A cosmic census

Monthly Notices of the Royal Astronomical Society

Monthly Notices of the Royal Astronomical Society is one of the world's leading primary research journals in astronomy and astrophysics, as well as one of the longest established. It publishes the results of original research in positional and dynamical astronomy, astrophysics, radio astronomy, cosmology, space research, and the design of astronomical instruments.

By Raphael Shirley, María Campos, Peter Hurley, Katarzyna Małek, and Seb Oliver
October 4^th 2021

A new census of the Universe will allow scientists to understand more about how galaxies are born, age, and die. The millions of galaxies that have been painstakingly catalogued come in many shapes and sizes and this new work shines a light on every variety that we can see.

The new measurements, which were published in Monthly Notices of the Royal Astronomical Society, will allow many other people to look for unusual and new types of galaxy hidden within the data. It will also help them to look at whole “populations” to better understand how they evolve. It has already been used to find interesting rare galaxies and to understand how and why they stand out from the crowd.

The international group of scientists, led by astronomers working with Professor Seb Oliver at the University of Sussex, decided to create the Herschel Extragalactic Legacy Project. This project was set up to understand images from the Herschel Space Observatory; a huge telescope in space which measured the far infrared light that is emitted from the cool dust in galaxies.

*Illustration of the Herschel Space Observatory which is at the center of the work*
*Credit: Ève Barlier*

They brought together observations from across the electromagnetic spectrum; from the bluest light emitted by hot young stars to the reddest which comes from cool dust. The team then used all this information to weigh galaxies, measure how far away they are, and count how many stars are being born within them.

Usually scientists use a small area of the night sky, but this new work brings together all of the best-studied regions allowing them to search through an unprecedented volume of the Universe. The more sky that we observe, the more rare objects we can find in order to understand all types of galaxies. One unusual object already found in the data was a giant black hole discovered only 1.4 billion years after the Big Bang.

By bringing together public data from many different telescopes and making sure everything is freely available, the team believe it will also open up data to more groups and maximise how many people can get involved. First author Raphael Shirley said: “it will be like a digital library of galaxies where anyone can take out a book on any galaxy that can be seen.” He is keen that this “open science” practice will be more widely adopted as it also means the public can use it. “Maybe there is an intrepid school student who might find an exciting new discovery hidden amongst the millions of galaxies that has been missed by the professionals.”

Raphael Shirley is an astronomer at the University of Southampton who uses wide area imaging surveys to understand galaxy formation and evolution. He has previously worked at the Instituto de Astrofísica de Canarias in Tenerife, Spain and was a Daphne Jackson research fellow at the Astronomy Centre, University of Sussex. Raphael is lead author of HELP: the Herschel Extragalactic Legacy Project recently published in Monthly Notices of the Royal Astronomical Society.

María Campos is an astronomy doctoral researcher at the University of Sussex. She conducts statistical analysis on large surveys to study galaxy evolution. She finished her Master's in Astrophysics at the Universidad de La Laguna in Tenerife, Spain and joined the Herschel team at RAL Space in Oxford, UK, where she worked with data from ESA's Herschel Space Observatory. She has co-authored several papers including HELP: the Herschel Extragalactic Legacy Project.

Peter Hurley is an astronomer at the Astronomy Centre, the University of Sussex, who models extragalactic survey data with probabilistic models in order to understand galaxy evolution. He was a project scientist for the Herschel Extragalactic Legacy Project and developed the probabilistic modelling tool XID+ as part of the project.

Katarzyna Małek is a Professor of Astrophysics at National Centre for Nuclear Research in Poland. Her current research activities focus on modelling the spectral energy distribution of galaxies that are luminous in the infrared.

Seb Oliver is a Professor of Astrophysics at University of Sussex and led the €2.5M, European Commission funded programme “The Herschel Extragalactic Legacy Project, HELP”. His expertise is in large surveys of the sky, especially using space telescopes sensitive to infrared radiation. He exploits a variety statistical analysis techniques to analyse these large data sets to probe the evolution of galaxies over cosmic time. He has over 290 papers in refereed journals, with over 23,000 citations. He has applied data analysis techniques from astronomy to a number of areas including, dementia diagnosis and drought forecasting.

Monthly Notices of the Royal Astronomical Society

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