3-dimensional kinematics in low foreground extinction windows of the Galactic bulge

Aims. This is the second in a series of papers that attempt to unveil the kinematic structure of the Galactic bulge through studying radial velocities and proper motions. We report here ~15000 new proper motions for three low foreground-extinction off-axis fields of the Galactic bulge. Methods. Proper motions were derived from a combination of Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2) and Advanced Camera for Surveys (ACS) images taken 8 and 9 years apart, and ACS observations taken 9 and 10 years apart, and they reach accuracies better than 0.9 mas/yr for more than ~10000 objects with magnitudes F814W < 24. Results. The proper motion distributions in these fields are similar to those of Galactic minor axis bulge fields. We observe the rotation of main sequence stars below the turn-off within the Galactic bulge, as in the minor axis fields. Conclusions. Our stellar proper motions measurements show a significant bulge rotation for fields as far from the galactic plane as b=-8.

Context. The astrometry towards the Galactic bulge is hampered by high stellar crowding and patchy extinction. This effect is particularly severe for optical surveys such as the European Space Agency satellite Gala. Aims. In this study, we assess the consistency of proper motion measurements between optical (Gaia DR3) and near-infrared (VIRAC2) catalogues in comparison with proper motions measured with the Hubble Space Telescope (HST) observations in several crowded fields towards the Galactic bulge and in Galactic globular clusters. Methods. Assuming that the proper motion measurements are well characterised, the uncertainty-normalised proper motion differences between pairs of catalogues are expected to follow a normal distribution. A deviation from a normal distribution defines the inflation factor r. By multiplying the proper motion uncertainties with the appropriate inflation factor values, the Gaia (VIRAC2) proper motion measurements are brought into a 1σ agreement with the HST proper motions. Results. The inflation factor (r) depends on stellar surface density. For the brightest stars in our sample (G &lt; 18), the dependence on G-band magnitude is strong, corresponding to the most precise Gaia DR3 proper motions. We used the number of observed Gaia DR3 sources as a proxy for the stellar surface density. Assuming that the HST proper motion measurements are well determined and free from systematic errors, we find that Gaia DR3 proper motion uncertainties are better characterised, having r &lt; 1.5 in fields with a stellar number density with fewer than 200 Gaia DR3 sources per arcmin2, and are underestimated by up to a factor of 4 in fields with stellar densities higher than 300 sources per arcmin2. For the most crowded fields in VIRAC2, the proper motion uncertainties are underestimated by a factor of 1.1 up to 1.5, with a dependence on J-band magnitude. In all fields, the brighter sources have the higher r value. At the faint end (G &gt; 19), the inflation factor is close to 1, meaning that the proper motions already fully agree with the HST measurements within 1σ. Conclusions. In the crowded fields common to both catalogues, VIRAC2 proper motions agree with HST proper motions and do not need an inflation factor for their uncertainties. Because of the depth and completeness of VIRAC2 in these fields, it is an ideal complement to Gaia DR3 for proper motion studies towards the Galactic bulge.

We report the progress in our measurement of the 3-D kinematics in several low foreground extinction windows of the Galactic Bulge. In order to complete the 3-D kinematics of as many stars as possible, proper motions and radial velocities have been obtained using HST WFPC2-ACS and VLT VIMOS respectively. Our preliminary results for fields close to the galactic minor axis show a significant vertex deviation, which can be directly related to a signature of triaxility. This is one of the strongest proofs to date of the presence of the stellar bar in the galactic bulge.

The final version of the XPM catalogue, created by the authors, contains about 314 million stellar positions and absolute proper motions and covers the whole celestial sphere without gaps in the magnitude range 10 m < B < 22 m . The analysis of stellar positions and proper motions of the XPM catalogue is presented. The coordinate axes, defined by the XPM catalogue, were shown to have an ambiguity of rotation relative to the LQAC quasars and ICRF2 sources less than 0.2 mas yr −1 . It is concluded that the XPM catalogue is the independent realization of the ICRS in the optical and near-infrared wavelengths in the sense of obtaining of proper motions. The absolute proper motions of XPM stars were compared with the similar data from the HCRF modern catalogues. The proper motions of stars in these catalogues were shown to have the appreciable random and systematic errors.

