On the origin of the North Celestial Pole Loop

TL;DR

This study investigates the 3D structure and origin of the North Celestial Pole Loop using high-resolution dust and H I data, suggesting it formed from the Local Bubble's gas expansion rather than a supernova event.

Contribution

It provides a detailed 3D geometric and dynamical analysis of the NCPL, proposing a new formation scenario linked to the Local Bubble and past star formation activity.

Findings

Material aligned with the Radcliffe wave near Polaris and Ursa Major.

The NCPL cavity is a protrusion of the Local Bubble filled with warm gas.

The shape and lack of OB stars suggest a formation from gas expansion, not supernovae.

Abstract

The North Celestial Pole Loop (NCPL) provides a unique laboratory for studying the early stage precursors of star formation. Uncovering its origin is key to understanding the dynamical mechanisms that control the evolution of its contents. In this study, we explore the 3D geometry and the dynamics of the NCPL using high-resolution dust extinction data and H I data, respectively. We find that material toward Polaris and Ursa Major is distributed along a plane similarly oriented to the Radcliffe wave. The Spider projected in between appears disconnected in 3D, a discontinuity in the loop shape. We find that the elongated cavity that forms the inner part of the NCPL is a protrusion of the Local Bubble (LB) likely filled with warm (possibly hot) gas that passes through and goes beyond the location of the dense clouds. An idealized model of the cavity as a prolate spheroid oriented toward the observer, reminiscent of the cylindrical model proposed by Meyerdierks et al. (1991), encompasses the protrusion and fits into arcs of warm H I gas expanding laterally to it. As first argued by Meyerdierks et al. (1991), the non-spherical geometry of the cavity and the lack of OB stars interior to it disfavor an origin caused by a single point-like source of energy or multiple supernovae. Rather, the formation of the protrusion could be related to the propagation of warm gas from the LB into a pre-existing non-uniform medium in the lower halo, the topology of which was likely shaped by past star formation activity along the Local Arm.