Radial distribution of gas and dust in the two spiral galaxies M99 and
  M100
  By combining Herschel-SPIRE data with archival Spitzer, HI, and CO maps, we
investigate the spatial distribution of gas and dust in the two famous
grand-design spirals M99 and M100 in the Virgo cluster. Thanks to the unique
resolution and sensitivity of the Herschel-SPIRE photometer, we are for the
first time able to measure the distribution and extent of cool, submillimetre
(submm)-emitting dust inside and beyond the optical radius. We compare this
with the radial variation in both the gas mass and the metallicity. Although we
adopt a model-independent, phenomenological approach, our analysis provides
important insights. We find the dust extending to at least the optical radius
of the galaxy and showing breaks in its radial profiles at similar positions as
the stellar distribution. The colour indices f350/f500 and f250/f350 decrease
radially consistent with the temperature decreasing with radius. We also find
evidence of an increasing gas to dust ratio with radius in the outer regions of
both galaxies.
