scholarly journals The Milky Way’s disc of classical satellite galaxies in light of Gaia DR2

2019 ◽  
Vol 491 (2) ◽  
pp. 3042-3059 ◽  
Author(s):  
Marcel S Pawlowski ◽  
Pavel Kroupa
Keyword(s):  
Wide Distribution ◽  
Independent Data ◽  
Proper Motions ◽  
Underlying Distribution ◽  
Satellite Systems ◽  
Angular Momenta ◽  
Recent Group ◽  
Satellite Galaxies ◽  
Gaia Dr2 ◽  
True Correlation

ABSTRACT We study the correlation of orbital poles of the 11 classical satellite galaxies of the Milky Way, comparing results from previous proper motions with the independent data by Gaia DR2. Previous results on the degree of correlation and its significance are confirmed by the new data. A majority of the satellites co-orbit along the Vast Polar Structure, the plane (or disc) of satellite galaxies defined by their positions. The orbital planes of eight satellites align to <20° with a common direction, seven even orbit in the same sense. Most also share similar specific angular momenta, though their wide distribution on the sky does not support a recent group infall or satellites-of-satellites origin. The orbital pole concentration has continuously increased as more precise proper motions were measured, as expected if the underlying distribution shows true correlation that is washed out by observational uncertainties. The orbital poles of the up to seven most correlated satellites are in fact almost as concentrated as expected for the best-possible orbital alignment achievable given the satellite positions. Combining the best-available proper motions substantially increases the tension with ΛCDM cosmological expectations: <0.1 per cent of simulated satellite systems in IllustrisTNG contain seven orbital poles as closely aligned as observed. Simulated systems that simultaneously reproduce the concentration of orbital poles and the flattening of the satellite distribution have a frequency of <0.1 per cent for any number of k > 3 combined orbital poles, indicating that these results are not affected by a look-elsewhere effect. This compounds the Planes of Satellite Galaxies Problem.

scholarly journals Gaia EDR3 Proper Motions of Milky Way Dwarfs. II Velocities, Total Energy, and Angular Momentum

2021 ◽  
Vol 922 (2) ◽  
pp. 93
Author(s):  
Francois Hammer ◽  
Jianling Wang ◽  
Marcel S. Pawlowski ◽  
Yanbin Yang ◽  
Piercarlo Bonifacio ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Total Energy ◽  
Large Scale ◽  
Milky Way ◽  
Radial Velocities ◽  
Proper Motions ◽  
Satellite Systems ◽  
Angular Momenta ◽  
Total Energies ◽  
Mass Profile

Abstract Here we show that precise Gaia EDR3 proper motions have provided robust estimates of 3D velocities, angular momentum, and total energy for 40 Milky Way dwarfs. The results are statistically robust and are independent of the Milky Way mass profile. Dwarfs do not behave like long-lived satellites of the Milky Way because of their excessively large velocities, angular momenta, and total energies. Comparing them to other MW halo populations, we find that many are at first passage, ≤2 Gyr ago, i.e., more recent than the passage of Sagittarius, ∼4–5 Gyr ago. We suggest that this is in agreement with the stellar populations of all dwarfs, for which we find that a small fraction of young stars cannot be excluded. We also find that dwarf radial velocities contribute too little to their kinetic energy when compared to satellite systems with motions only regulated by gravity, and some other mechanism must be at work such as ram pressure. The latter may have preferentially reduced radial velocities when dwarf progenitors entered the halo until they lost their gas. It could also explain why most dwarfs lie near their pericenter. We also discover a novel large-scale structure perpendicular to the Milky Way disk, which is made by 20% of dwarfs orbiting or counter-orbiting with the Sagittarius dwarf.

scholarly journals Gaia DR2 reveals a very massive runaway star ejected from R136

