The Evolution of Optical Depth in the Lyα Forest: Evidence Against Reionization at<i>z</i>∼6

Becker, George D.; Rauch, Michael; Sargent, W. L. W.

doi:10.1086/517866

Cited by 243 publications

(330 citation statements)

References 55 publications

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“…Very recently, Giallongo et al (2015) found 22 AGN candidates at z 4 in the Candel/GOOD-S/Chandra Deep Field South field, which is suggestive of a prominent contribution of AGNs to the ionising background in the range 4 z 6.5. The resulting H I photoionisation rate is indeed consistent with various estimates at the same redshifts, based on both the flux-decrement and proximity-effect techniques (Becker et al 2007;Calverley et al 2011). …”

Section: Introductionsupporting

confidence: 84%

High-redshift active galactic nuclei and H I reionisation: limits from the unresolved X-ray background

Haardt

Salvaterra

2015

A&A

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The rapidly declining population of bright quasars at z 3 appears to make an increasingly smaller contribution to the ionising background at the H I Lyman limit. It is thererfore generally thought that massive stars in (pre-)Galactic systems may provide the additional ionising flux needed to complete H I reionisation by z 6. A galaxy-dominated background, however, may require that the escape fraction of Lyman continuum radiation from high-redshift galaxies is as high as 10%, which is somewhat at odds with (admittedly scarce) observational constraints. High escape fractions from dwarf galaxies have been advocated, or, alternatively, a so-far undetected (or barely detected) population of unobscured, high-redshift faint AGNs. Here we examine the latter hypothesis and show that such sources, to be consistent with the measured level of the unresolved X-ray background at z = 0, can provide a fraction of the H II filling factor no larger than 13% by z 6. The fraction rises to 27% in the somewhat extreme case of a constant comoving redshift evolution of the AGN emissivity. This still calls for a mean escape fraction of ionising photons from high-z galaxies of 10%.

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Section: Introductionsupporting

confidence: 84%

High-redshift active galactic nuclei and H I reionisation: limits from the unresolved X-ray background

Haardt

Salvaterra

2015

A&A

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“…Observations of the Gunn-Peterson trough in quasar spectra at z > 6 (Fan et al 2006) and transmission in the Lyα forest for z < 6 (Becker et al 2001;Djorgovski et al 2001;Fan et al 2001) suggests the epoch of reionization ends at z ∼ 6 (QHII(z ∼ 6) > 0.99). These constraints on the neutral fraction of hydrogen at the end of reionization rely on detailed modelling of both the IGM and ionizing sources making their accuracy (and therefore the exact end of reionization) the subject of debate (Becker, Rauch & Sargent 2007;Furlanetto & Mesinger 2009;Mesinger 2010;McGreer, Mesinger & Fan 2011;Robertson et al 2013). McGreer, Mesinger & Fan (2011) use the covering fraction of 'dark' pixels in quasar spectra to obtain the more conservative constraints of QHII(z = 5.5) > 0.8 and QHII(z = 6) > 0.5 on the end of reionization.…”

Section: Amdm Reionization Historymentioning

confidence: 99%

Galaxy UV-luminosity function and reionization constraints on axion dark matter

Bozek¹,

Marsh²,

Silk³

et al. 2015

Monthly Notices of the Royal Astronomical Society

173

208

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If the dark matter (DM) were composed of axions, then structure formation in the Universe would be suppressed below the axion Jeans scale. Using an analytic model for the halo mass function of a mixed DM model with axions and cold dark matter, combined with the abundance-matching technique, we construct the UV-luminosity function. Axions suppress high-z galaxy formation and the UV-luminosity function is truncated at a faintest limiting magnitude. From the UV-luminosity function, we predict the reionization history of the universe and find that axion DM causes reionization to occur at lower redshift. We search for evidence of axions using the Hubble Ultra Deep Field UV-luminosity function in the redshift range z = 6-10, and the optical depth to reionization, τ , as measured from cosmic microwave background polarization. All probes we consider consistently exclude m a 10 −23 eV from contributing more than half of the DM, with our strongest constraint ruling this model out at more than 8σ significance. In conservative models of reionization a dominant component of DM with m a = 10 −22 eV is in 3σ tension with the measured value of τ , putting pressure on an axion solution to the cusp-core problem. Tension is reduced to 2σ for the axion contributing only half of the DM. A future measurement of the UV-luminosity function in the range z = 10-13 by JWST would provide further evidence for or against m a = 10 −22 eV. Probing still higher masses of m a = 10 −21 eV will be possible using future measurements of the kinetic Sunyaev-Zel'dovich effect by Advanced ACTPol to constrain the time and duration of reionization.

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“…Several groups have made these measurements by measuring the mean transmission of QSO UV flux through the Ly forest (McDonald & Miralda-Escudé 2001;Tytler et al 2004;Bolton et al 2005;Bolton & Haehnelt 2007;Becker et al 2007), or by measuring the extent of the proximity effect (Carswell et al 1982) around high-redshift QSOs (Scott et al 2000(Scott et al , 2002. Figure 17 shows the current estimates for the total photoionization rate at high redshift, compared with our estimate of the contribution from QSOs at z $ 3:2.…”

Section: Qso Contribution To Hmentioning

confidence: 99%

High‐Redshift QSOs in the SWIRE Survey and thez∼3 QSO Luminosity Function

Siana

Polletta

Smith

et al. 2008

ApJ

101

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We use a simple optical /infrared (IR) photometric selection of high-redshift QSOs that identifies a Lyman break in the optical photometry and requires a red IR color to distinguish QSOs from common interlopers. The search yields 100 z $ 3 (U-dropout) QSO candidates with 19 < r 0 < 22 over 11.7 deg 2 in the ELAIS-N1 ( EN1) and ELAIS-N2 (EN2) fields of the Spitzer Wide-area Infrared Extragalactic (SWIRE) Legacy Survey. The z $ 3 selection is reliable, with spectroscopic follow-up of 10 candidates confirming that they are all QSOs at 2:83 < z < 3:44. We find that our z $ 4 ( g 0 -dropout) sample suffers from both unreliability and incompleteness but present seven previously unidentified QSOs at 3:50 < z < 3:89. Detailed simulations show our z $ 3 completeness to be $80%Y90% from 3:0 < z < 3:5, significantly better than the $30% Y 80% completeness of the SDSS at these redshifts. The resulting luminosity function extends 2 mag fainter than SDSS and has a faint-end slope of ¼ À1:42 AE 0:15, consistent with values measured at lower redshift. Therefore, we see no evidence for evolution of the faint-end slope of the QSO luminosity function. Including the SDSS QSO sample, we have now directly measured the space density of QSOs responsible for $70% of the QSO UV luminosity density at z $ 3. We derive a maximum rate of H i photoionization from QSOs at z $ 3:2, À ¼ 4:8 ; 10 À13 s À1 , about half of the total rate inferred through studies of the Ly forest. Therefore, star-forming galaxies and QSOs must contribute comparably to the photoionization of H i in the intergalactic medium at z $ 3.

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The Evolution of Optical Depth in the Lyα Forest: Evidence Against Reionization atz∼6

Cited by 243 publications

References 55 publications

High-redshift active galactic nuclei and H I reionisation: limits from the unresolved X-ray background

High-redshift active galactic nuclei and H I reionisation: limits from the unresolved X-ray background

Galaxy UV-luminosity function and reionization constraints on axion dark matter

High‐Redshift QSOs in the SWIRE Survey and thez∼3 QSO Luminosity Function

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