Showing papers by "Robert F. Carswell published in 2004"

The power spectrum of the flux distribution in the Lyman α forest of a large sample of UVES QSO absorption spectra (LUQAS)

Abstract: The flux power spectra of the Lyman a forest from a sample of 27 quasi-stellar objects (QSOs) taken with the high-resolution Ultraviolet Echelle Spectrograph (UVES) on the Very Large Telescope (VLT) are presented. We find a similar fluctuation amplitude at the peak of the '3D' flux power spectrum at k ∼ 0.03 s km -1 as the study by Croft et al. (2002), in the same redshift range. The amplitude of the flux power spectrum increases with decreasing redshift if corrected for the increase in the mean flux level as expected if the evolution of the flux power spectrum is sensitive to the gravitational growth of matter density fluctuations. This is in agreement with the findings of McDonald et al. (2000) at larger redshift. The logarithmic slope of the '3D' flux power spectrum, P F (k), at large scales k < 0.03 s km -1 , is 1.4 ± 0.3, i.e. 0.3 shallower than that found by Croft et al. but consistent within the errors.

The effect of (strong) discrete absorption systems on the Lyman α forest flux power spectrum

Abstract: We demonstrate that the Lyman a forest flux power spectrum of 'randomized' quasi-stellar object (QSO) absorption spectra is comparable in shape and amplitude to the flux power spectrum of the original observed spectra. In the randomized spectra a random shift in wavelength has been added to the observed absorption lines as identified and fitted with VPFIT. At 0.03 s km -1 15 contribute at large scales, k < 0.03 s km -1 . We further show that a fraction of ≥ 15 per cent of the mean flux decrement is contributed by strong absorbers at z ≥ 2.1. Analysis of the flux power spectrum which use numerical simulations with too few strong absorption systems calibrated with the observed mean flux may underestimate the inferred rms fluctuation amplitude and the slope of the initial dark matter power spectrum.

Cosmological evolution of heavy-element and H2 abundances

Abstract: Spectroscopic observations of distant quasars have resulted in the detection of molecular hydrogen in intervening damped Lyman α absorption clouds (DLAs). We use observations compiled from different experimental groups to show that the molecular hydrogen abundance exhibits a dramatic increase over a cosmological time period corresponding to 13 to 24 per cent of the age of the Universe. We also tentatively show that the heavy-element abundances in the same gas clouds exhibit a faster and more well-defined cosmological evolution compared with the general DLA population over the same time baseline. We argue that this latter point is unsurprising, because the general DLA population arises in a wide variety of galaxy types and environments, and thus a spans broad range of ISM gas-phases and abundances at the same cosmic time. DLAs exhibiting H2 absorption may therefore circumvent this problem, efficiently identifying a narrower class of objects, and provide a more sensitive probe of cosmological chemical evolution.