and thick disks are $0.43 \pm 0.13$ kpc and $1.91 \pm 0.26$ kpc, respectively. By jointly fitting total intensity and spectral index profiles with one-dimensional advection and diffusion models, we find that CREs are advected outward from the disk with the velocity increasing with height in a power law. Beyond $\sim3$ kpc, the velocity exceeds the escape speed of $\sim400$ km s$^{-1}$, indicating a strong wind. We further identify a possible superbubble of radius $\sim3$ kpc filled with soft X-ray emitting hot gas and surrounded by an HI shell and a bright H$\alpha$ rim. These results demonstrate that radio continuum observations provide a powerful probe of cosmic-ray-driven winds in normal star-forming spiral galaxies.