Cassiopeia A: Dust factory revealed via submillimetre polarimetry

Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.11). 09/2008; 394(3). DOI: 10.1111/j.1365-2966.2009.14453.x
Source: arXiv


If Type II supernovae – the evolutionary end points of short-lived, massive stars – produce a significant quantity of dust
(>0.1 M⊙) then they can explain the rest-frame far-infrared emission seen in galaxies and quasars in the first Gyr of the Universe.
Submillimetre (submm) observations of the Galactic supernova remnant, Cas A, provided the first observational evidence for
the formation of significant quantities of dust in Type II supernovae. In this paper, we present new data which show that
the submm emission from Cas A is polarized at a level significantly higher than that of its synchrotron emission. The orientation
is consistent with that of the magnetic field in Cas A, implying that the polarized submm emission is associated with the
remnant. No known mechanism would vary the synchrotron polarization in this way and so we attribute the excess polarized submm
flux to cold dust within the remnant, providing fresh evidence that cosmic dust can form rapidly. This is supported by the
presence of both polarized and unpolarized dust emission in the north of the remnant where there is no contamination from
foreground molecular clouds. The inferred dust polarization fraction is unprecedented (fpol∼ 30 per cent) which, coupled with the brief time-scale available for grain alignment (<300 yr), suggests that supernova dust
differs from that seen in other Galactic sources (where fpol= 2−7 per cent) or that a highly efficient grain alignment process must operate in the environment of a supernova remnant.

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Available from: Steve John Maddox, Sep 27, 2012
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    • "For example, observations of the SNR Cas A result in a few times 10 −5 M ⊙ of hot dust (>170 K) and a few times 10 −2 M ⊙ of warm and cold dust (< 150 K) for the entire SNR (e.g., Arendt et al, 1999; Douvion et al, 2001b; Hines et al, 2004; Krause et al, 2004; Rho et al, 2008). An amount of ∼ 1M ⊙ of dust at a temperature of ∼ 20 K was recently suggested by Dunne et al (2009). Observations with the Herschel Space Observatory result in a resolved cool dust component (∼ 35 K) in the unshocked interior of Cas A with an estimated mass of 7.5 × 10 −2 M ⊙ of dust (Barlow et al, 2010). "
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