2018 ◽  
Vol 619 ◽  
pp. A78 ◽  
Author(s):  
D. J. Lennon ◽  
C. J. Evans ◽  
R. P. van der Marel ◽  
J. Anderson ◽  
I. Platais ◽  
...  
Keyword(s):  
Lower Limit ◽  
Proper Motion ◽  
Evolutionary History ◽  
Massive Star ◽  
Position Angle ◽  
Proper Motions ◽  
Central Cluster ◽  
Dynamical Constraints ◽  
Runaway Stars ◽  
Gaia Dr2

A previous spectroscopic study identified the very massive O2 III star VFTS 16 in the Tarantula Nebula as a runaway star based on its peculiar line-of-sight velocity. We use the Gaia DR2 catalog to measure the relative proper motion of VFTS 16 and nearby bright stars to test if this star might have been ejected from the central cluster, R136, via dynamical ejection. We find that the position angle and magnitude of the relative proper motion (0.338±0.046 mas yr−1, or approximately 80±11 km s−1) of VFTS 16 are consistent with ejection from R136 approximately 1.5±0.2 Myr ago, very soon after the cluster was formed. There is some tension with the presumed age of VFTS 16 that, from published stellar parameters, cannot be greater than 0.9+0.3−0.2 Myr. Older ages for this star would appear to be prohibited due to the absence of He I lines in its optical spectrum, since this sets a firm lower limit on its effective temperature. The dynamical constraints may imply an unusual evolutionary history for this object, perhaps indicating it is a merger product. Gaia DR2 also confirms that another very massive star in the Tarantula Nebula, VFTS 72 (alias BI 253; O2 III-V(n)((f*)), is also a runaway on the basis of its proper motion as measured by Gaia. While its tangential proper motion (0.392±0.062 mas yr−1 or 93±15 km s−1) would be consistent with dynamical ejection from R136 approximately 1 Myr ago, its position angle is discrepant with this direction at the 2σ level. From their Gaia DR2 proper motions we conclude that the two ∼100 M⊙ O2 stars, VFTS 16 and VFTS 72, are fast runaway stars, with space velocities of around 100 km s−1 relative to R136 and the local massive star population. The dynamics of VFTS 16 are consistent with it having been ejected from R136, and this star therefore sets a robust lower limit on the age of the central cluster of ∼1.3 Myr.

scholarly journals Gaia DR2 proper motions of dwarf galaxies within 420 kpc

2018 ◽  
Vol 619 ◽  
pp. A103 ◽  
Author(s):  
T. K. Fritz ◽  
G. Battaglia ◽  
M. S. Pawlowski ◽  
N. Kallivayalil ◽  
R. van der Marel ◽  
...  
Keyword(s):  
Milky Way ◽  
Dwarf Galaxies ◽  
High Mass ◽  
Proper Motions ◽  
Proper Understanding ◽  
Satellite Problem ◽  
Cosmological Context ◽  
Good Consistency ◽  
Gaia Dr2 ◽  
Limited Accuracy

A proper understanding of the Milky Way (MW) dwarf galaxies in a cosmological context requires knowledge of their 3D velocities and orbits. However, proper motion (PM) measurements have generally been of limited accuracy and are available only for more massive dwarfs. We therefore present a new study of the kinematics of the MW dwarf galaxies. We use the Gaia DR2 for those dwarfs that have been spectroscopically observed in the literature. We derive systemic PMs for 39 galaxies and galaxy candidates out to 420 kpc, and generally find good consistency for the subset with measurements available from other studies. We derive the implied Galactocentric velocities, and calculate orbits in canonical MW halo potentials of low (0.8 × 1012 M⊙) and high mass (1.6 × 1012 M⊙). Comparison of the distributions of orbital apocenters and 3D velocities to the halo virial radius and escape velocity, respectively, suggests that the satellite kinematics are best explained in the high-mass halo. Tuc III, Crater II, and additional candidates have orbital pericenters small enough to imply significant tidal influences. Relevant to the missing satellite problem, the fact that fewer galaxies are observed to be near apocenter than near pericenter implies that there must be a population of distant dwarf galaxies yet to be discovered. Of the 39 dwarfs: 12 have orbital poles that do not align with the MW plane of satellites (given reasonable assumptions about its intrinsic thickness); 10 have insufficient PM accuracy to establish whether they align; and 17 satellites align, of which 11 are co-orbiting and (somewhat surprisingly, in view of prior knowledge) 6 are counter-orbiting. Group infall might have contributed to this, but no definitive association is found for the members of the Crater-Leo group.

