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

Abstract

We discuss new observational constraints on the abundance of faint high-redshift Ly emitters secured from a deep Keck near-infrared spectroscopic survey that utilizes the strong magnification provided by lensing galaxy clusters. In each of nine clusters, we have undertaken a systematic ''blind'' search for line emission with NIRSPEC in the J band within carefully selected regions that offer very high magnifications (k10; Y50;) for background sources with redshifts z ' 10. The high magnification enables the detection of emission at unprecedented flux limits (10 41 Y10 42 ergs s À1 ). As the comoving volumes probed are small, our survey is designed to address the important question of whether low-luminosity galaxies could provide the dominant ionizing flux at z $ 10. Our survey has yielded six promising (>5 ) candidate Ly emitters that lie between z = 8.7 and z = 10.2. We carefully discuss the validity of our detections and the likelihood that the detected line is Ly in light of earlier, apparently false, claims. Lower redshift line interpretations can be excluded, with reasonable assumptions, through the nondetection of secondary emission in further spectroscopy undertaken with LRIS and NIRSPEC. Nonetheless, as a result of our tests, we argue that at least two of our candidates are likely to be at z ' 10. Given the small survey volume, this suggests there is a large abundance of low-luminosity star-forming sources at z ' 8Y10. While the predicted reionization photon budget depends upon a large number of physical assumptions, our first glimpse at the z ' 10 universe suggests that low-luminosity starforming galaxies contribute a significant proportion of the UV photons necessary for cosmic reionization.

What if LIGO’s gravitational wave detections are strongly lensed by massive galaxy clusters?

“…multiple-imaging of a single galaxy -by massive galaxy clusters plays an invaluable role in discovering and studying new populations of objects at high redshift (e.g. Mellier et al 1991;Franx et al 1997;Ellis et al 2001;Smith et al 2002;Kneib et al 2004;Stark et al 2007;Willis et al 2008;Wardlow et al 2013;Bouwens et al 2014;Zheng et al 2014;Atek et al 2015;McLeod et al 2015). Indeed, gravitational magnification by massive clusters -albeit not multiple-imaging -was instrumental in the first detections of sub-mm galaxies (Smail, Ivison & Blain 1997;Ivison et al 1998).…”

On the physical properties ofz≈6–8 galaxies

“…Cuby et al 2007;Stark et al 2007b;Willis et al 2008;Hibon et al 2009;Sobral et al 2009). Furthermore, because of their faintness the photometry available is inadequate in terms of depth to allow studies of their stellar populations.…”

Limits on the luminosity function of Lyαemitters atz= 7.7

“…The determination of the Lyα luminosity function (LF) with infrared arrays is being actively pursued by several groups, either through narrow-band imaging (e.g Willis et al 2008;Cuby et al 2007) or through blind spectroscopy along the critical lines of galaxy clusters used as gravitational telescopes (Richard et al 2006;Stark et al 2007;Bouwens et al 2008). High-z galaxies are also being discovered using the dropout technique between the optical and near infrared domains, either in the field (see e.g.…”