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K. Krelove, R. Ciardullo, J.J. Feldmeier (Penn State University), G.H. Jacoby (NOAO)
Onband/offband [O~III] \lambda 5007 surveys of intracluster space in Virgo and Fornax appear to suggest that these clusters possess a substantial population of intracluster planetary nebulae. If correct, then the implication is that a sizeable fraction of the stellar mass of these clusters resides outside of any galaxy. However, it is still not proven that these objects are, indeed, [O~III] \lambda 5007 emitting planetary nebulae; they may instead be [O~II] \lambda 3727 emitting galaxies at z \approx 0.35 or Ly\alpha\ sources at z \approx 3.13. To estimate the density of background emission line sources, we conducted a search for faint [O~III] \lambda 5007 point sources in three ``blank fields'', covering a total of 576 square arcminutes, located well away from any galaxy or cluster.
To aid in our search for background candidates, we have developed an IRAF package to perform automated detection and screening for objects that resemble intracluster planetary nebulae. We use this package in tandem with manual blinking to determine the density of contaminants in IPN surveys. We find that the number of contaminating objects is approximately forty per square degree down to a limiting flux of 5 \times 10-17~ergs~s-1~cm-2, and an equivalent width limit of EW \geq 90 Å~. We compare the density of contaminants to the density of intracluster planetaries found in surveys, and show that the contamination rate is approximately 20%.
This work was partially funded by NSF grant AST-9529270.