Galactic Bar Research Articles

The role of bars on the dynamical-friction-driven inspiral of massive objects

ABSTRACT In this paper, we systematically explore the impact of a galactic bar on the inspiral time-scale of a massive object (MO) within a Milky Way-like galaxy. We integrate the orbit of MOs in a multicomponent galaxy model via a semi-analytical approach that accounts for dynamical friction generalized to rotationally supported backgrounds. We compare the MO evolution in a galaxy featuring a Milky Way-like rotating bar to the evolution within an analogous axisymmetric galaxy without the bar. In agreement with previous studies, we find that the bar presence may significantly affect the inspiral, sometimes making it shorter by a factor of a few, and sometimes hindering it for a Hubble time. The erratic behaviour is mainly impacted by the relative phase at which the MO encounters the stronger bar-induced resonances. In particular, the effect of the bar is more prominent for initially in-plane, prograde MOs, especially those crossing the bar co-rotation radius or outer Lindblad resonance. In the barred galaxy, we find the sinking of the most massive MOs ($\gtrsim 10^{7.5}\, \mathrm{M}_{\odot {}}$) approaching the galaxy from large separations (≳8 kpc) to be most efficiently hampered. Neglecting the effect of global torques associated with the non-symmetric mass distribution is thus not advisable even within an idealized, smooth galaxy model; we further note that spiral patterns are unlikely to affect the inspiral due to their transient and fluctuating nature. We speculate that the sinking efficiency of massive black holes involved in minor galaxy mergers may be hampered in barred galaxies, making them less likely to host a gravitational wave signal accessible to low-frequency detectors.

The Milky Way’s middle-aged inner ring

Aims. We investigate the metallicity, age, and orbital anatomy of the inner Milky Way, specifically focussing on the outer bar region. Methods. We integrated a sample of APOGEE DR16 inner Galaxy stars in a state of the art bar-bulge potential with a slow pattern speed and investigated the link between the resulting orbits and their [Fe/H] and ages. By superimposing the orbits, we built density, [Fe/H], and age maps of the inner Milky Way, which we divided further using the orbital parameters eccentricity, |Xmax|, and |Zmax|. Results. We find that at low heights from the Galactic plane, the Galactic bar gradually transitions into a radially thick, vertically thin, elongated inner ring with average solar [Fe/H]. This inner ring is mainly composed of stars with AstroNN ages between 4 and 9 Gyr with a peak in age between 6 and 8 Gyr, making the average age of the ring ∼6 Gyr. The vertical thickness of the ring decreases markedly towards younger ages. We also find very large L4 Lagrange orbits that have average solar to super-solar metallicities and intermediate ages. Lastly, we confirm a clear X-shape in the [Fe/H] and density distributions at large Galactic heights. Conclusions. The orbital structure obtained for the APOGEE stars reveals that the Milky Way hosts an inner ring-like structure between the planar bar and corotation. This structure is on average metal rich, intermediately aged, and enhances the horizontal metallicity gradient along the bar’s major axis.

Explaining deep learning of galaxy morphology with saliency mapping

ABSTRACT We successfully demonstrate the use of explainable artificial intelligence (XAI) techniques on astronomical data sets in the context of measuring galactic bar lengths. The method consists of training convolutional neural networks on human classified data from Galaxy Zoo in order to predict general galaxy morphologies, and then using SmoothGrad (a saliency mapping technique) to extract the bar for measurement by a bespoke algorithm. We contrast this to another method of using a convolutional neural network to directly predict galaxy bar lengths. These methods achieved correlation coefficients of 0.76 and 0.59, and root mean squared errors of 1.69 and 2.10 respective to human measurements. We conclude that XAI methods outperform conventional deep learning in this case, which could be reasonably explained by the larger data sets available when training the models. We suggest that our XAI method can be used to extract other galactic features (such as the bulge-to-disc ratio) without needing to collect new data sets or train new models. We also suggest that these techniques can be used to refine deep learning models as well as identify and eliminate bias within training data sets.

Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia EDR3 stars brighter than G = 18.5

We present a catalogue of 362 million stellar parameters, distances, and extinctions derived from Gaia’s Early Data Release (EDR3) cross-matched with the photometric catalogues of Pan-STARRS1, SkyMapper, 2MASS, and AllWISE. The higher precision of the Gaia EDR3 data, combined with the broad wavelength coverage of the additional photometric surveys and the new stellar-density priors of the StarHorse code, allows us to substantially improve the accuracy and precision over previous photo-astrometric stellar-parameter estimates. At magnitude G = 14 (17), our typical precisions amount to 3% (15%) in distance, 0.13 mag (0.15 mag) in V-band extinction, and 140 K (180 K) in effective temperature. Our results are validated by comparisons with open clusters, as well as with asteroseismic and spectroscopic measurements, indicating systematic errors smaller than the nominal uncertainties for the vast majority of objects. We also provide distance- and extinction-corrected colour-magnitude diagrams, extinction maps, and extensive stellar density maps that reveal detailed substructures in the Milky Way and beyond. The new density maps now probe a much greater volume, extending to regions beyond the Galactic bar and to Local Group galaxies, with a larger total number density. We publish our results through an ADQL query interface (gaia.aip.de) as well as via tables containing approximations of the full posterior distributions. Our multi-wavelength approach and the deep magnitude limit render our results useful also beyond the next Gaia release, DR3.

Class I Methanol Masers Related to Shocks Induced by Bar Rotation in the Nearby Starburst Galaxy Maffei 2

Abstract We report the detection of class I methanol maser at the 36.2 GHz transition toward the nearby starburst galaxy Maffei 2 with the Karl G. Jansky Very Large Array. Observations of the 36.2 GHz transition at two epochs separated by ∼4 yr show consistencies in both the spatial distribution and flux density of the methanol emission in this transition. Similar to the detections in other nearby starbursts the class I methanol masers sites are offset by a few hundred pc from the center of the galaxy and appear to be associated with the bar edges of Maffei 2. Narrow spectral features with line widths of a few km s−1 are detected, supporting the hypothesis that they are masing. Compared to other nearby galaxies with the detections in the 36.2 GHz methanol maser transition, the maser detected in Maffei 2 has about an order of magnitude higher isotropic luminosity, and thus represents the first confirmed detection of class I methanol megamasers. The spatial distribution of the 36.2 GHz maser spot clusters may trace the rotational gas flow of the galactic bar, providing direct evidence that the class I methanol maser is related to shocks induced by galactic bar rotation. A tentative detection in the 6.7 GHz class II methanol maser (at a 5σ level) is also reported. This is comparable in luminosity to some of the 6.7 GHz maser sources detected in Galactic star-forming regions. The 6.7 GHz methanol emission appears to be associated with star formation activity in a smaller volume, rather than related to the larger-scale galactic activities.

GASKAP Pilot Survey Science. II. ASKAP Zoom Observations of Galactic 21 cm Absorption

Abstract Using the Australian Square Kilometre Array Pathfinder to measure 21 cm absorption spectra toward continuum background sources, we study the cool phase of the neutral atomic gas in the far outer disk, and in the inner Galaxy near the end of the Galactic bar at longitude 340°. In the inner Galaxy, the cool atomic gas has a smaller scale height than in the solar neighborhood, similar to the molecular gas and the super-thin stellar population in the bar. In the outer Galaxy, the cool atomic gas is mixed with the warm, neutral medium, with the cool fraction staying roughly constant with the Galactic radius. The ratio of the emission brightness temperature to the absorption, i.e., 1 − e −τ , is roughly constant for velocities corresponding to Galactic radius greater than about twice the solar circle radius. The ratio has a value of about 300 K, but this does not correspond to a physical temperature in the gas. If the gas causing the absorption has kinetic temperature of about 100 K, as in the solar neighborhood, then the value 300 K indicates that the fraction of the gas mass in this phase is one-third of the total H i mass.

Evidence of distant spiral arms in the Galactic disk quadrant IV from VVV red clump giants

AbstractThe discovery of new clear windows in the Galactic plane using the VVV near-IR extinction maps allows the study of the structure of the Milky Way (MW) disk. The ultimate goal of this work is to map the spiral arms in the far side of the MW, which is a relatively unexplored region of our Galaxy, using red clump (RC) giants as distance indicators. We search for near-IR clear windows located at low Galactic latitudes ($|b|< 1$deg) in the MW disk using the VVV near-IR extinction maps. We have identified two new windows named VVV WIN 1607–5258 and VVV WIN 1475–5877, respectively, that complement the previously known window VVV WIN 1713–3939. We analyse the distribution of RC stars in these three clear near-IR windows and measure their number density along the line of sight. This allows us to find overdensities in the distribution and measure their distances along the line of sight. We then use the VVV proper motions in order to measure the kinematics of the RC stars at different distances. We find enhancements in the distance distribution of RC giants in all the studied windows, interpreting them as the presence of spiral arms in the MW disk. These structures are absent in the current models of synthetic population for the same MW lines of sight. We were able to trace the end of the Galactic bar, the Norma arm, as well as the Scutum–Centaurus arm in the far disk. Using the VVV proper motions, we measure the kinematics for these Galactic features, confirming that they share the bulk rotation of the Galactic disk.

