Galaxy evolution at high redshift exploiting large galaxy surveys

  • Pierandrea Guarnieri

Student thesis: Doctoral Thesis


In this thesis I summarise the work done along with my supervisors andcollaborators during my Doctor of Philosophy degree at the Institute of Cosmologyand Gravitation, University of Portsmouth.

We performed multiple studies to further investigate galaxy formationand evolution with a special focus on the high-redshift universe. We madeuse of some of the most advanced galaxy surveys accessible to my supervisors,namely the Dark Energy Survey and the Spitzer Extra-galactic VolumeRepresentative Survey.

Data from the former survey was utilised for the first time to probe the existenceand properties of the most massive galaxies right after their formationat primordial times (>̰ 1011 M, z∼4). My work exploited the theoreticalpredictions made by my supervisors and their previous collaborators, and I was the first one testing those predictions with the real Dark Energy Surveydata. Starting from ∼5 million sources we first performed extensive data cleaning and analysis, such as removing stars and artefacts as well as prioritising the most promising initial candidates using colour-colour selection maps. We then used a photometric redshift code and stellar population models to fit the observed data and calculate the photometric redshift and physical properties of each candidate. We further developed a series of selection cuts, including goodness of fit and probability distribution functions, tonally narrow down our nal selection of best candidates to 233 individual massive, high-z galaxies. This is the largest sample of massive, high-z candidate galaxies published so far. I led the refereed publication which describes all the work. Our work provides the general community with a precious sample to be followed-up with current and future telescopes to acquire spectra and confirm their cosmic distances. We started this process with a Gemini Telescope proposal aimed at observing three of these sources. We have been granted time and the data obtained is currently under processing.
My other main research project utilised - again for the first time - a 13- band photometry catalogue of ∼750; 000 galaxies from ∼5 sq. deg. of the Spitzer Extra-galactic Volume Representative Survey to investigate the mass assembly of massive galaxies across cosmic time. For this research I have calculated the galaxy stellar mass function up to z ∼ 4:5. I have first fitted stellar population models to all the galaxy data in order to calculate their photometric redshifts, ages and stellar masses. The uniqueness of this survey is its unparalleled combination of width and depth as well as the sampling of rest-frame near-IR bands. These features make this survey especially important to investigate the massive (∼1012.5 M end of the galaxy stellar mass function at high redshift. Our results will compose the most ambitious measurements performed in this context. Within this project, we present detailed analysis of our photometric redshift validation procedure, by investigating any specic population of outliers (based on their stellar mass, age and more) and by utilising a set of spectroscopic data for 40; 000 galaxies. We also explore their consequences in the galaxy stellar mass function context. This extensive material will be published by my collaborators, including myself in the future.
Further contributions of mine to other scientic publications are presented
at the end.
Date of AwardMar 2019
Original languageEnglish
SupervisorClaudia Maraston (Supervisor), Daniel B. Thomas (Supervisor) & Violeta Gonzalez-Perez (Supervisor)

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