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Spectroscopy of the Lens Galaxy of Q0957+561A,B. Implications of a possible central massive dark object

E. Mediavilla·M. Serra-Ricart·A. Oscoz·L. J. Goicoechea·J. Buitrago
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Abstract

We present new long-slit William Herschel Telescope spectroscopic observations of the lens galaxy G1 associated with the double-imaged QSO 0957+561A,B. The obtained central stellar velocity dispersion, sigma_l = 310 +/- 20 km/s, is in reasonable agreement with other measurements of this dynamical parameter. Using all updated measurements of the stellar velocity dispersion in the internal region of the galaxy (at angular separations < 1".5) and a simple isotropic model, we discuss the mass of a possible central massive dark object. It is found that the data of Falco et al. (1997) suggest the existence of an extremely massive object of (0.5-2.1) x 10E10/h M_\odot (80% confidence level), whereas the inclusion of very recent data (Tonry & Franx 1998, and this paper) substantially changes the results: the compact central mass must be $\le$ 6 x10E9/h M_\odot at the 90% confidence level. We note that, taking into account all the available dynamical data, a compact nucleus with a mass of 10E9/h M_\odot (best fit) cannot be ruled out.

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E. Mediavilla, M. Serra-Ricart, A. Oscoz, L. J. Goicoechea, J. Buitrago. 1999-05-17. Spectroscopy of the Lens Galaxy of Q0957+561A,B. Implications of a possible central massive dark object. https://doi.org/10.1086/308473

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