Lopsided galactic bars

Most of the observed and simulated galactic bars are symmetric in the face-on view. However, there are indeed cases of bars that are off-center with respect to the disk or have an asymmetric shape. The only well-known example showing both these features is the Large Magellanic Cloud. We report on the identification of several lopsided galactic bars in the Illustris TNG100 simulation found among a sample of elongated bar-like galaxies studied in the past. The bars show a clear asymmetry in the face-on view, which is in the shape of a footprint. We measured the evolution of the different parameters of the bars’ shape and asymmetry as a function of time and find that the asymmetry is preserved for a few Gyr. It can grow together with a bar or appear later, after bar formation. We considered two scenarios leading to the formation of lopsided bars using controlled simulations. In the first, a Milky Way-like galaxy interacts with a massive companion placed on a radial orbit in the plane of the disk and perpendicular to the orientation of the bar at the time of the first passage. In the second, the galaxy initially has an off-center disk and the growth of the bar and its asymmetry is more similar to the one found in IllustrisTNG galaxies, where it is also preceded by the presence of an asymmetric disk. It is thus possible that lopsided bars are born in lopsided disks, although in some cases, the time difference between the occurrence of the asymmetry in the two components is quite large.

Dynamically Driven Inflow onto the Galactic Center and its Effect upon Molecular Clouds

Abstract The Galactic bar plays a critical role in the evolution of the Milky Way’s Central Molecular Zone (CMZ), driving gas toward the Galactic Center via gas flows known as dust lanes. To explore the interaction between the CMZ and the dust lanes, we run hydrodynamic simulations in arepo, modeling the potential of the Milky Way’s bar in the absence of gas self-gravity and star formation physics, and we study the flows of mass using Monte Carlo tracer particles. We estimate the efficiency of the inflow via the dust lanes, finding that only about a third (30% ± 12%) of the dust lanes’ mass initially accretes onto the CMZ, while the rest overshoots and accretes later. Given observational estimates of the amount of gas within the Milky Way’s dust lanes, this suggests that the true total inflow rate onto the CMZ is 0.8 ± 0.6 M ⊙ yr−1. Clouds in this simulated CMZ have sudden peaks in their average density near the apocenter, where they undergo violent collisions with inflowing material. While these clouds tend to counter-rotate due to shear, co-rotating clouds occasionally occur due to the injection of momentum from collisions with inflowing material (∼52% are strongly counter-rotating, and ∼7% are strongly co-rotating of the 44 cloud sample). We investigate the formation and evolution of these clouds, finding that they are fed by many discrete inflow events, providing a consistent source of gas to CMZ clouds even as they collapse and form stars.

Bayesian inference of three-dimensional gas maps

Carbon monoxide (CO) is the best tracer of Galactic molecular hydrogen (H2). Its lowest rotational emission lines are in the radio regime, and thanks to Galactic rotation, emission at different distances is Doppler shifted. For a given gas flow model, the observed spectra can thus be deprojected along the line of sight to infer the gas distribution. We used the CO-line survey of Dame et al. (2001, ApJ, 547, 792) to reconstruct the three-dimensional density of H2. We considered the deprojection as a Bayesian variational inference problem. The posterior distribution of the gas densities allowed us to estimate the mean and uncertainty of the reconstructed density. Unlike most of the previous attempts, we took the correlations of gas on a variety of scales into account, which allowed us to correct for some of the well-known pathologies, such as finger-of-god effects. The two gas flow models that we adopted incorporate a Galactic bar that induces radial motions in the inner few kiloparsecs and thus offers spectral resolution towards the Galactic centre. We compared our gas maps with those of earlier studies and characterise their statistical properties, for instance the radial profile of the average surface mass density.

