scholarly journals Mapping the tilt of the Milky Way bulge velocity ellipsoids with ARGOS and Gaia DR2

2021 ◽  
Vol 502 (2) ◽  
pp. 1740-1752
Author(s):  
Iulia T Simion ◽  
Juntai Shen ◽  
Sergey E Koposov ◽  
Melissa Ness ◽  
Kenneth Freeman ◽  
...  
Keyword(s):  
Large Scale ◽  
Milky Way ◽  
Longitudinal Velocity ◽  
Major Axis ◽  
Specific Model ◽  
Likelihood Method ◽  
Line Of Sight ◽  
Galactic Centre ◽  
Stellar Kinematics ◽  
Gaia Dr2

ABSTRACT Until the recent advent of Gaia Data Release 2 (DR2) and deep multi-object spectroscopy, it has been difficult to obtain 6D phase space information for large numbers of stars beyond 4 kpc, in particular towards the Galactic Centre, where dust and crowding are significant. We combine line-of-sight velocities from the Abundances and Radial velocity Galactic Origins Survey (ARGOS) with proper motions from Gaia DR2 to obtain a sample of ∼7000 red clump stars with 3D velocities. We perform a large-scale stellar kinematics study of the Milky Way bulge to characterize the bulge velocity ellipsoids in 20 fields. The tilt of the major-axis of the velocity ellipsoid in the radial-longitudinal velocity plane, or vertex deviation, is characteristic of non-axisymmetric systems and a significant tilt is a robust indicator of non-axisymmetry or bar presence. We compare the observations to the predicted kinematics of an N-body boxy-bulge model formed from dynamical instabilities. In the model, the lv values are strongly correlated with the angle (α) between the bulge major-axis and the Sun-Galactic centre line of sight. We use a maximum likelihood method to obtain an independent measurement of α, from bulge stellar kinematics alone, performing a robust error analysis. The most likely value of α given our model is α = (29 ± 3)○, with an additional systematic uncertainty due to comparison with one specific model. In Baade’s window, the metal-rich stars display a larger vertex deviation (lv = −40○) than the metal-poor stars (lv = 10○) but we do not detect significant lv−metallicity trends in the other fields.

scholarly journals Kinematics with Gaia DR2: the force of a dwarf

2019 ◽  
Vol 490 (1) ◽  
pp. 797-812 ◽  
Author(s):  
I Carrillo ◽  
I Minchev ◽  
M Steinmetz ◽  
G Monari ◽  
C F P Laporte ◽  
...  
Keyword(s):  
Milky Way ◽  
Line Of Sight ◽  
Galactic Centre ◽  
Time Intervals ◽  
Opposite Trend ◽  
Bayesian Inference Method ◽  
Velocity Information ◽  
Bending Modes ◽  
Short Time ◽  
Gaia Dr2

ABSTRACT We use Gaia DR2 astrometric and line-of-sight velocity information combined with two sets of distances obtained with a Bayesian inference method to study the 3D velocity distribution in the Milky Way disc. We search for variations in all Galactocentric cylindrical velocity components (Vϕ, VR, and Vz) with Galactic radius, azimuth, and distance from the disc mid-plane. We confirm recent work showing that bulk vertical motions in the R–z plane are consistent with a combination of breathing and bending modes. In the x–y plane, we show that, although the amplitudes change, the structure produced by these modes is mostly invariant as a function of distance from the plane. Comparing to two different Galactic disc models, we demonstrate that the observed patterns can drastically change in short time intervals, showing the complexity of understanding the origin of vertical perturbations. A strong radial VR gradient was identified in the inner disc, transitioning smoothly from 16 km s−1 kpc−1 at an azimuth of 30° < ϕ < 45° ahead of the Sun-Galactic centre line to −16 km s−1 kpc−1 at an azimuth of −45° < ϕ < −30° lagging the solar azimuth. We use a simulation with no significant recent mergers to show that exactly the opposite trend is expected from a barred potential, but overestimated distances can flip this trend to match the data. Alternatively, using an N-body simulation of the Sagittarius dwarf–Milky Way interaction, we demonstrate that a major recent perturbation is necessary to reproduce the observations. Such an impact may have strongly perturbed the existing bar or even triggered its formation in the last 1–2 Gyr.

