Defense
Student: Marcelo Ciani Vicentin
Program: Astronomy
Title: "Brightest Cluster Galaxies as Tracers of Structure Formation: From Simulations to Observations"
Advisor: Prof. Dr. Laerte Sodré Junior - IAG/USP
Judging Comitee:
- Prof. Dr Laerte Sodré Junior - Presidente e Orientador - IAG/USP
- Prof. Dr. Eduardo Serra Cypriano - IAG/USP
- Profa. Dra. Ângela Cristina Krabbe - IAG/USP
- Profa. Dra. Ana Laura O’Mill - OAC/UNC (por videoconferência)
- Prof. Dr. Rubens Eduardo Garcia Machado - UTFPR
- Prof. Dr. André Luís Batista Ribeiro – UESC (por videoconferência)
Other Members:
- Profa. Dra. Paula Rodrigues Teixeira Coelho – IAG/USP
- Dr. Ricardo Lourenco Correia Ogando – ON/MCTI
- Prof. Dr. Paulo Afrânio Lopes - OV/UFRJ
- Profa. Dra. Cristina Furlanetto - UFRGS
- Prof. Dr. Gastão Bierrenbach Lima Neto - IAG/USP
- Profa. Dra. Claudia Lucia Mendes de Oliveira - IAG/USP
Abstract:
Galaxy clusters represent the most massive gravitationally bound structures in the Universe, and their progenitors–protoclusters–are key laboratories for studying the early phases of structure formation and galaxy evolution. This thesis investigates the connection between Brightest Cluster Galaxies (BCGs), large-scale environment, and the identification of clusters and protoclusters in wide photometric surveys, combining cosmo- logical simulations and observational data from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). In the first part, we analyze the stellar mass assembly of BCGs using the L-GALAXIES semi-analytic model applied to the Millennium simulation. Tracing 180 galaxy clusters and their progenitors, we show that (proto)BCGs grow through distinct evolutionary pathways, forming their stars early (z ∼ 4) but assembling the bulk of their mass later, mainly via mergers. Their progenitors consistently occupy the densest regions of forming structures, supporting their role as reliable tracers of early cluster collapse. The second part presents a new density–based algorithm for identifying galaxy clusters and protoclusters at 0.1 < z < 2 in wide-field photometric surveys. Using realis- tic mock lightcones (PCcones), we optimize the selection of (proto)BCGs as the central tracers of overdense regions and assign galaxy members through probabilistic models in- volving stellar mass, spatial proximity to the BCG, and photometric redshift. The method achieves high purity and completeness across a wide halo-mass range and establishes ro- bust halo mass–richness relations. In the third part, we apply this algorithm to the HSC-SSP Wide survey, incorpo- rating improved deep-learning photometric redshifts and generating a catalog of 16,007 (proto)cluster candidates. These systems trace dominant peaks in the stellar-mass density field up to z ∼ 2. The comparison with existing catalogs reveals strong complementarity among different methodologies, although it also selects an interesting set of candidates that does not intersect with those identified by other algorithms, highlighting the impor- tance of applying diverse techniques for the detection of these structures. Together, these results establish a coherent framework linking the physics of BCG evolution with the detection of large-scale structures in photometric data, providing an extensive sample of (proto)cluster candidates for future spectroscopic follow-up.
Keywords:
photometric surveys, simulations, galaxy clusters, brightest cluster galaxies, galaxy formation and evolution, high-redshift