The velocity dispersion profile of NGC 6388 from resolved-star spectroscopy: No evidence of a central cusp and new constraints on the black hole mass

Journal Article · Sat Jun 01 00:00:00 EDT 2013 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/769/2/107· OSTI ID:22342083

Lanzoni, B.; Mucciarelli, A.; Ferraro, F. R.; Miocchi, P.; Dalessandro, E.; Pallanca, C.; Massari, D. ^[1]; Origlia, L.; Bellazzini, M. ^[2]

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1. Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna, Viale Berti Pichat 6/2, I-40127 Bologna (Italy)
2. INAF-Osservatorio Astronomico di Bologna, Via Ranzani 1, I-40127 Bologna (Italy)

By combining high spatial resolution and wide-field spectroscopy performed, respectively, with SINFONI and FLAMES at the ESO/VLT we measured the radial velocities of more than 600 stars in the direction of NGC 6388, a Galactic globular cluster which is suspected to host an intermediate-mass black hole. Approximately 55% of the observed targets turned out to be cluster members. The cluster velocity dispersion has been derived from the radial velocity of individual stars: 52 measurements in the innermost 2'', and 276 stars located between 18'' and 600''. The velocity dispersion profile shows a central value of ∼13 km s{sup –1}, a flat behavior out to ∼60'' and a decreasing trend outward. The comparison with spherical and isotropic models shows that the observed density and velocity dispersion profiles are inconsistent with the presence of a central black hole more massive than ∼2000 M {sub ☉}. These findings are at odds with recent results obtained from integrated light spectra, showing a velocity dispersion profile with a steep central cusp of 23-25 km s{sup –1} at r < 2'' and suggesting the presence of a black hole with a mass of ∼1.7 × 10{sup 4} M {sub ☉}. We also found some evidence of systemic rotation with amplitude A {sub rot} ∼ 8 km s{sup –1} in the innermost 2'' (0.13 pc), decreasing to A {sub rot} = 3.2 km s{sup –1} at 18'' < r < 160''.

• OSTI ID: 22342083
• Journal Information: Astrophysical Journal, Vol. 769, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
AMPLITUDES
APPROXIMATIONS
BLACK HOLES
COMPARATIVE EVALUATIONS
CUSPED GEOMETRIES
DENSITY
DISPERSIONS
FLAMES
LIMITING VALUES
MASS
NITRIC OXIDE
RADIAL VELOCITY
ROTATION
SPATIAL RESOLUTION
SPECTRA
SPECTROSCOPY
SPHERICAL CONFIGURATION
STAR EVOLUTION
STARS
VISIBLE RADIATION