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The distribution of gas and dark matter in galaxies

Event Type
Department of Astronomy
134 Astronomy
Aug 24, 2023   12:00 pm  
Di Wen, Groningen University
Originating Calendar
Astronomy Colloquium Speaker Calendar

Studies of nearby galaxies have revealed a clear tendency for atomic hydrogen to be distributed in a flatter and more extended disk than CO emission. I present a Bayesian method to derive constraints on the HI distributon for galaxies from the EDGE-CALIFA sample where high resolution CO rotation curves are available. To test our method we apply it to galaxies in the THINGS sample where high-resolution rotation curves and radial profiles are available. We construct integrated HI spectra from the THINGS data and from simplified, axisymmetric model fits to examine our ability to recover the original profiles from the spectra.

Anomalous flux ratios between strongly lensed images can provide a key test of the dark matter sub-halo population, and hence the nature of dark matter. However, the observed anomalous flux ratios at radio frequencies can also be the result of systematics associated with our lack of knowledge about the source structure, source variability, propagation effects and microlensing of compact objects within the lensing galaxy. To rule out these effects for a quadruple lens sample, I present preliminary results from our monitoring and high angular resolution imaging at 15 GHz. We find evidence for a frequency-dependent flux ratio in at least one case, likely from free-free absorption within the lensing galaxy, and scattering of the lensed images by the ionized medium in the lens.

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