We present observations of the Mopra carbon monoxide (CO) survey of the Southern Galactic Plane, covering Galactic longitudes spanning $l = 250^{\circ}$ ($-110^{\circ}$) to $l = 355^{\circ}$ ($-5^{\circ}$), with a latitudinal coverage of at least $|b|<1^\circ$, totalling an area of $>$210 deg$^{2}$. These data have been taken at 0.6 arcmin spatial resolution and 0.1 km s$^{-1}$ spectral resolution, providing an unprecedented view of the molecular gas clouds of the Southern Galactic Plane in the 109–115 GHz $J = 1-0$ transitions of $^{12}$CO, $^{13}$CO, C$^{18}$O, and C$^{17}$O.

Large scale optical and infrared surveys have revealed numbers of accretion-derived stellar features within the halo of the Galaxy. These coherent tail-like features are produced by encounters with satellite dwarf galaxies. We conducted an SiO and H2O maser survey towards O-rich AGBs towards the orbital plane of the Sgr Stellar Stream from 2016. Up to now, maser emissions have been found from 60 sources, most of which are detected for the first time. However, their distances and kinematics suggest they are still disk stars.

We present GECKOS (Generalising Edge-on galaxies and their Chemical bimodalities, Kinematics, and Outflows out to Solar environments), a new ESO VLT/MUSE large program. The main aim of GECKOS is to reveal the variation in key physical processes of disk formation by connecting Galactic Archaeology with integral field spectroscopic observations of nearby galaxies. Edge-on galaxies are ideal for this task: they allow us to disentangle the assembly history imprinted in thick disks and provide the greatest insights into outflows. The GECKOS sample of 35 nearby edge-on disk galaxies is designed to trace the assembly histories and properties of galaxies across a large range of star formation rates, bulge-to-total ratios, and boxy and non-boxy bulges. GECKOS will deliver spatially resolved measurements of stellar abundances, ages, and kinematics, as well as ionised gas metallicities, ionisation param- eters, pressure, and inflow and outflow kinematics; all key parameters for building a complete chemodynamical picture of disk galaxies. With these data, we aim to extend Galactic analysis methods to the wider galaxy population, reaping the benefits of detailed Milky Way studies, while probing the diverse mechanisms of galaxy evolution.

The discovery of new clear windows in the Galactic plane using the VVV near-IR extinction maps allows the study of the structure of the Milky Way (MW) disk. The ultimate goal of this work is to map the spiral arms in the far side of the MW, which is a relatively unexplored region of our Galaxy, using red clump (RC) giants as distance indicators. We search for near-IR clear windows located at low Galactic latitudes ( $|b|< 1$ deg) in the MW disk using the VVV near-IR extinction maps. We have identified two new windows named VVV WIN 1607–5258 and VVV WIN 1475–5877, respectively, that complement the previously known window VVV WIN 1713–3939. We analyse the distribution of RC stars in these three clear near-IR windows and measure their number density along the line of sight. This allows us to find overdensities in the distribution and measure their distances along the line of sight. We then use the VVV proper motions in order to measure the kinematics of the RC stars at different distances. We find enhancements in the distance distribution of RC giants in all the studied windows, interpreting them as the presence of spiral arms in the MW disk. These structures are absent in the current models of synthetic population for the same MW lines of sight. We were able to trace the end of the Galactic bar, the Norma arm, as well as the Scutum–Centaurus arm in the far disk. Using the VVV proper motions, we measure the kinematics for these Galactic features, confirming that they share the bulk rotation of the Galactic disk.

At the time of this meeting, the latest Gaia data release is EDR3, published on 3 December 2020, but the next one, DR3, will appear soon, on 13 June 2022. This contribution describes, on the one hand, Gaia EDR3 results on massive stars and young stellar clusters, placing special emphasis on how a correct treatment of the astrometric and photometric calibration yields results that are simultaneously precise and accurate. On the other hand, it gives a brief description of the exciting results we can expect from Gaia DR3.

We use the AREPO numerical code to model the structure of a Milky Way like galaxy (MW) via a suite of simulations composed of a stellar disc and bulge, a dark matter halo, and a gaseous disc under isothermal conditions. For each model, we produce longitude velocity (l-v) maps of the gas surface densities to extract the skeletons of the main features (arms, bar), and the contours defining the terminal velocities of the gas. We compare these with observations via a number of diagnostic tools, and select the model that best reproduces the main observed features of the Milky Way.

