---

Spinning fields in galaxy clusters

Probing the rotation of cluster galaxies with C-EAGLE and Sunyaev-Zel’dovich signals

Abstract:

The dynamics of galaxies and galaxy clusters is an incredible probe for studying their origin and evolution. However, their complex environment constitutes a real challenge for disentangling the individual processes occurring within the Circum-Galactic Medium (CGM) and Inter-Galactic Medium (IGM). As shown in my previous Master project, the kinetic Sunyaev-Zel’dovich (kSZ) effect is able to probe the motion of hot ionised gas in the IGM and CGM, imprinting a very characteristic diplole signature in the case of rotating media. This project investigates the rotational SZ signals (rkSZ) from the EAGLE and C-EAGLE simulations, in order to search for correlation between the rotation of galaxies and clusters and the underlying dark matter density field.

---

Twin galaxies in the early Universe

Serendipitous discovery of a physical binary quasar at redshift z=1.76

Abstract:

Binary quasars are extremely rare objects, used to investigate clustering on very small scales at different redshifts. The cases where the two quasar components are gravitationally bound, known as physical binary quasars, can also exhibit enhanced astrophysical activity and therefore are of particular scientific interest. Here we present the serendipitous discovery of a physical pair of quasars with an angular separation of Δθ = (8.76 ± 0.11) arcsec. The redshifts of the two quasars are consistent within the errors and measured as z = (1.76 ± 0.01). Under the motivated assumption that the pair does not arise from a single gravitationally lensed quasar, the resulting projected physical separation was estimated as (76 ± 1) kpc. For both targets we detected Si IV, C IV, C III], and Mg II emission lines. However, the two quasars show significantly different optical colours, one being among the most reddened quasars at z > 1.5 and the other with colours consistent with typical quasar colours at the same redshift. Therefore it is ruled out that the sources are a lensed system. This is our second serendipitous discovery of a pair of two quasars with different colours, having a separation ≲ 10 arcsec, which extends the very limited catalogue of known quasar pairs. We ultimately argue that the number of binary quasars may have been significantly underestimated in previous photometric surveys, due to the bias arising from paired quasars with very different colours.

---

Substructures in galaxy clusters

Observability study using the MACSIS hydrodynamical simulation and Sunyaev-Zel’dovich signals

Abstract:

In the Lambda Cold Dark Matter cosmology, galaxy clusters are the latest objects to have formed in a process known as hierarchical structure formation. As a result, clusters should retain some memory of smaller objects (galaxy groups, or sub-halos) that have merged over the past few billion years, leading to a complex internal substructure. Identifying cluster substructure with multi-wavelength techniques is currently an extremely active observational area, which aims at studying the dynamic environment of the largest objects in the Universe. In this work, we use high-resolution hydrodynamical simulations to model massive galaxy clusters, study their hot ionised gas and map their shadow projected from the Cosmic Microwave Background. This phenomenon, known as the Sunyaev-Zel’dovich effect, is the main focus of our project and provides us with information about the thermodynamics and bulk motion of the hot gas in clusters. In my presentation, I will briefly touch upon the astrophysics of the Sunyaev-Zel’dovich effect, explaining its importance in the context of galaxy clusters research. I will then draw the attention to the most recent results of our project, including mock observation from hydrodynamical simulations, substructure detection algorithms and the impact of our findings on next-generation observations in microwave bands.

Left: visualisation of the gas distribution in largest MACSIS halo and the surrounding cosmic web filaments at redshift z = 0.57, populated with smaller halos. The colour coding expresses the density of the gas, ranging from blue (diffuse) to red (dense). Right: schematic relative to the figure on the left, highlighting the predominant halos and their infall towards the cluster. The IGM associated with the main halo is known as ICM and is marked by the central black circle, while the IGM associated with smaller objects is marked in red. The figure also displays the diffuse IGM arranged along the filaments of the cosmic web. Image and animation created using the glnemo software and PGF/Tikz modules.