STELLAR POPULATIONS OF Lyα EMITTERS AT z ∼ 6–7: CONSTRAINTS ON THE ESCAPE FRACTION OF IONIZING PHOTONS FROM GALAXY BUILDING BLOCKS

By Yoshiaki Ono, M. Ouchi, K. Shimasaku, J. Dunlop, D. Farrah, R. McLure, S. Okamura. 2010

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We investigate the stellar populations of Lyα emitters (LAEs) at z = 5.7 and 6.6 in a 0.65 deg2 sky of the Subaru/XMM-Newton Deep Survey (SXDS) Field, using deep images taken with the Subaru/Suprime-Cam, United Kingdom Infrared Telescope/Wide Field Infrared Camera, and Spitzer/Infrared Array Camera (IRAC). We produce stacked multiband images at each redshift from 165 (z = 5.7) and 91 (z = 6.6) IRAC-undetected objects to derive typical spectral energy distributions (SEDs) of z ∼ 6–7 LAEs for the first time. The stacked LAEs have as blue UV continua as the Hubble Space Telescope (HST)/Wide Field Camera 3 (WFC3) z-dropout galaxies of similar MUV, with a spectral slope β ∼ −3, but at the same time they have red UV-to-optical colors with detection in the 3.6 μm band. Using SED fitting we find that the stacked LAEs have low stellar masses of ∼(3–10) × 107 M☉, very young ages of ∼1–3 Myr, negligible dust extinction, and strong nebular emission from the ionized interstellar medium, although the z = 6.6 object is fitted similarly well with high-mass models without nebular emission; inclusion of nebular emission reproduces the red UV-to-optical colors while keeping the UV colors sufficiently blue. We infer that typical LAEs at z ∼ 6–7 are building blocks of galaxies seen at lower redshifts. We find a tentative decrease in the Lyα escape fraction from z = 5.7 to 6.6, which may imply an increase in the intergalactic medium neutral fraction. From the minimum contribution of nebular emission required to fit the observed SEDs, we place an upper limit on the escape fraction of ionizing photons of fionesc ∼ 0.6 at z = 5.7 and ∼0.9 at z = 6.6. We also compare the stellar populations of our LAEs with those of stacked HST/WFC3 z-dropout galaxies.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/bdf34df174a574066664e81331f2e57bc32de911

