The North Polar Spur and Aquila Rift

TL;DR

This study uses X-ray data and interstellar extinction analysis to determine that the North Polar Spur is a galactic halo object located over 1 kpc away, behind the Aquila Rift.

Contribution

It provides a new distance estimate for the NPS using X-ray extinction and gas velocity data, clarifying its position relative to the Aquila Rift.

Findings

NPS is located behind the Aquila Rift.

A lower limit of 1.01 kpc is established for NPS distance.

NPS is identified as a galactic halo object.

Abstract

Soft X-ray intensity at 0.89 keV along the North Polar Spur is shown to follow the extinction law due to the interstellar gas in the Aquila Rift by analyzing the ROSAT archival data, which proves that the NPS is located behind the rift. The Aquila-Serpens molecular clouds, where the X-ray optical depth exceeds unity, are shown to have a mean LSR velocity of v=7.33 +/- 1.94 km/s, corresponding to a kinematic distance of r=0.642 +/- 0.174 kpc. Assuming a shell structure, a lower limit of the distance to NPS is derived to be 1.01 +/- 0.25 kpc, with the shell center being located farther than 1.1 kpc. Based on the distance estimation, we argue that the NPS is a galactic halo object.