Gian Luigi Granato

Context . Observations of the rest-frame far-infrared (far-IR) emission of galaxies suggest a mild increase in dust temperature T _dust with redshift. However, constraining T _dust in high-redshift systems remains challenging due to limited sampling of the far-IR spectral energy distribution (SED). Aims . We present and discuss the redshift evolution of T _dust , predicted by a cosmological galaxy evolution simulation with dust treatment, and interpret its dependence on other galaxy physical properties. Methods . We used a semi-analytic model of galaxy formation that includes an explicit treatment of dust, post-processed with radiative transfer. Dust temperatures were derived by applying modified blackbody SED fitting to the simulated galaxies, mirroring the methodology adopted in most observational studies. Results . The dust temperature of our simulated galaxies increases with redshift, in broad agreement with observational results. A feature-importance analysis reveals that the star formation rate surface density Σ _SFR and the dust-to-gas ratio (DTG) are the main drivers of dust temperature, tracing the intensity of the interstellar radiation field and the optical depth of warm molecular clouds, respectively. Galaxies with higher star formation rate surface densities and lower DTGs – common conditions at high- z – are associated with warmer dust. We provide a simple relation to estimate DTG from Σ _SFR , T _dust , and redshift. Variations in dust grain size and chemical composition have a negligible impact on T _dust . Our results are particularly relevant to the study of dust properties in observations of high-z galaxies, where far-IR dust emission is not fully sampled.

We present the public release of OpenGadget3 (OG3), a substantially extended and re-organised version of the widely used Gadget-2/3 family of cosmological simulation codes. Since G2 was made publicly available, the absence of continued official development led to the creation of numerous, mutually incompatible developer versions of G3 across the community. This made it effectively impossible to track bug fixes, reproduce published results, or consistently credit the many individual contributors. OG3 addresses this by consolidating these disparate developments into a single, documented, and continuously maintained code base, released under the GNU GPLv3 through a GitLab repository (with an accompanying wiki), regularly synchronised with the active developer branch, and supported by a dedicated continuous-integration (CI) pipeline.OG3 retains the core algorithmic backbone of its predecessors, a Barnes\&Hut oct-tree combined with a Particle-Mesh method for gravity, and a choice of Smoothed Particle Hydrodynamics or Meshless-Finite-Mass solvers for gas dynamics, within a hybrid MPI/OpenMP parallelisation framework, extended with GPU offloading via OpenACC and OpenMP. The code integrates an extensive suite of sub-resolution and physical modules, including primordial chemistry, radiative cooling, star formation, stellar feedback and chemical enrichment, dust formation and evolution, black hole growth and AGN feedback, MHD, thermal conduction, physical viscosity, SIDM, and massive neutrinos.OG3 introduces new features improving robustness, reproducibility, and usability: a flexible mixed-precision framework spanning 16- to 128-bit representations; expert-level tagged parameters with restart-time change log; extensive consistency checks against invalid configurations; and FAIR-compliant reporting of all settings, parameters, and specific publications.(shortened and abridged)

Context. The velocity anisotropy profiles, β ( r ), of galaxy clusters are directly related to the shape of the orbits of their member galaxies. Knowledge of β ( r ) is important in order to understand the assembly process of clusters and the evolutionary processes of their galaxies, and to improve the determination of cluster masses based on cluster kinematics. Aims. We determined the β ( r ) of nine massive clusters at redshift 0.19 ≤ z ≤ 0.45 from the CLASH-VLT dataset, with ≃150–950 spectroscopic members each, to understand how much cluster-to-cluster variance exists in the β ( r ) of different clusters and what the main driver of this variance is. Methods. We selected spectroscopic cluster members with the CLUMPS algorithm calibrated on cosmological simulations. We applied the MAMPOSSt code to the distribution of cluster members in projected phase-space to constrain the cluster mass profile, M ( r ), using priors derived from a previous gravitational lensing analysis. Given the MAMPOSSt best-fit solution for M ( r ), we then solved the inversion of the Jeans equation to determine β ( r ) without assumptions of its functional form. We also ran the DS+ code to identify subclusters and characterize the dynamical status of our clusters. Results. The average ⟨ β ( r )⟩ is slightly radial; the anisotropy increases from β ≃ 0.2 at the cluster center to β ≃ 0.5 at the virial radius. There is substantial variance in the β ( r ) of the individual clusters that cannot be entirely accounted for by the observational uncertainties. Clusters of lower mass and with a low concentration per given mass have more tangential β ( r ) profiles. A comparison with previous works in the literature suggests that orbits are more radial in clusters at higher z . A comparison with cluster-sized halos in cosmological hydrodynamical simulations indicates a very good agreement for the average ⟨ β ( r )⟩, but a smaller variance in the profiles than observed. Conclusions. Massive clusters cannot be characterized by a unique universal β ( r ). The orbital distribution of cluster galaxies carries information on the merging history of the cluster.