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

2018 ◽  
Vol 616 ◽  
pp. L9 ◽  
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.

scholarly journals The geometry of the gas surrounding the Central Molecular Zone: on the origin of localized molecular clouds with extreme velocity dispersions

2019 ◽  
Vol 488 (4) ◽  
pp. 4663-4673 ◽  
Author(s):  
Mattia C Sormani ◽  
Robin G Treß ◽  
Simon C O Glover ◽  
Ralf S Klessen ◽  
Ashley T Barnes ◽  
...  
Keyword(s):  
Molecular Clouds ◽  
Gas Flow ◽  
Milky Way ◽  
Line Of Sight ◽  
Galactic Centre ◽  
Molecular Gas ◽  
Distinct Population ◽  
Data Cubes ◽  
Velocity Dispersions

ABSTRACT Observations of molecular gas near the Galactic Centre (|l| &lt; 10°, |b| &lt; 1°) reveal the presence of a distinct population of enigmatic compact clouds that are characterized by extreme velocity dispersions ($\Delta v \gt 100\, {\rm km\, s^{-1}}$). These extended velocity features are very prominent in the data cubes and dominate the kinematics of molecular gas just outside the Central Molecular Zone (CMZ). The prototypical example of such a cloud is Bania Clump 2. We show that similar features are naturally produced in simulations of gas flow in a realistic barred potential. We analyse the structure of the features obtained in the simulations and use this to interpret the observations. We find that the features arise from collisions between material that has been infalling rapidly along the dust lanes of the Milky Way bar and material that belongs to one of the following two categories: (i) material that has ‘overshot’ after falling down the dust lanes on the opposite side; (ii) material which is part of the CMZ. Both types of collisions involve gas with large differences in the line-of-sight velocities, which is what produces the observed extreme velocity dispersions. Examples of both categories can be identified in the observations. If our interpretation is correct, we are directly witnessing (a) collisions of clouds with relative speeds of $\sim 200\, {\rm km\, s^{-1}}$ and (b) the process of accretion of fresh gas onto the CMZ.

scholarly journals The GALAH survey and Gaia DR2: Linking ridges, arches, and vertical waves in the kinematics of the Milky Way

2019 ◽  
Vol 489 (4) ◽  
pp. 4962-4979 ◽  
Author(s):  
Shourya Khanna ◽  
Sanjib Sharma ◽  
Thor Tepper-Garcia ◽  
Joss Bland-Hawthorn ◽  
Michael Hayden ◽  
...  
Keyword(s):  
Large Scale ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Elemental Abundance ◽  
Space Distribution ◽  
Orbital Energy ◽  
Small Scale ◽  
Constant Energy ◽  
Third Dimension ◽  
Gaia Dr2

ABSTRACT Gaia DR2 has revealed new small-scale and large-scale patterns in the phase-space distribution of stars in the Milky Way. In cylindrical Galactic coordinates $(R,\phi ,z)$, ridge-like structures can be seen in the $(R,V_\phi)$ plane and asymmetric arch-like structures in the $(V_R,V_\phi)$ plane. We show that the ridges are also clearly present when the third dimension of the $(R,V_\phi)$ plane is represented by $\langle z \rangle$, $\langle V_z \rangle$, $\langle V_R \rangle$, $\langle$[Fe/H]$\rangle$, and $\langle [\alpha /{\rm Fe}]\rangle$. The maps suggest that stars along the ridges lie preferentially close to the Galactic mid-plane ($|z|\lt 0.2$ kpc), and have metallicity and $\alpha$ elemental abundance similar to that of the Sun. We show that phase mixing of disrupting spiral arms can generate both the ridges and the arches. It also generates discrete groupings in orbital energy – the ridges and arches are simply surfaces of constant energy. We identify eight distinct ridges in the Gaia DR2 data: six of them have constant energy while two have constant angular momentum. Given that the signature is strongest for stars close to the plane, the presence of ridges in $\langle z \rangle$ and $\langle V_z \rangle$ suggests a coupling between planar and vertical directions. We demonstrate, using N-body simulations that such coupling can be generated both in isolated discs and in discs perturbed by an orbiting satellite like the Sagittarius dwarf galaxy.

scholarly journals Search for globular clusters associated with the Milky Way dwarf galaxies using Gaia DR2

2020 ◽  
Vol 500 (1) ◽  
pp. 986-997
Author(s):  
Kuan-Wei Huang ◽  
Sergey E Koposov
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Galactic Centre ◽  
Imaging Data ◽  
Credible Intervals ◽  
Specific Frequency ◽  
Number Counts ◽  
Gaia Dr2

