z ~ 2.5 - 3 Ionizers in the GOODS-N Field

TL;DR

This study investigates potential ionizing sources at redshifts 2.5-3 in the GOODS-N field using deep UV imaging and spectroscopy, finding that AGNs dominate the ionizing flux while candidate galaxies contribute minimally.

Contribution

First comprehensive spectroscopic survey combining deep UV imaging and multi-instrument data to identify and characterize ionizing sources at z ~ 2.5-3 in GOODS-N.

Findings

Bright AGN at z=2.583 dominates ionizing flux.

Candidate galaxies contribute less than needed for reionization.

Foreground contamination affects some candidate identifications.

Abstract

We use deep F275W imaging from the $Hubble$ Deep UV Legacy Survey (HDUV) and G280 grism spectroscopy from $HST$/WFC3, along with new and archival optical spectra from Keck/DEIMOS, to search for candidate ionizing sources in the GOODS-N field at z ~ 2.5 - 3. Spectroscopic identification of our UV-selected sources are 99% complete to F275W = 25.5 in the region of the UV imaging, and we identify 6 potential ionizing galaxies or AGNs at z ~ 3. By far the brightest of these is a z = 2.583 AGN that totally dominates the ionizing flux in the region, with a specific ionizing volume emissivity at $912~ \AA$ of $\epsilon_{912}$ = $8.3^{27}_{1.4} \times 10^{24}$ erg s$^{-1}$ Hz$^{-1}$ Mpc$^{-3}$. Based on our spectroscopic data, we find four candidates are contaminated by foreground galaxies at z ~ 0.5 - 0.7. At $\epsilon_{912}$ = $2.2^{7.2}_{0.4} \times 10^{23}$ erg s$^{-1}$ Hz$^{-1}$ Mpc$^{-3}$, the remaining candidate galaxy's contribution to the ionizing background lies well below the flux required to ionize the intergalactic medium at z ~ 2.5 - 3, consistent with previous observations that show AGNs provide the bulk of the ionizing background at these redshifts.