Optically Faint Massive Balmer Break Galaxies at z > 3 in the CANDELS/GOODS Fields

Abstract

We present a sample of 33 Balmer break galaxies (BBGs) selected as Hubble Space Telescope /F160W dropouts in the deepest CANDELS/GOODS fields ( H ≳ 27.3 mag) but relatively bright in Spitzer /IRAC ([3.6], [4.5] < 24.5 mag), implying red colors (median and quartiles: ). Half of these BBGs are newly identified sources. Our BBGs are massive ( ), high-redshift ( ), dusty ( ) galaxies. The spectral energy distributions (SEDs) of half of our sample indicate that they are star-forming galaxies with typical specific star formation rates (SFRs) of 0.5–1.0 Gyr −1 , qualifying them as main-sequence (MS) galaxies at 3 <  z  < 6. One-third of these SEDs indicate the presence of prominent emission lines (H β + [O iii ], H α + [N ii ]) boosting the IRAC fluxes and red colors. Approximately 20% of the BBGs are very dusty ( A ( V ) ∼ 2.5 mag) starbursts with strong mid-to-far-infrared detections and extreme SFRs (SFR > 10 3 M ☉ yr −1 ) that place them above the MS. The rest, 30%, are post-starbursts or quiescent galaxies located >2 σ below the MS with mass-weighted ages older than 700 Myr. Only two of the 33 galaxies are X-ray-detected active galactic nuclei (AGNs) with optical/near-infrared SEDs dominated by stellar emission, but the presence of obscured AGNs in the rest of the sources cannot be discarded. Our sample accounts for 8% of the total number density of galaxies at z  > 3, but it is a significant contributor (30%) to the general population of red galaxies at 4 <  z  < 6. Finally, our results point out that one of every 30 massive galaxies in the local universe was assembled in the first 1.5 Gyr after the big bang, a fraction that is not reproduced by state-of-the-art galaxy formation simulations.