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Citations in the corpus

THE HETDEX PILOT SURVEY. II. THE EVOLUTION OF THE Lyα ESCAPE FRACTION FROM THE ULTRAVIOLET SLOPE AND LUMINOSITY FUNCTION OF 1.9 (2010, methodology): “…1998; Rhoads et al. 2000; Kudritzki et al. 2000; Malhotra & Rhoads 2002; Ouchi et al. 2003; Gawiser et al. 2006a; Ajiki et al. 2006; Gronwall et al. 2007; Ouchi et al. 2008; Nilsson et al. 2009a; Finkelstein et al. 2009; Guaita et al. 2010; Hayes et al. 2010a; Ono et al. 2010; Adams et al. 2011).”
THE ABUNDANCE OF STAR-FORMING GALAXIES IN THE REDSHIFT RANGE 8.5–12: NEW RESULTS FROM THE 2012 HUBBLE ULTRA DEEP FIELD CAMPAIGN (2012, methodology): “Following techniques described in Robertson et al. (2010a) and Ono et al. (2010), we have simulated model spectra for young low metallicity dust-free galaxies including the contribution from strong nebular lines.”
KECK SPECTROSCOPY OF 3 < z < 7 FAINT LYMAN BREAK GALAXIES: THE IMPORTANCE OF NEBULAR EMISSION IN UNDERSTANDING THE SPECIFIC STAR FORMATION RATE AND STELLAR MASS DENSITY (2012, background): “…spanning the redshift range 3 < z < 7 (e.g., Egami et al. 2005; Eyles et al. 2005; Labbé et al. 2006; Eyles et al. 2007; Stark et al. 2007, 2009; Ono et al. 2010; González et al. 2010; Labbé et al. 2010a,b; González et al. 2011a; Lee et al. 2012; Reddy et al. 2012b; Curtis-Lake et al. 2012).”
Rest-frame ultraviolet-to-optical spectral characteristics of extremely metal-poor and metal-free galaxies (2011, background): “Thus, the nebular emission is a very important spectral component (Zackrisson, Bergvall, & Leitet 2008; Schaerer & de Barros 2009, 2010; Inoue 2010; Ono et al. 2010; Raiter, Schaerer, & Fosbury 2010).”
THE RELATION BETWEEN STAR FORMATION RATE AND STELLAR MASS FOR GALAXIES AT 3.5 ⩽ z ⩽ 6.5 IN CANDELS (2014, background): “…photons as LHβ = 4.78 × 10 −13 1 − fesc 1 + 0.6fesc NLyC [erg s −1], (1) where fesc is the fraction of ionizing Lyman continuum (LyC) photons escaping the galaxy into the IGM and NLyC is the production rate of Hydrogen-ionizing photons (see also Osterbrock & Ferland 2006; Ono et al. 2010).”
SPECTROSCOPIC CONFIRMATION OF THREE z-DROPOUT GALAXIES AT z = 6.844–7.213: DEMOGRAPHICS OF Lyα EMISSION IN z ∼ 7 GALAXIES (2011, background): “Although this possible problem is not directly related to the discussion and conclusions of this paper, similar conflicts between stellar age and dynamical time are found in other papers (e.g., Schaerer & de Barros 2009, 2010; Ono et al. 2010), highlighting the need for further research.”
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).”
ON THE REDSHIFT EVOLUTION OF THE Lyα ESCAPE FRACTION AND THE DUST CONTENT OF GALAXIES (2010, background): “Based upon the fitting of spectral energy distributions (SED) to stacked broadband fluxes, Ono et al. (2010) estimate fLyαesc = (36 +68 −35) % and (4 +180 −3.8 ) at the same redshifts.”
Full-data Results of Hubble Frontier Fields: UV Luminosity Functions at z ∼ 6–10 and a Consistent Picture of Cosmic Reionization (2017, background): “Ono et al. (2010) investigated the stellar populations of Lyα emitters at z ∼ 6, and obtained weak upper limits of fesc ∼ 0.6 at z = 5.7 and fesc ∼ 0.9 at z = 6.6, based on the constraints on the nebular emission line fluxes.”
STATISTICS OF 207 Lyα EMITTERS AT A REDSHIFT NEAR 7: CONSTRAINTS ON REIONIZATION AND GALAXY FORMATION MODELS (2010, background): “Because our LAEs have a UV continuum magnitude of ∼ 27 mag on average (Ono et al. 2010a,b), results of Ouchi et al. (2004b) and Lee et al. (2009) suggest that fSFduty is .”
The mass evolution of the first galaxies: stellar mass functions and star formation rates at 4 < z < 7 in the CANDELS GOODS-South field (2014, methodology): “Nebular emission lines and continuum are added to the templates following a method similar to previous high-redshift fitting methods, e.g. Ono et al. (2010); Schaerer & de Barros (2010); McLure et al. (2011), Salmon et al. (2014).”
NEW CONSTRAINTS ON COSMIC REIONIZATION FROM THE 2012 HUBBLE ULTRA DEEP FIELD CAMPAIGN (2013, background): “We also considered stellar populations reddened by nebular continuum emission (e.g., Schaerer & de Barros 2009, 2010; Ono et al. 2010; Robertson et al. 2010), which in principle could allow relatively young, metal poor populations with largerξion to fall into the window ofβ values found by Dunlop…”
EVIDENCE FOR PopIII-LIKE STELLAR POPULATIONS IN THE MOST LUMINOUS Lyα EMITTERS AT THE EPOCH OF REIONIZATION: SPECTROSCOPIC CONFIRMATION (2015, background): “Its nature is likely similar to other metal-poor Lyα emitters (Nagao et al. 2008; Ono et al. 2010, 2012).”
COMPLETING THE CENSUS OF Lyα EMITTERS AT THE REIONIZATION EPOCH (2011, background): “LAEs are generally recognized to be young, less massive galaxies with little dust (E(B − V ) < 0.05 at z ∼ 6 (Ono et al. 2010) and even at z ∼3 (Gronwall et al. 2007)), though old and massive stellar populations are found in some LAEs (Finkelstein et al. 2009).”
VERY STRONG EMISSION-LINE GALAXIES IN THE WFC3 INFRARED SPECTROSCOPIC PARALLEL SURVEY AND IMPLICATIONS FOR HIGH-REDSHIFT GALAXIES, (2011, background): “Ono et al. 2010; Watson et al. 2010; Raiter et al. 2010; Finlator et al. 2011; McLure et al. 2011; Inoue 2011) dealing with SED modeling.”
THE 2012 HUBBLE ULTRA DEEP FIELD (UDF12): OBSERVATIONAL OVERVIEW (2012, background): “…obtained on the ultraviolet spectral slopes and stellar populations of these early star-forming galaxies at z∼ 7− 8 (Bouwens et al. 2009, 2010, 2012, Ono et al. 2010, Bunker et al. 2010, Finkelstein et al. 2010, 2012b,a, Yan et al. 2011b,a, McLure et al. 2010, 2011, Grazian et al. 2011, 2012,…”
AN INTENSELY STAR-FORMING GALAXY AT z ∼ 7 WITH LOW DUST AND METAL CONTENT REVEALED BY DEEP ALMA AND HST OBSERVATIONS (2013, methodology): “Nebular continuum and line emission, estimated from the ionizing photons from young stars, are optionally included following the metallicity-dependent prescriptions presented in Schaerer & de Barros (2009); Ono et al. (2010b).”
Big Three Dragons: A z = 7.15 Lyman-break galaxy detected in [O iii] 88 μm, [C ii] 158 μm, and dust continuum with ALMA (2018, methodology): “For fair comparisons of the data points, we uniformly derive β from two photometry values following the equation (1) of Ono et al. (2010).”
SILVERRUSH. IV. Lyα luminosity functions at z = 5.7 and 6.6 studied with ∼1300 Lyα emitters on the 14–21 deg2 sky (2017, background): “From these observations, it has been revealed that LAEs are in an early phase of galaxy evolution, i.e., LAEs are young, less massive, less dusty, and in highly ionized state (e.g., Ono et al. 2010b; Ono et al. 2010a; Nakajima & Ouchi 2014; Kusakabe et al. 2015; Inoue et al. 2016).”