scholarly journals Reconstruction of asteroid spin states from Gaia DR2 photometry

2018 ◽  
Vol 620 ◽  
pp. A91 ◽  
Author(s):  
J. Ďurech ◽  
J. Hanuš
Keyword(s):  
Rotation Period ◽  
Inversion Method ◽  
Triaxial Ellipsoid ◽  
Independent Data ◽  
Rotation Periods ◽  
Shape Models ◽  
Pole Parameter ◽  
Data Points ◽  
Sidereal Rotation ◽  
Gaia Dr2

Context. In addition to stellar data, Gaia Data Release 2 (DR2) also contains accurate astrometry and photometry of about 14 000 asteroids covering 22 months of observations. Aims. We used Gaia asteroid photometry to reconstruct rotation periods, spin axis directions, and the coarse shapes of a subset of asteroids with enough observations. One of our aims was to test the reliability of the models with respect to the number of data points and to check the consistency of these models with independent data. Another aim was to produce new asteroid models to enlarge the sample of asteroids with known spin and shape. Methods. We used the lightcurve inversion method to scan the period and pole parameter space to create final shape models that best reproduce the observed data. To search for the sidereal rotation period, we also used a simpler model of a geometrically scattering triaxial ellipsoid. Results. By processing about 5400 asteroids with at least 10 observations in DR2, we derived models for 173 asteroids, 129 of which are new. Models of the remaining asteroids were already known from the inversion of independent data, and we used them for verification and error estimation. We also compared the formally best rotation periods based on Gaia data with those derived from dense lightcurves. Conclusions. We show that a correct rotation period can be determined even when the number of observations N is less than 20, but the rate of false solutions is high. For N > 30, the solution of the inverse problem is often successful and the parameters are likely to be correct in most cases. These results are very promising because the final Gaia catalogue should contain photometry for hundreds of thousands of asteroids, typically with several tens of data points per object, which should be sufficient for reliable spin reconstruction.

scholarly journals Measuring proper motions of galactic dwarf galaxies with Hubble Space Telescope

2007 ◽  
Vol 3 (S248) ◽  
pp. 244-247 ◽  
Author(s):  
S. Piatek ◽  
C. Pryor
Keyword(s):  
Research Group ◽  
Dwarf Galaxies ◽  
Hubble Space Telescope ◽  
Proper Motions ◽  
Future Directions ◽  
Space Telescope ◽  
The Past ◽  
Scientific Justification ◽  
Satellite Galaxies ◽  
Using Data

AbstractOver the past several years, our research group has been measuring proper motions for nearby dwarf satellite galaxies using data taken with the Hubble Space Telescope. In order to measure proper motions with an expected size of several tens of milliarcseconds per century using a time baseline of 2-4 years, our work required that positions of stars and QSOs be measured to an accuracy of ~0.25 mas (~0.005 pixel). This contribution reviews the scientific justification of this work and our methodology. It concludes with a few general results and future directions.

scholarly journals Prediction of stellar occultations by distant solar system bodies in the Gaia era

2017 ◽  
Vol 12 (S330) ◽  
pp. 382-385
Author(s):  
Josselin Desmars ◽  
Julio Camargo ◽  
Bruno Sicardy ◽  
Felipe Braga-Ribas ◽  
Roberto Vieira-Martins ◽  
...  
Keyword(s):  
Solar System ◽  
Orbit Determination ◽  
Proper Motions ◽  
Close Vicinity ◽  
Gaia Dr1 ◽  
Solar System Objects ◽  
Stellar Occultations ◽  
Solar System Bodies ◽  
Transneptunian Objects ◽  
Gaia Dr2

