Papers › Exploring the interaction between the MW and LMC with a large sample of blue...
Exploring the interaction between the MW and LMC with a large sample of blue horizontal branch stars from the DESI survey
Amanda Byström, Sergey E. Koposov, Sophia Lilleengen, Ting S. Li, Eric Bell, Leandro Beraldo e Silva, Andreia Carrillo, Vedant Chandra, Oleg Y. Gnedin, Jiwon Jesse Han, Gustavo E. Medina, Joan Najita, Alexander H. Riley, Guillaume Thomas, Monica Valluri, Jessica N. Aguilar, Steven Ahlen, Carlos Allende Prieto, David Brooks, Todd Claybaugh, Shaun Cole, Kyle Dawson, Axel de la Macorra, Andreu Font-Ribera, Jaime E. Forero-Romero, Enrique Gaztañaga, Satya Gontcho A Gontcho, Anthony Kremin, Andrew Lambert, Martin Landriau, Laurent Le Guillou, Michael E. Levi, Aaron Meisner, Ramon Miquel, John Moustakas, Francisco Prada, Ignasi Pérez-Ràfols, Graziano Rossi, Eusebio Sanchez, David Schlegel, Michael Schubnell, David Sprayberry, Gregory Tarlé, Benjamin A. Weaver, Hu Zou
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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 9,866 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 degrees 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, 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 two years 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.
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