Further observational evidence for a critical ionizing luminosity in active galaxies
Abstract
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 Q_{H I}∼ 10^{56} 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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- October 2017
- DOI:
- 10.1093/mnras/stx1572
- arXiv:
- arXiv:1706.06508
- Bibcode:
- 2017MNRAS.470.4600C
- Keywords:
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- galaxies: active;
- galaxies: fundamental parameters;
- galaxies: ISM;
- quasars: absorption lines;
- radio lines: galaxies;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Accepted by MNRAS