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arXiv · 1706.06508

Further Observational Evidence for a Critical Ionising Luminosity in Active Galaxies

S. J. Curran·R. W. Hunstead·H. M. Johnston·M. T. Whiting·E. M. Sadler·J. R. Allison·C. Bignell
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Abstract

We report the results of a survey for HI 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/ultra-violet photometry to determine the ionising photon rate for four. Adding these to the literature, the hypothesis that there is a critical rate of logQ = 56 ionising photons per second is now significant at ~7 sigma. This reaffirms our assertion that searching z > 3 active galaxies for which optical redshifts are available selects sources in which the ultra-violet luminosity is sufficient to ionise all of the neutral gas in the host galaxy.

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S. J. Curran, R. W. Hunstead, H. M. Johnston, M. T. Whiting, E. M. Sadler, J. R. Allison, C. Bignell. 2017-06-20. Further Observational Evidence for a Critical Ionising Luminosity in Active Galaxies. https://doi.org/10.1093/mnras/stx1572

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