HST Proper Motion Measurements of Supernova Remnant N132D: Center of Expansion and Age

TL;DR

This study measures the proper motions of ejecta in supernova remnant N132D using Hubble data over 16 years, determining its center of expansion and age, and analyzing explosion asymmetry and expansion dynamics.

Contribution

It provides the first precise proper motion-based measurements of N132D's center of expansion and age, improving previous estimates and demonstrating the ejecta's ballistic expansion into a cavity.

Findings

Center of expansion determined with 2.9 arcsecond uncertainty.

Explosion age estimated at 2770 ± 500 years.

Ejecta proper motions are ballistic and indicate expansion into an ISM cavity.

Abstract

We present proper motion measurements of oxygen-rich ejecta of the LMC supernova remnant N132D using two epochs of Hubble Space Telescope Advanced Camera for Surveys data spanning 16 years. The proper motions of 120 individual knots of oxygen-rich gas were measured and used to calculate a center of expansion (CoE) of $\alpha$=05:25:01.71 and $\delta$=-69:38:41.64 (J2000) with a 1-$\sigma$ uncertainty of 2.90 arcseconds. This new CoE measurement is 9.2 and 10.8 arcseconds from two previous CoE estimates based on the geometry of the optically emitting ejecta. We also derive an explosion age of 2770 $\pm$ 500 yr, which is consistent with recent age estimates of $\approx 2500$ yr made from 3D ejecta reconstructions. We verify our estimates of the CoE and age using a new automated procedure that detected and tracked the proper motions of 137 knots, with 73 knots that overlap with the visually identified knots. We find the proper motions of ejecta are still ballistic, despite the remnant's age, and are consistent with the notion that the ejecta are expanding into an ISM cavity. Evidence for explosion asymmetry from the parent supernova is also observed. Using the visually measured proper motion measurements and corresponding center of expansion and age, we compare N132D to other supernova remnants with proper motion ejecta studies.