A Lyman Break Galaxy Candidate at z~9

TL;DR

This paper reports the discovery of a candidate galaxy at redshift approximately 9, using multi-wavelength photometry, suggesting minimal evolution of the UV luminosity function from z~9 to z~3, pending confirmation.

Contribution

First identification of a z~9 Lyman Break Galaxy candidate using NICMOS and Spitzer data, with photometric redshift analysis and implications for galaxy evolution.

Findings

96% probability of z>7 for the galaxy

Lower limit on number density of phi > 3.8 x 10^{-6} Mpc^{-3}

Indication of little evolution in UV luminosity function from z~9 to z~3

Abstract

We report the discovery of a z~9 Lyman Break Galaxy (LBG) candidate, selected from the NICMOS Parallel Imaging Survey as a J-dropout with J110 - H160 = 1.7. Spitzer/IRAC photometry reveals that the galaxy has a blue H160 - 3.6 um color, and a spectral break between 3.6 and 4.5 um. We interpret this break as the Balmer break, and derive a best-fit photometric redshift of z~9. We use Monte Carlo simulations to test the significance of this photometric redshift, and show a 96% probability of z>7. We estimate a lower limit to the comoving number density of such galaxies at z~9 of phi > 3.8 x 10^{-6} Mpc^{-3}. If the high redshift of this galaxy is confirmed, this will indicate that the luminous end of the rest-frame UV luminosity function has not evolved substantially from z~ 9 to z~3. Still, some small degeneracy remains between this z~9 model and models at z~2-3; deep optical imaging (reaching I ~ 29 AB) can rule out the lower-z models.