AbstractStellar occultations are a unique technique to access physical characteristics of distant solar system objects from the ground. They allow the measure of the size and the shape at kilometric level, the detection of tenuous atmospheres (few nanobars), and the investigation of close vicinity (satellites, rings) of Transneptunian objects and Centaurs. This technique is made successful thanks to accurate predictions of occultations. Accuracy of the predictions depends on the uncertainty in the position of the occulted star and the object's orbit. The Gaia stellar catalogue (Gaia Collaboration (2017)) now allows to get accurate astrometric stellar positions (to the mas level). The main uncertainty remains on the orbit. In this context, we now take advantage of the NIMA method (Desmars et al.(2015)) for the orbit determination and of the Gaia DR1 catalogue for the astrometry. In this document, we show how the orbit determination is improved by reducing current and some past observations with Gaia DR1. Moreover, we also use more than 45 past positive occultations observed in the 2009-2017 period to derive very accurate astrometric positions only depending on the position of the occulted stars (about few mas with Gaia DR1). We use the case of (10199) Chariklo as an illustration. The main limitation lies in the imprecision of the proper motions which is going to be solved by the Gaia DR2 release.

Investigation of relative motion in the triple system ADS 48 on the basis of Gaia DR2 and Pulkovo 26-inch refractor observations

2021 ◽  
pp. 89-98
Author(s):  
O. V. KIYAEVA ◽  
R. YA. ZHUCHKOV ◽  
I.S. IZMAILOV
Keyword(s):  
High Precision ◽  
Relative Motion ◽  
Apparent Motion ◽  
Triple System ◽  
Radial Velocities ◽  
Proper Motions ◽  
The Family ◽  
Outer Pair ◽  
Motion Parameters ◽  
Gaia Dr2

There are high-precision positions, proper motions, parallaxes and radial velocities at the instant 2015.5 for all three components of the star ADS 48 ABF in the catalogue Gaia DR2 (2018). According to these data relative motions and the family of orbits were calculated by the Apparent Motion Parameters (AMP) method (Kiselev and Kiyaeva, 1980), and the best orbit was chosen for the inner pair AB. A perturbation with the period of 11 years was discovered according to Pulkovo observations of the outer pair. The reasons for the perturbation are discussed.

scholarly journals Characterizing dynamical stages of open clusters located in the Sagittarius spiral arm

2019 ◽  
Vol 488 (2) ◽  
pp. 1635-1651 ◽  
Author(s):  
M S Angelo ◽  
A E Piatti ◽  
W S Dias ◽  
F F S Maia
Keyword(s):  
Structural Parameters ◽  
Three Dimensional ◽  
Dynamical Evolution ◽  
Open Clusters ◽  
Mass Star ◽  
Proper Motions ◽  
Concentration Parameter ◽  
Low Mass ◽  
Gaia Dr2 ◽  
Spiral Arm

Abstract The study of dynamical properties of Galactic open clusters (OCs) is a fundamental prerequisite for the comprehension of their dissolution processes. In this work, we characterized 12 OCs, namely: Collinder 258, NGC 6756, Czernik 37, NGC 5381, Ruprecht 111, Ruprecht 102, NGC 6249, Basel 5, Ruprecht 97, Trumpler 25, ESO 129−SC32, and BH 150, projected against dense stellar fields. In order to do that, we employed Washington CT1 photometry and Gaia DR2 astrometry, combined with a decontamination algorithm applied to the three-dimensional astrometric space of proper motions and parallaxes. From the derived membership likelihoods, we built decontaminated colour–magnitude diagrams, while structural parameters were obtained from King profiles fitting. Our analysis revealed that they are relatively young OCs (log(t  yr−1) ∼7.3–8.6), placed along the Sagittarius spiral arm, and at different internal dynamical stages. We found that the half-light radius to Jacobi radius ratio, the concentration parameter and the age to relaxation time ratio describe satisfactorily their different stages of dynamical evolution. Those relative more dynamically evolved OCs have apparently experienced more important low-mass star loss.

