Mikkel Juhl Hobert Master's Defense – University of Copenhagen

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Mikkel Juhl Hobert Master's Defense

Title: The role of core collapse supernovae in the context of dust production in the early universe.

Supervisor: Darach Watson

Abstract:

Recent research based on infrared observations of high-z galaxies have confirmed the presence of significant amounts of dust in the early universe, only a few hundred million years after the onset of the first stars. This poses a problem to our current physical understanding of the environmental circumstances under which the dust is formed, since it suggests that the dust must have been produced and injected into the interstellar medium at an incredibly fast rate. Because of their lifetimes of only a few million years, core collapse supernovae of high mass stars may play a crucial role in the context of early dust production. So far, however, observations have failed to detect the necessary dust yields in order to explain the large dust masses we see in the young galaxies. It wasn't until quite recently that a massive dust reservoir of up to ~1 Msun of cold dust was observed in the SN1987A in the Large Magellanic Cloud using far infrared measurements  from the Herschel Space Observatory.

Motivated by this recent observation, in this project I aim to study a sample of young type II supernova remnants in the Magellanic Clouds. My goal is to estimate the largest possible amount of cold dust that can possibly have been produced by each remnant, mainly based on the far infrared and sub millimeter surveys done by the Herschel Open Time Key Programme HERITAGE, with the inclusion of mid infrared observations from the MIPS instrument on the Spitzer Space Telescope.

My sample consists of the young and relatively isolated core collapse supernova remnants, N11L, N23, N132D, 0N49 and N63A with the inclusion of the previous results of SN1987A in the Large Magellanic Cloud. By performing careful measurements of each remnant using aperture photometry, I extract the flux densities for each remnant over the mid and far infrared and sub millimeter regimes. I then fit the spectral energy distributions with a two component modified blackbody spectrum for three distinct dust models of silicates and amorphous carbon. Using the ATCA, SHASSA and MAGMA surveys of neutral, ionized and molecular hydrogen and local dust-to-gas mass ratios in order to account for the swept-up dust mass from the interstellar medium.

I find that the average cold dust yield per supernova is still fairly uncertain. At first sight, the three remnants N11L, N23 and N132D does not appear to contain significant amounts of cold dust with Md/Msun ~ 0. The total dust masses in N49 and N63A are upwards of Md/Msun ~ 10-20. Using the gas surveys I suspect that the dust masses observed in N49 may be mostly swept-up material. N63A, however, is peculiar and the high flux densities may partly be due to significant contributions from synchrotron radiation and atomic lines, neither which I accounted for.

All in all I find that the total dust masses strongly depend on the chosen dust model and that the measurements are highly limited by difficulties in the background subtraction. However, the data weakly suggests that, on average, that core collapse supernovae may not by themselves be the key contributors to dust in the early universe.

Censor: Max Stritzinger, Aarhus University

Link to thesis >>