Context. Gaia DR2 has delivered full-sky six-dimensional measurements for millions of stars, and the quest to understand the dynamics of our Galaxy has entered a new phase. Aims. Our aim is to reveal ...and characterise the kinematic substructure of the different Galactic neighbourhoods, to form a picture of their spatial evolution that can be used to infer the Galactic potential, its evolution, and its components. Methods. We take approximately 5 million stars in the Galactic disk from the Gaia DR2 catalogue and build the velocity distribution in different Galactic neighbourhoods distributed along 5 kpc in Galactic radius and azimuth. We decompose their distribution of stars in the VR–Vϕ plane with the wavelet transformation and asses the statistical significance of the structures found. Results. We detect distinct kinematic substructures (arches and more rounded groups) that diminish their azimuthal velocity as a function of Galactic radius in a continuous way, connecting volumes up to 3 kpc apart in some cases. The average rate of decrease is ∼23 km s−1 kpc−1. In azimuth, the variations are much smaller. We also observe different behaviours: some approximately conserve their vertical angular momentum with radius (e.g. Hercules), while others seem to have nearly constant kinetic energy (e.g. Sirius). These two trends are consistent with the approximate predictions of resonances and phase mixing, respectively. Besides, the overall spatial evolution of Hercules is consistent with being related to the outer Lindblad resonance of the Galactic bar. In addition, we detect new kinematic structures that only appear at either inner or outer Galactic radius, different from the solar neighbourhood. Conclusions. The strong and distinct variation observed for each kinematic substructure with position in the Galaxy, along with the characterisation of extrasolar moving groups, will allow to better model the dynamical processes affecting the velocity distributions.
Combining the precise parallaxes and optical photometry delivered by Gaia’s second data release with the photometric catalogues of Pan-STARRS1, 2MASS, and AllWISE, we derived Bayesian stellar ...parameters, distances, and extinctions for 265 million of the 285 million objects brighter than G = 18. Because of the wide wavelength range used, our results substantially improve the accuracy and precision of previous extinction and effective temperature estimates. After cleaning our results for both unreliable input and output data, we retain 137 million stars, for which we achieve a median precision of 5% in distance, 0.20 mag in V-band extinction, and 245 K in effective temperature for G ≤ 14, degrading towards fainter magnitudes (12%, 0.20 mag, and 245 K at G = 16; 16%, 0.23 mag, and 260 K at G = 17, respectively). We find a very good agreement with the asteroseismic surface gravities and distances of 7000 stars in the Kepler, K2-C3, and K2-C6 fields, with stellar parameters from the APOGEE survey, and with distances to star clusters. Our results are available through the ADQL query interface of the Gaia mirror at the Leibniz-Institut für Astrophysik Potsdam (gaia.aip.de) and as binary tables at data.aip.de. As a first application, we provide distance- and extinction-corrected colour-magnitude diagrams, extinction maps as a function of distance, and extensive density maps. These demonstrate the potential of our value-added dataset for mapping the three-dimensional structure of our Galaxy. In particular, we see a clear manifestation of the Galactic bar in the stellar density distributions, an observation that can almost be considered direct imaging of the Galactic bar.
The evolution of the Milky Way disk, which contains most of the stars in the Galaxy, is affected by several phenomena. For example, the bar and the spiral arms of the Milky Way induce radial ...migration of stars
and can trap or scatter stars close to orbital resonances
. External perturbations from satellite galaxies can also have a role, causing dynamical heating of the Galaxy
, ring-like structures in the disk
and correlations between different components of the stellar velocity
. These perturbations can also cause 'phase wrapping' signatures in the disk
, such as arched velocity structures in the motions of stars in the Galactic plane. Some manifestations of these dynamical processes have already been detected, including kinematic substructure in samples of nearby stars
, density asymmetries and velocities across the Galactic disk that differ from the axisymmetric and equilibrium expectations
, especially in the vertical direction
, and signatures of incomplete phase mixing in the disk
. Here we report an analysis of the motions of six million stars in the Milky Way disk. We show that the phase-space distribution contains different substructures with various morphologies, such as snail shells and ridges, when spatial and velocity coordinates are combined. We infer that the disk must have been perturbed between 300 million and 900 million years ago, consistent with estimates of the previous pericentric passage of the Sagittarius dwarf galaxy. Our findings show that the Galactic disk is dynamically young and that modelling it as time-independent and axisymmetric is incorrect.
The Galactic warp revealed by Gaia DR2 kinematics Poggio, E; Drimmel, R; Lattanzi, M G ...