Context. The census of the globular clusters (GCs) in the Milky Way is still a work in progress. The advent of new deep surveys has made it possible to discover many new star clusters both in the Galactic disk and bulge, but many of these new candidates have not yet been studied in detail, leaving a veil on their true physical nature. Aims. We explore the nature of 19 new GC candidates in the Galactic bulge by analysing their colour–magnitude diagrams (CMDs) in the near-infrared (NIR) using the VISTA Variables in the Via Láctea Survey (VVV) database. We estimate their main astrophysical parameters: reddening and extinction, distance, total luminosity, mean cluster proper motions (PMs), metallicity, and age. Methods. We obtain the cluster catalogues including the likely cluster members by applying a decontamination procedure on the observed CMDs based on the vector PM diagrams from VIRAC2. We adopt NIR reddening maps in order to calculate the reddening and extinction for each cluster, and then estimate the distance moduli and heliocentric distances. Metallicities and ages are evaluated by fitting theoretical stellar isochrones. We also calculate their luminosities in comparison with known Galactic GCs. Results. We estimate a wide reddening range of 0.25 ⩽ E(J − Ks)⩽2.0 mag and extinction 0.11 ⩽ AKs ⩽ 0.86 mag for the sample clusters, as expected in the bulge regions. The range of heliocentric distances is 6.8 ⩽ D ⩽ 11.4 kpc. This allows us to place these clusters between 0.56 and 3.25 kpc from the Galactic centre, assuming R⊙ = 8.2 kpc. Also, their PMs are kinematically similar to the typical motion of the Galactic bulge, apart from VVV-CL160, which shows different PMs. We also derive their metallicities and ages, finding −1.40⩽ [Fe/H] ⩽ 0.0 dex and t ≈ 8 − 13 Gyr respectively. The luminosities are calculated both in Ks- and V-bands, recovering −3.4 ⩽ MV ⩽ −7.5. We also examine the possible RR Lyrae members found in the cluster fields. Conclusions. Based on their positions, kinematics, metallicities, and ages, and comparing our results with the literature, we conclude that nine candidates are real GCs, seven need more observations to be fully confirmed as GCs, and three candidates are discarded as GCs and appear to be younger open clusters.

Context. The VISTA Variables in the Via Láctea Extended Survey (VVVX) allows us to probe previously unexplored regions of the inner Milky Way (MW), especially those that are affected by stellar crowding and strong extinction. Aims. Our long-term goal is to identify new star clusters and investigate them to reveal their true nature. In particular, we are looking for new candidate globular clusters (GCs) located in the Galactic bulge and disk, with the aim of completing the census of the MW GC system. Methods. We searched and characterised new GCs, using a combination of the near-infrared (IR) VVVX survey and Two Micron All Sky survey (2MASS) datasets, and the optical Gaia Early Data Release 3 (EDR3) photometry and its precise proper motions (PMs). Results. We report the discovery of a new Galactic GC, named Garro 02, situated at RA = 18:05:51.1, Dec = −17:42:02 and l = 12.°042, b = +1.°656. Performing a PM-decontamination procedure, we built a final catalogue with all cluster members, on which we performed a photometric analysis. We calculated a reddening of E(J − Ks) = 1.07 ± 0.06 mag and extinction of AKs = 0.79 ± 0.04 mag in the near-IR; while E(BP − RP) = 2.40 ± 0.01 mag and AG = 4.80 ± 0.02 mag in optical passbands. Its heliocentric distance is D = 5.6 ± 0.8 kpc, which places Garro 02 at a Galactocentric distance of RG = 2.9 kpc and Z = 0.006 kpc above the Galactic plane. We also estimated the metallicity and age by comparison with known GCs and by fitting PARSEC isochrones, finding [Fe/H] = −1.30 ± 0.2 dex and age = 12 ± 2 Gyr. We derived the mean cluster PM of (µα*,µδ) = (−6.07 ± 0.62, −6.15 ± 0.75) mas yr−1. We calculated the cluster luminosity in the near-IR of MKs = −7.52 ± 1.23 mag, which is equivalent to MV = −5.44 mag. The core and tidal radii from the radial density profile are rc = 1.25 ± 0.27 arcmin (2.07 pc) and rt = 7.13 ± 3.83 arcmin (11.82 pc), respectively. Conclusions. We confirm Garro 02 as a new genuine Galactic GC, located in the MW bulge. It is a low-luminosity, metal-poor, and old GC, and it is a lucky survivor of the strong dynamical processes that occurred during the MW’s entire life.

