News

In Fontanot et al. 2026, we present predictions from a realization of our GAEA model, implementing a prescription for a variable stellar initial mass function (IMF). This is inspired by high-resolution numerical simulations that account for the role of cosmic rays (CR) as regulators of the star formation rate (SFR) in giant molecular clouds. In our approach, SFR density is assumed to be a proxy for the CR density, providing a link between the IMF shape and the predicted physical conditions of the star forming interstellar medium. Our results show that, in our model framework, assuming such a variable IMF reproduces several properties of the z>6 galaxy population, with no further modification of the feedback model, including their UV luminosity functions up to z~13. In order to compare model predictions with available estimates for the galaxy stellar mass function (GSMF), we reconstruct stellar masses from the model's synthetic photometry assuming a universal IMF, reflecting standard observational practice. Under this approach, we show that the model can reproduce the evolution of the GSMF up to the highest redshifts accessible. Our findings highlight the need to consider a variable IMF shape in the error budget associated with stellar mass estimates. We show that the evolution of both the slope and normalization of the gas-phase mass metallicity relation can be used as powerful discriminant between models of early galaxy formation assuming different IMF evolution. 

In Osman et al. 2026, we present a novel self-consistent implementation of dust formation by stars, destruction by supernova shocks and hot gas, and growth within the dense interstellar medium (ISM) in our GAEA model. Our new model DUSTY-GAEA is able to reproduce the dust build-up as a function of stellar mass out to z ∼ 6, the scaling relations between the dust-to-gas and dust-to-metal ratios and the stellar mass and metallicity in the local Universe, and the dust mass function both in the local Universe and out to z ∼ 1. In the framework of our model, dust growth dominates the cosmic dust budget out to z ∼ 8, and we find that observational constraints beyond the local Universe can be reproduced only when assuming such efficient dust growth in the dense ISM. Nevertheless, reproducing the estimated number densities of dust-rich galaxies at higher redshifts remains challenging, as also found in independent theoretical work. We discuss our model predictions in comparison with both observational data and independent theoretical efforts, and we highlight how further observational constraints at high redshifts would help constrain dust models.

In Kamran et al. 2026, we characterize the HI--halo mass relation, its redshift evolution, and its intrinsic scatter, identifying its secondary dependences. We use the latest version of our GAEA model, applied to the Millennium-I and Millennium-II simulations, to predict the HI mass function (HIMF) and the HI--halo mass relation from the present day to redshift z~5. At z=0, the model reproduces the observed HIMF and its decomposition by host-halo mass. The median HI--halo mass relation rises with halo mass, peaks near 10^{11.7} Msun, declines as central galaxies are quenched by feedback from active galactic nuclei, and rises again where satellites dominate, approaching a single power law at high redshift. We show that the substantial scatter, of about 0.5 dex, is not random but is governed by halo assembly: at fixed mass, higher-spin, later-forming, and less-concentrated halos are systematically HI-richer, with spin together with either concentration or formation time accounting for part of this scatter and leaving an intrinsic dispersion of about 0.3 dex. We encode the median relation, these secondary trends, and the intrinsic scatter in a compact, physically motivated prescription expressed entirely in terms of quantities available in dark-matter halo catalogs. This prescription reproduces the full scatter and enables the construction of large-volume 21-cm mock catalogs for interpreting ongoing intensity-mapping measurements with SKA precursor facilities, such as MeerKAT, and for preparing for forthcoming surveys with the SKA.

In Zakharova et al. 2026, we investigate how galaxy properties, such as stellar mass and star formation rate, correlate with their position within the cosmic web. We use our GAEA model and the IllustrisTNG simulation to reconstruct the environmental histories of galaxies that today reside in filaments between z = 0 and z = 4. We find that filament galaxies at z = 0 are a heterogeneous mix of populations with distinct environmental histories, and a clear dependency on the infall times into filaments. The vast majority of filament galaxies at z = 0 have experienced group processing at some stage of their evolution, with only ∼20% of galaxies remaining centrals throughout their life. For low-mass filament galaxies (9 < log10(Mstar/Msun)< 10), both GAEA and TNG100 confirm that environmental effects are primarily driven by group processing: satellite galaxies in this mass range stop growing stellar mass and exhibit elevated quenched fractions, whereas their central counterparts in filaments have properties that are similar to those of field galaxies. In contrast, massive galaxies (log10(Mstar/Msun)> 10) are affected by the filament environment, regardless of being centrals or satellites. Massive galaxies that have never been satellites and that entered filaments more than 9 Gyr ago show accelerated stellar mass assembly and higher quenched fractions relative to the field, due to a higher frequency of merger events inside filaments. Moreover, the most massive log((Mstar/Msun)> 11) galaxies typically accreted onto filaments over 9 Gyr ago and have never become satellites within a larger halo, highlighting the role of filaments in building up the high-mass end of the galaxy population.

