No evidence for large-scale outflows in the extended ionised halo of
  ULIRG Mrk273
  We present deep new GTC/OSIRIS narrow-band images and optical WHT/ISIS
long-slit spectroscopy of the merging system Mrk273 that show a spectacular
extended halo of warm ionised gas out to a radius of $\sim45$ kpc from the
system nucleus. Outside of the immediate nuclear regions (r > 6 kpc), there is
no evidence for kinematic disturbance in the ionised gas: in the extended
regions covered by our spectroscopic slits the emission lines are relatively
narrow (FWHM $\lesssim$ 350 km$\rm s^{-1}$) and velocity shifts small
(|$\Delta$V| $\lesssim{} $250 km$\rm s^{-1}$). This is despite the presence of
powerful near-nuclear outflows (FWHM > 1000 km$\rm s^{-1}$; |$\Delta$V| > 400
km$\rm s^{-1}$; r < 6 kpc). Diagnostic ratio plots are fully consistent with
Seyfert 2 photo-ionisation to the NE of the nuclear region, however to the SW
the plots are more consistent with low-velocity radiative shock models. The
kinematics of the ionised gas, combined with the fact that the main structures
are aligned with low-surface-brightness tidal continuum features, are
consistent with the idea that the ionised halo represents tidal debris left
over from a possible triple-merger event, rather than a reservoir of outflowing
gas.