ABSTRACT We report the result of searching for globular clusters (GCs) around 55 Milky Way (MW) satellite dwarf galaxies within the distance of 450 kpc from the Galactic Centre except for the Large and Small Magellanic Clouds and the Sagittarius dwarf. For each dwarf, we analyse the stellar distribution of sources in Gaia DR2, selected by magnitude, proper motion, and source morphology. Using the kernel density estimation of stellar number counts, we identify 11 possible GC candidates. Cross-matched with existing imaging data, all 11 objects are known either GCs or galaxies and only Fornax GC 1–6 among them are associated with the targeted dwarf galaxy. Using simulated GCs, we calculate the GC detection limit $M_{\rm V}^{\rm lim}$ that spans the range from $M_{\rm V}^{\rm lim}\sim -7$ for distant dwarfs to $M_{\rm V}^{\rm lim}\sim 0$ for nearby systems. Assuming a Gaussian GC luminosity function, we compute that the completeness of the GC search is above 90 per cent for most dwarf galaxies. We construct the 90 per cent credible intervals/upper limits on the GC specific frequency SN of the MW dwarf galaxies: 12 &lt; SN &lt; 47 for Fornax, SN &lt; 20 for the dwarfs with −12 &lt; MV &lt; −10, SN &lt; 30 for the dwarfs with −10 &lt; MV &lt; −7, and SN &lt; 90 for the dwarfs with MV &gt; −7. Based on SN, we derive the probability of galaxies hosting GCs given their luminosity, finding that the probability of galaxies fainter than MV = −9 to host GCs is lower than 0.1.

scholarly journals Accretion in the Center of the Milky Way

1997 ◽  
Vol 163 ◽  
pp. 659-662
Author(s):  
Wolfgang J. Duschl ◽  
Susanne von Linden
Keyword(s):  
Molecular Clouds ◽  
Large Scale ◽  
Milky Way ◽  
Galactic Center ◽  
Radial Velocities ◽  
Line Of Sight ◽  
Giant Molecular Clouds ◽  
Large Scale Motion ◽  
Scale Motion

AbstractWe have analyzed the distribution of giant molecular clouds and their radial velocities in the inner ~ 300 pc of the Milky Way in order to deduce the characteristic properties of its large scale motion. We find radial inflow of matter towards the Galactic Center of ~ 10−2 M⊙/yr. Moreover, we have determined the position of individual clouds along the line of sight.

scholarly journals On testing CDM and geometry-driven Milky Way rotation curve models with Gaia DR2

2020 ◽  
Vol 496 (2) ◽  
pp. 2107-2122 ◽  
Author(s):  
Mariateresa Crosta ◽  
Marco Giammaria ◽  
Mario G Lattanzi ◽  
Eloisa Poggio
Keyword(s):  
Milky Way ◽  
State Of The Art ◽  
Mass Density ◽  
Proper Motions ◽  
Stellar Kinematics ◽  
Flat Rotation Curves ◽  
General Relativistic ◽  
Gravitational Contribution ◽  
Gaia Dr2 ◽  
Disc Galaxies

ABSTRACT Flat rotation curves (RCs) in disc galaxies provide the main observational support to the hypothesis of surrounding dark matter (DM). Despite of the difficulty in identifying the DM contribution to the total mass density in our Galaxy, stellar kinematics, as tracer of gravitational potential, is the most reliable observable for gauging different matter components. From the Gaia second data release catalogue, we extracted parallaxes, proper motions, and line-of-sight velocities of unprecedented accuracy for a carefully selected sample of disc stars. This is the angular momentum supported population of the Milky Way (MW) that better traces its observed RC. We fitted such data to both a classical, i.e. including a DM halo, velocity profile model, and a general relativistic one derived from a stationary axisymmetric galaxy-scale metric. The general relativistic MW RC results statistically indistinguishable from its state-of-the-art DM analogue. This supports the ansatz that a weak gravitational contribution due to the off-diagonal term of the metric, by explaining the observed flatness of MW’s RC, could fill the gap in a baryons-only MW, thus rendering the Newtonian-origin DM a general relativity-like effect. In the context of Local Cosmology, our findings are suggestive of the Galaxy’s phase space as the exterior gravitational field in equilibrium far from a Kerr-like inner source, possibly with no need for extra matter to account for the disc kinematics.

scholarly journals Simultaneous calibration of spectro-photometric distances and the Gaia DR2 parallax zero-point offset with deep learning

2019 ◽  
Vol 489 (2) ◽  
pp. 2079-2096 ◽  
Author(s):  
Henry W Leung ◽  
Jo Bovy
Keyword(s):  
Milky Way ◽  
Zero Point ◽  
Galactic Centre ◽  
Dynamical Structure ◽  
The Sun ◽  
Large Area ◽  
Data Set ◽  
The Mean ◽  
Gaia Dr2 ◽  
Flexible Model

