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

Pampliega, B. A., Pérez González, P. G., Barro, G., Sánchez, H. D., Eliche Moral, M. C., Cardiel, N., Hernán Caballero, A., Rodríguez Muñoz, L., Blazquer, P. S., Esquej, P. 2019. Optically Faint Massive Balmer Break Galaxies at z > 3 in the CANDELS/GOODS Fields. Astrophysical Journal 876, 2 DOI: 10.3847/1538-4357/ab14f2

We present a sample of 33 Balmer break galaxies (BBGs) selected as Hubble Space Telescope /F160W dropouts in the deepest CANDELS/GOODS fields (H greater than or similar to 27.3 mag) but relatively bright in Spitzer/IRAC ([3.6], [4.5] < 24.5 mag), implying red colors (median and quartiles: < H – [3.6]> = 3.1(2.8)(3.4) mag). Half of these BBGs are newly identified sources. Our BBGs are massive (< log(M/M-circle dot)> = 10.8(10.4)(11.0)), high-redshift (< z > = 4.8(4.4)(5.1)), dusty (< A (V)> = 2.0(1.5)(2.0)mag) 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 beta + [O III], H alpha + [N II]) boosting the IRAC fluxes and red colors. Approximately 20% of the BBGs are very dusty (A (V) similar to 2.5 mag) starbursts with strong mid-to-far-infrared detections and extreme SFRs (SFR > 10(3) M-circle dot yr(-1)) that place them above the MS. The rest, 30%, are post-starbursts or quiescent galaxies located >2 sigma 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 log(M/M-circle dot) > 10 galaxies at z > 3, but it is a significant contributor (30%) to the general population of red log(M/M-circle dot) > 11 galaxies at 4 < z < 6. Finally, our results point out that one of every 30 massive log(M/M-circle dot) > 11 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.

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