Abstract
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 larger than 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 larger than 2.5. We
also serendipitously found two mask fillers at redshift larger than 2.5, which
originally were assigned photometric redshifts between 2.0 and 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 and 1528 km/s. We revised the spectral energy
distribution fitting U-band through 8 micron 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 larger than 1e10 solar masses, with four having stellar masses 5e10
solar masses. 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 redshifts around 3. The
incidence of high-velocity outflows (approximately 40 per cent within our
sample) is also much higher than among massive galaxies at redshifts below 1.
(Abridged)
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