Origin of the Diffuse, Far Ultraviolet Emission in the Interarm Regions
  of M101
  We present images from the Solar Blind Channel on HST that resolve hundreds
of far ultraviolet (FUV) emitting stars in two ~1 kpc$^2$ interarm regions of
the grand-design spiral M101. The luminosity functions of these stars are
compared with predicted distributions from simple star formation histories, and
are best reproduced when the star formation rate has declined recently (past
10-50 Myr). This pattern is consistent with stars forming within spiral arms
and then streaming into the interarm regions. We measure the diffuse FUV
surface brightness after subtracting all of the detected stars, clusters and
background galaxies. A residual flux is found for both regions which can be
explained by a mix of stars below our detection limit and scattered FUV light.
The amount of scattered light required is much larger for the region
immediately adjacent to a spiral arm, a bright source of FUV photons.
