A Remarkably Luminous Galaxy at z=11.1 Measured with Hubble Space Telescope Grism Spectroscopy

TL;DR

This paper reports the spectroscopic confirmation of a remarkably luminous galaxy at redshift 11.1, extending the observable universe's early galaxy formation epoch and demonstrating the potential of upcoming telescopes like JWST and WFIRST.

Contribution

First spectroscopic confirmation of a galaxy at z=11.1, showing early galaxy build-up and high luminosity at this epoch, using Hubble WFC3/IR grism spectroscopy.

Findings

Galaxy GN-z11 is at z=11.1, just 400 million years after the Big Bang.

The galaxy's UV luminosity exceeds typical values at z~6-8 by three times.

Spectroscopic data suggest a stellar mass of approximately 10^9 solar masses.

Abstract

We present Hubble WFC3/IR slitless grism spectra of a remarkably bright $z\gtrsim10$ galaxy candidate, GN-z11, identified initially from CANDELS/GOODS-N imaging data. A significant spectroscopic continuum break is detected at $\lambda=1.47\pm0.01~\mu$m. The new grism data, combined with the photometric data, rule out all plausible lower redshift solutions for this source. The only viable solution is that this continuum break is the Ly$\alpha$ break redshifted to ${z_\mathrm{grism}=11.09^{+0.08}_{-0.12}}$, just $\sim$400 Myr after the Big Bang. This observation extends the current spectroscopic frontier by 150 Myr to well before the Planck (instantaneous) cosmic reionization peak at z~8.8, demonstrating that galaxy build-up was well underway early in the reionization epoch at z>10. GN-z11 is remarkably and unexpectedly luminous for a galaxy at such an early time: its UV luminosity is 3x larger than L* measured at z~6-8. The Spitzer IRAC detections up to 4.5 $\mu$m of this galaxy are consistent with a stellar mass of ${\sim10^{9}~M_\odot}$. This spectroscopic redshift measurement suggests that the James Webb Space Telescope (JWST) will be able to similarly and easily confirm such sources at z>10 and characterize their physical properties through detailed spectroscopy. Furthermore, WFIRST, with its wide-field near-IR imaging, would find large numbers of similar galaxies and contribute greatly to JWST's spectroscopy, if it is launched early enough to overlap with JWST.