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Constraints on the Galactic bar from the Hercules stream as traced with RAVE across the Galaxy

Antoja, T; Helmi, A; Dehnen, W; Bienayme, O; Bland-Hawthorn, J; Famaey, B; Freeman, K; ... Zwitter, T; + view all (2014) Constraints on the Galactic bar from the Hercules stream as traced with RAVE across the Galaxy. Astronomy & Astrophysics , 563 , Article A60. 10.1051/0004-6361/201322623. Green open access

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Abstract

Non-axisymmetries in the Galactic potential (spiral arms and bar) induce kinematic groups such as the Hercules stream. Assuming that Hercules is caused by the effects of the outer Lindblad resonance of the Galactic bar, we model analytically its properties as a function of position in the Galaxy and its dependence on the bar’s pattern speed and orientation. Using data from the RAVE survey we find that the azimuthal velocity of the Hercules structure decreases as a function of Galactocentric radius, in a manner consistent with our analytical model. This allows us to obtain new estimates of the parameters of the Milky Way’s bar. The combined likelihood function of the bar’s pattern speed and angle has its maximum for a pattern speed of Ωb = (1.89 ± 0.08) × Ω0, where Ω0 is the local circular frequency. Assuming a solar radius of 8.05 kpc and a local circular velocity of 238 km s-1, this corresponds to Ωb = 56 ± 2 km s-1 kpc-1. On the other hand, the bar’s orientation φb cannot be constrained with the available data. In fact, the likelihood function shows that a tight correlation exists between the pattern speed and the orientation, implying that a better description of our best fit results is given by the linear relation Ωb/Ω0 = 1.91 + 0.0044(φb(deg) − 48), with standard deviation of 0.02. For example, for an angle of φb = 30 deg the pattern speed is 54.0 ± 0.5 km s-1 kpc-1. These results are not very sensitive to the other Galactic parameters such as the circular velocity curve or the peculiar motion of the Sun, and are robust to biases in distance.

Type: Article
Title: Constraints on the Galactic bar from the Hercules stream as traced with RAVE across the Galaxy
Open access status: An open access version is available from UCL Discovery
DOI: 10.1051/0004-6361/201322623
Publisher version: https://doi.org/10.1051/0004-6361/201322623
Language: English
Additional information: This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: Galaxy: kinematics and dynamics / Galaxy: structure / Galaxy: disk / Galaxy: evolution
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/10076795
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