TDCOSMO

XVII. New time delays in 22 lensed quasars from optical monitoring with the ESO-VST 2.6m and MPG 2.2m telescopes

¹ European Southern Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile
² Institute of Physics, Laboratory of Astrophysics, École Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, 1290 Versoix, Switzerland
³ Kavli Institute for Particle Astrophysics and Cosmology and Department of Physics, Stanford University, Stanford, CA, USA
⁴ Institute for Particle Physics and Astrophysics, ETH Zurich, Wolfgang-Pauli-Strasse 27, CH-8093 Zurich, Switzerland
⁵ Department of Physics, TUM School of Natural Sciences, Technical University of Munich, Garching, Germany
⁶ Institut de Ciències del Cosmos, Universitat de Barcelona, Martí i Franquès, 1, E-08028 Barcelona, Spain
⁷ ICREA, Pg. Lluís Companys 23, Barcelona E-08010, Spain
⁸ Institute of Astrophysics, Universidad Andres Bello Fernandez Concha 700, Las Condes, Santiago, Chile
⁹ Millennium Institute of Astrophysics, Santiago, Chile
¹⁰ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
¹¹ Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
¹² Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794, USA
¹³ Fermi National Accelerator Laboratory, PO Box 500 Batavia, IL 60510, USA
¹⁴ Department of Physics and Astronomy, University of California, Davis, 1 Shields Ave., Davis, CA 95616, USA
¹⁵ Kavli Institute for Cosmological Physics, University of Chicago, Chicago IL 60637, USA
¹⁶ Instituto de Física y Astronomía, Universidad de Valparaíso, Avda. Gran Bretaña 1111, Playa Ancha, Valparaíso 2360102, Chile
¹⁷ STAR Institute, University of Liège, Quartier Agora – Allée du six Août, 19c, B-4000 Liège, Belgium
¹⁸ Max Planck Institute for Astrophysics, Karl-Schwarzschild-Strasse 1, D-85740 Garching, Germany
¹⁹ Institute of Astronomy and Astrophysics, Academia Sinica, PO Box 23-141 Taipei 10617, Taiwan
²⁰ Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA
²¹ STFC Hartree Centre, Sci-Tech Daresbury, Keckwick Lane, Daresbury, Warrington WA4 4AD, UK
²² DARK, Niels Bohr Institute, University of Copenhagen, Jagtvej 155A, DK-2200 Copenhagen N, Denmark
²³ Department of Physics and Astronomy, Lehman College of the CUNY, Bronx, NY 10468, USA
²⁴ Department of Astrophysics, American Museum of Natural History, Central Park West and 79th Street, New York, NY 10024, USA
²⁵ Institute of Cosmology and Gravitation, University of Portsmouth, Burnaby Rd, Portsmouth PO1 3FX, UK
²⁶ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
²⁷ Centro de Astroingeniería, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Macul, 7820436 Santiago, Chile
²⁸ Departamento de Matemática y Física Aplicadas, Facultad de Ingeniería, Universidad Católica de la Santísima Concepción, Alonso de Rivera 2850, Concepción, Chile

^⋆ Corresponding author.

Received: 18 January 2025
Accepted: 24 March 2025

Abstract

We present new time delays, the main ingredient of time delay cosmography, for 22 lensed quasars resulting from high-cadence r-band monitoring on the 2.6 m ESO VLT Survey Telescope and Max-Planck-Gesellschaft 2.2 m telescope. Each lensed quasar was typically monitored for one to four seasons, often shared between the two telescopes to mitigate the interruptions forced by the COVID-19 pandemic. The sample of targets consists of 19 quadruply and 3 doubly imaged quasars, which received a total of 1918 hours of on-sky time split into 21 581 wide-field frames, each 320 seconds long. In a given field, the 5-σ depth of the combined exposures typically reaches the 27^th magnitude, while that of single visits is 24.5 mag – similar to the expected depth of the upcoming Vera-Rubin LSST. The fluxes of the different lensed images of the targets were reliably de-blended, providing not only light curves with photometric precision down to the photon noise limit, but also high-resolution models of the targets whose features and astrometry were systematically confirmed in Hubble Space Telescope imaging. This was made possible thanks to a new photometric pipeline, lightcurver, and the forward modelling method STARRED. Finally, the time delays between pairs of curves and their uncertainties were estimated, taking into account the degeneracy due to microlensing, and for the first time the full covariance matrices of the delay pairs are provided. Of note, this survey, with 13 square degrees, has applications beyond that of time delays, such as the study of the structure function of the multiple high-redshift quasars present in the footprint at a new high in terms of both depth and frequency. The reduced images will be available through the European Southern Observatory Science Portal.