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Identifier 000435114
Title Populations of ultraluminous X-ray sources in nearby galaxies
Alternative Title Πληθυσμοί πηγών ακτίνων-Χ σε κοντινούς γαλαξίες
Author Κοβλακάς, Κωνσταντίνος K.
Thesis advisor Ζέζας, Ανδρέας
Reviewer Κυλάφης, Νικόλαος
Χαρμανδάρης, Βασίλειος
Παπαδάκης, Ιωσήφ
Τάσσης, Κωνσταντίνος
Φράγκος, Αναστάσιος
Reig, Pablo
Abstract Ultraluminous X-ray sources (ULXs) are the most energetic non-explosive stellar systems, with luminosities exceeding the Eddington limit for stellar-mass black hole. Since ULXs are rare they are predominantly found at large distances. Therefore, only a handful of systems have been studied thoroughly, with the general properties of ULXs being still a matter of debate. The study of ULXs in the context of the host galaxies can constrain models for their formation and evolution. In this thesis, we create a census of ULX populations in the local Universe, and we revisit their connection with the parameters of the host galaxies. First, we create a all-sky, value-added catalogue of galaxies at distances up to 200 Mpc, the Heraklion Extragalactic Catalogue (HECATE), providing all the necessary information for the detailed study of ULXs in nearby galaxies. By associating the HECATE with the Chandra Source Catalog 2.0, we deliver a census of ULX populations in galaxies up to a distance of 40 Mpc. We estimate the number of ULXs in the sample galaxies, and probe its correlation with star-formation rate, stellar mass, and metallicity. For the first time, we account for the contribution of low-mass X-ray binaries (which scale with stellar mass, M). In addition, we confirm the known anti-correlation of the ULX rate with the metallicity of the host galaxy, and attribute to this effect, the excess of ULXs in low-mass and late-type galaxies in our sample. Regarding the specific ULX frequency in early-type galaxies, we find that it is in agreement with previous demographic results. However, we discover an excess in low-stellar-mass early-type galaxies, which we reproduce using binary population synthesis models, and realistic star-formation histories. Ultimately, using X-ray images from Chandra observations, we simulate the effect of source blending when targeting galaxies at distances from 10 Mpc up to 100 Mpc. We find that at larger distances (>60 Mpc), source confusion leads to a systematic overestimation in the number of ULXs.
Language English
Subject Binary stars
Galaxy catalogs
X-ray astronomy
Αστρονομία ακτίνων-Χ
Διπλοί αστέρες
Κατάλογοι γαλαξιών
Issue date 2021-01-18
Collection   School/Department--School of Sciences and Engineering--Department of Physics--Doctoral theses
  Type of Work--Doctoral theses
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