2D chemical evolution models

II. Effects of multiple spiral arm patterns on O, Eu, Fe, and Ba abundance gradients

¹ INAF Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, 34131 Trieste, Italy
e-mail: emanuele.spitoni@inaf.it
² Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Bd de l’Observatoire, CS 34229, 06304 Nice cedex 4, France
³ Dipartimento di Fisica, Sezione di Astronomia, Università di Trieste, Via G.B. Tiepolo 11, 34143 Trieste, Italy
⁴ INFN Sezione di Trieste, Via Valerio 2, 34134 Trieste, Italy
⁵ Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
⁶ Osservatorio Astrofisico di Torino, Istituto Nazionale di Astrofisica (INAF), 10025 Pino Torinese, Italy

Received: 30 June 2023
Accepted: 17 October 2023

Abstract

Context. According to observations and numerical simulations, the Milky Way could exhibit several spiral-arm modes of various pattern speeds, with the slower patterns located at larger galactocentric distances.

Aims. Our aim is to quantify the effects of the spiral arms on the azimuthal variations in the chemical abundances of oxygen and iron and for the first time of neutron-capture elements (europium and barium) in the Galactic disc. We assume a model based on multiple spiral-arm modes with different pattern speeds. The resulting model is an updated version of previous 2D chemical evolution models.

Methods. We apply new analytical prescriptions for the spiral arms in a 2D Galactic disc chemical evolution model, exploring the possibility that the spiral structure is formed by the overlap of chunks with different pattern speeds and spatial extent.

Results. The predicted azimuthal variations in abundance gradients are dependent on the considered chemical element. Elements synthesised on short timescales (i.e. oxygen and europium in this study) exhibit larger abundance fluctuations. Moreover, for progenitors with short lifetimes, the chemical elements returned to the ISM perfectly trace the star formation perturbed by the passage of the spiral arms. The map of the star formation rate (SFR) predicted by our chemical evolution model with multiple patterns of spiral arms presents arcs and arms compatible with those revealed by multiple tracers (young upper-main sequence stars, Cepheids, and the distribution of stars with low radial actions). Finally, our model predictions are in good agreement with the azimuthal variations that emerged from the analysis of Gaia DR3 GSP-Spec [M/H] abundance ratios, if at most recent times the pattern speeds match the Galactic rotational curve at all radii.

Conclusions. We provide an updated version of a 2D chemical evolution model capable of tracing the azimuthal density variations created by the presence of multiple spiral patterns. We show that elements synthesised on short timescales exhibit larger abundance fluctuations.