Observations multi-longueur d’onde d’amas et de groupes de galaxies proches
Clusters and groups of galaxies are dynamic environments, continually perturbed. On the one hand, the supermassive black hole of the central galaxy can release powerful rela- tivistic jets compensating the radiative losses of the intracluster or intragroup medium. This mechanism is called active galactic nucleus feedback. On the other hand, the interaction between the cluster or the group with other galaxies can also generate important perturba- tions such as shocks or cold fronts. In general, these internal or external perturbations leave their footprints into the observations of clusters and groups covering the entire electromag- netic spectrum. In this thesis, the multi-wavelength observational study of one group and one cluster of galaxies, both nearby, is presented. Overall, this work has contributed to the comprehension of some of the complex processes characterizing these environments. First, the analysis of deep observations (380 ks) from the X-ray observatory Chandra of the galaxy NGC 4472 (z = 0.0038), the dominant galaxy of a group falling into the Virgo cluster, is presented. These new observations have allowed the detailed study of the radio lobe dynamics. Rims of cold gas surrounding the radio lobes have been detected and seem to be constituted of gas originating from the group center. We estimate the energy required to lift this gas from the center of NGC 4472 to be ∼ 1056 erg. We have also led the analysis of the abundance distribution of different elements (O, Ne, Mg, Si et Fe) from the X-ray spectrum. Second, we have produced a radio-frequency map of the Perseus cluster (z = 0.018), obtained from new Karl G. Jansky Very Large Array observations at 230-470 MHz in B configuration. The data reduction and calibration steps as well as the imaging process were specifically adjusted for the analysis of these observations, taking into account the strong presence of radio frequency interferences at these frequencies and the presence of the ex- tremely bright central active galactic nucleus in the cluster center. The observations have revealed a multitude of new structures associated with the cluster central diffuse radio emis- sion, the mini-halo. These structures include several radial filaments stretching in different directions, a concave structure correlating with the bay and several other correspondences with the X-ray structures such as cold fronts. These results show that mini-halos are there- fore not simply diffuse, uniform radio sources, but rather have a rich variety of complex structures. A comprehensive picture of the dynamics of the filamentary emission-line nebula sur- rounding NGC 1275, the dominant galaxy of the Perseus cluster, has been revealed with the observations of SITELLE («Spectromètre Imageur à Transformée de Fourier pour l’Étude en Long et en Large des raies d’Émission»), a new optical imaging Fourier transform spec- trometer at Canada-France-Hawaii Telescope. With its wide field of view of 11′ × 11′, it is the only instrument of this type covering the 80kpc × 55kpc (3.8′ × 2.6′ at the distance of NGC 1275) large nebula in its entirety. Our analysis of these observations shows a smooth radial gradient of the [N II]λ6583/Hα line ratio, suggesting a change in the ionization source and mechanism across the nebula. We have produced for the first time a complete detailed velocity map of the filaments. This map reveal a previously unknown rich velocity structure. The velocity map shows no visible general radial trend or rotation, indicating that filaments are not falling uniformly onto the galaxy, nor being uniformly pulled out from it. A com- parison between these measurements and the Hitomi results on the Perseus cluster is also presented. Finally, we have created a high-resolution image at 230-470 MHz of the Perseus cluster with new Karl G. Jansky Very Large Array A configuration observations. The high dynamic range and resolution achieved in this image have allowed the identification of new structures. Most of the extended mini-halo emission filling the core of the Perseus cluster disappears in these observations due to the high resolution and only some of the brightest western parts remain visible. The central radio emission fills the inner X-ray cavities and extends toward the outer cavities. As the outer cavities are visible at lower frequencies, we are therefore catching the spectral turnover at around 350 MHz. Beyond the central emission surrounding NGC 1275, we also describe and analyze the morphology of four complex radio sources harbored in the Perseus cluster: IC 310, NGC 1265, CR 15 and NGC 1272. These radio galaxies are infalling into the Perseus cluster. We detect distortions in the tail of IC 310 as well as two distinct jets. We report the presence of a global radio filamentary structure associated with the galaxy NGC 1265. Lastly, the radio galaxies CR 15 and NGC 1272 are also resolved in this high-resolution image.
Galaxies Jets Cavities Mini-halos Galaxy clusters and groups Active galactic nuclei Intracluster and intragroup medium X-ray astronomy Radio astronomy Fourier transform spectroscopy Supermassive black holes