New results from the magellan imacs spectroscopic lyα survey: Nicmos observations of lyα emitters at z = 5.7

Abstract

We present NICMOS J110 (rest-frame 1200-2100 Å) observations of the three z = 5.7 Lyα emitters discovered in the blind multislit spectroscopic survey by Martin et al. These images confirm the presence of the two sources that were previously only seen in spectroscopic observations. The third source, which is undetected in our J110 observations, has been detected in narrowband imaging of the Cosmic Origins Survey, so our nondetection implies a rest-frame equivalent width >146Å (3σ). The two J110-detected sources have more modest rest-frame equivalent widths of 30-40 Å, but all three are typical of high-redshift Lyα emitters. In addition, the J110-detected sources have UV luminosities that are within a factor of 2 of L UV*, and sizes that appear compact (rhl ∼ 0″.15) in our NIC2 images-consistent with a redshift of 5.7. We use these UV-continuum and Lyα measurements to estimate the i 775-z850 colors of these galaxies and show that at least one and possibly all three would be missed by the i-dropout Lyman break galaxy selection. These observations help demonstrate the utility of multislit narrowband spectroscopy as a technique for finding faint emission-line. © 2010 The American Astronomical Society. All rights reserved.