arXiv subjects

Luca Sala

Publications and source records attributed to Luca Sala.

6 recordsLinked to original sources

arXiv2026

Rates of tidal disruption events from constrained cosmological simulations of the local Universe: population properties and implications for transient surveys

(abridged) Motivated by upcoming surveys like LSST, we estimate tidal disruption event (TDE) rates using the constrained cosmological Simulation of the LOcal Web (SLOW) to test the limitations of traditional 2D analytical extrapolations within a fully 3D framework. We aim to provide reliable TDE budgets extracted from the simulated zoom-in volumes of the digital counterparts of the Coma, Hercules, Shapley, Virgo, and Perseus supercluster environments, and the Fornax galaxy cluster. From the zoom-in boundary volumes of the six environments, reaching radial extents of $55-92\,$Mpc, we extracted black hole demographics (including spin) and their host galaxy properties to establish a filter scheme that strictly preserves dynamically stable "main-sequence" black holes. We further classified host galaxies as cuspy or cored based on the slope of their 3D stellar density profile measured within $1\,$kpc as a proxy for unresolved nuclear structure and applied the relativistic Kesden efficiency correction to the filtered sample. We find an average volumetric and per black hole TDE rate of $\approx 600\,$Gpc$^{-3}\,$yr$^{-1}$ and $\approx 4.5\times 10^{-5}\,$yr$^{-1}$ across all six environments, respectively. Although our absolute TDE rates match early literature estimates, the underlying spatial distribution fundamentally differs. Central core rates are heavily reduced by dynamical depletion and direct capture constraints, meaning the total TDE budget is overwhelmingly dominated by cuspy satellite galaxies in the extended cluster halos. TDE yields are driven by black hole demographics and spatial concentration rather than total cluster mass. Actively assembling superclusters (e.g., Hercules) reduce per-black-hole TDE efficiencies via merger-driven black hole mass growth, whereas low-mass environments (e.g., Fornax) are highly efficient due to unmerged, low-mass black holes.

astro-ph.HE↗

arXiv2026

ABISS: Evaluating Text-to-SQL Systems Through Agent Interaction

Large Language Models (LLMs) demonstrate high performance on curated Text-to-SQL benchmarks; nevertheless, real-world users frequently pose ambiguous or unanswerable questions that current systems handle poorly. Three interconnected gaps hinder progress: incomplete taxonomies, realistic benchmark generation for real-world settings, and static user interaction. We address all of the above issues through three contributions: (1) a unified taxonomy of 8 categories covering ambiguous and unanswerable questions; (2) a multi-agent generation pipeline with a two-stage process (NLQ generation followed by SQL grounding) and an explicit Category Conformance validation stage, producing questions from arbitrary databases validated by a council of local open-source models; and (3) ABISS (Ambiguity Benchmark using Interaction-Simulated Sessions), a dynamic simulation environment where Text-to-SQL agents interact with style-aware simulated users across multi-turn dialogues. Experiments with eight open-source models on ABISS-BIRD and ABISS-Spider reveal two fundamental bottlenecks. The first is subcategory classification: models detect that a question is problematic yet struggle to pinpoint the specific subcategory. The second is clarification-conditioned SQL generation: even after receiving useful user information, models often still fail in the final resolution step. Providing the ground truth category yields large gains in both execution and feedback across both datasets, yet ambiguous-question execution remains low even under oracle category labels. We release our code for data generation and benchmark on GitHub (https://github.com/giosullutrone/ABISS-Evaluating-Text-to-SQL-Systems-Through-Agent-Interaction).

cs.DB↗

arXiv2025

A novel sub-grid model for super-Eddington accretion of spinning black holes in galaxy-scale simulations

Super-Eddington accretion has been proposed to explain the existence of black holes (BHs) with masses exceeding a billion solar masses within the first billion years after the Big Bang. We present a novel accretion disc-based sub-grid model for BH mass and spin evolution in the super-Eddington regime, implemented in the hydrodynamics code GIZMO. In our model, motivated by results of radiation-hydrodynamics simulations of accretion discs, the growth of the BH is mediated by a sub-grid accretion disc, comprising an inner photon-trapping region described by simulation-based fitting formulae and an outer thin $\alpha$-disc with three regions. We incorporate a self-consistent spin evolution prescription that transitions between the Bardeen-Petterson effect and inner thick-disc precession, depending on the accretion rate. We perform a suite of idealised simulations of a BH embedded in a gaseous circumnuclear disc and a spherically distributed stellar component to explore the conditions under which super-Eddington accretion can be sustained in the environment of a realistic galactic nucleus. Simulations with misaligned gas inflows onto an initially aligned BH-disc system yield very high Eddington ratios, triggered by the rapid removal of disc angular momentum via inflows. These results highlight the importance of angular momentum misalignment in enabling super-Eddington accretion and suggest that such episodes are difficult to trigger unless the system resides in a highly dynamical environment -- a condition more likely to occur in high-redshift galaxies. Our model potentially provides a way to grow moderate-mass BH seeds to the sizes required to explain the bright high-redshift quasars.

