Scientists use JWST image to measure galaxy distance

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

But while it’s easy to see these smudged galaxies in the image, it’s not easy to tell how far away far they are in fact.

A new study uploaded to arXiv and submitted to Astronomy & Astrophysics Letters, 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 >7.5, suggesting an incredible distance of around 13 billion light-years. To put that into perspective, the universe is 13.8 billion years old. The researchers put their confidence level at 68% so more research needs to be done, but this is an exciting finding.

“The JWST imagery is absolutely stunning and beautiful, showing many more multi-lens background sources, which allowed us to significantly refine our lens mass model,” says first author Dr. Gabriel Bartosch Caminha of the Max Planck Institute for Astrophysics in Germany.

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

Gravitational lensed objects are made brighter and larger due to a large object in front, gravitationally distorting their light. The large object functions as a lens to distort light rays. This can allow us to see much further distances, but they also spread out and duplicate, giving us the long structures that 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 with a letter. Gravitational lensing duplicated these galaxies three or four times.

In this image, the various multi-lens background galaxies are numbered, with cyan colors indicating previously known multi-image systems and green colors indicating new multi-lens sources. The insets show magnified images of a very distant galaxy with substructure indicated by the green arrows. Credit: NASA, ESA, CSA and STScI (annotations by MPA)

These gravitationally lensed galaxies are incredibly distant, so models are needed to determine the size and distance of the object closest to the gravitational lensed object. All of this together will allow researchers to provide the distance.

For example, the galaxy 13 billion light-years away has been crystallized into three separate images in the image, and its brightness is magnified several times.

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

“The spectacular JWST images show a wide variety of strong-lens galaxies, which can be studied in detail with our precise model.”



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