A spectroscopic follow-up program of very massive galaxies at 3<z<4: confirmation of spectroscopic redshifts, and a high fraction of powerful AGN

Understand

We present the analysis and results of a spectroscopic follow-up program of a mass-selected sample of six galaxies at 3 < z < 4 using data from Keck-NIRSPEC and VLT-Xshooter.

• We confirm the z > 3 redshifts for half of the sample through the detection of strong nebular emission lines, and improve the zphot accuracy for the remainder of the sample through the combination of photometry and spectra.
• The modeling of the emission-line-corrected spectral energy distributions (SEDs) adopting improved redshifts confirms the very large stellar masses of the sample (M_* ~ 1.5-4 x 10^11 Msun) in the first 2 Gyrs of cosmic history, with a diverse range in stellar ages, star formation rates and dust content.
• From the analysis of emission line luminosities and widths, and far-infrared (FIR) fluxes we confirm that >80% of the sample are hosts to luminous hidden active galactic nuclei (AGNs), with bolometric luminosities of ~10^(44-46) erg/s.