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We fit the mass and radial profile of the Orphan-Chenab Stream's (OCS) dwarfgalaxy 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 OCSprogenitor falling into the Milky Way on the 1.5 PetaFLOPS MilkyWay@homedistributed supercomputer. We infer the internal structure of the OCS'sprogenitor under the assumption that it was a spherically symmetric dwarfgalaxy comprised of a stellar system embedded in an extended dark matter halo.We optimize the evolution time, the baryonic and dark matter scale radii, andthe baryonic and dark matter masses of the progenitor using a differentialevolution algorithm. The likelihood score for each set of parameters isdetermined by comparing the simulated tidal stream to the angular distributionof OCS stars observed in the sky. We fit the total mass of the OCS's progenitorto ($2.0\pm0.3$) $\times 10^7 M_\odot$ with a mass-to-light ratio of$\gamma=73.5\pm10.6$ and ($1.1\pm0.2$)$\times10^6M_{\odot}$ within 300 pc ofits center. Within the progenitor's half-light radius, we estimate total a massof ($4.0\pm1.0$)$\times10^5M_{\odot}$. We also fit the current sky position ofthe progenitor's remnant to be$(\alpha,\delta)=((166.0\pm0.9)^\circ,(-11.1\pm2.5)^\circ)$ and show that it isgravitationally unbound at the present time. The measured progenitor mass is onthe low end of previous measurements, and if confirmed lowers the mass range ofultrafaint dwarf galaxies. Our optimization assumes a fixed Milky Waypotential, OCS orbit, and radial profile for the progenitor, ignoring theimpact of the Large Magellanic Cloud.

Estimate of the Mass and Radial Profile of the Orphan-Chenab Stream's Dwarf Galaxy Progenitor Using MilkyWay@home