Near Field Cosmology: The Origin of the Galaxy and the Local Group
The Galaxy has built up through a process of accretion and merging over billions of years which continues to this day. Astronomers are now embarking on a new era of massive stellar surveys over the coming decade.
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Near Field Cosmology: The Origin of the Galaxy and the Local Group Joss Bland-Hawthorn and Kenneth Freeman
The Galaxy has built up through a process of accretion and merging over billions of years which continues to this day. Astronomers are now embarking on a new era of massive stellar surveys over the coming decade. These campaigns will derive three-dimensional space motions and heavy element abundances for millions of stars throughout the Galaxy and its neighbours. The new observations will reveal signatures of the formation and early evolution of the Local Group; this is what we mean by ‘near field cosmology.’ We set this new course of study within the context of fossil signatures from galaxy surveys and the high redshift universe. We discuss the complex relationship between baryons and dark matter over cosmic time, and introduce a synthetic framework that will allow both numerical simulations and the impending data deluge to be compared. We also include relevant source materials for the young near-field cosmologist and some historical perspectives.
1.1 Prologue In an earlier review, we outlined the concept of near field cosmology to emphasize the fact that there are ancient signatures all around us today providing evidence of the formation processes that led to the Galaxy and the Local Group (Freeman and Bland-Hawthorn 2002). We see ancient stars around us in the old thin disk, the thick disk, the stellar halo, the inner bulge, and in satellite dwarf galaxies. About half of all stars in the Galaxy today formed before a redshift z ∼ 1. The Hubble Space Telescope (HST) probes these early formation epochs directly during a time when J. Bland-Hawthorn (B) Sydney Institute for Astronomy, University of Sydney, Sydney, NSW 2006, Australia e-mail: [email protected] K. Freeman Mount Stromlo Observatory, Australia National University, Weston Creek, ACT 2611, Australia e-mail: [email protected] B. Moore (ed.), The Origin of the Galaxy and Local Group, Saas-Fee Advanced Course 37, DOI: 10.1007/978-3-642-41720-7_1, © Springer-Verlag Berlin Heidelberg 2014
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J. Bland-Hawthorn and K. Freeman
gas accretion, star formation and feedback processes were greatly enhanced. But how do we connect the past with the present? There are no easy answers. Here we revisit our earlier review, extend our discussion to observable fossils from the Big Bang to the present day, with an updated discussion of the complete inventory of baryons. The desire to connect present-day galaxies and the distant Universe has a long history that began long before it was possible to compare both epochs directly. We now speak of galactic and stellar archaeology. Eggen et al. (1962) were the first to show that it is possible to study galactic archaeology using stellar abundances and stellar dynamics; this is probably the most influential paper on the subject of galaxy formation. In 1966, Fred Hoyle wrote “It is not too much to say that the understanding of why there are these different kinds of galaxy, of how galaxies originate, constitutes the bi
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