Deep NIR Surveys in the Galactic Plane: A General Overview and the Study of Scutum’s Spiral Arm

Despite the impressive advances in Galactic structure studies, thanks to the large astronomical surveys, there remain several open questions. Although at low distances, optical surveys can bring us important information, the potential of NIR surveys, combined with the optical data, should be considered. In the present work, we explore the stellar distribution through the most recent NIR surveys toward low latitudes (|b| < 2° for 20° ≤ ℓ ≤ 346°) in the Galactic disk, such as 2MASS (entire plane), UKIDSS (20° ≤ ℓ ≤ 231°), and VVV-PSF data (295° ≤ ℓ ≤ 346°), avoiding directions toward the Galactic bar and bulge. Our final compilation contains nearly 140 million stars. We used this sample to perform total star counts at different longitudes, obtaining longitudinal profiles that are compared with those of other authors. For some directions, we obtained the stellar density as a function of distance to investigate the stellar distribution in the Galactic disk. As an example, the variation of the counts toward the Scutum arm tangential direction reveals the stellar content of two spiral arms, e.g., Sagittarius and Scutum. These are the preliminary results of a study that will cover a large extension of the Galactic disk.

Identifying resonances of the Galactic bar in Gaia DR2: II. Clues from angle space

ABSTRACT The Milky Way disc exhibits intricate orbit substructure of still debated dynamical origin. The angle variables (θϕ, θR) – which are conjugates to the actions (L$z$, JR), and describe a star’s location along its orbit – are a powerful diagnostic to identify l:m resonances via the orbit shape relation ΔθR/Δθϕ = −m/l. In the past, angle signatures have been hidden by survey selection effects (SEs). Using test particle simulations of a barred galaxy, we demonstrate that Gaia should allow us to identify the Galactic bar’s outer Lindblad resonance (OLR;l = +1, m = 2) in angle space. We investigate strategies to overcome SEs. In the angle data of the Gaia Data Release 2 (DR2) Radial Velocity Spectrometer (RVS) sample, we independently identify four candidates for the OLR and therefore for the pattern speed Ωbar. The strongest candidate, Ωbar ∼ 1.4Ω0, positions the OLR above the ‘Sirius’ moving group, agrees with measurements from the Galactic Centre, and might be supported by higher order resonances around the ‘Hercules/Horn’. But it misses the classic orbit orientation flip, as discussed in the companion study on actions. The candidate Ωbar ∼ 1.2Ω0 was also suggested by the action-based study, has the OLR at the ‘Hat’, is consistent with slow bar models, but still affected by SEs. Weaker candidates are Ωbar = 1.6Ω0 and 1.74Ω0. In addition, we show that the stellar angles do not support the ‘Hercules/Horn’ being created by the OLR of a fast bar. We conclude that – to resolve if ‘Sirius’ or ‘Hat’ is related to the bar’s OLR – more complex dynamical explanations and more extended data with well-behaved SEs are required.

Molecular gas and star formation within 12 strong galactic bars observed with IRAM-30 m

Context.While some galactic bars show recent massive star formation (SF) along them, some others do not. Whether bars with low level of SF are a consequence of low star formation efficiency, low gas inflow rate, or dynamical effects remains a matter of debate.Aims.In order to study the physical conditions that enable or prevent SF, we perform a multi-wavelength analysis of 12 strongly barred galaxies with total stellar masses log10(M⋆/M⊙)∈[10.2, 11], chosen to host different degrees of SF along the bar major axis without any prior condition on gas content. We observe the CO(1–0) and CO(2–1) emission within bars with the IRAM-30 m telescope (beam sizes of 1.7–3.9 kpc and 0.9–2.0 kpc, respectively; 7–8 pointings per galaxy on average).Methods.We estimated molecular gas masses (Mmol) from the CO(1–0) and CO(2–1) emissions. SF rates (SFRs) were calculated from GALEX near-ultraviolet (UV) and WISE 12 μm images within the beam-pointings, covering the full bar extent (SFRs were also derived from far-UV and 22 μm).Results.We detect molecular gas along the bars of all probed galaxies. Molecular gas and SFR surface densities span the ranges log10(Σmol/[M⊙pc−2]) ∈ [0.4,2.4] and log10(ΣSFR/[M⊙pc−1kpc−2]]) ∈ [−3.25, −0.75], respectively. The star formation efficiency (SFE; i.e., SFR/Mmol) in bars varies between galaxies by up to an order of magnitude (SFE ∈[0.1, 1.8] Gyr−1). On average, SFEs are roughly constant along bars. SFEs are not significantly different from the mean value in spiral galaxies reported in the literature (∼0.43 Gyr−1), regardless of whether we estimateMmolfrom CO(1–0) or CO(2–1). Interestingly, the higher the total stellar mass of the host galaxy, the lower the SFE within their bars. In particular, the two galaxies in our sample with the lowest SFE and ΣSFR(NGC 4548 and NGC 5850, SFE ≲ 0.25 Gyr−1, ΣSFR ≲ 10−2.25 M⊙yr−1kpc−2,M⋆ ≳ 1010.7 M⊙) are also those hosting massive bulges and signs of past interactions with nearby companions.Conclusions.We present a statistical analysis of the SFE in bars for a sample of 12 galaxies. The SFE in strong bars is not systematically inhibited (either in the central, middle, or end parts of the bar). Both environmental and internal quenching are likely responsible for the lowest SFEs reported in this work.

