Currently, I spend most of my time working on simulations of the formation of intracluster light. However, I am also involved with the observational team here at Case which is using the CWRU Burrell Schmidt telescope at Kitt Peak to detect ICL in the Virgo cluster, along with my advisor Chris Mihos, as well as Case astronomers Paul Harding, and Heather Morrison.
Observing ICL is very difficult since we are looking for features which are at or below about 0.1-1% of sky brightness. However, there is an awful lot of information there about the evolution of both the cluster as a whole and the individual galaxies in the cluster.
In total, we have about half a dozen fields in Virgo in which we have made observations of the ICL. Each field consists of somewhere between 20-80 15 minute stacked exposures. Getting all this data means we (especially Chris) spend a LOT of time at the Schmidt observing; something like 6 weeks a year, just on the observing for this project. It has been an ongoing project for the last several years and will continue to be for several years into the future.
I have done a significant portion of the actual observing on two of our fields. In March of 2005 we imaged the M87-M89 field and in February and April of 2006 we got the M49-NGC4365 field. What I am showing here are only our quick and dirty reductions that we did at the telescope to assess data quality. Science reductions, unfortunately, take a bit longer. In these images the flat-fielding is fair, the sky subtraction was done by eye, the images are stacked using simple linear pixel offsets, and, most importantly, bright stars have not been removed.
M87 is the big elliptical on the upper right of this image, and the monster galaxy at the heart of the Virgo cluster. M89 is the slightly smaller elliptical on the top left. Also, for the record, the color is completely false, just to make it easier to see certain features.
We have definitely detected some very interesting features around M87 and M89, associated with them interacting with their smaller neighbor galaxies. Be aware that some of the bright stuff at the very edges is from low signal-to-noise or just poor sky subtraction. Unfortunately, we had some major problems with this field in that we are observing galactic cirrus. Galactic cirrus are clouds of dust in the Milky Way which reflect light from MW stars. We are certainly not going to be able to detect faint ICL features where there is cirrus. The faint features which I highlighted with green ellipses are from galactic cirrus and correspond to high emission in IR dust maps. We learned from this one to check the IR maps first!
Above is an image of the same piece of sky from the Sloan Digital Sky Survey that I grabbed from their navigate tool. As you can plainly see, our imaging is much deeper and we are finding extremely faint features.
M49 is the big elliptical in the upper left and is one of the largest galaxies in the Virgo cluster. The big elliptical in the lower left is NGC4365.
M49 has an huge halo is is definitely interacting with some of its small neighbors. However NGC4365 is the really interesting one in this field. There is obsviously some really interesting ICL extending from it to the small group of galaxies to the southwest, not to mention the galaxies to the northeast. There are a lot of bright stars in this field and it shows how big an impact they can have and how important it is for us to subtract them properly. For instance that group of stars to the bottom left of center creates a huge area of faint light, almost all of which is probably thier extended stellar profiles.
Again, I have included the SDSS image for comparison.
I have lots more images from the Burrell Schmidt in my pretty pictures gallery.
Created by Craig Rudick, 2006.
Last modified 05/08/06.