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Abstract
The origin of interstellar dust in galaxies is poorly understood, particularly the relative contributions from supernovae and the cool stellar winds of low-intermediate mass stars. Here, we present Herschel PACS and SPIRE photometry at 70-500um of the historical young supernova remnants: Kepler and Tycho; both thought to be the remnants of Type Ia explosion events. We detect a warm dust component in Kepler's remnant with T = 82K and mass 0.0031Msun; this is spatially coincident with thermal X-ray emission optical knots and filaments, consistent with the warm dust originating in the circumstellar material swept up by the primary blast wave of the remnant. Similarly for Tycho's remnant, we detect warm dust at 90K with mass 0.0086Msun. Comparing the spatial distribution of the warm dust with X-rays from the ejecta and swept-up medium, and Ha emission arising from the post-shock edge, we show that the warm dust is swept up interstellar material. We find no evidence of a cool (25-50 K) component of dust with mass >0.07Msun as observed in core-collapse remnants of massive stars. Neither the warm or cold dust components detected here are spatially coincident with supernova ejecta material. We compare the lack of observed supernova dust with a theoretical model of dust formation in Type Ia remnants which predicts dust masses of 0.088(0.017)Msun for ejecta expanding into surrounding densities of 1(5)cm-3. The model predicts that silicon- and carbon-rich dust grains will encounter the interior edge of the observed dust emission at 400 years confirming that the majority of the warm dust originates from swept up circumstellar or interstellar grains (for Kepler and Tycho respectively). The lack of cold dust grains in the ejecta suggests that Type Ia remnants do not produce substantial quantities of iron-rich dust grains and has important consequences for the 'missing' iron mass observed in ejecta.
Highlights
Dust in galaxies is thought to be produced by in the stellar winds of both low-intermediate mass (LIM) Asymptotic Giant Branch (AGB) stars (e.g. Gehrz 1989; Whittet 2003; Sargent et al 2010) and, to an unknown extent, by massive stars (Hofner 2009; Gomez et al 2010; Andrews et al 2011; Gall, Hjorth & Anderson 2011a)
We confirm a previously known warm dust component in Kepler’s remnant with Td = 82+−46 K, somewhat cooler than the dust previously detected by Spitzer and Infrared Space Observatory (ISO), and revise the dust mass to ∼ (3.1+−00..86) × 10−3 M⊙
The warm dust is spatially coincident with thermal X-ray emission and optical knots and filaments on the outer edges of the shockfront, confirming that this component originates in the material swept up by the primary blast-wave
Summary
Dust in galaxies is thought to be produced by in the stellar winds of both low-intermediate mass (LIM) Asymptotic Giant Branch (AGB) stars (e.g. Gehrz 1989; Whittet 2003; Sargent et al 2010) and, to an unknown extent, by massive stars (Hofner 2009; Gomez et al 2010; Andrews et al 2011; Gall, Hjorth & Anderson 2011a). Recent observations with the Balloonborne Large Aperture Submillimeter Telescope, BLAST and the Herschel Space Observatory showed it was difficult to distinguish between cold dust in the remnant and cold dust from intervening interstellar clouds using photometry alone (Sibthorpe et al 2010; Barlow et al 2010) These studies revealed a new cool component of dust in Cas A with mass 0.08 M⊙ at ∼ 35 K, yet even if all of the dust survived the passage through the shock, the dust mass is about one order of magnitude lower than necessary to solve the dust budget problem.
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