ABSTRACT Gaia measures the five astrometric parameters for stars in the Milky Way, but only four of them (positions and proper motion, but not distance) are well measured beyond a few kpc from the Sun. Modern spectroscopic surveys such as APOGEE cover a large area of the Milky Way disc and we can use the relation between spectra and luminosity to determine distances to stars beyond Gaia’s parallax reach. Here, we design a deep neural network trained on stars in common between Gaia and APOGEE that determines spectro-photometric distances to APOGEE stars, while including a flexible model to calibrate parallax zero-point biases in Gaia DR2. We determine the zero-point offset to be $-52.3 \pm 2.0\, \mu \mathrm{as}$ when modelling it as a global constant, but also train a multivariate zero-point offset model that depends on G, GBP − GRP colour, and Teff and that can be applied to all ≈58 million stars in Gaia DR2 within APOGEE’s colour–magnitude range and within APOGEE’s sky footprint. Our spectro-photometric distances are more precise than Gaia at distances ${\gtrsim} 2\, \mathrm{kpc}$ from the Sun. We release a catalogue of spectro-photometric distances for the entire APOGEE DR14 data set which covers Galactocentric radii $2\, \mathrm{kpc} \lesssim R \lesssim 19\, \mathrm{kpc}$; ${\approx} 150\, 000$ stars have ${\lt} 10{{\ \rm per\ cent}}$ uncertainty, making this a powerful sample to study the chemo-dynamical structure of the disc. We use this sample to map the mean [Fe/H] and 15 abundance ratios [X/Fe] from the Galactic Centre to the edge of the disc. Among many interesting trends, we find that the bulge and bar region at $R \lesssim 5\, \mathrm{kpc}$ clearly stands out in [Fe/H] and most abundance ratios.

scholarly journals The Mass Distribution in the Galactic Centre Estimated from OH/IR Stars

1989 ◽  
Vol 136 ◽  
pp. 503-508 ◽  
Author(s):  
M. Lindqvist ◽  
A. Winnberg ◽  
H. J. Habing ◽  
H. E. Matthews ◽  
F. M. Olnon
Keyword(s):  
Density Distribution ◽  
Mass Distribution ◽  
Mass Density ◽  
Major Axis ◽  
Galactic Centre ◽  
Stellar Kinematics ◽  
Galactocentric Distance ◽  
Preliminary Results ◽  
Ir Stars ◽  
Axis Parallel

The preliminary results of a search for OH/IR stars in the Galactic Centre using the VLA are presented. The goal of this project is to determine the mass density distribution from a few parsecs up to about 120 pc of the Galactic Centre using stellar kinematics. Up to now, 125 OH/IR stars have been found. The distribution of the stars is clearly elongated with the major axis parallel to the galactic equator. The stars show a rotation of 117 km s−1 deg−1 with a dispersion of 90 km s−1. Two preliminary models have been applied in order to determine the enclosed mass, resulting in M(r)=4.0·106·r1.4 Mo, where r is the galactocentric distance in parsecs.

scholarly journals Age demographics of the Milky Way disc and bulge

2020 ◽  
Vol 492 (3) ◽  
pp. 3128-3142 ◽  
Author(s):  
J Grady ◽  
V Belokurov ◽  
N W Evans
Keyword(s):  
Large Scale ◽  
Milky Way ◽  
Axial Ratio ◽  
Galactic Centre ◽  
Pulsation Period ◽  
Viewing Angle ◽  
Stellar Ages ◽  
Inside Out ◽  
Bar Formation ◽  
Stellar Density

ABSTRACT We exploit the extensive Gaia Data Release 2 set of long-period variables to select a sample of O-rich Miras throughout the Milky Way disc and bulge for study. Exploiting the relation between Mira pulsation period and stellar age/chemistry, we slice the stellar density of the Galactic disc and bulge as a function of period. We find that the morphology of both components evolves as a function of stellar age/chemistry with the stellar disc being stubby at old ages, becoming progressively thinner and more radially extended at younger stellar ages, consistent with the picture of inside-out and upside-down formation of the Milky Way’s disc. We see evidence of a perturbed disc, with large-scale stellar overdensities visible both in and away from the stellar plane. We find that the bulge is well modelled by a triaxial boxy distribution with an axial ratio of ∼1:0.4:0.3. The oldest of the Miras (∼9–10 Gyr) show little bar-like morphology, while the younger stars appear inclined at a viewing angle of ∼21° to the Sun–Galactic Centre line. This suggests that bar formation and buckling took place 8–9 Gyr ago, with the older Miras being hot enough to avoid being trapped by the growing bar. We find the youngest Miras to exhibit a strong peanut morphology, bearing the characteristic X-shape of an inclined bar structure.

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