# University of Hertfordshire

## The Milky Way bar/bulge in proper motions: a 3D view from VIRAC & Gaia

Research output: Contribution to journalArticlepeer-review

### Standard

The Milky Way bar/bulge in proper motions: a 3D view from VIRAC & Gaia. / Clarke, Jonathan P.; Wegg, Christopher; Gerhard, Ortwin; Smith, Leigh C.; Lucas, Philip; Wylie, Shola M.

In: Monthly Notices of the Royal Astronomical Society, Vol. 489, No. 3, 11.2019, p. 3519-3538.

Research output: Contribution to journalArticlepeer-review

### Author

Clarke, Jonathan P. ; Wegg, Christopher ; Gerhard, Ortwin ; Smith, Leigh C. ; Lucas, Philip ; Wylie, Shola M. / The Milky Way bar/bulge in proper motions: a 3D view from VIRAC & Gaia. In: Monthly Notices of the Royal Astronomical Society. 2019 ; Vol. 489, No. 3. pp. 3519-3538.

### Bibtex

@article{de97bb63db5a4c99ba812248064cf40c,
title = "The Milky Way bar/bulge in proper motions: a 3D view from VIRAC & Gaia",
abstract = " We have derived absolute proper motions of the entire Galactic bulge region from VIRAC and Gaia. We present these as both 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, 3-dimensional view of the Milky Way barred bulge kinematics. We find a gradient in the mean longitudinal proper motion, $\mu_l$, 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, $\sim1.1$, near the minor axis and reaches $\sim1.4$ near the disc plane. The integrated $$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{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. ", keywords = "astro-ph.GA", author = "Clarke, {Jonathan P.} and Christopher Wegg and Ortwin Gerhard and Smith, {Leigh C.} and Philip Lucas and Wylie, {Shola M.}", note = "{\textcopyright} 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.", year = "2019", month = nov, doi = "10.1093/mnras/stz2382", language = "English", volume = "489", pages = "3519--3538", journal = "Monthly Notices of the Royal Astronomical Society", issn = "0035-8711", publisher = "Oxford University Press", number = "3", } ### RIS TY - JOUR T1 - The Milky Way bar/bulge in proper motions: a 3D view from VIRAC & Gaia AU - Clarke, Jonathan P. AU - Wegg, Christopher AU - Gerhard, Ortwin AU - Smith, Leigh C. AU - Lucas, Philip AU - Wylie, Shola M. N1 - © 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. PY - 2019/11 Y1 - 2019/11 N2 - We have derived absolute proper motions of the entire Galactic bulge region from VIRAC and Gaia. We present these as both 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, 3-dimensional view of the Milky Way barred bulge kinematics. We find a gradient in the mean longitudinal proper motion, \mu_l, 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, \sim1.1, near the minor axis and reaches \sim1.4 near the disc plane. The integrated$$ 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 $\mathrm{km \, s^{-1} \, kpc^{-1}}$, is able to reproduce all observed features impressively well. Dynamical models like this will be key to unlocking the full potential of these data.

AB - We have derived absolute proper motions of the entire Galactic bulge region from VIRAC and Gaia. We present these as both 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, 3-dimensional view of the Milky Way barred bulge kinematics. We find a gradient in the mean longitudinal proper motion, $\mu_l$, 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, $\sim1.1$, near the minor axis and reaches $\sim1.4$ near the disc plane. The integrated  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 $\mathrm{km \, s^{-1} \, kpc^{-1}}$, is able to reproduce all observed features impressively well. Dynamical models like this will be key to unlocking the full potential of these data.

KW - astro-ph.GA

U2 - 10.1093/mnras/stz2382

DO - 10.1093/mnras/stz2382

M3 - Article

VL - 489

SP - 3519

EP - 3538

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

SN - 0035-8711

IS - 3

ER -