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Scientific background
Scientific background
Most of the stars in the local Universe, more than 60%, are found within high-mass elliptical (spheroidal) galaxies, called Early-Type Galaxies (ETG). These galaxies represent only 30% of the galaxy population therefore, they are, on average, the most massive galaxies in the Universe. Why the processes of stellar mass growth in galaxies has led to lock more than 60% of the stars in ETGs is still unclear. Galaxy formation models predict that these high-mass galaxies are assembled along the cosmic time mainly through subsequent mergers of preexisting smaller galaxies, possibly accompanied by episodes of star formation. In contrast, the observed properties of the stellar populations of the ETGs in the local Universe suggest for them a rapid formation taken place far back in time. Recent JWST observations show the presence of high-mass galaxies already formed in the early Universe, corroborating some of the tensions between model predictions and observations in the nearby Universe. Actually, the observations collected so far point toward a formation scenario in which high mass galaxies form most of their stellar mass very rapidly at very early epoch. This extremely rapid assembly which should take place during the first billion years of cosmic history is a major challenge for our understanding of galaxy formation physics.
(Saracco et al. 2020, ApJ,, 905). The spectrum of a galaxy is the sum of the stellar and gas emission. The absorption lines trace the stellar component: their width is related to the stellar velocity dispersion; their strength traces the element abundances (metallicity) and the stellar age. The emission lines trace the gas component, gas kinematic, element abundances and star formation.
Aims and analysis
The aim is to reconstruct the mass assembly history of massive early-type galaxies constraining the different processes responsible for their formation and stellar mass growth. The analysis focuses on the stellar population properties (stellar age and metallicity) and dynamical properties (stellar velocity dispersion, dynamical mass) which will be derived from spectra of massive ETGs at different redshifts (cosmic epochs) and in different density environments (field and cluster). The relationships among these quantities are traced along the cosmic time to reconstruct the evolution they experienced.
Master thesis proposals
The student will work locally with Dr. Paolo Saracco and in close collaboration with Francesco La Barbera and C. Tortora (AO Capodimonte), C. Spiniello (Univ. Oxford, UK), R. De Propris (FINCA-Univ. Turku), D. Marchesini (Tuft University, USA), and the other collaborators to the project aimed at reconstructing the mass assembly of massive galaxies.
Thesis #1: The properties of Relic galaxies
Thesis #1: The properties of Relic galaxies
If galaxies build-up through mergers, which are stochastic processes, then a small fraction of the massive galaxies formed at early epochs should survive by chance, and remain intact until the present day. These local massive, compact (small radii) and quiescent galaxies are called “relics” as they are massive fossils of the ancient Universe. Therefore, relics are the perfect laboratories to study the processes that shaped the mass assembly of massive galaxies in the early Universe. The aim of this thesis is to identify the main processes involved in the assembly of massive ETGs by deriving the stellar population properties and dynamical properties of a sample of the most massive and compact (dense) galaxies in the local Universe to reconstruct their star formation history.
Thesis #2: The role of the environment in the mass assembly of massive galaxies
Thesis #2: The role of the environment in the mass assembly of massive galaxies
The formation of massive ETGs through merging of smaller galaxies would be a natural consequence of the hierarchical paradigm of structures’ formation. Theoretically, one would expect an accelerated and earlier-on formation of galaxies in clusters, where many mechanisms (mergers, interactions, AGN activity and ram pressure stripping) are much more frequent than in the field. Hence, the environment is expected to affect the properties of galaxies since their formation. The aim of this thesis is to define the role played by the environment in shaping the properties of massive ETGs by comparing the stellar properties (age, metallicity and dynamics) and the SFH derived for a sample of ETGs in cluster with those of a sample in the field, both samples being at a redshift when the age of the Universe was 40% of the present age.
Thesis #3: Testing the role of AGNs in the stellar mass growth of galaxies
Thesis #3: Testing the role of AGNs in the stellar mass growth of galaxies
Active Galactic Nuclei (AGN) are thought to play a role in the modulation and quenching of star formation in a galaxy, the main mechanism by which a galaxy increases its stellar mass. The aim of this thesis is to investigate the possible connection between AGN and stellar mass growth of the host galaxy by studying the correlations between AGN properties (luminosity, black hole mass) and host galaxy properties (stellar mass and mass density, age, SFH, structural properties), and by comparing the properties of galaxies hosting an AGN with those of a control sample of galaxies without AGN.
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