Space Telescope Observations of Globular Clusters

Symposium - International Astronomical Union ◽

10.1017/s0074180900147722 ◽

1985 ◽

Vol 113 ◽

pp. 481-498

Author(s):

John N. Bahcall

Keyword(s):

Black Hole ◽

Globular Clusters ◽

Luminosity Function ◽

Elliptical Galaxies ◽

Core Collapse ◽

Massive Black Hole ◽

Space Telescope ◽

Galactic Clusters ◽

Mass Segregation

Six proposed Space Telescope programs involving globular clusters are described. The projects appropriate for galactic clusters are: the detection of white dwarfs, the study of the faint end of the Population II luminosity function, the measurement of mass segregation, and the search for a cusp in the density distribution caused by core collapse or by a massive black hole. The two programs that involve extragalactic globular clusters are: the determination of the luminosity function of clusters around different galaxies and the measurement of tidal radii of clusters surrounding elliptical galaxies.

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Hubble Space Telescope Studies of the Dense Central Regions of Globular Clusters

Symposium - International Astronomical Union ◽

10.1017/s0074180900001340 ◽

1996 ◽

Vol 174 ◽

pp. 19-28

Author(s):

Puragra Guhathakurta ◽

Brian Yanny ◽

Donald P. Schneider ◽

John N. Bahcall

Keyword(s):

Density Profile ◽

Globular Clusters ◽

Hubble Space Telescope ◽

Stellar Populations ◽

Core Collapse ◽

Red Giants ◽

Space Telescope ◽

Blue Straggler ◽

Central Regions ◽

Stellar Density

We present results from an ongoing program to probe the dense central parts of Galactic globular clusters using multicolor Hubble Space Telescope images (WF/PC-I and WFPC2). Our sample includes the dense clusters M15, 47 Tuc, M30, NGC 6624, M3 and M13. The two main goals of our program are to measure the shape of stellar density profile in clusters (the slope of the density cusp in post core collapse clusters, in particular) and to understand the nature of evolved stellar populations in very dense regions and their variation as a function of radius. The latter includes studies of blue straggler stars and of the central depletion of bright red giants. Our recent WFPC2 study of M15 is described in detail.

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11.16. On the origin of density cusp in galactic nuclei by central black hole

Symposium - International Astronomical Union ◽

10.1017/s0074180900085703 ◽

1998 ◽

Vol 184 ◽

pp. 487-488

Author(s):

T. Nakano ◽

T. Fukushige ◽

J. Makino

Keyword(s):

Black Hole ◽

Hubble Space Telescope ◽

Outer Region ◽

Elliptical Galaxies ◽

Heating Process ◽

Massive Black Hole ◽

Weak Density ◽

The Galaxy ◽

Galaxy Model ◽

Inner Region

We investigated the dynamical reaction of the central region of galaxies to a falling massive black hole by N-body simulations. As the initial galaxy model, we used an isothermal King model and placed a massive black hole at around the half-mass radius of the galaxy. We found that the central core of the galaxy is destroyed by the heating due to the black hole and a very weak density cusp (ρ ∝ r−α, with α ∼ 0.5) is formed around the center. This result is consistent with recent observations of large elliptical galaxies by Hubble Space Telescope (Lauer et al. 1995; Byun et al. 1996; Gebhardt et al. 1996; Faber et al. 1996; Kormendy et al. 1996). The radius of the weak cusp region is large for large black hole mass. The velocity of the stars become tangentially anisotropic in the inner region, while in the outer region the stars have radially anisotropic velocity dispersion. Our result naturally explains the mechanism of the formation of the weak cusp found in the previous simulations of galaxy merging, and implies that the weak cusp observed in large elliptical galaxies may be formed by the heating process by sinking black holes during merging events.

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Dynamics in the Centres of Triaxial Elliptical Galaxies

Symposium - International Astronomical Union ◽

10.1017/s0074180900185213 ◽

1987 ◽

Vol 127 ◽

pp. 241-248

Author(s):

Ortwin E. Gerhard

Keyword(s):

