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We present new time delays, the main ingredient of time delay cosmography, for 22 lensed quasars resulting from high-cadencer-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-σdepth of the combined exposures typically reaches the 27thmagnitude, 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 inHubbleSpace Telescope imaging. This was made possible thanks to a new photometric pipeline,lightcurver, and the forward modelling methodSTARRED. 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.
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Expectations for time-delay measurements in active galactic nuclei with the Vera Rubin Observatory
Context.TheVera RubinObservatory will provide an unprecedented set of time-dependent observations of the sky. The planned Legacy Survey of Space and Time (LSST), operating for ten years, will provide dense light curves for thousands of active galactic nuclei (AGN) in deep drilling fields (DDFs) and less dense light curves for millions of AGN from the main survey (MS). Aims.We model the prospects for measuring the time delays for the AGN emission lines with respect to the continuum, using these data. Methods.We modeled the artificial light curves using the Timmer-König algorithm. We used the exemplary cadence to sample them (one for the MS and one for the DDF), we supplement light curves with the expected contamination by the strong emission lines (Hβ, Mg II, and CIV, as well as with Fe II pseudo-continuum and the starlight). We chose suitable photometric bands that are appropriate for the redshift and compared the assumed line time-delay with the recovered time delay for 100 statistical realizations of the light curves. Results.We show that time delays for emission lines can be well measured from the main survey for the bright tail of the quasar distribution (about 15% of all sources) with an accuracy within 1σerror. For the DDF, the results for fainter quasars are also reliable when the entire ten years of data are used. There are also some prospects to measure the time delays for the faintest quasars at the lowest redshifts from the first two years of data, and possibly even from the first season. The entire quasar population will allow us to obtain results of apparently high accuracy, but in our simulations, we see a systematic offset between the assumed and recovered time delay that depends on the redshift and source luminosity. This offset will not disappear even in the case of large statistics. This problem might affect the slope of the radius-luminosity relation and cosmological applications of quasars if no simulations are performed that correct for these effects.
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- Award ID(s):
- 2106990
- PAR ID:
- 10522723
- Publisher / Repository:
- Astronomy & Astrophysics
- Date Published:
- Journal Name:
- Astronomy & Astrophysics
- Volume:
- 675
- ISSN:
- 0004-6361
- Page Range / eLocation ID:
- A163
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1051/0004-6361/202345844
