A long-standing and still debated question concerns the physical processes that have driven the formation and evolution of galaxies across the full mass spectrum, from massive elliptical systems to low-mass dwarf galaxies. Galaxies are the outcome of complex interactions between baryons and dark matter, shaped by processes such as star formation, feedback, merging, and environmental effects. As such, they preserve a fossil record of the assembly of their stellar and dark matter components over cosmic time.
Massive elliptical galaxies, which dominate the high-mass end of the galaxy population, are often considered the end point of galaxy evolution and represent particularly valuable laboratories thanks to their high luminosities and relatively simple stellar structures. At the opposite extreme, dwarf galaxies, characterized by shallow gravitational potentials, are highly sensitive to feedback and environmental processes. This makes them key probes of galaxy formation physics and of the nature of dark matter (Tortora et al. 2025b). Together, massive and dwarf galaxies provide a complementary view of galaxy evolution across a wide range of masses and environments (Tortora et al. 2025a), and offer powerful constraints on the properties of dark matter.
To date, integrated stellar population measurements combined with kinematical and dynamical constraints have largely been limited to galaxy samples at very low redshift. However, a new generation of wide-field spectroscopic and imaging surveys will dramatically expand the available data, extending such studies to redshifts of z ≃ 1 and beyond for large and statistically significant samples (e.g. StePS@WEAVE, 4MOST). These observations will open a unique window onto the joint evolution of stellar and dark matter components as a function of cosmic time, galaxy mass, and environment, enabling stringent tests of hierarchical galaxy assembly models based on millions of galaxies (e.g. Tortora et al. 2009, 2014, 2018, 2019).
In addition, the recent advent of wide-field surveys such as Euclid has opened a new discovery space, revealing thousands of dwarf galaxies beyond the Local Group (Marleau et al. 2025a, Marleau et al. 2025b). Spectroscopic follow-up observations of these systems will be essential to unveil their physical nature and evolutionary histories.
Broad-band colours and spectra can be used to constrain stellar masses and stellar population properties. Total (stellar plus dark matter) dynamical masses can be derived from velocity dispersion measurements obtained from spectroscopy, using Jeans modelling or virial relations. These approaches have proven to be highly efficient for determining galaxy masses in large samples, with relatively low computational cost compared to more complex methods. In the coming years, such analyses will be applied to millions of galaxies observed with the aforementioned facilities. This work will rely on a variety of datasets, including photometry from KiDS@VST, Euclid, and other surveys, as well as spectroscopy from SDSS, BOSS, and upcoming observations from StePS@WEAVE, 4MOST, and dedicated spectroscopic follow-ups.
Depending on the student’s academic level (PhD, Master’s, or Bachelor’s), and at an appropriate level of complexity, the student will focus on one or more of the following topics:
- Determining stellar masses and stellar population parameters through SED fitting or by developing machine-learning techniques, using multi-wavelength imaging and catalogs
- Measuring galaxy light profiles to define physical scales, and deriving structural parameters (e.g. half-light radius, Sérsic index) through classical Sérsic fitting (e.g. GALFIT) or using our in-house machine-learning code GALNET (Li et al. 2022)
- Applying Jeans modelling and/or virial estimators to derive total dynamical masses
- Determining dark matter fractions, mass density slopes, and dynamical constraints on the stellar Initial Mass Function (IMF)
- Exploring the impact of systematic effects (e.g. stellar population and IMF gradients, rotational support, black hole mass, galaxy shape)
- Studying scaling relations of these quantities as a function of mass, redshift, and environment
- Exploring predictions from alternative theories of gravity (e.g. MOND, emergent gravity, Tortora et al. 2014, 2018) or different dark matter models (e.g. warm, fuzzy, or self-interacting dark matter). In particular, the central mass density slopes of dwarf galaxies are highly sensitive to both feedback processes and the nature of dark matter
- Comparing observational results with predictions from cosmological simulations (e.g. TNG, CAMELS, DREAMS, Busillo et al. 2023; Busillo et al. 2025)
- Interpreting the results within the broader framework of contemporary galaxy formation and evolution models
Through this project, PhD, Master’s, or Bachelor’s students will gain expertise in stellar mass estimation via SED fitting and/or structural parameter analysis and/or dynamical modelling. Depending on the project focus, they may also explore both standard dark matter frameworks and alternative theories of gravity.
The proposed work within MASSED will be carried out at the INAF–Osservatorio Astronomico di Capodimonte (Napoli) under the supervision of Crescenzo Tortora, an expert in galaxy evolution, galaxy dynamics, and gravitational lensing; core team member of the StePS@WEAVE and StePS@4MOST surveys; lead of the “Physical Parameters and Redshift” work package within the Euclid Local Universe Science Working Group; and co-chair of the LSST Strong Lensing Science Collaboration. The project will benefit from close collaboration with experts in stellar populations, dynamical analysis, strong lensing and machine learning in the Napoli area and within the aforementioned collaborations.
Contact: Crescenzo Tortora