LEGO – Reconstructing the building blocks of the Galaxy by chemical tagging

31/10/2025 Page maintained by Michele Bellazzini - Last updated on 31/10/2025

LEGO – Reconstructing the building blocks of the Galaxy by chemical tagging

LEGO is a PRIN-MUR 2022 project (grant PRIN 2022LLP8TK_001, CUP code: C53D23001160006, funded by the European Union – NextGenerationEU)  led by Prof. Alessio Mucciarelli (UniBo) with a INAF Research Unit  at the Osservatorio di Astrofisica e Scienza dello Spazio di  Bologna. The INAF RU is led by Dr. Michele Bellazzini, with Dr. Donatella Romano as a participant.

The main goal of LEGO is to add the chemical composition dimension to the endeavour of reconstructing the history of hierarchical build up of the Milky Way galaxy as the template of the process of galaxy formation for which we can obtain the most extensive and detailed information. This ambitious goal has been pursued, within the framework set up by the results of the ESA Gaia mission,  along three main line of research 1. obtaining detailed and very homogeneous chemical composition of stars in substructures of the Galactic halo, globular clusters and dwarf galaxy satellites of the Milky Way to verify their origin and association with ancient merging events (chemical tagging), also with the help of 2. suitable chemical evolution models as fundamental tools to interpret observed chemical pattern and reconstruct the evolution of the baryons in the MW and in its structural components and satellites, and 3. to explore the metallicity distribution of the various components and satellites of the MW, also as a function of age, and of newly discovered tidal streams tracing the disruption of small MW satellites (low mass dwarf galaxies and globular clusters). The characterisation of known relics and of satellites of the MW that may record the traces of their own hierarchical build up was an additional line of investigation. In this framework, a new extensive calibration of a distance indicator of general use has also been provided as a tool to derive accurate distances to stellar systems, as this is a key ingredient of the chain leading to chemical and age characterisation.

 

  Sky map of the thin tidal streams discovered and/or characterised in Ibata et al. (2024) with points colour-coded according to the mean metallicity of the streams.

The activity has been very fruitful in all the lines of research. In particular, the members of the LEGO INAF RU co-authored sixteen papers  related to LEGO science goals on international refereed journals that have already received 170 citations in the international literature, while some work is still to be completed (end of the project February 28, 2026). Tutoring undergraduate, PhD and  post-doc students that collaborated to the project was an important activity in which we have been involved. The funds we received with this PRIN MUR 2022 grant allowed us to participate to several international meetings for the dissemination and discussion of LEGO scientific results, fostering new research projects and collaborations, to visit colleagues working on similar topics and collaborators around the world, and collecting new observational data for the project.

Distribution in the plane of angular momentum in the direction perpendicular to the Galactic Disc vs. total energy  of a large sample of stars in the solar neighbourhood for which the metallicity was derived from Stromgren photometry, in different metallicity bins (from Bellazzini et al. 2024, A&A, 681, A236).

LEGO Publications by members of the INAF RU

  1. Alvarez Garay, D.S, Mucciarelli, A., Bellazzini, M., et al., 2024, MgAl burning chain in ω Centauri, A&A, 681, A54
  2. Bellazzini, M., Massari, D., Ceccarelli, E., Mucciarelli, A., et al. 2024, Metal-poor stars with disc-like orbits. Possible traces of the Galactic disc at very early epochs, A&A, 683, A136
  3. Ceccarelli, E., Massari, D., Mucciarelli, A., Bellazzini, M., …, Cusano, F., Romano, D., …, et al., 2024, A Walk on the Retrograde Side (WRS) project. I. Tidying-up the retrograde halo with high-resolution spectroscopy, A&A, 684, A37
  4. Ibata, R., …, Bellazzini, M., …, et al., 2024, Charting the Galactic Acceleration Field. II. A Global Mass Model of the Milky Way from the STREAMFINDER Atlas of Stellar Streams Detected in Gaia DR3, 2024, ApJ, 967, 89
  5. Gatto, M, Ripepi, V., Bellazzini, M., et al., 2024, The YMCA (Yes, Magellanic Clouds Again) survey: Probing the outer regions of the Magellanic system with VST, A&A, 690, A164
  6. Bellazzini, M., Pascale, R., 2024, The red giant branch tip in the SDSS, PS1, JWST, NGRST, and Euclid photometric systems: Calibration in optical passbands using Gaia DR3 synthetic photometry, A&A, 691, A42
  7. Ceccarelli, E., Mucciarelli, A., Massari, D., Bellazzini, M., Matsuno, T., 2024, A comparative high-resolution spectroscopic analysis of in situ and accreted globular clusters, A&A, 691, A226
  8. Rossi, M., Romano, D., Mucciarelli, A., et al., 2024, The earliest phases of CNO enrichment in galaxies, A&A, 691, A284
  9. Ferraro, F.R, …, Romano, D., Mucciarelli, A., …, et al., 2025, The Bulge Cluster Origin (BulCO) survey at the ESO-VLT: Probing the early history of the Milky Way assembly. Design and first results in Liller 1,A&A, 696, A179
  10. Massari, D., Bellazzini, M., Libralato, M., et al., 2025, The Hubble Missing Globular Cluster Survey: I. Survey overview and the first precise age estimate for ESO452-11 and 2MASS-GC01, A&A, 698, A197
  11. Palla, M., Molero, M., Romano, D., Mucciarelli, A., 2025, Europium, we have a problem: Modelling r-process enrichment across Local Group galaxies, A&A, 699, A209
  12. Liberatori, A., Alvarez Garay, D. A., Palla, M., Mucciarelli, A., Bellazzini, M., Romano, D., 2025, A chemical close-up of the main body of the Sagittarius dwarf galaxy, A&A, 699, A356
  13. Spitoni, E., Palla, M., Magrini, L., …, Romano, D., et al., 2025, Shaping Galactic habitability: Impact of stellar migration and gas giant, A&A, 700, A58
  14. Nguyen, C., Cescutti, G., Matteucci, F., …, Mucciarelli, A., Romano, D., …, et al., 2025, Lithium evolution in the Galactic thin disc from Main-Sequence and early Red-Giant-Branch star, A&A, in press
  15. Muraveva, T., Bellazzini, M., Garofalo, A.,  et al., 2025, Exploring the Sagittarius stream with RR Lyrae stars from Gaia Data Release 3, A&A, 701, A228
  16. Jerabkova, T., Romano, D., Kroupa, P., …, Mucciarelli, A., …, et al., 2025, Cosmic Threads: Interlinking the Stellar Initial Mass Function from Star-Birth to Galaxies, Mem. SAIt, in press
  17. Ceccarelli, E., Massari, D., Mucciarelli, A., Palla, M.,  Bellazzini, M., Helmi, A., 2025, A Walk on the Retrograde Side (WRS) project. II. Chemistry to disentangle in situ and accreted components in Thamnos, A&A, in press

[In the above list, the names of LEGO participants is highlighted. In boldface members of the LEGO INAF RU, in italic members of other LEGO RUs]

Participations to meeting and workshops to present and discuss results related to LEGO (INAF RU)

[Page to be updated until the completion of the LEGO project, on February 28, 2026.]