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The degeneracy among the disk, bulge and halo contributions to galaxy rotation curves prevents an understanding of the distribution of baryons and dark matter in disk galaxies. In an attempt to break this degeneracy, we present an analysis of the spiral galaxy strong gravitational lens SDSS J2141-0001, discovered as part of the SLACS survey. We present new Hubble Space Telescope multicolor imaging, gas and stellar kinematics data derived from long-slit spectroscopy, and K-band LGS adaptive optics imaging, both from the Keck telescopes. We model the galaxy as a sum of concentric axisymmetric bulge, disk and halo components and infer the contribution of each component, using information from gravitational lensing and gas kinematics. This analysis yields a best-fitting total (disk plus bulge) stellar mass of log₁₀ (Mstar/Msun) = 10. 99 (+0. 11, -0. 25). The photometric data combined with stellar population synthesis models yield log₁₀ (Mstar/Msun) = 10. 970. 07, and 11. 210. 07 for the Chabrier and Salpeter IMFs, respectively. Accounting for the expected gas fraction of 20% reduces the lensing plus kinematics stellar mass by 0. 100. 05 dex, resulting in a Bayes factor of 11. 9 in favor of a Chabrier IMF. The dark matter halo is roughly spherical, with minor to major axis ratio q₇₀₋₎=0. 91 (+0. 15, -0. 13). The dark matter halo has a maximum circular velocity of V₌₀ₗ=276 (+17, -18) km/s, and a central density parameter of log₁₀ₕ/₂=5. 9 (+0. 9, -0. 5). This is higher than predicted for uncontracted dark matter haloes in LCDM cosmologies, log₁₀ₕ/₂=5. 2, suggesting that either the halo has contracted in response to galaxy formation, or that the halo has a higher than average concentration. At 2. 2 disk scale lengths the dark matter fraction is f₃₌=0. 55 (+0. 20, -0. 15), suggesting that SDSS J2141-0001 is sub-maximal.
Dutton et al. (Mon,) studied this question.