Delayed Stellar Mass Assembly in the Low Surface Brightness Dwarf Galaxy
  KDG215
  We present HI spectral line and optical broadband images of the nearby low
surface brightness dwarf galaxy KDG215. The HI images, acquired with the Karl
G. Jansky Very Large Array (VLA), reveal a dispersion dominated ISM with only
weak signatures of coherent rotation. The HI gas reaches a peak mass surface
density of 6 M$_{\odot}$ pc$^{-2}$ at the location of the peak surface
brightness in the optical and the UV. Although KDG215 is gas-rich, the
H$\alpha$ non-detection implies a very low current massive star formation rate.
In order to investigate the recent evolution of this system, we have derived
the recent and lifetime star formation histories from archival Hubble Space
Telescope images. The recent star formation history shows a peak star formation
rate $\sim$1 Gyr ago, followed by a decreasing star formation rate to the
present day quiescent state. The cumulative star formation history indicates
that a significant fraction of the stellar mass assembly in KDG215 has occurred
within the last 1.25 Gyr. KDG215 is one of only a few known galaxies which
demonstrates such a delayed star formation history. While the ancient stellar
population (predominantly red giants) is prominent, the look-back time by which
50% of the mass of all stars ever formed had been created is among the youngest
of any known galaxy.
