Active galactic nuclei (AGN) drive powerful, multiphase outflows that are thought to play a key role in galaxy evolution. The hot, shocked phase of these outflows ($T \gtrsim 10^{ 6} \rm{ \ K}$) is expected to dominate the energy content, but is challenging to observe due to its long cooling time and low emissivity. The cool phase ($T \lesssim 10^{ 4} \rm{ \ K}$) is easier to detect observationally, but it traces a less energetic outflow component. In prior simulations of the interaction between an energy-driven AGN outflow and a clumpy ISM, we found that mixing between hot wind and cool ISM clouds produces a new, highly radiative, phase at $T \approx 10^{ 6-7} \rm{ \ K}$ which fuels the formation of a long-lived ($\geq 5\ \rm{ Myr}$) cool outflow. We investigate the X-ray emission generated by thermal Bremsstrahlung and high-ionisation metal line emission in this mixing phase, finding that it could contribute significantly to the X-ray output of the outflow. This mixing-induced X-ray emission is strongest in the part of the outflow propagating equatorially through the disc, and is extended on scales of $D\simeq 3-4\ \rm{ kpc}$. For quasar luminosities of $L_{ \rm{ AGN}}\simeq 10^{ 45-46}\rm{ \ erg\ s^{ -1}}$, the resulting X-ray luminosity is equivalent to that expected from star formation rates $\rm{ SFR}\simeq 10-200\ \rm{ M_\odot\ yr^{ -1}}$, showing that it could be an important source of soft X-rays in AGN host galaxies. Our results suggest that this extended emission could be resolvable in local quasars ($z\lesssim 0.11$) using high spatial-resolution X-ray observatories such as Chandra, or proposed missions such as AXIS and Lynx.
Categories: astro-ph.GA