The Spatial Structure of the M87 Globular Cluster System

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Session 46 -- Seyfert Galaxies and LINERS
Display presentation, Thursday, January 13, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[46.14] The Spatial Structure of the M87 Globular Cluster System

Dean E. McLaughlin, William E. Harris (McMaster University), David A. Hanes (Queen's University)

Wide--field ($\sim 14^{\prime} \times 14^{\prime}$) CCD photometry in $V$ of a field centered on M87 = NGC 4486 is used to examine the spatial structure, luminosity function, and specific frequency of the galaxy's globular cluster system (GCS). The salient results are as follows: (1) The radial profile of the GCS shows an excess component which coincides in position and size with the cD envelope of the galaxy's halo. (2) In projection, the GCS of M87 is definitely elliptical in shape, with a major axis position angle which roughly coincides with that of the galaxy isophotes. However, its ellipticity increases with galactocentric radius faster than does the ellipticity of the underlying halo light. (3) The luminosity function of the GCS is well described by a Gaussian of dispersion $\sigma=1.73$, and peak magnitude $V^0=24.2$. We confirm earlier claims that the bright half of the luminosity function shows no significant variation with galactocentric radius, out to $R\simeq6.8^{\prime}$. (4) We compute the ratio of globular cluster numbers to halo luminosity (specific frequency, $S_N$) as a function of galactocentric radius in M87, and confirm that the global $S_N$ of the system is $\sim3$ times greater than in other, more normal Virgo ellipticals. We briefly discuss this high--$S_N$ phenomenon and the implications of our results for the process of cD envelope formation.

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