This thesis is part of a project which attempts to unveil the structure of the galactic bulge of our galaxy through the study of the kinematics of stars in low foreground extinction windows.Thus, in order to effectively constraint the phase-space distribution function of the galactic bulge, we have collected a large number of radial velocities (~3200) and proper motions (~50000) in six of those ``windows'' with low extinction across the bulge. In addition, a self-consistent Schwarzschild model to study the distribution of stellar orbits in the galactic bulge has been produced.

A proper motion study of a field of 20′ × 20′ inside Plaut's low extinction window (l,b)=(0o, −8o), has been completed. Relative proper motions and photographicBVphotometry have been derived for ~ 21,000 stars reaching toV~ 20.5 mag, based on the astrometric reduction of 43 photographic plates, spanning over 21 years of epoch difference. Proper motion errors are typically 1 mas yr−1. Cross-referencing with the 2MASS catalog yielded a sample of ~ 8700 stars, from which predominantly disk and bulge subsamples were selected photometrically from theJHcolor-magnitude diagram. The two samples exhibited different proper-motion distributions, with the disk displaying the expected reflex solar motion. Galactic rotation was also detected for stars between ~2 and ~3 kpc from us. The bulge sample, represented by red giants, has an intrinsic proper motion dispersion of (σl, σb) = (3.39, 2.91)±(0.11, 0.09) mas yr−1, which is in good agreement with previous results. A mean distance of$6.37^{+0.87}_{-0.77}$kpc has been estimated for the bulge sample, based on the observedKmagnitude of the horizontal branch red clump. The metallicity [M/H] distribution was also obtained for a subsample of 60 bulge giants stars, based on calibrated photometric indices. The observed [M/H] shows a peak value at [M/H] ~ −0.1 with an extended metal poor tail and around 30% of the stars with supersolar metallicity. No change in proper motion dispersion was observed as a function of [M/H]. We are currently in the process of obtaining CCDUBV RIphotometry for the entire proper-motion sample of ~ 21,000 stars.

The study of the internal kinematics of galaxies provides insights into their past evolution, current dynamics, and future trajectory. The Large Magellanic Cloud (LMC), as the largest and one of the nearest satellite galaxies of the Milky Way (MW), presents unique opportunities to investigate these phenomena in great detail. We aim to investigate the internal kinematics of the LMC by deriving precise stellar proper motions using data from the VISTA survey of the Magellanic Clouds system (VMC). The main objective is to refine the LMC’s dynamical parameters using improved proper motion measurements exploiting the additional epochs of observations from the VMC survey. We utilised high-precision proper motion measurements from the VMC survey, leveraging an extended time baseline from approximately 2 to 10 years. This extension significantly enhanced the precision of the proper motion data, reducing uncertainties from 6 mas yr^-1 in prior studies using the VMC dataset to 1.5 mas yr^-1. Using this data, we derived geometrical and kinematic parameters, and generated velocity maps and rotation curves in the LMC disc plane and the sky plane, for both young and old stellar populations. Finally, we compared a suite of dynamical models that simulate the interaction of the LMC with the MW and Small Magellanic Cloud (SMC), against the observations. The tangential rotation curve reveals an asymmetric drift between young and old stars, while the radial velocity curve for the young population shows an increasing trend within the inner bar region, suggesting non-circular orbits. The internal rotation map confirms the clockwise rotation around the dynamical centre of the LMC, which is consistent with previous predictions. A significant residual motion was detected towards the north-east of the LMC, directed away from the centre. This feature observed in the inner disc region is kinematically connected with a substructure identified in the periphery known as Eastern Substructure 1. This motion of the LMC sources suggests a possible tidal influence from the MW, combined with the effects of the recent close pericentre passage of the SMC ∼150 Myr ago.

