Near-Infrared Photometry of the Irregular Satellites of Jupiter and Saturn

We present JHKs photometry of 10 Jovian and 4 Saturnian irregular satellites,taken with the Near-InfraRed Imager (NIRI) at the 8-m Gemini North Observatoryon Mauna Kea, Hawaii. The observed objects have near-infrared colors consistentwith C, P and D-type asteroids, although J XII Ananke and S IX Phoebe show weakindications of possible water features in the H filter. The four members of theHimalia-family have similar near-infrared colors, as do the two members of theGallic family, S XX Paaliaq and S XXIX Siarnaq. From low resolution normalizedreflectance spectra based on the broadband colors and covering 0.4 to 2.2microns, the irregular satellites are identified as C-type (J VII Pasiphae, JVI Himalia and S IX Phoebe), P-type (J XII Ananke and J XVIII Themisto) andD-type (J IX Carme and J X Sinope), showing a diversity of origins of theseobjects.Comment: Accepted by ApJ Letters (emulateapj, 8pages, including 4 figures); Typos corrected, references adde