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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - BUILDUP (Galaxy Buildup in the Young Universe: from the First Billion Years through the Peak Activity Epoch)

Teaser

Summary

Deep galaxy surveys are the most valuable asset to understand the history of our Universe. Still to date, important
discrepancies still exist between galaxy formation models and the results of galaxy observations, most notably for galaxies in the young Universe. The BUILDUP
Project aims to reconstruct the history of galaxy buildup from the first billion years of cosmic time
through the peak activity epoch of the Universe, which occurred 10 billion years ago, providing
fundamental constraints for galaxy formation models.

Work performed

In order to address the general goal of this Project, we are working with the most comprehensive infrared galaxy survey ever conducted with the Spitzer Space Telescope for the study of the early Universe (Spitzer Exploration Science Programme SMUVS - PI K. Caputi). The unprecedented characteristics of this survey, which has obtained deep infrared images over a relatively large area of the sky, are allowing us to study 66,000 galaxies present in the Universe in the first few billions years of cosmic time. Our main results in the BUILDUP Project so far can be summarised as follows.

1) We have discovered a new population of intense star-forming galaxies when the Universe was only 1.5 billion years old, i.e. about 10% of its present age. Although in number these galaxies were only a small percentage of all galaxies in the Universe, their individual star formation rates were so high that they were making altogether half of all the stars being formed in the Universe at those cosmic times.

2) We have found that there are fundamental differences in the evolution of large and small galaxies in the young Universe. This refers to the way in which they form their stars, as well as how star formation eventually declines to make galaxies become quiescent.

3) We have quantitatively probed, for the first time, the large-scale structure traced by galaxies when the Universe was only a few billion years old. The early onset of galaxy large-scale structure is one of the key predictions of the most accepted cosmological model, which is the Lambda cold dark matter model.

In addition, we are conducting simulations to prepare for the scientific exploitation of the galaxy surveys that we will conduct with the forthcoming James Webb Space Telescope (JWST). This will be one of the most important telescopes operating next decade and is expected to revolutionise our view of the early Universe. With our ongoing work, we the BUILDUP Team are positioning ourselves as leaders for the analysis of JWST data.

Final results

The strategic importance of the BUILDUP Project resides in bridging current infrared galaxy surveys with the next generation of much more sensitive galaxy surveys for the early Universe, which will be possible with the JWST. In the second part of the Project, we envisage continue exploiting the SMUVS Exploration Science Programme, as well as expand our study of the young Universe by making use of ancillary datasets. One of the most important aspects that we will address is the presence of massive galaxies in the very early Universe, when the Universe was in its first billion year of age. This topic is particularly relevant for galaxy formation models, as nowadays there is serious tension between their predictions for the early Universe and observations. Our new study will lead to one of the most exciting results of the BUILDUP Project: shedding light on how some of the most massive galaxies that we see in our Universe today were formed at early cosmic times.
Finally, with JWST\'s launch quickly approaching, we will ensure to achieve a leading position for the scientific exploitation of the most ambitious space mission that has been conceived to date.