Context. Green valley (GV) galaxies are objects defined on a colour–magnitude diagram, or a colour–mass diagram, as being associated with a transition from a star-forming to a quiescent state (quenching), or vice versa (rejuvenation). Aims. We studied the sub-millimetre emission of galaxies in the GV and linked it with their physical evolutionary properties. Methods. We exploited a semi-analytic model (SAM) for galaxy evolution that includes a detailed treatment of dust production and evolution in galactic contexts. We modelled the observational properties of simulated galaxies by post-processing the SAM catalogues with the spectral synthesis and radiative transfer code GRASIL. Results. Our model produces a clear bimodality (and thus a GV) in the colour–mass diagram, although some tensions arise when compared to observations. After introducing a new criterion for identifying the GV in any dataset, we find that GV galaxies, at fixed stellar mass, have 250 μm luminosities approximately half those of blue galaxies, while red galaxies exhibit luminosities of up to an order of magnitude lower. While specific star formation rates drop sharply during quenching, the dust content remains relatively high during the GV transition, powering sub-millimetre emission. Rejuvenating galaxies in the GV, which were previously red, have experienced a star formation burst that shifts their colour to green, but their S _250 μm fluxes remain low due to their still low dust masses. Conclusions. Our galaxy evolution model highlights the delay between star formation and dust evolution, showing that sub-millimetre emission is not always a safe indicator of star formation activity, with quenching (rejuvenating) GV galaxies featuring relatively high (low) sub-millimetre emission.

Context. The study of protoclusters at cosmic noon is essential for understanding the impact of the environment and of the transformational processes occurring during this epoch on galaxy properties. Aims. This work tests the predictions regarding galaxy evolution of the DIANOGA cosmological hydrodynamical simulations of cluster progenitors at z = 2.2 by comparing them with observations and investigates the environmental effects on galaxy populations by comparing simulated protoclusters with an average volume of the Universe. Methods. We analyzed 14 DIANOGA protoclusters and a cosmological box of 49 cMpc/h per side simulated with OpenGADGET3. We compared predictions and observations of the galaxy stellar mass function (GSMF), the star-forming maif sequence (MS), the fraction of star-forming gas, gas depletion times, and the fraction of quenched galaxies. We also computed the rest-frame UV to near-IR colors of galaxies with the SKIRT-9 radiation transfer code to analyze UVJ diagrams. Results. We find that the DIANOGA simulations produce a GSMF in broad agreement with observations. The simulated GSMF shows a higher fraction of high-mass galaxies (M_* > 10¹⁰ M_⊙) in massive halos in protoclusters compared to the cosmological box. The same signal, albeit with a lower significance, is also observed in the wide-field protocluster structures, indicating an accelerated evolution of galaxies before their infall into massive halos. Our simulations underestimate star formation rates of galaxies both in protoclusters and in the cosmological box compared to the observed counterparts due to an underestimation of the star-forming gas reservoirs. We find a weak suppression of star formation rates in protocluster galaxies (∼0.05 dex) compared to the cosmological box, which increases up to ∼0.25 dex in massive halos, reflecting suppressed cold gas reservoirs. The quenched galaxy fraction varies significantly across different protocluster halos, which is consistent with observations at z ∼ 2 − 2.5. The simulations showed a strong dependence of quenched fractions on host halo mass as well as an excess of quenched galaxies in the wide-field protocluster region outside the most massive halos in comparison with the cosmological box. Our UVJ diagram analysis showed qualitative agreement with observed color distributions of star-forming and quenched galaxies, except for few massive galaxies in the cores of massive halos where age-dependent extinction results in steeper reddening vectors than typically assumed in observational studies.

