Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996aas...18911101k&link_type=abstract
American Astronomical Society, 189th AAS Meeting, #111.01; Bulletin of the American Astronomical Society, Vol. 28, p.1423
Astronomy and Astrophysics
Astronomy
Scientific paper
The stellar kinematics of the low-luminosity elliptical galaxy NGC 4486B have been measured in seeing FWHM = 0farcs66 with the Canada-France-Hawaii Telescope. Lauer et al. (1996, ApJL, in press) have shown that NGC 4486B is similar to M31 in having a double nucleus. We show that it also resembles M31 in its dynamics. The region near the double nucleus rotates more rapidly than the rest of the galaxy and has a steep velocity dispersion gradient. The central dispersion, sigma = 257 +/- 9 km s(-1) , is much higher than expected for an elliptical galaxy of absolute magnitude M_B =~ -16.8 (distance = 16 Mpc). Even more than M31, NGC 4486B is far above the scatter in the Faber-Jackson correlation between sigma and bulge luminosity. Given the observed brightness distribution, this implies that the central mass-to-light ratio is unusually high. We construct dynamical models with isotropic velocity dispersions; these imply that NGC 4486B contains a central dark object, probably a black hole (BH), of mass M_ (5.3(+3.0}_{-2.5) ) x 10(8) M_sun. Smaller masses are allowed if the velocity distribution is anisotropic, but M_ is likely to be _>atop {( ~ }) 10(8) M_sun. This BH detection reinforces the observed correlation of M_ with bulge luminosity (Kormendy & Richstone 1995, ARA&A, 33, 581). We now know of two nearby galaxies with double nuclei; this increases the need for an explanation that allows the double structure to last longer than the (short!) dynamical friction timescale of an accretion. The detection of a central dark object in NGC 4486B supports models in which double nuclei depend on the presence of a BH (e.g., Tremaine 1995, AJ, 110, 628). JK's work was supported by NSF grant AST-9219221. RB was supported by SFB 375 and by the Max-Planck-Gesellschaft. The Nuker team was supported by HST data analysis funds through grant GO-02600.01-87A and by NSERC.
Bender Ralf
Dressler Alan
Gebhardt Karl
Green Richard
Grillmair Carl C.
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