Contributed Talk - Splinter Magnetic

Thursday, 24 September 2020, 11:25   (virtual room H)

The cosmic ray-driven wind in the starburst galaxy NGC 5775

Volker Heesen (1), George Heald (2), Sarrvesh Sridhar (3), and Ralf-Juergen Dettmar (4)
(1) Univ. of Hamburg, (2) CSIRO, (3) ASTRON, (4) Univ. of Bochum

Galactic winds are one of the most important processes shaping the evolution of galaxies, leading to sustained loss of mass, energy, and angular momentum. Cosmic rays are thought to play a crucial role facilitating them by transporting energy and momentum onto the ionised gas and thus counteracting the adiabatic cooling of the gas in the outflow. In order to study the influence of cosmic rays on the galactic wind in the starburst galaxy NGC 5775, we present new 140-MHz radio continuum observations using the LOW Frequency ARray (LOFAR), allowing us to trace cosmic ray electrons and magnetic fields far into the halo of the galaxy. In order to understand the nature of the disc-halo flow, we implement an iso-thermal wind with a tunable ‘flux tube’ (approximately hyperboloidal) geometry. This model is successful in matching the vertical distribution of nonthermal radio emission, and the vertical steepening of the associated spectral index, in a consistent conceptual framework with few free parameters. We estimate the implied mass-loss rate, which is comparable to the the star formation rate if the escape velocity is reached. We explore the role that the wind may play in influencing the vertical gradient in rotational velocity that has been identified in this and other galaxies.