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Title:
Freshly Formed Dust in the Cassiopeia A Supernova Remnant as Revealed by the Spitzer Space Telescope
Authors:
Rho, J.; Kozasa, T.; Reach, W. T.; Smith, J. D.; Rudnick, L.; DeLaney, T.; Ennis, J. A.; Gomez, H.; Tappe, A.
Affiliation:
AA(Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125; , .), AB(Department of Cosmosciences, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan.), AC(Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125; , .), AD(Steward Observatory, 933 North Cherry Avenue, Tucson, AZ 85712.), AE(Department of Astronomy, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455.), AF(MIT Kavli Institute, 77 Massachusetts Avenue, Room NE80-6079, Cambridge, MA 02139.), AG(Department of Astronomy, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455.), AH(School of Physics and Astronomy, University of Wales, Cardiff, Wales, UK.), AI(Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125; , .; Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138.)
Publication:
The Astrophysical Journal, Volume 673, Issue 1, pp. 271-282. (ApJ Homepage)
Publication Date:
01/2008
Origin:
UCP
ApJ Keywords:
ISM: Dust, Extinction, Stars: Supernovae: General, ISM: Supernova Remnants
DOI:
10.1086/523835
Bibliographic Code:
2008ApJ...673..271R

Abstract

We performed Spitzer Infrared Spectrograph mapping observations covering nearly the entire extent of the Cassiopeia A supernova remnant (SNR), producing mid-infrared (5.5-35 μm) spectra every 5"-10". Gas lines of Ar, Ne, O, Si, S, and Fe, and dust continua were strong for most positions. We identify three distinct ejecta dust populations based on their continuum shapes. The dominant dust continuum shape exhibits a strong peak at 21 μm. A line-free map of 21 μm peak dust made from the 19-23 μm range closely resembles the [Ar II], [O IV], and [Ne II] ejecta-line maps, implying that dust is freshly formed in the ejecta. Spectral fitting implies the presence of SiO2, Mg protosilicates, and FeO grains in these regions. The second dust type exhibits a rising continuum up to 21 μm and then flattens thereafter. This ``weak 21 μm'' dust is likely composed of Al2O3 and C grains. The third dust continuum shape is featureless with a gently rising spectrum and is likely composed of MgSiO3 and either Al2O3 or Fe grains. Using the least massive composition for each of the three dust classes yields a total mass of 0.020 Msolar. Using the most massive composition yields a total mass of 0.054 Msolar. The primary uncertainty in the total dust mass stems from the selection of the dust composition necessary for fitting the featureless dust as well as 70 μm flux. The freshly formed dust mass derived from Cas A is sufficient from SNe to explain the lower limit on the dust masses in high-redshift galaxies.
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