2020/12/16 by J-B Salomon, J. -B. Salomon, Rodrigo Ibata +10 · 1 voice · 1 citation
Physics and Astronomy · #Andromeda #Andromeda Galaxy #Astrometry #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Declination #Galactic Center #Galaxies: Formation, Evolution, Phenomena #Galaxy #Milky Way #Photometry (optics) #Physics #Proper motion #Radial velocity #Stars #Stellar kinematics #Stellar, planetary, and galactic studies #astro-ph.GA
paper · pdf · doi:10.1093/mnras/stab2253
10 pages, 7 figures, Accepted for publication in MNRAS
arxiv published 2020/12/16 · openalex created_date 2020/12/21 · openalex publication_date 2021/08/03 · arxiv created 2021/09/03 · arxiv updated 2021/09/06 · openalex updated_date 2026/08/06
Abstract We present an analysis of the proper motion of the Andromeda galaxy (M31), based on the Early Third Data Release of the Gaia mission. We use the Gaia photometry to select young blue main sequence stars, and apply several quality cuts to obtain clean samples of these tracers. After correcting the proper motion measurements for the internal rotation of the M31 disk motion, we derive an apparent motion of 52.5 ± 5.8 μas/yr with respect to the Gaia reference frame, or 61.9 ± 9.7 μas/yr after applying a zero-point correction determined from quasars within 20deg from M31 and a correction from systemic biases. Accounting for the Solar reflex motion we deduce a relative velocity between Andromeda and the Milky way (in a non-rotating frame at the current location of the Sun) of 42.2 ± 39.3 km s−1 along right ascension (40.0 ± 39.3 km s−1 along galactic longitude) and −59.4 ± 30.3 km s−1 along declination (−60.9 ± 30.3 km s−1 along galactic latitude), with a total transverse velocity of Vtrans = 82.4 ± 31.2 km s−1. These values are consistent with (but more accurate than) earlier Hubble Space Telescope measurements that predict a future merger between the two galaxies. We also note a surprisingly large difference in the derived proper motion between the blue stars in M31 and samples of red stars that appear to lie in that galaxy. We propose several hypotheses to explain the discrepancy but found no clear evidence with the current data to privilege any one of them.