scholarly journals The Milky Way bar/bulge in proper motions: a 3D view from VIRAC and Gaia

2019 ◽  
Vol 489 (3) ◽  
pp. 3519-3538 ◽  
Author(s):  
Jonathan P Clarke ◽  
Christopher Wegg ◽  
Ortwin Gerhard ◽  
Leigh C Smith ◽  
Phil W Lucas ◽  
...  
Keyword(s):  
Proper Motion ◽  
Milky Way ◽  
Selection Function ◽  
Full Potential ◽  
Proper Motions ◽  
Bulge Region ◽  
Similar Distance ◽  
Pattern Speed ◽  
The Mean ◽  
Red Clump

Abstract We have derived absolute proper motions of the entire Galactic bulge region from VVV Infrared Astrometric Catalogue (VIRAC) and Gaia. We present these both as integrated on-sky maps and, after isolating standard candle red clump (RC) stars, as a function of distance using RC magnitude as a proxy. These data provide a new global, 3D view of the Milky Way barred bulge kinematics. We find a gradient in the mean longitudinal proper motion, $\langle \mu _ l^\star \rangle $, between the different sides of the bar, which is sensitive to the bar pattern speed. The split RC has distinct proper motions and is colder than other stars at similar distance. The proper motion correlation map has a quadrupole pattern in all magnitude slices showing no evidence for a separate, more axisymmetric inner bulge component. The line-of-sight integrated kinematic maps show a high central velocity dispersion surrounded by a more asymmetric dispersion profile. $\sigma _{\mu _l} / \sigma _{\mu _b}$ is smallest, ≈1.1, near the minor axis and reaches ≈1.4 near the disc plane. The integrated $\langle \mu_b\rangle$ pattern signals a superposition of bar rotation and internal streaming motion, with the near part shrinking in latitude and the far part expanding. To understand and interpret these remarkable data, we compare to a made-to-measure barred dynamical model, folding in the VIRAC selection function to construct mock maps. We find that our model of the barred bulge, with a pattern speed of 37.5 $\mathrm{ \mathrm{ km \, s^{-1}} \, kpc^{-1} }$, is able to reproduce all observed features impressively well. Dynamical models like this will be key to unlocking the full potential of these data.

New VIRAC proper motion maps show signature of galactic boxy/peanut bulge

2019 ◽  
Vol 14 (S353) ◽  
pp. 29-30
Author(s):  
Jonathan P. Clarke ◽  
Christopher Wegg ◽  
Ortwin Gerhard ◽  
Leigh C. Smith ◽  
Phil W. Lucas ◽  
...  
Keyword(s):  
Proper Motion ◽  
Dynamical Model ◽  
Line Of Sight ◽  
Selection Function ◽  
Kinematic Structure ◽  
Proper Motions ◽  
Galactic Bulge ◽  
Bulge Region ◽  
Pattern Speed ◽  
Red Clump

AbstractWe have derived absolute proper motions of stars in the Galactic bulge region combining the VVV InfraRed Astrometric Catalogue (VIRAC) and Gaia. We use the proper motions to study the kinematic structure of the bulge both integrated along the line-of-sight and in magnitude intervals using red clump stars as standard candles. In parallel we compare to a made-to-measure barred dynamical model, folding in the VIRAC selection function, to understand and interpret the structures that we observe. The barred dynamical model, which contains a boxy/peanut bulge, and has a pattern speed of 37.5 kms−1 kpc−1, is able to reproduce all structures impressively well.

scholarly journals Proper motions in the Galactic bulge: Plaut's window

2007 ◽  
Vol 3 (S245) ◽  
pp. 351-354
Author(s):  
Katherine Vieira ◽  
Dana Cassetti-Dinescu ◽  
René A. Méndez ◽  
R. Michael Rich ◽  
Terrence M. Girard ◽  
...  
Keyword(s):  
Proper Motion ◽  
Galactic Rotation ◽  
Red Giants ◽  
Proper Motions ◽  
Motion Study ◽  
Solar Motion ◽  
Two Samples ◽  
Red Clump ◽  
Good Agreement ◽  
Peak Value

AbstractA 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.

