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One of the major challenges in observational cosmology is related to the redshift evolution of the average hydrogen ionization in the Universe. In order to probe the ionization level of the IGM and the ionization capabilities of bright QSOs at z=4, we have selected a sample of 2508 QSOs from the SDSS survey (DR14) at 3.6<z<4.6 and -29.0<M1450<-26.0. Starting from UV/optical rest-frame spectra of the whole QSO sample, we estimate the escape fraction and free path individually for each of them. We calculate the Lyman Continuum (LyC) escape fraction as the flux ratio blue-ward (~900 A rest-frame) and red-ward (~930 A rest-frame) of the Lyman limit. We then obtain the probability distribution function (PDF) of the individual free paths of the QSOs in the sample and study its evolution in luminosity and redshift, comparing our results with the ones found in literature so far. We find a lower limit to the mean LyC escape fraction of 0.49, in agreement with the values obtained for both brighter and fainter sources at the same redshift. We show that the free paths of ionizing photons are characterized by a skewed distribution function peaked at low values, with an average of ~49-59 proper Mpc at z~4, after excluding possible associated absorbers. This value is larger than the one obtained at the same redshift by many authors in the literature using different techniques. Finally, we also find that the redshift evolution of this parameter results to be possibly milder than previously thought. Our new determination of the mean free path at z~4 implies that previous estimates of the HI photo-ionization rate Gamma_HI available in the literature should be corrected by a factor of 1.2-1.7. These results have important implications if extrapolated at the epoch of reionization.
Identifying the mechanisms driving the escape of Lyman Continuum (LyC) photons is crucial to find Lyman Continuum Emitter (LCE) candidates. To understand the physical properties involved in the leakage of LyC photons, we investigate the connection be
We present a new constraint on the Lyman Continuum (LyC) escape fraction at z~1.3. We obtain deep, high sensitivity far-UV imaging with the Advanced Camera for Surveys (ACS) Solar Blind Channel (SBC) on the Hubble Space Telescope (HST), targeting 11
Based on results by recent surveys, the number of bright quasars at redshifts z>3 is being constantly revised upwards. Current consensus is that at bright magnitudes ($M_{1450}le -27$) the number densities of such sources could have been underestimat
The escape fraction of ionizing photons from galaxies is a crucial quantity controlling the cosmic ionizing background radiation and the reionization. Various estimates of this parameter can be obtained in the redshift range, z=0--6, either from dire
Simulations have indicated that most of the escaped Lyman continuum photons escape through a minority of solid angles with near complete transparency, with the remaining majority of the solid angles largely opaque, resulting in a very broad and skewe