Estimate of the Mass and Radial Profile of the Orphan-Chenab Stream's
  Dwarf Galaxy Progenitor Using MilkyWay@home
  We fit the mass and radial profile of the Orphan-Chenab Stream's (OCS) dwarf
galaxy progenitor by using turnoff stars in the Sloan Digital Sky Survey (SDSS)
and the Dark Energy Camera (DEC) to constrain N-body simulations of the OCS
progenitor falling into the Milky Way on the 1.5 PetaFLOPS MilkyWay@home
distributed supercomputer. We infer the internal structure of the OCS's
progenitor under the assumption that it was a spherically symmetric dwarf
galaxy comprised of a stellar system embedded in an extended dark matter halo.
We optimize the evolution time, the baryonic and dark matter scale radii, and
the baryonic and dark matter masses of the progenitor using a differential
evolution algorithm. The likelihood score for each set of parameters is
determined by comparing the simulated tidal stream to the angular distribution
of OCS stars observed in the sky. We fit the total mass of the OCS's progenitor
to ($2.0\pm0.3$) $\times 10^7 M_\odot$ with a mass-to-light ratio of
$\gamma=73.5\pm10.6$ and ($1.1\pm0.2$)$\times10^6M_{\odot}$ within 300 pc of
its center. Within the progenitor's half-light radius, we estimate total a mass
of ($4.0\pm1.0$)$\times10^5M_{\odot}$. We also fit the current sky position of
the progenitor's remnant to be
$(\alpha,\delta)=((166.0\pm0.9)^\circ,(-11.1\pm2.5)^\circ)$ and show that it is
gravitationally unbound at the present time. The measured progenitor mass is on
the low end of previous measurements, and if confirmed lowers the mass range of
ultrafaint dwarf galaxies. Our optimization assumes a fixed Milky Way
potential, OCS orbit, and radial profile for the progenitor, ignoring the
impact of the Large Magellanic Cloud.
