The metallicity distribution and abundance ratios of the Galactic bulge are reviewed. Issues raised by different groups in recent work, in particular the high metallicity end, a comparison between the oxygen abundances derived from different indicators, the [OI] 630nm and IR OH lines, and the issue of measuring giants vs. dwarfs, are discussed. Finally, abundances in bulge globular clusters are briefly described.

The formation and evolution of the Milky Way bulge can be constrained by studying elemental abundances of bulge stars. Due to the large and variable visual extinction in the line-of-sight towards the bulge, an analysis in the near-IR is preferred. Here, I will present some preliminary results of an on-going project in which elemental abundances, especially those of the C, N, and O elements, of bulge stars are investigated by analysing CRIRES spectra observed with the VLT.

We examine the bar instability in models with an exponential disk and a cuspy NFW-like dark matter (DM) halo inspired by cosmological simulations. Bar evolution is studied as a function of numerical resolution in a sequence of models spanning 104 – 108 DM particles - including a multi-mass model with an effective resolution of 1010. The goal is to find convergence in dynamical behaviour. We characterize the bar growth, the buckling instability, pattern speed decay through resonant transfer of angular momentum, and possible destruction of the DM halo cusp. Overall, most characteristics converge in behaviour for halos containing more than 107 particles in detail. Notably, the formation of the bar does not destroy the density cusp in this case. These higher resolution simulations clearly illustrate the importance of discrete resonances in transporting angular momentum from the bar to the halo.

The presence of exponential bulges and anti-truncated disks has been noticed in many lenticular galaxies. In fact, it could be expected because the very formation of S0 galaxies includes various processes of secular evolution. We discuss how to distinguish between a pseudobulge and an anti-truncated disk, and also what particular mechanisms may be responsible for the formation of anti-truncated disks. Some clear examples of lenticular galaxies with a multi-tier exponential stellar structure are presented, – among them two central group giant S0s seen face-on and perfectly axisymmetric.

I discuss how the chemical abundance distributions, kinematics and age distributions of stars in the thin and thick disks of the Galaxy can be used to decipher the merger history of the Milky Way, a typical large galaxy. The observational evidence points to a rather quiescent past merging history, unusual in the context of the ‘consensus’ cold-dark-matter cosmology favoured from observations of structure on scales larger than individual galaxies.

Recent data have revealed a clear distinction between the abundance patterns of the Milky Way (MW) thick and thin disks, suggesting a different origin for each of these components. In this work we first review the main ideas on the formation of the thin disk. From chemical evolution arguments we show that the thin disk should have formed on a long timescale. We also show clear signs that the local stellar samples are contaminated by stars coming from inner radii. We then check what would have to be changed in such a model in order to explain the observables in the thick disk. We find that a model in which the thick disk forms on a much shorter timescale than thin disk and with a star formation efficiency of around a factor of 10 larger than that in the thin disk can account for the observed abundance ratio shifts of several elements between thick and thin disk stars. Moreover, the lack of scatter in the abundance ratio patterns of both the thick and thin disks suggest both components to have been formed in situ by gas accretion and not by mergers of smaller stellar systems. Especially for the thick disk, this last constraint becomes a strong one if its metallicity distribution extends to, at least, solar. Finally, we briefly discuss the interplay between present deuterium abundance and present infall rates in connection with the thin disk evolution.

The past history and origin of the different Galactic stellar populations are manifested in their different chemical abundance patterns. We obtained new elemental abundances for 553 F and G dwarf stars, to more accurately quantify these patterns for the thin and thick disks. However, the exact definition of disk membership is not straightforward. Stars that have a high likelihood of belonging to the thin disk show different abundance patterns from those for the thick disk. In contrast, we show that stars for the Hercules Stream do not show unique abundance patterns, but rather follow those of the thin and thick disks. This strongly suggests that the Hercules Stream is a feature induced by internal dynamics within the Galaxy rather than the remnant of an accreted satellite.

We use Beryllium to investigate star formation in the early Galaxy. Be has been demonstrated to be a good indicator of time in these early epochs. By analyzing the so-far largest sample of halo and thick disk metal poor stars, we find a clear scatter in Be for a given value of [Fe/H] and [O/H]. The scatter is very pronounced for Halo stars, while it is marginal for thick disk stars. Our halo stars separate in the [α/Fe] - Be diagram, showing two main branches: one indistinguishable from the thick disk stars, and one with lower [α/Fe] ratio. The stars belonging to this branch are characterized by highly eccentric orbits and small perigalactic radius (Rmin). Their kinematics are consistent with an accreted component.

