Exploring the interaction between the MW and LMC with a large sample of blue horizontal branch stars from the DESI survey

Journal Article · Wed Jul 23 20:00:00 EDT 2025 · Monthly Notices of the Royal Astronomical Society

DOI:https://doi.org/10.1093/mnras/staf1219· OSTI ID:3010595

Byström, Amanda ^[1]; Koposov, Sergey E ^[2]; Lilleengen, Sophia ^[3]; Li, Ting S ^[4]; Bell, Eric ^[5]; Beraldo e Silva, Leandro ^[6]; Carrillo, Andreia ^[7]; Chandra, Vedant ^[8]; Gnedin, Oleg Y ^[5]; Han, Jiwon Jesse ^[8]; Medina, Gustavo E ^[4]; Najita, Joan ^[9]; Riley, Alexander H ^[3]; Thomas, Guillaume ^[10]; Valluri, Monica ^[5]; Aguilar, Jessica N ^[11]; Ahlen, Steven ^[12]; Prieto, Carlos Allende ^[13]; Brooks, David ^[14]; Claybaugh, Todd ^[11] ; Cole, Shaun ^[3]; Dawson, Kyle ^[15]; de la Macorra, Axel ^[16]; Font-Ribera, Andreu ^[17]; Forero-Romero, Jaime E ^[18]; Gaztañaga, Enrique ^[19]; Gontcho, Satya Gontcho A ^[11]; Kremin, Anthony ^[11]; Lambert, Andrew ^[11]; Landriau, Martin ^[11]; Le Guillou, Laurent ^[20]; Levi, Michael E ^[11]; Meisner, Aaron ^[9]; Miquel, Ramon ^[21]; Moustakas, John ^[22]; Prada, Francisco ^[23]; Pérez-Ràfols, Ignasi ^[24]; Rossi, Graziano ^[25]; Sanchez, Eusebio ^[26]; Schlegel, David ^[11]; Schubnell, Michael ^[27]; Sprayberry, David ^[9]; Tarlé, Gregory ^[5]; Weaver, Benjamin A ^[9]; Zou, Hu ^[28]

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1. Institute for Astronomy, University of Edinburgh, Royal Observatory , Blackford Hill, Edinburgh EH9 3HJ ,
2. Institute for Astronomy, University of Edinburgh, Royal Observatory , Blackford Hill, Edinburgh EH9 3HJ ,; Institute of Astronomy, University of Cambridge , Madingley Road, Cambridge CB3 0HA ,
3. Institute for Computational Cosmology, Durham University Department of Physics, , South Road, Durham DH1 3LE ,
4. University of Toronto Department of Astronomy & Astrophysics, , Toronto, ON M5S 3H4 ,
5. University of Michigan Department of Astronomy, , Ann Arbor, MI 48109 ,
6. University of Michigan Department of Astronomy, , Ann Arbor, MI 48109 ,; University of Arizona Steward Observatory and Department of Astronomy, , 933 N, Cherry Ave, Tucson, AZ 85721 ,
7. Institute for Computational Cosmology, Durham University Department of Physics, , South Road, Durham DH1 3LE ,; Carleton College Department of Physics and Astronomy, , 1 North College Street, Northfield, MN 55057 ,
8. Harvard-Smithsonian Center for Astrophysics , 60 Garden Street, Cambridge, MA 02138 ,
9. NSF NOIRLab , 950 N. Cherry Ave., Tucson, AZ 85719 ,
10. Instituto de Astrofísica de Canarias , C/ Vía Láctea, s/n, E-38205 La Laguna, Tenerife ,
11. Lawrence Berkeley National Laboratory , 1 Cyclotron Road, Berkeley, CA 94720 ,
12. Boston University Physics Department, , 590 Commonwealth Avenue, Boston, MA 02215 ,
13. Instituto de Astrofísica de Canarias , C/ Vía Láctea, s/n, E-38205 La Laguna, Tenerife ,; Universidad de La Laguna (ULL) Departamento de Astrofísica, , E-38206 La Laguna, Tenerife ,
14. University College London Department of Physics & Astronomy, , Gower Street, London WC1E 6BT ,
15. The University of Utah Department of Physics and Astronomy, , 115 South 1400 East, Salt Lake City, UT 84112 ,
16. Instituto de Física, Universidad Nacional Autónoma de México , Cd. de México C.P. 04510 ,
17. University College London Department of Physics & Astronomy, , Gower Street, London WC1E 6BT ,; Institut de Física d’Altes Energies (IFAE), The Barcelona Institute of Science and Technology, Campus UAB , E-08193 Bellaterra Barcelona ,
18. Universidad de los Andes Departamento de Física, , Cra. 1 No. 18A-10, Edificio Ip, CP 111711, Bogotá ,; Observatorio Astronómico, Universidad de los Andes , Cra. 1 No. 18A-10, Edificio H, CP 111711, Bogotá ,
19. Institut d’Estudis Espacials de Catalunya (IEEC) , E-08034 Barcelona ,; Institute of Cosmology and Gravitation, University of Portsmouth, Dennis Sciama Building , Portsmouth PO1 3FX ,; Institute of Space Sciences, ICE-CSIC, Campus UAB, Carrer de Can Magrans s/n , E-08913 Bellaterra, Barcelona ,
20. Sorbonne Université, CNRS/IN2P3, Laboratoire de Physique Nucléaire et de Hautes Energies (LPNHE) , F-75005 Paris ,
21. Institut de Física d’Altes Energies (IFAE), The Barcelona Institute of Science and Technology, Campus UAB , E-08193 Bellaterra Barcelona ,; Institució Catalana de Recerca i Estudis Avançats , Passeig de Lluís Companys, 23, E-08010 Barcelona ,
22. Siena College Department of Physics and Astronomy, , 515 Loudon Road, Loudonville, NY 12211 ,
23. Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía, s/n , E-18008 Granada ,
24. Universitat Politècnica de Catalunya Departament de Física, EEBE, , c/Eduard Maristany 10, E-08930 Barcelona ,
25. Sejong University Department of Physics and Astronomy, , Seoul 143-747 ,
26. CIEMAT , Avenida Complutense 40, E-28040 Madrid ,
27. University of Michigan Department of Astronomy, , Ann Arbor, MI 48109 ,; University of Michigan Department of Physics, , Ann Arbor, MI 48109 ,
28. National Astronomical Observatories, Chinese Academy of Sciences , A20 Datun Road, Chaoyang District, Beijing 100012 ,