scholarly journals The last breath of the Sagittarius dSph

2020 ◽  
Vol 497 (4) ◽  
pp. 4162-4182 ◽  
Author(s):  
Eugene Vasiliev ◽  
Vasily Belokurov
Keyword(s):  
Milky Way ◽  
Dwarf Galaxy ◽  
3D Structure ◽  
Major Axis ◽  
Final State ◽  
Tidal Forces ◽  
The Galaxy ◽  
The Mean ◽  
Red Clump ◽  
Astrometric Data

ABSTRACT We use the astrometric and photometric data from Gaia Data Release 2 and line-of-sight velocities from various other surveys to study the 3D structure and kinematics of the Sagittarius dwarf galaxy. The combination of photometric and astrometric data makes it possible to obtain a very clean separation of Sgr member stars from the Milky Way foreground; our final catalogue contains 2.6 × 105 candidate members with magnitudes G < 18, more than half of them being red clump stars. We construct and analyse maps of the mean proper motion and its dispersion over the region ∼30 × 12 deg, which show a number of interesting features. The intrinsic 3D density distribution (orientation, thickness) is strongly constrained by kinematics; we find that the remnant is a prolate structure with the major axis pointing at ∼45° from the orbital velocity and extending up to ∼5 kpc, where it transitions into the stream. We perform a large suite of N-body simulations of a disrupting Sgr galaxy as it orbits the Milky Way over the past 2.5 Gyr, which are tailored to reproduce the observed properties of the remnant (not the stream). The richness of available constraints means that only a narrow range of parameters produce a final state consistent with observations. The total mass of the remnant is $\sim \!4\times 10^8\, \mathrm{M}_\odot$, of which roughly a quarter resides in stars. The galaxy is significantly out of equilibrium, and even its central density is below the limit required to withstand tidal forces. We conclude that the Sgr galaxy will likely be disrupted over the next Gyr.

scholarly journals Proper Motions With Respect to the Extragalactic Reference Frame

1990 ◽  
Vol 141 ◽  
pp. 407-417
Author(s):  
A. R. Klemola
Keyword(s):  
Reference Frame ◽  
Proper Motion ◽  
Milky Way ◽  
Proper Motions ◽  
Stellar Proper Motions

The Lick proper motion program, one of several using galaxies as a reference frame, is summarized with a statement of work accomplished for the non-Milky Way sky. The problem of identifying relatively transparent regions at low galactic latitudes is discussed, with tabular results presented for 41 windows from the literature having observable galaxies. These fields may be helpful for attaching stellar proper motions directly to the extragalactic frame.

scholarly journals Using ground based data as a precursor for Gaia in getting proper motions of satellites

2017 ◽  
Vol 12 (S330) ◽  
pp. 210-213
Author(s):  
Tobias K. Fritz ◽  
Sean T. Linden ◽  
Paul Zivick ◽  
Nitya Kallivayalil ◽  
Jo Bovy
Keyword(s):  
Adaptive Optics ◽  
Globular Cluster ◽  
Proper Motion ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Optical Data ◽  
Line Of Sight ◽  
Wide Field ◽  
Proper Motions ◽  
Tidal Stream

AbstractWe present our effort to measure the proper motions of satellites in the halo of the Milky Way with mainly ground based telescopes as a precursor on what is possible with Gaia. For our first study, we used wide field optical data from the LBT combined with a first epoch of SDSS observations, on the globular cluster Palomar 5 (Pal 5). Since Pal 5 is associated with a tidal stream it is very useful to constrain the shape of the potential of the Milky Way. The motion and other properties of the Pal 5 system constrain the inner halo of the Milky Way to be rather spherical. Further, we combined adaptive optics and HST to get an absolute proper motion of the globular cluster Pyxis. Using the proper motion and the line-of-sight velocity we find that the orbit of Pyxis is rather eccentric with its apocenter at more than 100 kpc and its pericenter at about 30 kpc. The dynamics excludes an association with the ATLAS stream, the Magellanic clouds, and all satellites of the Milky Way at least down to the mass of Leo II. However, the properties of Pyxis, like metallicity and age, point to an origin from a dwarf of at least the mass of Leo II. We therefore propose that Pyxis originated from an unknown relatively massive dwarf galaxy, which is likely today fully disrupted. Assuming that Pyxis is bound to the Milky Way we derive a 68% lower limit on the mass of the Milky Way of 9.5 × 1011 M⊙.

