Probing High-z galaxies and dark matter with gravitational lensing

Abstract

X-ray analyses showed the galaxy cluster MS 2137.3-2353 is dynamically relaxed, suggesting it should have a simple mass profile. However, despite only a few multiply-lensed systems present, previous lens models still cannot reproduce the curvature of the radial arc. In the first part of this Thesis, I constructed robust lens models for MS 2137.3-2353 to probe a potential SMBH or CDM sub-halo near this radial arc. My lens models correctly reproduced the position of all the lens images used as constraints and predicted their morphologies, revealing radial arc is simply curved by two neighbouring cluster members. Furthermore, the mass profile inferred by my lens models shows discrepancies with the mass pro- files inferred by weak-lensing measurement, implying the cluster may not be fully virialised in the outer region. Moreover, in the central region where the BCG is located, the mass profile of my lens model is NFW-like, consistent with what the previous lens model reported, once again showing consistency with the picture that BCG is grown by merger. In addition, as a secondary aim, I also studied the morphologies of two lensed low-mass galaxies at the cosmic high noon, suggesting they can be two distinct merger systems or two galaxies with low surface mass densities compared with high-mass galaxies at the same epoch.

Since the release of the first JWST science images, thirty-seven high-z candidates claimed at 10 ≲ z ≲ 20, based on photo-z measurements, behind the galaxy clus- ter SMACS J0723.3-7323 have been reported. Such a surprisingly large number of high-z galaxies posed a challenge to the standard cosmological models of structure formation. In the second part of this Thesis, I present a lens model for SMACS J0723.3-7323, constrained by the positions and, when available, the red- shifts of the lens images of seventeen multiply-lensed systems. My lens model successfully reproduces the positions and correctly predicts the morphologies and brightnesses ratios of these multiply-lensed counterparts, as well as determined the redshifts of twelve multiply-lensed galaxies lacking spec-z measurements geometrically to be at 1.4 ≳ z ≳ 6.7. Based on this lens model, I created a lens finder map that defines the region over which predicting galaxies beyond a certain z are ought to be multiply-lensed. Applying the map to three high-z candidates claimed at 10 ≲ z ≲ 20, I found no multiply-lensed counterparts at their lens model-predicted locations, implying these galaxies lie at z ≲ 1.7−3.2. In place of spectroscopy, creating the lens finder maps for other galaxy clusters is urgently needed to test and constrain the redshifts inferred from photometry for a rapidly increasing number of high-z candidates found with JWST.

Building on the main results I presented in this Thesis, and that from the iPTF16geu project in which I am involved. Future work is needed to focus on: 1. Investigating the dynamical state of galaxy cluster at large radii. 2. Creating lens finder maps for other galaxy clusters observed by JWST to test more high-z candidates. 3. Studying the effect of triaxial mass profile on lens image creation. 4. Testing ψDM with more lensing systems.