Bright Strongly Lensed Galaxies at Redshift z~ 6-7 behind the Clusters Abell 1703 and CL0024+161

TL;DR

This paper reports the discovery of three bright, strongly-lensed galaxies at redshifts around 6-7 behind galaxy clusters, revealing their properties, potential physical associations, and implications for high-redshift galaxy populations.

Contribution

First identification of multiple bright, strongly-lensed galaxies at z~6-7 with detailed photometric analysis and lensing models, highlighting complex high-redshift galaxy structures.

Findings

One galaxy is among the brightest known at z>5.5.

Two galaxies are likely physically associated at similar redshifts.

Complex systems with dual nuclei may be common at high redshift.

Abstract

We report on the discovery of three bright, strongly-lensed objects behind Abell 1703 and CL0024+16 from a dropout search over 25 square arcminutes of deep NICMOS data, with deep ACS optical coverage. They are undetected in the deep ACS images below 8500 A and have clear detections in the J and H bands. Fits to the ACS, NICMOS and IRAC data yield robust photometric redshifts in the range z~6-7 and largely rule out the possibility that they are low-redshift interlopers. All three objects are extended, and resolved into a pair of bright knots. The bright i-band dropout in Abell 1703 has an H-band AB magnitude of 23.9, which makes it one of the brightest known galaxy candidates at z>5.5. Our model fits suggest a young, massive galaxy only ~ 60 million years old with a mass of ~ 1E10 solar mass. The dropout galaxy candidates behind CL0024+16 are separated by 2.5" (~ 2 kpc in the source plane), and have H-band AB magnitudes of 25.0 and 25.6. Lensing models of CL0024+16 suggest that the objects have comparable intrinsic magnitudes of AB ~ 27.3, approximately one magnitude fainter than L* at z~6.5. Their similar redshifts, spectral energy distribution, and luminosities, coupled with their very close proximity on the sky, suggest that they are spatially associated, and plausibly are physically bound. Combining this sample with two previously reported, similarly magnified galaxy candidates at z~6-8, we find that complex systems with dual nuclei may be a common feature of high-redshift galaxies.