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Unravelling the BADGRS Paradox – Probing the blue and dusty gas-rich sources in the Herschel ATLAS using integral field spectroscopy

Ballard, Zoe Ann 2021. Unravelling the BADGRS Paradox – Probing the blue and dusty gas-rich sources in the Herschel ATLAS using integral field spectroscopy. MPhil Thesis, Cardiff University.
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We present integral field spectroscopy of a pilot sample of Blue And Dusty Gas-Rich Sources, or BADGRS, discovered in the first dust-selected survey from the Herschel ATLAS. These BADGRS make up over 50% of the local volume of H-ATLAS and have puzzlingly paradoxical properties; they are blue but dusty, with bright UV emission despite high dust masses; they are hot but cold, with lower than average dust temperatures despite bright UV emission; they are young but old, with blue colours and high gas fractions, indicating a young population, whilst having high dust masses and being metal rich, indicating an older population; and they are metal rich but CO poor, they have low ratios of molecular hydrogen mass over dust mass, despite being metal rich in their central regions. We observe this pilot sample of BADGRS with the KOALA integral field unit, and describe in detail the data reduction and calibration process carried out; custom scripts were created and parts of the existing AAO pipeline adapted to carry out the data reduction for KOALA and solve issues found with the data, and create the highest quality data cubes possible. We investigate the dust attenuation law of one of the pilot BADGRS, UGC 9215, with the blue but dusty paradox in mind. We fit the spectra in each special bin to extract emission line fluxes. We apply a model using the Balmer emission lines H-alpha, H-beta, H-gamma and H-delta, and their intrinsic line ratios, to constrain the slope, delta, of the Salim et al. (2018) modified reddening law. We find a delta of -0.25 for UGC 9215, steeper than the starburst attenuation curve of Calzetti et al. (2000), but shallower than similar galaxies in the Salim et al. (2018) sample. A shallow attenuation curve can indicate a more complex, clumpy dust geometry, as well as, in galaxies that are dusty and star forming, the presence of a high fraction of unobscured OB stars and regions where the galaxy has become transparent to UV radiation. These findings may indicate that the blue but dusty BADGRS are not paradoxical at all, but have merely been caught in a stage of their evolution where they have clumpy dust, and regions that are transparent to the UV radiation of the young OB stars present.

Item Type: Thesis (MPhil)
Status: Unpublished
Schools: Physics and Astronomy
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Uncontrolled Keywords: astronomy, astrophysics, galaxies, dust, dust attenuation laws, integral field spectroscopy, integral field unit, KOALA IFU, BADGRS, optical spectroscopy, emission lines, data reduction
Date of First Compliant Deposit: 6 October 2021
Last Modified: 04 Aug 2022 01:34

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