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FRBs: the Dispersion Measure of Host Galaxies

Jaroszyński M.

Acta Astronomica

2020

Vol. 70, No. 2

87--100

Using the results of the IllustrisTNG simulation we estimate the dispersion measure which may be attributed to halos of so called host galaxies of fast radio bursts sources (FRBs). Our results show that in contradiction to assumptions used to show the applicability of FRBs to cosmological tests, both the dispersion measure and its standard deviation calculated for host galaxies with given stellar mass in general increase with the redshift. The effect is not strong and cosmological tests using FRBs will be possible, but to preserve the level of statistical uncertainty the number of FRBs with known redshift in a sample should be increased by 15%-35% depending on circumstances. We show various statistical characteristics of ionized gas surrounding galaxies, the resulting dispersion measure and their dependence on the host galaxy stellar mass, redshift, and the projected distance of a FRB source from its host center.

Local Group Velocity Versus Gravity: Nonlinear Effects

Ciecieląg P., Chodorowski M., Kudlicki A.

Acta Astronomica

2001

Vol. 51, No. 2

103--115

We use numerical simulations to study the relation between the velocity of the Local Group (LG) and its gravitational acceleration. This relation serves as a test for the kinematic origin of the CMB dipole and as a method for estimating β≡Ω0.6/b. We calculate the misalignment angle between the two vectors and compare it to the observed value for the PSCz survey. The latter value is beyond the upper limit of the 90% confidence interval for the angle; therefore, the nonlinear effects are unlikely to be responsible for the whole observed misalignment. We also study the relation between the amplitudes of the LG velocity and gravity vectors. In an Ω=1 Universe, the smoothed gravity of the LG turns out to be a biased low estimator of the LG (unsmoothed) velocity. In an Ω=0.3 Universe, the estimator is biased high. The discussed biases are, however, only a few per cent, thus the linear theory works to good accuracy. The gravity-based estimator of the LG velocity has also a scatter that limits the precision of the estimate of β in the LG velocity-gravity comparisons. The random error of β due to nonlinear effects amounts to several per cent.