Our view of the structure and dynamics of our Galaxy has progressed, pushed by the acquisition of ever larger datasets that encompass wider perspectives. At the dawn of the Gaia era, we are about to enter a phase of unprecedented detail in our view of our Galaxy. This opens up the possibility of using new analysis tools, or the use of traditional tools at newer scales. However, to extract the most of the Gaia database, it is necessary to immerse our theoretical models within Gaia mock catalogues to derive proper inferences about the structure of our Galaxy. We will review several tools developed by our group to construct and analyze realistic Gaia mock catalogues and some of the lessons we have learnt from them.

We explore the possibility of detecting and characterising the warp of the stellar disc of our Galaxy using the synthetic Gaia data and the UCAC4 proper motion catalogue. We develop a new kinematic model for the galactic warp. We generate random realisations of test particles which evolve in a realistic Galactic potential warped adiabatically to various final configurations. The Gaia selection function, its errors model and a realistic 3D extinction map are applied to mimic three tracer populations: OB, A and Red Clump stars. A family of Great Circle Cell Counts (GC3) methods is used. They are ideally suited to find the tilt and twist of a collection of rings, which allow us to detect and measure the warp parameters. Moreover, We look for the kinematic signature of the warp in the μb proper motions of stars as a function of galactic longitude. Using the UCAC4 proper motions, we do not obtain a similar trend as the one we expect from our warp model. We explore a possible source of this discrepancy in terms of systematics caused by a residual spin of the Hipparcos celestial reference frame (HCRF) with respect to the extra-galactic inertial one.

We present a proper-motion study on models of the dwarf spheroidal galaxy Sculptor, based on the predicted proper-motion accuracy of Gaia measurements. Gaia will measure proper motions of several hundreds of stars for a Sculptor-like system. Even with an uncertainty on the proper motion of order 1.5 times the size of an individual proper-motion value of ∼10 mas/century, we find that it is possible to recover Sculptor's systemic proper motion at its distance of 79 kpc.

We compare the stellar motion around a spiral arm created in two different scenarios, transient/co-rotating spiral arms and density-wave-like spiral arms. We generate Gaia mock data from snapshots of the simulations following these two scenarios using our stellar population code, SNAPDRAGONS, which takes into account dust extinction and the expected Gaia errors. We compare the observed rotation velocity around a spiral arm similar in position to the Perseus arm, and find that there is a clear difference in the velocity features around the spiral arm between the co-rotating spiral arm and the density-wave-like spiral arm. Our result demonstrates that the volume and accuracy of the Gaia data are sufficient to clearly distinguish these two scenarios of the spiral arms.

The current sample of HVSs have small constraining power for Galactic Astrophysics. In this contribution, we show that Gaia will radically change this situation. Our preliminary results suggests an increase of at least an order of magnitude in the detected sample (a few hundreds in total), with a much wider mass range, that goes up to ∼5 M⊙. Detections will be mostly within a few tens of kpc from the Sun, while the outer halo, where current HVSs were detected, will likely remain out of reach.

Hypervelocity stars are those that have speeds exceeding the escape speed and are hence unbound from the Milky Way. We investigate a sample of low-mass hypervelocity candidates obtained using data from the high-precision SDSS Stripe 82 catalogue, which we have combined with spectroscopy from the 200-inch Hale Telescope at Palomar Observatory. We find four good candidates, but without metallicities it is difficult to pin-down their distances and therefore total velocities. Our best candidate has a significant likelihood that it is escaping the Milky Way for a wide-range of metallicities.

Some recent observations of Classical Cepheids, RR Lyrae and Mira variables are used to illustrate their continued importance as standard candles. Gaia will provide a calibration of these stars as distance indicators which should lead to a greatly improved understanding of the formation and evolution of our Galaxy as well as a vital calibration of the extra-galactic distance scale. The importance of infrared observations, as well as a deeper understanding of interstellar reddening and photometric systems, will play a part if the Gaia calibration is to be put to good use.

With Gaia currently in nominal mission mode and sending data to earth, the challenge for the astronomical community is to prepare for the use of what will be at the time of release one of the largest and most complex astronomical catalogues ever produced. Use of parallax data is not straightforward due to the presence of many statistical biases and selection effects. We present an overview of a techniques for correct use of the Gaia parallax information, which relies on statistical modelling of the data in order to infer derived quantities such as distance and absolute magnitude in an unbiased way. The methods rely on a Bayesian methodology and have been applied to case studies on normal stars, variable stars, open clusters and the LMC.

The Large Magellanic Cloud (LMC) is the closest large satellite of the Milky Way (MW) and the first step of the extragalactic distance scale, hence knowing the distance to the LMC and its three-dimensional structure contributes to the definition of the entire cosmic distance ladder. RR Lyrae stars are old objects which trace the halo of the LMC. They can be used as distance indicators because they follow a period-luminosity-metallicity (PLKsZ) relation in the Ks passband. The purpose of this study was the derivation of a new PLKsZ relation for RR Lyrae stars in the LMC based on the multi-epoch Ks photometry obtained by the VISTA survey of the Magellanic Clouds system (VMC, Cioni et al. 2011).

