SKAO |

The galaxy–halo connection

Wed, 29 Jul 2026 00:00:00 +0000

A central axis of my work is the development of empirical models linking dark matter haloes to galaxies, in order to generate realistic mock galaxy catalogues for SKAO and Euclid.

As a major outcome of my Ph.D. thesis I created SCAMPy, a hybrid C++/Python library for painting observed galaxy populations on top of the dark matter halo/sub-halo hierarchy of N-body simulations. It implements the Sub-halo Clustering and Abundance Matching scheme: a Halo Occupation Distribution prescription first selects which sub-haloes host galaxies, then sub-halo abundance matching assigns observable properties to each object. The method requires only the observed distribution of the target property — a luminosity function, say — and the clustering statistics of the target population. The result is a computationally efficient, fully data-driven way to produce mocks that reproduce both the 1- and 2-point statistics of any observed sample, from high-redshift Lyman-break galaxies to low-redshift radio sources. SCAMPy has since become a core ingredient in the simulation pipelines used for SKAO preparatory science.

During a research stay at SKAO Headquarters I also contributed to T-RECS, a tool for simulating radio sources in continuum and HI line, now widely used in the radio-cosmology community for survey design and theoretical modelling.

This line of work recently culminated in a comprehensive framework for constructing full-sky empirical mock catalogues of the radio sky: a modular pipeline combining a simulated dark-matter light-cone, built from the high-resolution DEMNUni N-body simulations, with empirically sampled galaxy populations generated by T-RECS and assigned to haloes via an extended version of SCAMPy. The resulting catalogues cover the full 4π steradians down to redshift z = 5 and place multiple radio populations on a common light-cone: continuum-emitting AGN and star-forming galaxies alongside HI line-emitting sources. No single existing approach had previously combined full-sky coverage, multiple radio populations, empirical flexibility and modularity.

I currently lead a European collaboration integrating these pipelines to enable joint radio continuum and line studies. In this context I coordinated the HI Simulations chapter for the next edition of Advancing Astrophysics with the SKA (AASKA II), bringing together researchers from four continents to compile a comprehensive description and comparison of the simulations available for studying post-reionization HI.

Currently: extending the framework to incorporate multi-wavelength counterparts, connecting radio populations to their optical, infrared and sub-mm emission for cross-survey analyses combining SKAO with Euclid and other facilities. I am also exploring reinforcement-learning approaches to extend the empirical models underlying the galaxy–halo connection.

Key papers: · ·

Software: ·

SCAMPy

Sat, 01 Aug 2020 00:00:00 +0000

Role: author & maintainer. Stack: C++ core (object-oriented, polymorphic) wrapped in Python.

SCAMPy implements the Sub-halo Clustering and Abundance Matching (SCAM) scheme, which combines the classical Halo Occupation Distribution with sub-halo abundance matching. The procedure runs in two steps: the HOD prescription selects which sub-haloes host galaxies, then SHAM assigns an observable property of choice to each selected sub-halo. It requires only the 1- and 2-point statistics of the target population as input — typically an observed luminosity function and its clustering — which makes the method fully data-driven rather than dependent on a physical galaxy-formation model.

The core functionalities are written in C++ and make wide use of polymorphism for flexibility and computational efficiency; the whole library is wrapped in Python so it can be driven from a scripting interface or embedded in a larger pipeline. Mock catalogues produced this way reproduce both the abundance and the clustering of the target sample, and the approach applies across a wide redshift range, from high-redshift Lyman-break galaxies to low-redshift radio sources.

SCAMPy came out of my Ph.D. thesis and has since become a core ingredient in simulation pipelines used for SKAO preparatory science, including the full-sky radio mock catalogues described in my .

Presented in Monthly Notices of the Royal Astronomical Society 498, 2095 (2020) — see . Also indexed in the Astrophysics Source Code Library as ascl:2002.006.

T-RECS

Mon, 01 May 2023 00:00:00 +0000

Role: contributor — HI emission extension. Stack: Fortran executables with Python tooling for catalogue cross-matching. Lead author & maintainer: Anna Bonaldi (SKAO).

T-RECS produces simulated catalogues of radio sources with user-defined frequencies, sky area and depth. The original model covers radio continuum emission for the two main populations of radio galaxies — AGN and star-forming galaxies — including polarisation and clustering. It is now widely used in the radio-cosmology community for survey design and theoretical modelling.

During a research stay at SKAO Headquarters in Manchester I contributed to the second generation of the code, which extends T-RECS to HI line emission. That work builds the HI model on current HI mass function estimates, adds prescriptions to convert HI mass to integrated flux, and models source size, morphology and kinematics including rotational velocity and line width. It also introduces prescriptions that associate an HI mass with the existing continuum SFG and AGN populations, which is what makes it possible to cross-match HI and continuum catalogues and build HI × continuum simulated observations.

T-RECS supplies the radio emission properties in the full-sky mock pipeline described in my , where its populations are assigned to dark-matter haloes via SCAMPy.

The HI extension is presented in Monthly Notices of the Royal Astronomical Society 524, 993 (2023) — see .