Galaxies: formation

Abstract. The Milky Way harbours two disks that appear distinct concerning scale-heights, kinematics, and elemental abundance patterns. Recent years have seen a surge of studies of the elemental abundance trends in the disks using high resolution spectroscopy. Here I will review and discuss the currently available data. Special focus will also be put on how we define stars to be members of either disk, and how current models of galaxy formation favour that thick disks are formed from several accreted bodies. The ability for the stellar abundance trends to test such predictions are discussed. 

Based on currently available elemental abundance data and age determinations, the thick disk could have formed either through a violent, heating merger or through accretion of (substantial) satellites in a hierarchical galaxy formation scenario. The fast monolithic-like collapse is getting more and more problematic as data are gathered. It would be especially crucial to establish if there is an age-metallicity relation in the thick disk or not as in that case the thick disk could not have formed in that way (since the models indicate that the formation time-scale for the stars in the thick disk would be very short, see [7]). 

Most of the work reported here has been conducted within the ESO Large Programme 165.N-0276 Galaxy Formation, Early Nucleosynthesis, and the First Stars , which has covered 4 periods 65-68, from April 2000 to November 2001, with a total of 38 nights in visitor mode. The team had R. Cayrel as PI, and 13 Cols ... 

We have used the infra-red triplet (921.286 nm, 922.809 nm and 923.754 nm) to determine the sulphur abundance in the 32 giants from ESO s Large Program Galaxy Formation, Early Nucleosynthesis, and First Stars . 

Detailed elemental abundances are now available for several individual stars in the Galaxy s dwarf satellites (Shetrone et a1. 2001, 2003 Geisler et al. 2005 also see the reviews in this proceedings). A comparison of these abundance ratios to those of stars in the Galaxy can be used to address several questions related to galaxy formation and evolution, as well as stellar nucleosynthesis. 

The metallicity distribution function (MDF) in galaxy halos contains other important clues about the process of galaxy formation. In recent years, a wealth of MDF data have been collected for the Milky Way (eg. [3], [4]), M3I (eg. [I]),... 

Nowadays, the star formation history (SFH), initial mass function (IMF) and detailed chemical properties have been determined for many dwarfs, both in the Local Group and outside it (e.g. Grebel, Shetrone, Tolstoy, these proceedings). This in principle allows us to base theories of late-type galaxy formation and evolution on firmer grounds, by reducing the free parameter space. 

In the next very few years stellar abundances and kinematics will be available for as many stars as redshifts are now available for galaxies. This abundance of information can, provided we approach the analysis and interpretation with due imagination, advance the astrophysics of galaxy formation as much as Cosmology has advanced over the last few decades. No doubt our image of galaxy evolution will be similarly revolutionised. 

The epoch and mode of galaxy formation are not well known, but both quasars and star-forming galaxies are known with redshifts up to about 7, corresponding to an era when the expanding Universe was only 1/8 of its present size, and the emission-line spectra of quasars indicate a large heavy-element abundance (solar or more Hamann Ferland 1999), suggesting prior stellar activity. The first stars, on the other hand, known as Population IIP, would have been devoid of metals whether they differed from normal stars in other basic characteristics, notably their mass distribution, is not known, since no completely metal-free stars have been... 

M. S. Longair, Galaxy Formation, Springer, Berlin, 1998, and John A. Peacock, Cosmological Physics, Cambridge University Press 1999. Many aspects of background radiation at all wavelengths are discussed in... 

Longair, M. S. 1998, Galaxy Formation, Berlin Springer-Verlag. 

There is currently no way of distinguishing between these possibilities, and neither is at all comprehendable from the point of view of any extant theory of galaxy formation—all of which are deeply embedded in the standard model of modern cosmology. 

Our analysis gave strong support to the Zeldovich pancake scenario. This model was based essentially on the neutrino dominated dark matter model. However, some important differences between the model and observations were detected. First of all, there exists a rarefied population of test particles in voids absent in real data. This was the first indication for the presence of biasing in galaxy formation - there is primordial gas and dark matter in voids,... 

Abstract I describe recent challenges in dark matter. I review the budgets for baryonic and nonbaryonic dark matter. Problems with cold dark matter in the context of galaxy formation are summarized, and possible solutions are presented. I conclude with a description of the prospects for observing cold dark matter. 

Ejection via early winds is inferred in the enriched intracluster medium. Observations of Mpc-scale holes around Lyman break galaxies, detected via studying absorption of the IGM towards background quasars, support an explanation in terms of early winds from L galaxies. The so-called cooling catastrophe in galaxy formation theory, which results in overly luminous massive galaxies can be avoided if early winds eject an amount of baryons comparable to that retained in stars. 

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