On the H\alpha\ faintness of the North Polar Spur

TL;DR

This paper measures the H-alpha to radio intensity ratio in the North Polar Spur, finding it significantly lower than typical supernova remnants, supporting a Galactic-Centre explosion origin over a local remnant.

Contribution

It provides observational evidence favoring the Galactic-Centre explosion model for the North Polar Spur based on H-alpha and radio data analysis.

Findings

H-alpha to radio intensity ratio in NPS is ≤ 50

Ratio is two orders of magnitude lower than typical supernova remnants

Supports the Galactic-Centre explosion model over local supernova remnant hypothesis

Abstract

The ratio of H$\alpha$ intensity to 1.4 GHz radio continuum intensity in the North Polar Spur (NPS) is measured to be $\lesssim 50$, two orders of magnitude smaller than the values of $\sim 10^4$ observed in the typical shell-type old supernova remnants, Cygnus Loop and S147. The extremely low H$\alpha$-to-radio intensity ratio favours the Galactic-Centre explosion model for NPS, which postulates a giant shock wave at a distance of several kilo parsecs in the hot and low-density Galactic halo with low hydrogen recombination rate, over the local supernova(e) remnant model.