Chemical Radial Gradients for the Bulge Bar Stellar Populations from the APOGEE Survey
Year: 2026
Type: article
Abstract: The Milky Way bulge bar is composed of multiple populations. Using chemical and kinematical planes, we segregate six populations in a bulge bar sample observed by the APOGEE survey: two with bar-driven orbits, two with eccentric orbits, and two with low-eccentricity orbits, each composed of low- and high-[Mg/Fe] stars. Our sample spans −2.0 ≲ [Fe/H] ≲ +0.5 and Galactocentric distance R Gal < 6 kpc. We use chemical abundances from APOGEE DR17 for the elements Mg, Si, Ca, Al, K, Mn, Co, Ni, and Fe and from the BAWLAS catalog for Ce and Nd. We find that the low- and high-[Mg/Fe] stars with low-eccentricity orbits, which exhibit chemical and orbital characteristics similar to those of the low- and high-[ α /Fe] disks, display slightly negative and positive metallicity gradients, respectively. This result for the low-[Mg/Fe], low-eccentricity stars indicates a break in the global thin-disk metallicity gradient. The high-eccentricity populations with both low and high [Mg/Fe] show approximately flat metallicity gradients. In general, the [X/H] gradients of all elements for all populations follow Fe, except for the neutron-capture elements Ce and Nd. For all elements, the high-[Mg/Fe] bar population shows a much steeper positive [X/H] gradient than the nearly flat gradient for the low-[Mg/Fe] bar stars. The positive [X/H] gradients observed among our high-[Mg/Fe] bar stars probably reflect an age variation along the peanut structure. This interpretation agrees with the N -body simulations. Such steep positive gradients have also been reported in some high-redshift ( z ∼ 4–10) galaxies.
Source: The Astrophysical Journal
Authors: J. V. Sales-Silva, K. Cunha, V. V. Smith, S. Daflon, D. Souto, R. Guerço, V. Loaiza-Tacuri, A. Queiroz, C. Chiappini, I. Minchev, S. R. Majewski, B. Barbuy, D. Bizyaev, José G. Fernández-Trincado, Peter M. Frinchaboy, S. Hasselquist, D. Horta, Henrik Jönsson, T. Masseron, N. Prantzos, R. P. Schiavon, M. Schultheis, M. Zoccali
Institutions: National Observatory, Ministry of Science, Technology and Innovation, University of Arizona, NSF NOIRLab, Universidade Federal de Sergipe, Universidad Católica del Norte, Universidad de La Laguna, Instituto de Astrofísica de Canarias, Leibniz Institute for Astrophysics Potsdam, University of Virginia, Universidade de São Paulo, New Mexico State University, Lomonosov Moscow State University, Texas Christian University, Space Telescope Science Institute, Royal Observatory, University of Edinburgh, Malmö University, Centre National de la Recherche Scientifique, Institut d'Astrophysique de Paris, Sorbonne Université, Liverpool John Moores University, Université Côte d'Azur, Lagrange Laboratory, Observatoire de la Côte d’Azur, Pontificia Universidad Católica de Chile
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
Funders: National Science Foundation, Deutsche Forschungsgemeinschaft, Ministério da Ciência, Tecnologia e Inovação, Conselho Nacional de Desenvolvimento Científico e Tecnológico, Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, Agencia Nacional de Investigación y Desarrollo
Awards: G2320926664, RAPID: Fast Mobility Particle Size Measurements during the 4th Fire Lab at Missoula Experiment (FLAME IV) Study, Collaborative Research: Chemical History of the Milky Way as Seen Through Open Clusters using SDSS and Gaia, G8622980593, CENTRO DE ASTROFISICA Y TECNOLOGIAS AFINES (CATA)
OpenAlex ID: W7135398354