The Physics of Galaxy Formation and Evolution
Date Issued
2016
Author(s)
D'ONOFRIO, MAURO
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Lake, George
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Chiosi, Cesare
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Einasto, Jaan
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Kroupa, Pavel
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de Carvalho, Reinaldo Ramos
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Ciotti, Luca
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Matteucci, Francesca
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Moss, David L.
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Longair, Malcolm S.
Abstract
The theoretical studies about galaxy formation and evolution are the subject of this Chapter. They started with the recognition that the Hubble sequence is not a simple morphological description of galaxies, but a possible scheme separating and characterizing the physical processes that bring galaxies to their present form. When the Hubble tuning fork reached its actual shape—around 1936 with the discovery of the S0 galaxies—, the Hertzsprung-Russell diagram that revealed the existence of the main sequence of stellar structures was already in place, but its explanation in terms of nuclear reactions was still to come (the p-p chain of Bethe appeared in 1939). Just before the end of the WWII the time was mature for the concept of stellar populations formulated by Baade, but only 20 years later appeared the first monolithic collapse model of galaxies formation by Eggen et al. (1962). In 1964 Arno Penzias and Robert Woodrow Wilson measured the CMB radiation opening the way toward the current cosmological model. With the 1970s the idea that merging events have produced many of the actual galaxy structures appeared in the literature with the Toomre’ works. Leonard Searle and Robert Zinn proposed that galaxies form by the coalescence of smaller progenitors. At the same time the discovery of the existence of dark matter (DM) rapidly changed our idea of galaxies and how structures form in the Universe. White & Rees and Fall & Efstathiou developed the actual view of galaxy formation, in which baryons fall into the potential wells of hierarchically growing dark matter structures. The two decades 1980s–1990s have seen the development of Semi-Analytic Models (SAM) of galaxy formation and evolution and of numerical hydrodynamical simulations of increasing resolution and complexity. With the new century, the Universe was discovered to accelerate its expansion and thanks to the big redshift galaxy surveys the idea of the cosmic web started to be accepted. Today the dominating paradigm is that provided by the CDM cosmology, a framework in which the Universe is believed to be composed of 70% of dark energy (DE), 26% of cold and hot DM, and 4% of baryons. Within this model the values of the cosmological parameters, such as the Hubble expansion rate H0, are known with great accuracy. This is the precision cosmology era, a very awkward situation in which the cosmological parameters are known very well, but we do not know what the Universe is composed of.
The following interviews go over some theoretical investigations that, along this century of extra-galactic research, tried to shed some light on the galaxy formation and evolution. Section 8.2 deals with the first attempts to simulate the Hubble tuning fork from basic physical principles. Then, in Sect.8.3 we better define the differences between the monolithic scenario of galaxy formation and the hierarchical scheme, introducing some hybrid versions of the two frameworks. In Sects. 8.4 and 8.5 we provide a much clear view of the star formation history, i.e. of the convolution of the Initial Mass Function (IMF) and the Star Formation Rate (SFR). The role of feedback is analyzed in Sect. 8.6, that of chemical enrichment in Sect. 8.7, and that of Magnetic Fields in Sect. 8.8. We finally propose a panoramic view of the comparisons between observations and models in Sect. 8.9.
Coverage
From the Realm of the Nebulae to Populations of Galaxies
Volume
435
Start page
585
Ads BibCode
2016ASSL..435..585D
Rights
open.access
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