scholarly journals The VMC survey

2020 ◽  
Vol 641 ◽  
pp. A134
Author(s):  
Thomas Schmidt ◽  
Maria-Rosa L. Cioni ◽  
Florian Niederhofer ◽  
Kenji Bekki ◽  
Cameron P. M. Bell ◽  
...  
Keyword(s):  
Proper Motion ◽  
Milky Way ◽  
Dwarf Galaxies ◽  
Dynamical Evolution ◽  
Large Magellanic Cloud ◽  
Small Population ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Proper Motions ◽  
Flow Motion

Context. The Magellanic Clouds are a nearby pair of interacting dwarf galaxies and satellites of the Milky Way. Studying their kinematic properties is essential to understanding their origin and dynamical evolution. They have prominent tidal features and the kinematics of these features can give hints about the formation of tidal dwarfs, galaxy merging and the stripping of gas. In addition they are an example of dwarf galaxies that are in the process of merging with a massive galaxy. Aims. The goal of this study is to investigate the kinematics of the Magellanic Bridge, a tidal feature connecting the Magellanic Clouds, using stellar proper motions to understand their most recent interaction. Methods. We calculated proper motions based on multi-epoch Ks-band aperture photometry, which were obtained with the Visible and Infrared Survey Telescope for Astronomy (VISTA), spanning a time of 1−3 yr, and we compared them with Gaia Data Release 2 (DR2) proper motions. We tested two methods for removing Milky Way foreground stars using Gaia DR2 parallaxes in combination with VISTA photometry or using distances based on Bayesian inference. Results. We obtained proper motions for a total of 576 411 unique sources over an area of 23 deg2 covering the Magellanic Bridge including mainly Milky Way foreground stars, background galaxies, and a small population of possible Magellanic Bridge stars (< 15 000), which mostly consist of giant stars with 11.0 <  Ks <  19.5 mag. The first proper motion measurement of the Magellanic Bridge centre is 1.80 ± 0.25 mas yr−1 in right ascension and −0.72 ± 0.13 mas yr−1 in declination. The proper motion measurements of stars along the Magellanic Bridge from the VISTA survey of the Magellanic Cloud system (VMC) and Gaia DR2 data confirm a flow motion from the Small to the Large Magellanic Cloud. This flow can now be measured all across the entire length of the Magellanic Bridge. Conclusions. Our measurements indicate that the Magellanic Bridge is stretching. By converting the proper motions to tangential velocities, we obtain ∼110 km s−1 in the plane of the sky. Therefore it would take a star roughly 177 Myr to cross the Magellanic Bridge.

scholarly journals Globular clusters in the era of precision astrometry

2019 ◽  
Vol 14 (S351) ◽  
pp. 412-415
Author(s):  
Paolo Bianchini
Keyword(s):  
Formation Mechanism ◽  
Proper Motion ◽  
Measurement Errors ◽  
Globular Clusters ◽  
Tangential Component ◽  
Proper Motions ◽  
The Mean ◽  
Motion Measurements ◽  
Precision Astrometry

Abstracthe study of the kinematics of globular clusters (GCs) offers the possibility of unveiling their long term evolution and uncovering their yet unknown formation mechanism. Gaia DR2 has strongly revitalized this field and enabled the exploration of the 6D phase-space properties of Milky Way GCs, thanks to precision astrometry. However, to fully leverage on the power of precision astrometry, a thorough investigations of the data is required. In this contribution, we show that the study of the mean radial proper motion profiles of GCs offers an ideal benchmark to assess the presence of systematics in crowded fields. Our work demonstrates that systematics in Gaia DR2 for the closest 14 GCs are below the random measurement errors, reaching a precision of ∼0.015 mas yr−1 for mean proper motion measurements. Finally, through the analysis of the tangential component of proper motions, we report the detection of internal rotation in a sample of ∼50 GCs, and outline the implications of the presence of angular momentum for the formation mechanism of proto-GC. This result gives the first taste of the unparalleled power of Gaia DR2 for GCs science, in preparation for the subsequent data releases.

scholarly journals VVV WIN 1733−3349: a low extinction window to probe the far side of the Milky Way bulge

2020 ◽  
Vol 494 (1) ◽  
pp. L32-L36 ◽  
Author(s):  
R K Saito ◽  
D Minniti ◽  
R A Benjamin ◽  
M G Navarro ◽  
J Alonso-García ◽  
...  
Keyword(s):  
Stellar Population ◽  
Milky Way ◽  
Galactic Structure ◽  
Density Fluctuations ◽  
Surrounding Area ◽  
Low Latitude ◽  
The Past ◽  
Near Ir ◽  
The Mean ◽  
Red Clump

