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Disentangling Baryons and Dark Matter in the Spiral Gravitational Lens B1933+503

Suyu, S. H. and Hensel, S. W. and McKean, J. P. and Fassnacht, C. D. and Treu, T. and Halkola, A. and Norbury, M. and Jackson, N. and Schneider, P. and Thompson, D. and Auger, M. W. and Koopmans, L. V. E. and Matthews, K. (2012) Disentangling Baryons and Dark Matter in the Spiral Gravitational Lens B1933+503. Astrophysical Journal, 750 (1). p. 10. ISSN 0004-637X.

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Measuring the relative mass contributions of luminous and dark matter in spiral galaxies is important for understanding their formation and evolution. The combination of a galaxy rotation curve and strong lensing is a powerful way to break the disk-halo degeneracy that is inherent in each of the methods individually. We present an analysis of the 10 image radio spiral lens B1933+503 at zl = 0.755, incorporating (1) new global very long baseline interferometry observations, (2) new adaptive-optics-assisted K-band imaging, and (3) new spectroscopic observations for the lens galaxy rotation curve and the source redshift. We construct a three-dimensionally axisymmetric mass distribution with three components: an exponential profile for the disk, a point mass for the bulge, and a Navarro-Frenk-White (NFW) profile for the halo. The mass model is simultaneously fitted to the kinematics and the lensing data. The NFW halo needs to be oblate with a flattening of a/c = 0.33^(+0.07)_(–0.05) to be consistent with the radio data. This suggests that baryons are effective at making the halos oblate near the center. The lensing and kinematics analysis probe the inner ~10 kpc of the galaxy, and we obtain a lower limit on the halo scale radius of 16 kpc (95% credible intervals). The dark matter mass fraction inside a sphere with a radius of 2.2 disk scale lengths is f_(DM, 2.2) = 0.43+0.10 –0.09. The contribution of the disk to the total circular velocity at 2.2 disk scale lengths is 0.76^(+0.05)_(–0.06), suggesting that the disk is marginally submaximal. The stellar mass of the disk from our modeling is log10(M_*/M_☉) = 11.06^(+0.09)_(–0.11) assuming that the cold gas contributes ~20% to the total disk mass. In comparison to the stellar masses estimated from stellar population synthesis models, the stellar initial mass function of Chabrier is preferred to that of Salpeter by a probability factor of 7.2.

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Treu, T.0000-0002-8460-0390
Additional Information:© 2012 American Astronomical Society. Received 2011 October 10; accepted 2012 February 18; published 2012 April 10. We thank Matteo Barnabè, Aaron Dutton, and Phil Marshall for useful discussions, and the anonymous referee for the constructive comments that improved the presentation of the paper. S.H.S. and T.T. acknowledge support from the Packard Foundation through a Packard Research Fellowship to T.T. S.H.S. is supported in part through HST grants 11588 and 10876. C.D.F. acknowledges support from NSF-AST-0909119. L.V.E.K. is supported in part by an NWO-VIDI program subsidy (project No. 639.042.505). This work was supported in part by the Deutsche Forschungsgemeinschaft under the Transregio TR-33, “The Dark Universe.” The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The European VLBI Network is a joint facility of European, Chinese, South African, and other radio astronomy institutes funded by their national research councils. Some of the data presented in this paper were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors also recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.
Funding AgencyGrant Number
Packard Foundation Packard Research FellowshipUNSPECIFIED
Hubble Space Telescope (HST)11588
Hubble Space Telescope (HST)10876
Deutsche Forschungsgemeinschaft (DFG)Transregio TR-33
Subject Keywords:galaxies: halos; galaxies: individual (B1933+503); galaxies: kinematics and dynamics; galaxies: spiral; gravitational lensing: strong
Record Number:CaltechAUTHORS:20120523-103538599
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Official Citation:Disentangling Baryons and Dark Matter in the Spiral Gravitational Lens B1933+503 S. H. Suyu et al. 2012 ApJ 750 10
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:31611
Deposited By: Jason Perez
Deposited On:23 May 2012 18:32
Last Modified:05 Oct 2017 22:30

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