About me


I am currently a PhD student at the University of Melbourne under the supervision of prof. Stuart Wyithe.

My PhD research focuses on some statistical effects of strong gravitational lensing on the galaxy population.
In particular, I studied the magnification bias at the bright end of the galaxy luminosity function, and the expected distributions of galaxy scale lenses in ongoning and future surveys.

Before the PhD, I was raised in the modern metropolis of Casalbuttano ed Uniti (Italy). I eventually moved to Milan, where I lived at Collegio di Milano and studied Physics at the University of Milan. There I graduated under prof. Claudio Grillo and prof. Giuseppe Bertin. In my master thesis I studied the presence of rotation and the state of dynamical relaxation in the galactic component of two clusters of galaxies.

Some research highlights

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  • VDF evolution from strong lensing statistics

  • A model for galaxy-galaxy strong lensing statistics in survey

  • Magnification bias depends on source size-L relation

Velocity dispersion function evolution from strong lensing statistics

The redshift and size distributions of galaxy scale strong lenses depend on the evolution of early-type galaxies (ETGs) in the redshift range 0.2 < z < 1. We use this dependence to constrain the velocity dispersion function (VDF) evolution from the Strong Lensing Legacy Survey (SL2S) sample of lenses. Our modeling of the lens population includes lens identifiability given survey parameters, and constrains the evolution of the VDF based on the redshift distributions of sources and lenses as well as the distribution of Einstein radii. We consider five different assumptions for the reference VDF at redshift zero and two sets of scaling relations for the VDF. We find that in all cases the observed lens sample favors a slow evolution of both the VDF normalization factor and the VDF characteristic velocity with redshift which is consistent with a VDF that is constant in redshift for z < 1.

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A model for galaxy-galaxy strong lensing statistics in surveys

Photometric wide-area observations in the next decade will be capable of detecting a large number of galaxy-scale strong gravitational lenses, increasing the gravitational lens sample size by orders of magnitude. To aid in forecasting and analysis of these surveys, we construct a flexible model based on observed distributions for the lens and source properties and test it on the results of past lens searches, including SL2S, SuGOHI and searches on the COSMOS HST and DES fields. We use this model to estimate the expected yields of some current and planned surveys, including Euclid Wide, Vera Rubin LSST, and Roman High Latitude Wide Area. The model proposed includes a set of free parameters to constrain on the identifiability of a lens in an image, allowing construction of prior probability distributions for different lens detection methods. The code used in this work is made publicly available.

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Magnification bias depends on source size-L relation

The bright end of the rest-frame ultraviolet luminosity function (UVLF) of high-redshift galaxies is modified by gravitational lensing magnification bias. Motivated by recent discoveries of very high-z galaxies with JWST, we study the dependence of magnification bias on the finite size of sources at 6 < z < 14. We calculate the magnification probability distributions and use these to calculate the magnification bias assuming a rest-frame Schechter UVLF for galaxies at redshift 6 < z < 14. We find that the finite size of bright high-redshift galaxies together with lens ellipticity significantly suppresses magnification bias, producing an observed bright end which declines more sharply than the power law resulting from assumption of point sources. By assuming a luminosity-size relation for the source population and comparing with the observed z = 6 galaxy luminosity function from Harikane et al. (2022), we show that the UVLF can be used to set mild constraints on the galaxies intrinsic size, favouring smaller galaxies compared to the fiducial luminosity-size relation.

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  • Dynamics of the galactic component of two cluster of galaxies

Dynamics of the galactic component of two cluster of galaxies

The galactic component in clusters is commonly thought to be generally nonrotating and in a dynamical state different from that of a collisionally relaxed system. In practice, a test for such conditions is often not available. We consider the member galaxies of the two clusters Abell S1063 and MACS J1206.2−0847 and study the possible presence of mean rotation and some properties of their distribution in phase space. We look for empirical evidence of factors normally found in collisionally relaxed systems and other characteristics of violently relaxed collisionless systems. Starting from the CLASH-VLT data, we obtained positions, stellar masses, and individual line-of-sight velocities for a large number of galaxies (NAS1063 ≈ 1200 and NM1206 ≈ 650) extending out to ≈1.6 (Abell) and ≈2.5 (MACS) times the radius r200. We studied the spatial distribution of the galaxy velocities and the properties of the available galaxy sets when divided into stellar mass bins. To test the presence of velocity dispersion anisotropy, we compared the results based on the Jeans equations with those obtained by assuming a specific form of the galaxy distribution function incorporating the picture of violent relaxation, where the total gravitational potential is imposed as set by the available gravitational lensing observations. We find evidence of systematic rotation in both clusters, with significant rotation in each core (within 0.5' from the center) and no signatures of rotation at large radii. While no signs of energy equipartition were found, there is a clear indication of (stellar) mass segregation. Velocity dispersion anisotropy is present and qualitatively similar to what has been found in violently relaxed collisionless systems. This last conclusion is strengthened by the overall success in matching the observations with the predictions of the physically justified distribution function.

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