The fall of the Northern Unicorn: Tangential motions in the Galactic Anti-centre with SDSS and Gaia

T. J. L. de Boer, V. Belokurov, S. E. Koposov

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

We present the first detailed study of the behaviour of the stellar proper motion across the entire Galactic anticentre area visible in the Sloan Digital Sky Survey (SDSS) data. We use recalibrated SDSS astrometry in combination with positions from Gaia DR1 to provide tangential motion measurements with a systematic uncertainty <5 km s−1 for the Main Sequence stars at the distance of the Monoceros Ring. We demonstrate that Monoceros members rotate around the Galaxy with azimuthal speeds of ∼230 km s−1, only slightly lower than that of the Sun. Additionally, both vertical and azimuthal components of their motion are shown to vary considerably but gradually as a function of Galactic longitude and latitude. The stellar overdensity in the anti-centre region can be split into two components, the narrow, stream-like ACS and the smooth Ring. According to our analysis, these two structures show very similar but clearly distinct kinematic trends, which can be summarized as follows: the amplitude of the velocity variation in vϕ and vz in the ACS is higher compared to the Ring, whose velocity gradients appear to be flatter. Currently, no model available can explain the entirety of the data in this area of the sky. However, the new accurate kinematic map introduced here should provide strong constraints on the genesis of the Monoceros Ring and the associated substructure.
Original languageEnglish
JournalMonthly Notices of the Royal Astronomical Society
Early online date15 Sept 2017
DOIs
Publication statusPublished - 1 Jan 2018

Keywords / Materials (for Non-textual outputs)

  • astro-ph.GA

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