The Taiwan ECDFS Near-Infrared Survey: Very Bright End of the Luminosity Function at z>7

TL;DR

The paper reports on a deep near-infrared survey in the ECDFS field, identifying a rare galaxy candidate at z>7 that challenges existing models of early galaxy formation.

Contribution

It introduces new color selection criteria and a deconvolution method for IRAC flux measurement, leading to the identification of a luminous high-z galaxy candidate.

Findings

Only one z>7 candidate found, TENIS-ZD1.

TENIS-ZD1 is a young starburst galaxy with a stellar mass of 3.2×10^10 M_sun.

The candidate challenges current galaxy formation models.

Abstract

The primary goal of the Taiwan ECDFS Near-Infrared Survey (TENIS) is to find well screened galaxy candidates at z>7 (z' dropout) in the Extended Chandra Deep Field-South (ECDFS). To this end, TENIS provides relatively deep J and Ks data (~25.3 ABmag, 5-sigma) for an area of 0.5*0.5 degree. Leveraged with existing data at mid-infrared to optical wavelengths, this allows us to screen for the most luminous high-z objects, which are rare and thus require a survey over a large field to be found. We introduce new color selection criteria to select a z>7 sample with minimal contaminations from low-z galaxies and Galactic cool stars; to reduce confusion in the relatively low angular resolution IRAC images, we introduce a novel deconvolution method to measure the IRAC fluxes of individual sources. Illustrating perhaps the effectiveness at which we screen out interlopers, we find only one z>7 candidate, TENIS-ZD1. The candidate has a weighted z_phot of 7.8, and its colors and luminosity indicate a young (45M years old) starburst galaxy with a stellar mass of 3.2*10^10 M_sun. The result matches with the observational luminosity function analysis and the semi-analytic simulation result based on the Millennium Simulations, which may over predict the volume density for high-z massive galaxies. The existence of TENIS-ZD1, if confirmed spectroscopically to be at z>7, therefore poses a challenge to current theoretical models for how so much mass can accumulate in a galaxy at such a high redshift.