A new sample of gravitational lenses followed up with the VLT and Keck

By Tania Barone
[email protected]

Gravitational lenses are powerful cosmic “magnifying glasses” that can be used to explore a broad range of astrophysical phenomena in both the background lensed galaxy (the “source”) and the foreground lens (the “deflector”). The bright and highly magnified source galaxies offer the best possible view of early galaxy formation at high-redshift (1 < z < 4) at high spatial resolutions (sub-kpc scales) out of reach for even the most powerful telescopes. Additionally, by using the light from the background source as a probe, we can study the dark matter and faint gas in the haloes of the foreground deflector systems, which can range from individual galaxies to groups and clusters.

The difficulty, however, is that bright (R <=22 AB mag) systems are incredibly rare. As a result, high-quality lens samples are extremely limited and even more so in the southern sky. Luckily, the AGEL survey is working on the solution!


How strong lensing works
A diagram explaining how strong gravitational lensing occurs. (Image credit: ALMA (ESO/NRAO/NAOJ), L. Calçada (ESO), Y. Hezaveh et al.)

The ASTRO 3D Galaxy Evolution with Lenses (AGEL) survey (Tran et al. submitted; arXiv:2205.05307) is an ongoing survey aiming to confirm ~100 bright strong gravitational lenses. Possible strong lens candidates were first identified by Jacobs et al. (2019a, 2019b) who applied machine learning to trawl through the hundreds of millions of galaxies imaged in the DES and DECaLS fields to search for signatures of strong lensing. From a sample of ~5000 possible candidates, the AGEL team has been obtaining spectroscopic follow-up observations of the highest confidence targets to build up a final sample of ~100 spectroscopically confirmed gravitational lenses. As part of our spectroscopic campaign, we have so far confirmed over 40 lenses using spectra obtained with the VLT’s X-shooter spectrograph (and a similar number with ESI and NIRES on Keck), and have successful upcoming proposals to revisit some of the most interesting targets with MUSE on the VLT.

As we approach our goal of ~100 confirmed lenses, the AGEL team are shifting focus to a range of interesting science results that have emerged from our observations, so stay tuned for future science highlights from AGEL!

Happy face lens
Our AGEL team mascot, the happy face lens, imaged by the Hubble Space Telescope.


Michael Murphy is the Australian representative on the ESO Science Technical Committee. Contact: [email protected]

Sarah Sweet is the Australian representative on the ESO Users Committee. Contact: [email protected]

Stuart Ryder is a Program Manager with AAL. Contact: [email protected]

Guest posts are also welcome – please submit these to [email protected]