Stars form in embedded star clusters which play a key role in determining the properties of a galaxy's stellar population. A large fraction of newly born massive stars are shot out from dynamically unstable embedded-cluster cores spreading them to large distances before they explode. Embedded clusters blow out their gas once the feedback energy from the new stellar population overcomes its binding energy, leading to cluster expansion and in many cases dissolution into the galaxy. Galactic disks may be thickened by such processes, and some thick disks may be the result of an early epoch of vigorous star-formation. Binary stellar systems are disrupted in clusters leading to a lower fraction of binaries in the field, while long-lived clusters harden degenerate-stellar binaries such that the SNIa rate may increase by orders of magnitude in those galaxies that were able to form long-lived clusters. The stellar initial mass function of the whole galaxy must be computed by adding the IMFs in the individual clusters. The resulting integrated galactic initial mass function (IGIMF) is top-light for SFRs < 10 M⊙/yr, and its slope and, more importantly, its upper stellar mass limit depend on the star-formation rate (SFR), explaining naturally the mass–metallicity relation of galaxies. Based on the IGIMF theory, the re-calibrated Hα-luminosity–SFR relation implies dwarf irregular galaxies to have the same gas-depletion time-scale as major disk galaxies, implying a major change of our concept of dwarf-galaxy evolution. A galaxy transforms about 0.3 per cent of its neutral gas mass every 10 Myr into stars. The IGIMF-theory also naturally leads to the observed radial Hα cutoff in disk galaxies without a radial star-formation cutoff. It emerges that the thorough understanding of the physics and distribution of star clusters may be leading to a major paradigm shift in our understanding of galaxy evolution.

We have derived a complete magnitude-limited sample of 440 Galactic open clusters in the solar neighborhood, with integrated V-magnitude brighter than 8 mag. This sample can be used to infer the present-day luminosity and mass functions of open clusters up to a given age; it can even be used to construct the initial mass and luminosity function (IMF, ILF) of clusters (defined as visible clusters with age 4 – 8 Myr). The high-mass end of the cluster IMF is a power-law with a slope of −2 or slightly shallower (−1.7) while the luminous cluster ILF has a power-slope of −1, in agreement with what is found for extragalactic clusters. Both distribution functions show a turnover, starting at 300 M⊙ and integrated magnitude −3 mag, respectively. The overall birthrate of clusters is 0.4 clusters per kpc2 and per Myr. The average present-day cluster mass is 700 M⊙, while the average initial cluster mass is 4500 M⊙. The difference of these two average masses indicates the high infant mortality and/or weight loss of Galactic open clusters (due to dynamical evolution).

We present an update of the Bologna Open Clusters Chemical Evolution project (BOCCE, in short). We are conducting a photometric and spectroscopic survey of Open Clusters, to be used as tracers of the Galactic disk properties and evolution. We obtain the clusters parameters (age, distance, metallicity, and detailed abundances) in a precise and homogeneous way. We have collected data for about 40 Open Clusters and have fully analyzed the photometric data for about one half and the spectra for one quarter of them. We present here results based on these works and indicate what will come next.

The mass reinserted by young stars of an emerging massive compact cluster shows a bimodal hydrodynamic behaviour. In the inner part of the cluster, it is thermally unstable, while in its outer parts it forms an out-blowing wind. The chemical homogeneity/inhomogeneity of low/high mass clusters demonstrates the relevance of this solution to the presence of single/multiple stellar populations. We show the consequences that the thermal instability of the reinserted mass has to the galactic super-winds.

We present evidence that the accretion of warm gas onto the Galaxy today is at least as important as cold gas accretion. For more than a decade, the source of the bright Hα emission (up to 750 mR†) along the Magellanic Stream has remained a mystery. We present a hydrodynamical model that explains the known properties of the Hα emission and provides new insights on the lifetime of the Stream clouds. The upstream clouds are gradually disrupted due to their interaction with the hot halo gas. The clouds that follow plough into gas ablated from the upstream clouds, leading to shock ionisation at the leading edges of the downstream clouds. Since the following clouds also experience ablation, and weaker Hα (100–200 mR) is quite extensive, a disruptive cascade must be operating along much of the Stream. In order to light up much of the Stream as observed, it must have a small angle of attack (≈ 20°) to the halo, and this may already find support in new Hi observations. Another prediction is that the Balmer ratio (Hα/Hβ) will be substantially enhanced due to the slow shock; this will soon be tested by upcoming WHAM observations in Chile. We find that the clouds are evolving on timescales of 100–200 Myr, such that the Stream must be replenished by the Magellanic Clouds at a fairly constant rate (≳ 0.1 M⊙ yr−1). The ablated material falls onto the Galaxy as a warm drizzle; diffuse ionized gas at 104 K is an important constituent of galactic accretion. The observed Hα emission provides a new constraint on the rate of disruption of the Stream and, consequently, the infall rate of metal-poor gas onto the Galaxy. We consider the stability of Hi clouds falling towards the Galactic disk and show that most of these must break down into smaller fragments that become partially ionized. The Galactic halo is expected to have huge numbers of smaller neutral and ionized fragments. When the ionized component of the infalling gas is accounted for, the rate of gas accretion is ~0.4 M⊙ yr−1, roughly twice the rate deduced from Hi observations alone.

Studies of the halo gas in the Milky Way and in nearby spiral galaxies show the presence of gas complexes that cannot be reconciled with an internal (galactic fountain) origin and are direct evidence of gas accretion. Estimating gas accretion rates from these features consistently gives values, which are one order of magnitude lower than what is needed to feed the star formation. I show that this problem can be overcome if most of the accretion is in fact “hidden” as it mixes with the galactic fountain material coming from the disk. This model not only provides an explanation for the missing gas accretion but also reproduces the peculiar kinematics of the halo gas in particular the vertical rotation gradient. In this view this gradient becomes indirect evidence for gas accretion.

