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The velocity field of our Milky Way outer stellar halo based on DESI DR2

Journal Article · · No journal information
OSTI ID:3029820
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  1. Shanghai Jiao Tong U.; Tsung-Dao Lee Inst., Shanghai; Shanghai Jiaotong U.
  2. Shanghai Jiao Tong U.; Shanghai Jiaotong U.
  3. Edinburgh U., Inst. Astron.; Cambridge U.
  4. Durham U., ICC
  5. U. Michigan, Dept. Astron.
  6. Toronto U.
  7. Edinburgh U., Inst. Astron.
  8. UC, Santa Cruz, Inst. Part. Phys.
  9. Natl. Solar Observ., Tucson
  10. Rio de Janeiro Observ.
  11. University Coll. London
  12. Taiwan, Natl. Tsing Hua U.
  13. LBL, Berkeley
  14. Boston U.
  15. Milan U.; Brera Observ.
  16. UNAM, Mexico
  17. Barcelona, IFAE
  18. Andes U., Bogota
  19. LBL, Berkeley; UC, Berkeley, Math. Dept.
  20. Barcelona, IEEC; Portsmouth U., ICG
  21. LBL, Berkeley; Virginia U.
  22. Fermilab
  23. Chicago U., KICP; Ohio State U.
  24. LPNHE, Paris
  25. Barcelona, IFAE; ICREA, Barcelona
  26. Siena Coll., Loudonville
  27. Portsmouth U., ICG
  28. Waterloo U.; Perimeter Inst. Theor. Phys.
  29. IAA, Granada
  30. Barcelona, Polytechnic U.
  31. Sejong U.
  32. Madrid, CIEMAT
  33. Michigan U., MCTP; Syracuse U.; Michigan U.; KEK, Tsukuba; Hiroshima Shudo U.
  34. Durham U.; Durham U., ICC
  35. Michigan U.; KEK, Tsukuba; Hiroshima Shudo U.
  36. Beijing Observ.
+ Show Author Affiliations
Using 64,000 halo K giants from Dark Energy Spectroscopic Instrument (DESI) second Data Release (DR2), we decompose the Milky Way (MW) stellar halo between 3 and 160 kpc into metal-rich (MR) and metal-poor (MP) components via a Gaussian mixture model (GMM). The two populations are nearly equal in number but chemically and kinematically distinct: MR stars occupy highly radial orbits with velocity anisotropy of beta ~0.94 and metallicity dispersion sigma([Fe/H]) ~0.17 dex, without obvious dependence on distance, and are mainly contributed by Gaia-Sausage/Enceladus (GSE) debris. MR component dominates the inner 30 kpc and re-emerges beyond 50 kpc, implying GSE debris can extend to ~70-80 kpc. MP stars exhibit a weaker radial bias of beta ~0.46, decreasing to -0.5 beyond 80 kpc, and with a larger metallicity dispersion of sigma([Fe/H]) ~0.46 dex, showing signatures of multiple minor mergers. Both components exhibit net prograde rotation at ~10-30 kpc with a stronger azimuthal signal in the MP population. The non-equilibrium motions of the outer halo (>50 kpc) are quantified with a dipole-plus-contraction velocity field. We find that the outer halo is simultaneously contracting (~-19 km/s, distance-independent) and subject to reflex motions (increases from -19 to -44 km/s with radius), reflecting the perturbation from the Large Magellanic Cloud (LMC). We also confirm a linear dependence of mean polar velocity for the outer stellar halo on the dipole velocity field, a direct consequence of the LMC and MW interaction. Our results provide a quantitative distance-resolved description of the MW's last major accretion event and its ongoing response to the first infall of the LMC.
Research Organization:
Portsmouth U., ICG; Madrid, CIEMAT; Syracuse U.; Milan U.; Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States); Beijing Observ.; Tsung-Dao Lee Inst., Shanghai; Natl. Solar Observ., Tucson; Rio de Janeiro Observ.; Edinburgh U., Inst. Astron.; LPNHE, Paris; Toronto U.; Brera Observ.; Siena Coll., Loudonville; Michigan U.; Hiroshima Shudo U.; Chicago U., KICP; UC, Berkeley, Math. Dept.; IAA, Granada; Andes U., Bogota; Michigan U., MCTP; UC, Santa Cruz, Inst. Part. Phys.; KEK, Tsukuba; Perimeter Inst. Theor. Phys.; Barcelona, Polytechnic U.; Shanghai Jiao Tong U.; Sejong U.; UNAM, Mexico; Barcelona, IFAE; Ohio State U.; Shanghai Jiaotong U.; Cambridge U.; ICREA, Barcelona; University Coll. London; Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States); Durham U., ICC; Virginia U.; Waterloo U.; Barcelona, IEEC; Taiwan, Natl. Tsing Hua U.; U. Michigan, Dept. Astron.; Boston U.; Durham U.
Sponsoring Organization:
US Department of Energy
DOE Contract Number:
89243024CSC000002;
OSTI ID:
3029820
Report Number(s):
FERMILAB-PUB-26-0245-PPD; oai:inspirehep.net:3140560; arXiv:2604.01628
Journal Information:
No journal information, Journal Name: No journal information
Country of Publication:
United States
Language:
English

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