Detection of intracluster planetary nebulae in the Coma Cluster

[O III] X5007 emission lines of 16 intracluster planetary nebula (PN) candidates in the Coma Cluster were detected with a multislit imaging spectroscopy technique using the Faint Object Camera and Spectrograph on the Subaru telescope. The identification of these faint emission sources as PNs is supported by (1) their pointlike flux distribution in both space and wavelength, with tight limits on the continuum flux; (2) the identification of the second [O in] X4959 line in the only object at high enough velocity that this line too falls into the filter bandpass; (3) emission-line fluxes consistent with PNs at 100 Mpc distance, in the range 2.8 × 10^-19 to 1.7 × 10^-18 ergs s^-1 cm^-2; and (4) a narrow velocity distribution approximately centered on the systemic velocity of the Coma Cluster. Comparing with the velocities of galaxies in our field, we conclude that the great majority of these candidates would be intracluster PNs, free floating in the Coma Cluster core. Their velocity dispersion is ∼760 km s^-1, and their mean velocity is lower than that of the galaxies. The velocity distribution suggests that the intracluster stellar population has different dynamics from the galaxies in the Coma Cluster core.