Quadrupole signature as a kinematic diagnostic to constrain bar properties : implications for the Milky Way

Abstract

The presence of a 'butterfly' or a quadrupole structure in the stellar mean radial velocity ($<V_R>$) field of the Milky Way is well known from the Gaia and the APOGEE surveys. Past studies indicated that a stellar bar can excite such a quadrupole feature in the $<V_R>$ distribution. However, a systematic study investigating the co-evolution of bar and quadrupole structure is largely missing. Furthermore, whether this quadrupole structure in $<V_R>$ can be used as a robust kinematic diagnostic to constrain bar properties, particularly for the Milky Way, is still beyond our grasp. Here, we investigate the bar-induced quadrupole feature using a suite of isolated $N$-body models forming prominent bars and a sample of Milky Way-like barred galaxies from the TNG50 cosmological simulation. We demonstrate that the properties of the quadrupole (strength, length, and orientation) are strongly correlated with the bar properties, regardless of the choice of the thin/thick disc stars; thereby making the quadrupole feature an excellent kinematic diagnostic for constraining the bar properties. In presence of spirals, the estimator which takes into account the phase-angle of $m=4$ Fourier moment, serves as a more appropriate estimator for measuring the length of the quadrupole. Further, we constructed a novel Gaia-like mock dataset from a simulated bar model while incorporating the dust extinction and the broad trends of observational errors of the Gaia survey. The quadrupole properties (strength and length) estimated from those Gaia-like mock data are larger ($\sim 35-45$ percent) when compared with their true values. We showed that the majority of this effect is due to the uncertainty in parallax measurement. This demonstrates that the quadrupole structure in Gaia data is likely a result of dominant Gaia parallax errors/biases, almost masking the true inherent signature of the MW bar.

15 pages, 1 table, 13 figures (including appendix), accepted for publication in A&A

References in corpus (25)

• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• Simulating galaxy formation with black hole driven thermal and kinetic feedback
• Dynamics of Barred Galaxies
• Dynamical modelling of the Galactic bulge and bar: the Milky Way's bar pattern speed, stellar, and dark matter mass distribution
• The Structure of the Milky Way's Bar Outside the Bulge
• The mass distribution in the Galactic Centre from interferometric astrometry of multiple stellar orbits
• Gaia Data Release 3: Mapping the asymmetric disc of the Milky Way
• Quantifying stellar radial migration in an N-body simulation: blurring, churning, and the outer regions of galaxy discs
• An Iterative Method for Constructing Equilibrium Phase Models of Stellar Systems
• The parallax zero point offset from Gaia EDR3 data
• Gas Dynamics in the Galaxy: Total Mass Distribution and the Bar Pattern Speed
• Variations in the width, density, and direction of the Palomar 5 tidal tails
• Hic sunt dracones: Cartography of the Milky Way spiral arms and bar resonances with Gaia Data Release 2
• Effect of bars on the galaxy properties
• The vertical effects of disc non-axisymmetries from perturbation theory: the case of the Galactic bar
• Dynamically constraining the length of the Milky Way bar
• Evidence of Bar-induced Secular Evolution in the Inner Regions of Stellar Discs in Galaxies: What Shapes Disc Galaxies?
• Bars and boxy/peanut bulges in thin and thick discs. II. Can bars form in hot thick discs?
• Numerical code for multi-component galaxies: from N-body to chemistry and magnetic fields
• Timing the Milky Way bar formation and the accompanying radial migration episode
• Looking for a needle in a haystack: Measuring the length of a stellar bar
• The pattern speeds of vertical breathing waves
• Bars and boxy/peanut bulges in thin and thick discs III. Boxy/peanut bulge formation and evolution in presence of thick discs
• Rediscovering the Milky Way with orbit superposition approach and APOGEE data I. Method validation
• Quantifying the influence of bars on action-based dynamical modelling of disc galaxies