An improved measurement of the flux distribution of the Ly-alpha forest in QSO absorption spectra: the effect of continuum fitting, metal contamination and noise properties

-S. Kim, T.; S. Bolton, J.; Viel, M.; G. Haehnelt, M.; F. Carswell, R.

Abstract

We have performed an extensive Voigt profile analysis of the neutral hydrogen (HI) and metal absorption present in a sample of 18 high resolution, high signal-to-noise QSO spectra observed with VLT/UVES. We use this analysis to separate the metal contribution from the HI absorption and present an improved measurement of the flux probability distribution function (PDF) due to HI absorption alone at = 2.07, 2.52, and 2.94. The flux PDF is sensitive to the continuum fit in the normalised flux range 0.8 < F < 1.0 and to metal absorption at 0.2 < F < 0.8. Our new measurements of the flux PDF due to HI absorption alone are systematically lower at 0.2 < F < 0.8 by up to 30% compared to the widely used measurement of McDonald et al. (2000), based on a significantly smaller sample of Keck/HIRES data. This discrepancy is probably due to a combination of our improved removal of the metal absorption and cosmic variance, since variations in the flux PDF between different lines-of-sight are large. The HI effective optical depth at 1.7 < z < 4 is best fit with a single power law, (0.0023 +-0.0007) (1+z)^(3.65 +- 0.21), in good agreement with previous measurements from comparable data. As also found previously, the effect of noise on the flux distribution is not significant in high resolution, high signal-to-noise data.

Citation

-S. Kim, T., S. Bolton, J., Viel, M., G. Haehnelt, M., & F. Carswell, R. (2007). An improved measurement of the flux distribution of the Ly-alpha forest in QSO absorption spectra: the effect of continuum fitting, metal contamination and noise properties. Monthly Notices of the Royal Astronomical Society, 382(4), 1657–1674. https://doi.org/10.1111/j.1365-2966.2007.12406.x

• Journal Article Type: Article
• Acceptance Date: Sep 3, 2007
• Online Publication Date: Nov 26, 2007
• Publication Date: 2007-12
• Deposit Date: Sep 16, 2019
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 382
• Issue: 4
• Pages: 1657–1674
• DOI: https://doi.org/10.1111/j.1365-2966.2007.12406.x
• Keywords: Astrophysics
• Public URL: https://nottingham-repository.worktribe.com/output/2462346
• Publisher URL: https://academic.oup.com/mnras/article/382/4/1657/1147101