Rest-frame ultraviolet spectra of massive galaxies at z similar to 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. In this paper we aim to: (1) confirm spectroscopically the redshifts of a sample of massive galaxies selected with photometric redshifts z(phot) > 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 approximate to 2000) FORS2 rest-frame UV spectra for 11 targets. We confirmed that 9 out of 11 have spectroscopic redshifts z(spec) > 2.5. We also serendipitously found two mask fillers at redshift z(spec) > 2.5, which originally were assigned photometric redshifts 2.0 <z(phot) <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 from 480 km s(-1) to 1518 km s(-1). The two galaxies with highest velocity show signs of AGN. We revised the spectral energy distribution fitting U-band through 8 mu m photometry, including the analysis of a power-law component subtraction to identify the possible presence of active galactic nuclei (AGN). The revised stellar masses of all but one of our targets are greater than or similar to 10(10) M-circle dot, with four having stellar masses >5x10(10) M-circle dot. Three galaxies have a significant power-law component in their spectral energy distributions, which indicates that they host AGN. We conclude that massive galaxies are characterised by significantly higher velocity outflows than the typical Lyman break galaxies at z similar to 3. The incidence of high-velocity outflows (similar to 40% within our sample) is also much higher than among massive galaxies at z <1, which is consistent with the powerful star formation and nuclear activity that most massive galaxies display at z > 2.