Orbital Dynamics in a Triaxial Barred Galaxy Model. I. The 2D System

Abstract We present the planar orbital dynamics of a realistic barred galaxy model, containing a nucleus (bulge), a triaxial bar, and a disk. After conducting a systematic and exhaustive orbit classification, we manage to determine how the dynamical parameters associated with the bar (mass, semiaxes, and angular velocity) affect the nature of the trajectories of the test particle. In our analysis, we distinguish not only between ordered, chaotic, and escaping motions but also between different types of regular orbits. More specifically, we reveal how the main types of regular orbits are influenced by the changes in the parameters of the galactic bar. Of particular interest is the phenomenon of trapped chaos that occurs in this galaxy model.

Galactic bar resonances inferred from kinematically hot stars in Gaia EDR3

ABSTRACT Using a numerical simulation of an isolated barred disc galaxy, we first demonstrate that the resonances of the inner bar structure induce more prominent features in the action space distribution for the kinematically hotter stars, which are less sensitive to the local perturbation, such as the transient spiral arms. Then, we analyse the action distribution for the kinematically hotter stars selected from the Gaia EDR3 data as the stars with higher values of radial and vertical actions. We find several resonance features, including two new features, in the angular momentum distribution similar to what are seen in our numerical simulations. We show that the bar pattern speeds of about Ωbar ∼ 34 and 42 km s−1 kpc−1 explain all these features equally well. The resonance features we find correspond to the inner 4:1, co-rotation (CR), outer 4:1, outer Lindblad, and outer 4:3 (CR, outer 4:1, outer Lindblad, outer 4:3, and outer 1:1) resonances, when Ωbar ∼ 34 (42) km s−1 kpc−1 is assumed.

Fast galaxy bars continue to challenge standard cosmology

ABSTRACT Many observed disc galaxies harbour a central bar. In the standard cosmological paradigm, galactic bars should be slowed down by dynamical friction from the dark matter halo. This friction depends on the galaxy’s physical properties in a complex way, making it impossible to formulate analytically. Fortunately, cosmological hydrodynamical simulations provide an excellent statistical population of galaxies, letting us quantify how simulated galactic bars evolve within dark matter haloes. We measure bar strengths, lengths, and pattern speeds in barred galaxies in state-of-the-art cosmological hydrodynamical simulations of the IllustrisTNG and EAGLE projects, using techniques similar to those used observationally. We then compare our results with the largest available observational sample at redshift z = 0. We show that the tension between these simulations and observations in the ratio of corotation radius to bar length is 12.62σ (TNG50), 13.56σ (TNG100), 2.94σ (EAGLE50), and 9.69σ (EAGLE100), revealing for the first time that the significant tension reported previously persists in the recently released TNG50. The lower statistical tension in EAGLE50 is actually caused by it only having five galaxies suitable for our analysis, but all four simulations give similar statistics for the bar pattern speed distribution. In addition, the fraction of disc galaxies with bars is similar between TNG50 and TNG100, though somewhat above EAGLE100. The simulated bar fraction and its trend with stellar mass both differ greatly from observations. These dramatic disagreements cast serious doubt on whether galaxies actually have massive cold dark matter haloes, with their associated dynamical friction acting on galactic bars.

Resolving local and global kinematic signatures of satellite mergers with billion particle simulations

ABSTRACT In this work, we present two new ∼109 particle self-consistent simulations of the merger of a Sagittarius-like dwarf galaxy with a Milky Way (MW)-like disc galaxy. One model is a violent merger creating a thick disc, and a Gaia–Enceladus/Sausage-like remnant. The other is a highly stable disc which we use to illustrate how the improved phase space resolution allows us to better examine the formation and evolution of structures that have been observed in small, local volumes in the MW, such as the z−vz phase spiral and clustering in the vR−vϕ plane when compared to previous works. The local z−vz phase spirals are clearly linked to the global asymmetry across the disc: we find both 2-armed and 1-armed phase spirals, which are related to breathing and bending behaviours, respectively. Hercules-like moving groups are common, clustered in vR−vϕ in local data samples in the simulation. These groups migrate outwards from the inner galaxy, matching observed metallicity trends even in the absence of a galactic bar. We currently release the best-fitting ‘present-day’ merger snapshots along with the unperturbed galaxies for comparison.

