STATISTICS OF 207 Lyα EMITTERS AT A REDSHIFT NEAR 7: CONSTRAINTS ON REIONIZATION AND GALAXY FORMATION MODELS

By M. Ouchi, K. Shimasaku, H. Furusawa, Tomoki Saito, Makiko Yoshida, M. Akiyama, Yoshiaki Ono, T. Yamada, K. Ota, N. Kashikawa and 5 more. 2010

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We present the Lyα luminosity function (LF), clustering measurements, and Lyα line profiles based on the largest sample to date of 207 Lyα emitters (LAEs) at z = 6.6 on the 1 deg2 sky of Subaru/XMM-Newton Deep Survey field. Our z = 6.6 Lyα LF including cosmic variance estimates yields the best-fit Schechter parameters of ϕ* = 8.5+3.0−2.2 × 10−4 Mpc−3 and L*Lyα = 4.4+0.6−0.6 × 1042 erg s−1 with a fixed α = −1.5, and indicates a decrease from z = 5.7 at the ≳90% confidence level. However, this decrease is not large, only ≃30% in Lyα luminosity, which is too small to have been identified in the previous studies. A clustering signal of z = 6.6 LAEs is detected for the first time. We obtain the correlation length of r0= 2–5 h−1100 Mpc and a bias of b= 3–6, and find no significant boost of clustering amplitude by reionization at z = 6.6. The average hosting dark halo mass inferred from clustering is 1010–1011 M☉, and a duty cycle of LAE population is roughly ∼1%, albeit with large uncertainties. The average of our high-quality Keck/DEIMOS spectra shows an FWHM velocity width of 251 ± 16 km s−1. We find no large evolution of the Lyα line profile from z = 5.7 to 6.6, and no anti-correlation between Lyα luminosity and line width at z = 6.6. The combination of various reionization models and our observational results about the LF, clustering, and line profile indicates that there would exist a small decrease of the intergalactic medium's (IGM's) Lyα transmission owing to reionization, but that the hydrogen IGM is not highly neutral at z = 6.6. Our neutral-hydrogen fraction constraint implies that the major reionization process took place at z ≳ 7.

