Spiral-like features in the disc revealed by Gaia DR3 radial actions
Creators: name: Palicio, Pedro Alonso
name: Recio-Blanco, Alejandra
name: Poggio, Eloisa
name: Antoja, Teresa
name: McMillan, Paul
name: Spitoni, Emanuele
Publisher: name: Zenodo
Year: 2023
Subjects: Galaxy
Galactic dynamics
Spiral arms
Milky Way
Actions

description: The so-called action variables are specific functions of the positions and velocities that remain constant along the stellar orbit. The astrometry provided by Gaia Early Data Release 3 (EDR3), combined with the velocities inferred from the Radial Velocity Spectrograph (RVS) spectra of Gaia DR3, allows for the estimation of the actions and orbital parameters for the largest volume of stars to date (33.6 million sources). In Palicio et al. (2023), we computed these quantities and explored them with the aim of locating structures in the Galactic disc. Using Gaia DR3 photometric data, we selected a subset of giant stars with better astrometry as a control sample.<br> We found that the maps of the percentiles of the radial action J<sub>R</sub> reveal arc-like segments. In particular, we found three arc-shape regions dominated by circular orbits at inner radii, whose location and shape suggest a connection with the spiral arms. The spatial distribution of the control sample, moreover, shows overdensities similar to those interpreted as spiral arms using upper main sequence stars (Poggio et al. 2021). For Galactic coordinates (X, Y, Z), we found good agreement with the literature in the innermost region for the Scutum-Sagittarius spiral arms. At larger radii, a low J<sub>R</sub> structure tracks the Local arm at negative X, while for the Perseus arm, the agreement is restricted to the X&lt;2 kpc region, with a displacement with respect to the literature at more negative longitudes. We detected a high J<sub>R</sub> area at a Galactocentric radii of 10.5 kpc, consistent with some estimations of the outer Lindblad resonance location. We conclude that the pattern in the dynamics of the old stars is consistent in several places with the spatial distribution of the spiral arms traced by young populations, with small potential contributions from the moving groups.
description: P. A. Palicio acknowledges the financial support from the Centre national d'études spatiales (CNES). E. Spitoni and A. Recio-Blanco received funding from the European Union's Horizon 2020 research and innovation program under SPACE-H2020 grant agreement number 101004214 (EXPLORE project). This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement N. 101063193. TA acknowledges the grant RYC2018-025968-I funded by MCIN/AEI/10.13039/501100011033 and by "ESF Investing in your future". This work was (partially) funded by the Spanish MICIN/AEI/10.13039/501100011033 and by "ERDF A way of making Europe" by the "European Union" through grant RTI2018-095076-BC21, and the Institute of Cosmos Sciences University of Barcelona (ICCUB, Unidad de Excelencia 'María de Maeztu') through grant CEX2019-000918-M. PJM acknowledges project grants from the Swedish Research Council (Vetenskaprådet, Reg: 2017- 03721; 2021-04153). This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement.
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