The spiral pattern rotation speed of the Galaxy and the corotation radius with Gaia DR2

ABSTRACTWe report the identification of possible extended star debris candidates beyond the cluster tidal radius of NGC 6362 based on the second Gaia data release (Gaia DR2). We found 259 objects possibly associated with the cluster lying in the vicinity of the giant branch and 1–2 magnitudes fainter/brighter than the main-sequence turn-off in the cluster colour–magnitude diagram and which cover an area on the sky of ∼4.1 deg2 centred on the cluster. We traced back the orbit of NGC 6362 in a realistic Milky Way potential, using the gravpot16 package, for 3 Gyr. The orbit shows that the cluster shares similar orbital properties as the inner disc, having peri-/apogalactic distances, and maximum vertical excursion from the Galactic plane inside the corotation radius (CR), moving inwards from CR radius to visit the inner regions of the Milky Way. The dynamical history of the cluster reveals that it has crossed the Galactic disc several times in its lifetime and has recently undergone a gravitational shock, ∼15.9 Myr ago, suggesting that less than 0.1 per cent of its mass has been lost during the current disc-shocking event. Based on the cluster’s orbit and position in the Galaxy, we conclude that the possible extended star debris candidates are a combined effect of the shocks from the Galactic disc and evaporation from the cluster. Lastly, the evolution of the vertical component of the angular momentum shows that the cluster is strongly affected dynamically by the Galactic bar potential.

Download Full-text

The Distribution of Open Clusters in the Galaxy

Frontiers in Astronomy and Space Sciences ◽

10.3389/fspas.2021.656474 ◽

2021 ◽

Vol 8 ◽

Author(s):

Hektor Monteiro ◽

Douglas A. Barros ◽

Wilton S. Dias ◽

Jacques R. D. Lépine

Keyword(s):

Galactic Plane ◽

Rotation Velocity ◽

Open Clusters ◽

Space Distribution ◽

Proper Motions ◽

Corotation Radius ◽

The Galaxy ◽

Galactic Abundance ◽

Galactic Orbit ◽

Gaia Dr2

In this work we explore the new catalog of galactic open clusters that became available recently, containing 1,750 clusters that have been re-analyzed using the Gaia DR2 catalog to determine the stellar memberships. We used the young open clusters as tracers of spiral arms and determined the spiral pattern rotation speed of the Galaxy and the corotation radius, the strongest Galactic resonance. The sample of open clusters used here is increased by dozens of objects with respect to our previous works. In addition, the distances and ages values are better determined, using improvements to isochrone fitting and including an updated extinction polynomial for the Gaia DR2 photometric band-passes, and the Galactic abundance gradient as a prior for metallicity. In addition to the better age determinations, the catalog contains better positions in the Galactic plane and better proper motions. This allow us to discuss not only the present space distribution of the clusters, but also the space distribution of the clusters's birthplaces, obtained by integration of the orbits for a time equal to their age. The value of the rotation velocity of the arms (28.5 ± 1.0 km s−1 kpc−1) implies that the corotation radius (Rc) is close to the solar Galactic orbit (Rc/R0 = 1.01±0.08), which is supported by other observational evidence discussed in this text. A simulation is presented, illustrating the motion of the clusters in the reference frame of corotation. We also present general statistics of the catalog of clusters, like spatial distribution, distribution relative to height from the Galactic plane, and distribution of ages and metallicity. An important feature of the space distribution, the corotation gap in the gas distribution and its consequences for the young clusters, is discussed.

Download Full-text

The pattern speed of the Milky Way bar from transverse velocities

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1827 ◽

2019 ◽

Vol 488 (4) ◽

pp. 4552-4564 ◽

Cited By ~ 28

Author(s):

Jason L Sanders ◽

Leigh Smith ◽

N Wyn Evans

Keyword(s):

