We use the SDSS-Gaia Catalogue to identify six new pieces of halo substructure .
SDSS-Gaia is an astrometric catalogue that exploits SDSS data release 9 to provide first epoch photometry for objects in the Gaia source catalogue .
We use a version of the catalogue containing 245 316 stars with all phase space coordinates within a heliocentric distance of \sim 10 kpc .
We devise a method to assess the significance of halo substructures based on their clustering in velocity space .
The two most substantial structures are multiple wraps of a stream which has undergone considerable phase mixing ( S1 , with 94 members ) and a kinematically cold stream ( S2 , with 61 members ) .
The member stars of S1 have a median position of ( X,Y,Z ) = ( 8.12 , -0.22 , 2.75 ) kpc and a median metallicity of [ Fe/H ] = -1.78 .
The stars of S2 have median coordinates ( X,Y,Z ) = ( 8.66 , 0.30 , 0.77 ) kpc and a median metallicity of [ Fe/H ] = -1.91 .
They lie in velocity space close to some of the stars in the stream reported by Helmi et al .
( 1999 ) .
By modelling , we estimate that both structures had progenitors with virial masses \approx 10 ^ { 10 } M _ { \odot } and infall times \gtrsim 9 Gyr ago .
Using abundance matching , these correspond to stellar masses between 10 ^ { 6 } and 10 ^ { 7 } M _ { \odot } .
These are somewhat larger than the masses inferred through the mass-metallicity relation by factors of 5 to 15 .
Additionally , we identify two further substructures ( S3 and S4 with 55 and 40 members ) and two clusters or moving groups ( C1 and C2 with 24 and 12 ) members .
In all 6 cases , clustering in kinematics is found to correspond to clustering in both configuration space and metallicity , adding credence to the reliability of our detections .