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Dust and Gas in Different Galactic Environments

Daniela Pinheiro Goncalves

Doctor of Philosophy 2013
Graduate Department of Astronomy and Astrophysics, University of Toronto

This thesis encompasses the study of the mid-infrared (IR) dust properties in diffuse high latitude cirrus and in the dense environments of supernova remnants (SNRs) in the plane of our Galaxy. Unlike the well known emission properties of dust grains in the diffuse ISM in the far-IR and submillimeter, the mid-IR spectrum is still relatively unconstrained. We extend the correlation of dust emission with H I column densities to mid-IR wavelengths and look for evidence of variations in the emissivity of dust associated with local and halo gas. This is accomplished by spatially correlating the IR maps from the IRIS/IRAS survey at 12, 25, 60 and 100 μm with H I column density maps inferred from 21-cm line emission observations obtained with the GBT (at a 9' resolution). We find that IVCs (halo clouds thought to be part of the Galactic fountain) show color ratios consistent with a dust evolution scenario in which large dust grains are shattered into smaller ones (VSGs). The low 12 μm emission found suggests a reduced abundance of PAHs in IVCs. We also address the IR extragalactic emission seen in our residual maps and quantify its power spectrum behaviour. Continuing with the mid-IR theme, we conducted a comprehensive study of the morphology and energetics of SNRs in the plane of our Galaxy. We make use of the Spitzer MIPSGAL (at 24 and 70 μm) and GLIMPSE (at 8 μm) surveys to detected infrared counterparts to SNR candidates in Green’s catalog. We find that a third of the sample shows IR emission and calculate the corresponding fluxes. We explore the relation between IR colors to place constraints on the different IR SNRs emission mechanisms. Aided by archival radio data, we find that most candidates detected show IR-to-radio ratios consistent with SNRs with a few exceptions displaying ratios seen in H II regions. Finally, we explore the connection between the IR and the high-energy X-ray emission of SNRs and find a good morphological association between the 24 μm emission and the X-ray features in younger remnants. The IR power is often greater.

Reproduced with permission. library@astro.utoronto.ca
August 16, 2013