Globular Cluster Photometry with the Hubble Space Telescope. V. WFPC2 Study of M15's Central Density Cusp

Abstract

We describe images of the center of the dense globular cluster M15 (NGC 7078) obtained with the Hubble Space Telescope Wide Field and Planetary Camera 2 (WFPC2). Data taken in the F336W, F439W, and F555W filters (approximately U, B, and V) are used to study the surface density distribution of the $\sim 3\times 10^4$~stars detected in a 5~arcmin${}^2$ region within $r<2^{\prime }$ (6.7pc) of the cluster center. The surface density of stars in M15 (after correction for the effects of incompleteness and photometric bias/scatter) is well represented by a power law in radius: $N(r)\sim r^{-0.82\pm 0.12}$, over the radial range $0.3^{\prime \prime }$ (0.017pc) to $6^{\prime \prime }$. The observed power law is remarkably similar to what is expected if the center of the cluster harbors a massive black hole. Non-parametric estimates of the density profile show a monotonic rise with decreasing radius all the way in to $r=0.3^{\prime \prime }$, the smallest radius at which the density can be reliably measured; there is no indication that the profile flattens at smaller radii. Any flat core of radius larger than $2^{\prime \prime }$ (0.11pc) in the stellar distribution is ruled out at the $>95$\% significance level. The star count profile is consistent with that expected from core-collapse models or with the predicted distribution around a massive (few times $10^3{M}_{\odot }$) black hole. The close triplet of bright stars, AC~214, is within $0.5^{\prime \prime }$ ($1.5\sigma$) of the cluster centroid position.

24 pages, TeX format, 14 postscript figures, Full tables at ftp://eku.sns.ias.edu/pub/GLOBULAR_CLUSTERS/m15-wfpc2 Figure 1 available from [email protected]. Figure 2 at http://www.ucolick.org/~raja/images/m15.ubv.gif To appear in The Astronomical Journal, January 1996

Cited by in corpus (33)

• Stellar Collisions During Binary-Binary and Binary-Single Star Interactions
• Hubble Space Telescope Evidence for an Intermediate-Mass Black Hole in the Globular Cluster M15: II. Kinematical Analysis and Dynamical Modeling
• Relativistic Binaries in Globular Clusters
• Monte-Carlo Simulations of Globular Cluster Evolution - I. Method and Test Calculations
• On the central structure of M15
• Surface Brightness Profiles of Galactic Globular Clusters from Hubble Space Telescope Images
• The dynamical M/L-profile and distance of the globular cluster M15
• Globular cluster systems in nearby dwarf galaxies - II. Nuclear star clusters and their relation to massive Galactic globular clusters
• CFHT Adaptive Optics Observations of the Central Kinematics in M15
• On the disruption of pulsar and X-ray binaries in globular clusters
• Hubble Space Telescope Evidence for an Intermediate-Mass Black Hole in the Globular Cluster M15: I. STIS Spectroscopy and WFPC2 Photometry
• The puzzling dynamical status of the core of the globular cluster NGC 6752
• An ultracompact X-ray binary in the globular cluster M15 (NGC7078)
• The Global Kinematics of the Globular Cluster M15
• Resolving the Controversy Over the Core Radius of 47 Tucanae (NGC 104)
• Astrophysics on the GRAPE Family of Special Purpose Computers
• A Stringent Limit on the Accretion Luminosity of the Possible Central Black Hole in the Globular Cluster M15
• The Discovery of a Very Faint X-ray Transient in the Globular Cluster M15
• Globular Cluster Photometry with the Hubble Space Telescope VII. Color Gradients and Blue Stragglers in the Central Region of M30 (NGC 7099) from WFPC2 Observations
• Unveiling the core of the Globular Cluster M15 in the Ultraviolet
• Gas Accretion by Globular Clusters and Nucleated Dwarf Galaxies and the Formation of the Arches and Quintuplet Clusters
• Two-Component Fokker-Planck Models for the Evolution of Isolated Globular Clusters
• The global mass function of M15
• Fokker-Planck Models for M15 without a Central Black Hole: The Role of the Mass Function
• The X-ray source population of the globular cluster M15: Chandra high resolution imaging
• Extinction Curves, Distances, and Clumpiness of Diffuse Interstellar Dust Clouds
• X-ray and UV Variability in the Core of M15: the nature of X2127+119/AC211
• Relativistic Binaries in Globular Clusters
• The Discovery of a Second Luminous Low Mass X-ray Binary in the Globular Cluster M15
• Radial Color Gradient and Main Sequence Mass Segregation in M30 (NGC 7099)
• The Luminous Erupting Dwarf Nova CV1 in the Dense Globular Cluster M15
• Microlensing of Globular Clusters as a Probe of Galactic Structure
• High-resolution optical imaging of the core of the globular cluster M15 with FastCam