QUBRICS project
QUasars as BRIght beacons for Cosmology in the Southern hemisphere
The QUBRICS project aims to identify new, bright and high-redshift QSOs (or beacons) in the Southern Hemisphere. We used photometric data in publicly available surveys, analyzed by means of machine learning methods in order to identify QSO candidates to be observed spectroscopically using facilities in the South. Finally, we used the acquired knowledge to address specific aspects of cosmology. The QUBRICS project already produced several published papers, a few more are currently under review, and more papers are yet to come. Note that the problem of finding high-redshift QSOs in the sky, is actually two-fold: we need to distinguish QSOs from stars, galaxies, and other sources in the first place, then we need to estimate a redshift in order to discard low redshift candidates. The envisioned roadmap to tackle the problem is to create a database collecting photometric data, and use it to train both classification and regression models, which eventually allowed us to identify QSO candidates.
Another goal of the QUBRICS project is to take advantage of the newly identified QSOs by using them as probes for the intervening medium. Along the lines of sight to these powerful light beacons, every parcel of the intervening gas selectively absorbs wavelengths of light, providing information about the spatial distributions, motions, temperature, chemical enrichment, and ionization histories of gaseous structures from redshift seven and beyond until the present.
In particular, thanks to QSO absorption lines, it is possible to address issues, e.g., what were the physical conditions of the primordial universe? What fraction of the matter was in a diffuse medium and what fraction and how early condensed in clouds? Where are most of the baryons at the various redshifts? When and how did the formation of galaxies and large-scale structure start? How early and in what amount have metals been produced? When and how (after the Dark Ages following recombination) did the universe get reionized? What was the typical radiation field, how homogeneous, and what was producing it? Which constraints on cosmological parameters and types of dark matter (e.g., neutrinos) are derived from the large-scale structure traced by the inter-galactic medium? Does the standard Big Bang nucleosynthesis model make the correct predictions about the primordial element abundances and the temperature evolution of the CMB? Do fundamental constants of physics (e.g., the fine-structure constant, α, or the proton-to-electron mass ratio, μ) vary with cosmic time? Does general relativity correctly describe the expansion of our universe? In order to efficiently pursue these and other similar lines of investigation, it is essential to have the brightest possible light beacons in the background.
