VIRAC: the VVV Infrared Astrometric Catalogue

Smith, Leigh C.; Lucas, P. W.; Kurtev, R.; Smart, R. L.; Minniti, D.; Borissova, J.; Jones, H. R. A.; Zhang, Z. H.; Marocco, F.; Peña, C. Contreras; Gromadzki, M.; Kuhn, Michael A.; Drew, J. E.; Pinfield, D. J.; Bedin, L. R.

doi:10.1093/mnras/stx2789

Cited by 147 publications

(123 citation statements)

References 61 publications

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“…Unfortunately, the optical astrometry mission, Gaia (Gaia Collaboration et al 2016), cannot see the NSD because of the heavy dust extinction in the optical band. Recently, the proper motion is measured from the VVV survey data, the VIRAC catalogue (Smith et al 2018), with a median uncertainty of 0.67 mas yr −1 for stars with 11 < K s < 14 mag. The absolute proper motion is also measured using the Gaia reference frame (Clarke et al 2019;.…”

Section: Discussionmentioning

confidence: 99%

Age dating the Galactic bar with the nuclear stellar disc

Baba

Kawata

2020

Monthly Notices of the Royal Astronomical Society

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We perform an N-body/hydrodynamics simulation of an isolated Milky Way-like galaxy and demonstrate that the formation epoch of the galactic bar can be identified from the age distribution of the nuclear stellar disc (NSD). The bar formation triggers the gas inflow in the bar region, and the gas inflow reaches the central subkpc region followed by an intense star formation for ∼ 1 Gyr. The star formation in the central sub-kpc region forms the thinner, kinematically cooler and rotating NSD component. Consequently, the formation epoch of the galactic bar becomes the oldest limit of the NSD stellar populations, which tells us the formation epoch of the bar. We also discuss that a challenge to measure the age distribution of the NSD in the Milky Way is contamination from the other stellar components, such as a classical bulge component, whose contamination may not be negligible in the central region. We demonstrate that transverse velocities of tracer stars, which will be measured by the near-infrared space astrometry mission, JASMINE, are crucial to kinematically distinguish the NSD from the other stellar component.

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Section: Discussionmentioning

confidence: 99%

Age dating the Galactic bar with the nuclear stellar disc

Baba

Kawata

2020

Monthly Notices of the Royal Astronomical Society

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“…In that work, we derived the mean transverse velocities v and v b and corresponding uncertainties as a function of distance across the bar/bulge region from ∼ 45 million giant stars in VVV. We used a combination of proper motions from Gaia DR2 (Gaia Collaboration et al 2018) and VIRAC v1.1 (Smith et al 2018), an astrometric catalogue derived from the VVV observations calibrated absolutely using Gaia DR2. In small fields of 0.2 deg × 0.2 deg across the VVV bulge footprint, the bulge giants (both red giant branch and red clump) were selected in a unextincted colour-magnitude box of 0.4 < (J − K s ) 0 < 1 and 11.5 < K s0 < 14.5 using a two-dimensional extinction map from the method of Gonzalez et al (2011).…”

Section: Application To Datamentioning

confidence: 99%

The pattern speed of the Milky Way bar from transverse velocities

Sanders

Smith

Evans

2019

Monthly Notices of the Royal Astronomical Society

130

102

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We use the continuity equation to derive a method for measuring the pattern speed of the Milky Way's bar/bulge from proper motion data. The method has minimal assumptions but requires complete coverage of the non-axisymmetric component in two of the three Galactic coordinates. We apply our method to the proper motion data from a combination of Gaia DR2 and VISTA Variables in the Via Lactea (VVV) to measure the pattern speed of the bar as Ω p = (41 ± 3) km s −1 kpc −1 (where the error is statistical). This puts the corotation radius at (5.7 ± 0.4) kpc, under the assumptions of the standard peculiar motion of the Sun and the absence of non-axisymmetric streaming in the Solar neighbourhood. The obtained result uses only data on the near-side of the bar which produces consistent measurements of the distance and velocity of the centre of the Galaxy. Addition of the data on the far-side of the bar pulls the pattern speed down to Ω p = (31 ± 1) km s −1 kpc −1 but requires a lower transverse velocity for the Galactic centre than observed. This suggests systematics of 5 − 10 km s −1 kpc −1 dominate the uncertainty. We demonstrate using a dynamically-formed bar/bulge simulation that even with the limited field of view of the VVV survey our method robustly recovers the pattern speed.

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“…Potential reference sources are The sub-array pattern is visible, as are regions in which linear (a gradient across the sub-array) or constant offset (flat colour in the subarray) correction methods were applied depending on VVV source density and the number of available Gaia counterparts. selected from Gaia DR2 as those with 5 parameter solutions, as-trometric_gof_al < 3, and astrometric_excess_noise_sig < 2, and from VIRAC as having no proper motion error flags (see section 4.2 of Smith et al 2018). Lindegren et al (2018) also discuss using the unit weight error for Gaia DR2 astrometric quality cuts, and since starting this work the reduced unit weight error has been officially recommended as the astrometric quality indicator.…”

Section: Astrometrymentioning

confidence: 99%

Transverse kinematics of the Galactic bar-bulge from VVV and Gaia

Sanders

Smith

Evans

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We analyse the kinematics of the Galactic bar-bulge using proper motions from the ESO public survey Vista Variables in the Via Lactea (VVV) and the second Gaia data release. Gaia has provided some of the first absolute proper motions within the bulge and the near-infrared VVV multi-epoch catalogue complements Gaia in highly-extincted low-latitude regions. We discuss the relative-to-absolute calibration of the VVV proper motions using Gaia. Along lines of sight spanning −10 < / deg < 10 and −10 < b/ deg < 5, we probabilistically model the density and velocity distributions as a function of distance of ∼ 45 million stars. The transverse velocities confirm the rotation signature of the bar seen in spectroscopic surveys. The differential rotation between the double peaks of the magnitude distribution confirms the X-shaped nature of the bar-bulge. Both transverse velocity components increase smoothly along the near-side of the bar towards the Galactic centre, peak at the Galactic centre and decline on the far-side. The anisotropy is σ /σ b ≈ 1.1 − 1.3 within the bulk of the bar, reducing to 0.9 − 1.1 when rotational broadening is accounted for, and exhibits a clear Xshaped signature. The vertex deviation in and b is significant | ρ b | 0.2, greater on the nearside of the bar and produces a quadrupole signature across the bulge indicating approximate radial alignment. We have re-constructed the 3D kinematics from the assumption of triaxiality, finding good agreement with spectroscopic survey results. In the co-rotating frame, we find evidence of bar-supporting x1 orbits and tangential bias in the in-plane dispersion field.

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VIRAC: the VVV Infrared Astrometric Catalogue

Cited by 147 publications

References 61 publications

Age dating the Galactic bar with the nuclear stellar disc

Age dating the Galactic bar with the nuclear stellar disc

The pattern speed of the Milky Way bar from transverse velocities

Transverse kinematics of the Galactic bar-bulge from VVV and Gaia

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