Role of galactic bars in the formation of spiral arms: a study through orbital and escape dynamics—I

In the present work we have developed a three-dimensional gravitational model of barred galaxies, in order to study orbital and escape dynamics of the stars inside their central barred region. Our gravitational model is composed of four components, central nucleus, bar, disc and dark matter halo. Furthermore we have analysed the model for two different types of bar potentials. The study has been carried out for a Hamiltonian system and thorough numerical studies have been done in order to categorize regular and chaotic motions of stars. We have seen that escape mechanism has only seen near saddle points ($L_2$, $L_4$ and $L_2^{'}$, $L_4^{'}$) of the Hamiltonian system. Orbital structures in $x$ - $y$ plane indicate that this escaping motion corresponds to the two ends of the bar. Classifications of orbits are found by calculating maximal Lyapunov exponent of the stellar trajectories corresponding to a specific initial condition vector. Poincar\'e surface section maps are studied in both $x$ - $y$ and $x$ - $p_x$ ($p_x$ is the momentum along $x$ - direction) plane to get a complete view of the escape properties of the system in the phase space. Also we studied in detail how the chaotic dynamics varies with mass, length and nature of the bar. We found that under suitable physical conditions the chaos plays a pivotal role behind the formation of grand design or poor spiral pattern for stronger bars and ring structures for weaker bars.

Galaxy Zoo: 3D – crowdsourced bar, spiral, and foreground star masks for MaNGA target galaxies

ABSTRACT The challenge of consistent identification of internal structure in galaxies – in particular disc galaxy components like spiral arms, bars, and bulges – has hindered our ability to study the physical impact of such structure across large samples. In this paper we present Galaxy Zoo: 3D (GZ:3D) a crowdsourcing project built on the Zooniverse platform that we used to create spatial pixel (spaxel) maps that identify galaxy centres, foreground stars, galactic bars, and spiral arms for 29 831 galaxies that were potential targets of the MaNGA survey (Mapping Nearby Galaxies at Apache Point Observatory, part of the fourth phase of the Sloan Digital Sky Surveys or SDSS-IV), including nearly all of the 10 010 galaxies ultimately observed. Our crowdsourced visual identification of asymmetric internal structures provides valuable insight on the evolutionary role of non-axisymmetric processes that is otherwise lost when MaNGA data cubes are azimuthally averaged. We present the publicly available GZ:3D catalogue alongside validation tests and example use cases. These data may in the future provide a useful training set for automated identification of spiral arm features. As an illustration, we use the spiral masks in a sample of 825 galaxies to measure the enhancement of star formation spatially linked to spiral arms, which we measure to be a factor of three over the background disc, and how this enhancement increases with radius.

Influence of the Galactic bar on the kinematics of the disc stars with Gaia EDR3 data

ABSTRACT A model of the Galaxy with the outer ring R1R2 can explain the observed distribution of the radial, VR, and azimuthal, VT, velocity components along the Galactocentric distance, R, derived from the Gaia EDR3 data. We selected stars from the Gaia EDR3 catalogue with reliable parallaxes, proper motions, and line-of-sight velocities lying near the Galactic plane, |z| < 200 pc, and in the sector of the Galactocentric angles |θ| < 15° and calculated the median velocities VR and VT in small bins along the distance R. The distribution of observed velocities appears to have some specific features: the radial velocity VR demonstrates a smooth fall from +5 km s−1 at the distance of R ≈ R0 − 1.5 kpc to −3 km s−1 at R ≈ R0 + 1.0 kpc while the azimuthal velocity VT shows a sharp drop by 7 km s−1 in the distance interval R0 < R < R0 + 1.0 kpc, where R0 is the solar Galactocentric distance. We build a model of the Galaxy including bulge, bar, disc, and halo components, which reproduces the observed specific features of the velocity distribution in the Galactocentric distance interval |R − R0| < 1.5 kpc. The best agreement corresponds to the time 1.8 ± 0.5 Gyr after the start of the simulation. A model of the Galaxy with the bar rotating at the angular velocity of Ωb = 55 ± 3 km s−1 kpc−1, which sets the OLR of the bar at the distance of R0 − 0.5 ± 0.4 kpc, provides the best agreement between the model and observed velocities. The position angle of the bar, θb, corresponding to the best agreement between the model and observed velocities is θb = 45 ± 15°.