Current & Past Research

Weak lensing measurements with Euclid

The ESA’s space probe Euclid, with a scheduled launch in September 2022, has been conceived to investigate their properties by measuring the coherent distortions in the images of 1.5 billion galaxies caused by the differential deflection of light by intervening large-scale structures, with a resolution similar to that of the Hubble Space Telescope (HST). This is because the amplitude of this ‘cosmic shear’ signal is directly related to the distribution of total matter and the expansion history of the Universe. In order to address these questions, more than an order of magnitude improvement in the quality and quantity of observational data is needed: the typical change in the ellipticity caused by gravitational lensing is about a percent, which is much smaller than the intrinsic ellipticities of galaxies. Weak lensing measurements rely on accurate galaxy shape measurements, which in turn rely on a stable, small and well-known image point-spread function (PSF). The aim of the project is to contribute to the development of techniques for weak lensing galaxy shape measurements. The HST archive constitutes an important training and calibration sample for Euclid shape measurements. In particular, VIS-like images based on HST input are needed to characterize selection and shear measurement biases. The goal of this work is to understand how the details of the HST-based emulations (i.e., details of the HST processing) influence these biases and their effects. It is important to ensure that the calibration of the HST data is done sufficiently well that remaining uncertainties do not affect our subsequent analysis for Euclid.

Ultra Compact Massive Galaxies in KiDS

The existence of ultra-compact (Re < 1.5 kpc) and massive (M⋆ > 8×1010 M⊙) galaxies (UCMGs) at z < 1 and their evolution up to the local Universe challenges the currently accepted galaxy formation models. UCMGs are supposedly made of only “in situ” stars since they missed the “accretion” channels of size growth of the two-phase formation process. They survived without experiencing any interaction, massive and compact until today, the “relic” galaxies or old low-z UCMGs. The main goal of the project is to find and confirm UCMGs from wide-sky photometric surveys. We assembled the largest sample of photometrically selected UCMG candidates across the largest area of 333 deg2 at z < 0.5. After the identification of the candidates, spectroscopic validation is necessary to obtain precise spectroscopic redshifts and confirm the compactness of the systems. Thanks to a 3-years long multi-site and multi-telescope spectroscopic campaign, consisting of ~ 150 hours of observations, we built the largest sample of true UCMGs ever collected, comprising 92 spectroscopically confirmed objects at 0.1 < z < 0.5, putting together our current and past results and some literature data. Moreover, thanks to already awarded high quality spectroscopic data (within the INSPIRE ESO Large Program), we will take a further step forward to our final goal, which is to unequivocally prove that a fraction of the red and dead nuggets, which formed at z > 2, evolved undisturbed and passively into local “relics”.

The quest for Cosmic strings

The existence of cosmic strings was first proposed by Thomas Kibble in 1976. They are hypothetical remnants of the early universe whose formation is a predicted result of spontaneous symmetry breaking. Being relics of the phase transitions that produced them, if they are stable and survive for a significant amount of time, they may leave an imprint on many astrophysical and cosmological observables. In this way, Cosmic Strings (CS) provide us with the possibility to understand fundamental physical processes, offering us a unique window on the early universe that would otherwise be inaccessible to us. We developed an effective strategy to detect and characterize these elusive physical entities. Our procedure is a mix of two methods for CS search: the analysis of the anisotropy of the CMB radiation and the detection of the strong gravitational lensing effects of remote sources by a CS. Even if no definitive conclusion can be drawn at this point, we thus found some observational signatures expected from Cosmic Strings, using for the first time two indipendent methods in combination.

You can find all my papers from here.