The study presents the first measurements of the changing strengths of oxygen emission-lines from the present-day and up to 12.5 billion years ago. The main conclusions of this study is that the strength of doubly-ionized oxygen increases going back in time, while the strength of singly-ionized oxygen increases up to 11 billion years ago and then decreases for the remaining 1 – 2 billion years. The cause of the two different evolutions is due to the changing physical conditions inside star-forming galaxies where the amount of ionizing energy inputted into the gas by newly formed stars is much higher in the early Universe. The results of this paper helps to set the framework for future surveys using the next-generation telescopes, such as the upcoming James Webb Space Telescope (JWST), that will allow for us to study the conditions inside star-forming galaxies even further into the past to the era of the first galaxies.

This paper has been published in the Monthly Notices of the Royal Astronomical Society and includes collaborations from US and UK institutions. The paper was co-authored by David Sobral [Lancaster University], Bahram Mobasher [UC Riverside], Ian Smail [Durham University], Behnam Darvish [Caltech], Hooshang Nayyeri [UC Irvine], Shoubaneh Hemmati [IPAC/Caltech], and John Stott [Oxford University].