Subfields: Astronomy and Astrophysics, Instrumentation

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Citations in the corpus

• VERY STRONG EMISSION-LINE GALAXIES IN THE WFC3 INFRARED SPECTROSCOPIC PARALLEL SURVEY AND IMPLICATIONS FOR HIGH-REDSHIFT GALAXIES, (2011, background): “However, at redshift z ∼ 6.5 for instance, Ouchi et al. (2010) and Kashikawa et al. (2011) use also the color blueward of the Lyα emission to detect the Lyman break of the NB921-selected galaxies.”
• AN ATLAS OF z = 5.7 AND z = 6.5 Lyα EMITTERS, (2010, methodology): “Ouchi et al. (2010), using Keck DEIMOS spectra, reverse the Kashikawa et al. 2006 result and find evidence at the 2.5 sigma level for Fig.”
• Inferences on the timeline of reionization at z ∼ 8 from the KMOS Lens-Amplified Spectroscopic Survey (2019, unknown): “Ouchi et al. (2010); McGreer et al. (2014); Sobacchi & Mesinger (2015); Mesinger et al. (2015); Davies et al. (2018); Greig et al. (2018); Mason et al. (2018a) and the Planck Collaboration et al. (2016).”
• Can the intergalactic medium cause a rapid drop in Lyα emission at z > 6? (2014, methodology): “We generate 5000 randomly-oriented sightlines, originating from 100 halos with massesMhalo ≈ 1010.5−11M , roughly corresponding to the host halo masses of the observed population of high-z galaxies, inferred through abundance matching and clustering (e.g. Ouchi et al. 2010).”
• Spectroscopic detections of C iii] λ1909 Å at z ≃ 6–7: a new probe of early star-forming galaxies and cosmic reionization (2014, background): “2 among the most extreme Lyα emitters at z ' 6 (e.g., Ouchi et al. 2010; Stark et al. 2011; Pentericci et al. 2011; Curtis-Lake et al. 2012).”
• NEW OBSERVATIONS OF z ∼ 7 GALAXIES: EVIDENCE FOR A PATCHY REIONIZATION (2014, background): “…clustering have the potential to reveal the signature of patchy reionization, although early results have been inconclusive (Kashikawa et al. 2011, Ouchi et al. 2010) In this paper we present new observations of z∼ 7 candidates, significantly increasing the statistics of previous works…”
• AN INTENSELY STAR-FORMING GALAXY AT z ∼ 7 WITH LOW DUST AND METAL CONTENT REVEALED BY DEEP ALMA AND HST OBSERVATIONS (2013, methodology): “…abundance and integrated properties of the earliest galaxies beyond a redshift of z ≃ 6 selected via optical and near-infrared (NIR) photometry (e.g. Bouwens et al. 2010a; McLure et al. 2010; Castellano et al. 2010; Ouchi et al. 2010; Ellis et al. 2013; McLure et al. 2012; Schenker et al. 2012).”
• Lyα Emitting Galaxies as a Probe of Reionisation (2014, background): “Interestingly, Ouchi et al. (2010) have shown that the evolution in the Lyα luminosity functions of LAEs is consistent with a reduction of ∼ 30% in luminosity.”
• SPECTROSCOPIC CONFIRMATION OF THREE z-DROPOUT GALAXIES AT z = 6.844–7.213: DEMOGRAPHICS OF Lyα EMISSION IN z ∼ 7 GALAXIES (2011, methodology): “The effect of cosmic variance was quantified by Ouchi et al. (2010), who claimed a factor of 2− 10 range in the number density of LAEs in an extensive survey covering an area of 1 deg2.”
• HUBBLE FRONTIER FIELDS FIRST COMPLETE CLUSTER DATA: FAINT GALAXIES AT z ∼ 5–10 FOR UV LUMINOSITY FUNCTIONS AND COSMIC REIONIZATION (2014, background): “…moderately large neutral hydrogen fraction at z & 6 is implied by the Lyα damping wing absorption features in the spectra of gammaray bursts (GRBs) at z ∼ 6 (Totani et al. 2006, 2013) and Lyα emitters at z ∼ 6 − 7 (Kashikawa et al. 2006; Ouchi et al. 2010; Kashikawa et al. 2011; Konno et al. 2014).”
• Extragalactic science, cosmology, and Galactic archaeology with the Subaru Prime Focus Spectrograph (2012, methodology): “Combining large samples of bright continuum-selected galaxies at intermediate redshifts with LAEs at the highest redshifts will allow us to trace the evolution in number-density and clustering of star-forming galaxies all the way toz = 7, as well as to probe cosmic reionization.”
• SPECTROSCOPIC CONFIRMATION OF z ∼ 7 LYMAN BREAK GALAXIES: PROBING THE EARLIEST GALAXIES AND THE EPOCH OF REIONIZATION (2011, background): “However the picture, coming essentially from narrow band surveys for LAEs is still unclear, since other authors claimed instead that there is hardly any evolution in the density of LAEs at redshift beyond 7 (e.g. Tilvi et al. 2010) or that the evolution is only modest (Ouchi et al. 2010).”
• Systematic Identification of LAEs for Visible Exploration and Reionization Research Using Subaru HSC (SILVERRUSH). I. Program strategy and clustering properties of ∼2000 Lyα emitters at z = 6–7 over the 0.3–0.5 Gpc2 survey area (2017, methodology): “The color selection criteria are similar to those of Ouchi et al. (2008, 2010), which are defined as i − NB816 ≥ 1.2 and g > g3σ and[ (r ≤ r3σ and r − i ≥ 1.0) or (r > r3σ ) ] (1) and z − NB921 ≥ 1.0 and g > g3σ and r > r3σ and[ (z ≤ z3σ and i − z ≥ 1.3) or (z > z3σ ) ] (2) for z = 5.7 and 6.6…”
• KECK SPECTROSCOPY OF FAINT 3 < z < 8 LYMAN BREAK GALAXIES: EVIDENCE FOR A DECLINING FRACTION OF EMISSION LINE SOURCES IN THE REDSHIFT RANGE 6 < z < 8 (2011, methodology): “As Lyα photons are resonantly scattered by neutral hydrogen, the abundance of Lyα emitters should decrease as observations probe into the era where there is neutral gas (e.g., Malhotra & Rhoads 2004, Ouchi et al. 2010, Kashikawa et al. 2011).”
• SPECTROSCOPIC CONFIRMATION OF TWO LYMAN BREAK GALAXIES AT REDSHIFT BEYOND 7 (2010, background): “…the Lyα and the distribution of its equivalent width in high-z galaxies can provide useful constrains on the ionization state of the intergalactic medium (IGM) at epochs less than 800 Myr vanzella@oats.inaf.it after the Big-Bang (e.g. Fontana et al. 2010, F10 in the following; Ouchi et al. 2010).”
• Star Formation in the Milky Way and Nearby Galaxies (2012, background): “…has been given to measurements of the redshifted Lyα line (λrest = 121.6nm) as a tracer of star-forming galaxies, especially at high redshifts where it provides unique sensitivity to both low-mass star-forming galaxies and intergalactic gas clouds or “blobs” (e.g., Ouchi et al. 2009, 2010).”