Ph.D. in Physics

Eventi del Dottorato

Dottorato in Fisica

Journal Club Seminari 2022

10/06/2022 ore 14:00
AULA A (primo piano - Via Della vasca Navale n. 84)
ore 14:00 Giulia Degni
(DOTTORATO IN FISICA) Cosmic Voids and their surroundings: a new cosmological probe
Abstract Journal Club Giulia Degni
June 2022
Since the discovery of the expansion of the Universe, one of the main problems in physics relies on the investigation of the nature of dark energy and the exploration of alternative theories of gravity. According to the standard model in Cosmology, the CDM, almost 95% of our Universe, the dark components, is unknown, it is fundamental to develop new techniques to study and analyze the Universe. A powerful tool is given us from the observation of the Large Scale Structure of the Universe. Modern surveys are able to provide a huge amount of data and it is possible to develop detailed maps of the observable Universe tracing the distribution of galaxies. Inside these maps it is possible to identify
the different kind of structure which the Universe is made up: galaxy clusters (highest density regions), filaments (high density regions connecting galaxyclusters) and cosmic voids (lowest density regions). Recently, cosmic voids have proven to be powerful cosmological probes to study the nature of the accelerated expansion of the Universe by putting constraints on cosmological parameters.
The importance of cosmic voids, large empty underdense regions in space, relies mainly on their shape: on average, voids are intrinsically spherically symmetric and, once rescaled by their size, possess a universal density profile. From an observational perspective, voids are identified from spectroscopic galaxy redshift surveys, i.e., from the spatial distribution of galaxies whose observedredshifts
are used to infer distances. As a result, the observed shape of the voids is
not spherical but distorted by two effects. The first one derives from assuming an incorrect cosmological model. The second one originates from ignoring the Doppler due to the proper motion of the galaxy that, on top of the recession velocity, contributes to the observed redshift. Therefore, is it possible to use cosmic voids to extract cosmological information and constrain the nature ofthe dark components.
ore 14:45 Ivano Saccheo
(DOTTORATO IN FISICA) Mean SED of hyper-luminous QSOs
-Mean SED of hyper-luminous QSOs-
The study of AGN SED provides both a direct description of the physical processes responsible
for the emission in different bands and a comprehensive picture of sources energy budgets. In this talk, I will present the characterization of the mean SED of a sample composed of the most luminous type 1 QSOs (the WISSH sample, Lbol>1047 erg/s at z~2-4.5, focusing on the differences
we find with respect to the typical SED of less luminous sources. I will also present the mean SED derived from different sub-samples of QSOs showing peculiar spectral features (BAL vs non-
BAL QSO and CIV weak vs non CIV weak QSOs) and the bolometric corrections obtained for 5100 Å and 3 μm luminosities.
By extending this analysis to the more heterogeneous SDSS QSO catalog, I will discuss whether our results can be generalized to the entire population of hyper-luminous QSOs. Finally, I will
discuss the location of WISSH QSOs in the recently proposed star-forming vs AGN dominated galaxy diagnostic diagram (Symeonidis & Page 2021) and its possible extension up to z = 4.5.
Chair:

info: journal club time table

ore 14:00	Giulia Degni (DOTTORATO IN FISICA)	Cosmic Voids and their surroundings: a new cosmological probe Abstract Journal Club Giulia Degni June 2022 Since the discovery of the expansion of the Universe, one of the main problems in physics relies on the investigation of the nature of dark energy and the exploration of alternative theories of gravity. According to the standard model in Cosmology, the CDM, almost 95% of our Universe, the dark components, is unknown, it is fundamental to develop new techniques to study and analyze the Universe. A powerful tool is given us from the observation of the Large Scale Structure of the Universe. Modern surveys are able to provide a huge amount of data and it is possible to develop detailed maps of the observable Universe tracing the distribution of galaxies. Inside these maps it is possible to identify the different kind of structure which the Universe is made up: galaxy clusters (highest density regions), filaments (high density regions connecting galaxyclusters) and cosmic voids (lowest density regions). Recently, cosmic voids have proven to be powerful cosmological probes to study the nature of the accelerated expansion of the Universe by putting constraints on cosmological parameters. The importance of cosmic voids, large empty underdense regions in space, relies mainly on their shape: on average, voids are intrinsically spherically symmetric and, once rescaled by their size, possess a universal density profile. From an observational perspective, voids are identified from spectroscopic galaxy redshift surveys, i.e., from the spatial distribution of galaxies whose observedredshifts are used to infer distances. As a result, the observed shape of the voids is not spherical but distorted by two effects. The first one derives from assuming an incorrect cosmological model. The second one originates from ignoring the Doppler due to the proper motion of the galaxy that, on top of the recession velocity, contributes to the observed redshift. Therefore, is it possible to use cosmic voids to extract cosmological information and constrain the nature ofthe dark components.
ore 14:45	Ivano Saccheo (DOTTORATO IN FISICA)	Mean SED of hyper-luminous QSOs -Mean SED of hyper-luminous QSOs- The study of AGN SED provides both a direct description of the physical processes responsible for the emission in different bands and a comprehensive picture of sources energy budgets. In this talk, I will present the characterization of the mean SED of a sample composed of the most luminous type 1 QSOs (the WISSH sample, Lbol>1047 erg/s at z~2-4.5, focusing on the differences we find with respect to the typical SED of less luminous sources. I will also present the mean SED derived from different sub-samples of QSOs showing peculiar spectral features (BAL vs non- BAL QSO and CIV weak vs non CIV weak QSOs) and the bolometric corrections obtained for 5100 Å and 3 μm luminosities. By extending this analysis to the more heterogeneous SDSS QSO catalog, I will discuss whether our results can be generalized to the entire population of hyper-luminous QSOs. Finally, I will discuss the location of WISSH QSOs in the recently proposed star-forming vs AGN dominated galaxy diagnostic diagram (Symeonidis & Page 2021) and its possible extension up to z = 4.5.
Chair: