MASS SEGREGATION IN NGC 2298: LIMITS ON THE PRESENCE OF AN INTERMEDIATE MASS BLACK HOLE
- Department of Physics, University of Pisa, Largo Bruno Pontecorvo 3, I-56127 Pisa (Italy)
- Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, CO, 80309-0389 (United States)
- Space Science Department, European Space Agency, Keplerlaan 1, 2200 AG Noordwijk (Netherlands)
- Department of Astronomy and Maryland Astronomy Center for Theory and Computation, University of Maryland, College Park, MD 20742-2421 (United States)
Theoretical investigations have suggested the presence of intermediate mass black holes (IMBHs, with masses in the 100-10000 M{sub sun} range) in the cores of some globular clusters (GCs). In this paper, we present the first application of a new technique to determine the presence or absence of a central IMBH in globular clusters that have reached energy equipartition via two-body relaxation. The method is based on the measurement of the radial profile for the average mass of stars in the system, using the fact that a quenching of mass segregation is expected when an IMBH is present. Here, we measure the radial profile of mass segregation using main-sequence stars for the globular cluster NGC 2298 from resolved source photometry based on Hubble Space Telescope (HST/ACS) data. NGC 2298 is one of the smallest galactic globular clusters, thus not only it is dynamically relaxed but also a single ACS field of view extends to about twice its half-light radius, providing optimal radial coverage. The observations are compared to expectations from direct N-body simulations of the dynamics of star clusters with and without an IMBH. The mass segregation profile for NGC 2298 is quantitatively matched to that inferred from simulations without a central massive object over all the radial range probed by the observations, that is from the center to about two half-mass radii. Profiles from simulations containing an IMBH more massive than {approx}300-500 M{sub sun} (depending on the assumed total mass of NGC 2298) are instead inconsistent with the data at about 3{sigma} confidence, irrespective of the initial mass function and binary fraction chosen for these runs. Our finding is consistent with the currently favored formation scenarios for IMBHs in GCs, which are not likely to apply to NGC 2298 due to its modest total mass. While providing a null result in the quest of detecting a central black hole in globular clusters, the data-model comparison carried out here demonstrates the feasibility of the method which can also be applied to other globular clusters with resolved photometry in their cores.
- OSTI ID:
- 21333713
- Journal Information:
- Astrophysical Journal, Vol. 699, Issue 2; Other Information: DOI: 10.1088/0004-637X/699/2/1511; Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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