Improved constraints on Galactic Centre ejection of hypervelocity stars based on novel search method
Monthly Notices of the Royal Astronomical Society, vol. 533, pp. 2747–2761
Abstract
ABSTRACT Hypervelocity stars (HVSs) are stars which have been ejected from the Galactic Centre (GC) at velocities of up to a few thousand $\text{km}\, \text{s}^{-1}$. They are tracers of the Galactic potential and can be used to infer properties of the GC, such as the initial mass function and assembly history. HVSs are rare, however, with only about a dozen promising candidates discovered so far. In this work, we make use of a novel, highly efficient method to identify new HVS candidates in Gaia. This method uses the nearly radial trajectories of HVSs to infer their distances and velocities based on their position and Gaia proper motion alone. Through comparison of inferred distances with Gaia parallaxes and photometry, we identified 600 HVS candidates with G < 20 including the previously discovered S5-HVS1, out of which we obtained ground-based follow-up observations for 196 stars. As we found no new HVSs based on their radial velocity, we used detailed HVS ejection simulations to significantly improve previous HVS ejection rate constraints. In particular, the ejection rate of HVSs more massive than 1 $\mathrm{M_\odot }$ cannot be higher than $10^{-5}$ yr$^{-1}$ at $2\sigma$ significance. Additionally, we predict that there are 5–45 unbound HVSs in the complete Gaia catalogue ($1\sigma$ interval), most of which will be main-sequence stars of a few M$_\odot$ at heliocentric distances of tens to hundreds of kpc. By comparing our results to literature HVS candidates, we find an indication of either a time-dependent ejection rate of HVSs or a non-GC origin of previously identified HVS candidates.
Authors 9
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Leiden University · Leiden Observatory
Affiliation as printed
Leiden Observatory, Leiden University , P.O. Box 9513, NL-2300 RA Leiden , the Netherlands
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Leiden University · Leiden Observatory
Affiliation as printed
Leiden Observatory, Leiden University , P.O. Box 9513, NL-2300 RA Leiden , the Netherlands
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University of Cambridge · Royal Observatory · University of Edinburgh
Affiliation as printed
Institute for Astronomy, University of Edinburgh, Royal Observatory , Blackford Hill, Edinburgh EH9 3HJ , UK
Institute of Astronomy, University of Cambridge , Madingley Road, Cambridge CB3 0HA , UK
Kavli Institute for Cosmology, University of Cambridge , Madingley Road, Cambridge CB3 0HA , UK
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Affiliation as printed
European Southern Observatory , Karl-Schwarzschild-Strasse 2, D-85748 Garching bei Munchen , Germany
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Leiden University · Leiden Observatory
Affiliation as printed
Leiden Observatory, Leiden University , P.O. Box 9513, NL-2300 RA Leiden , the Netherlands
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Leiden University · Leiden Observatory
Affiliation as printed
Leiden Observatory, Leiden University , P.O. Box 9513, NL-2300 RA Leiden , the Netherlands
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Affiliation as printed
David A. Dunlap Department of Astronomy and Astrophysics, University of Toronto , 50 St George Street, Toronto, ON M5S 3H4 , Canada
Dunlap Institute for Astronomy and Astrophysics, University of Toronto , 50 St George Street, Toronto, ON M5S 3H4 , Canada
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Isaac Newton Group · Foundation for Research and Technology Hellas
Affiliation as printed
Institute of Astrophysics, Foundation for Research and Technology-Hellas , 71110 Heraklion, Crete , Greece
Isaac Newton Group of Telescopes , Apartado 321, E-38700 Santa Cruz de La Palma, Canary Islands , Spain
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University of Nottingham · Isaac Newton Group
Affiliation as printed
Isaac Newton Group of Telescopes , Apartado 321, E-38700 Santa Cruz de La Palma, Canary Islands , Spain
School of Physics & Astronomy, University of Nottingham , Nottingham NG7 2RD , UK
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