Monthly notices of the Royal Astronomical Society. Letters,
11/2018, Letnik:
481, Številka:
1
Journal Article
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ABSTRACT Using Gaia DR2 astrometry, we map the kinematic signature of the Galactic stellar warp out to a distance of 7 kpc from the Sun. Combining Gaia DR2 and 2-Micron All Sky Survey photometry, we ...identify, via a probabilistic approach, $599 \, 494$ upper main sequence (UMS) stars and $12\, 616\, 068$ giants without the need for individual extinction estimates. The spatial distribution of the UMS stars clearly shows segments of the nearest spiral arms. The large-scale kinematics of both the UMS and giant populations show a clear signature of the warp of the Milky Way, apparent as a gradient of 5–6 km s−1 in the vertical velocities from 8 to 14 kpc in Galactic radius. The presence of the signal in both samples, which have different typical ages, suggests that the warp is a gravitationally induced phenomenon.
Context.
The
β
Pictoris moving group is one of the most well-known young associations in the solar neighbourhood and several members are known to host circumstellar discs, planets, and comets. ...Measuring its age precisely is essential to the study of several astrophysical processes, such as planet formation and disc evolution, which are strongly age-dependent.
Aims.
We aim to determine a precise and accurate dynamical traceback age for the
β
Pictoris moving group.
Methods.
Our sample combines the extremely precise
Gaia
DR2 astrometry with ground-based radial velocities measured in an homogeneous manner. We use an updated version of our algorithm to determine dynamical ages. The new approach takes into account a robust estimate of the spatial and kinematic covariance matrices of the association to improve the sample selection process and to perform the traceback analysis.
Results.
We estimate a dynamical age of 18.5
−2.4
+2.0
Myr for the
β
Pictoris moving group. We investigated the spatial substructure of the association at the time of birth and we propose the existence of a core of stars that is more concentrated. We also provide precise radial velocity measurements for 81 members of
β
Pic, including ten stars with the first determinations of their radial velocities.
Conclusions.
Our dynamical traceback age is three times more precise than previous traceback age estimates and, more importantly, for the first time it reconciles the traceback age with the most recent estimates of other dynamical, lithium depletion boundaries and isochronal ages. This has been possible thanks to the excellent astrometric and spectroscopic precisions, the homogeneity of our sample, and the detailed analysis of binaries and membership.
Aims.
We aim to measure the proper motion along the Sagittarius stream, which is the missing piece in determining its full 6D phase space coordinates.
Methods.
We conduct a blind search of ...over-densities in proper motion from the
Gaia
second data release in a broad region around the Sagittarius stream by applying wavelet transform techniques.
Results.
We find that for most of the sky patches, the highest intensity peaks delineate the path of the Sagittarius stream. The 1500 peaks identified depict a continuous sequence spanning almost 2
π
in the sky, only obscured when the stream crosses the Galactic disk. Altogether, around 100 000 stars potentially belong to the stream as indicated by a coarse inspection of the color-magnitude diagrams. From these stars, we determine the proper motion along the Sagittarius stream, making it the proper-motion sequence with the largest span and continuity ever measured for a stream. A first comparison with existing
N
-body models of the stream reveals some discrepancies, especially near the pericenter of the trailing arm and an underestimation of the total proper motion for the leading arm.
Conclusions.
Our study provides a starting point for determining the variation of the population of stars along the stream, the distance to the stream from the red clump stars, and the solar motion. It also permits much more accurate measurement of the Milky Way potential.
Context.
The Sagittarius (Sgr) stream is one of the best tools that we currently have to estimate the mass and shape of our Galaxy. However, assigning membership and obtaining the phase-space ...distribution of the stars that form the tails of the stream is quite challenging.
Aims.
Our goal is to produce a catalogue of the RR Lyrae stars of Sgr and obtain an empiric measurement of the trends along the stream in sky position, distance, and tangential velocity.
Methods.
We generated two initial samples from the
Gaia
DR2 RR Lyrae catalogue: one selecting only the stars within ±20° of the orbital plane of Sagittarius (Strip), and the other resulting from application of the Pole Count Map (nGC3) algorithm. We then used the model-independent, deterministic method developed in this work to remove most of the contamination by detecting and isolating the stream in distance and proper motions.
Results.
The output is two empiric catalogues: the Strip sample (higher-completeness, lower-purity) which contains 11 677 stars, and the nGC3 sample (higher-purity, lower-completeness) with 6608 stars. We characterise the changes along the stream in all the available dimensions, namely the five astrometric dimensions plus the metallicity, covering more than 2
π
rad in the sky, and obtain new estimates for the apocentres and the mean Fe/H of the RR Lyrae population. Also, we show the first map of the two components of the tangential velocity thanks to the combination of distances and proper motions. Finally, we detect the bifurcation in the leading arm and report no significant difference between the two branches in terms of metallicity, kinematics, or distance.
Conclusions.
We provide the largest sample of RR Lyrae candidates of Sgr, which can be used as input for a spectroscopic follow-up or as a reference for the new generation of models of the stream through the interpolators in distance and velocity that we constructed.