In 2004 the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS) project undertook a very deep ACS/WFC exposure-set of the Sgr-I low-reddening window in the Galactic Bulge, with repeat observations 2.04 years later. The combination of superb first-epoch sampling, wide field of view and high PSF stability of ACS/WFC on Hubble allows proper motions to be extracted for more than 137,000 objects, over 85,000 to accuracy better than 0.3 mas yr−1. We present these proper motions and outline some of the uses to which they have been put, including the separation of a pure-Bulge sample and the inner Galactic rotation curve.

The systematic differences between the stellar positions and proper motions of the XPM and UCAC4 catalogs have been obtained in the form of decompositions into vector spherical harmonics by taking into account the magnitude equation. The systematic components have been extracted with a probability of at least 0.98 by dividing 41 316 676 stars into groups corresponding to 12 J magnitude bins with a width of 0.5m for mean values from 10m.25 to 15m.75. A study of the systematic differences between the equatorial coordinates suggests that the range of systematic differences between the XPM and UCAC4 positions exceeds the corresponding range of differences between PPMXL and UCAC4 by a factor of 5, especially for bright stars in the range being investigated. Analysis of the orientation of the XPM and UCAC4 reference frames has shown that their mutual rotation is 2–4 mas around the X axis and 7–10 mas around the Z axis. These angles depend on the magnitude of stars. Since two systems of proper motions are given in the XPM catalog, XPMx and XPMp, we have decomposed the proper motion differences XPMx–XPMp into vector spherical harmonics and found these differences to be free from the magnitude equation. An important fact is that the first-order zonal coefficients have turned out to be greatest in absolute value. The toroidal coefficient t1,0,1,0 found has shown that the XPMx and XPMp reference frames of proper motions rotate relative to each other around the Z axis with an angular velocity of 0.45 mas yr−1. It should be added that the range of systematic differences XPMx–XPMp is 2.1 mas yr−1 in right ascension and 1.7 mas yr−1 in declination. The angular velocities of mutual rotation of the XPMp and UCAC4 reference frames change within the range from 0.6 to 2.2 mas yr−1, while the analogous range for the XPMх and UCAC4 catalogs is 0.3–1.8 mas yr−1. The angular velocity and coordinates of the pole of the mutual rotation axis depend on the magnitude of stars. The parameters of the mutual rotation around the Z axis derived from the differences XPMx–UCAC4 and XPMp–UCAC4 change from 0.03 ± 0.06 to 1.73 ± 0.06 mas yr−1 and from 0.49 ± 0.06 to 2.19 ± 0.06 mas yr−1, respectively. Based on our analysis, we have shown that the XPMcatalog actually comprises two catalogs, XPM(XSC) and XPM(PSC), in which the stellar positions coincide at the standard epoch J2000 and differ at any other epoch. The decomposition coefficients of the systematic differences XPM–UCAC4 we obtained allow the stellar positions and proper motions from one catalog to be reduced to the system of the other catalog by taking into account this duality.

Hypervelocity stars (HVSs) are amongst the fastest objects in our Milky Way. These stars are predicted to come from the Galactic center (GC) and travel along unbound orbits across the Galaxy. In the coming years, the ESA satellite Gaia will provide the most complete and accurate catalogue of the Milky Way, with full astrometric parameters for more than $1$ billion stars. In this paper, we present the expected sample size and properties (mass, magnitude, spatial, velocity distributions) of HVSs in the Gaia stellar catalogue. We build three Gaia mock catalogues of HVSs anchored to current observations, exploring different ejection mechanisms and GC stellar population properties. In all cases, we predict hundreds to thousands of HVSs with precise proper motion measurements within a few tens of kpc from us. For stars with a relative error in total proper motion below $10 \%$, the mass range extends to ~$10 M_{\odot}$ but peaks at ~$1$ $M_\odot$. The majority of Gaia HVSs will therefore probe a different mass and distance range compared to the current non-Gaia sample. In addition, a subset of a few hundreds to a few thousands of HVSs with $M$ ~ $3$ $M_\odot$ will be bright enough to have a precise measurement of the three-dimensional velocity from Gaia alone. Finally, we show that Gaia will provide more precise proper motion measurements for the current sample of HVS candidates. This will help identifying their birthplace narrowing down their ejection location, and confirming or rejecting their nature as HVSs. Overall, our forecasts are extremely encouraging in terms of quantity and quality of HVS data that can be exploited to constrain both the Milky Way potential and the GC properties.