The Large Magellanic Cloud (LMC) is a Milky Way (MW) satellite that is massive enough to gravitationally attract the MW disc and inner halo, causing significant motion of the inner MW with respect to the outer halo. In this work, we probe this interaction by constructing a sample of 9866 blue horizontal branch (BHB) stars with radial velocities from the DESI spectroscopic survey out to 120 kpc from the Galactic centre. This is the largest spectroscopic set of BHB stars in the literature to date, and it contains four times more stars with Galactocentric distances beyond 50 kpc than previous BHB catalogues. Using the DESI BHB sample combined with SDSS BHBs, we measure the bulk radial velocity of stars in the outer halo and observe that the velocity in the Southern Galactic hemisphere is different by 3.7σ from the North. Modelling the projected velocity field shows that its dipole component is directed at a point 22 deg away from the LMC along its orbit, which we interpret as the travel direction of the inner MW. The velocity field includes a monopole term that is –24 km s^–1⁠, which we refer to as compression velocity. This velocity is significantly larger than predicted by the current models of the MW and LMC interaction. This work uses DESI data from its first 2 yr of observations, but we expect that with upcoming DESI data releases, the sample of BHB stars will increase and our ability to measure the MW–LMC interaction will improve significantly.

• Research Organization: University of Utah, Salt Lake City, UT (United States)
• Sponsoring Organization: Science & Technology Facilities Council (STFC); Natural Sciences and Engineering Research Council of Canada (NSERC); USDOE Office of Science (SC), High Energy Physics (HEP); U.S. National Science Foundation (NSF), Division of Astronomical Sciences
• Contributing Organization: DESI
• Grant/Contract Number: SC0009959; AC02-05CH11231
• OSTI ID: 3010595
• Alternate ID(s): OSTI ID: 3007043
• Journal Information: Monthly Notices of the Royal Astronomical Society, Journal Name: Monthly Notices of the Royal Astronomical Society Journal Issue: 2 Vol. 542; ISSN 0035-8711; ISSN 1365-2966
• Publisher: Oxford University Press (OUP)
• Country of Publication: United States
• Language: English

Related Subjects

Galaxy: evolution
Galaxy: halo
Galaxy: kinematics and dynamics
Magellanic Clouds