Browsing by Author "Hoyle, Fiona"
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Item Open Access The H I mass function and velocity width function of void galaxies in the Arecibo Legacy Fast ALFA Survey.(2014) Hoyle, Fiona; Moorman, Crystal M.We measure the H i mass function (HIMF) and velocity width function (WF) across environments over a range of masses, 7.2Item Open Access An observational signal of the void shape correlation and its link to the cosmic web(10/04/2015) Hoyle, Fiona; Hoyle, FionaThe shapes of cosmic voids are prone to distortions caused by external tidal forces since their low densities imply a lower internal resistance. This susceptibility of the void shapes to tidal distortions makes them useful as indicators of large-scale tidal and density fields, despite the practical difficulty in defining them. Using the void catalog constructed by Pan et al. from the Seventh Data Release of the Sloan Digital Sky Survey (SDSS DR7), we detect a clear 4s signal of spatial correlations of the void shapes on a scale of - 20 h 1 Mpc and show that the signal is robust against the projection of the void shapes onto the plane of sky. By constructing a simple analytic model for the void shape correlation, within the framework of tidal torque theory, we demonstrate that the void shape correlation function scales linearly with the two-point correlation function of the linear density field. We also find direct observational evidence for the cross-correlation of the void shapes with the large-scale velocity shear field that was linearly reconstructed by Lee et al. from SDSS DR7. We discuss the possibility of using the void shape correlation function to break the degeneracy between the density parameter and the power spectrum amplitude and to independently constrain the neutrino mass as well.Item Open Access Photometric properties of void galaxies in the Sloan Digital Sky Survey.(2012) Hoyle, Fiona; Hoyle, FionaUsing the sample presented by Pan et al., we analyse the photometric properties of 88 794 void galaxies and compare them to galaxies that reside in higher density environments with the same absolute magnitude distribution as the void galaxies. We analysed the Sloan Digital Sky Survey Data Release 7 and found a total of 1054 dynamically distinct voids with radius larger than 10 h−1 Mpc. The voids are not empty, but are underdense, with δρ/ρ < −0.9 in their centres. In this paper, we study the photometric properties of these void galaxies. We look at the u − r colours as an indication of star formation activity and the inverse concentration index as an indication of galaxy type. We find that void galaxies are statistically bluer than galaxies found in higher density environments with the same magnitude distribution. We examine the colours of the galaxies as a function of magnitude, dividing the galaxies into bright, medium, faint and dwarf groups, and we fit each colour distribution with a double-Gaussian model for the red and blue subpopulations. As we move from bright to dwarf galaxies, the population of red galaxies steadily decreases and the fraction of blue galaxies increases in both voids and walls; however, the fraction of blue galaxies in the voids is always higher and bluer than in the walls. We also split the void and wall galaxies into samples depending on galaxy type, as measured by the inverse concentration index. We find that late-type void galaxies are bluer than late-type wall galaxies and the same holds for early galaxies. We also find that early-type and dwarf void galaxies are blue in colour. We also study the properties of void galaxies as a function of their distance from the centre of the void. We find very little variation in the properties, such as magnitude, colour and type, of void galaxies as a function of their location in the void. The only exception is that the dwarf void galaxies may live closer to the centres of voids. As shown by Pan et al., the centres of voids have very similar density contrast and hence all void galaxies live in very similar density environments, which may explain the lack of variation of galaxy properties with location within voids.