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Seminarium środowe


"Using the Alcock-Paczyński test to constrain the amplitude of the cosmological constant"

Andrzej Sołtan (CAMK, Warsaw)

The galaxy autocorrelation function (ACF) is constructed using the galaxies selected from the DR12 of the SDSS. The ACF amplitude increase at separa- tions expected to those generated by the Baryon Acoustic Oscillations (BAO) is clearly detected. We study the dependence of this correlation signal on the angle between the line of sight and vectors defined by galaxy pairs. Using the Alcock-Paczyński test we estimate acceptable amplitudes of the matter and cosmological constant density parameters, Ωm and ΩΛ. Only flat cosmological models are considered, e.g. Ωm + ΩΛ = 1. We found that in the local Universe 0.25 . Ωm . 0.45, what is in agreement with the results based the CMB me- asurements. Strong stoochastic variations of local galaxy concentrations generate substantial scatter of the ACF signal unrelated to the BAO, what significantly degrades the accuracy of the present estimates.


"On the hot flows in AWDs: broadband noise, spectral characteristics and disk structure"

Solen Balman (Department of Astronomy and Space Sciences, Istanbul University)

Cataclysmic Variables (CVs) and related systems (e.g., AM CVn, Symbiotics) are compact systems with white dwarf (WD) primaries referred as accreting white dwarfs (AWDs). They are excellent laboratories to study astrophysical plasmas, accretion flows and disks, gas dynamics, outflows, and transient outbursts. Broadband noise and its variations in accretion flows have been a diagnostic tool for understanding the structure of accretion disks together with accretion history and state changes. CVs demonstrate band limited noise (mainly 1-6 mHz) in the optical, UV and X-ray energy bands, which can be adequately explained in the framework of the model of propagating fluctuations yielding break frequencies. I will discuss broadband noise structure in CVs with a broader sense including some different nonmagnetic AWDs elaborating on similarities along with spectral characteristics. The spectral and/or broadband noise studies show that advective hot flow structure (ADAF-like) resides inside nonmagnetic CV disks mainly detected in the X-ray regime (Balman 2020, Balman et al. 2022 and references therein) indicating other characteristics like outflows in the X-rays and warm absorber effects.


"Tidally induced bars in galaxies"

Ewa L. Łokas (CAMK, Warsaw)

Galactic bars are generally believed to form via disk instability. There is however another channel for the formation of these structures: by tidal effects. I will review the process of formation and evolution as well as describe the properties of bars induced in galaxies as a result of tidal interactions between them and a larger or equal-mass companion. I will start by describing the results of controlled simulations of dwarf galaxies orbiting the Milky Way and then move to normal-size galaxies interacting during flybys or orbiting galaxy clusters. Then I will place this scenario in the cosmological context and discuss tidally induced bars in galaxies formed in the simulations of the IllustrisTNG project, including a recently identified analog of the Sagittarius dwarf.