Using the Atacama Large Millimeter/submillimeter Array [ALMA], and many other telescopes on the ground and in space, an international team of astronomers obtained the best view yet of a collision that took place between two galaxies when the Universe was only half its current age. They enlisted the help of a galaxy-sized magnifying glass to reveal otherwise invisible detail. These new studies of the galaxy H-ATLAS J142935.3-002836 have shown that this complex and distant object looks like the well-known local galaxy collision, the Antennae Galaxies.
The cosmic lenses are created by massive structures like galaxies and galaxy clusters, which deflect the light from objects behind them due to their strong gravity — an effect, called gravitational lensing. The magnifying properties of this effect allow astronomers to study objects which would not be visible otherwise and to directly compare local galaxies with much more remote ones, seen when the Universe was significantly younger.
H-ATLAS J142935.3-002836 (or just H1429-0028 for short) is one of these sources and was found in the Herschel Astrophysical Terahertz Large Area Survey [H-ATLAS]. Although very faint in visible light pictures, it is among the brightest gravitationally lensed objects in the far-infrared regime found so far, even though we are seeing it at a time when the Universe was just half its current age.
The system of the two colliding galaxies observed resembles the Antennae Galaxies. This is a spectacular collision between two galaxies, which are believed to have had a disc structure in the past. While the Antennae system is forming stars at a rate of only a few tens of the mass of our Sun each year, H1429-0028 turns more than 400 times the mass of the Sun of gas into new stars each year.
Rob Ivison, The European Southern Obersatory’s [ESO] Director of Science and a co-author of the new study, concludes: “ALMA enabled us to solve this conundrum because it gives us information about the velocity of the gas in the galaxies, which makes it possible to disentangle the various components, revealing the classic signature of a galaxy merger. This beautiful study catches a galaxy merger red handed as it triggers an extreme starburst.”