Scientists use James Webb Space Telescope image to measure distance of lensed galaxies

The first image the James Webb Space Telescope (JWST) showed us was galaxy cluster SMACS J0723.3−7327 (or SMACS J0723 for short) with a large number of gravitationally lensed background galaxies.

But although it’s easy to see those smeared galaxies in the image, it’s not easy to tell just how far away they actually are.

A new study uploaded to arXiv and submitted to Astronomy & Astrophysics Letters, has used the first image to help model the ‘lens mass’ of SMACS J0723.

The model proposes that one of the galaxies in the image could have a redshift of > 7.5, suggesting a distance of around an incredible 13 billion light years away. To put that in perspective, the universe is 13.8 billion years old. The researchers have put their confidence level at 68% so more research needs to be done, but it’s an exciting find.

“The JWST imaging is absolutely astounding and beautiful, showing many more multiply lensed background sources, which allowed us to substantially refine our lens mass model,” says first author Dr Gabriel Bartosch Caminha from the Max Planck Institute for Astrophysics in Germany.

The researchers originally took data from the Hubble Space Telescope and the Multi Unit Spectroscopic Explorer to build a ‘pre-JWST’ lens model, and then refined it with the new JWST near-infrared image.

Gravitationally lensed objects are made brighter and bigger due to a large object in front, gravitationally warping their light. The large object works like a lens to distort the light rays. This can allow us to see much further away distances, but they also smear and duplicate, giving us the long structures you can see in the image.

In the annotated image below, each galaxy has a number, and multiple versions of the same galaxy are specified by a letter. The gravitational lensing has duplicated these galaxies three or four times. 

These gravitationally lensed galaxies are incredibly far away, so models are required to work out the size and distance of the closer objectto the gravitationally lensed object. All of this together will allow the researchers to provide the distance.

For example, the galaxy that’s 13 billion light years away has been lensed into three distinct images in the picture and its luminosity is magnified many multiple times.

“Our accurate mass model forms the foundation for the exploration of the JWST data,” says Professor Sherry Suyu, also from the Max Plank Institute.

“The spectacular JWST images show a great variety of strongly lensed galaxies, which can be studied in detail thanks to our accurate model.”