Periodic Reporting for period 2 - PiCOGAMBAS (Precision Cosmology with Galaxy and Microwave Background surveys)
Okres sprawozdawczy: 2023-02-01 do 2024-01-31
Understanding the universe we live in is one of the challenges that pushed mankind to look at the sky since the dawn of civilization. In modern times, accurate astrophysical observations have allowed us to turn questions like "how did the universe begin?" or "what the universe if made of?" into scientific problems.
The standard cosmological model predicts that the universe started in a hot and dense phase commonly known as Big Bang and then underwent an accelerated expansion called inflation where the seeds of the matter density perturbation that later evolved in galaxies and stars were generated. After inflation the universe expanded slowly since the beginning of a new accelerated phase a few billion years ago driven by an unknown energy component called dark energy. Understanding the nature of inflation and dark energy are two of the main questions that cosmologists hope to answer in the next decade using observations of the large scale structures (LSS) of the universe (galaxies, galaxy clusters etc.) and of the Cosmic Microwave Background (CMB), the relic light of the Big Bang. These observations will also help solving one of the key open question on the standard model of particle physics: the nature of the neutrino mass.
During its journey towards us, the CMB interacts with the LSS as they form. These leave several distinct imprints in the CMB photons: their gravitational force deflects the CMB photon's trajectories (CMB lensing) and CMB photons exchange energy with the energetic particles trapped in the LSS (SZ effect). Combining observations of the CMB and data of galaxy surveys mapping the LSS, we can thus study the properties of the matter distribution of the universe and its evolution with two different and complementary techniques. In particular, comparing the mass maps acquired with CMB and galaxy surveys (cross-correlation) will sharpen our understanding of the universe beyond what can be normally achieved and will allow us to go beyond the limiting factor affecting the analyses of both kinds of data sets when performed independently of each other.
With the new generation of CMB experiments (e.g. Simons Observatory -- SO) and galaxy surveys (e.g. the ESA mission Euclid) that have started observing the sky at the same time in 2023, this field has the potential to deliver multiple "firsts" in cosmology in the coming years. To fully exploit this potential, we need to better understand the statistical methods involved in the cross-correlation of CMB and galaxy surveys, test their robustness, design new techniques and observables capable of extracting the maximum amount of information from the data.
All these questions are at the core of the PiCOGAMBAS project which delivered robust data analysis methods, new data sets and cosmological constraints, and identified innovative approaches that will produce exciting results in cosmology in the coming years.
The standard cosmological model predicts that the universe started in a hot and dense phase commonly known as Big Bang and then underwent an accelerated expansion called inflation where the seeds of the matter density perturbation that later evolved in galaxies and stars were generated. After inflation the universe expanded slowly since the beginning of a new accelerated phase a few billion years ago driven by an unknown energy component called dark energy. Understanding the nature of inflation and dark energy are two of the main questions that cosmologists hope to answer in the next decade using observations of the large scale structures (LSS) of the universe (galaxies, galaxy clusters etc.) and of the Cosmic Microwave Background (CMB), the relic light of the Big Bang. These observations will also help solving one of the key open question on the standard model of particle physics: the nature of the neutrino mass.
During its journey towards us, the CMB interacts with the LSS as they form. These leave several distinct imprints in the CMB photons: their gravitational force deflects the CMB photon's trajectories (CMB lensing) and CMB photons exchange energy with the energetic particles trapped in the LSS (SZ effect). Combining observations of the CMB and data of galaxy surveys mapping the LSS, we can thus study the properties of the matter distribution of the universe and its evolution with two different and complementary techniques. In particular, comparing the mass maps acquired with CMB and galaxy surveys (cross-correlation) will sharpen our understanding of the universe beyond what can be normally achieved and will allow us to go beyond the limiting factor affecting the analyses of both kinds of data sets when performed independently of each other.
With the new generation of CMB experiments (e.g. Simons Observatory -- SO) and galaxy surveys (e.g. the ESA mission Euclid) that have started observing the sky at the same time in 2023, this field has the potential to deliver multiple "firsts" in cosmology in the coming years. To fully exploit this potential, we need to better understand the statistical methods involved in the cross-correlation of CMB and galaxy surveys, test their robustness, design new techniques and observables capable of extracting the maximum amount of information from the data.
All these questions are at the core of the PiCOGAMBAS project which delivered robust data analysis methods, new data sets and cosmological constraints, and identified innovative approaches that will produce exciting results in cosmology in the coming years.
CMB lensing is the key observable for cross-correlation with LSS. It can be reconstructed from CMB temperature and polarization maps. I demonstrated that lensing reconstruction is insensitive to instrumental systematics and provided public tools to study such problems. I devised new methods to reconstruct CMB lensing that are robust to modeling systematics and enabled the measurements of new effects to test the theory of gravity. I also discovered new potential artifacts appearing in lensing reconstruction and proposed a model to mitigate their impact in the future.
Alongside these works, I studied new applications of CMB-LSS cross-correlation techniques. I showed that CMB lensing-LSS cross-correlations with Euclid and SO data can tighten the cosmological constraints on dark energy achievable by Euclid alone by ~2x. Often the analysis of Euclid data will require the use of simulations and mock data based on cosmological N-body simulations. These are normally computationally very expensive especially if galaxy formation must be included. I proposed new approaches to speed up this task using machine learning techniques. Using such simulations I identified new ways of constraining the mass of neutrinos using underdense regions of the universe (cosmic voids) and CMB lensing. One of the goals of Euclid is to constrain the physics of dark energy. Dark energy leaves specific imprints in the CMB temperature. I delivered the first statistical tool to exploit such signature (ISW effect) in cross-correlation with CMB lensing on data of ESA Planck satellite. Such tool will be a reference for the coming decade.
