SPECTROSCOPIC CONFIRMATION OF THREE z-DROPOUT GALAXIES AT z = 6.844–7.213: DEMOGRAPHICS OF Lyα EMISSION IN z ∼ 7 GALAXIES

By Yoshiaki Ono, M. Ouchi, B. Mobasher, Mark Dickinson, K. Penner, K. Shimasaku, B. Weiner, J. Kartaltepe, K. Nakajima, H. Nayyeri and 3 more. 2011

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We present the results of our ultra-deep Keck/DEIMOS spectroscopy of z-dropout galaxies in the Subaru Deep Field and Great Observatories Origins Deep Survey's northern field. For 3 out of 11 objects, we detect an emission line at ∼1 μm with a signal-to-noise ratio of ∼10. The lines show asymmetric profiles with high weighted skewness values, consistent with being Lyα, yielding redshifts of z = 7.213, 6.965, and 6.844. Specifically, we confirm the z = 7.213 object in two independent DEIMOS runs with different spectroscopic configurations. The z = 6.965 object is a known Lyα emitter, IOK-1, for which our improved spectrum at a higher resolution yields a robust skewness measurement. The three z-dropouts have Lyα fluxes of 3 × 10−17 erg s−1 cm−2 and rest-frame equivalent widths EWLyα0 = 33–43 Å. Based on the largest spectroscopic sample of 43 z-dropouts, which is the combination of our and previous data, we find that the fraction of Lyα-emitting galaxies (EWLyα0 > 25 Å) is low at z ∼ 7; 17% ± 10% and 24% ± 12% for bright (MUV ≃ −21) and faint (MUV ≃ −19.5) galaxies, respectively. The fractions of Lyα-emitting galaxies drop from z ∼ 6 to 7 and the amplitude of the drop is larger for faint galaxies than for bright galaxies. These two pieces of evidence would indicate that the neutral hydrogen fraction of the intergalactic medium increases from z ∼ 6 to 7 and that the reionization proceeds from high- to low-density environments, as suggested by an inside-out reionization model.

Subfields: Astronomy and Astrophysics, Global and Planetary Change, Instrumentation

View Paper: https://www.semanticscholar.org/paper/abc55e0b1ba8847aeb368d0be9cb8812828b1637

