E. Mediavilla et al., Spectroscopy of the lens galaxy of Q0957+561A,B: Implications of a possible central massive dark object, ASTROPHYS J, 531(2), 2000, pp. 635-641
We present new long-slit William Herschel Telescope spectroscopic observati
ons of the lens galaxy G1 associated with the double-imaged QSO 0957+561A,B
. The central stellar velocity dispersion obtained, sigma(l) = 310 +/- 20 k
m s(-1), is in reasonable agreement with other measurements of this dynamic
al parameter. Using all updated measurements of the stellar velocity disper
sion in the internal region of the galaxy (at angular separations <1 ".5) a
nd a simple isotropic model, we discuss the mass of a possible central mass
ive dark object. We find that the data of Falco et al. suggest the existenc
e of an extremely massive object of (0.5-2.1) x 10(10) h(-1) M. (80% confid
ence level), whereas the inclusion of very recent data substantially change
s the results: the compact central mass must be less than or equal to 6 x 1
0(9) h(-1) M. at the 90% confidence level. We note that, taking into accoun
t all the available dynamical data, a compact nucleus with a mass of 109 h(
-1) M. (best fit) cannot be ruled out.