A SUBARU ARCHIVAL SEARCH FOR FAINT TRANS-NEPTUNIAN OBJECTS

Abstract

We present the results of a survey for trans-neptunian objects (TNOs) based on Subaru archival images, originally collected by Sheppard et al. (2005) as part of a search for irregular satellites of Uranus. The survey region covers 2.8 deg 2 , centered on Uranus and observed near opposition on two adjacent nights. Our survey reaches half its maximum detection efficiency atR=25.69 ± 0.01. The objects detected correspond to 82 TNOs, five Centaurs, and five irregular satellites. We model the cumulative number of TNOs brighter than a given apparent magnitude with both a single and double power law. The best fit single power law, with one object per square degree at magnitude R0=22.6 +0.3 −0.4 and a slope of α=0.51 +0.5 −0.6 , is inconsistent with the results of similar searches with shallower limiting magnitudes. The best fit double power law, with a bright-end slope α1=0.7 +0.2 −0.1, a faint-end slope α2=0.3 +0.2 −0.2 , a differential number density at R = 23 σ23=2.0 +0.5 −0.5 and a magnitude break in the slope at Req=24.3 +0.8 −0.1 , is more likely than the single power law by a Bayes factor of �26. This is the first survey with sufficient depth and areal coverage to identify the magnitude at which the break occurs without relying on the results of other surveys. We estimate barycentric distances for the 73 objects that have 24 hr arcs; only two have heliocentric distances as large as �50 AU. We combine the distribution of observed distances with the size distribution that corresponds to a double power law luminosity function to set a tight constraint on the existence of a distant TNO population. We can exclude such a population at 60 AU, with 95% confidence, assuming it has the same size distribution and albedo as the observed TNOs, if it exceeds 8% of mass of the observed TNOs. Subject headings: Kuiper Belt – Outer Solar System – Trans-neptunian Object