Dozens of newly found gravitational lenses may provide light on early galaxies

Pictures of gravitational lenses from the AGEL survey. The pictures are centred on the foreground galaxy and include the object name. Each panel includes the confirmed distance to the foreground galaxy (zdef) and distant background galaxy (zsrc). Credit: Kim-Vy H. Tran et al, The Astronomical Journal (2022). DOI: 10.3847/1538-3881/ac7da2

Earlier this year, a machine learning system detected up to 5,000 possible gravitational lenses, which might revolutionize our understanding of galaxy evolution since the Big Bang. Kim-Vy Tran of ASTRO 3D and UNSW Sydney, together with colleagues, have now evaluated 77 of the lenses using the Keck Observatory in Hawaii and the Very Large Telescope in Chile. Her worldwide team and confirmed that 68 of the 77 are powerful gravitational lenses spanning huge cosmic distances. This 88% success rate shows that the algorithm is trustworthy and that hundreds of additional gravitational lenses might be created. Gravitational lenses have been difficult to come by, and just a few hundred are now in service.

Kim-Vy Tran's study, published today in The Astronomical Journal, shows spectroscopic confirmation of powerful gravitational lenses previously found using Convolutional Neural Networks built by ASTRO 3D and Swinburne University data scientist Dr. Colin Jacobs. The research is part of the study ASTRO 3D Galaxy Evolution with Lenses (AGEL).

Dr. Tran of the ARC Centre of Excellence for All Sky Astrophysics in 3-Dimensions (ASTRO3D) and the University of New South Wales (UNSW) remarked, "Our spectroscopy allowed us to map a 3D picture of the gravitational lenses to show they are genuine and not just chance superposition." Our objective with AGEL is to spectroscopically confirm roughly 100 strong gravitational lenses visible throughout the year from both the Northern and Southern hemispheres.

The publication is the outcome of a worldwide partnership involving researchers from Australia, the United States, the United Kingdom, and Chile. The study was made feasible by the creation of an algorithm that searches for certain digital signatures.

Dr. Tran stated that using this, we could identify thousands of lenses rather than just a few handfuls.

Einstein predicted that light bends around huge objects in space in the same manner as light bends through a lens, which led to the discovery of gravitational lensing. As a result, it substantially amplifies pictures of galaxies that we would not be able to see otherwise. While astronomers have long employed cosmic magnifying glasses to study distant galaxies, discovering them in the first place has been difficult.

According to Dr. Tran, because these lenses are so thin, you won't be able to identify them if your images are hazy.

While these lenses improve our ability to view objects millions of light years distant, they should also allow us to "see" the invisible dark matter that makes up the majority of the Universe.

According to Dr. Tran, the majority of the bulk is dark. We know that mass bends light, therefore if we can measure how much light is bent, we can calculate how much mass there must be.

Having a larger number of gravitational lenses at varying distances will also provide us with a more complete picture of the chronology dating back practically to the Big Bang.

According to Dr. Tran, the more magnifying glasses you have, the more chance you have of surveying these more distant items. We want to improve our understanding of the demography of extremely young galaxies. Then, somewhere between those very early first galaxies and us, there's a lot of development going on, with small star-forming areas converting pure gas into the Milky Way's first stars. So, using these lenses at different distances, we can look at different moments in the cosmic chronology to see how things evolve over time, from the very earliest galaxies to the present.

Dr. Tran's team was global in scope, with each group bringing unique expertise.

She stated that being able to interact with colleagues from other colleges has been critical, both in starting the study and now in continuing with all of the follow-up observations.

According to Professor Stuart Wyithe of the University of Melbourne, who is also the Director of the ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (Astro 3D), each gravitational lens is unique and teaches us something new.

Apart from being gorgeous structures, gravitational lenses, he claims, gives a doorway into examining how mass is dispersed in very distant galaxies that are not visible using conventional methods. The research opens up the possibility of seeing how galaxies gain their mass by presenting strategies to use these new vast data sets of the sky to seek many new gravitational lenses.

Swinburne University Professor Karl Glazebrook, Dr. Tran's Co-Science Lead on the research, paid gratitude to the work that has gone before.

According to him, Dr. Colin Jacobs of Swinburne University pioneered this method. He went through tens of millions of photos of galaxies to narrow the sample to 5,000. We had no idea the success rate would be that high. The Hubble Space Telescope is now providing photographs of these lenses, which vary from breathtakingly beautiful to exceedingly bizarre sights that will require some work to decipher.

Another co-science lead on the work, Associate Professor Tucker Jones of UC Davis, praised the new sample as a major step forward in understanding how galaxies originate over the course of the Universe. These early galaxies normally appear as little fuzzy blobs, but the lensing magnification lets us to discern their structure with much higher clarity. They are great targets for our most powerful telescopes to provide us with the finest image of the early cosmos conceivable. We may learn about these primordial galaxies' appearance, composition, and interactions with their environment thanks to the lensing phenomenon.

Journal Information: Kim-Vy H. Tran et al, The AGEL Survey: Spectroscopic Confirmation of Strong Gravitational Lenses in the DES and DECaLS Fields Selected Using Convolutional Neural Networks, The Astronomical Journal (2022). DOI: 10.3847/1538-3881/ac7da2