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Combining quasars and galaxies to trace large-scale structure

Grant number: 15/11442-0
Support type:Scholarships in Brazil - Doctorate
Effective date (Start): December 01, 2015
Effective date (End): May 31, 2020
Field of knowledge:Physical Sciences and Mathematics - Astronomy - Extragalactic Astrophysics
Principal Investigator:Luis Raul Weber Abramo
Grantee:Carolina Queiroz de Abreu Silva
Home Institution: Instituto de Física (IF). Universidade de São Paulo (USP). São Paulo , SP, Brazil
Associated research grant:12/00800-4 - The 3-D universe: astrophysics with large galaxy surveys, AP.TEM
Associated scholarship(s):19/06766-1 - Selection of Quasar candidates based on multi-band photometric data, BE.EP.DR


Galaxies and quasars are the main extragalactic byproducts of surveys such as the Sloan Digital Sky Survey (I-II-III), WiggleZ, J-PAS, etc. However, the near-degeneracy of quasars with stars in color-color and color-magnitude plots makes it very hard to identify those objects with broad-band imaging, which is how SDSS and WiggleZ can target quasars. However, there is now a concrete possibility of mapping a massive number of quasars, over a large area, with the narrow-band optical survey J-PAS. During the M.Sc. project of the student, Carolina Queiroz, we optimized the widely used photometric redshift and typing codes BPZ (Benítez 2000) and LePhare (Arnouts et al. 1999; Ilbert et al. 2006) to identify AGNs (type I and II), and to distinguish them from stars and unresolved galaxies. A Bayesian technique was employed to help break the degeneracies that arise, and can degrade the quality of the catalogs through both misidentification and catastrophic redshift errors. On the other hand, during two other parallel M.Sc. projects (by Lucas F. Secco and Arthur M. Loureiro) we developed the method to do the Fourier analysis of multi-tracer cosmological surveys. The method was tested and validated on simulated data, and the results were collected in the paper arXiv: 1505.04106. The field is now ripe for a joint analysis of galaxies and quasars, both in more realistic simulations (namely, N-body simulations with semi-analytical recipes for halo occupation distributions of different types of objects) and in existing cosmological surveys (in particular, the photometric and spectroscopic SDSS catalog). Finally, the ongoing A-PLUS survey will also detect millions of galaxies and quasars over a wide range of redshifts, and over a large area (more than 14,000 square degrees). The survey should be completed in around three years, which makes it an ideal case to employ the experience we will accumulate during the period of this Ph.D. (AU)