  Aims: Using XMM-Newton data, we have aimed to study the nuclear outflow of
the nearby starburst galaxy NGC 253 in X-rays with respect to its morphology
and to spectral variations along the outflow. Methods: We analysed XMM-Newton
RGS spectra, RGS brightness profiles in cross-dispersion direction, narrow band
RGS and EPIC images and EPIC PN brightness profiles of the nuclear region and
of the outflow of NGC 253. Results: We detect a diversity of emission lines
along the outflow of NGC 253. This includes the He-like ions of Si, Mg, Ne and
O and their corresponding ions in the next higher ionisation state.
Additionally transitions from Fe XVII and Fe XVIII are prominent. The derived
temperatures from line ratios along the outflow range from 0.21+/-0.01 to
0.79+/-0.06 keV and the ratio of Fe XVII lines indicates a predominantly
collisionally ionised plasma. Additionally we see indications of a recombining
or underionized plasma in the Fe XVII line ratio. Derived electron densities
are 0.106+/-0.018 cm^-3 for the nuclear region and 0.025+/-0.003 cm^-3 for the
outflow region closest to the centre. The RGS image in the O VIII line energy
clearly shows the morphology of an outflow extending out to ~750 pc along the
south-east minor axis, while the north-west part of the outflow is not seen in
O VIII due to the heavy absorption by the galactic disc. This is the first time
that the hot wind fluid has been detected directly. The limb brightening seen
in Chandra and XMM-Newton EPIC observations is only seen in the energy range
containing the Fe XVII lines (550-750 eV). In all other energy ranges between
400 and 2000 eV no clear evidence of limb brightening could be detected.
