Astrophysics |
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The SDSS Cluster Selection Algorithm The Sloan Primary Standard Star System The X-Ray Fundamental Plane of Clusters The Butcher Oemler Effect in Complete Samples of Clusters The Luminosity Function in Complete Samples of Clusters |
When I plotted the current data on clusters in a radius-surface brightness-temperature space, I found that the dimensionality of the data was only 2: that is, it was planar. This means that there is a tight relationship between the radius-surface brightness pair and x-ray temperature.
Since surface brightness and temperature are distance independent, this may be used as a distance indicator. Since clusters are know to great redshifts, I will attempt to measure the cosmological parameter q0.
I have measured the BO blue fraction in a pair of x-ray selected cluster samples. X-ray selection is a much more rational selection technique for clusters than selection by optical overdensity ("looking for it").
There is a range of blue fractions at z=1/3: at least 20 percent of clusters do not have any measurable blue fraction.
At z=0 there is a range of blue fractions! At least half of clusters here have 15 percent blue fractions, comparable to the clusters at z=0.2.
The Butcher-Oemler effect turns out to be a selection effect, but turned on its head. Butcher and Oemler somehow selected against "blue" clusters at z=0.
With Jon Gardner (Durham), I am measuring the K-band luminosity function in complete samples of clusters at z=1/3 and z=0.
Since the luminosity function is a direct output in most theories of galaxy formation, we shall have a nice constraint on evolution in the universe.
| A description of the monitor telescope system, the telescope that is going to define the Sloan photometric system. |
| Cooling flows seem to be dumping large amounts of mass at the centers of clusters. The problem is, no one has seen a trace of the mass once it drops cooler than x-rays. Dave Jewitt and I went looking for ultra-cold mass by looking for thermal emission by dust. We didn't find any, just one more in a string of failures by observers to find it the 10-100s of solar masses that the theorists say must be dropped there per year. |
| Gravitational lenses found in radio surveys have a tendency to be very, very red. This one was as well, as Gerry Luppino and I showed by imaging in the K-band. We interpreted these red lens systems as being lensed radio galaxies, based on their position on a plot of R-K vs. K color-magnitude diagram amidst quasars and radio galaxies from a similar radio survey. The current interpretation in the literature is that they are normal quasars reddened by dust in the lensing galaxy, but I think we are right on this one. |
| The first very red gravitational lens to be found. It had R-K > 6.5 (!) and changed in morphology from the V band to the K band. |
More details and the papers themselves.
