Exploring the Universe with radio and optical galaxy surveys

During the last two decades we have entered a "golden era" of cosmology. Using satellites and ground based telescopes we have gathered high quality data from the very early Universe, essentially from light emitted right after the Big Bang explosion, as well as from the late Universe, through the light emitted from stars and galaxies.

However, a big part of our Universe's history and volume remains unexplored. A way to attack this challenge is by observing the light emitted from the neutral hydrogen (HI) that filled the Universe for a long time after the Big Bang and before the first galaxies were formed. After that time HI resides within galaxies, so we can also use it as a novel way to study the late Universe. This is my main area of research; it is exciting because it opens a new observational window into the Universe and can push the boundaries of our understanding of astrophysics and cosmology.

In the next few years, HI surveys of exquisite sensitivity will be performed using radio telescopes, and part of the proposed research is working on new techniques in order to maximise their science output. I have pioneered a new observational method that does not require the -difficult and expensive- detection of individual galaxies but maps the entire HI flux coming from many galaxies together in large 3D pixels (across the sky and along time). I aim to use this technique to provide a 3D map of the Universe using HI intensity mapping data from the MeerKAT and SKA arrays. MeerKAT is a radio telescope located in Karoo, South Africa, and it is a pathfinder for the Square Kilometre Array (SKA), which is going to be the largest radio telescope in the world.

My main goal is to build a complete pipeline for the cosmological analysis of the HI intensity mapping signal from instruments like MeerKAT and the SKA. This pipeline will also account for the possibility of powerful synergies between HI and traditional optical galaxy surveys, by including cross-correlations data analysis tools. This is useful in order to obtain measurements that are free of systematic contaminations that often plague individual surveys (but drop out when combining them), and therefore more robust. I aim to perform the first ever measurements of HI and cosmological parameters in the radio wavelength using the intensity mapping technique, exploit multi-wavelength synergies, and revolutionarise our understanding of galaxy evolution and dark energy.

I am also working on two of the largest and best optical galaxy surveys of the next decade, the Euclid satellite mission and the ground-based Large Synoptic Survey telescope, whose main goals are to measure dark energy and understand the initial conditions of the Universe. In Euclid, I am working on various projects including building the software tools that are going to be used for the analysis of the data as soon as they become available. I am also working on the very challenging task of modelling the way galaxies cluster on small scales, in order to extract useful information for cosmology. I am also using tailored simulations to assess how well Euclid will measure the largest cosmological scales in order to characterise the initial conditions of the Universe. In both Euclid and LSST, I am working on synergies with radio experiments. My goal is to find innovative ways to optimally combine optical and radio surveys, in order to maximise their joint scientific output.

Another exciting part of working with these surveys is the huge amount of data that are going to be available. For example, the Phase 1 of the SKA is expected to generate 300 petabytes of data products every year. My research includes developing modernised and innovative data processing and analysis pipelines, which is required for the success of these amazing surveys.

The beneficiaries of this research include: (1) early career researchers (2) geophysics and medical physics (3) the Alan Turing Institute (4) South African economy and welfare (5) the public

(1) Early career researchers will benefit from this research in many ways. First of all, working on this project involves applying state-of-the-art and innovative data analysis techniques, as well as preparing the software tools and pipelines for the Euclid, LSST, and MeerKAT/SKA. Hence, early career researchers will develop a variety of skills that will help them excel in any career path - in academia or industry- they choose to follow. These benefits are not only expected for the PDRAs (and possible STFC funded PhD students) working on this project, but for a large number of international researchers, most notably students and PDRAs based in South Africa. This is going to be greatly enhanced by the participation of the PI in SA-DISCnet, an STFC-funded project for creating a collaborative data science training network across South Africa and the UK, part of SEPNET and AIMS (African Institute of Mathematical Science). The immediate beneficiaries will be astronomy and cosmology students and researchers, but the longer term use of our publicly available tools will benefit students and researchers from other branches of physics, engineering, and computer science.

(2) The PI's research project is crucial for the success of the innovative technique of HI intensity mapping. After the first generation of very large sky HI intensity mapping surveys has been commissioned, we will immediately start preparing for future experiments. The use of new technologies such as Phased Array Feeds (PAFs) can revolutionise cosmology with HI intensity mapping, and the success of this case is crucial to promote their use. Note that this technology has already been used for radio astronomy, for the first time, in the Australian Square Kilometre Array Pathfinder - ASKAP. The PI is in close contact with the Advanced Instrumentation team in ASTRON (Netherlands), and her research is instrumental for the science case promoting new technologies for the SKA. PAF technology has outstanding potential outside astronomy. Notable examples include geophysics and medical physics, that could greatly benefit from the very rapid imaging made possible by PAFs.

(3) The data volumes generated by the surveys that the project will exploit are enormous. Euclid, LSST, and MeerKAT/SKA will produce multi-Petabyte data sets during their lifetime. At the same time, the global need for understanding interlinked datasets is greater than ever. The Alan Turing Institute is the national institute for data science, which QMUL is joining this year. Its mission is "to make great leaps in data science research in order to change the world for the better". The PI is going to collaborate closely with the Institute to develop collaborative programmes of research.

(4) The SA-DISCnet project will pilot an innovative course of training and internships for the next generation of data analysts, focusing on South Africa's economic development and welfare in the 21st century. Data intensive science is a major global growth area, and the PI will combine her participation in SA-DISCnet with her proposal's research products (for example the publicly available simulations and data analysis tools) to contribute further to this cause.

(5) Large sky radio and optical galaxy surveys are much about exploring the unknown and their findings will enrich humankind's understanding of Nature. The PI will use the motivation, the background, the developed tools and results of her research in public outreach activities (e.g. teaching in schools, open days, stargazing live) to generate public awareness of science.