Deep near-IR images from the VISTA Variables in the Vía Láctea ( VVV ) Survey were used to search for RR Lyrae stars within 100 arcmin from the Galactic Centre .
A large sample of 960 RR Lyrae of type ab ( RRab ) stars were discovered .
A catalog is presented featuring the positions , magnitudes , colors , periods , and amplitudes for the new sample , in addition to estimated reddenings , distances , and metallicities , and measured individual relative proper motions .
We use the reddening-corrected Wesenheit magnitudes , defined as W _ { K _ { s } } = K _ { s } -0.428 \times ( J - K _ { s } ) , in order to isolate bona-fide RRL belonging to the Galaxy Centre , finding that 30 RRab are foreground/background objects .
We measure a range of extinctions from A _ { K _ { s } } = 0.19 to 1.75 mag for the RRab in this region , finding that large extinction is the main cause of the sample incompleteness .
The mean period is P = 0.5446 \pm 0.0025 days , yielding a mean metallicity of [ Fe / H ] = -1.30 \pm 0.01 ( \sigma = 0.33 ) dex for the RRab sample in the Galactic Centre region .
The median distance for the sample is D = 8.05 \pm 0.02 kpc .
We measure the RRab surface density using the less reddened region sampled here , finding a density of 1000 RRab/sq deg at a projected Galactocentric distance R _ { G } = 1.6 deg .
Under simple assumptions , this implies a large total mass ( M > 10 ^ { 9 } M _ { \odot } ) for the old and metal-poor population contained inside R _ { G } .
We also measure accurate relative proper motions , from which we derive tangential velocity dispersions of \sigma V _ { l } = 125.0 and \sigma V _ { b } = 124.1 km/s along the Galactic longitude and latitude coordinates , respectively .
The fact that these quantities are similar indicate that the bulk rotation of the RRab population is negligible , and implies that this population is supported by velocity dispersion .
In summary , there are two main conclusions of this study .
First , the population as a whole is no different from the outer bulge RRab , predominantly a metal-poor component that is shifted respect the Oosterhoff type I population defined by the globular clusters in the halo .
Second , the RRab sample , as representative of the old and metal-poor stellar population in the region , have high velocity dispersions and zero rotation , suggesting a formation via dissipational collapse .