Proper Motion ◽

Transverse Velocity ◽

Galactic Centre ◽

Complete Coverage ◽

Motion Data ◽

Corotation Radius ◽

The Galaxy ◽

Pattern Speed ◽

Peculiar Motion ◽

Gaia Dr2

ABSTRACT We use the continuity equation to derive a method for measuring the pattern speed of the Milky Way’s bar/bulge from proper motion data. The method has minimal assumptions but requires complete coverage of the non-axisymmetric component in two of the three Galactic coordinates. We apply our method to the proper motion data from a combination of Gaia DR2 and VISTA Variables in the Via Lactea (VVV) to measure the pattern speed of the bar as $\Omega _\mathrm{p}=(41\pm 3)\, \mathrm{km\, s^{-1}\, kpc^{-1}}$ (where the error is statistical). This puts the corotation radius at $(5.7\pm 0.4)\, \mathrm{kpc}$, under the assumptions of the standard peculiar motion of the Sun and the absence of non-axisymmetric streaming in the Solar neighbourhood. The obtained result uses only data on the near side of the bar which produces consistent measurements of the distance and velocity of the centre of the Galaxy. Addition of the data on the far side of the bar pulls the pattern speed down to $\Omega _\mathrm{p}=(31\pm 1)\, \mathrm{km\, s^{-1}\, kpc^{-1}}$ but requires a lower transverse velocity for the Galactic centre than observed. This suggests systematics of $5-10\, \mathrm{km\, s^{-1}kpc^{-1}}$ dominate the uncertainty. We demonstrate using a dynamically formed bar/bulge simulation that even with the limited field of view of the VVV survey our method robustly recovers the pattern speed.

Download Full-text

Direct Determination of the Spiral Pattern Rotation Speed of the Galaxy

The Astrophysical Journal ◽

10.1086/431456 ◽

2005 ◽

Vol 629 (2) ◽

pp. 825-831 ◽

Cited By ~ 94

Author(s):

Wilton S. Dias ◽

J. R. D. Lepine

Keyword(s):

Rotation Speed ◽

Direct Determination ◽

Spiral Pattern ◽

The Galaxy

Download Full-text

Density waves in disk galaxies

Symposium - International Astronomical Union ◽

10.1017/s0074180900101135 ◽

1967 ◽

Vol 31 ◽

pp. 313-317 ◽

Cited By ~ 8

Author(s):

C. C. Lin ◽

F. H. Shu

Keyword(s):

Mathematical Analysis ◽

Spiral Structure ◽

Stellar System ◽

Collective Modes ◽

Disk Galaxies ◽

Spiral Pattern ◽

Density Waves ◽

The Galaxy ◽

Detailed Mathematical Analysis

Density waves in the nature of those proposed by B. Lindblad are described by detailed mathematical analysis of collective modes in a disk-like stellar system. The treatment is centered around a hypothesis of quasi-stationary spiral structure. We examine (a) the mechanism for the maintenance of this spiral pattern, and (b) its consequences on the observable features of the galaxy.

Download Full-text

On the maintenance of spiral structure

Symposium - International Astronomical Union ◽

10.1017/s0074180900014364 ◽

1979 ◽

Vol 84 ◽

pp. 151-153

Author(s):

James W-K. Mark ◽

Linda Sugiyama ◽

Robert H. Berman ◽

Giuseppe Bertin

Keyword(s):

Spiral Structure ◽

Travelling Waves ◽

Integral Condition ◽

Stimulated Emission ◽

Stellar Disk ◽

Wave System ◽

Wave Amplification ◽

Corotation Radius ◽

The Galaxy ◽

Central Regions

A concentrated nuclear bulge with about 30% of the galaxy mass is sufficient (Lin, 1975; Berman and Mark, 1978) to eliminate strong bar-forming instabilities which dominate the dynamics of the stellar disk. Weak bar-like or oval distortions might remain depending on the model. In such systems self-excited discrete modes give rise to global spiral patterns which are maintained in the presence of differential rotation and dissipation (cf. especially the spiral patterns in Bertin et al., 1977, 1978). These spiral modes are standing waves that are physically analyzable (Mark, 1977) into a superposition of two travelling waves propagating in opposite directions back and forth between galactic central regions and corotation (a resonator). Only a few discrete pattern frequencies are allowed. An interpretation is that the central regions and corotation radius must be sufficiently far apart so that a Bohr-Sommerfeld type of phase-integral condition is satisfied for the wave system of each mode. The temporal growth of these modes is mostly due to an effect of Wave Amplification by Stimulated Emission (of Rotating Spirals, abbrev. WASERS, cf. Mark 1976) which occurs in the vicinity of corotation. In some galaxies one mode might be predominent while other galaxies could exhibit more complicated spiral structure because several modes are present. Weak barlike or oval distortions hardly interfere with the structure of these modes. But they might nevertheless contribute partially towards strengthening the growth of one mode relative to another, as well as affecting the kinematics of the gaseous component.

Download Full-text

The escape speed curve of the Galaxy obtained from Gaia DR2 implies a heavy Milky Way

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833748 ◽

2018 ◽

Vol 616 ◽

pp. L9 ◽

Cited By ~ 41

Author(s):

G. Monari ◽

B. Famaey ◽

I. Carrillo ◽

T. Piffl ◽

M. Steinmetz ◽

...

