Session Y07: Lensing Probes of Dark Matter

Mapping Dark Matter from the Hubble Frontier Fields Clusters

The outskirts of clusters make the best, and most efficient locations to observe and trace the mass assembly processes of the Cosmic Web. Residing at the vertices of this Cosmic Web (Bond et al. 1996), galaxy clusters grow by steady accretion of matter from the surroundings, as well as by discrete mergers with nearby groups and clusters. Supported by simulations, this scenario predictions regarding the total mass content and distribution in filaments themselves remain largely untested. Filaments are vital elements of the cosmic census, containing up to half the baryonic mass of the Universe as a `warm hot intergalactic medium' but also the majority of the dark matter. Recently, some of the most massive and disturbed clusters have been the centre of attention thanks to the \emph{Hubble Frontier Fields} (HFF) initiative, which constitutes the largest commitment ever of \emph{Hubble Space Telescope} (HST) time to the exploration of the distant Universe via gravitational lensing by massive galaxy clusters. These clusters were chosen for their strong lens properties, and are all highly disturbed objects, showing major and minor merging on-going processes, making them ideal target to trace the Cosmic Web assembly. While combining strong and weak-lensing regimes to map the total mass with X-rays observations of the hot gas and spectroscopy of cluster galaxies to look at their direction of motion, we can thus study the dynamical scenarios in place within these massive galaxy clusters, and trace the sub-structures engaged in these processes. I will present the latest results we obtained on the HFF clusters, and discuss the different caveats present on both the observing and simulation sides. Finally, I will present the upcoming BUFFALO large HST programme, the 'spatial extension' of the HFF that will start in July 2018.   

Measuring the mass function of dark matter subhalos with ALMA observations of strong gravitational lenses

The number of observed dwarf satellites of the Milky Way is orders of magnitude lower than the predictions of cold dark matter (CDM) simulations, an issue known as the "Missing Satellite Problem". In this talk, I will discuss how in strong lensing systems we can detect low-mass dark matter subhalos in the lens galaxies by measuring the gravitationally-induced distortions that subhalos induce in the lensed images of background sources. Measuring the abundance of dark matter subhalos with strong lensing allows us to determine their mass function and to compare it with the predictions of CDM and other dark matter models. I will present our current constraints on the abundance of subhalos using ALMA data and provide a brief overview of our ongoing observational campaign to place stronger constraints at lower masses.   

Mapping the Cosmos with the Dark Energy Survey: Y1 and Beyond

The first year data from the Dark Energy Survey (DES Y1) provides the most powerful optical survey dataset to date. In this talk I will first give an overall summary of the cosmology results from the DES Y1 dataset combining galaxy clustering and weak gravitational lensing. Next, I will describe our work in generating and testing the wide-field weak lensing mass maps from the galaxy shape measurements and some exciting applications for the maps. The maps provide complementary information compared to conventional 2-point measurements in cosmology. The methodology developed in this work will be applied to future DES datasets on the full 5000 square degree footprint.