Cluster Ages to Reconstruct the Milky Way Assembly (CARMA)
Year: 2026
Type: article
Abstract: We present a new age determination of 24 globular clusters (GCs) dynamically associated with the main accretion events experienced by the Milky Way (MW), as part of the Cluster Ages to Reconstruct the Milky Way Assembly (CARMA) project’s effort to trace the Galaxy’s assembly history. We used deep and homogeneous archival Hubble Space Telescope data, and applied the CARMA isochrone-fitting code to derive homogeneous estimates of age, metallicity, reddening, and distance modulus for systems dynamically associated with Gaia-Sausage-Enceladus (GSE), the Sagittarius dwarf galaxy (Sag), the Helmi streams (H99), and the Sequoia galaxy (Seq). These 24 new determinations are supplemented by 11 previously studied GSE clusters to construct the complete age-metallicity relation (AMR) of the GSE system. We find that each progenitor system describes a well-defined AMR, with a distinct slope and extent reflecting its individual star-formation efficiency and chemical enrichment history. By fitting analytical AMR models within a Markov chain Monte Carlo framework, we quantify the stellar mass and accretion time for each progenitor galaxy. This results in the first detailed merger tree obtained from strictly homogeneous chronological information, according to which the Low-energy-Kraken-Heracles (LKH) system is the first merger experienced by the MW that brought GCs in, followed by Sequoia, H99, GSE, and finally Sgr. The most significant events in terms of stellar mass are LKH, GSE, and Sgr, which together contribute a total of ∼2.5×10 9 M ⊙ . This corresponds to more than 95% of the stellar mass accreted by the MW from mergers massive enough to host GCs.
Source: Astronomy and Astrophysics
Institutions: Universidad de La Laguna, Universidade de Vigo, Osservatorio di Astrofisica e Scienza dello Spazio, National Institute for Astrophysics, University of Bologna, Collurania Teramo Observatory, Instituto de Astrofísica de Canarias, Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, University of Groningen, Universidad de Granada, Liverpool John Moores University
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
Funders: National Aeronautics and Space Administration, Space Telescope Science Institute, Ministerio de Ciencia, Innovación y Universidades, European Space Agency, European Commission, Ministero dell’Istruzione, dell’Università e della Ricerca, Ministerio de Ciencia e Innovación, Agencia Estatal de Investigación
Awards: G1105844351, G1272900390, G1855990336, G2262748287, G2309174360, G2601397997, G2660406951, G300979063, G3480869486, G3518538256, G3681454997, G4042783231, G425668148, G430777504, G433322167, G4518818167, G464105488, G4651445947, G5080475149, G5421974903, G5611110931, G5635532810, G58316358, G6253723710, G6273510985, G6285680282, G6950864665, G7060297222, G7084143925, G745419941, G7655492302, G767601387, G7805626310, G7863371703, G7988610560, G8497050386, G899581758
OpenAlex ID: W7204278728