Search for dark galaxies through the ages

Auld, Robbie Richard 2007. Search for dark galaxies through the ages. PhD Thesis, Cardiff University.

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Abstract

The work I have performed for this thesis covers a number of different areas of astronomy. My work on the LSBs is an in-depth exploration of the gas morphology and kinematics of these unusual objects. The focus is on the star forming abilities of the galaxy sample, but the HI observations also reveal a rich variety of gas morphology and motion, which are not necessarily apparent at other wavelengths. As well as being LSB, they are neutral gas-rich objects. As such they are more suited to being detected by HI surveys than by optical surveys. The Arecibo Galaxy Environment Survey (AGES) is a survey that expects to detect a large number of this type of galaxy and a large proportion of the thesis has been dedicated to my involvement with the survey. This has included designing and implementing the observing strategy, testing the data reduction pipeline, producing the final data, testing their quality and examining the efficiency of the survey detection methods. I have demonstrated some uses the AGES data can be put to from discovering hitherto undetected galaxies, through measuring the cosmic distribution of neutral hydrogen, to evaluating the cosmic significance of dark galaxies. The last point forms the central theme throughout the thesis. Of the 69 detections made by AGES in the first two datacubes, 55 do not have previous Hi measurements and 26 are previously uncatalogued. An Hi mass function (HIMF) was produced from the first galaxies detected by AGES. The best fit line to the data was a Schechter function with the parameters: a = -1.28 0.17, = 0.0076 0.0027 and M* = 7.7 1.8 x 109 M0. Using the HIMF the calculated value for the space density of neutral hydrogen was found to be pni = 7.5q3 x 107MQ Mpc-3, which is consistent with previous measurements. The overall contribution of HI to the Universal energy density was calculated from this value and found to be Qhi = 4.1 J x 10-4, confirming previous measurements of this value. Assuming the two candidates are indeed optically dark, based on this value the contribution of dark galaxies was calculated to be 4% to their respective mass bins, and less than 0.5% overall. The number density was found to be ndark 6.6 x 10-4 Mpc-3. Hence it would appear that dark galaxies are not numerous enough nor of substantial mass to be able to account for the 'missing mass' or to be able to fully represent the high number of dark matter haloes produced by CDM simulations.

Item Type:	Thesis (PhD)
Status:	Unpublished
Schools:	Physics and Astronomy
Subjects:	Q Science > QB Astronomy
ISBN:	9781303209345
Date of First Compliant Deposit:	30 March 2016
Last Modified:	25 Jul 2024 15:26
URI:	https://orca.cardiff.ac.uk/id/eprint/54594

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