Abstract
Early Formation and Evolution of Bulge and HalO (EFEBHO) The main aim of this project is to robustly understand the structure of the Galactic spheroid (Halo, Bulge) with unrivaled detail and solid statistical accuracy. This will be achieved by fully exploiting publicly available, cutting-edge datasets of old stellar tracers (RRLs), and by complementing them with both our forefront unique ancillary spectroscopic and photometric datasets and state-of-the-art theoretical modeling (pulsation, chemo-dynamical, N-body/hydrodynamical simulations). The scientific objective and the novelty of the methodological approach make this project unique, with potentially far-reaching implications for our understanding of the early formation and evolution of the MW. A full characterisation of Gaia field RRLs. New optical, NIR and MIR pulsation relations for Halo RRLs. Global Halo metallicity distribution of RRLs. Alpha-element abundances of Halo RRLs. Comparison between observed and theoretical RRL Halo density profile. New distances, metallicities and reddenings for Halo RRLs. Intrinsic stellar parameters of Gaia RRLs through the theoretical modeling of their multifilter light-curves. Neutron capture element distribution, Iron peak distribution and Halo Halo metallicity gradient traced by RRLs; halo structure, chemical enrichment history and mass assembly, traced by RRLs. Census of RRLs in the Ursa Minor dSph and in the Draco dSph. ACHIEVED RESULTS: The work of the Bologna Unit, as described in the proposal, focused mainly on the theoretical/dynamical aspects of the project. In particular, as the RRLyr population resides in the stellar halo of our galaxy, it is of primary importance first to build sufficiently general and flexible dynamical models to be successively applied to observations. The Bologna Unit developed multi-component (disk, dark matter halo) dynamical models of axisymmetric (disk) galaxies allowing for a quite general (and observationally motivated) choice of the velocity dispersion tensors and of the ordered velocity fields of each component. The problem has been solved from first principle first analytically, and then through the construction of numerical codes that solve and project the anisotropi Jeans equations of each density component. In parallel, it has been derived an analytical, very simple, and extremely accurate approximation (based on asymptotic expansions) of the ellipsoidal Sersic profile, for arbitrary values of the Service index. Such a profile is commonly adopted to describe the density distribution of the stellar halos in galaxies, and due to the simplicity of our approximation, it has been implemented in our code. A presentation to a conference has been done. These are the publications of our research unit related to this part of the project: 2025MNRAS, 544, 2200D Anisotropy ansatz for the Jeans equations: oblate galaxies De Deo, Leonardo; Ciotti, Luca; Pellegrini, Silvia 2025A&A...694A.118C; An accurate and simple asymptotically matched deprojection of the Sérsic law Ciotti, L.; De Deo, L.; Pellegrini, S. 2024eas..conf..828D Constraints on orbital anisotropy in axisymmetric systems from the Jeans equations De Deo, Leonardo; Ciotti, Luca; Pellegrini, Silvia 2024MNRAS.530.1796D Anisotropy ansatz for the axisymmetric Jeans equations De Deo, Leonardo; Ciotti, Luca; Pellegrini, Silvia 2024MNRAS.527.9904M Jeans modelling of weakly flattened ellipsoidal systems Mancino, Antonio; Ciotti, Luca; Pellegrini, Silvia and Federica Giannetti 2023MNRAS.525.2758C The face-on projection of the Miyamoto & Nagai discs Ciotti, Luca Our developed modeling technique has been also applied to the construction of the dynamical models used for hydrodynamical simulations of gas flows in axisymmetric galaxies: 2025ApJ...990..194P X-Ray Halos of Early-type Galaxies with Active Galactic Nucleus Feedback and Accretion from a Circumgalactic Medium: Models and Observations Pellegrini, Silvia; Ciotti, Luca; Gan, Zhaoming; Kim, D.W.; Osstriker, J.P. 2023MNRAS.524.5787Z Active galactic nuclei feedback in an elliptical galaxy (III): the impacts and fate of cosmological inflow Zhu, Bocheng; Yuan, Feng; Ji, Suoqing; Peng, Yingjie; Ho, Luis C.; Ostriker, Jeremiah P.; Ciotti, Luca We also studied how hierarchical merging proceeds at the dwarf galaxy scales. To this purpose, we used deep imaging data acquired with the Large Binocular Telescope, dedicated follow-up observations with HST, and public Euclid data, to identify the presence of stellar streams and sub-structures around dwarf galaxies in the Local Volume (Bellazzini et al. 2024; Sacchi et al. 2024; Hunt et al 2025; Correnti et al 2025: Annibali et al., submitted, Perez-Millan et al., in prep). The observed properties of the stellar and gaseous components for systems with clear signs of interaction were successfully reproduced through N-body, hydrodynamical simulations of dwarf galaxies merging with smaller satellites (Pascale et al., 2025). “The Smallest Scale of Hierarchy Survey (SSH): IV. Characterization of asymmetries in the dwarf sample” Perez-Millan, D., Annibali, F., et al., in preparation “Euclid: Early Release Observations -- The extended stellar component of the IC10 dwarf galaxy” Annibali, F., et al., submitted to A&A; “DDO 68-C: HST Confirms Yet Another Companion of the Isolated Dwarf Galaxy DDO 68” Correnti, M., Annibali, F., et al. 2025, ApJ., 982, 1, 31, , 2025. “Euclid: Early Release Observations -Deep anatomy of nearby galaxies” Hunt, L., Annibali, F., et al. 2025, A&A;, 697, A9. “The Smallest Scale of Hierarchy Survey (SSH): III. Dwarf-dwarf satellite merging phenomena in the low-mass regime” Sacchi, E., Bellazzini, M., Annibali, F., et al. 2024, A&A;, 691, A65. “Old massive clusters (and a nuclear star cluster?) in the tidal tails of NGC 5238” Bellazzini, M., Annibali, F., et al. 2024, A&A;, 690, L12. “Beyond the surface: Hydrodynamical N-body simulations of the interacting dwarf galaxies NGC 5238 and UGC 8760” Pascale, R., Annibali, F., et al 2024, A&A;, 688, A144.
Project details
Unibo Team Leader: Luca Ciotti
Unibo involved Department/s:
Dipartimento di Fisica e Astronomia "Augusto Righi"
Coordinator:
Inaf - Istituto Nazionale Astrofisica(Italy)
Total Unibo Contribution: Euro (EUR) 19.002,00
Project Duration in months: 24
Start Date:
28/09/2023
End Date:
28/02/2026
