A multinational team of astronomers, led by Dr Hugo Messias of the Universidad de Concepción in Chile and the Universidade de Lisboa in Portugal, has discovered an extremely distant pair of merging galaxies named H-ATLAS J142935.3-002836 (H1429-0028 for short) with help of a gravitational lens.
H-ATLAS J142935.3-002836, an object seen by the Hubble Space Telescope and the Keck-II telescope on Hawaii with the help of a gravitational lens. In this image one can see the foreground galaxy that is doing the lensing, which resembles how our Milky Way Galaxy would appear if seen edge-on; but around this galaxy there is an almost complete ring – the smeared out image of a star-forming galaxy merger far beyond. Image credit: ESO / NASA / ESA / W. M. Keck Observatory.
Dr Messias explained: “while astronomers are often limited by the power of their telescopes, in some cases our ability to see detail is hugely boosted by natural lenses, created by the Universe. Einstein predicted in his theory of general relativity that, given enough mass, light does not travel in a straight line but will be bent in a similar way to light refracted by a normal lens.”
These 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 that would otherwise be invisible and to directly compare local galaxies with much more remote ones, when the Universe was significantly younger.
For these gravitational lenses to work, however, the foreground lensing galaxy and the one beyond need to be precisely aligned.
“These chance alignments are quite rare and tend to be hard to identify, but, recent studies have shown that by observing at far-infrared and millimeter wavelengths we can find these cases much more efficiently,” said Dr Messias, who is the lead author of a paper published in the journal Astronomy & Astrophysics (arXiv.org pre-print).
Discovered by the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS), H1429-0028 is among the brightest gravitationally lensed objects in the far-infrared regime found so far, even though astronomers are seeing it at a time when the Universe was just half its current age.
To study H1429-0028 in detail, Dr Messias and colleagues used the most powerful telescopes in the world and in space – NASA’s Hubble Space Telescope, the Atacama Large Millimeter/submillimeter Array (ALMA), the Keck Observatory, the Karl G. Jansky Very Large Array (VLA) and others.
The Hubble and Keck images revealed a detailed gravitationally induced ring of light around the foreground galaxy. These images also showed that the lensing galaxy is an edge-on disc galaxy – similar to our Milky Way Galaxy – which obscures parts of the background light due to the large dust clouds it contains.
But this obscuration is not a problem for ALMA and the VLA, since these two telescopes observe cosmic objects at longer wavelengths, which are unaffected by dust.
Using the combined data, the astronomers discovered that the background system was actually an ongoing collision between two galaxies.
The system of these two colliding galaxies resembles an object that is much closer to us – 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.
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Hugo Messias et al. 2014. Herschel-ATLAS and ALMA: HATLAS J142935.3-002836, a lensed major merger at redshift 1.027. A&A, vol. 568, A92; doi: 10.1051/0004-6361/201424410
