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This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 896778
MARACHAS Rationale:
Structures in our universe grow hierarchically, where small structures (stars and galaxies) assemble first and later on galaxies group together in large potential wells to form clusters. Clusters of galaxies are the largest structure observable in our Universe and can contain more than hundreds of galaxies. Nonetheless, the stars in the galaxies contribute to only a little of their mass. Indeed, the main matter component is dark matter. Little is known about dark matter besides that it interacts through gravity with ordinary matter. For instance, we believe that every galaxy carries its own small halo of dark matter, and when they fall into a cluster part of that halo is stripped and diffused into the larger halo of the cluster. In this study, I will be using the gravitational lensing effect to answer questions on the evolution of dark matter components that make up the majority of clusters. In my case, gravitational lensing refers to the bending of the light emitted by a galaxy located far behind the cluster, due to the mass of the cluster itself. I will study the galaxies and their dark matter falling in the cluster and losing their dark matter to the profit of the cluster, also called the sub-halos mass loss. This will bring new insights into the overall structure evolution in our Universe, and answer fundamental questions about dark matter properties. Based on my experience gained during my PhD and postdoc at the University of Michigan, returning to the EU to conduct this study will allow me to increase my ability to design, program and develop large analyses of observational data. The experienced contributors will greatly promote such challenging observational analysis and have the expertise to link this work to the latest theoretical predictions thanks to Durham’s state-of-the-art cosmological simulations. This will broaden my skills, giving me an (important) opportunity to work with theorists.
Most of the script devellop are made using my lenstool python wrapper: https://git-cral.univ-lyon1.fr/CALENDS/pylenstool
Measurements of the global properties of the Universe indicate that its matter content is composed of 15% luminous matter and 85% Dark Matter (Planck Collaboration). Since the first observational evidence of “missing mass” in 1933 in the Coma Cluster (Zwicky 1933), we have been trying to understand what it is made of. The predominant model is that of non-collisional cold dark matter. However, other alternatives exist, proposing either a change in the laws of gravity (e.g., MOdified Newtonian Dynamics: Milgrom, et al. 1983), different dark materials (Warm Dark Matter and Hot Dark Matter: Primack et al. 1984), or different forms of interactions between particles (e.g., Mass Discrepancy Acceleration Relation: Famaey et al. 2018, Self Interacting Dark Matter-SIDM: Wandelt et al. 2001). Clusters of galaxies are the structures with the largest total mass of dark matter and represent ideal laboratories to study it. Recent studies hypothesizing SIDM have placed an upper limit on its moment transfer cross section per unit mass σDM/m0.22 cm2 g−1 (Harvey et al. 2019, and Figure 1). Currently, only three tests are put forward to constrain the self-interaction of dark matter: the flatness of the dark matter profile, the ellipticity of the main dark matter halo (Robertson et al. 2019), and the separation between the density peaks of light and dark matter (Harvey et al. 2019). Hierarchical models of structure growth show that when entering a cluster, galaxies start spiralling down the potential well and lose 10% to 50% of their mass after a few Gyrs (Han et al. 2016, Van den Bosch 2017), mainly through tidal stripping (Bosch & Ogiya 2018, Green et al. 2019). On average, a cluster at z=0 would have increased its mass by a factor of 5 from z=1 (Fahkouri et al. 2008; See Figure 1), mainly due to infalling sub-halos (Wu et al. 2013). The details of the mass accretion at their cores are not well understood. The importance of sub-halos infalling into clusters compared to other mechanisms (pure accretion, cluster mergers) has been estimated from simulations (Bahe et al. 2019) but hardly studied observationally. Previous studies have observed the evolution of sub-halo mass within clusters (Richard et al. 2010, Golden-Marx and Miller 2019) but did not connect it to the cluster growth itself. Recently, Niemiec et al. (2022), map the mass-to-light ratio within the clusters, predominately at its core for the oldest cluster members. The rate of this dark matter mass stripping is intimately tied to the properties of dark matter and will impact the fate of galaxies within clusters.
Recently, Mahler et al. (2020) estimated a staggering 33% sub-halos mass fraction in SPT-CL J0356−5337, a lensing clusters at redshift 1. This is not inconsistent with the conclusions from Richard et al. (2010), which correlates the sub-halos mass fraction with the magnitude gap, known to be proxy for cluster age.
Future JWST proposal will follow the MARACHAS as new way to access lensing cluster at higher redshift! Stay tuned
The lens model database is hosted: https://astro.dur.ac.uk/~rgph65/model_intro.html
And will be constantly updated
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