view Abstract Citations (34) References (79) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On Stellar Streaming Motions in Triaxial Objects: The Case of the Galactic Center Vietri, M. Abstract The stellar dynamical consequences of assuming that the tilted ring of H I gas at about r = 1.5 kpc is in a steady state are explored. It is shown that this implies that the Galactic bulge is triaxial and counterrotating with respect to the disk. Two self-consistent models for a bulge in a realistic Galactic potential are obtained by means of a modification of Schwarzschild's (1979) method. It is concluded that it is not possible to construct a realistic triaxial object such that figure rotation and the matter streaming have opposite signs in an inertial reference frame. Observations of planetary nebulae and OH/IR stars in the Galactic center do not favor a model in which the bulge stars rotate in the direction opposite to that of the disk material. These findings make it unlikely that the 22 deg tilt of the H I ring at r = 1.5 kpc can be explained in terms of the tilted stable retrograde anomalous orbits in a rotating triaxial bulge. Publication: The Astrophysical Journal Pub Date: July 1986 DOI: 10.1086/164320 Bibcode: 1986ApJ...306...48V Keywords: Galactic Nuclei; Galactic Rotation; Gas Dynamics; Hydrogen Ions; Stellar Motions; Astronomical Models; Density Distribution; Galactic Bulge; Milky Way Galaxy; Radial Distribution; Streams; Astrophysics; GALAXIES: INTERNAL MOTIONS; GALAXIES: NUCLEI; GALAXIES: STRUCTURE full text sources ADS | data products SIMBAD (2) NED (1)

view Abstract Citations (49) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Kinematics of the late M stars in the galactic nuclear bulge Mould, J. R. Abstract The radial velocity dispersion is determined for a sample of late M stars in the nuclear bulge of the Galaxy. Although these stars are chemically among the youngest in the spheroidal subsystem and may be physically younger by a few billion years, they have a velocity dispersion of 113 ± 11 km s-1, similar to that of the oldest objects in the halo. Publication: The Astrophysical Journal Pub Date: March 1983 DOI: 10.1086/160774 Bibcode: 1983ApJ...266..255M Keywords: Galactic Bulge; Galactic Nuclei; Late Stars; M Stars; Milky Way Galaxy; Radial Velocity; Stellar Motions; Giant Stars; Kinematics; Stellar Evolution; Stellar Spectra; Stellar Spectrophotometry; Astrophysics full text sources ADS |

We validate the 2010ApJ...716....1B kinematic models for the Milky Way's disk and halo stars with Gaia Data Release 3 data. Bond et al. constructed models for stellar velocity distributions using stellar radial velocities measured by the Sloan Digital Sky Survey (SDSS) and stellar proper motions derived from SDSS and the Palomar Observatory Sky Survey astrometric measurements. These models describe velocity distributions as functions of position in the Galaxy, with separate models for disk and halo stars that were labeled using SDSS photometric and spectroscopic metallicity measurements. We find that the Bond et al. model predictions are in good agreement with recent measurements of stellar radial velocities and proper motions by the Gaia survey. In particular, the model accurately predicts the skewed non-Gaussian distribution of rotational velocity for disk stars and its vertical gradient, as well as the dispersions for all three velocity components. Additionally, the spatial invariance of velocity ellipsoid for halo stars when expressed in spherical coordinates is also confirmed by Gaia data at galacto-centric radial distances of up to 15 kpc.