Severe interstellar extinction toward the Galactic plane has prevented the investigation of stellar populations in that region. Pulsating variable stars, particularly Cepheids and Miras, are useful tracers because their distances and ages can be determined accurately. Infrared observations of these variable stars in the obscured regions can provide useful information about the hidden parts of the Galaxy. These objects can also provide complimentary information to observations made by the Gaia spacecraft because highly-obscured objects cannot be detected by Gaia. We have carried out a near-infrared survey of variable stars near the Galactic bulge, between − 10 and + 10 degrees in galactic longitude, using the IRSF 1.4 m telescope and SIRIUS near-infrared camera in South Africa. Here as an initial result we report the discovery of 19 classical Cepheids behind the bulge.

Disentangling the 3D structure of interstellar extinction is a key requirement for understanding the Galaxy and a crucial step towards taking full advantage of the data Gaia will provide.

We present a scheme for using stellar catalogues to map the three-dimensional distributions of extinction and dust within our Galaxy, employing Gaussian random fields and a simple physical model of the interstellar medium that assumes a Kolmogorov-like power spectrum of turbulent fluctuations. As extinction is modelled as a random field, the spatial resolution of the resulting maps is set naturally by the data available; there is no need to impose any spatial binning.

I briefly discuss the range of supernova science that will be possible with Gaia.

The Gaia Photometric Science Alerts (GSA) group is the Gaia Data Processing and Analysis Consortium (DPAC) unit responsible for releasing alerts on Gaia transient candidates from a daily flow of initially reduced data. In preparation for obtaining the rates for different transient families with Gaia, one of the main goals of GSA is to reliably identify and characterize the candidates. In this article, we describe the simulations used to understand and predict possible selection effects and the techniques used to identify the nature of the transient alerts provided by Gaia.

The Gaia Science Alerts project (GSA) aims to augment a precision survey of the Milky Way with a controlled, precision survey of all classes of transient phenomena. While onboard BP/RP spectra from Gaia will ultimately allow us to classify many Gaia Alerts based on Gaia data alone, in the initial phases of the GSA project it is necessary to verify and classify discoveries with ground-based spectroscopic followup. In this article, we describe a subset of the ongoing Gaia Alerts followup programmes, and some of the initial science results from this work.

We demonstrate the eclipsing binary detection performance of the Gaia variability analysis and processing pipeline using Hipparcos data. The automated pipeline classifies 1 067 (0.9%) of the 118 204 Hipparcos sources as eclipsing binary candidates. The detection rate amounts to 89% (732 sources) in a subset of 819 visually confirmed eclipsing binaries, with the period correctly identified for 80% of them, and double or half periods obtained in 6% of the cases.

In this contribution I provide some thoughts on the options for future space astrometry missions, with a focus on global astrometry. The next big step in space astrometry ideally would open up a new accuracy or wavelength domain (or a combination of both), although a future repeat of the Gaia mission is an option that should seriously be considered. I outline the scientific and technical challenges on the way to global sub-μas astrometry, and make some basic recommendations for achieving this goal.

This paper gives a brief overview of the Gaia Research for European Astronomy Training (GREAT) network activity plan for the period 2015–2020, aiming to support the maximisation of scientific exploitation of the data from Gaia.

The main goal of Galactic Archaeology is to understand the formation and evolution of the basic Galactic components. This requires sophisticated chemo-dynamical modeling, where disk asymmetries (e.g., perturbations from the bar, spirals, and mergers) and non-equilibrium processes are taken into account self-consistently. Here we discuss the current status of Galactic chemo-dynamical modeling and focus on a recent hybrid technique, which helps circumvent traditional problems with chemical enrichment and star formation encountered in fully self-consistent cosmological simulations. We show that this model can account for a number of chemo-kinematic relations in the Milky Way, as discussed in previous works. In addition, we demonstrate that our model matches well the observed age-[α/Fe] relation and that blurring may be insufficient to explain the scatter in the age-metallicity relation.

Data from the recently launched Gaia satellite in combination with data from large spectroscopic and asteroseismology surveys will allow great progress in unraveling the evolutionary history of the Milky Way disk over the next decade. Here, I briefly review the progress made with observations in the solar neighborhood in constraining the main processes involved in the formation and evolution of the Galactic disk. I then focus on recent new insights on the chemo-dynamical structure of the disk from SEGUE and APOGEE data. I conclude by summarizing the current state of knowledge and what evolutionary actors best explain the data that we have now, and by looking forward to the most informative measurements that Gaia and other surveys can make.

In this proceeding I will shortly discuss radial migration in disc galaxies and the Milky Way in particular. I discuss the most important evidence for radial migration, i.e. the increasing width of the metallicity distribution with age, while the mean metallicity of stars remains constant. In the second part I briefly discuss thick disc creation by migration, the question of preferential migration with vertical action and its impact on Galactic kinematics.