Small Jupiter Trojans Survey with the Subaru/Hyper Suprime-Cam

Abstract

We observed the L4 Jupiter Trojans (JTs) swarm using the Hyper Suprime-Cam attached to the 8.2 m Subaru Telescope on 2015 March 30 (UT). The survey covered ∼26 deg² of sky area near the opposition and around the ecliptic plane with a 240 s exposure time in the r-band filter through the entire survey. We detected 631 L4 JTs in the survey field with a detection limit of m _r = 24.4 mag. We selected 481 objects with absolute magnitude H _r < 17.4 mag and heliocentric distance r < 5.5 au as an unbiased sample and then used them to estimate the size distribution. Assuming a geometric albedo of 0.07, the size range of our unbiased sample is ∼2-20 km in diameter (D). We fit a single-slope power law to the cumulative size distribution and found that the best-fit index (b) is b = 1.84 ± 0.05 in N(> D) \propto {D}^-b. The slope value (α) of the corresponding absolute magnitude distribution (N(H) \propto {10}^{α H}) is 0.37 ± 0.01. This α is consistent with that of the faint-end slope presented by Wong & Brown. The size distribution obtained from this survey is slightly different from the results of previous surveys with a similar size range, which reported broken power-law or double power-law slopes in their cumulative size distribution. Our results insist that the slope of b = 1.84 continues from H = 14.0 to at least H = 17.4. Since this work contains the largest L4 JT samples and is 1 mag deeper than the study by Wong & Brown, we believe that our study has obtained the most robust size distribution of small JTs so far. Combining the cataloged L4 JTs and our survey, we show the entire size distribution of L4 JTs up to H _r = 17.4 mag.

Based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.