Morphological Evidence for the eROSITA Bubbles Being Giant and Distant Structures

TL;DR

This study uses dust distribution and radio polarization data to demonstrate that the eROSITA bubbles are giant, distant structures approximately 10 kpc in size, rooted at the Galactic Center, resolving previous conflicting views.

Contribution

The paper provides morphological and distance evidence that the eROSITA bubbles are large, 10-kpc scale structures, unifying the North Polar Spur and Lotus Petal Cloud as parts of a single giant bubble.

Findings

NPS and LPC are distant, with lower limits of 1 kpc.

Polarized radio arcs align with the bubble's shock front.

The bubble's shape fits a 3D skewed cup model rooted at the Galactic Center.

Abstract

There are two contradictory views of the eROSITA bubbles: either a 10 kpc-scale pair of giant bubbles blown by the Galactic center (GC), or a 100 pc-scale local structure coincidentally located in the direction of GC. A key element of this controversy is the distance to the bubbles. Based on the 3D dust distribution in the Galactic plane, we found three isolated, distant (500-800 pc) clouds at intermediate Galactic latitudes. Their projected morphologies perfectly match the X-ray shadows on the defining features of the north eROSITA bubble, i.e., the North Polar Spur (NPS) and the Lotus Petal Cloud (LPC), indicating that both the NPS and LPC are distant with a distance lower limit of nearly 1kpc. In the X-ray dark region between the NPS and LPC, we found a few polarized radio arcs and attributed them to the bubble's shock front. These arcs match up perfectly with the outer border of the NPS and LPC and provide a way to define the bubble's border. The border defined in this way can be well described by the line-of-sight tangent of a 3D skewed cup model rooted in the GC. We conclude that, instead of being two independent, distant features, NPS and LPC compose a single, giant bubble, which, therefore, is most plausibly a 10-kpc scale bubble rooted at the GC.