Revisiting the Proper Motions of M31 and M33 Using Massive Supergiant Stars with Gaia DR3

Abstract

The proper motions (PMs) of M31 and M33 are key to understanding the Local Group's dynamical evolution. However, measurement discrepancies between Gaia blue and red samples, regarding whether the transverse velocity is remarkable, introduce significant ambiguity. In this work, we remeasure the systemic PMs of M31 and M33 using massive supergiant stars from Gaia Data Release 3. Clean disk tracers are selected via color-color diagrams, with foreground contaminants removed through kinematic and astrometric cuts. We identify the discrepancy in M31's blue and red samples as arising from systematic differences between Gaia's 5-parameter (5p) and 6-parameter (6p) astrometric solutions. The 6p solution, applied to sources lacking accurate color information, relies on a pseudo-color approximation, leading to lower precision and larger uncertainties. Two key limitations of the 6p solution are: 1) degraded astrometric accuracy for very red sources (GBP - GRP > 2.6); 2) significant PM zero-point offsets. In our sample, red sources are dominated by the 6p solution, while blue sources include a substantial fraction of 5p sources; this mismatch drives the observed discrepancy. By excluding extreme red sources and calibrating PM zero-points separately for 5p and 6p sources using background quasars, we reduce the discrepancy, bringing blue and red measurements into agreement within 1 sigma. We ultimately report the most robust Gaia-based PMs using high-quality 5p sources. For M31, we obtain (μ_α*, μ_δ)_M31 = (45.9 +/- 8.1, -20.5 +/- 6.6) μas/yr, consistent with, but more precise than, the HST result. For M33, we find (μ_α*, μ_δ)_M33 = (45.3 +/- 9.7, 26.3 +/- 7.3) μas/yr, agreeing with VLBA measurement within 1.5 sigma. These results support a first infall scenario for M33.

arXiv comment15 pages, 8 figures, 4 tables, Accepted for publication in A&A

References in corpus (56)

• Gaia Data Release 2. Summary of the contents and survey properties
• The observed properties of dwarf galaxies in and around the Local Group
• Grids of stellar models with rotation - I. Models from 0.8 to 120 Msun at solar metallicity (Z = 0.014)
• Small-Scale Challenges to the $\Lambda$CDM Paradigm
• Gaia Early Data Release 3: The astrometric solution
• Star Formation Histories, Abundances and Kinematics of Dwarf Galaxies in the Local Group
• Gaia Early Data Release 3: Parallax bias versus magnitude, colour, and position
• Gaia Early Data Release 3: Photometric content and validation
• LCDM-based models for the Milky Way and M31 I: Dynamical Models
• The remnants of galaxy formation from a panoramic survey of the region around M31
• The Chandra Source Catalog
• The Star Formation Histories of Local Group Dwarf Galaxies I. Hubble Space Telescope / Wide Field Planetary Camera 2 Observations
• Gaia Early Data Release 3 -- Catalogue validation
• A Survey of Local Group Galaxies Currently Forming Stars. I. UBVRI Photometry of Stars in M31 and M33
• Distance to M31 With the HST and Hipparcos Red Clump Stars
• The M31 Velocity Vector. II. Radial Orbit Towards the Milky Way and Implied Local Group Mass
• 2MASS NIR photometry for 693 candidate globular clusters in M31 and the Revised Bologna Catalogue
• HI kinematics and dynamics of Messier 31
• The Evolution of Massive Stars. I. Red Supergiants in the Magellanic Clouds
• A wide-field HI mosaic of Messier 31. II.The disk warp, rotation and the dark matter halo
• A deep kinematic survey of planetary nebulae in the Andromeda Galaxy using the Planetary Nebula Spectrograph
• The Geometric Distance and Proper Motion of the Triangulum Galaxy (M33)
• The M31 Velocity Vector. I. Hubble Space Telescope Proper Motion Measurements
• Orbits of Massive Satellite Galaxies: I. A Close Look at the Large Magellanic Cloud and a New Orbital History for M33
• M31 Transverse Velocity and Local Group Mass from Satellite Kinematics
• The vast thin plane of M31 co-rotating dwarfs: an additional fossil signature of the M31 merger and of its considerable impact in the whole Local Group
• The Planetary Nebula System of M33
• The metallicity profile of M31 from spectroscopy of hundreds of HII regions and PNe
• The M31 Velocity Vector. III. Future Milky Way-M31-M33 Orbital Evolution, Merging, and Fate of the Sun
• First Gaia Dynamics of the Andromeda System: DR2 Proper Motions, Orbits, and Rotation of M31 and M33
• A New Catalog of HII Regions in M31
• Gaia Data Release 3: The extragalactic content
• The distance of M33 and the stellar population in its outskirts
• An updated survey of globular clusters in M31. II Newly discovered bright and remote clusters
• Red Supergiants in the Andromeda Galaxy (M31)
• The Yellow and Red Supergiants of M33
• Yellow Supergiants in the Andromeda Galaxy (M31)
• Determination of the Local Standard of Rest using the LSS-GAC DR1
• The Circular Velocity Curve of the Milky Way from 5 to 25 kpc using luminous red giant branch star
• The stellar halo and outer disk of M33
• Dynamical signatures of a LCDM-halo and the distribution of the baryons in M33
• A Spectroscopic Survey of Massive Stars in M31 and M33
• On the mass of the Local Group
• Galactic masers: kinematics, spiral structure and the disk dynamic state
• A Catalog of Star Cluster Candidates in M33
• A survey of diffuse interstellar bands in the Andromeda galaxy: optical spectroscopy of M31 OB stars
• The Transverse velocity of the Andromeda system, derived from the M31 satellite population
• The Red Supergiant Content of M31
• Formation of a giant HI bridge between M31 and M33 from their tidal interaction
• A census of orbital properties of the M31 satellites
• The Red Supergiant Content of M31 and M33
• The Local Group Mass in the light of Gaia
• The Local Group's mass: probably no more than the sum of its parts
• Estimation of the masses in the Local Group by Gradient Boosted Decision Trees
• Future merger of the Milky Way with the Andromeda galaxy and the fate of their supermassive black holes
• Reassessing the proper motions of M31/M33 with Gaia DR3. Unraveling systematic uncertainties