scholarly journals Prediction of astrometric microlensing events from Gaia DR2 proper motions

2018 ◽  
Vol 620 ◽  
pp. A175 ◽  
Author(s):  
J. Klüter ◽  
U. Bastian ◽  
M. Demleitner ◽  
J. Wambsganss
Keyword(s):  
Proper Motion ◽  
Proper Motions ◽  
Stellar Objects ◽  
Gravitational Microlensing ◽  
Data Release ◽  
The Future ◽  
Nested Intervals ◽  
Excellent Tool ◽  
Gaia Dr2

Context. Astrometric gravitational microlensing is an excellent tool to determine the mass of stellar objects. Using precise astrometric measurements of the lensed position of a background source in combination with accurate predictions of the positions of the lens and the unlensed source it is possible to determine the mass of the lens with an accuracy of a few percent. Aims. Making use of the recently published Gaia Data Release 2 (DR2) catalogue, we want to predict astrometric microlensing events caused by foreground stars with high proper motion passing a background source in the coming decades. Results. We selected roughly 148 000 high-proper-motion stars from Gaia DR2 with μtot > 150 mas yr−1 as potential lenses. We then searched for background sources close to their paths. Using the astrometric parameters of Gaia DR2, we calculated the future positions of source and lens. With a nested-intervals algorithm we determined the date and separation of the closest approach. Using Gaia DR2 photometry we determined an approximate mass of the lens, which we used to calculate the expected microlensing effects. Conclusions. We predict 3914 microlensing events caused by 2875 different lenses between 2010 and 2065, with expected shifts larger than 0.1 mas between the lensed and unlensed positions of the source. Of those, 513 events are expected to happen between 2014.5 and 2026.5 and might be measured by Gaia. For 127 events we also expect a magnification between 1 mmag and 3 mag.

scholarly journals The mass of our Galaxy from satellite proper motions in the Gaia era

2020 ◽  
Vol 494 (4) ◽  
pp. 5178-5193 ◽  
Author(s):  
T K Fritz ◽  
A Di Cintio ◽  
G Battaglia ◽  
C Brook ◽  
S Taibi
Keyword(s):  
Milky Way ◽  
Anisotropy Parameter ◽  
Large Magellanic Cloud ◽  
Mass Determination ◽  
Proper Motions ◽  
Radial Density ◽  
Full Sample ◽  
Scale Free ◽  
Virial Mass ◽  
Gaia Dr2

ABSTRACT We use Gaia DR2 systemic proper motions of 45 satellite galaxies to constrain the mass of the Milky Way using the scale-free mass estimator of Watkins et al. (2010). We first determine the anisotropy parameter β, and the tracer satellites’ radial density index γ to be β = $-0.67^{+0.45}_{-0.62}$ and γ = 2.11 ± 0.23. When we exclude possible former satellites of the Large Magellanic Cloud, the anisotropy changes to β = $-0.21^{+0.37}_{-0.51}$. We find that the index of the Milky Way’s gravitational potential α, which is dependent on the mass itself, is the parameter with the largest impact on the mass determination. Via comparison with cosmological simulations of Milky Way-like galaxies, we carried out a detailed analysis of the estimation of the observational uncertainties and their impact on the mass estimator. We found that the mass estimator is biased when applied naively to the satellites of simulated Milky Way haloes. Correcting for this bias, we obtain for our Galaxy a mass of $0.58^{+0.15}_{-0.14}\times 10^{12}$ M⊙ within 64 kpc, as computed from the inner half of our observational sample, and $1.43^{+0.35}_{-0.32}\times 10^{12}$ M⊙ within 273 kpc, from the full sample; this latter value extrapolates to a virial mass of $M_\mathrm{vir\, \Delta =97}=1.51^{+0.45}_{-0.40} \times 10^{12}\,{\rm M}_{\odot }$ corresponding to a virial radius of Rvir = 308 ± 29 kpc. This value of the Milky Way mass lies in-between other mass estimates reported in the literature, from various different methods.

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