The properties of Jovian Trojan asteroids listed in SDSS Moving Object Catalogue 3

We analyse 1187 observations of about 860 unique candidate Jovian Trojan asteroids listed in the 3rd release of the Sloan Digital Sky Survey (SDSS) Moving Object Catalogue. The sample is complete at the faint end to r = 21.2 mag (apparent brightness) and H = 13.8 (absolute brightness, approximately corresponding to 10 km diameter). A subset of 297 detections of previously known Trojans were used to design and optimize a selection method based on observed angular velocity that resulted in the remaining objects. Using a sample of objects with known orbits, we estimate that the candidate sample contamination is about 3 per cent. The well-controlled selection effects, the sample size, depth and accurate five- band UV-IR photometry enabled several new findings and the placement of older results on a firmer statistical footing. We find that there are significantly more asteroids in the leading swarm (L4) than in the trailing swarm (L5): N(L4)/ N(L5) = 1.6 +/- 0.1, independently of limiting object's size. The overall counts normalization suggests that there are about as many Jovians Trojans as there are main-belt asteroids down to the same size limit, in agreement with earlier estimates. We find that Trojan asteroids have a remarkably narrow colour distribution ( root mean scatter of only similar to 0.05 mag) that is significantly different from the colour distribution of the main-belt asteroids. The colour of Trojan asteroids is correlated with their orbital inclination, in a similar way for both swarms, but appears uncorrelated with the object's size. We extrapolate the results presented here and estimate that the Large Synoptic Survey Telescope will determine orbits, accurate colours and measure light curves in six photometric bandpasses for about 100 000 Jovian Trojan asteroids.