To understand the physical properties of the interstellar medium (ISM) in various scales, we should investigate it with pc-scale resolution over kpc scale coverage. Here, we report the sub-kpc scale Gas Density Histogram (GDH) of the Milky Way. GDH is a histogram of averaged density and corresponds to the probability density distribution (PDF) of gas volume density. We use galactic plain survey data (l =10∘− 50∘) at 12CO and 13CO (J = 1 − 0) obtained as a part of the FOREST Unbiased Galactic plane Imaging survey with the Nobeyama 45m telescope (FUGIN). With this method and data, we are free from spatial structure and molecular cloud identification. GDH can be well fitted with single or double log-normal distribution; which we call as the low-density log-normal (L-LN) and high-density log-normal (H-LN) components. We found both the H-LN fraction (fH) and L-LN width (σL) along the gas density axis show a coherent structure on the longitude-velocity diagram. It suggests that there is a relationship between the ISM property and kpc scale structure in the Milky Way.

The velocity-space distribution of the solar neighborhood stars shows complex substructures (moving groups) including the well-known Hercules stream. Recently, the Gaia observation revealed their detailed structures, but their origins are still in debate. We analyzed a high-resolution N-body simulation of a Milky Way (MW)-like galaxy. To find velocity-space distributions similar to that of the solar neighborhood stars, we used Kullback-Leibler divergence (KLD), which is a metric to measure similarities between probability distributions. The KLD analysis shows the time evolution and the spatial variation of the velocity-space distribution. Velocity-space distributions with small KLDs (i.e. high similarities) are frequently but not always detected around in the simulated MW. In the velocity-map with smallest KLD, the velocity-space substructures are made from bar resonances.

In the efforts to map the Milky Way structure, the central regions have remained very difficult to probe. The VISTA Variables in the Vía Láctea Survey (VVV) is a near-IR variability Survey that scans 560 sq.deg. across the Milky Way bulge and an adjacent section of the southern mid-plane. The main goal of the VVV Survey is to build a 3D map of the structure of the inner Galaxy and characterize its stellar populations. This survey has discovered different kinds of objects, such as globular clusters, Microlensing events, RR Lyrae stars, Cepheids, WITs, among others. The extension of the Survey (VVVX) is observing until 2020, tripling the areal coverage, and complementing the variability studies done by the VVV Survey.

The unprecedented amount and accuracy of kinematic data from the second release of the Gaia mission have started revolutionizing our understanding of the dynamics of the Milky Way disk. The detailed stellar velocity field in the Galactic disk should allow us to constrain with unprecedented precision the parameters of the non-axisymmetric modes of the disk. We present here the status of our current modelling efforts in this area, and their implication on the dynamics of the Galactic bar in particular.

Whiting 1 is a faint and young globular cluster embedded in the Sag dSph. It has similar distance, metalicity and radial velocity with the trailing stream of the Sag. Due to these special properties, Whiting 1 was suggested to be associated with the trailing stream of Sag. However, its origin is still unclear and further investigation of its relation with Sgr dSph is needed. In this work, we use DECaLS data to search the tidal tail of Whiting 1, with the aim of looking for spatial connection between Whiting 1 and Sgr dSph. With Matched Filter method, we detected a tidal tail around the main body of Whiting 1. This tail extends to at least 0.5 degree and aligns with the mean orbit direction of Sgr dSph. This tail is newly detected and it provides additional evidence of the association between Whiting 1 and Sgr trailing stream.

We have derived absolute proper motions of stars in the Galactic bulge region combining the VVV InfraRed Astrometric Catalogue (VIRAC) and Gaia. We use the proper motions to study the kinematic structure of the bulge both integrated along the line-of-sight and in magnitude intervals using red clump stars as standard candles. In parallel we compare to a made-to-measure barred dynamical model, folding in the VIRAC selection function, to understand and interpret the structures that we observe. The barred dynamical model, which contains a boxy/peanut bulge, and has a pattern speed of 37.5 kms−1 kpc−1, is able to reproduce all structures impressively well.

In order to study the most reddened areas of the Milky Way we used near-IR data from the VVV Survey. For the first time, the VISTA telescope allows us to observe the mid-plane through the Galactic bulge and study the disk in the other side of the Milky Way. Motivated by the detection of hundreds of microlensing events in the inner regions of the Galaxy, we propose three new configurations of microlensing events, placing the sources in the far-disk and the lenses in the far-disk/bulge/near-disk. These new configurations will change the usual way to interpret the timescale distributions due to the different populations along the line of sight, that exhibit varied transverse velocities and relative distances.

