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

Abstract

We use deep F275W imaging from the Hubble Deep UV Legacy Survey (HDUV) and G280 grism spectroscopy from the Hubble Space Telescope/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 six potential ionizing galaxies or active galactic nuclei (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 Å of {ɛ }₉₁₂={8.3}_1.4²⁷× {10}²⁴ erg s^-1 Hz^-1 Mpc^-3. Based on our spectroscopic data, we find that four candidates are contaminated by foreground galaxies at z ∼ 0.5-0.7. At {ɛ }₉₁₂={2.2}_0.4^7.2× {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 that AGNs provide the bulk of the ionizing background at these redshifts.