The Distance and Dynamical History of the Virgo Cluster Ultradiffuse
  Galaxy VCC 615
  We use deep Hubble Space Telescope imaging to derive a distance to the Virgo
Cluster ultradiffuse galaxy (UDG) VCC 615 using the tip of the red giant branch
(TRGB) distance estimator. We detect 5,023 stars within the galaxy, down to a
50% completeness limit of F814W = 28.0, using counts in the surrounding field
to correct for contamination due to background sources and Virgo intracluster
stars. We derive an extinction-corrected F814W tip magnitude of $m_{\rm tip,0}
= 27.19^{+0.07}_{-0.05}$, yielding a distance of $d=17.7^{+0.6}_{-0.4}$ Mpc.
This places VCC 615 on the far side of the Virgo Cluster ($d_{\rm Virgo} = 16.5
Mpc$), at a Virgocentric distance of 1.3 Mpc and near the virial radius of the
main body of Virgo. Coupling this distance with the galaxy's observed radial
velocity, we find that VCC 615 is on an outbound trajectory, having survived a
recent passage through the inner parts of the cluster. Indeed, our orbit
modeling gives a 50% chance the galaxy passed inside the Virgo core (r<620 kpc)
within the past Gyr, although very close passages directly through the cluster
center (r<200 kpc) are unlikely. Given VCC 615's undisturbed morphology, we
argue that the galaxy has experienced no recent and sudden transformation into
a UDG due to the cluster potential, but rather is a long-lived UDG whose
relatively wide orbit and large dynamical mass protect it from stripping and
destruction by Virgo cluster tides. Finally, we also describe the serendipitous
discovery of a nearby Virgo dwarf galaxy projected 90 arcseconds (7.2 kpc) away
from VCC 615.