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Citations in the corpus

The assembly of ‘normal’ galaxies at z ∼ 7 probed by ALMA (2015, background): “Y dropout (Castellano et al. 2010; Ono et al. 2012) and all of them have solid spectroscopic confirmations, through the detection of Lyα with clearly asymmetric profile due to absorption of the blue side by the intervening IGM (Vanzella et al. 2011; Ono et al. 2012).”
CANDELS: THE CONTRIBUTION OF THE OBSERVED GALAXY POPULATION TO COSMIC REIONIZATION (2012, background): “…yielded a much lower success rate of Lyα emission detection than there should have been given the Lyα EW distributions atz= 4 – 6 (Stark et al. 2010; Fontana et al. 2010; Pentericci et al. 2011; Ono et al. 2012; Schenker et al. 2012; Treu et al. 2012), implying neutral fractions as high as ∼50%.”
EVIDENCE FOR PopIII-LIKE STELLAR POPULATIONS IN THE MOST LUMINOUS Lyα EMITTERS AT THE EPOCH OF REIONIZATION: SPECTROSCOPIC CONFIRMATION (2015, background): “This is exactly what is found by Matthee et al. (2015), in agreement with spectroscopic results from Ono et al. (2012).”
NEW CONSTRAINTS ON COSMIC REIONIZATION FROM THE 2012 HUBBLE ULTRA DEEP FIELD CAMPAIGN (2013, background): “…et al. 2013), precise determinations of the galaxyuminosity function at redshiftsz ∼ 7−8 (Schenker et al. 2012a; McLure et al. 2012), robust ultraviolet (UV) spectral slope measurements atz ∼ 7 − 8 (Dunlop et al. 2012b), and sizeluminosity relation measures at redshiftsz ∼ 6− 8 (Ono et al. 2012a).”
THE UV LUMINOSITY FUNCTION OF STAR-FORMING GALAXIES VIA DROPOUT SELECTION AT REDSHIFTS z ∼ 7 AND 8 FROM THE 2012 ULTRA DEEP FIELD CAMPAIGN (2012, background): “In a related paper, Ono et al. (2012) validate these choices by measuring half-light radii, rhl, for stacks of our highredshift samples, and find values of 0.36 kpc at both z ∼ 7 and 8, which translate to angular half-light radii of 0.07′′ (not including any broadening due to the PSF).”
NEW OBSERVATIONS OF z ∼ 7 GALAXIES: EVIDENCE FOR A PATCHY REIONIZATION (2014, methodology): “(2) The 11 bright z-dropout observed by Ono et al. (2012) in the SDF field of which 3 have bright Lyα in emission.”
Ultraviolet emission lines in young low-mass galaxies at z ≃ 2: physical properties and implications for studies at z > 7 (2014, background): “Asa result of the attenuation of Lyα in z ≃ 7 galaxies (e.g., Schenker et al. 2012, Ono et al. 2012, Pentericci et al. 2012, Treu et al. 2013, Schenker et al. 2014), these UV emission lines likely provide our best hope of confirming very high redshift galaxies with groundbased facilities.”
An extreme [O III] emitter at z = 3.2: a low metallicity Lyman continuum source (2015, background): “…of candidate of strong Hβ+[O iii] emitters has been identified at much higher redshift (z > 6.5) by looking at the Spitzer/IRAC excess in channels 1 or 2 (depending on redshift; Schaerer & de Barros 2010; Ono et al. 2012; Labbé et al. 2013; Smit et al. 2014, 2015; Roberts-Borsani et al. 2015).”
LINE-EMITTING GALAXIES BEYOND A REDSHIFT OF 7: AN IMPROVED METHOD FOR ESTIMATING THE EVOLVING NEUTRALITY OF THE INTERGALACTIC MEDIUM (2014, methodology): “…over 6 < z < 8 allowing the construction of a redshift-dependent Lyα fraction, xLyα, which falls sharply from a value of ≃ 50% at z ≃ 6 (Stark et al. 2010) to less than 10% at and beyond z ≃ 7 (Pentericci et al. 2011; Schenker et al. 2012; Ono et al. 2012; Treu et al. 2012; Pentericci et al. 2014).”
Hyper-Eddington accretion flows on to massive black holes (2015, background): “Among highz galaxies, Lyα emitters (LAE) have prominent Lyα emission, typically LLyα ∼ 1042−44 erg s−1 (Ouchi et al. 2003; Hu et al. 2004; Malhotra & Rhoads 2004; Kashikawa et al. 2006; Shimasaku et al. 2006; Ouchi et al. 2008, 2010; Ono et al. 2010, 2012).”
Lyα EMISSION FROM A LUMINOUS z = 8.68 GALAXY: IMPLICATIONS FOR GALAXIES AS TRACERS OF COSMIC REIONIZATION (2015, background): “While formally fairly uncertain, it is comparable to line properties secured with MOSFIRE for the other bright galaxies at zphot & 7.5 selected in CANDELS with red IRAC colors (F13, O15).”
The galaxy luminosity function at z ≃ 6 and evidence for rapid evolution in the bright end from z ≃ 7 to 5 (2014, methodology): “…of the ground-based imaging surveys utilised here compared to HST imaging, coupled with the small measured sizes of LBGs (Curtis-Lake et al. 2014; Ono et al. 2012), precludes any discrimination based on size, and hence we must carefully assess the available multiwavelength information to remove…”
HUBBLE FRONTIER FIELDS FIRST COMPLETE CLUSTER DATA: FAINT GALAXIES AT z ∼ 5–10 FOR UV LUMINOSITY FUNCTIONS AND COSMIC REIONIZATION (2014, background): “…in a GRB spectrum (Totani et al. 2006; McQuinn et al. 2008), evolution of the Lyα luminosity function and Lyα emitter clustering (Ota et al. 2008; Ouchi et al. 2010; Konno et al. 2014), and the Lyα emitting galaxy fraction evolution (Pentericci et al. 2011; Schenker et al. 2012; Ono et al. 2012).”