Context. The structure and dynamics of the central bar of the Milky Way (MW) are still under debate whilst being fundamental ingredients for the evolution of our Galaxy. The recent Gaia DR3 offers an ...unprecedented detailed view of the 6D phase space of the MW, allowing for a better understanding of the complex imprints of the bar on the phase space. Aims. We aim to identify and characterise the dynamical moving groups across the MW disc, and use their large-scale distribution to help constrain the properties of the Galactic bar. Methods. We used 1D wavelet transforms of the azimuthal velocity ( V ϕ ) distribution in bins of radial velocity to robustly detect the kinematic substructure in the Gaia DR3 catalogue. We then connected these structures across the disc to measure the azimuthal ( ϕ ) and radial ( R ) gradients of V ϕ of the moving groups. We simulated thousands of perturbed distribution functions using backward integration, sweeping a large portion of parameter space of feasible Galaxy models that include a bar, in order to compare them with the data and to explore and quantify the degeneracies. Results. The radial gradient of the Hercules moving group (∂ V ϕ /∂ R = 28.1 ± 2.8 km s −1 kpc −1 ) cannot be reproduced by our simple models of the Galaxy that show much larger slopes both for a fast and a slow bar. This suggests the need for more complex dynamics (e.g. a different bar potential, spiral arms, a slowing bar, a complex circular velocity curve, external perturbations, etc.). We measured an azimuthal gradient for Hercules of ∂ V ϕ /∂ ϕ = −0.63 ± 0.13 km s −1 deg −1 and find that it is compatible with both the slow and fast bar models. Our analysis points out that in using this type of analysis, at least two moving groups are needed to start breaking the degeneracies. Conclusions. We conclude that it is not sufficient for a model to replicate the local velocity distribution; it must also capture its larger-scale variations. The accurate quantification of the gradients, especially in the azimuthal direction, will be key for the understanding of the dynamics governing the disc.
We present a catalogue of 362 million stellar parameters, distances, and extinctions derived from
Gaia
’s Early Data Release (EDR3) cross-matched with the photometric catalogues of Pan-STARRS1, ...SkyMapper, 2MASS, and AllWISE. The higher precision of the
Gaia
EDR3 data, combined with the broad wavelength coverage of the additional photometric surveys and the new stellar-density priors of the
StarHorse
code, allows us to substantially improve the accuracy and precision over previous photo-astrometric stellar-parameter estimates. At magnitude
G
= 14 (17), our typical precisions amount to 3% (15%) in distance, 0.13 mag (0.15 mag) in
V
-band extinction, and 140 K (180 K) in effective temperature. Our results are validated by comparisons with open clusters, as well as with asteroseismic and spectroscopic measurements, indicating systematic errors smaller than the nominal uncertainties for the vast majority of objects. We also provide distance- and extinction-corrected colour-magnitude diagrams, extinction maps, and extensive stellar density maps that reveal detailed substructures in the Milky Way and beyond. The new density maps now probe a much greater volume, extending to regions beyond the Galactic bar and to Local Group galaxies, with a larger total number density. We publish our results through an ADQL query interface (
gaia.aip.de
) as well as via tables containing approximations of the full posterior distributions. Our multi-wavelength approach and the deep magnitude limit render our results useful also beyond the next
Gaia
release, DR3.
Context.
Open clusters (OCs) trace the evolution of the Galactic disc with great accuracy.
Gaia
and large ground-based spectroscopic surveys make it possible to determine their properties and study ...their kinematics with unprecedented precision.
Aims.
We study the kinematical behaviour of the OC population over time. We take advantage of the latest age determinations of OCs to investigate the correlations of the 6D phase-space coordinates and orbital properties with age. The phase-space distribution, age-velocity relation, and action distribution are compared to those of field stars. We also investigate the rotation curve of the Milky Way traced by OCs, and we compare it to that of other observational or theoretical studies.
Methods.
We gathered nearly 30 000 radial velocity (RV) measurements of OC members from both
Gaia
-RVS data and ground-based surveys and catalogues. We computed the weighted mean RV, Galactic velocities, and orbital parameters of 1382 OCs. We investigated their distributions as a function of age and by comparison to field stars.
Results.
We provide the largest RV catalogue available for OCs, half of it based on at least three members. Compared to field stars, we note that OCs are not on exactly the same arches in the radial-azimuthal velocity plane, while they seem to follow the same diagonal ridges in the Galactic radial distribution of azimuthal velocities. Velocity ellipsoids in different age bins all show a clear anisotropy. The heating rate of the OC population is similar to that of field stars for the radial and azimuthal components, but it is significantly lower for the vertical component. The rotation curve drawn by our sample of clusters shows several dips that match the wiggles derived from nonaxisymmetric models of the Galaxy. From the computation of orbits, we obtain a clear dependence of the maximum height and eccentricity on age. Finally, the orbital characteristics of the sample of clusters as shown by the action variables follow the distribution of field stars. The additional age information of the clusters indicates some (weak) age dependence of the known moving groups.
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