astro-ph.GA↗

arXiv2023

Supermassive black hole spin evolution in cosmological simulations with OpenGadget3

Mass and spin of massive black holes (BHs) at the centre of galaxies evolve due to gas accretion and mergers with other BHs. Besides affecting e.g. the evolution of relativistic jets, the BH spin determines the efficiency with which the BH radiates energy. Using cosmological, hydrodynamical simulations, we investigate the evolution of the BH spin across cosmic time and its role in controlling the joint growth of supermassive BHs and their host galaxies. We implement a sub-resolution prescription that models the BH spin, accounting for both BH coalescence and misaligned accretion through a geometrically thin, optically thick disc. We investigate how BH spin evolves in two idealised setups, in zoomed-in simulations, and in a cosmological volume. The latter simulation allows us to retrieve statistically robust results as for the evolution and distribution of BH spins as a function of BH properties. We find that BHs with $M_{\rm BH}\lesssim 2 \times 10^{7}\;{\rm M}_{\odot}$ grow through gas accretion, occurring mostly in a coherent fashion that favours spin-up. Above $M_{\rm BH}\gtrsim 2 \times 10^{7}~{\rm M}_{\odot}$ the gas angular momentum directions of subsequent accretion episodes are often uncorrelated with each other. The probability of counter-rotating accretion and hence spin-down increases with BH mass. In the latter mass regime, BH coalescence plays an important role. The spin magnitude displays a wide variety of histories, depending on the dynamical state of the gas feeding the BH and the relative contribution of mergers and gas accretion. As a result of their combined effect, we observe a broad range of values of the spin magnitude at the high-mass end. Our predictions for the distributions of BH spin and spin-dependent radiative efficiency as a function of BH mass are in very good agreement with observations.

astro-ph.GA↗

arXiv2020

Black hole spin evolution in warped accretion discs

Massive black holes (BHs) inhabiting galactic nuclei can be described by two parameters only, i.e. mass and spin, that change through cosmic time in response to accretion and merger events. While most numerical simulations accurately track the BH mass, spin evolution is rarely taken into account. In this work, we implement and validate a self-consistent sub-grid model for the evolution of the BH mass and spin via gas accretion in the hydrodynamics code GIZMO. The model assumes that accretion from resolved scales does not occur instantaneously, but is mediated by a sub-grid geometrically thin $\alpha$-disc. After validating our model semi-analytically, we test it in an idealized environment consisting of a circumnuclear disc, where gas accretion onto the accretion disc is consistently determined by GIZMO. In the absence of any accretion-related feedback, the spin evolution closely traces that observed in the semi-analytical models and depends on the free parameters of our implementation, such as the initial BH spin, angular momentum of the accretion disc, and the radius at which the gas inflow circularises. In GIZMO, we also couple our model with the biconical-outflow model presented in a companion paper, wherein the feedback axis is always aligned with the BH spin. In this last case, the evolution of the central BH differs significantly from the previous cases, since the feedback process modifies the gas dynamics and its inflow rates from resolved scales. Such an interaction cannot be modeled by simple semi-analytical models and should be treated using full N-body hydrodynamical simulations.

astro-ph.GA↗

arXiv2020

Non-isotropic feedback from accreting spinning black holes

Active galactic nuclei (AGN) are massive black holes (BHs) caught in the act of accreting gas at the centre of their host galaxies. Part of the accreting mass is converted to energy and released into the surrounding medium, in a process loosely referred to as AGN feedback. Most numerical simulations include AGN feedback as a sub-grid model, wherein energy or momentum (or both) is coupled to the nearby gas. In this work, we implement a new momentum-driven model in the hydrodynamics code GIZMO, in which accretion from large scales is mediated by a sub-grid accretion disc model, and gas particles are stochastically kicked over a bi-conical region, to mimic observed kinetic winds. The feedback cone's axis can be set either parallel to the angular momentum of the gas surrounding the BH or to the BH spin direction, which is self-consistently evolved within the accretion-disc model. Using a circumnuclear disc (CND) as a test bed, we find that (i) the conical shape of the outflow is always visible and is weakly dependent on the launching orientation and aperture, resulting in comparable mass inflows and outflows; (ii) the cone's orientation is also similar amongst our tests, and it is not always the same as the initial value, due to the interaction with the CND playing a crucial role in shaping the outflow; and (iii) the velocity of the outflow, instead, differs and strongly depends on the interplay with the CND.

astro-ph.GA↗