The ACS Virgo Cluster Survey. X. Half-Light Radii of Globular Clusters in Early-Type Galaxies: Environmental Dependencies and a Standard Ruler for Distance Estimation

We have measured half-light radii, rh, for thousands of globular clusters (GCs) belonging to the 100 early-type galaxies observed in the ACS Virgo Cluster Survey and the elliptical galaxy NGC 4697. An analysis of the dependencies of the measured half-light radii on both the properties of the GCs themselves and their host galaxies reveals that, in analogy with GCs in the Galaxy but in a milder fashion, the average half-light radius increases with increasing galactocentric distance or, alternatively, with decreasing galaxy surface brightness. For the first time, we find that the average half-light radius decreases with the host galaxy color. We also show that there is no evidence for a variation of rh with the luminosity of the GCs. Finally, we find in agreement with previous observations that the average rh depends on the color of GCs, with red GCs being ~17% smaller than their blue counterparts. We show that this difference is probably a consequence of an intrinsic mechanism, rather than projection effects, and that it is in good agreement with the mechanism proposed by Jordán. We discuss these findings in light of two simple pictures for the origin of the rh of GCs and show that both lead to a behavior in rough agreement with the observations. After accounting for the dependencies on galaxy color, galactocentric radius, and underlying surface brightness, we show that the average GC half-light radii ⟨rh⟩ can be successfully used as a standard ruler for distance estimation. We outline the methodology, provide a calibration for its use, and discuss the prospects for this distance estimator with future observing facilities. We find ⟨rh⟩ = 2.7 ± 0.35 pc for GCs with (g - z) = 1.2 mag in a galaxy with color (g - z)gal = 1.5 mag and at an underlying surface z-band brightness of μz = 21 mag arcsec-2. Using this technique, we place an upper limit of 3.4 Mpc on the 1 σ line-of-sight depth of the Virgo Cluster. Finally, we examine the form of the rh distribution for our sample galaxies and provide an analytic expression that successfully describes this distribution.

[1]  J. Tonry,et al.  The Advanced Camera for Surveys Virgo Cluster Survey. V. Surface Brightness Fluctuation Calibration for Giant and Dwarf Early-Type Galaxies , 2005 .

[2]  S. Djorgovski,et al.  The ACS Virgo Cluster Survey. VII. Resolving the Connection between Globular Clusters and Ultracompact Dwarf Galaxies , 2005, astro-ph/0503566.

[3]  J. Tonry,et al.  The ACS Virgo Cluster Survey. IV. Data Reduction Procedures for Surface Brightness Fluctuation Measurements with the Advanced Camera for Surveys , 2005, astro-ph/0501325.

[4]  A. Jordán.  A Possible Explanation for the Size Difference of Red and Blue Globular Clusters , 2004, astro-ph/0408313.

[5]  J. Tonry,et al.  The ACS Virgo Cluster Survey. II. Data Reduction Procedures , 2004, astro-ph/0406433.

[6]  J. Brinkmann,et al.  The Origin of the Mass-Metallicity Relation: Insights from 53,000 Star-forming Galaxies in the Sloan Digital Sky Survey , 2004, astro-ph/0405537.

[7]  J. Tonry,et al.  The ACS Virgo Cluster Survey. III. Chandra and Hubble Space Telescope Observations of Low-Mass X-Ray Binaries and Globular Clusters in M87 , 2004, astro-ph/0405188.

[8]  J. Tonry,et al.  The ACS Virgo Cluster Survey. I. Introduction to the Survey , 2004, astro-ph/0404138.

[9]  H. Jerjen,et al.  Distances, Metallicities, and Ages of Dwarf Elliptical Galaxies in the Virgo Cluster from Surface Brightness Fluctuations , 2003, astro-ph/0310779.

[10]  P. Côté,et al.  The ACS Virgo Cluster Survey III. Chandra and HST observations of low-mass X-Ray binaries and globular clusters in M87 , 2004 .

[11]  S. Larsen,et al.  On the Size Difference between Red and Blue Globular Clusters , 2003, astro-ph/0304434.

[12]  Doug Geisler,et al.  The Globular Cluster System of NGC 1399. I. A Wide-Field Photometric Study , 2003, astro-ph/0301223.

[13]  L. Ferrarese.  Beyond the Bulge: A Fundamental Relation between Supermassive Black Holes and Dark Matter Halos , 2002, astro-ph/0203469.

[14]  K. Ashman,et al.  Some Constraints on the Formation of Globular Clusters , 2001, astro-ph/0107146.

[15]  Supercomputing,et al.  Hubble Space Telescope photometry of globular clusters in the Sombrero galaxy , 2001, astro-ph/0107082.

[16]  P. Côté,et al.  Dynamics of the Globular Cluster System Associated with M87 (NGC 4486). II. Analysis , 2001, astro-ph/0106005.

