The Pristine survey XIII: Uncovering the very metal-poor tail of the thin disc

Emma Fernández-Alvar*, Georges Kordopatis, Vanessa Hill, Else Starkenburg, Akshara Viswanathan, Nicolas F. Martin, Guillaume F. Thomas, Julio F. Navarro, Khyati Malhan, Federico Sestito, Jonay I. González Hernández, Raymond G. Carlberg

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

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We evaluate the rotational velocity of stars observed by the Pristine survey towards the Galactic anticentre spanning a wide range of metallicities from the extremely metal-poor regime ([Fe/H] < -3) to nearly solar metallicity. In the Galactic anticentre direction, the rotational velocity (Vφ) is similar to the tangential velocity in the galactic longitude direction (Vℓ). This allows us to estimate Vφ from Gaia early data release 3 (Gaia EDR3) proper motions for stars without radial velocity measurements. This substantially increases the sample of stars in the outer disc with estimated rotational velocities. Our stellar sample towards the anticentre is dominated by a kinematical thin disc with a mean rotation of ∼-220 km s-1. However, our analysis reveals the presence of more stellar substructures. The most intriguing is a well-populated extension of the kinematical thin disc down to [Fe/H] ∼-2. A scarcer fast-rotating population reaching the extremely metal-poor regime down to [Fe/H] ∼-3.5 is also detected but without statistical significance to unambiguously state whether this is the extremely metal-poor extension of the thin disc or the high-rotating tail of hotter structures (like the thick disc or the halo). In addition, a more slowly rotating kinematical thick disc component is also required to explain the observed Vℓ distribution at [Fe/H] > -1.5. Furthermore, we detect signatures of a 'heated disc', the so-called Splash, at metallicities higher than ∼-1.5. Finally, at [Fe/H] < -1.5 our anticentre sample is dominated by a kinematical halo with a net prograde motion.

Original languageEnglish
Pages (from-to)1509-1525
Number of pages17
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Early online date17-Sept-2021
Publication statusPublished - 1-Nov-2021


  • Galaxy: abundances
  • Galaxy: disc
  • Galaxy: kinematics and dynamics

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