Black Hole ◽

Large Angle ◽

Elliptical Galaxies ◽

Central Density ◽

Massive Black Hole ◽

Upper Limits ◽

Density Concentration ◽

The Masses ◽

Future Work ◽

Spherical Potential

Orbits in the inner kpc of a triaxial galaxy are discussed, taking into account the effect of a central density concentration like a massive black hole, a dense stellar nucleus, or a de Vaucouleurs-type cusp. Since the box orbits that form the backbone of a triaxial galaxy pass arbitrarily close to the centre after long enough time, they will eventually be subjected to large-angle deflections by a central point mass, and the triaxiality of the inner part of the system will thereby be destroyed. A 108 M⊙ black hole is estimated to affect box orbits out to 1kpc in a Hubble time, while a similar influence of the observed (extended) nucleus in M31 reaches out to 500pc in the bulge. Regular box orbits persist, however, in systems with singular central density profiles such as implied by carrying the r1/4 law all the way to the centre. This result can be approximately understood in terms of the frequency ratio Ωr/Ωθ remaining close to the harmonic value of 2 for many orbits in the corresponding spherical potential. Finally, I discuss observable consequences of the box orbit scattering process and future work, and use the presence of isophote twists in the central parts of a number of elliptical galaxies to obtain approximate upper limits on the masses of the black holes these systems may contain.

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Mass Functions & Stellar Populations of Globular Clusters

Highlights of Astronomy ◽

10.1017/s1539299600018256 ◽

1998 ◽

Vol 11 (2) ◽

pp. 603-608

Author(s):

P. Guhathakurta ◽

G. Piotto ◽

E. Vesperini

Keyword(s):

Globular Clusters ◽

Luminosity Function ◽

Core Collapse ◽

Wide Field ◽

Spread Function ◽

Central Regions ◽

Photometric Error ◽

Empirical Point ◽

Mass Functions ◽

Image Simulations

I present a summary of results from various HST photometric studies of the dense central regions of Galactic globular clusters that my collaborators and I have carried out over the last 6 years. The dataset includes short exposures of 47 Tuc, M15, M3 and M13 obtained with the aberrated Planetary Camera-I (PC-I) and F555W (“V”) and F785LP (“I”) filters, as well as post-refurbishment Wide Field Planetary Camera 2 (WFPC2) snapshots of the post core collapse clusters M15, M30, and NGC 6624 in F336W (“U”), F439W (“B”), and V. Recently, a very deep, doubly oversampled PC-I U image of the core of 47 Tuc, and accompanying B and V images, have also been analyzed. In addition, we have carried out extensive checks of incompleteness and photometric error with the help of multiband image simulations that mimic the relevant characteristics of the HST PC-I and WFPC2 images: empirical point spread function, crowding effects based on a realistic density profile and stellar luminosity function (LF), noise, undersampling, A/D saturation, etc..

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A simple two-component description of mass segregation for anisotropic globular clusters

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319006707 ◽

2019 ◽

Vol 14 (S351) ◽

pp. 528-531

Author(s):

S. Torniamenti ◽

G. Bertin ◽

P. Bianchini

Keyword(s):

Numerical Simulations ◽

Globular Clusters ◽

Elliptical Galaxies ◽

Dynamical Models ◽

Two Component ◽

Partial Energy ◽

Energy Equipartition ◽

Mass Segregation ◽

The One ◽

Component Models

AbstractAs a result of the slow action of two-body encounters, globular clusters develop mass segregation and attain a condition of only partial energy equipartition even in their central, most relaxed regions. Realistic numerical simulations show that, during the process, a radially-biased anisotropy profile slowly builds up, mimicking that resulting from incomplete violent relaxation. Commonly used dynamical models, such as the one-component King models, cannot describe these properties. Here we show that simple two-component models based on a distribution function originally conceived to describe elliptical galaxies, recently truncated and adapted to the context of globular clusters, can describe in detail what is observed in complex and realistic numerical simulations.

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Globular Clusters in Dwarf Elliptical Galaxies

Symposium - International Astronomical Union ◽

10.1017/s0074180900223899 ◽

2002 ◽

Vol 207 ◽

pp. 303-305

Author(s):

Bryan W. Miller ◽

Jennifer M. Lotz ◽

Henry C. Ferguson ◽

Massimo Stiavelli ◽

Bradley C. Whitmore

Keyword(s):

Globular Cluster ◽

Globular Clusters ◽

Luminosity Function ◽

Elliptical Galaxies ◽

Preliminary Results ◽

The Galaxy ◽

Dwarf Elliptical Galaxies

We present preliminary results on the shape of the globular cluster luminosity function and the colors and inferred metallicities of the clusters in dwarf elliptical galaxies imaged with HST. The luminosity function (LF) of the GC candidates is consistent with a Gaussian-shaped LF similar to that in giant ellipticals. Also, with a mean color of (V - I) = 0.94, most of the GCs appear to be old and metal-poor ([Fe/H] = −1.4) like GCs in the Galaxy and in nearby giant ellipticals. This suggests that the bulk of the clusters were formed more than 10 Gyr ago.

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