  The nearby ultra-compact multiplanetary system YZ Ceti consists of at least
three planets. The orbital period of each planet is the subject of discussion
in the literature due to strong aliasing in the radial velocity data. The
stellar activity of this M dwarf also hampers significantly the derivation of
the planetary parameters. With an additional 229 radial velocity measurements
obtained since the discovery publication, we reanalyze the YZ Ceti system and
resolve the alias issues. We use model comparison in the framework of Bayesian
statistics and periodogram simulations based on a method by Dawson and Fabrycky
to resolve the aliases. We discuss additional signals in the RV data, and
derive the planetary parameters by simultaneously modeling the stellar activity
with a Gaussian process regression model. To constrain the planetary parameters
further we apply a stability analysis on our ensemble of Keplerian fits. We
resolve the aliases: the three planets orbit the star with periods of $2.02$ d,
$3.06$ d, and $4.66$ d. We also investigate an effect of the stellar rotational
signal on the derivation of the planetary parameters, in particular the
eccentricity of the innermost planet. Using photometry we determine the stellar
rotational period to be close to $68$ d. From the absence of a transit event
with TESS, we derive an upper limit of the inclination of $i_\mathrm{max} =
87.43$ deg. YZ Ceti is a prime example of a system where strong aliasing
hindered the determination of the orbital periods of exoplanets. Additionally,
stellar activity influences the derivation of planetary parameters and modeling
them correctly is important for the reliable estimation of the orbital
parameters in this specific compact system. Stability considerations then allow
additional constraints to be placed on the planetary parameters.