In De Lucia et al. 2025, we investigate the environments of massive quiescent galaxies at 3 < z < 5 using our GAEA model. We show that model high-z quiescent galaxies are alpha-enhanced and exhibit a wide range of stellar metallicities, in broad agreement with current observational estimates. Massive high-z quiescent galaxies in our model occupy a range of environments, from void-like regions to dense knots at the intersections of filaments. Quiescent galaxies in underdense regions typically reside in halos that collapsed early and grew rapidly at high redshift, though this trend becomes difficult to identify observationally due to a large intrinsic scatter in star formation histories. The descendants of high-z massive quiescent galaxies display a broad distribution in mass and environments at z=0, reflecting the stochastic nature of mergers. About one third of these systems remain permanently quenched in our model, while most rejuvenation events are merger-driven and more common in overdense regions. 

In Cantarella et al 2025, we discuss GAEA predictions for the very high-redshift Universe. We show that GAEA successfully reproduces a wide range of high-z observational estimates including: the galaxy stellar mass function up to z~13 and the galaxies+AGN UV luminosity function up to z~10. We find that UV emission from AGN represents an important contribution at the bright end up to z~8, but becomes negligible at higher redshift. Our model reproduces well the observed mass-metallicity relation at z<4, while it slightly overestimates the normalization of the relation at earlier cosmic epochs. We investigate the impact of different physical mechanisms, such as an enhanced star formation efficiency coupled with a reduced stellar feedback or a negligible stellar feedback at z>10. In the framework of our model, both the galaxy stellar mass and UV luminosity functions at  z>10 can be explained by assuming feedback-free starbursts in high-density molecular clouds. However, we show that this model variant leads to a slight increase of the normalization of the z>10 mass-metallicity relation, strengthening the tension with available data. A model with negligible stellar feedback at  z>10 also predicts larger numbers of massive and bright galaxies aligning well with observations, but it also overestimates the metallicity of the interstellar medium. We show that these model variants can in principle be discriminated using the relation between the star formation rate and galaxy stellar mass.

In Fontanot et al. 2025, we study the properties and environments of z>6 bright quasars as predicted by our GAEA model. We show that at z>6 bright QSOs live in a variety of environments, and that secular processes like disc instability are responsible for triggering roughly the same number of QSOs as galaxy mergers. About half of the regions these high-z QSOs include other active galaxies in sizeable number, the other host galaxies being relatively isolated. The large field-to-field variance in the the number of companions (both active and non-active) recently reported from JWST observations is fairly well reproduced by GAEA predictions. Descendants of host galaxies at z=0 cover a wide range of physical properties and environments with only a small fraction of the hosts of high-z QSOs ending up in massive galaxy clusters. Viceversa, GAEA predicts that only a small fraction of Bright Central Galaxies have a bright z>6 QSOs among their progenitors. Our results suggest that luminous high-z QSO loosely trace the progenitors of low-z galaxy clusters, and that additional information about the environment of high-z QSOs are required to identify the most promising proto-cluster candidates.

Faisst et al. (2025) present the stellar mass-metallicity relation and mass-metallicity star formation relation of 18 massive main sequence galaxies at z~5 from the ALPINE-CRISTAL-JWST sample. Little evolution is found at the massive end of the MZR between z~5 and cosmic noon at a~2, suggesting a fast metal enrichment at early times. Observational estimates are compared to the most recent version (in preparation) of our GAEA model including an explicit treatment for dust. The model is used to interpret current estimates and discuss future evolution of the ALPINE-CRISTAL-JWST galaxies at later cosmic epochs. 

In Xie et al. (2025), we our GAEA model and TNG simulation to investigate whether cluster galaxies suffer from strong RPS that is sufficient to remove a significant fraction of their gas during the first pericentric passage. By tracing the orbit of galaxies since 2.5Rvir, we find in both GAEA and TNG that about half of the galaxies in Virgo-like halos did not suffer strong RPS during the first pericentric passage. In Coma-like halos, almost all galaxies have suffered strong RPS during the first pericentric passage, which can remove all gas from low-mass galaxies but is insufficient to significantly reduce the gas content of more massive galaxies. In general, results from TNG and GAEA are consistent, with the RPS being only slightly stronger in TNG than in GAEA. Our findings suggest that most cluster galaxies maintain a notable fraction of their gas and continue forming stars after the first pericentric passage, except for those with a low stellar mass in very massive halos. 

