The distribution of globular clusters in M87

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dc.contributor.authorGrillmair, Carl Johannen_US
dc.date.accessioned2024-08-13T22:57:34Z
dc.date.available2024-08-13T22:57:34Z
dc.date.copyright1985en_US
dc.date.issued1985
dc.degree.departmentDepartment of Physics
dc.degree.departmentDepartment of Physics and Astronomy
dc.degree.levelMaster of Science M.Sc.en
dc.description.abstractDeep CCD observations of a field one arcminute east of the core of M87 are analyzed to determine the luminosity and spatial distribution of M87's globular cluster system. Using the crowded­ field photometry package DAOPHOT, cluster positions and magnitudes are determined to a limiting magnitude of Blime 25.5. Completeness of the sample as a function of magnitude is determined by analyzing, in an identical manner, images containing the original data as well as a specified number of artificial stellar profiles of known magnitudes. Contamination of the sample by background galaxies and foreground stars is estimated by similarly analyzing CCD observations of a field somewhat removed from M87. Correcting the observations for completeness and background­-foreground contamination, we have determined a luminosity function for globular clusters in the region 50 to 160 arcseconds from the apparent center of M87. This luminosity function does not follow the functional form used to represent the luminosity distribution of globular clusters in the Local Group. On the other hand, a direct comparison of M87 globular clusters with those in M31 and the Galaxy does not rule out a "universal" form for the luminosity function. In an effort to detect a radial trend in the luminosity function, completeness of the sample is also determined as a function of projected galactocentric radius. Over the radial region 20 to 160 arcseconds, we find no conclusive evidence for such a trend. In addition, a comparison of the present sample with observations of previous investigators indicates that there is no strong trend in the luminosity function within the region 0.3 to 9 arcminutes. On the other hand, we find the radial surface density profile of globular clusters to be significantly shallower than that determined by previous investigators for larger radii. Assuming an M87 mass profile as suggested by recent X-ray observations, we demonstrate that the overall shape of the surface density profile can be well-fitted by simple models invoking highly radial anisotropies in the globular cluster velocity dispersion. Combining this with the lack of a significant trend in the luminosity function, we conclude that evolutionary processes such as dynamical friction and globular cluster stripping have probably not been very effective in the region under consideration. We suggest that the observed distribution, along with the anomalously large number(~ 20000) of globular clusters associated with M87, is likely to be the product of conditions prevailing at the time of M87's initial collapse.
dc.format.extent178 pages
dc.identifier.urihttps://hdl.handle.net/1828/17976
dc.rightsAvailable to the World Wide Weben_US
dc.titleThe distribution of globular clusters in M87en_US
dc.typeThesisen_US

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