Testing the recovery of the NGC 6505 Einstein ring in deep OSN 1.5 m imaging
Year: 2026
Type: article
Abstract: The discovery of a complete Einstein ring around the nearby elliptical galaxy NGC 6505 ( z = 0.042) by the Euclid mission provides a rare, precisely characterised low-redshift strong lens. Its Einstein radius, θ E = 2.500″, is comparable to the angular resolution attainable from typical mid-aperture ground-based facilities, which makes the recoverability of the ring from the ground an open practical question. We tested whether the ring can be recovered in deep Cousins-R imaging of NGC 6505 obtained with the 1.5 m T150 telescope at the Sierra Nevada Observatory (OSN), totalling 8.03 h of integration at a final effective seeing with a full width at half maximum (FWHM) of 2.47″ ( θ E /FWHM = 1.01). After subtracting a non-parametric isophotal model of the galaxy, we searched the residual for coherent arc- or ring-like structure and found none at the Euclid -measured Einstein radius, with a maximum value of 1.5 σ for the adopted radial recovery metric. An injection–recovery experiment using a simplified Euclid -informed synthetic ring, processed through the same isophotal-modelling and residual-analysis pipeline, yielded a maximum recovered significance between 0.42 σ and 1.86 σ across three point spread function descriptions, which is below our operational 3 σ recovery threshold in every case. We interpret this as a dataset-specific non-recovery driven by the θ E ≈ FWHM regime of these observations and not as a general detectability law.
Source: Astronomy and Astrophysics
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
OpenAlex ID: W7168404771