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Investigating the dust distribution in galaxy disks with DustPedia and NIKA2

Evans, Ruth 2019. Investigating the dust distribution in galaxy disks with DustPedia and NIKA2. PhD Thesis, Cardiff University.
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This thesis presents the results of a multi-wavelength study into the 3D distribution of dust in the haloes of galaxies. A sample of 31 nearby, edge-on galaxies from the DustPedia database is used to measure the vertical extent of dust above the central plane of galaxy disks at the Herschel PACS 100 & 160 μm and SPIRE 250, 350 & 500 μm bands. I generate a 3D model of the dust to match each galaxy based on the exponential TRIPLEX function, which ensures that line-of-sight effects of inclination can be accounted for when measuring the vertical scaleheight. The brightness profiles of each galaxy are plotted against the models, an inclined thin disk, and the stellar disk to measure the extent to which the dust is distributed. 11 of the sample galaxies show evidence of an extraplanar dust component, with NGC 4222 exhibiting the most extended structure out to 4 kpc. The galaxy maps and models are stacked at each wavelength to increase the sensitivity of the observations over that of a single map. I carry out the same procedure on WISE 3.4 μm data which traces the oldest, and most extended, stellar population for comparison of the dust scaleheight versus stellar scaleheight (Ød/Øs). I find that the dust is more vertically extended than the stellar disk by at least a factor of 1-1.3 at each wavelength. I fit two-component modified blackbody SEDs to the stacked maps, and find a total dust mass for the sample of 9.54+0.90 °2.67£109MØ, an order of magnitude greater than previous estimates. At 500 μm, the flux is in excess of that predicted by the model (assuming Ø = 1.7). These results may indicate the presence of a large cold dust reservoir that has been previously unaccounted for in the literature. I test the dust temperatures required to account for the sub-millimetre excess and find that a very cold dust component of around ª7 K fits well to the data, however the dust mass increases by a further 2 orders of magnitude which is likely to be unphysical. The dust temperature at increasing distance up to 2 kpc from the plane is found increase slightly yet with a relatively flat gradient, in line with radiative transfer models, although large errors at vertical distances greater than ª2 pixels have hindered further analysis of temperature dependence on scale height. I also utilise the first high-resolution 1.2 and 2mmNIKA2 observations of NGC 891 and M99 as science verification for the IMEGIN Large Programme. A twocomponent blackbody spectrum is fitted to the data and dust temperatures and masses estimated. I find a cold to warm dust ratio of 42.6 and 41.3 for the galaxies respectively, and total dust masses of 8.5 ±0.4£107MØ and 1.0 ±0.6£108MØ. The temperatures of the cold and warm components are found to be 20.9 and 34.9 K for NGC 891, and 21.2 and 37.7 K for M99. These values are consistent with the literature, and we do not find evidence of a hidden cold dust component at the NIKA2 wavelengths or any sub-mm/mm excess.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Physics and Astronomy
Subjects: Q Science > QB Astronomy
Uncontrolled Keywords: Galaxies, Galaxy Disks, Edge-On Galaxies, Cosmic Dust, DustPedia, NIKA2
Funders: STFC
Date of First Compliant Deposit: 2 July 2019
Last Modified: 02 Jul 2019 09:07

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