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From the First Galaxies to the Milky Way (XGAL)

CAAUL Researchers: David Sobral (PI), Jorryt Matthee, Carolina Duarte, Miguel DomingosJesse van de Sande, Sérgio Santos
Work Group: Galaxies and Cosmology

In order to understand how galaxies form and evolve, we need to conduct detailed studies up to very high look-back times (high redshift), gathering large and robust samples of galaxies over representative volumes. In the last 5 years, we have led a significant effort towards achieving such goals for the last 50% of the age of the Universe and, as a consequence, we have derived by far the largest samples of distant (high-z) H-alpha selected star-forming galaxies. These have allowed us to detail the nature and evolution of star-forming galaxies like our own Milky Way over the last 6 billion years, with very high impact results.

Figure 1: This schematic diagram shows how the Universe is thought to have evolved from the Big Bang to the present day. Data from the UKIRT, VLT and Subaru observatories allowed the astronomers to take four precise and comparable snapshots of the Universe when it was, 2, 4, 6 and 9 billion years old, each containing hundreds of star-forming galaxies. By comparing the different snapshots, astronomers were able to accurately track what has changed over the last 11 billion years. Credit: Chandra / NASA / NOAO / KIPAC

Recently, we have started an even more ambitious set of projects, in order to extend our understanding to even earlier epochs in the Universe, and we have already been able to derive the first fully self-consistent star-formation history of the Universe. Our results not only show that the overall star formation activity has been strongly declining over the last 11 billion years, but also reconcile fundamental observables in the Universe, greatly contributing to our understanding. Now is the time to identify and understand what is driving the strong decline in the cosmic star formation history, but also to extend our studies to even earlier times in the history of the Universe. We are doing this very effectively by extending our very wide narrow-band surveys all the way to z~9, potentially confirming and studying the most distant galaxies ever found. This project is taking full advantage of the very significant amount of telescope time that we have been awarded (and will be applying for) on some of the most competitive facilities such as Subaru, ESO/VLT and ALMA. We aim to explore our uniquely large samples of very distant galaxies (selected with the same method across cosmic time) to understand exactly how/why/when galaxies like our own formed and how/why they evolve in the way they do, over the last 13 billion years.

Figure 2: This diagram indicates the changing ‘GDP’ of the Universe over time. The new results indicate that, measured by mass, the production rate of stars has dropped by 97% since its peak 11 billion years ago.
Credit: D. Sobral.

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