A Detailed Kinematic Map of Cassiopeia A's Optical Main Shell and Outer High-Velocity Ejecta

TL;DR

This study provides the most detailed 3D kinematic map of Cassiopeia A's optical ejecta, revealing a torus-like structure, ring formations, and high-velocity outflows, offering insights into the remnant's explosion dynamics.

Contribution

It offers the highest resolution Doppler maps of Cas A's optical material, revealing detailed 3D structures and challenging assumptions about the remnant's true geometry and explosion asymmetry.

Findings

Optically bright ejecta form a tilted torus with velocity asymmetry.

Ejecta are arranged in nearly circular rings, possibly from radioactive plumes.

Outer high-velocity knots suggest wide-angle outflows from deep within the progenitor.

Abstract

We present three-dimensional kinematic reconstructions of optically emitting material in the young Galactic supernova remnant Cassiopeia A (Cas A). These Doppler maps have the highest spectral and spatial resolutions of any previous survey of Cas A and represent the most complete catalog of its optically emitting material to date. We confirm that the bulk of Cas A's optically bright ejecta populate a torus-like geometry tilted approximately 30 degrees with respect to the plane of the sky with a -4000 to +6000 km/s radial velocity asymmetry. Near-tangent viewing angle effects and an inhomogeneous surrounding CSM/ISM environment suggest that this geometry and velocity asymmetry may not be faithfully representative of the remnant's true 3D structure or the kinematic properties of the original explosion. The majority of the optical ejecta are arranged in several well-defined and nearly circular ring-like structures with diameters between approximately 30 arcsec (0.5 pc) and 2 arcmin (2 pc). These ejecta rings appear to be a common phenomenon of young core-collapse remnants and may be associated with post-explosion input of energy from plumes of radioactive 56Ni-rich ejecta that rise, expand, and compress non-radioactive material. Our optical survey also encompassed Cas A's faint outlying ejecta knots and exceptionally high-velocity NE and SW streams of S-rich debris often referred to as `jets'. These outer knots, which exhibit a chemical make-up suggestive of an origin deep within the progenitor star, appear to be arranged in opposing and wide-angle outflows with opening half-angles of approximately 40 degrees.