A Probable z ~ 7 Galaxy Strongly Lensed by the Rich Cluster A2218: Exploring the Dark Ages

By Jean-Paul Kneib, Richard S. Ellis, Michael R. Santos, J. Richard. 2004

182 citations recorded by the source corpus.

We discuss the observational properties of a remarkably faint triply imaged galaxy revealed in a deep z′-band Advanced Camera for Surveys observation of the lensing cluster A2218 (z = 0.175). A well-constrained mass model for the cluster, which incorporates the outcome of recent Keck spectroscopic campaigns, suggests that the triple system arises via a high-redshift (z > 6) source viewed at high magnification (≃25 times). Optical and infrared photometry from Hubble Space Telescope and the Keck Observatory confirms the lensing hypothesis and suggests that a significant discontinuity occurs in the spectral energy distribution within the wavelength interval 9250-9850 Å. If this break is associated with Gunn-Peterson absorption from neutral hydrogen, a redshift of 6.6 < z < 7.1 is inferred. Deep Keck spectroscopy conducted using both optical and infrared spectrographs fails to reveal any prominent emission lines in this region. However, an infrared stellar continuum is detected whose decline below 9800 Å suggests a spectroscopic redshift toward the upper end of the range constrained photometrically, i.e., z ≃ 7. Regardless of the precise redshift, the source is remarkably compact (≲1 h kpc) and faint (zF850LP = 28.0) yet is undergoing vigorous star formation at a rate ≃2.6 M☉ yr-1. An intriguing property is the steep slope of the ultraviolet continuum implied by the photometry, which may suggest that the source is representative of an early population of galaxies responsible for cosmic reionization. Independent verification of these results is highly desirable, but our attempts highlight the difficulty of studying such sources with present facilities and the challenges faced in pushing back the frontiers of the observable universe beyond z ~ 6.5.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/0f60bff125cc976748d59285236e8d06bb1744f3

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Citations in the corpus

THE ABUNDANCE OF STAR-FORMING GALAXIES IN THE REDSHIFT RANGE 8.5–12: NEW RESULTS FROM THE 2012 HUBBLE ULTRA DEEP FIELD CAMPAIGN (2012, background): “In favorable cases, their multiply-imaged nature offers a lower limit on their angular diameter distance (Ellis et al. 2001; Kneib et al. 2004).”
New Multiply-Lensed Galaxies Identified in ACS/NIC3 Observations of Cl0024+1654, Using an Improved Mass Model (2009, background): “…for which some of the very highest redshift galaxies are known because of high magnification by massive clusters (Franx et al. 1997, Frye & Broadhurst 1998, Frye , Broadhurst & Beńıtez 2002, Kneib et al. 2004, Stark et al. 2007, Bouwens et al. 2008, Bradley et al. 2008, Zheng et al. 2009).”
The End of the Reionization Epoch Probed by Lyα Emitters at z = 6.5 in the Subaru Deep Field (2006, background): “…distant galaxies at the edge of the cosmic reionization era beyond z = 6 in both dropout searches (Dickinson et al. 2004; Bouwens et al. 2003, 2005; Kneib et al. 2004; Pelló et al. 2004; Stanway et al. 2005) to find their strong Lyman breaks and narrowband (NB) searches (Hu et al. 2002; Cuby et…”
THE CLUSTER LENSING AND SUPERNOVA SURVEY WITH HUBBLE: AN OVERVIEW (2011, background): “In fact, the majority of m < 25.5 AB, z >∼ 6.5 galaxy candidates have been found in cluster fields (e.g., Kneib et al. 2004; Bradley et al. 2008; Zheng et al. 2009; Bradley et al. 2011; Schenker et al. 2012).”
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A Keck Survey for Gravitationally Lensed Lyα Emitters in the Redshift Range 8.5 < z < 10.4: New Constraints on the Contribution of Low-Luminosity Sources to Cosmic Reionization (2007, background): “For several objects recently located via this technique (Ellis et al. 2001; Kneib et al. 2004; Santos et al. 2004; Egami et al. 2005), stellar continuum slopes, Lyman-α profiles and star formation rates have been determined for sources whose intrinsic flux is close to the faintest direct imaging…”
The Frontier Fields lens modelling comparison project (2016, methodology): “…method, it had been shown that (a) cluster galaxies must be included, typically with a mass in proportion to their luminosity, in order the solution to have predictive power to find multiple images and that (b) a dark-matter component should be added (see Kneib et al. 2004; Broadhurst et al. 2005).”
HUBBLE SPACE TELESCOPE COMBINED STRONG AND WEAK LENSING ANALYSIS OF THE CLASH SAMPLE: MASS AND MAGNIFICATION MODELS AND SYSTEMATIC UNCERTAINTIES (2014, background): “…in which background galaxies are also multiply imaged, allowing for high-resolution constraints to be placed on the mass distribution and profile (Kneib et al. 2004; Broadhurst et al. 2005; Smith et al. 2005; Limousin et al. 2008; Newman et al. 2009; Richard et al. 2010, 2014; Bradač et al.…”
z ~ 7-10 Galaxies in the HUDF and GOODS Fields: UV Luminosity Functions (2008, background): “Only one z & 7 candidate (i.e., A1689-zD1: Bradley et al. 2008) and one z ∼ 6.5 candidate (Kneib et al. 2004) is found over these fields to the same magnitude limit (i.e., 25.5 AB mag) as is considered in the Richard et al. (2006) search.”
The SUBARU Deep Field Project: Lymanα Emitters at a Redshift of 6.6 (2004, methodology): “In this respect, our survey may not suffer from strong amplification by gravitational lensing, unlike several surveys made with the help of gravitational lensing (Ellis et al. 2001; Hu et al. 2002; Santos et al. 2004; Kneib et al. 2004; Pelló et al. 2004a).”
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Galaxies at z ~ 6: The UV Luminosity Function and Luminosity Density from 506 HUDF, HUDF Parallel ACS Field, and GOODS i-Dropouts (2005, background): “A similar evolution from bluer spectral slopes has already been noted in a number of other highredshift (z > 3) studies (Lehnert & Bremer 2003; Kneib et al. 2004; B06a; Bouwens et al. 2004c; Schaerer & Pelló 2005; Yan et al. 2005; cf. Ouchi et al. 2004).”
Mass and magnification maps for the Hubble Space Telescope Frontier Fields clusters: implications for high-redshift studies (2014, background): “…the study of distant background galaxies that would be unobservable without the magnification provided by the cluster lens (e.g. Ellis et al. 2001; Kneib et al. 2004; Richard et al. 2008; C© 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society at U…”
Simulations and Analytic Calculations of Bubble Growth during Hydrogen Reionization (2006, background): “…Oh 2002, Becker et al. 2005), high redshift gamma ray bursts (e.g. Barkana & Loeb 2004a; Totani et al. 2005), high redshift galaxy surveys (e.g. Kneib et al. 2004), and small-scale CMB measurements (Santos et al. 2003; Zahn et al. 2005; McQuinn et al. 2005), providing a wealth of observational…”
CLASH: THREE STRONGLY LENSED IMAGES OF A CANDIDATE z ≈ 11 GALAXY (2012, background): “Complementary to these searches of “blank” fields are searches behind strongly lensing galaxy clusters (Kneib et al. 2004; Bradley et al. 2008; Bouwens et al. 2009; Bradač et al. 2009; Maizy et al. 2010; Richard et al. 2011; Hall et al. 2012; Bradley et al. 2012a; Zitrin et al. 2012a; Wong et al.…”