CMB B-mode polarization is a unique probe of the physics of inflation. Gravitational lensing and galactic emissions can however make this signal undetectable. I showed that using maps of galaxies and future multi-frequency observations of the CMB we can improve the current inflation constraints by ~20x. Alternative probes of inflation can be obtained from non-Gaussian statistics of the density perturbations. Local deviations from the CMB emission law (spectral distortions) provide unique information on this. I reanalyzed the only available spectral distortion data produced in the 1990s and improved the status of the field by 2x after 25 years. My approach will allow to constrain new inflation models with CMB data in the 2030s. I also investigated alternative physical processes active in the early universe involving dark matter candidates called axions and set new constraints on them using POLARBEAR and Planck data.
My spectral distortions result, when compared to expectations of these effects from realistic numerical simulations, allowed me to constrained models of galaxy formation for the first time. I demonstrated that SO can also deliver transformational results in this field, clarifying the role of the magnetic field in the process of star formation. I tested this new technique on precursor data from the Planck satellite.
During my last year of work I analyzed data of the ESA Gaia mission and produced Quaia, the largest ever produced catalog of quasars, bright objects powered by supermassive black holes. Quaia was made public and I used it to constrain the evolution of matter fluctuations in the universe in a regime never investigated before.
These results were presented in over 10 invited contributions at international institutions and conferences.
Alongside these works, I studied new applications of CMB-LSS cross-correlation techniques. I showed that CMB lensing-LSS cross-correlations with Euclid and SO data can tighten the cosmological constraints on dark energy achievable by Euclid alone by ~2x. Often the analysis of Euclid data will require the use of simulations and mock data based on cosmological N-body simulations. These are normally computationally very expensive especially if galaxy formation must be included. I proposed new approaches to speed up this task using machine learning techniques. Using such simulations I identified new ways of constraining the mass of neutrinos using underdense regions of the universe (cosmic voids) and CMB lensing. One of the goals of Euclid is to constrain the physics of dark energy. Dark energy leaves specific imprints in the CMB temperature. I delivered the first statistical tool to exploit such signature (ISW effect) in cross-correlation with CMB lensing on data of ESA Planck satellite. Such tool will be a reference for the coming decade.
CMB B-mode polarization is a unique probe of the physics of inflation. Gravitational lensing and galactic emissions can however make this signal undetectable. I showed that using maps of galaxies and future multi-frequency observations of the CMB we can improve the current inflation constraints by ~20x. Alternative probes of inflation can be obtained from non-Gaussian statistics of the density perturbations. Local deviations from the CMB emission law (spectral distortions) provide unique information on this. I reanalyzed the only available spectral distortion data produced in the 1990s and improved the status of the field by 2x after 25 years. My approach will allow to constrain new inflation models with CMB data in the 2030s. I also investigated alternative physical processes active in the early universe involving dark matter candidates called axions and set new constraints on them using POLARBEAR and Planck data.
My spectral distortions result, when compared to expectations of these effects from realistic numerical simulations, allowed me to constrained models of galaxy formation for the first time. I demonstrated that SO can also deliver transformational results in this field, clarifying the role of the magnetic field in the process of star formation. I tested this new technique on precursor data from the Planck satellite.
During my last year of work I analyzed data of the ESA Gaia mission and produced Quaia, the largest ever produced catalog of quasars, bright objects powered by supermassive black holes. Quaia was made public and I used it to constrain the evolution of matter fluctuations in the universe in a regime never investigated before.
These results were presented in over 10 invited contributions at international institutions and conferences.
PiCoGAMBAS main results include:
- The first study of the impact of instrumental systematics on CMB lensing measurements that became a reference in the field.
- The first assessment of the impact of non-linear effects in a new, optimal class of statistical estimator of CMB lensing reconstruction.
- The discovery of new effects and observables previously unknown in the field of cross-correlation.
- New measurements of CMB spectral distortion that improved the status of the field after 25 years.
- The largest quasar catalog ever produced (Quaia) derived from data of the ESA Gaia mission.
- The first cosmological constraints using Gaia data and their cross-correlation with CMB that demonstrated the strength of space-based observatories for this kind of science and served as precursor for the analysis of Euclid data.
I have presented these results in several talks for the general public, artists, teachers and professionals in both the USA and Europe. The results of the work on Quaia have been covered by a dedicated press release by ESA that sparked the interest of major general newspapers across the globe.
- The first study of the impact of instrumental systematics on CMB lensing measurements that became a reference in the field.
- The first assessment of the impact of non-linear effects in a new, optimal class of statistical estimator of CMB lensing reconstruction.
- The discovery of new effects and observables previously unknown in the field of cross-correlation.
- New measurements of CMB spectral distortion that improved the status of the field after 25 years.
- The largest quasar catalog ever produced (Quaia) derived from data of the ESA Gaia mission.
- The first cosmological constraints using Gaia data and their cross-correlation with CMB that demonstrated the strength of space-based observatories for this kind of science and served as precursor for the analysis of Euclid data.
I have presented these results in several talks for the general public, artists, teachers and professionals in both the USA and Europe. The results of the work on Quaia have been covered by a dedicated press release by ESA that sparked the interest of major general newspapers across the globe.