Using the VISTA Survey Telescope at ESO’s La Silla Paranal Observatory, astronomers have discovered almost 600 new massive galaxies in the distant Universe.
The VISTA telescope has discovered a horde of previously hidden giant galaxies that existed when the Universe was in its infancy. By discovering and studying more of these galaxies than ever before, astronomers have for the first time found out exactly when such galaxies first appeared. A few of the newly discovered early galaxies are shown in this image. Image credit: ESO / UltraVISTA Team / TERAPIX / CNRS / INSU / CASU.
The astronomers made a census of faint galaxies when the age of the Universe was between just 0.75 and 2.1 billion years old.
They used images from the UltraVISTA survey, one of six projects using the VISTA (Visible and Infrared Survey Telescope for Astronomy) telescope to survey the sky at near-infrared wavelengths.
“We uncovered 574 new massive galaxies (objects with masses of more than 50 billion solar masses) – the largest sample of such hidden galaxies in the early Universe ever assembled,” said Dr Karina Caputi University of Groningen in the Netherlands, lead author of a paper in the September 2015 issue of the Astrophysical Journal (arXiv.org preprint).
“Studying these early galaxies allows us to answer a simple but important question: when did the first massive galaxies appear?”
Imaging the cosmos at near-infrared wavelengths allowed Dr Caputi and co-authors to see objects that are both obscured by dust, and very distant, created when the Universe was just an infant.
The astronomers discovered an explosion in the numbers of these galaxies in a very short amount of time. A large fraction of the giant galaxies we see in the nearby Universe were already formed just 3 billion years after the Big Bang.
“We found no evidence of these massive galaxies earlier than around 1 billion years after the Big Bang, so we’re confident that this is when the first massive galaxies must have formed,” explained co-author Dr Henry Joy McCracken, of the Institut d’Astrophysique de Paris in France.
The newly-discovered massive galaxies are marked in this image of the UltraVISTA field. Image credit: ESO / UltraVISTA Team / TERAPIX / CNRS / INSU / CASU.
In addition, the team found that massive galaxies were more plentiful than had been thought.
Galaxies that were previously hidden make up half of the total number of massive galaxies present when the Universe was between 1.1 and 1.5 billion years old.
“Our results indicate that some very massive galaxies are present since the Universe was only a billion years old,” the scientists said.
The new findings, however, contradict current models of how galaxies evolved in the early Universe, which do not predict any massive galaxies at these early times.
“To complicate things further, if massive galaxies are unexpectedly dustier in the early Universe than astronomers predict then even UltraVISTA wouldn’t be able to detect them,” the astronomers said.
“If this is indeed the case, the currently-held picture of how galaxies formed in the early Universe may also require a complete overhaul.”
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K.I. Caputi et al. 2015. Spitzer bright, UltraVISTA faint sources in COSMOS: the contribution to the overall population of massive galaxies at z=3-7. ApJ 810, 73; doi: 10.1088/0004-637X/810/1/73
