On the Threshold of the Reionization Epoch

By S. George Djorgovski, S. Castro, Daniel Stern, A. Observatory, Caltech, Jet propulsion Laboratory. 2001

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Discovery of the cosmic reionization epoch would represent a significant milestone in cosmology. We present Keck spectroscopy of the quasar SDSS 1044-0125, at z = 5.73. The spectrum shows a dramatic increase in the optical depth at observed wavelengths λ ≳ 7550 Å, corresponding to zabs ≳ 5.2. Only a few small, narrow transmission regions are present in the spectrum beyond that point and out to the redshifts where the quasar signal begins. We interpret this result as a signature of the trailing edge of the cosmic reionization epoch, which we estimate to occur around ⟨z⟩ ~ 6 (as indeed confirmed by subsequent observations by Becker et al.) and extending down to z ~ 5.2. This behavior is expected in the modern theoretical models of the reionization era, which predict a patchy and gradual onset of reionization. The remaining transmission windows we see may correspond to the individual reionization bubbles (Strömgren spheres) embedded in a still largely neutral intergalactic medium, intersected by the line of sight to the quasar. Future spectroscopic observations of quasars at comparable or larger redshifts will provide a more detailed insight into the structure and extent of the reionization era.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/2b49ef197197c0e1ed661a5762d9744cb734fd9f

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Formation of z~6 Quasars from Hierarchical Galaxy Mergers (2006, background): “…& Peterson 1965) in their spectra, which place these quasars at the end of the epoch of reionization (e.g., Fan et al. 2001; Becker et al. 2001; Djorgovski et al. 2001; Lidz et al. 2002; Songaila & Cowie 2002; White et al. 2003; Sokasian et al. 2003); and (4) a lack of evolution in the…”
Line-driven Winds, Ionizing Fluxes, and Ultraviolet Spectra of Hot Stars at Extremely Low Metallicity. I. Very Massive O Stars (2002, background): “Very massive stars are also very likely the progenitors of gamma-ray bursts (MacFayden, Woosley, & Heger 2001; Djorgovski et al. 2001b; Kulkarni et al. 2000; Reichardt 2001), which then—as tracers of the cosmic star formation history— might originate to a large fraction at very high redshift (Bromm…”
Cosmic reionization by stellar sources: population III stars (2003, background): “The situation is exacerbated at higher redshifts where observations by Fan et al. (2000), Becker et al. (2001) and Djorgovski et al. (2001) imply that the IGM was highly ionized at z 6 even though the emissivity from bright quasars was probably unimportant.”
Implications for Cosmic Reionization from the Optical Afterglow Spectrum of the Gamma-Ray Burst 050904 at z = 6.3 (2005, background): “Thedram aticincreaseofthe opticaldepth ofthe Ly forestwith increasing redshiftatz> 5:2 (Djorgovski et al. 2001) and the subsequent discovery ofbroad and black troughsofLy absorption (the G P troughs)in the spectra ofz> 6 quasars(Beckeretal.2001;W hite etal.”
The Fate of the First Galaxies. II. Effects of Radiative Feedback (2001, background): “If reionization takes place at redshift z ∼ 6, as recent high-redshift quasar observations seem to suggest (Becker et al. 2001; Djorgovski et al. 2001), the run shown by the long-dashed line reionizes the universe too early, while the run shown by the short-dashed line reionizes the universe too…”
Evolution of the Ionizing Background and the Epoch of Reionization from the Spectra of z ∼ 6 Quasars (2001, background): “Djorgovski et al. (2001) also observed a particularly dark region of length ∼ 5 Mpc at z ∼ 5.4, along the line of sight to the z ∼ 5.8 quasar SDSS 1044–0125.”
Evidence of patchy hydrogen reionization from an extreme Lyα trough below redshift six (2014, background): “…on when reionization ended come from the evolution of intergalactic Lyα opacity near z ∼ 6, as measured in the spectra of highredshift quasars (e.g., Djorgovski et al. 2001; Becker et al. 2001; Fan et al. 2002; White et al. 2003; Songaila 2004; Fan et al. 2006) and gamma ray bursts (e.g.,…”
The End of the Reionization Epoch Probed by Lyα Emitters at z = 6.5 in the Subaru Deep Field (2006, background): “Such an overdense region could be kept neutral until later epochs, trapping bright ionizing sources like luminous QSOs, in which the appearance of Gunn-Peterson troughs are detected at lower z: z ∼ 5.2−5.8 (Becker et al. 2001; Djorgovski et al. 2001).”
The effects of photoionization on galaxy formation – I. Model and results at z=0 (2001, background): “…of 10% reionization does not occur until much later, at z ≈ 5.5 (which may be slightly too low to be consistent with recent measurements of the Gunn-Peterson effect in quasars at z ≈ 6: Fan et al. 2000; Djorgovski et al. 2001; Becker et al. 2001), but otherwise proceeds in much the same way.”
Galaxy UV-luminosity function and reionization constraints on axion dark matter (2014, background): “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 reionisation ends at z ∼ 6 (Q(z ∼ 6) > 0.99).”
Four Quasars above Redshift 6 Discovered by the Canada-France High-z Quasar Survey (2007, unknown): “…are detected towards SDSS J1044-0125 atz = 2.2786 and SDSS J1306+0356 at z = 2.20 and 2.53, while there is no MgII absorption towards SDSS J0836+0054, SDSS J1030+0524 and SDSS J1148+5251 (Becker et al. 2001; Djorgovski et al. 2001; Fan et al. 2003; White et al. 2003; Ryan-Weber et al. 2006).”
Probing the Ionization State of the Universe at z > 6 (2003, background): “High resolution spectra of the Lyα forest at z ∼ 5 (Songaila, Hu, Cowie & McMahon 1999; Djorgovski et al. 2001; Songaila & Cowie 2002) do show small transparent windows, but they are rare.”
A Probable z ~ 7 Galaxy Strongly Lensed by the Rich Cluster A2218: Exploring the Dark Ages (2004, background): “After decades of lower limits on the redshift at which it occurred, recent observations of QSOs discovered by the Sloan Digital Sky Survey (Becker et al. 2001; Djorgovski et al. 2001; Fan et al. 2002) suggest that reionization was just finishing at z 6 6:5.”
Implications of the Lag-Luminosity Relationship for Unified Gamma-Ray Burst Paradigms (2002, background): “Djorgovski et al. (2001) and Becker et al. (2001) conclude that the reionization era was complete near z 5 6.”
The GMRT Epoch of Reionization experiment: a new upper limit on the neutral hydrogen power spectrum at z≈ 8.6 (2010, methodology): “There is also substantial information on the neutral content of the intergalactic medium (IGM) since z ∼ 6 via observations of the Gunn-Peterson trough (Gunn & Peterson 1965) in quasar spectra (Djorgovski et al. 2001; Becker et al. 2001; Fan et al. 2006; Willott et al. 2007).”