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Photometry alone is not sufficient to unambiguously distinguish betweenultra-faint star clusters and dwarf galaxies because of their overlap inmorphological properties. Here we report on VLT/GIRAFFE spectra of candidatemember stars in two recently discovered ultra-faint satellites Reticulum 2 andHorologium 1, obtained as part of the ongoing Gaia-ESO Survey. We identify 18members in Reticulum 2 and 5 in Horologium 1. We find Reticulum 2 to have avelocity dispersion of ~3.22 km/s, implying a M/L ratio of ~ 500. We haveinferred stellar parameters for all candidates and we find Reticulum 2 to havea mean metallicity of [Fe/H] = -2.46+/-0.1, with an intrinsic dispersion of ~0.29, and is alpha-enhanced to the level of [alpha/Fe]~0.4. We conclude thatReticulum 2 is a dwarf galaxy. We also report on the serendipitous discovery offour stars in a previously unknown stellar substructure near Reticulum 2 with[Fe/H] ~ -2 and V_hel ~ 220 km/s, far from the systemic velocity of Reticulum2. For Horologium 1 we infer a velocity dispersion of 4.9^{+2.8}_{-0.9} km/sand a consequent M/L ratio of ~ 600, leading us to conclude that Horologium 1is also a dwarf galaxy. Horologium 1 is slightly more metal-poor than Reticulum2 [Fe/H] = -2.76 +/- 0.1 and is similarly alpha-enhanced: [alpha/Fe] ~ 0.3.Despite a large error-bar, we also measure a significant spread ofmetallicities of 0.17 dex which strengthen the evidence that Horologium 1 isindeed a dwarf galaxy. The line-of-sight velocity of Reticulum 2 is offset bysome 100 km/s from the prediction of the orbital velocity of the LMC, thusmaking its association with the Cloud uncertain. However, at the location ofHorologium 1, both the backward integrated LMC's orbit and the LMC's halo arepredicted to have radial velocities similar to that of the dwarf. Therefore, itis likely that Horologium 1 is or once was a member of the Magellanic Family.

Kinematics and chemistry of recently discovered Reticulum 2 and Horologium 1 dwarf galaxies