Searching for the lost Unicorn: a prominent feature in the radial velocity distribution of stars in Vela from Gaia DR2 data

Stellar streams are ubiquitous in the Galactic halo and they can be used to improve our understanding of the formation and evolution of the Milky Way as a whole. The so-called Monoceros Ring might have been the result of satellite accretion. Guglielmo et al. have used N-body simulations to search for the progenitor of this structure. Their analysis shows that, if the Ring has a dwarf galaxy progenitor, it might be found in the background of one out of eight specific areas in the sky. Here, we use Gaia DR2 data to perform a systematic exploration aimed at confirming or rejecting this remarkable prediction. Focusing on the values of the radial velocity to uncover possible multimodal spreads, we identify a bimodal Gaussian distribution towards Galactic coordinates (l, b) = (271 degrees, +2 degrees) in Vela, which is one of the locations of the progenitor proposed by Guglielmo et al. This prominent feature with central values 60 +/- 7 and 97 +/- 10 km s(-1), may signal the presence of the long sought progenitor of the Monoceros Ring, but the data might also be compatible with the existence of an unrelated, previously unknown, kinematically coherent structure.