Polarization and Dust Properties of Newly-Formed Dust in Cassiopeia A

Principal Investigator

Jeonghee Rho

Proposal ID

07_0047

Category

ISM_AND_CIRCUMSTELLAR_MATTER

Keywords

• CHEMICAL ABUNDANCES
• DUST
• SUPERNOVA REMNANTS
• SUPERNOVAE

Abstract

The large reservoirs of dust observed in some high redshift galaxies are difficult to explain without core- collapse supernovae (CCSNe) as a dominant dust production source. Theoretical studies tend to support efficient dust condensation in CCSNe, but the number of CCSNe with robust detections of >0.1 Msun of dust remains scarse (SN1987A, Cas A, Crab Nebula, and G54.1+0.3). Our lack of knowledge on the composition of freshly produced grains make supernova dust masses uncertain by factors of a few. The average size of supernova dust will furthermore strongly affect the fraction of grains that will survive supernova shocks before mixing with pre-existing interstellar dust. Larger grains would be less susceptible to shock processing, but the absence of constraints on the average supernova grain size make it impossible to anticipate the net dust production efficiency of CCSNe. Dust polarisation levels sensitively depend on the size, shape and composition of dust grains, and provide a unique way of constraining the nature of supernova dust species. Previous polarization observations with SCUBA-pol at 850 micron covered the northern part of Cas A and a large fractional polarization originates from the cold dust within the SNR, indicating a highly efficient alignment mechanism for the grains. We propose SOFIA HAWC+ polarimetric observations of the Cas A SNR at 154 and 214 micron targeting the peak of the dust SED emission, which covers most of the SNR. Cas A is an obvious target for dust polarisation studies with the recent detection of a large dust reservoir (0.2- 0.6 Msun) and polarization has previously been detected at 850 micron. The characterization of grain composition will allow us to quantify the exact mass of freshly condensed grains in Cas A and will provide invaluable constraints on the carbon yields for nucleosynthesis models of progenitors with initial masses of 25 Msun. The inferred grain size will be crucial to determine the resistance of supernova dust to shocks and to infer the net supernova dust mass that is eventually injected into the ISM, which is vital to understand whether CCSNe are able to account for the large dust masses detected in high-redshift galaxies.