Context. Molecular hydrogen (H₂) plays a crucial role in the formation and evolution of galaxies, serving as the primary fuel reservoir for star formation. In a metal-enriched Universe, H₂ forms mostly through catalysis on interstellar dust grain surfaces. However, due to the complexities of modelling this process, star formation in cosmological simulations often relies on empirical or theoretical frameworks that have only been validated in the local Universe to estimate the abundance of H₂. Aims. The goal of this work is to model the connection between the processes of star, dust, and H₂ formation in our cosmological simulations. Methods. Building upon our recent integration of a dust evolution model into the star formation and feedback model MUPPI, we included the formation of molecular hydrogen on the surfaces of dust grains. We also accounted for the destruction of molecules and their shielding from harmful radiation. Results. The model reproduces, reasonably well, the main statistical properties of the observed galaxy population for the stellar, dust, and H₂ components. The evolution of the molecular hydrogen cosmic density (ρ_H2) in our simulated boxes peaks around redshift z = 1.5, consistent with observations. Following its peak, ρ_H2 decreases by a factor of two towards z = 0, which is a milder evolution than observed. Similarly, the evolution of the molecular hydrogen mass function since z = 2 displays a gentler evolution when compared to observations. Our model recovers satisfactorily the integrated molecular Kennicut-Schmidt (mKS) law between the surface star formation rate (Σ_SFR) and surface H₂ density (Σ_H2) at z = 0. This relationship is already evident at z = 2, albeit with a higher normalization. We find hints of a broken power law with a steeper slope at higher Σ_H2. We also study the H₂-to-dust mass ratio in galaxies as a function of their gas metallicity and stellar mass, observing a decreasing trend with respect to both quantities. The H₂-to-dust mass fraction for the global population of galaxies is higher at higher redshift. The analysis of the atomic-to-molecular transition on a particle-by-particle basis suggests that gas metallicity cannot reliably substitute the dust-to-gas ratio in models attempting to simulate dust-promoted H₂.

The large-scale environment of the cosmic web is believed to impact galaxy evolution, but there is still no consensus regarding the mechanisms. We use a semi-analytic model (SAM) galaxy catalog to study the star formation and dust content of local galaxies in different cosmic environments of the cosmic web—namely voids, filaments, walls, and nodes. We find a strong impact of the environment only for galaxies with M _stars ≲ 10^10.8 M _⊙: the less dense the environment, the larger the star formation rate and dust content at fixed stellar mass. This is attributed to the fact that galaxies in less dense environments typically feature younger stellar populations, a slower evolution of their stellar mass, and delayed star formation compared to galaxies in denser environments. As for galaxies with M _stars ≳ 10^10.8 M _⊙, the differences among environments are milder, due to the disk-instability-driven supermassive black hole (SMBH) growth implemented in the SAM, which makes SMBH growth, and thus galaxy quenching, environment-insensitive. We qualitatively test our predictions against observations by identifying environments in Sloan Digital Sky Survey Data Release 16 using dust masses derived from the GAMA survey. The agreement is encouraging, particularly at log M stars / M ⊙ ≳ 10.5 – 11 , where the specific star formation rates and dust masses appear quite environment-insensitive. This result confirms the importance of in situ growth channels of SMBHs.

Observations suggest that the amount of galactic dust in the Universe decreased by a factor ∼2 − 3 during the last ∼8 Gyr. However, cosmological models of galaxy evolution usually struggle to explain this decrease. Here we use the semi-analytic model (SAM) L-Galaxies2020 to show that this drop may be reproduced assuming standard prescriptions for dust production and evolution. We extend the SAM with i) a state-of-the-art dust model which adopts the two-size approximation and ii) a new disc instability criterion which triggers bulge and central black hole growth. The model reproduces some fundamental properties of the local galaxy population, such as the fraction of spheroid-dominated galaxies and some scaling relations involving dust. Moreover, the model predicts a galactic dust drop from z ∼ 1 → 0, which becomes closer to the observed one when adopting the new treatment of disc instabilities. This result is related to the newly implemented super-massive black hole growth during disc instabilities, which enhances the quenching of massive galaxies. Consequently, these objects feature a lower gas and dust content. We provide a census of the contribution of all the processes affecting the galactic dust content. Accretion is the dominant dust mass growth process. Destruction by supernovae, astration and ejection by winds have all a non-negligible role in decreasing the overall dust content in galaxies below z ∼ 1. We also discuss predictions concerning extra-galactic dust, confirming that a sputtering efficiency lower than the canonical one is required to match the few available observations.