Gravity of Giant Cluster Magnifies Light and Radio Waves from Distant Galaxy

The newly-discovered galaxy, named VLAHFF-J071736+374506 (J0717+3745 for short), is likely the faintest radio-emitting object yet found, according to astronomers with 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. Pullout shows the distant galaxy J0717+3745, far beyond the cluster, and likely the faintest radio-emitting object ever detected. The prominent red-orange objects are radio relics — large structures possibly caused by shock waves — inside MACS J0717.5+3745. Image credit: Heywood et al. / Sophia Dagnello, NRAO / AUI / NSF / STScI.

The J0717+3745 galaxy lies at a distance of more than 8 billion light-years from Earth.

Its light and radio waves have been bent by the gravitational-lensing effect of a massive galaxy cluster.

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

“The radio image of J0717+3745 has been magnified more than six times by the gravitational lens,” said Oxford University 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 of about one 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 deform the fabric of space itself.

When light or radio waves pass one of these objects, such as MACS J0717.5+3745, their path is changed slightly.

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

“This is exactly why we want to use these galaxy clusters as powerful cosmic lenses to learn more about the objects behind them.”

“The magnification provided by the gravitational lens, combined with extremely sensitive imaging from NSF’s Karl G. Jansky Very Large Array (VLA), gave us an unprecedented look at 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,” Dr. Jimenez-Andrade said.

“This is giving us valuable insights on star formation in such low-mass galaxies at that time and how they eventually assembled into more massive galaxies.”

The team’s results will appear in two papers to be published in the Astrophysical Journal.


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

E.F. Jiménez-Andrade et al. 2021. The VLA Frontier Field Survey: A Comparison of the Radio and UV/optical size of 0.3≲z≲3 star-forming galaxies. ApJ, in press; arXiv: 2103.07807

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