Interpreting the transmission windows of distant quasars |
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| Authors: | A Maselli A Ferrara S Gallerani |
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| Institution: | Max-Planck-Institut für Astrophysik, Karl-Schwarzschild Str. 1, 85748 Garching, Germany;Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy;Institute of Physics, Eötvos University, Pazmany P. s. 1/A, 1117 Budapest, Hungary;Osservatorio Astrofisico di Roma, Via di Frascati 33, 00040 Monte Porzio Catone, Italy |
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| Abstract: | We propose the apparent shrinking criterion (ASC) to interpret the spatial extent, R w, of transmitted flux windows in the absorption spectra of high- z quasars. The ASC can discriminate between the two regimes in which R w corresponds either to the physical size, R H ii , of the quasar H ii region or to the distance, R maxw , at which the transmitted flux drops to =0.1 and a Gunn–Peterson (GP) trough appears. In the first case H ii region (HR) regime], one can determine the intergalactic medium mean H i fraction, x H I ; in the second proximity region (PR) regime], the value of R w allows one to measure the local photoionization rate and the local enhancement of the photoionization rate, ΓG , due to nearby/intervening galaxies. The ASC has been tested against radiative transfer+smoothed particle hydrodynamics numerical simulations, and applied to a sample of 15 high- z ( z > 5.8 ) quasar spectra. All sample quasars are found to be in the PR regime; hence, their observed spectral properties (inner flux profile, extent of transmission window) cannot reliably constrain the value of x H i . Four sample quasars show evidence for a local enhancement (up to 50 per cent) in the local photoionization rate possibly produced by a galaxy overdensity. We discuss the possible interpretations and uncertainties of this result. |
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| Keywords: | radiative transfer methods: numerical intergalactic medium quasars: general cosmology: theory large scale structure of Universe |
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