Clustering Properties of Low-Redshift QSO Absorption Line Systems Towards the Galactic Poles
Abstract
The clustering properties of a three-dimensional sample of low-redshift absorption line systems concentrated towards the North and South Galactic Poles, and obtained with the Faint Object Spectrograph of the Hubble Space Telescope, are examined. There are 588 total absorption lines detected in the complete sample from 13 QSOs. There are 339 lines identified as Ly α, 19 of which belong to heavy-element systems. There are also five likely C scIV doublets and one Mg scII doublet, for which the Ly-alpha line is not accessible. There is significant evidence, based upon the cumulative pair distributions, that the low-redshift Ly-alpha lines are not randomly distributed, regardless of the scale or form of the clustering. The line-of-sight correlation function shows a positive and significant clustering signal on scales of 2.5 to 5 Mpc/h, and an amplitude of 1.00 +/-0.37, for systems with rest equivalent width, W, exceeding 0.24A. Most of this signal can be accounted for by a small number of Ly-alpha 'clumps', each containing about 5 systems, and spanning about 20 Mpc/h. There is also significant evidence for clustering on scales up to 10 Mpc/h for Ly-alpha systems with W > 0.1A. The clustering amplitude on these scales appears to grow as the limiting equivalent width of the sample is raised. The fraction of Ly-alpha lines that may be clustered in the same way as the heavy-element systems detected at higher redshifts is about 40%, for systems with W > 0.24A. There is no clear evidence that the Ly-alpha systems are distributed in redshift 'spikes' like the galaxies, however, there is some evidence for an 83 Mpc/h 'periodicity' in the distribution of the higher equivalent width systems. The three-dimensional Ly-alpha radial correlation function shows no significant departures from a random sample at any scale or using any limiting equivalent width. These results are in broad agreement with the idea that the low-redshift Ly-alpha forest is composed of two populations (or a set of populations), one which is closely associated with the same structures traced by luminous galaxies and heavy-element systems, and one which is more diffuse and occupies the less dense regions of space.
- Publication:
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Ph.D. Thesis
- Pub Date:
- 1997
- Bibcode:
- 1997PhDT.........3V
- Keywords:
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- Physics: Astronomy and Astrophysics