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18th of April 2018
ATNF Colloquium
Galaxy Evolution with HI Intensity Mapping
by Laura Wolz (University of Melbourne)
Abstract: Intensity mapping surveys of neutral hydrogen (HI) are a novel way to measure the large scale matter distribution of our Universe and thus constrain cosmological parameters describing the Universal expansion. The next generation of radio telescopes and interferometers are being designed and built to optimise the detection of the HI line at low spatial resolution allowing efficient mapping of large volumes. The impact of instrumental systematics of radio observations on cosmological measurements can be significantly reduced by cross-correlating the HI signal with galaxy surveys. The cross-correlation also offers an innovative way to statistically detect the average HI content of the optically-selected galaxy sample since the noise on the cross-power spectrum measurement scales with the galaxy HI temperature. I will give an introduction into the intensity mapping technique and prospects of the on-going and future experiments, such as the Square Kilometre Array (SKA). I will review the latest HI signal detection in data taken by the Parkes telescope in cross-correlation with the 2dF galaxy survey. I will present studies on the potential of future intensity mapping experiments in constraining galaxy evolution processes, such as the global HI density as well as HI scaling relations in galaxies. I will show how the SKA pathfinder experiments can detect the relevant scales of the cross-power spectrum and probe the HI content of medium redshift galaxies to faint for direct detection with radio telescopes.

The figure above shows the neutral hydrogen (HI) intensity maps taken by the 21cm Multi-Beam receiver of the Parkes telescope at 0.057 < z < 0.098 covering ~1,300 sqdeg. The upper two panel show the data before and after foreground removal and the lower panel presents the inverse noise weight approximately proportional to the integration time per pixel. The cross-correlation of the HI maps with data of the 2dF Galaxy Redshift Survey indicates lower clustering amplitudes on smaller scales than expected, particularly HI seems to avoid red galaxies. (Image credit: Anderson et al (arXiv:1710.00424))

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