Galaxies: Formation, Evolution, Phenomena

We study the early dynamical evolution of young dense star clusters by using Monte Carlo simulations for systems with up to N = 10 7 stars. Rapid mass segregation of massive main-sequence stars and the development of the Spitzer instability can drive these systems to core collapse in a small fraction of the initial ha…

• MEHMET ATAKAN GÜRKAN

The standard model of cosmology has provided a good phenomenological description of a wide range of observations both at astrophysical and cosmological scales for several decades. This concordance model is constructed by a universal cosmological constant and supported by a matter sector described by the standard model…

• AYŞE NİHAN KATIRCI

The standard model of cosmology has provided a good phenomenological description of a wide range of observations both at astrophysical and cosmological scales for several decades. This concordance model is constructed by a universal cosmological constant and supported by a matter sector described by the standard model…

• MEHMET DEMİRCİ

Context. The quest for the cosmological parameters that describe our universe continues to motivate the scientific community to undertake very large survey initiatives across the electromagnetic spectrum. Over the past two decades, the Chandra and XMM-Newton observatories have supported numerous studies of X-ray-selec…

• SİNAN ALİŞ

We present a new study of the collisional runaway scenario to form an intermediate-mass black hole (IMBH, MBH≳ 100 M⊙) at the centre of a young, compact stellar cluster. The first phase is the formation of a very dense central core of massive stars (M*≃ 30–120 M⊙) through mass segregation and gravothermal collapse. Pr…

• MEHMET ATAKAN GÜRKAN

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• ÖZGÜR AKARSU

We work in the locally de Sitter background of an inflating universe and consider a massless, minimally coupled scalar with a quartic self-interaction. We use dimensional regularization to compute the fully renormalized scalar self-mass-squared at one- and two-loop order for a state which is released in Bunch–Davies v…

• VAKIF KEMAL ÖNEMLİ

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• ÖZGÜR AKARSU

Context. The XXL Survey is the largest survey carried out by the XMM-Newton satellite and covers a total area of 50 square degrees distributed over two fields. It primarily aims at investigating the large-scale structures of the Universe using the distribution of galaxy clusters and active galactic nuclei as tracers o…

• SİNAN ALİŞ

Inspired by the recent conjecture originated from graduated dark energy that the Universe has recently transitioned from anti--de Sitter vacua to de Sitter vacua, we extend the standard $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model by a cosmological constant (${\mathrm{\ensuremath{\Lambda}}}_{s}$) that switches si…

• ÖZGÜR AKARSU

Context. In the currently debated context of using clusters of galaxies as cosmological probes, the need for well-defined cluster samples is critical. Aims. The XXL Survey has been specifically designed to provide a well characterised sample of some 500 X-ray detected clusters suitable for cosmological studies. The ma…

• SİNAN ALİŞ

We present a further observational analysis of the ${\mathrm{\ensuremath{\Lambda}}}_{\mathrm{s}}\mathrm{CDM}$ model proposed in Akarsu et al. [Phys. Rev. D 104, 123512 (2021)]. This model is based on the recent conjecture suggesting the Universe has transitioned from anti--de Sitter vacua to de Sitter vacua (viz., the…

• ÖZGÜR AKARSU