2025/05/19 by Burman, Shivam, Malik, Sunil, Singh, Suprit +1
#Astrophysics of Galaxies (astro-ph.GA) #Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences
paper · doi:10.48550/arxiv.2505.13677
Most observational studies of galactic-scale magnetic fields using Faraday rotation rely on estimates of thermal electron densities in galaxies and their radial variations. However, the spatial distribution of electrons in the interstellar medium (ISM) is not clearly known. In this study, we propose and utilize collision-excited doublet emission line ratios of [S ii] λλ 6716, 6731 Å~and [O ii] λλ 3726, 3729 Å to estimate the electron densities (ne). To map their distribution in the galaxies, we employ Integral Field Unit (IFU) spectroscopic observations from the SDSS Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, utilising data products from both the Pipe3D and MaNGA Data Analysis Pipeline (DAP). We present a spatially resolved analysis of 13 face-on galaxies (inclination, i ≤ 10^∘), including 9 star-forming galaxies (SFGs) and 4 Non-SFGs. Azimuthally averaged radial profiles of ne are obtained using two different binning schemes: linear and non-linear. For the Pipe3D case, both SFGs and non-SFGs exhibit ne gradients, with higher densities of ne(S ii) = 165.6 ± 20.8 cm-3 in the inner disk region (r/Re ≤ 1.5), which decrease to 31 ± 4.5 cm-3 in the outer disk region (r/Re > 1.5). We also translate ne to the electron column density Ne assuming an evenly distributed thin disk profile, fairly excluding the central bulge regions. These electron density estimates at different radii provide valuable insights for resolving ambiguities in current and future studies of magnetic fields in galaxies.