Abstract
We report new constraints on the local escape speed of our Galaxy. Our analysis is based on a sample of high-velocity stars from the RAVE survey and two previously published data sets. We use cosmological simulations of disc galaxy formation to motivate our assumptions on the shape of the velocity distribution, allowing for a significantly more precise measurement of the escape velocity compared to previous studies. We find that the escape velocity lies within the range 498 <v(esc) <608 km s(-1) (90 per cent confidence), with a median likelihood of 544 km s(-1). The fact that v(esc)(2) is significantly greater than 2v(circ)(2) (where v(circ) = 220 km s(-1) is the local circular velocity) implies that there must be a significant amount of mass exterior to the solar circle, that is, this convincingly demonstrates the presence of a dark halo in the Galaxy. We use our constraints on v(esc) to determine the mass of the Milky Way halo for three halo profiles. For example, an adiabatically contracted NFW halo model results in a virial mass of 1.42(-0.54)(+1.14) x 10(12) M-circle dot and virial radius of (90 per cent confidence). For this model the circular velocity at the virial radius is 142(-21)(+31) km s(-1). Although our halo masses are model dependent, we find that they are in good agreement with each other.
Highlights
The existence of a dark halo around the Milky Way has been known for many years, its nature is still uncertain
If we are able to determine the escape speed at the solar neighbourhood, that is, the velocity that a star requires to escape the local gravitational field of the Milky Way, this can provide important constraints on the extent of the dark halo. The reason why this quantity is so important is because it is the only local dynamical measurement that can be used to probe the extent of the mass distribution outside the solar circle
When we apply the prior k ∈ [2.7, 4.7] we find that the 90 per cent confidence interval becomes 496 < vesc < 655 km s−1, with a median likelihood of vesc = 556 km s−1
Summary
The existence of a dark halo around the Milky Way has been known for many years, its nature is still uncertain. If we are able to determine the escape speed at the solar neighbourhood, that is, the velocity that a star requires to escape the local gravitational field of the Milky Way, this can provide important constraints on the extent of the dark halo. The reason why this quantity is so important is because it is the only local dynamical measurement that can be used to probe the extent of the mass distribution outside the solar circle. One needs a model for this mass distribution, the escape velocity (i.e. the local gravitational potential) can be used as a constraint from which it is possible to determine the total mass
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
