Microwave Continuum Emission and Dense Gas Tracers in NGC 3627:
  Combining Jansky VLA and ALMA Observations
  We present Karl G. Jansky Very Large Array (VLA) Ka band (33 GHz) and Atacama
Large Millimeter Array (ALMA) Band 3 (94.5 GHz) continuum images covering the
nucleus and two extranuclear star-forming regions within the nearby galaxy NGC
3627 (M 66), observed as part of the Star Formation in Radio Survey (SFRS).
Both images achieve an angular resolution of $\lesssim$2\arcsec, allowing us to
map the radio spectral indices and estimate thermal radio fractions at a linear
resolution of $\lesssim$90 pc at the distance of NGC 3627. The thermal fraction
at 33 GHz reaches unity at and around the peaks of each HII region; we
additionally observed the spectral index between 33 and 94.5 GHz to become both
increasingly negative and positive away from the peaks of the HII regions,
indicating an increase of non-thermal extended emission from diffusing
cosmic-ray electrons and the possible presence of cold dust, respectively.
While the ALMA observations were optimized for collecting continuum data, they
also detected line emission from the $J=1\rightarrow0$ transitions of HCN and
HCO$^{+}$. The peaks of dense molecular gas traced by these two spectral lines
are spatially offset from the peaks of the 33 and 94.5 GHz continuum emission
for the case of the extranuclear star-forming regions, indicating that our data
reach an angular resolution at which one can spatially distinguish sites of
recent star formation from the sites of future star formation. Finally, we find
trends of decreasing dense gas fraction and velocity dispersion with increasing
star formation efficiency among the three regions observed, indicating that the
dynamical state of the dense gas, rather than its abundance, plays a more
significant role in the star formation process.
