Galactic-Center Hyper-Shell Model for the North Polar Spurs

TL;DR

This study uses hydrodynamical simulations to model the North Polar Spurs as shock waves from energetic events in the Galactic Center, successfully reproducing observed X-ray features and exploring their origin.

Contribution

It introduces a detailed hydrodynamical model of the North Polar Spurs that explains their structure and X-ray brightness, linking them to past energetic events in the Galactic Center.

Findings

Simulation reproduces observed X-ray features of NPS.

Shadowed shock wave model explains the dumbbell shape.

Supports starburst or AGN activity as origin.

Abstract

The bipolar-hyper shell (BHS) model for the North Polar Spurs (NPS-E, -W, and Loop I) and counter southern spurs (SPS-E and -W) is revisited based on numerical hydrodynamical simulations. Propagations of shock waves produced by energetic explosive events in the Galactic Center are examined. Distributions of soft X-ray brightness on the sky at 0.25, 0.7, and 1.5 keV in a +/-50 deg x +/-50 deg region around the Galactic Center are modeled by thermal emission from high-temperature plasma in the shock-compressed shell considering shadowing by the interstellar HI and H2 gases. The result is compared with the ROSAT wide field X-ray images in R2, 4 and 6 bands. The NPS and southern spurs are well reproduced by the simulation as shadowed dumbbell-shaped shock waves. We discuss the origin and energetics of the event in relation to the starburst and/or AGN activities in the Galactic Center. [ High resolution pdf is available at http://www.ioa.s.u-tokyo.ac.jp/~sofue/htdocs/2016bhs/ ]