Lagging a Gaseous Halo with Nonthermal Radial Pressure Gradients

Over the last twenty years, extraplanar ionized and atomic gas has been observed to rotate slower than the gas in the midplane of most nearby edge-on spiral galaxies. This gas rotates more slowly with increasing height off of the disk. However, the cause of these lagging gaseous halos isn’t well understood. In this work, we explore observationally whether nonthermal radial pressure gradients from cosmic rays and magnetic fields may explain lagging gaseous halos. Under the equipartition assumption between magnetic field and cosmic ray energy densities, we model the 3D distribution of nonthermal pressure in the nearby spiral galaxy NGC 891 to see if the radial pressure gradient can explain the amplitudes of the observed lag. This is done using new jointly deconvolved Karl G. Jansky Very Large Array and Robert C. Byrd Green Bank Telescope 6 GHz radio continuum observations from the Continuum HAlos in Nearby Galaxies - an EVLA Survey. Such large fractional bandwidth continuum GBT datasets required us to develop a new data reduction pipeline for our 35 edge-on CHANG-ES galaxies. The joint deconvolution is the first application to radio continuum data of an algorithm developed by Rau et al. (2019) that incorporates multi-scale multi-frequency synthesis as well as mosaicking. The 3D distribution of the nonthermal pressure is derived from an adaptation of tilted-ring modeling of synchrotron emission.