An ALMA-HST Study of Millimeter Dust Emission and Star Clusters
  We present results from a joint ALMA-HST study of the nearby spiral galaxy
NGC 628. We combine the HST LEGUS database of over 1000 stellar clusters in NGC
628 with ALMA Cycle 4 millimeter/submillimeter observations of the cold dust
continuum that span ~15 square kpc including the nuclear region and western
portions of the galaxy's disk. The resolution -- 1.1" or approximately 50 pc at
the distance of NGC 628 -- allows us to constrain the spatial variations in the
slope of the millimeter dust continuum as a function of the ages and masses of
the nearby stellar clusters. Our results indicate an excess of dust emission in
the millimeter assuming a typical cold dust model for a normal star-forming
galaxy, but little correlation of the dust continuum slope with stellar cluster
age or mass. For the depth and spatial coverage of these observations, we
cannot substantiate the millimeter/submillimeter excess arising from the
processing of dust grains by the local interstellar radiation field. We detect
a bright unknown source in NGC 628 in ALMA bands 4 and 7 with no counterparts
at other wavelengths from ancillary data. We speculate this is possibly a dust
obscured supernova.
