Empirical scenarios of galaxy evolution

Our present understanding of the evolution of the Universe is not fully comprehensive. While the conventional LCDM cosmological model provides an explanation for the large-scale structure and evolution of the Universe, problems are encountered at the level of individual galaxies. For this reason, attention is now focused on empirical scenarios of the formation and evolution of galaxies, which are based on precision observations of high-redshift galaxies. During the last 10–15 years, several such scenarios have been proposed and subjected to verification. For example, the discovery in 2007–2009 of the unexpectedly rapid growth of giant elliptical galaxies enabled rejecting a major merger as the primary mechanism by which such objects are formed. A so-called two-stage scenario is now common in which a compact stellar ‘seed’ is formed at an early stage, after which an elliptic galaxy rapidly ‘swells’ due to multiple dissipationless minor mergers. The discovery of a population of quasars at $z$>6, whose central black holes have masses of the order of a billion solar masses or more, prompted the development of scenarios in which the black hole independ„ently grows at an early stage, to be later ‘coated’ with galaxies. In the same vein, the recent massive acquisition of integral-field spectroscopic data using large telescopes has enabled ‘pinning down’ the critical moment in the evolution of spiral galaxy dynamics at $z$=1, which was previously overlooked by cosmological models of the evolution of the Universe.