Context :

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 \pm 0.01 to 0.79 \pm 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 \pm 0.018 cm ^ { -3 } for the nuclear region and 0.025 \pm 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 \sim 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 .

Conclusions :