Studies on the halo rotation In the LAMOST-Gaia era
Hao Tian @ NAOC Collaborators: Chao Liu, Yan Xu, Xiang-Xiang Xue and Yougang Wang Why
• Rotation of the halo
• formation——hierarchical merging satellites
• AM transferred from the satellites to the halo
Bonaca et al. 2012 Why
• Rotation of the halo
• formation——hierarchical merging satellites
• AM transferred from the satellites to the halo
• Interaction between different components in the Milky Way Bonaca et al. 2012
• AM transferred from the bar/disk to the halo (Athanassoula’s work) Why now
• Large sample & accurate measurements of the velocity parameters
• LAMOST has released more than 9 million spectra data
• Provides the radial velocity and metallicity
• Gaia DR2 contains accurate proper motions (1.2 billion) and radial velocities (G<14) Data
• K giant stars selected from LAMOST DR5 (Liu et al 2014)
• Remove stars with metallicity [Fe/H]>-1
• Cross-matching with Gaia DR2 to obtain proper motion Method
• Bayesian method with a model including multi-components
• Halo, thick disk, possible another halo component
• Gaussian distribution for rotational velocity
• Errors are involved Rotation in the local volume
• [Fe/H] from LAMOST DR5
• RV, proper motion and distance from Gaia DR2
• Distance from Bailor-Jones et al. (2018)
• 3827 K giant stars left after the selection
• D<4 kpc and Derr/D<20%
• [Fe/H]<-1
• Median pm err <0.07 & median RVerr 1km/s Rotation in the local volume
• Model with three components
Halo Disk halo* Rotation in the local volume
• Model with three components
Halo Disk halo* Rotation in the local volume
• Model with three components
Halo Disk halo*
Helmi et al. 2018 Rotation variance
• PM from Gaia DR2
• [Fe/H], RV and distance from LAMOST
• Distance calculated by Carlin et al. 2015
• corrected by dividing 0.805, using the common stars within 3 kpc
• RV corrected by +5.38 Rotation variance
• [Fe/H], RV and distance from LAMOST
Liu et al. 2014 Rotation variance
• Space distribution
• S-sample
• 6 • SO-Sample • 12 • Multi-components model for Bayesian method Rotation variance S-sample SO-sample Rotation variance S-sample SO-sample Rotation variance S-sample • SO-sample Rotation variance S-sample SO-sample Rotation variance Decreasing trend Flat S-sample Increasing Decreasing trend SO-sample Rotation variance S-sample Decreasing, then flat Flat Flare disk SO-sample Increasing Decreasing trend Rotational variance S-sample SO-sample Comparison • TNG simulation • 481503———1:0.997:0.213 • 488174———1:0.988:0.312 • 516256———1:0.988:0.432 • 565997———1:0.995:0.325 • 542310———1:0.985:0.751 • 566857———1:0.982:0.749 • 575585———1:0.985:0.781 • 585204———1:0.985:0.808 star DM Comparison • TNG simulation • 481503———1:0.997:0.213 • 488174———1:0.988:0.312 • 516256———1:0.988:0.432 • 565997———1:0.995:0.325 • 542310———1:0.985:0.751 • 566857———1:0.982:0.749 • 575585———1:0.985:0.781 • 585204———1:0.985:0.808 star DM Rotation variance • The decreasing trend indicates an oblate halo profile • Observational evidence for the interaction between the halo and the disk • We do not find significant component of Gaia-Enceladus in the outer volumes • Large distance uncertainties make it more diffused • GE is not large enough (Mackereth & Bovy 2019, 1910.03590) Summary • We have accurately constrained the rotation velocity in the local volume • We have studied the variance of the rotation of the halo • flare of the disk • Rotation variance of the halo indicates an oblate halo profile • Observational evidence for the interaction between the halo and disk • No significant Gaia-Enceladus component found in the outer volume Thanks!