J/A+A/462/L9 Radial velocities in NGC 7099 (Scarpa+, 2007)
Using globular clusters to test gravity in the weak acceleration regime:
NGC 7099.
Scarpa R., Marconi G., Gilmozzi R., Carraro G.
<Astron. Astrophys. 462, L9 (2007)>
=2007A&A...462L...9S 2007A&A...462L...9S
ADC_Keywords: Clusters, globular ; Radial velocities
Keywords: gravitation - globular clusters: general -
globular clusters: individual: NGC 7099
Abstract:
A test of Newton's law of gravity in the low acceleration regime using
globular clusters is presented and new results for the core collapsed
globular cluster NGC 7099 given. The run of the gravitational
potential as a function of distance is probed by studying the velocity
dispersion profile of the cluster, as derived from a set of 125 radial
velocities with accuracy better than 1km/s. The velocity dispersion
profile is traced up to ∼18pc from the cluster center. The dispersion
is found to be maximal at the center, then decrease until 10±2pc
from the center, well inside the cluster tidal radius of 42pc. After
that the dispersion remains basically constant with an average value
of 2.2±0.3km/s. Assuming a total V magnitude of M(V)=-7.43mag for
NGC 7099, the acceleration at 10±2pc from the center is
1.1+0.4-0.3_τx10-8cm/s2, where τ is the mass-to-light
ratio. Thus, for τ≳2 typical of globular clusters, the flattening
of the velocity dispersion profile occurs for a value of the internal
acceleration of gravity that is fully consistent with
a0=1.2x10-8cm/s2 observed in galaxies. This new result for NGC
7099 brings to 4 the clusters with velocity dispersion profile probing
acceleration below a0. All four have been found to have a flat
dispersion profile at large radii where the acceleration is below
a0, thereby mimicking elliptical galaxies qualitatively and
quantitatively. Whether this indicates a failure of Newtonian dynamics
in the low acceleration limit or some more conventional dynamical
effect (e.g., tidal heating) is still unclear. However, the
similarities emerging between very different globular clusters, as
well as between globular clusters and elliptical galaxies, seem to
favor the first of these two possibilities.
Objects:
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RA (2000) DE Designation(s)
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21 40 22.03 -23 10 44.6 NGC 7099 = M 30
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
rv.dat 63 234 NGC 7099 radial velocities
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See also:
J/A+A/313/129 : Positions and magnitudes of M30 blue stars (Burgarella+ 1996)
J/AJ/112/1061 : BV photometry of NGC 7099 (Bergbusch 1996)
J/AJ/116/1757 : M30 UBV photometry (Guhathakurta+, 1998)
J/ApJ/518/262 : CCD VIc Photometry of M30 Stars (Sandquist+, 1999)
Byte-by-byte Description of file: rv.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- Name Identification (1)
16- 26 F11.7 deg RAdeg Right ascension in decimal degrees (J2000)
29- 39 F11.7 deg DEdeg Declination in decimal degrees (J2000)
42- 46 F5.2 mag Vmag Approximate V band magnitude
49- 56 F8.3 km/s RV Radial velocity
59- 63 F5.3 km/s e_RV Error in the radial velocity
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Note (1): Identification:
U600_43NNNNNN and ngc7099NNNN
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Acknowledgements: R. Scarpa, rscarpa(at)eso.org
(End) Patricia Vannier [CDS] 13-Nov-2006