The Giant Gemini GMOS survey of zem > 4.4 quasars – I. Measuring the mean free path across cosmic time

Worseck, G.; Prochaska, J.X.; O'Meara, J.; Becker, G.; Ellison, S.; Lopez, S.; Meiksin, A.; Ménard, B.; Murphy, M.; Fumagalli, M.

Abstract

We have obtained spectra of 163 quasars at zem > 4.4 with the Gemini Multi Object Spectrometers, the largest publicly available sample of high-quality, low-resolution spectra at these redshifts. From this data set, we generated stacked quasar spectra in three redshift intervals at z ∼ 5 to model the average rest-frame Lyman continuum flux and to assess the mean free path λ912mfp of the intergalactic medium to H I-ionizing radiation. At mean redshifts zq = (4.56, 4.86, 5.16), we measure λ912mfp=(22.2±2.3,15.1±1.8,10.3±1.6)h−170 proper Mpc with uncertainties dominated by sample variance. Combining our results with measurements from lower redshifts, the data are well modelled by a power law λ912mfp=A[(1+z)/5]η with A=(37±2)h−170 Mpc and η = −5.4 ± 0.4 at 2.3 < z < 5.5. This rapid evolution requires a physical mechanism – beyond cosmological expansion – which reduces the effective Lyman limit opacity. We speculate that the majority of H I Lyman limit opacity manifests in gas outside galactic dark matter haloes, tracing large-scale structures (e.g. filaments) whose average density and neutral fraction decreases with cosmic time. Our measurements of the mean free path shortly after H I reionization serve as a valuable boundary condition for numerical models thereof. Our measured λ912mfp≈10 Mpc at z = 5.2 confirms that the intergalactic medium is highly ionized without evidence for a break that would indicate a recent end to H I reionization.

Citation

Worseck, G., Prochaska, J., O'Meara, J., Becker, G., Ellison, S., Lopez, S., …Fumagalli, M. (2014). The Giant Gemini GMOS survey of zem > 4.4 quasars – I. Measuring the mean free path across cosmic time. Monthly Notices of the Royal Astronomical Society, 445(2), 1745-1760. https://doi.org/10.1093/mnras/stu1827

• Journal Article Type: Article
• Publication Date: Dec 1, 2014
• Deposit Date: Oct 17, 2014
• Publicly Available Date: Oct 17, 2014
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Royal Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 445
• Issue: 2
• Pages: 1745-1760
• DOI: https://doi.org/10.1093/mnras/stu1827
• Keywords: Galaxies: formation, Intergalactic medium, Quasars: absorption lines, Dark ages, Reionization, First stars, Diffuse radiation.
• Public URL: https://durham-repository.worktribe.com/output/1443629