We present the physical characterization of FSR 1758 , a new large , massive object very recently discovered in the Galactic Bulge .
The combination of optical data from the 2nd Gaia Data Release ( GDR2 ) and the DECam Plane Survey ( DECaPS ) , and near-IR data from the VISTA Variables in the Vía Láctea Extended Survey ( VVVX ) led to a clean sample of likely members .
Based on this integrated dataset , position , distance , reddening , size , metallicity , absolute magnitude , and proper motion of this object are measured .
We estimate the following parameters : \alpha = 17 : 31 : 12 , \delta = -39 : 48 : 30 ( J2000 ) , D = 11.5 \pm 1.0 kpc , E ( J - Ks ) = 0.20 \pm 0.03 mag , R _ { c } = 10 pc , R _ { t } = 150 pc , [ Fe / H ] = -1.5 \pm 0.3 dex , M _ { i } < -8.6 \pm 1.0 , \mu _ { \alpha } = -2.85 mas yr ^ { -1 } , and \mu _ { \delta } = 2.55 mas yr ^ { -1 } .
The nature of this object is discussed .
If FRS 1758 is a genuine globular cluster , it is one of the largest in the Milky Way , with a size comparable or even larger than that of \omega Cen , being also an extreme outlier in the size vs. Galactocentric distance diagram .
The presence of a concentration of long-period RR Lyrae variable stars and blue horizontal branch stars suggests that it is a typical metal-poor globular cluster of Oosterhoff type II .
Further exploration of a larger surrounding field reveals common proper motion stars , suggesting either tidal debris or that FRS 1758 is actually the central part of a larger extended structure such as a new dwarf galaxy , tentatively named as Scorpius .
In either case , this object is remarkable , and its discovery graphically illustrates the possibility to find other large objects hidden in the Galactic Bulge using future surveys .