ABSTRACT Windows of low extinction in the Milky Way (MW) have been used along the past decades for the study of the Galactic structure and the stellar population across the inner bulge and disc. Here, we report the analysis of another low extinction near-IR window discovered by the VISTA Variables in the Vía Láctea Survey (VVV). VVV WIN 1733−3349 is about half a degree in size and is conveniently located right in the MW plane, at Galactic coordinates (l, b) = (−5.2, −0.3). The mean extinction of VVV WIN 1733−3349 is $A_{K_{\mathrm{ s}}}$ = 0.61 ± 0.08 mag, which is much smaller than the extinction in the surrounding area. The excess in the star counts is consistent with the reduced extinction and complemented by studying the distribution of red clump (RC) stars. Thanks to the strategic low-latitude location of VVV WIN 1733−3349, we are able to interpret their RC density fluctuations with the expected overdensities due to the presence of the spiral arms beyond the bulge. In addition, we find a clear excess in the number of microlensing events within the window, which corroborates our interpretation that VVV WIN 1733−3349 is revealing the far side of the MW bulge.

scholarly journals The Lick Northern Proper Motion Program

1995 ◽  
Vol 166 ◽  
pp. 45-48 ◽  
Author(s):  
A.R. Klemola ◽  
R.B. Hanson ◽  
B.F. Jones
Keyword(s):  
Proper Motion ◽  
Milky Way ◽  
Proper Motions ◽  
Photographic Photometry

The Lick Northern Proper Motion (NPM) Program will provide absolute proper motions (referred to faint galaxies), equatorial coordinates, and two-color photographic photometry for some 300,000 stars with 8 < B < 18 covering the 70% of the sky north of declination −23°. Part 1 of the NPM program (NPM1), recently completed, covers the 72% of the northern sky (899 of 1,246 fields) outside the Milky Way. Two catalogs result from NPM1: The NPM1 Catalog (Klemola et al. 1993a, Hanson 1993a) contains 149,000 stars. The NPM1 Reference Galaxy List (Klemola et al. 1993b, Hanson 1993b) contains 50,000 faint galaxies. Klemola et al. (1987, 1994, 1995) describe the NPM program. Hanson et al. (1994) describe the NPM1 Catalogs.

scholarly journals Microarcsecond astrometry in the Local Group

2007 ◽  
Vol 3 (S248) ◽  
pp. 474-480
Author(s):  
A. Brunthaler ◽  
M. J. Reid ◽  
H. Falcke ◽  
C. Henkel ◽  
K. M. Menten
Keyword(s):  
Proper Motion ◽  
Milky Way ◽  
Local Group ◽  
Statistical Error ◽  
Dark Matter Halo ◽  
Proper Motions ◽  
Angular Rotation ◽  
Vlbi Observations ◽  
Ic 10 ◽  
Motion Measurements

AbstractMeasuring the proper motions and geometric distances of galaxies within the Local Group is very important for our understanding of its history, present state and future. Currently, proper motion measurements using optical methods are limited only to the closest companions of the Milky Way. However, given that VLBI provides the best angular resolution in astronomy and phase-referencing techniques yield astrometric accuracies of ≈ 10 micro-arcseconds, measurements of proper motions and angular rotation rates of galaxies out to a distance of ~ 1 Mpc are feasible. This paper presents results of VLBI observations in regions of H2O maser activity of the Local Group galaxies M33 and IC 10. Two masing regions in M33 are on opposite sides of the galaxy. This allows a comparison of the angular rotation rate (as measured by the VLBI observations) with the known inclination and rotation speed of the Hi gas disk leading to a determination of a geometric distance of 730 ± 100 ± 135 kpc. The first error indicates the statistical error of the proper-motion measurements, while the second error is the systematic error of the rotation model. Within the errors, this distance is consistent with the most recent Cepheid distance to M33. Since all position measurements were made relative to an extragalactic background source, the proper motion of M33 has also been measured. This provides a three dimensional velocity vector of M33, showing that this galaxy is moving with a velocity of 190 ± 59 km s−1 relative to the Milky Way. For IC 10, we obtain a motion of 215 ± 42 km s−1 relative to the Milky Way. These measurements promise a new handle on dynamical models for the Local Group and the mass and dark matter halo of Andromeda and the Milky Way.

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