A method to calculate gravitational accelerations within discrete localized regions in the Milky Way

Since past few decades, observations have improved so strongly that when modelling Milky Way (MW) dynamics it is required to include small perturbations to the modelling process. It is difficult task that we try to solve by selecting regions to model so small that the perturbation can be considered to give nearly constant effect. We use Solar Neighbourhood (SN) as our test sample and assume that the bar effects show more or less constant contribution to SN. By extrapolating and smoothing observed stars on their orbits, and requiring that smoothed and observed phase space are consistent we were able to deduce acceleration vector. We conclude from non-radial acceleration component that the bar must cause about one third of total acceleration near SN.

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“…The method of the present application is fully described in Kipper et al (2019). As a short recap, we select a well defined region near SN.…”

Section: Methods and Datamentioning

confidence: 99%

Measuring torque of galactic bar from Gaia DR2

Kipper

Tempel

2019

Proc. IAU

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“…In case of some form of perturbations, such as bar, the system can be modelled in a rotating frame to avoid the perturbations and time dependence, but it introduces an additional free parameter. This section will augment the orbital arc method (Kipper et al 2019(Kipper et al , 2020 to include the modelling of a region in the Galaxy being in a perturbed state. In this paper, we only aim to model perturbations that do not contain a significant amount of mass and are dominantly density perturbations leaving potential and acceleration field untouched.…”

Section: Improved Description Of Kinematicsmentioning

confidence: 99%

“…Z is the normalising constant, Kg is the kernel converting orbital arcs into a smooth probability distribution. More details are elaborated in Kipper et al (2019).…”

Section: Improving Statistical Descriptionmentioning

confidence: 99%

“…The modelling is done in a similar manner as we tested the method with mock data (Kipper et al 2019) although the statistical inference at present is done with a finer grid using 30 2 = 900 grid cells G = 32 times. We set a limit that no cell should have less than 10 stars to avoid too small grid cells, and high relative Poisson noise.…”

Section: Implementation Of the Modelling With Gaia Datamentioning

confidence: 99%

“…In our earlier paper (Kipper et al 2019) we presented a method to calculate gravitational potential derivatives (accelerations) in sufficiently small regions of a galaxy if one knows phase-space coordinates of a large number of stars in these regions. In a later paper (Kipper et al 2020) the method was applied for the Milky Way (MW) galaxy in the Solar neighbourhood (SN) using Gaia DR2 data.…”

Section: Introductionmentioning

confidence: 99%

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Non-equilibrium in the Solar Neighbourhood using dynamical modelling with Gaia DR2

Kipper,

Tenjes,

Tempel

et al. 2021

Preprint

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Matter distribution models of the Milky Way galaxy are usually stationary, although there are known to be wave-like perturbations in the disc at ∼ 10% level of the total density. Modelling of the overall acceleration field by allowing non-equilibrium is a complicated task. We must learn to distinguish whether density enhancements are persistent or not by their nature. In the present paper, we elaborate our orbital arc method to include the effects of massless perturbations and non-stationarities in the modelling. The method is tested by modelling of simulation data and shown to be valid. We apply the method to the Gaia DR 2 data within a region of ∼ 0.5 kpc from the Sun and confirm that acceleration field in the Solar Neighbourhood has a perturbed nature -the phase space density along the orbits of stars grow in the order of h 5% per Myr due to non-stationarity. This result is a temporally local value and can be used only within the timeframe of a few Myrs. An attempt to pinpoint the origin of the perturbation shows that the stars having larger absolute angular momentum are the main carriers of the local perturbation. As they are faster than the average thin disc star, they are either originating further away and are close in their pericentre or they are perturbed locally by a fast co-moving perturber, such as gas disc inhomogenities.

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Quantifying torque from the Milky Way bar using Gaia DR2

Kipper

Tenjes

Tuvikene

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We determine the mass of the Milky Way bar and the torque it causes, using Gaia DR2, by applying the orbital arc method. Based on this, we have found that the gravitational acceleration is not directed towards the centre of our Galaxy but a few degrees away from it. We propose that the tangential acceleration component is caused by the bar of the Galaxy. Calculations based on our model suggest that the torque experienced by the region around the Sun is $\approx 2400\, {\rm km^2\, s^{-2}}$ per solar mass. The mass estimate for the bar is $\sim 1.6\pm 0.3\times 10^{10}\, \mathrm{M_\odot }$. Using greatly improved data from Gaia DR2, we have computed the acceleration field to great accuracy by adapting the orbital Probability Density Function (oPDF) method (Han et al. 2016) locally and used the phase space coordinates of ∼4 × 105 stars within a distance of 0.5 kpc from the Sun. In the orbital arc method, the first step is to guess an acceleration field and then reconstruct the stellar orbits using this acceleration for all the stars within a specified region. Next, the stars are redistributed along orbits to check if the overall phase space distribution has changed. We repeat this process until we find an acceleration field that results in a new phase space distribution that is the same as the one that we started with; we have then recovered the true underlying acceleration.

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A method to calculate gravitational accelerations within discrete localized regions in the Milky Way

Cited by 5 publications

References 30 publications

Measuring torque of galactic bar from Gaia DR2

Measuring torque of galactic bar from Gaia DR2

Non-equilibrium in the Solar Neighbourhood using dynamical modelling with Gaia DR2

Quantifying torque from the Milky Way bar using Gaia DR2

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