Studying the kinematics of the giant star-forming region 30 Doradus. I.
  The data
  We present high-quality VLT-FLAMES optical spectroscopy of the nebular gas in
the giant star-forming region 30 Doradus. In this paper, the first of a series,
we introduce our observations and discuss the main kinematic features of 30
Dor, as revealed by the spectroscopy of the ionized gas in the region. The
primary data set consists of regular grid of nebular observations, which we
used to produce a spectroscopic datacube of 30 Dor, centered on the massive
star cluster R136 and covering a field-of-view of 10'x10'. The main emission
lines present in the datacube are from Halpha and [NII]6548,6584. The Halpha
emission-line profile varies across the region from simple single-peaked
emission to complex, multiple-component profiles, suggesting that different
physical mechanisms are acting on the excited gas. To analyse the gas
kinematics we fit Gaussian profiles to the observed Halpha features.
Unexpectedly, the narrowest Halpha profile in our sample lies close to the
supernova remnant 30 Dor B. We present maps of the velocity field and velocity
dispersion across 30 Dor, finding five previously unclassified expanding
structures. These maps highlight the kinematic richness of 30 Dor (e.g.
supersonic motions), which will be analysed in future papers.
