Gravity from a giant cluster amplifies light and radio waves from a distant galaxy


The newly discovered galaxy, named VLAHFF-J071736+374506 (J0717+3745 for short), is likely the faintest radio-emitting object ever found, according to astronomers from the VLA Frontier Fields Legacy Survey.

This composite image, taken by the Very Large Array and Hubble, shows the galaxy cluster MACS J0717.5+3745. The pullout shows the distant galaxy J0717+3745, far beyond the cluster, and possibly the faintest radio-emitting object ever detected. The prominent red-orange objects are radio relics – large structures likely caused by shock waves – inside MACS J0717.5+3745. Image credit: Heywood et al. / Sophia Dagnello, NRAO/AUI/NSF/STScI.

The galaxy J0717+3745 is located more than 8 billion light-years from Earth.

Its light and radio waves were bent by gravitational lensing from a massive galaxy cluster.

Known as MACS J0717.5+3745, the lens cluster is located more than 5 billion light-years away.

“The radio image of J0717+3745 was magnified more than six times by the gravitational lens,” said University of Oxford astronomer Ian Heywood and NRAO astronomer Eric Jimenez-Andrade.

Galaxy clusters contain thousands of galaxies of all ages, shapes, and sizes. Typically, they have a mass around a million billion times the mass of the Sun and form over billions of years as smaller groups of galaxies slowly come together.

Albert Einstein predicted in his theory of general relativity that massive objects will warp the fabric of space itself.

When light or radio waves pass in front of one of these objects, such as MACS J0717.5+3745, their trajectory is slightly altered.

“J0717+3745 is probably the faintest radio-emitting object ever detected,” Dr Heywood said.

“That’s exactly why we want to use these clusters of galaxies as powerful cosmic lenses to learn more about the objects behind them.”

“The magnification provided by the gravitational lens, combined with extremely sensitive imagery from the NSF’s Karl G. Jansky Very Large Array (VLA), has given us unprecedented insight into the structure of a galaxy 300 times less massive than our Milky Way at a time when the Universe was less than half its current age,” said Dr Jimenez-Andrade.

“This gives us valuable information about star formation in these low-mass galaxies at that time and how they eventually came together into more massive galaxies.”

The team’s findings will appear in two articles to be published in the Astrophysical Journal.


I. Heywood et al. 2021. The VLA Frontier Fields Survey: High-Resolution Deep Radio Imaging of MACS Lens Clusters at 3 and 6 GHz. ApJ, in the press; arXiv: 2103.07806

EF Jimenez-Andrade et al. 2021. The VLA Frontier Field Survey: A radio and UV/optical size comparison of 0.3≲z≲3 star-forming galaxies. ApJ, in the press; arXiv: 2103.07807


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