Many observers actually didn't intend to directly study intracluster light. Several were looking for dark matter and others were looking for Gravitational lenses. Many of the observers in the 60's and 70's were trying to study Low Surface Brightness galaxies or cluster galaxy luminosity functions and found intracluster light because it got in their way.
Recently, astronomers have been looking to IcL as a means of studying how galaxies interact in clusters. Much will be learned about the formation and structure of clusters and their galaxies if IcL can be fully examined.

Finding Intracluster Light

Intracluster light is very difficult to find. The principle observational problem stems from the simple fact that it is extremely faint (generally about 1% of the sky brightness). Compounding this problem is the fact that IcL can be easily obscured or overshadowed by scattered light from nearby stars and galaxies.
Other difficulties arise with each of the surface photometry methods. In the past, photographic plates were the principle tool for surface photometry observations. They have since been almost totally replaced by Charge Coupled Devices (CCD's). When using photographic plates, astronomers must contend with low dynamic range (the ability to see very bright and very faint objects at the same time). Photographic plates are also notorious for non-uniformites in their emulsions (imperfections in the photographic surface which can cause smudges and wrinkles in the image). If CCD's are employed, these problems are no longer an issue, but subtracting out the sky brightness remains a crucial and difficult step. Since IcL is such a dim component in a cluster image,it is very important to remove the sky brightness; but it is often difficult to determine where the IcL ends and the sky begins.

Other Ways to Study IcL: Computer Modeling and Planetary Nebulae

The discussions of observational methods and the history of IcL observations elsewhere at this site are describing surface photometry observations of intracluster light. Surface photometry is by no means the only method available for studying IcL (it is dealt with in detail here simply because it is the method used in the Popsicle project). A significant amount of work has been done in theoretical modeling of IcL using computer-generated simulations. One of the collaborators on the Popsicle project, Chris Mihos, is producing galaxy-harassment models which might help to explain the tidal debris observed in IcL in recent years.
Another method employed in the search for intracluster light is looking for individual stars and intracluster planetary nebulae (IPN) which might serve as tracers of IcL in nearby clusters. This method has not been as widely used as the surface photometry approach. Another Popsicle collaborator, John Feldmeier, is conducting a survey of the Virgo cluster for IPN as part of his doctoral thesis.


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