Early galaxy formation and its large-scale effects

Dayal, Pratika; Ferrara, Andrea

doi:10.1016/j.physrep.2018.10.002

Cited by 381 publications

(266 citation statements)

References 625 publications

(801 reference statements)

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“…A long-lasting debate is in progress on the sources responsible for the EoR. While the majority of the astrophysical community are favoring star-forming galaxies (SFGs) as the main drivers of HI reionization (Dayal & Ferrara 2018), alternative explanations based on Active Galactic Nuclei (AGNs) have been proposed (Giallongo et al 2012(Giallongo et al , 2015Madau & Haardt 2015;Grazian et al 2018;Boutsia et al 2018). It is widely accepted that QSOs and AGNs dominate the HI ionizing background at z < 3 (Haardt & Madau 2012;Fontanot et al 2012;Cristiani et al 2016;Faucher-Giguère 2019).…”

Section: Introductionmentioning

confidence: 99%

Lyman continuum escape fraction and mean free path of hydrogen ionizing photons for brightz∼ 4 QSOs from SDSS DR14

Romano

Grazian

Giallongo

et al. 2019

A&A

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Context. One of the major challenges in observational cosmology is related to the redshift evolution of the average hydrogen (HI) ionization in the Universe, as evidenced by the changing in the ionization level of the intergalactic medium (IGM) through cosmic time. In particular, starting from the first cosmic reionization, the rapid evolution of the IGM physical properties poses severe constraints for the identification of the sources responsible for keeping its high level of ionization up to lower redshifts. Aims. 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 drawn from the SDSS survey (DR14) in the redshift interval 3.6 ≤ z ≤ 4.6 and absolute magnitude range −29.0 M 1450 −26.0. Particularly, we focus on the estimate of the escape fraction of HI ionizing photons and their mean free path (MFP), which are fundamental in the characterization of the surrounding intergalactic medium. Methods. Starting from UV/optical rest-frame spectra of the whole QSO sample from the SDSS survey, we estimate the escape fraction and free path individually for each of them. We calculate the Lyman Continuum escape fraction as the flux ratio blue-ward (∼ 900 Å rest-frame) and red-ward (∼ 930 Å rest-frame) of the Lyman limit (LL). 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. Results. We find a lower limit to the mean Lyman Continuum 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 (AAs). This value is larger than the one obtained at the same redshift by many authors in the literature using different techniques. Moreover, the probability distribution function of free path gives a complementary information w.r.t. the mean free path derived through the stack technique. Finally, we also find that the redshift evolution of this parameter results to be possibly milder than previously thought. Conclusions. Our new determination of the mean free path at z ∼ 4 implies that previous estimates of the HI photo-ionization rate Γ 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.

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Section: Introductionmentioning

confidence: 99%

Lyman continuum escape fraction and mean free path of hydrogen ionizing photons for brightz∼ 4 QSOs from SDSS DR14

Romano

Grazian

Giallongo

et al. 2019

A&A

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“…The Epoch of Reionization (EoR) marks a major phase transition in the history of the Universe. High-energy photons from the first stars and galaxies permeate the intergalactic medium (IGM) and gradually ionize the neutral hydrogen (HI ) of the IGM until the Universe is fully ionized at z 6 (Fan et al 2006;Dayal & Ferrara 2018). While the number of constraints on the timing of reionization has been increasing in the past years (Planck Collaboration et al 2018;Mortlock et al 2011;Bolton et al 2011;Ouchi et al 2018;Konno et al 2018;Pentericci et al 2014;Schenker et al 2014;Hutter et al 2014Hutter et al , 2015, the exact time evolution of the ionization fraction and the percolation of the ionized regions into the IGM remain highly uncertain.…”

Section: Introductionmentioning

confidence: 99%

The 21 cm bispectrum during reionization: a tracer of the ionization topology

Hutter

Watkinson

Seiler

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We compute the bispectra of the 21cm signal during the Epoch of Reionization for three different reionization scenarios that are based on a dark matter N-body simulation combined with a self-consistent, semi-numerical model of galaxy evolution and reionization. Our reionization scenarios differ in their trends of ionizing escape fractions (f esc ) with the underlying galaxy properties and cover the physically plausible range, i.e. f esc effectively decreasing, being constant, or increasing with halo mass. We find the 21cm bispectrum to be sensitive to the resulting ionization topologies that significantly differ in their size distribution of ionized and neutral regions throughout reionization. From squeezed to stretched triangles, the 21cm bispectra features a change of sign from negative to positive values, with ionized and neutral regions representing below-average and above-average concentrations contributing negatively and positively, respectively. The position of the change of sign provides a tracer of the size distribution of the ionized and neutral regions, and allows us to identify three major regimes that the 21cm bispectrum undergoes during reionization. In particular the regime during the early stages of reionization, where the 21cm bispectrum tracks the peak of the size distribution of the ionized regions, provides exciting prospects for pinning down reionization with the forthcoming Square Kilometre Array.

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“…The first billion years of the Universe remain a compelling cosmological mystery, mostly due to the fact that observations of this period remain challenging (e.g. Barkana & Loeb 2007;Loeb & Furlanetto 2013;Mesinger 2016;Dayal & Ferrara 2018). One of the simplest and most powerful observations are the non-ionizing (∼1500Å rest-frame) ultra-violet luminosity functions (UV LFs).…”

Section: Introductionmentioning

confidence: 99%

Combining high-z galaxy luminosity functions with Bayesian evidence

Gillet

Mesinger

Park

2019

Monthly Notices of the Royal Astronomical Society

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Galaxy formation during the first billion years of our Universe remains a challenging problem at the forefront of astrophysical cosmology. Although these z ∼ > 6 galaxies are likely responsible for the last major phase change of our Universe, the epoch of reionization (EoR), detailed studies are possible only for relatively rare, bright objects. Characterizing the fainter galaxies which are more representative of the population as a whole is currently done mainly through their non-ionizing UV luminosity function (LF). Observing the faint end of the UV LFs is nevertheless challenging, and current estimates can differ by orders of magnitude.Here we propose a methodology to combine disparate high-z UV LF data sets in a Bayesian framework: Bayesian Data Averaging (BDA). Using a flexible, physicallymotivated galaxy model, we compute the relative evidence of various z = 6 UV LFs within the magnitude range −20 ≤ M UV ≤ −15 which is common to the data sets. Our model, based primarily on power-law scalings of the halo mass function, naturally penalizes systematically jagged data points as well as mis-estimated errors. We then use the relative evidence to weigh the posteriors obtained from disparate LF observations during the EoR, 6 ≤ z ≤ 10. The resulting LFs suggest that the star formation rate density (SFRD) integrated down to a UV magnitude of -17 represent 60.9 +11.3 −9.6 % / 28.2 +9.3 −10.1 % / 5.7 +4.5 −4.7 % of the total SFRD at redshifts 6 / 10 / 15. The BDA framework we introduce enables galaxy models to leverage multiple, analogous observational data sets.

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Early galaxy formation and its large-scale effects

Cited by 381 publications

References 625 publications

Lyman continuum escape fraction and mean free path of hydrogen ionizing photons for brightz∼ 4 QSOs from SDSS DR14

Lyman continuum escape fraction and mean free path of hydrogen ionizing photons for brightz∼ 4 QSOs from SDSS DR14

The 21 cm bispectrum during reionization: a tracer of the ionization topology

Combining high-z galaxy luminosity functions with Bayesian evidence

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