The dust mass in Cassiopeia A from a spatially resolved<i>Herschel</i>analysis

Abstract

Theoretical models predict that core-collapse supernovae (CCSNe) can be efficient dust producers (0.1–1.0 M&lt;inf&gt;&amp;odot;&lt;/inf&gt;), potentially accounting for most of the dust production in the early Universe. Observational evidence for this dust production efficiency is however currently limited to only a few CCSN remnants (e.g. SN 1987A, Crab nebula). In this paper, we revisit the dust mass produced in Cassiopeia A (Cas A), a ∼330-yr old O-rich Galactic supernova remnant (SNR) embedded in a dense interstellar foreground and background. We present the first spatially resolved analysis of Cas A based on &lt;it&gt;Spitzer&lt;/it&gt; and &lt;it&gt;Herschel&lt;/it&gt; infrared and submillimetre data at a common resolution of ∼0.6 arcmin for this 5 arcmin diameter remnant following a careful removal of contaminating line emission and synchrotron radiation. We fit the dust continuum from 17 to 500 μm with a four-component interstellar medium and supernova (SN) dust model. We find a concentration of cold dust in the unshocked ejecta of Cas A and derive a mass of 0.3–0.5 M&lt;inf&gt;&amp;odot;&lt;/inf&gt; of silicate grains freshly produced in the SNR, with a lower limit of ≥0.1–0.2 M&lt;inf&gt;&amp;odot;&lt;/inf&gt;. For a mixture of 50 per cent of silicate-type grains and 50 per cent of carbonaceous grains, we derive a total SN dust mass between 0.4 and 0.6 M&lt;inf&gt;&amp;odot;&lt;/inf&gt;. These dust mass estimates are higher than from most previous studies of Cas A and support the scenario of SN-dominated dust production at high redshifts. We furthermore derive an interstellar extinction map for the field around Cas A which towards Cas A gives average values of &lt;it&gt;A&lt;/it&gt;&lt;inf&gt;V&lt;/inf&gt; = 6–8 mag, up to a maximum of &lt;it&gt;A&lt;/it&gt;&lt;inf&gt;V&lt;/inf&gt; = 15 mag.