Further observational evidence for a critical ionizing luminosity in active galaxies

Journal article

We report the results of a survey for H I 21-cm absorption at redshifts of z ≳ 2.6 in a new sample of radio sources with the Green Bank and Giant Metrewave Radio Telescopes. From a total of 25 targets, we report zero detections in the 16 for which optical depth limits could be obtained. Based upon the detection rate for z ≥ 0.1 associated absorption, we would expect approximately four detections. Of the 11 which have previously not been searched, there is sufficient source-frame optical/ultraviolet photometry to determine the ionizing photon rate for four. Adding these to the literature, the hypothesis that there is a critical rate of QHI∼1056 ionizing photons per second (a monochromatic λ = 912 Å luminosity of LUV ∼ 1023 W Hz−1) is now significant at ≈7σ. This reaffirms our assertion that searching z ≳ 3 active galaxies for which optical redshifts are available selects sources in which the ultraviolet luminosity is sufficient to ionize all of the neutral gas in the host galaxy.

Authors: Curran, S; Hunstead, R; Johnston, H; Whiting, M; Sadler, E

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Oxford University Press
• Journal: Monthly Notices of the Royal Astronomical Society
• Volume: 470
• Issue: 4
• Pages: 4600-4607
• Publication date: 2017-06-22
• Acceptance date: 2017-06-20
• DOI: 10.1093/mnras/stx1572
• EISSN: 1365-2966
• ISSN: 0035-8711
• Language: English
• Keywords: galaxies: fundamental parameters; radio lines: galaxies; galaxies: ISM; quasars: absorption lines; galaxies: active