TY - JOUR

T1 - Constraints on the Galactic bar from the Hercules stream as traced with RAVE across the Galaxy

AU - Antoja, T.

AU - Helmi, A.

AU - Dehnen, W.

AU - Bienaymé, O.

AU - Bland-Hawthorn, J.

AU - Famaey, B.

AU - Freeman, K.

AU - Gibson, B. K.

AU - Gilmore, G.

AU - Grebel, E. K.

AU - Kordopatis, G.

AU - Kunder, A.

AU - Minchev, I.

AU - Munari, U.

AU - Navarro, J.

AU - Parker, Q.

AU - Reid, W. A.

AU - Seabroke, G.

AU - Siebert, A.

AU - Steinmetz, M.

AU - Watson, F.

AU - Wyse, R. F G

AU - Zwitter, T.

N1 - Copyright ESO 2014. First published in Astronomy and astrophysics 563, A60, 2014, published by EDP Sciences. The original publication is available at http://doi.org/10.1051/0004-6361/201322623

PY - 2014/3

Y1 - 2014/3

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=84896796123&partnerID=8YFLogxK

U2 - 10.1051/0004-6361/201322623

DO - 10.1051/0004-6361/201322623

M3 - Article

AN - SCOPUS:84896796123

VL - 563

SP - 1

EP - 17

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

SN - 0004-6361

M1 - A60

ER -