Free Astronomy Magazine January-February 2016

SPACE CHRONICLES patch of sky ever imaged to these depths at infrared wavelengths. The team combined these UltraVIS- TA observations with those from the NASA Spitzer Space Telescope, which probes the cosmos at even longer, mid-infrared wavelengths (ESO’s VISTA telescope observed in the near-infrared wavelength range 0.88–2.15 μ m while Spitzer performed observations in the mid- infrared at 3.6 and 4.5 μ m). “We uncovered 574 new massive galaxies — the largest sample of such hidden galaxies in the early Universe ever assembled,” explains Karina Caputi. “Studying them al- lows us to answer a simple but im- portant question: when did the first massive galaxies appear?” Imaging the cosmos at near-infra- red wavelengths allowed the as tron- omers to see objects that are both obscured by dust, and extremely distant, created when the Universe was just an infant. The expansion of space means that the more dis- tant a galaxy is, the faster it ap- pears to be speeding away from an observer on Earth. This stretching causes the light from these distant objects to be shifted into redder parts of the spectrum, meaning that observations in the near-to- mid infrared are necessary to cap- ture the light from these galaxies. The team discovered an explosion in the numbers of these galaxies in a very short amount of time. A large fraction of the massive gal- axies (more than 50 billion times the mass of the Sun) we now see around us in the nearby Universe were already formed just three bil- lion years after the Big Bang. “We found no evidence of these massive galaxies earlier than around one billion years after the Big Bang, so we’re confident that this is when the first massive galaxies must have formed,” concludes Henry Joy Mc- Cracken, a co-author of the study. In addition, the astronomers found that massive galaxies were more plentiful than had been thought. Galaxies that were previously hid- den make up half of the total num- ber of massive galaxies present when the Universe was between 1.1 and 1.5 billion years old (this is equivalent to redshifts between z=5 and z=4). These new results, however, contradict current mod- els of how galaxies evolved in the early Universe, which do not pre- dict any monster galaxies at these early times. To complicate things further, if massive galaxies are unexpectedly dustier in the early Universe than astronomers predict then even Ul- traVISTA wouldn’t be able to de- tect them. If this is indeed the case, the currently-held picture of how galaxies formed in the early Uni- verse may also require a complete overhaul. The Atacama Large Millimeter/sub- millimeter Array (ALMA) will also search for these game-changing dusty galaxies. If they are found they will also serve as targets for ESO’s 39-metre European Extreme- ly Large Telescope (E-ELT), which will enable detailed observations of some of the first ever galaxies. A few of the newly discovered massive galaxies are shown in close-up on these small subsets of the UltraVISTA field. [ESO/UltraVISTA team. Acknowledgement: TERAPIX/CNRS/INSU/CASU] T his video shows the massive gal- axies discov- ered in the early Uni- verse. [ESO/ UltraVISTA team. Ac- knowledge- ment: TERA- PIX/CNRS/IN SU/CASU] n