Fraser CainJul 25, 2023

Astronomers Find a Rare "Einstein Cross"

Astronomers use powerful gravitational lenses to peer farther into the Universe than they could with their telescopes alone. A foreground galaxy acts as a natural lens for a more distant galaxy, magnifying it and often splitting its light into several versions. When the alignment is almost perfect, the light is split four ways into an "Einstein Cross." Only a few of these have ever been discovered, and now astronomers have found a new one using the Dark Energy Spectroscopic Instrument. It's both beautiful and scientifically valuable for studying the distant Universe.

#desi #gravitationallens #einsteincross

http://arxiv.org/abs/2307.12470

DESI-253.2534+26.8843: A New Einstein Cross Spectroscopically Confirmed with VLT/MUSE and Modeled with GIGA-Lens

Gravitational lensing provides unique insights into astrophysics and cosmology, including the determination of galaxy mass profiles and constraining cosmological parameters. We present spectroscopic confirmation and lens modeling of the strong lensing system DESI-253.2534+26.8843, discovered in the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys data. This system consists of a massive elliptical galaxy surrounded by four blue images forming an Einstein Cross pattern. We obtained spectroscopic observations of this system using the Multi Unit Spectroscopic Explorer (MUSE) on ESO's Very Large Telescope (VLT) and confirmed its lensing nature. The main lens, which is the elliptical galaxy, has a redshift of $z_{L1} = 0.636\pm 0.001$, while the spectra of the background source images are typical of a starburst galaxy and have a redshift of $z_s = 2.597 \pm 0.001$. Additionally, we identified a faint galaxy foreground of one of the lensed images, with a redshift of $z_{L2} = 0.386$. We employed the GIGA-Lens modeling code to characterize this system and determined the Einstein radius of the main lens to be $θ_{E} =2.520{''}_{-0.031}^{+0.032}$, which corresponds to a velocity dispersion of $σ$ = 379 $\pm$ 2 km s$^{-1}$. Our study contributes to a growing catalog of this rare kind of strong lensing systems and demonstrates the effectiveness of spectroscopic integral field unit observations and advanced modeling techniques in understanding the properties of these systems.

arXiv.org
Show threadDustin Lang
@fraser Here's what it looks like in the DESI Legacy Imaging Surveys:
https://www.legacysurvey.org/viewer/?ra=253.2535&dec=26.8843&layer=ls-dr9&zoom=16
Legacy Survey Sky Browser

Jul 25, 2023 at 6:18pmWeb
Show threadFraser CainJul 25, 2023
@dstndstn Nice sleuthing. I wonder if there's a way to find them automatically in the data?
Show threadDustin LangJul 25, 2023
@fraser I tried feeding it to George Stein's "similarity search" galaxy finder, but the central galaxy isn't in the data set
https://georgestein-galaxy-search-streamlit-app-o7accj.streamlit.app/
Show threadJohn F WuJul 25, 2023
@dstndstn @fraser Dustin you also helped make astrometry.net, right? Could you try to find matching hashes to various Einstein cross configurations?
Show threadDustin LangJul 25, 2023
@jwuphysics @fraser Hah, that's a fun mash-up of two different projects of mine :)
Show threadDustin LangJul 25, 2023
@jwuphysics @fraser The problem would be, I expect, that they're too close together, so unlikely to all be indexed as part of the same hash!
Show threadDustin LangJul 25, 2023
@fraser In this case, we have the central galaxy and all four images in the catalog, so one could imagine building a geometric search
Show threadsimonbpJul 26, 2023
@dstndstn @fraser That's totally a shape that you could train a CNN to detect, but you'd have to make a boatload of synthetic images to train it properly.
Show threadFraser CainJul 26, 2023
@simonbp @dstndstn There aren't many. Maybe you could simulate them and then search for them that way.
Show threadsimonbpJul 26, 2023
@fraser @dstndstn Yeah, that's how you'd want to do it anyways so that you can calibrate your detection efficiency. That's what we do with KBO detections.
Show threadDustin LangJul 26, 2023
@simonbp @fraser Honestly, for such a simple configuration as an Einstein cross, where you *understand* what it looks like and the five objects are resolved and catalogued, I would ("just") write an algorithm to detect them in catalog space, rather than training a ML model.
Show threadFraser CainJul 26, 2023
@dstndstn @simonbp I suspect the more of these you can find, the more the astronomers would be grateful.