Rest-frame ultraviolet spectra of massive galaxies at z ~ 3: evidence of high-velocity outflows

Galaxy formation models invoke the presence of strong feedback mechanisms that regulate the growth of massive galaxies at high redshifts. Providing observational evidence of these processes is crucial to justify and improve these prescriptions. In this paper we aim to (1) confirm spectroscopically the redshifts of a sample of massive galaxies selected with photometric redshifts zphot > 2.5; (2) investigate the properties of their stellar and interstellar media; (3) detect the presence of outflows and measure their velocities. To achieve this, we analysed deep, high-resolution (R ≈ 2000) FORS2 rest-frame UV spectra for 11 targets. We confirmed that 9 out of 11 have spectroscopic redshifts zspec > 2.5. We also serendipitously found two mask fillers at redshift zspec > 2.5, which originally were assigned photometric redshifts 2.0 <zphot <2.5. In the four highest quality spectra we derived outflow velocities by fitting the absorption line profiles with models including multiple dynamical components. We found strongly asymmetric, high-ionisation lines, from which we derived outflow velocities ranging between 480 km s-1 and 1518 km s-1. The two highest velocity outflows correspond to galaxies with active galactic nuclei (AGNs). We revised the spectral energy distribution fitting U-band through 8 μm photometry, including the analysis of a power-law component subtraction to identify the possible presence of AGNs. The revised stellar masses of all but one of our targets are ≳ 1010 M⊙, with four having stellar masses > 5 × 1010 M⊙. Three galaxies have significant power-law components in their spectral energy distributions, indicating that they host AGNs. We conclude that massive galaxies are characterised by significantly higher velocity outflows than the typical Lyman-break galaxies at z ~ 3. The incidence of high-velocity outflows (~40% within our sample) is also much higher than among massive galaxies at z <1, consistent with the powerful star formation and nuclear activity that most massive galaxies display at z > 2