Time Delay Lens Modeling Challenge: I. Experimental Design
Strong gravitational lenses with measured time delay are a powerful tool to measure cosmological parameters, especially the Hubble constant ($H_0$). Recent studies show by combining just three multiply-imaged AGN systems, one can determine $H_0$ down to 3% precision. Furthermore, the number of time-delay lens is growing rapidly, enabling the determination of $H_0$ to 1% precision in the near future. However, it is important to ensure that systematic errors and biases remain subdominant. For this purpose, challenges with simulated datasets are a key component. Following the experience of the past challenge on time delay, where it was shown that time delays can be measured precisely and accurately at the sub-percent level, we now present the "Time Delay Lens Modeling Challenge" (TDLMC). The goal of TDLMC is to assess the present capabilities of lens modeling codes and assumptions and test the level of accuracy of inferred cosmological parameters given realistic mock datasets. We invite scientists to model a set of simulated HST observations of 50 mock lens systems. The systems are organized in rungs, with the complexity and realism increasing going up the ladder. The goal of the challenge is to infer $H_0$ for each rung, given the HST images, the time delay, and a stellar velocity dispersion of the deflector, for a fixed background cosmology. The TDLMC challenge will start with the mock data release on 2018 January 8th. The deadline for blind submission is different for each rung. The deadline for Rung0-1 is 2018 Sept. 8; the deadline for Rung2 is 2019 Apr. 8 and the one for Rung3 is 2019 Sept. 8. This first paper gives an overview of the challenge including the data design, and a set of metrics to quantify the modeling performance and challenge details. After the deadline, the results of the challenge will be presented in a companion paper with all challenge participants as co-authors.
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