Gravitationally lensed quasars and supernovae in future wide-field optical imaging surveys (1001.2037v2)

Abstract: Cadenced optical imaging surveys in the next decade will be capable of detecting time-varying galaxy-scale strong gravitational lenses in large numbers, increasing the size of the statistically well-defined samples of multiply-imaged quasars by two orders of magnitude, and discovering the first strongly-lensed supernovae. We carry out a detailed calculation of the likely yields of several planned surveys, using realistic distributions for the lens and source properties and taking magnification bias and image configuration detectability into account. We find that upcoming wide-field synoptic surveys should detect several thousand lensed quasars. In particular, the LSST should find 8000 lensed quasars, 3000 of which will have well-measured time delays, and also ~130 lensed supernovae, which is compared with ~15 lensed supernovae predicted to be found by the JDEM. We predict the quad fraction to be ~15% for the lensed quasars and ~30% for the lensed supernovae. Generating a mock catalogue of around 1500 well-observed double-image lenses, we compute the available precision on the Hubble constant and the dark energy equation parameters for the time delay distance experiment (assuming priors from Planck): the predicted marginalised 68% confidence intervals are \sigma(w_0)=0.15, \sigma(w_a)=0.41, and \sigma(h)=0.017. While this is encouraging in the sense that these uncertainties are only 50% larger than those predicted for a space-based type-Ia supernova sample, we show how the dark energy figure of merit degrades with decreasing knowledge of the the lens mass distribution. (Abridged)

• The paper presents a simulation framework predicting that LSST will detect over 8000 lensed quasars and around 130 lensed supernovae, significantly expanding current catalogs.
• The methodology integrates realistic lens models, including Singular Isothermal Ellipsoids and external shear, with source luminosity functions and magnification biases.
• The predicted lensing systems offer promising prospects for constraining dark energy and the Hubble constant through precise time delay measurements, contingent on accurate lens modeling.

Gravitationally Lensed Quasars and Supernovae in Upcoming Survey Programs

The paper by Oguri and Marshall focuses on the projected discovery capability of future wide-field optical imaging surveys for gravitationally lensed quasars (QSOs) and supernovae (SNe). The paper specifically examines how these surveys will expand the existing inventory of known lensing systems, offer opportunities for time delay measurements, and provide data useful for cosmological parameter estimation, particularly dark energy and the Hubble constant.

Methodology

The authors employ a detailed simulation framework grounded in realistic models of both lens and source populations to predict the yield of lensed QSOs and SNe in various forthcoming surveys. Their approach integrates lensing cross-sections, source luminosity functions, magnification biases, and observational constraints, such as image separation and brightness limits. Lens galaxies are modeled using Singular Isothermal Ellipsoids (SIE), along with external shear contributions, reflecting conditions best suited for galaxy-scale lenses.

Key Predictions and Results

• The analysis predicts a substantial increase in the number of detected lensed QSOs, with the Large Synoptic Survey Telescope (LSST) expected to identify over 8000 lensed QSOs, of which 3000 will have measurable time delays. This is a substantial leap from the current catalogs, increasing them by nearly two orders of magnitude.
• For lensed SNe, LSST is expected to detect approximately 130 instances over a 10-year operation, indicating a significant advance in the discovery of these rare systems. Compared to conventional deep-space supernova surveys conducted by other missions such as JDEM, LSST's ground-based strategy results in a larger field and hence greater number despite image quality differences.
• The calculation of redshift distributions and image properties for the lensing systems supports the feasibility of using these systems for constraining cosmological parameters, given certain assumptions about lens mass profile slopes.

Implications for Cosmological Studies

The predicted dataset from upcoming surveys could enable precise measurement of cosmological parameters through the time delay distance method. This technique offers direct Hubble constant calculations and insights into dark energy by leveraging the time delays between multiple images of the same source caused by gravitational lensing. In the LSST era, time delay measurements promise marginalised 68% confidence intervals of $\sigma(w_0)=0.15$, $\sigma(w_{\rm a})=0.41$, and $\sigma(h)=0.017$. These metrics indicate significant capacity for improving current cosmological models, contingent on our understanding of lens mass distribution.

Challenges and Future Perspectives

The primary limitation highlighted involves the accurate modeling of lens galaxy potentials, emphasizing the need for prior knowledge of the mean density profile slope, $\bar{\alpha}$. The constraints provided assume a prior on $\bar{\alpha}$ at a precision level of 0.005. Achieving such precision in observations will be essential for the lensing time delays from LSST to significantly enhance cosmological constraints.

Overall, the work presents a comprehensive framework for anticipating the role of large-scale surveys in gravitational lensing science. The methodologies and predictions set forth by Oguri and Marshall offer a robust foundation for understanding the evolving landscape of cosmological research facilitated by upcoming observational capabilities. As these surveys progress, their data will be pivotal in refining our understanding of both astrophysical and cosmological processes.