The Surface Brightness Fluctuations and Globular Cluster Populations of Virgo Elliptical and Lenticular Galaxies

Eric H. Neilsen, Jr.

Thesis work conducted at The Johns Hopkins University, Baltimore, MD

Ph.D. thesis directed by Zlatan I. Tsvetanov and Holland C. Ford; Ph.D. degree awarded 1999

The full text is available online as a compressed postscript file.

The Virgo cluster of galaxies is a complex system composed of several sub-clusters or ``clouds.'' Our understanding of this structure is severely limited by the small number of member galaxies for which high precision distance measurements are available. In this dissertation, I use Hubble Space Telescope archive images to measure precise distances to 15 elliptical and lenticular galaxies in the Virgo cluster using surface brightness fluctuations (SBF) (Tonry & Schneider 1988). Furthermore, I identify the globular clusters associated with these galaxies to a limiting magnitude significantly fainter than the peak of the globular cluster luminosity function (GCLF). Because the GCLF can also be used as a standard candle (see Whitmore 1997 for a review), these images provide independent distance measurements from the same data. In addition, the color distributions of the globular clusters provide an indication of the globular cluster formation history.

  1. The distances derived using SBF measurements in these images agree well with other distance measurements, including SBF measurements from the ground, measurements using the GCLF, and measurements using the fundamental plane relation, and are of higher precision.
  2. Many galaxies in the sample have distances similar to that of M87, the central galaxy of the largest Virgo cluster cloud. Several galaxies (M59, NGC 4660, and NGC 4550) are ahead or behind the large cloud centered on M87, revealing extention along the line of sight. A few additional galaxies, particularly M86, NGC 4365, and NGC 4476, have significanly larger distances, and are clearly not part of the M87 cloud.
  3. Using a simple model in which the mass of the M87 cloud is taken to be 4 1014 M0 (Bohringer et. al 1994), and direction of motion for each galaxy is on the line between that galaxy and M87, all sample galaxies except M86 are gravitationally bound to the M87 cloud. The data are consistent with M86 being gravitationally bound, but do not require it.
  4. Among those galaxies for which a suitably large sample of GC's could be measured, most had GC populations with clearly bimodal color distributions. The two peaks were found near V-I=1.0 and V-I=1.2 in most cases. The fraction of globular clusters in each park varied significantly. In one case (M86) only the blue peak was present, while in others (such as M49), there were more GC's in the red peak than the blue peak.
  5. In M87, where several fields were available at different distances from the center of the galaxy, the relative number of clusters in each peak of the color distribution was a function of distance from the center: fields near the center had a higher fraction of clusters in the red peak than that found in fields far from the center.