Title:Strong Lensing Constraints on Cluster and Galaxy-Scale Mass Distributions

Speaker: Prof. Massimo Meneghetti, INAF- Observatory of Astrophysics and Space Science of Bologna

Special Time: 3:00 pm Nov. 21th (Friday)

Location: Lecture Hall, 3rd floor

Tencent meeting：732-6480-4482

Abstract: Recent observations with HST and JWST allowed to collect hundreds of strong lensing features in several galaxy clusters. These features, including families of multiple images and gravitational arcs, allowed reconstructions of the mass distributions in the cluster central regions with unprecedented precision and accuracy, resolving not only the scale of cluster DM halos, but also the scales of cluster galaxies. The accuracy of the reconstructions on small scales was significantly improved by combining strong lensing with stellar kinematic measurements from MUSE spectroscopy.

Surprisingly, these lensing and dynamical analyses revealed that cluster galaxies are much more compact than found in high-resolution hydrodynamical simulations. Because of their high compactness, these galaxies are very efficient strong gravitational lenses embedded in their cluster hosts. Indeed, observed galaxy clusters seem to produce an excess of galaxy-galaxy strong lensing events (GGSL) compared to expectations in the LCDM model. In this talk, I will discuss the possible origins of this discrepancy, whether it can be due to how galaxy formation is modeled in the simulations, to biases in the mass reconstructions, or to wrong assumptions about the nature of dark matter.

I will show also that GGSL in galaxy clusters can be used to probe galaxy formation models via statistical studies of how galaxy-scale lenses are distributed within their host clusters. Future samples of GGSLs from ongoing large surveys such as Euclid will enable us to precisely characterize the GGSL signal in galaxy clusters as a function of the distance from the cluster centers statistically.  I will show that this signal depends on how AGN feedback affects star formation and gas depletion in galaxies and galaxy clusters.

CV:.

I got my Ph.D. at the University of Padova in 2004. Then I worked as a Post-doc at the Institute for Theoretical Astrophysics of the University of Heidelberg, in Germany. I am staff researcher at the INAF- Observatory of Astrophysics and Space Science of Bologna since 2006. From 2013 to 2015 I was on a sabbatical leave as NASA NPP fellow at the Jet Propulsion Lab in Pasadena (USA). My reasearch interests are in cosmology and structure formation, mainly using gravitational lensing as a probe of the matter distribution and the growth of cosmic structures. I am also interested in combining multiple probes of cluster mass distributions in order to study their formation and evolution (lensing, X-ray, SZ analyses). I am a founder of the Euclid mission, and I acted as coordinator of the Strong Lensing Working Group of the Euclid Consortium from the birth of the mission until 2024.