An AKARI Search for Intracluster Dust of Globular Clusters

Abstract

Abstract We report on observations of 12 globular clusters with the Far-Infrared Surveyor (FIS) aboard the AKARI satellite. Our goal is to search for emission from cold dust within clusters. We detected diffuse emissions toward NGC6402 and 2808, but the IRAS 100$\mu$m maps show the presence of strong background radiation. They are likely to have been emitted from the Galactic cirrus. We also detected 28 point-like sources mainly in WIDE-S images (90$\micron$). At least several of them are not associated with clusters, but background galaxies identified in external catalogs. We present the spectral energy distributions (SEDs) by combining near-and-mid infrared data obtained with the Infrared Camera (IRC), if possible. Those SEDs suggest that most of the point sources are background galaxies. For most of the other clusters, we have confirmed a lack of intracluster dust. We evaluated the upper limits of the intracluster dust mass to be between 10$^{-5}$ and 10$^{-3}\MO$, depending on the dust temperature. The inferred lifetime of the intracluster dust is shorter than 5Myr ($T_{\mathrm{d}}$$=$ 70K) or 50Myr (35K). Such a short lifetime indicates some mechanism(s) are at work to remove the intracluster dust. We also discuss its impact on the chemical evolution of globular clusters.