The LEAP of Pulsars in the Milky Way

TL;DR

This paper presents an analytical model of pulsar and supernova remnant distributions in the Milky Way, using Lambert equal area projections to reveal key structural factors and derive dispersion measures.

Contribution

It introduces a simple geometric model to replicate Galactic object distributions and provides an analytical expression for pulsar dispersion measures within the Galaxy.

Findings

Galactic plane concentration dominates distribution shape

Pulsars show larger dispersion than supernova remnants

Model enables dispersion measure-distance mapping

Abstract

The location of objects on the celestial sphere is a fundamental measurement in astronomy, and the distribution of these objects within the Milky Way is important for understanding their evolution as well as the large scale structure of the Galaxy. Here, physical concepts in Galactic astronomy are illustrated using straightforward mathematics and simplifying assumptions regarding the geometry of the Galaxy. Specifically, an analytical model for a smooth distribution of particles in an oblate ellipsoid is used to replicate the observed distributions of the Galactic coordinates for pulsars and supernova remnants. The distributions and the Lambert equal area projections (LEAPs) of the coordinates suggest that the dominant factors determining the general shape of the distributions are the heavy concentration of objects in the Galactic plane and the offset of the Galactic center from the coordinate system origin. The LEAPs and the distributions also show that the dispersion of pulsars about and along the plane are much larger than that for their progenitor supernovae. Additionally, the model can be used to derive an analytical expression for the dispersion measure along any line of sight within the Galaxy. The expression is used to create a hypothetical dispersion measure-distance map for pulsars in the Galaxy.