Near-Infrared Knots and Dense Fe Ejecta in the Cassiopeia A Supernova Remnant

Abstract

We report the results of broadband (0.95--2.46 $\mu$m) near-infrared spectroscopic observations of the Cassiopeia A supernova remnant. Using a clump-finding algorithm in two-dimensional dispersed images, we identify 63 "knots" from eight slit positions and derive their spectroscopic properties. All of the knots emit [Fe II] lines together with other ionic forbidden lines of heavy elements, and some of them also emit H and He lines. We identify 46 emission line features in total from the 63 knots and measure their fluxes and radial velocities. The results of our analyses of the emission line features based on principal component analysis show that the knots can be classified into three groups: (1) He-rich, (2) S-rich, and (3) Fe-rich knots. The He-rich knots have relatively small, $\lesssim 200{\mathrm{km}\mathrm{s}}^{-1}$, line-of-sight speeds and radiate strong He I and [Fe II] lines resembling closely optical quasi-stationary flocculi of circumstellar medium, while the S-rich knots show strong lines from O-burning material with large radial velocities up to $\sim 2000{\mathrm{km}\mathrm{s}}^{-1}$ indicating that they are supernova ejecta material known as fast-moving knots. The Fe-rich knots also have large radial velocities but show no lines from O-burning material. We discuss the origin of the Fe-rich knots and conclude that they are most likely "pure" Fe ejecta synthesized in the innermost region during the supernova explosion. The comparison of [Fe II] images with other waveband images shows that these dense Fe ejecta are mainly distributed along the southwestern shell just outside the unshocked ${}^{44}$Ti in the interior, supporting the presence of unshocked Fe associated with ${}^{44}$Ti.

arXiv comment38 pages, 12 figures, 4 tables; accepted in ApJ on 2017 Feb. 11

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• Mass-independent analysis of the stable isotopologues of gas-phase titanium monoxide -- TiO
• A Deep Near-Infrared [Fe II]+[Si I] Emission Line Image of the Supernova Remnant Cassiopeia A
• The Temperature and Ionization of Unshocked Ejecta in Cas A
• No evidence of AGN features in the nuclei of Arp 220 from JWST/NIRSpec IFS
• Detection of Pristine Circumstellar Material of the Cassiopeia A Supernova
• Aspherical Supernovae: Effects on Early Light Curves
• X-ray diagnostics of Cassiopeia A's "Green Monster": evidence for dense shocked circumstellar plasma
• He abundance of Dense Circumstellar Clumps in the Cassiopeia A Supernova Remnant
• Titanium hidden in dust
• Near-Infrared Spectroscopy of Dense Ejecta Knots in the Outer Eastern Area of the Cassiopeia A Supernova Remnant