2018, Clerc, N., Ramos-Ceja, M.E., Ridl, J., Lamer, G., Brunner, H., Hofmann, F., Comparat, J., Pacaud, F., Käfer, F., Reiprich, T.H., Merloni, A., Schmid, C., Brand, T., Wilms, J., Friedrich, P., Finoguenov, A., Dauser, T., Kreykenbohm, I.

Context. Studies of galaxy clusters provide stringent constraints on models of structure formation. Provided that selection effects are under control, large X-ray surveys are well suited to derive cosmological parameters, in particular those governing the dark energy equation of state. Aims. We forecast the capabilities of the all-sky eROSITA (extended ROentgen Survey with an Imaging Telescope Array) survey to be achieved by the early 2020s. We bring special attention to modelling the entire chain from photon emission to source detection and cataloguing. Methods. The selection function of galaxy clusters for the upcoming eROSITA mission is investigated by means of extensive and dedicated Monte-Carlo simulations. Employing a combination of accurate instrument characterisation and a state-of-the-art source detection technique, we determine a cluster detection efficiency based on the cluster fluxes and sizes. Results. Using this eROSITA cluster selection function, we find that eROSITA will detect a total of approximately 105 clusters in the extra-galactic sky. This number of clusters will allow eROSITA to put stringent constraints on cosmological models. We show that incomplete assumptions on selection effects, such as neglecting the distribution of cluster sizes, induce a bias in the derived value of cosmological parameters. Conclusions. Synthetic simulations of the eROSITA sky capture the essential characteristics impacting the next-generation galaxy cluster surveys and they highlight parameters requiring tight monitoring in order to avoid biases in cosmological analyses.

2019, Jullo, E., de la Torre, S., Cousinou, M.-C., Escoffier, S., Giocoli, C., Metcalf, R.B., Comparat, J., Shan, H.-Y., Makler, M., Kneib, J.-P., Prada, F., Yepes, G., Gottlöber, S.

The combination of galaxy-galaxy lensing (GGL) and redshift space distortion of galaxy clustering (RSD) is a privileged technique to test general relativity predictions and break degeneracies between the growth rate of structure parameter f and the amplitude of the linear power spectrum σ8. We performed a joint GGL and RSD analysis on 250 sq. deg using shape catalogues from CFHTLenS and CFHT-Stripe 82 and spectroscopic redshifts from the BOSS CMASS sample. We adjusted a model that includes non-linear biasing, RSD, and Alcock-Paczynski effects. We used an N-body simulation supplemented by an abundance matching prescription for CMASS galaxies to build a set of overlapping lensing and clustering mocks. Together with additional spectroscopic data, this helps us to quantify and correct several systematic errors, such as photometric redshifts. We find f(z = 0.57) = 0.95 ± 0.23, σ8(z = 0.57) = 0.55 ± 0.07 and ωm = 0.31 ± 0.08, in agreement with Planck cosmological results 2018. We also estimate the probe of gravity EG = 0.43 ± 0.10, in agreement with ΛCDM-GR predictions of EG = 0.40. This analysis reveals that RSD efficiently decreases the GGL uncertainty on ωm by a factor of 4 and by 30% on σ8. We make our mock catalogues available on the Skies and Universe database.