In Fontanot et al. 2025, we present model prediction from the latest version of the GAEA model coupled with merger trees extracted from the P-Millennium Simulation. We present, for the first time, GAEA predictions for the 2-point galaxy correlation function, and compare with available data in the redshift range 0<z<3. We show that our model reproduces nicely the main dependencies of the 2pCG as a function of stellar mass, star formation activity, HI content and redshift for galaxies with stellar mass >10^9 M⊙. Our work shows that the latest GAEA version captures correctly both the distribution of galaxies in the large-scale structure and the interplay between the main physical processes regulating the baryonic content of dark matter haloes.

In Cammelli et al. 2025, we study the growth of supermassive black holes from PopIII.1 seeds coupling our GAEA model with dark matter merger trees generated using the PINOCCHIO algorithm. The approach allows us to access the resolution necessary to resolve the minihaloes in which PopIII stars form. We present predictions for the properties of galaxy populations, and discuss implications for the PopIII.1 seeding mechanism. 

Lagos et al. 2025 presents a detailed study of the star formation histories of high-z massive quiescent galaxies from recently published theoretical models (including GAEA). The study discusses how the disparate predictions obtained from independent models can be tied to the adopted AGN feedback, and are testable with current facilities and upcoming observations. 

In Scharré et al. 2024 we combine our GAEA model with advanced photoionisation models and use results to make emission-line predictions at 0.4<z<2.5. We validate our methodology against observational and theoretical data at low-z and forecast the fraction of line-emitting galaxies that Euclid will observe at different cosmic epochs. Using our model results, we propose novel redshift-invariant tracers for the black hole accretion rate-to star formation rate ratio. Finally, we find that commonly used metallicity estimators display a gradual shifts in normalization with increasing redshift, in tentative agreement with recent JWST measurements. 

In Xie et al. 2024 we present predictions from the latest version of our model for the quenched fractions up to z~7, and study the physical mechanism responsible for quenching the first galaxies. We find that, independently of galaxy stellar mass, the dominant quenching mechanism at high redshift is feedback from central massive black holes in the form of quasar winds. This is triggered by mergers in more massive galaxies, and by disk instabilities in low-mass galaxies. Environmental quenching becomes (increasingly) important at lower redshift. 

In De Lucia et al. 2024 we present the latest version of our GAEA model, now merging our updated treatment of AGN feedback, including an explicit treatment of quasar winds, with our improved treatment of satellite evolution and explicit treatment of the partition of cold gas in its molecular and atomic components. This latest version of our model predicts specific star formation rat distributions that are in remarkable agreement with data in the local Universe, and quenched fractions that are in very nice agreement with data up to z~3-4.  Our new model predicts number densities of massive quiescent galaxies at z>3 that are the largest among recently published models, albeit still on the low side when compared with lates measurements based on JWST data. We shown that the expected cosmic variance is large, and that it can easily accomodate some of these recent measurements. 

In De Lucia et al. 2023 we present an end-to-end description of the formation process of globular clusters (GCs) which includes a treatment for their formation and dynamical evolution with our GAEA model. Our reference model reproduces well the observed correlation between the total mass in GCs and the parent halo mass. A deviation from linearity is predicted at low halo masses, which is driven by a strong dependence on morphological type. An environmental dependence of GC radii is required to reproduce the observed mass distribution of GCs in our Galaxy at the low-mass end. The metallicity distribution measured for Galactic GCs is well reproduced by our model, even though it predicts systematically younger GCs than observed. We argue that this adds further evidence for an anomalously early formation of the stars in our Galaxy.

In Zakharova et al. 2023 we apply DisPerSE to predictions from GAEA to investigate the correspondence between filaments extracted using the distribution of dark matter particles and galaxies, within the same cosmological volume. We focus in particular on filaments around massive clusters (Virgo and Coma-like). We find that filaments extracted using different tracers are broadly consistent but never coincide perfectly.   

Lustig et al. 2022 study the stellar population and structural properties of massive log(𝑀★/𝑀⊙) > 11 galaxies at 𝑧 ≈ 2.7 in the Magneticum and IllustrisTNG hydrodynamical simulations and in the GAEA semi-analytic model. No scarcity of quiescent galaxies is found at this high redshift, with GAEA reproducing quite well the fraction of observed quiescent galaxies.