Tag Archives: Gaia

Dynamics in the Galactic disk explaining radial and vertical velocities

Context: In our Paper I, by using statistical deconvolution methods, extended kinematics maps of Gaia-DR2 data have been produced in a range of heliocentric distances that are a factor of two to three larger than those analyzed previously by the Gaia Collaboration with the same data. It added the range of Galactocentric distances between 13 kpc and 20 kpc to the previous maps.
Aims: Here, we investigate the dynamical effects produced by different mechanisms that can explain the radial and vertical components of these extended kinematic maps, including a decomposition of bending and breathing of the vertical components. This paper as a whole tries to be a compendium of different dynamical mechanisms whose predictions can be compared to the kinematic maps.
Methods: Using analytical methods or simulations, we are able to predict the main dynamical factors and compare them to the predictions of the extended kinematic maps of Gaia-DR2.
Results: The gravitational influence of Galactic components that are different from the disk, such as the long bar or bulge, the spiral arms, or a tidal interaction with Sagittarius dwarf galaxy, may explain some features of the velocity maps, especially in the inner parts of the disk. However, they are not sufficient in explaining the most conspicuous gradients in the outer disk. Vertical motions might be dominated by external perturbations or mergers, although a minor component may be due to a warp whose amplitude evolves with time. Here, we show with two different methods, which analyze the dispersion of velocities, that the mass distribution of the disk is flared. Despite these partial explanations, the main observed features can only be explained in terms of out-of-equilibrium models, which are either due to external perturbers or to the fact that the disk has not had time to reach equilibrium since its formation.

Comments: 15 pages, 14 figures, accepted to be published in A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2001.05455 [astro-ph.GA]
(or arXiv:2001.05455v1 [astro-ph.GA] for this version)

Intervista su La Repubblica

Diapositiva1“In questi anni – spiega Francesco Sylos Labini, ricercatore del Cnr-Isc – la missione Gaia, un satellite dell’Agenzia spaziale europea progettato per indagare origine, evoluzione e struttura della Via Lattea, sta compiendo misurazioni astrometriche di altissima precisione, determinando la posizione di oltre un miliardo di stelle sulle quali è stato appena pubblicato il data release 2, il più grande e accurato censimento di informazioni quali posizioni, velocità e altre proprietà stellari. In particolare, è ora possibile esplorare lo spazio delle fasi (posizioni e velocità) di oltre sei milioni di stelle nel disco della Via Lattea. Le mappe delle velocità stellari pubblicate da Gaia coprono una distanza fino a 12 kilopaserc (kpc), unità di misura impiegata in astronomia per indicare la distanza fra oggetti celesti. Noi siamo stati in grado di estenderle fino a 20 kpc, tre volte in più rispetto alle mappe ufficiali, utilizzando una ricostruzione statistica della distanza”. – I ricercatori hanno quindi misurato deviazioni significative dalla circolarità nelle orbite medie delle stelle del disco della Via Lattea, insieme a un gradiente di velocità radiale di circa 40 km/s e di un gradiente di velocità verticale di 20 km/s.

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CNR COMUNICATO STAMPA 96/2018: La Via Lattea non è in equilibrio

46310467_10155856872102727_1616626076761456640_oLe stelle della nostra galassia dovrebbero girare intorno al nucleo con un moto di rotazione in equilibrio dinamico. Un team internazionale, cui partecipano ricercatori del Cnr-Isc, analizzando i dati del satellite Gaia, ha ottenuto le più estese mappe di velocità delle stelle della nostra galassia, che mettono in discussione l’ipotesi che le stelle ruotino con soli moti circolari. Sono stati, infatti, rivelati moti radiali e verticali e differenze nella velocità di rotazione in diverse zone stellari. Lo studio, pubblicato su Astronomy and Astrophysics, induce a rivedere anche le stime sulla materia oscura

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Gaia-DR2 extended kinematical maps. Part I: Method and application

Fig8a
CONTEXT. The Gaia Collaboration has used Gaia-DR2 sources with six-dimensional (6D) phase space information to derive kinematical maps within 5 kpc of the Sun, which is a reachable range for stars with relative error in distance lower than 20%.
AIMS. Here we aim to extend the range of distances by a factor of two to three, thus adding the range of Galactocentric distances between 13 kpc and 20 kpc to the previous maps, with their corresponding error and root mean square values.
METHODS. We make use of the whole sample of stars of Gaia-DR2 including radial velocity measurements, which consists in more than seven million sources, and we apply a statistical deconvolution of the parallax errors based on the Lucy’s inversion method of the Fredholm integral equations of the first kind, without assuming any prior.
RESULTS. The new extended maps provide lots of new and corroborated information about the disk kinematics: significant departures of circularity in the mean orbits with radial Galactocentric velocities between -20 and +20 km/s and vertical velocities between -10 and +10 km/s; variations of the azimuthal velocity with position; asymmetries between the northern and the southern Galactic hemispheres, especially towards the anticenter that includes a larger azimuthal velocity in the south; and others.
CONCLUSIONS. These extended kinematical maps can be used to investigate the different dynamical models of our Galaxy, and we will present our own analyses in the forthcoming second part of this paper. At present, it is evident that the Milky Way is far from a simple stationary configuration in rotational equilibrium, but is characterized by streaming motions in all velocity components with conspicuous velocity gradients.
Comments: 19 pages, 16 figures, accepted to be published in Astronomy and Astrophysics in the press; data of Figs. 8-12 and 16 publicly available
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:1810.13436 [astro-ph.GA]
(or arXiv:1810.13436v1 [astro-ph.GA] for this version)