Ionization of the atomic gas in redshifted radio sources
| Autor: | Matthew Whiting, Elaine M. Sadler, Richard W. Hunstead, R. Athreya, Helen M. Johnston, James R. Allison, S. J. Curran |
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| Rok vydání: | 2019 |
| Předmět: |
Physics
Giant Metrewave Radio Telescope Absorption spectroscopy 010308 nuclear & particles physics FOS: Physical sciences Astronomy and Astrophysics Quasar Astrophysics::Cosmology and Extragalactic Astrophysics Astrophysics Astrophysics - Astrophysics of Galaxies 01 natural sciences Redshift Galaxy Space and Planetary Science Astrophysics of Galaxies (astro-ph.GA) Ionization 0103 physical sciences Electromagnetic shielding Absorption (electromagnetic radiation) 010303 astronomy & astrophysics Astrophysics::Galaxy Astrophysics |
| Zdroj: | Monthly Notices of the Royal Astronomical Society. 484:1182-1191 |
| ISSN: | 1365-2966 0035-8711 |
| DOI: | 10.1093/mnras/stz038 |
| Popis: | We report the results of a survey for HI 21-cm absorption at z < 0.4 in a new sample of radio sources with the Giant Metrewave Radio Telescope. Of the 11 sources for which there are good data, we obtain zero detections, where four are expected upon accounting for the ionising photon rates and sensitivity. Adding these to the previously published values, we confirm that the non-detection of 21-cm absorption in active sources at high redshift is due to photo-ionisation of the gas rather than excitation by 21-cm photons (significant at 6.09 sigma and 2.90 sigma, respectively). We also confirm a strong correlation between the absorption strength and the reddening of the source, suggesting that dust plays a significant role in shielding the gas from the ambient ultra-violet field. An anti-correlation between the 21-cm detection rate and the radio turnover frequency is also found, which runs contrary to what is expected on the basis that the higher the turnover frequency, the more compact the source. It is, however, consistent with the hypothesis that the turnover frequency is related to the electron density, supported by a correlation between the turnover frequency and ionising photon rate. Accepted by MNRAS |
| Databáze: | OpenAIRE |
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