Caratteristiche principali dell'emissione di regioni HII

In questo elaborato ci si ripropone di studiare l'emissione delle regioni HII. Si può definire una regione HII come una zona molto calda di idrogeno ionizzato, che si trova in un background di idrogeno neutro più freddo. Vengono analizzati i processi di emissione nel continuo e in riga, e analizzate in particolare le nebulose planetarie

The probability of galaxy-galaxy strong lensing events in hydrodynamical simulations of galaxy clusters

Meneghetti et al. (2020) recently reported an excess of galaxy-galaxy strong lensing (GGSL) in galaxy clusters compared to expectations from the LCDM cosmological model. Theoretical estimates of the GGSL probability are based on the analysis of numerical hydrodynamical simulations in the LCDM cosmology. We quantify the impact of the numerical resolution and AGN feedback scheme adopted in cosmological simulations on the predicted GGSL probability and determine if varying these simulation properties can alleviate the gap with observations. We repeat the analysis of Meneghetti et al. (2020) on cluster-size halos simulated with different mass and force resolutions and implementing several independent AGN feedback schemes. We find that improving the mass resolution by a factor of ten and twenty-five, while using the same galaxy formation model that includes AGN feedback, does not affect the GGSL probability. We find similar results regarding the choice of gravitational softening. On the contrary, adopting an AGN feedback scheme that is less efficient at suppressing gas cooling and star formation leads to an increase in the GGSL probability by a factor between three and six. However, we notice that such simulations form overly massive subhalos whose contribution to the lensing cross-section would be significant while their Einstein radii are too large to be consistent with the observations. The primary contributors to the observed GGSL cross-sections are subhalos with smaller masses, that are compact enough to become critical for lensing. The population with these required characteristics appears to be absent in simulations.Comment: 13 pages, 11 figures. Submitted for publication on Astronomy and Astrophysic

An high-precision strong lensing model of the galaxy cluster PSZ1 G311.65-18.48

Strong gravitational lensing is one of the best performing methods to study the mass distribution in the central regions of galaxy clusters. The progress witnessed recently on the lens modeling techniques was made possible by the several observational programs conducted with the Hubble Space Telescope (HST) and complemented by spectroscopic observations of a relatively large number of massive galaxy clusters. In this work we use a new method to combine lensing and galaxy kinematics measurements to conduct a strong lensing analysis of the cluster PSZ1 G311.65-18.48, with the aim of constructing a parametric lens model of the mass distribution in its core. We use HST observations conducted in several bands, complemented with VLT/MUSE spectroscopic observations. The multiple image and cluster member catalogues are the main ingredients required for the construction of a parametric lens model with the software Lenstool. Throughout this thesis we describe the process that led to the construction of the cluster final model, which evolved through several intermediate steps where the model complexity increased progressively. The aim was to recover the mass distribution which minimizes the differences between observed and model-predicted multiple image positions. Our resulting reference model is the first lens model for this galaxy cluster ever published and reproduces the observed multiple images with very high accuracy. It can be used for several applications, including the characterization of the source producing the famous Sunburst Arc, or predicting the re-appearance of the possible transient source recently reported by Vanzella et al. (2020)