Classical Cepheids and RR Lyrae-type variable stars are widely-used tracers of young (< 300 Myr) and old (> 10 Gyr) stellar populations, respectively. These stars also serve as distance indicators allowing for Galactic structure studies. Robust detection of pulsating variables requires precise and relatively frequent observations over several years. Recently, the OGLE survey has discovered nearly 1,300 new genuine classical Cepheids and 15,000 RR Lyrae stars along the southern Galactic plane. Here, we present the picture of the Milky Way’s thin disk drawn with the Cepheids and the view of the Galactic old population that emerges from the set of known RR Lyrae stars.

The on-going phase mixing in the vertical direction of the Galactic disk has been discovered with the revolutionary Gaia DR2 data. It manifests itself as the snail shell in the Z–Vz phase space. To better understand the origin and properties of the phase mixing process, we study the phase-mixing signatures in moving groups (also known as the kinematic streams) with the Gaia DR2 data in the Galactic disk near the Solar circle. Interestingly, the phase space snail shell exists only in the main kinematic streams with |VR|≲ 50 km/s and |Vφ –VLSR|≲30 km/s, i.e., stars on dynamically “colder” orbits. Compared to the colder orbits, the hotter orbits may have phase-wrapped away already due to the much larger dynamical range in radial variation to facilitate faster phase mixing. These results help put tighter constraints on the vertical perturbation history of the Milky Way disk. To explain the lack of a well-defined snail shell in the hotter orbits, the disk should have been perturbed at least ∼400–500 Myr ago. Our results offer more support to the recent satellite-disk encounter scenario than the internal bar buckling perturbation scenario as the origin of the phase space mixing.

Stellar surveys and dynamical models have recently led to important progress on understanding the dynamical structure of the Milky Way’s bar and central box/peanut bulge. This talk briefly reviews the density structure of the bulge and bar from star count tomography, the cylindrical rotation of bulge stars, and the measurements of their stellar masses and pattern speed that have been obtained by fitting dynamical models to the combined star count and line-of-sight velocity data. Recent work deriving absolute proper motions throughout the bulge from the VIRAC survey and Gaia has led to a new 3D measurement of the barred bulge kinematics which is expected to greatly improve the dynamical models, and has already confirmed the relatively slow pattern speed (∼40 kms−1 kpc−1) obtained from the previous dynamical and gas-dynamical modelling.

We present new results on the Galactic bar/bulge transverse velocity structure using Gaia and the VISTA Variables in Via Lactea (VVV) survey. Gaia is complemented in high extinction regions by the multi-epoch infrared VVV observations for which derived relative proper motions can be tied to Gaia’s absolute frame. We extract kinematic maps (both 2D and 3D) of the Galactic bar/bulge, from which we measure the pattern speed of the bar using a novel technique. We focus on the evidence of an X-shaped bulge from the kinematic maps.

A recently discovered young, high-velocity giant star J01020100-7122208 is a good candidate of hypervelocity star ejected from the Galactic center, although it has a bound orbit. If we assume that this star was ejected from the Galactic center, it can be used to constrain the Galactic potential, because the deviation of its orbit from a purely radial orbit informs us of the torque that this star has received. Based on this assumption, we estimate the flattening of the Galactic dark matter halo by using the Gaia DR2 data and the circular velocity data. Our Bayesian analysis shows that the orbit of J01020100-7122208 favors a prolate halo within ~ 10 kpc from the Galactic center. The posterior distribution of the density flattening q shows a broad distribution at q ≳ 1 and peaks at q ≃ 1.5. Also, 98.5% of the posterior distribution is located at q > 1, highly disfavoring an oblate halo.

We have collected 2330 Cepheids to establish an intuitive 3D map of the Milky Way’s disk. As regards the warp amplitude, the Cepheid disk agrees well with the gas disk for radii up to 15 kpc. However, the mean line of nodes (LON) of the Cepheid disk deviates from the Galactic Center–Sun direction by 17.5±1.0°. This is a new and different result compared with previous results. The LON is not stable at any given radius, but it twists. The twisted pattern suggests that the formation of the Milky Way’s warp is dominated by the massive inner disk. The kinematic warp defined by the Cepheids is also in concordance with the spatial warp. In the 2020 era, the anticipated increasing number of new Cepheids will provide a key opportunity to view our Milky Way’s disk as a whole, and we expect that our knowledge of the disk’s main structural features will be much improved.

In the context of the STRucture and Evolution of the GAlaxy survey, we describe the preliminary results obtained for the fields around the globular cluster Pal 3 (about 2.75 square degrees), by exploiting the obtained g, r, i time series photometry. The final aim is to use variable stars as tools to verify and study the presence of streams around Pal 3. We found 20 candidate variable stars of which 7 RR Lyrae stars possibly belonging to Pal 3, also at large distance from the center. The distribution of the candidate RR Lyrae seems to confirm a preferential distribution in the north-east direction, confirming previous results in literature.