[17]  B. Whitmore,et al.  New Insights from HST Studies of Globular Cluster Systems. I. Colors, Distances, and Specific Frequencies of 28 Elliptical Galaxies , 2001, astro-ph/0103021.

[18]  J. P. Huchra,et al.  Properties of Globular Cluster Systems in Nearby Early-Type Galaxies , 2001, astro-ph/0102374.

[19]  Gerard A. Luppino,et al.  The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances , 2000, astro-ph/0011223.

[20]  R. Somerville,et al.  Profiles of dark haloes: evolution, scatter and environment , 1999, astro-ph/9908159.

[21]  M. West,et al.  The Principal Axis of the Virgo Cluster , 2000, astro-ph/0008470.

[22]  Zlatan Tsvetanov,et al.  The Structure of the Virgo Cluster from Surface Brightness Fluctuations in Hubble Space Telescope Images , 2000 .

[23]  D. McLaughlin.  Binding Energy and the Fundamental Plane of Globular Clusters , 2000, astro-ph/0002086.

[24]  J. Huchra,et al.  The Age Difference between the Globular Cluster Subpopulations in NGC 4472 , 1999 .

[25]  B. Whitmore,et al.  Wide Field Planetary Camera 2 Imaging of the Globular Cluster System of the S0 Galaxy NGC 3115 , 1998 .

[26]  D. Heggie,et al.  Basic N-body modelling of the evolution of globular clusters — I. Time scaling , 1998, astro-ph/9805344.

[27]  D. Geisler,et al.  Washington Photometry of the Globular Cluster System of NGC 4472. II. The Luminosity Function and Spatial Structure , 1997, astro-ph/9711194.

[28]  B. Whitmore,et al.  The Globular Cluster System in the Inner Region of M87 , 1997, astro-ph/9812199.

[29]  William E. Harris,et al.  A Catalog of Parameters for Globular Clusters in the Milky Way , 1996 .

[30]  E. Bertin,et al.  SExtractor: Software for source extraction , 1996 .

[31]  R. Pudritz,et al.  A Model for the Internal Structure of Molecular Cloud Cores , 1996, astro-ph/9605018.

[32]  Takashi Ichikawa,et al.  GALAXY COLORS IN VARIOUS PHOTOMETRIC BAND SYSTEMS , 1995 .

[33]  M. Currie,et al.  Distances to 64 Virgo dwarf-elliptical galaxies and the depth in their spatial distribution , 1995 .

[34]  S. White,et al.  Simulations of X-ray clusters , 1994, astro-ph/9408069.

[35]  N. Caon,et al.  On the shape of the light profiles of Early Type galaxies , 1993, astro-ph/9309013.

[36]  C. J. Butler,et al.  Stellar photometry : current techniques and future developments : proceedings of the IAU Colloquium no. 136 held in Dublin, Ireland 4-7 August 1992 , 1993 .

[37]  D. Lin,et al.  Globular cluster formation - The fossil record , 1992 .

[38]  S. Bergh,et al.  Diameters of Galactic globular clusters , 1991 .

[39]  T. Beers,et al.  Measures of location and scale for velocities in clusters of galaxies. A robust approach , 1990 .

[40]  John L. Tonry,et al.  A new technique for measuring extragalactic distances , 1988 .

[41]  P. Stetson.  DAOPHOT: A COMPUTER PROGRAM FOR CROWDED-FIELD STELLAR PHOTOMETRY , 1987 .

[42]  A. Sandage,et al.  Studies of the Virgo Cluster. II - A catalog of 2096 galaxies in the Virgo Cluster area. , 1985 .

[43]  J. Gunn,et al.  Dynamical studies of globular clusters based on photoelectric radial velocities of individual stars. I. M3. , 1979 .

[44]  G. Vaucouleurs,et al.  An outsider's view of the Galaxy: photometric parameters, scale lengths, and absolute magnitudes of the spheroidal and disk components of our Galaxy. , 1978 .

[45]  Alan P. Lightman,et al.  The dynamical evolution of globular clusters , 1978 .

[46]  S. Bergh.  Stellar Populations in Galaxies , 1972 .

[47]  L. Spitzer,et al.  Random Gravitational Encounters and the Evolution of Spherical Systems. IV Isolated Systems of Identical Stars , 1972 .

[48]  Ivan R. King,et al.  The structure of star clusters. III. Some simple dvriamical models , 1966 .

[49]  John A. Nelder,et al.  A Simplex Method for Function Minimization , 1965, Comput. J..

[50]  G. Vaucouleurs.  Structure of the Virgo Cluster of Galaxies. , 1961 .

[51]  W. A. Baum.  POPULATION INFERENCES FROM STAR COUNTS, SURFACE BRIGHTNESS AND COLORS , 1959 .