Bending instability in galactic discs. Advocacy of the linear theory

We demonstrate that in N-body simulations of isolated disc galaxies there is numerical vertical heating which slowly increases the vertical velocity dispersion and the disc thickness. Even for models with over a million particles in a disc, this heating can be significant. Such an effect is just the same as in numerical experiments by Sellwood (2013). We also show that in a stellar disc, outside a boxy/peanut bulge, if it presents, the saturation level of the bending instability is rather close to the value predicted by the linear theory. We pay attention to the fact that the bending instability develops and decays very fast, so it couldn't play any role in secular vertical heating. However the bending instability defines the minimal value of the ratio between the vertical and radial velocity dispersions $\sigma_z / \sigma_R \approx 0.3$ (so indirectly the minimal thickness) which could have stellar discs in real galaxies. We demonstrate that observations confirm last statement.Comment: 8 pages, 8 figures, accepted for publication in MNRA

Effect of the Environment on the Fundamental Plane of Elliptical Galaxies

We present an analysis of interacting E/S0 galaxies location on the Fundamental Plane. Using the NEMO package, we performed N-body simulations of close encounters and mergers between two spherical galaxies. We followed how structural and dynamical parameters (central density, half-mass radius and velocity dispersion)of galaxies are changed during the encounter. We analysed the dependence of these changes on initial mass concentration and presence of dark halo. The results of our simulations are used to discuss the Fundamental Plane for interacting early-type galaxies.Comment: Poster presented at JENAM-2000 (Joint European and National Astronomical meeting - S02. Morphology and dynamics of stellar systems: star clusters, galactic arms and rings

The observed radio/gamma-ray emission correlation for blazars with the Fermi-LAT and the RATAN-600 data

We study the correlation between gamma-ray and radio band radiation for 123 blazars, using the Fermi-LAT first source catalog (1FGL) and the RATAN-600 data obtained at the same period of time (within a few months). We found an apparent positive correlation for BL Lac and flat-spectrum radio quasar (FSRQ) sources from our sample through testing the value of the Pearson product-moment correlation coefficient. The BL Lac objects show higher values of the correlation coefficient than FSRQs at all frequencies, except 21.7 GHz, and at all bands, except $10-100$ GeV, typically at high confidence level (> 99%). At higher gamma-ray energies the correlation weakens and even becomes negative for BL Lacs and FSRQs. For BL Lac blazars, the correlation of the fluxes appeared to be more sensitive to the considered gamma-ray energy band, than to the frequency, while for FSRQ sources the correlation changed notably both with the considered radio frequency and gamma-ray energy band. We used a data randomization method to quantify the significance of the computed correlation coefficients. We find that the statistical significance of the correlations we obtained between the flux densities at all frequencies and the photon flux in all gamma-ray bands below 3 GeV is high for BL Lacs (chance probability $\sim 10^{-3} - 10^{-7}$). The correlation coefficient is high and significant for the $0.1-0.3$ GeV band and low and insignificant for the $10-100$ GeV band for both types of blazars for all considered frequencies.Comment: 14 pages, 5 tables, 8 figures, accepted to MNRA