Detection of extended millimeter emission in the host galaxy of 3C273
  and its implications for QSO feedback via high dynamic range ALMA imaging
  We estimate the amount of negative feedback energy injected into the ISM of
the host galaxy of 3C273, a prototypical radio loud quasar. We obtained 93, 233
and 343 GHz continuum images with the Atacama Large Millimeter/Sub-millimeter
Array (ALMA). After self calibration and point source subtraction, we reach an
image dynamic range of $\sim 85000$ at 93\ GHz, $\sim 39000$ at 233\ GHz and
$\sim 2500$ at 343\ GHz. These are currently the highest image dynamic range
obtained using ALMA. We detect spatially extended millimeter emission
associated with the host galaxy, cospatial with the Extended Emission Line
Region (EELR) observed in the optical. The millimeter spectral energy
distribution and comparison with centimeter data show that the extended
emission cannot be explained by dust thermal emission, synchrotron or thermal
bremsstrahlung arising from massive star formation. We interpret the extended
millimeter emission as thermal bremsstrahlung from gas directly ionized by the
central source. The extended flux indicates that at least $\sim 7\%$ of the
bolometric flux of the nuclear source was used to ionize atomic hydrogen in the
host galaxy. The ionized gas is estimated to be as massive as $10^{10}$ to
$10^{11}\ \mathrm{M_\odot}$, but the molecular gas fraction with respect to the
stellar mass is consistent with other ellipticals, suggesting that direct
ionization ISM by the QSO may not be sufficient to suppress star formation, or
we are witnessing a short timescale before negative feedback becomes
observable. The discovery of a radio counterpart to EELRs provides a new
pathway to studying the QSO-host ISM interaction.