We report the discovery that substructures/subhaloes of a galaxy-size halo tend to fall in together in groups in cosmological simulations, something that may explain the oddity of the MW satellite distribution. The original clustering at the time of infall is still discernible in the angular momenta of the subhaloes even for events which took place up to eight Gyrs ago, z ~ 1. This phenomenon appears to be rather common since at least 1/3 of the present-day subhaloes have fallen in groups in our simulations. Hence, this may well explain the Lynden-Bell & Lynden-Bell ghostly streams. We have also found that the probability of building up a flattened distribution similar to the MW satellites is as high as ~ 80% if the MW satellites were from only one group and ~ 20% when five groups are involved. Therefore, we conclude that the ‘peculiar’ distribution of satellites around the MW can be expected with the CDM structure formation theory. This non-random assignment of satellites to subhaloes implies an environmental dependence on whether these low-mass objects are able to form stars, possibly related to the nature of reionization in the early Universe.

The evolution of galactic disks from their early stages is dominated by gas dynamical effects like gas infall, galactic fountains, and galactic outflows, and more. The influence of these processes is only understandable in the framework of diverse gas phases differing in their thermal energies, dynamics, and element abundances. To trace the temporal and chemical evolution of galactic disks, it is therefore essential to model the interstellar gasdynamics combined with stellar dynamics, the interactions between gas phases, and star-gas mass and energy exchanges as detailed as possible. This article reviews the potential of state-of-the-art numerical schemes like Smooth-Particle and grid-based hydrodynamics and their ingredients, such as star-formation criteria and feedback, energy deposit and metal enrichment by stars, and the influence of gas-phase interactions on the galactic gas dynamics and chemistry.

Warps in the outer gaseous disks of galaxies are a ubiquitous phenomenon, but it is still unclear what generates them. One theory is that warps are generated internally through spontaneous bending instabilities. Other theories suggest that they result from the interaction of the outer disk with accreting extragalactic material. In this case, we expect to find cases where the circular velocity of the warp gas is poorly correlated with the rotational velocity of the galaxy disk at the same radius. Optical spectroscopy presents itself as an interesting alternative to 21-cm observations for testing this prediction, because (i) separating the kinematics of the warp from those of the disk requires a spatial resolution that is higher than what is achieved at 21 cm at low HI column density; (ii) optical spectroscopy also provides important information on star formation rates, gas excitation, and chemical abundances, which provide clues to the origin of the gas in warps. We present here preliminary results of a study of the kinematics of gas in the outer-disk warps of seven edge-on galaxies, using multi-hour VLT/FORS2 spectroscopy.

Star formation is enhanced in spiral arms because of a combination of orbit crowding, cloud collisions, and gravitational instabilities. The characteristic mass for the instability is 107M⊙ in gas and 105M⊙ in stars, and the morphology is the familiar beads on a string with 1-2 kpc separation. Similar instabilities occur in resonance rings and tidal tails. Sequential triggering from stellar pressure occurs in two ways. For short times and near distances, it occurs in the bright rims and dense knots that lag behind during cloud dispersal. For long times, it occurs in swept-up shells and along the periphery of cleared regions. The first case should be common but difficult to disentangle from independent star formation in the same cloud. The second case has a causality condition and a collapse condition and is often easy to recognize. Turbulent triggering produces a hierarchy of dense cloudy structure and an associated hierarchy of young star positions. There should also be a correlation between the duration of star formation and the size of the region that is analogous to the size-linewidth relation in the gas. The cosmological context is provided by observations of star formation in high redshift galaxies. Sequential and turbulent triggering is not yet observable, but gravitational instabilities are, and they show a scale up from local instabilities by a factor of ~3 in size and ~100 in mass. This is most easily explained as the result of an increase in the ISM turbulent speed by a factor of ~5. In the clumpiest galaxies at high redshift, the clumps are so large that they should interact with each other and merge in the center, where they form or contribute to the bulge.

Studies of the atomic phase of the interstellar medium, via the 21–cm spectral line of neutral hydrogen (H I), play a key rôle in our attempts to understand the structure and evolution of disk galaxies. We present here results from The H I Nearby Galaxy Survey (THINGS) and focus on the mass distribution as derived from the observed kinematics, and on the link between gas and star formation rate surface density, i.e., the Schmidt–Kennicutt law. Also, we briefly dwell on the wealth and wide variety of structures, often outlining what seem to be expanding shells surrounding sites of recent, massive star formation.

The molecular gas in galaxy disks shows much more galaxy to galaxy variation than does the atomic gas. Detailed studies show that this variation can be attributed to differences in hydrostatic pressure in the disks due largely to variations in the stellar surface density and the total gas surface density. One prediction of pressure modulated H2 formation is that the location where HI and H2 have equal surface densities occurs at a constant value of the stellar surface density in the disk. Observations confirm this constancy to 40%.