Keyword(s):

Mass Concentration ◽

Milky Way ◽

Galactic Centre ◽

High Concentration ◽

Circular Velocity ◽

Halo Stars ◽

Dark Matter Mass ◽

The Galaxy ◽

Escape Speed ◽

Gaia Dr2

We measure the escape speed curve of the Milky Way based on the analysis of the velocity distribution of ~2850 counter-rotating halo stars from the Gaia Data Release 2. The distances were estimated through the StarHorse code, and only stars with distance errors smaller than 10% were used in the study. The escape speed curve is measured at Galactocentric radii ranging from ~5 kpc to ~10.5 kpc. The local Galactic escape at the Sun’s position is estimated to be ve(r⊙) = 580 ± 63 km s−1, and it rises towards the Galactic centre. Defined as the minimum speed required to reach three virial radii, our estimate of the escape speed as a function of radius implies for a Navarro–Frenk–White profile and local circular velocity of 240 km s−1 a dark matter mass M200 = 1.28−0.50+0.68 × 1012 M⊙ and a high concentration c200 = 11.09−1.79+2.94. Assuming the mass-concentration relation of ΛCDM, we obtain M200 = 1.55−0.51+0.64 × 1012 M⊙ and c200 = 7.93−0.27+0.33 for a local circular velocity of 228 km s−1.

Download Full-text

The strange case of the peculiar spiral galaxy NGC 5474

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937284 ◽

2020 ◽

Vol 634 ◽

pp. A124 ◽

Cited By ~ 1

Author(s):

M. Bellazzini ◽

F. Annibali ◽

M. Tosi ◽

A. Mucciarelli ◽

M. Cignoni ◽

...

Keyword(s):

Old Age ◽

Spiral Galaxy ◽

The Other ◽

Spiral Pattern ◽

Stellar Content ◽

Peculiar Star ◽

Space Telescope ◽

Stellar Disc ◽

Star Forming ◽

The Galaxy

We present the first analysis of the stellar content of the structures and substructures identified in the peculiar star-forming galaxy NGC 5474, based on Hubble Space Telescope resolved photometry from the LEGUS survey. NGC 5474 is a satellite of the giant spiral M 101, and it is known to have a prominent bulge that is significantly off-set from the kinematic centre of the underlying H I and stellar disc. The youngest stars (age ≲ 100 Myr) trace a flocculent spiral pattern extending out to ≳8 kpc from the centre of the galaxy. On the other hand, intermediate-age (age ≳ 500 Myr) and old (age ≳ 2 Gyr) stars dominate the off-centred bulge and a large substructure residing in the south-western part of the disc (SW over-density) and they are not correlated with the spiral arms. The old age of the stars in the SW over-density suggests that this may be another signature of any dynamical interactions that have shaped this anomalous galaxy. We suggest that a fly by with M 101, generally invoked as the origin of the anomalies, may not be sufficient to explain all the observations. A more local and more recent interaction may help to put all the pieces of this galactic puzzle together.

Download Full-text

The Bulge-disc connection in the Milky Way

Proceedings of the International Astronomical Union ◽

10.1017/s174392130802752x ◽

2008 ◽

Vol 4 (S254) ◽

pp. 145-152

Author(s):

James Binney

Keyword(s):

Angular Momentum ◽

Stellar Population ◽

Milky Way ◽

Dark Halo ◽

Principal Characteristics ◽

Corotation Radius ◽

The Galaxy

AbstractBulges come in two flavours – classical and pseudo. The principal characteristics of each flavour are summarised and their impact on discs is considered. Classical bulges probably inhibit the formation of stellar discs. Pseudobulges exchange angular momentum with stars and gas in their companion discs, and also with its embedding dark halo. Since the structure of a pseudobulge depends critically on its angular momentum, these exchanges are expected to modify the bulge. The consequences of this modification are not yet satisfactorily understood. The Galaxy has a pseudobulge. I review the manifestations of its interaction with the disc. More work is needed on the dynamics of gas near the bulge's corotation radius, and on tracing the stellar population in the inner few hundred parsecs of the Galaxy.

Download Full-text

Leading wave as a component of the spiral pattern of the galaxy

Astronomy Letters ◽

10.1134/1.1862347 ◽

2005 ◽

Vol 31 (2) ◽

pp. 80-87 ◽

Cited By ~ 5

Author(s):

A. M. Mel’nik

Keyword(s):

Spiral Pattern ◽

The Galaxy

Download Full-text