KCWI Observations of the Extended Nebulae in Mrk 273

Ultraluminous infrared galaxies (ULIRGs) represent a critical stage in the merger-driven evolution of galaxies when AGN activity is common and AGN feedback is expected. We present high sensitivity and large field of view intergral field spectroscopy of the ULIRG Mrk 273 using new data from the Keck Cosmic Web Imager (KWCI). The KCWI data captures the complex nuclear region and the two extended nebulae in the northeast (NE) and southwest (SW) to $\sim 20$ kpc scales. Kinematics in the nuclear region show a fast, extended, bipolar outflow in the direction of the previously reported nuclear superbubbles spanning $\sim 5$ kpc, two to three times greater than the previously reported size. The larger scale extended nebulae on $\sim 20$ kpc show fairly uniform kinematics with FWHM $\sim 300 ~\kmps$ in the SW nebula and FWHM $\sim 120 ~\kmps$ in the NE nebula. We detect for the first time high ionization [NeV]3426, [OIII]4363 and HeII4684 emission lines in the extended NE nebula. Emission line ratios in the nuclear region correlate with the kinematic structures, with the bipolar outflow and the less collimated "outflow regions" showing distinct line ratio trends. Line ratio diagnostics of high ionization emission lines reveal non-trivial contribution from shock plus precursor ionization in the NE nebula and the nuclear region, mixed with AGN photoionization. These data are highly constraining for models of cool ionized gas existing ~20 kpc from a galactic nucleus.