Stellar dynamics in the strong-lensing central galaxy of Abell 1201: a low stellar mass-to-light ratio, a large central compact mass and a standard dark matter halo

Smith, Russell J.; Lucey, John R.; Edge, Alastair C.

Abstract

We analyse the stellar kinematics of the z = 0.169 brightest cluster galaxy in Abell 1201, using integral field observations acquired with the Multi-Unit Spectroscopic Explorer on the Very Large Telescope. This galaxy has a gravitationally lensed arc located at unusually small radius (∼5 kpc), allowing us to constrain the mass distribution using lensing and stellar dynamical information over the same radial range. We measure a velocity dispersion profile which is nearly flat at σ ≈ 285 km s−1 in the inner ∼5 kpc, and then rises steadily to σ ≈ 360 km s−1 at ∼30 kpc. We analyse the kinematics using axisymmetric Jeans models, finding that the data require both a significant dark matter halo (to fit the rising outer profile) and a compact central component, with mass Mcen ≈ 2.5 × 1010 M⊙ (to fit the flat σ in the inner regions). The latter component could represent a supermassive black hole, in which case it would be among the largest known to date. Alternatively Mcen could describe excess mass associated with a gradient in the stellar mass-to-light ratio. Imposing a standard Navarro–Frenk–White (NFW) dark matter density profile, we recover a stellar mass-to-light ratio ϒ, which is consistent with a Milky Way-like initial mass function (IMF). By anchoring the models using the lensing mass constraint, we break the degeneracy between ϒ and the inner slope γ of the dark matter profile, finding γ = 1.0 ± 0.1, consistent with the NFW form. We show that our results are quite sensitive to the treatment of the central mass in the models. Neglecting Mcen biases the results towards both a heavier-than-Salpeter IMF and a shallower-than-NFW dark matter slope (γ ≈ 0.5).

Citation

Smith, R. J., Lucey, J. R., & Edge, A. C. (2017). Stellar dynamics in the strong-lensing central galaxy of Abell 1201: a low stellar mass-to-light ratio, a large central compact mass and a standard dark matter halo. Monthly Notices of the Royal Astronomical Society, 471(1), 383-393. https://doi.org/10.1093/mnras/stx1573

• Journal Article Type: Article
• Acceptance Date: Jun 20, 2017
• Online Publication Date: Jun 22, 2017
• Publication Date: Oct 11, 2017
• Deposit Date: Sep 21, 2017
• Publicly Available Date: Oct 6, 2017
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Royal Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 471
• Issue: 1
• Pages: 383-393
• DOI: https://doi.org/10.1093/mnras/stx1573
• Public URL: https://durham-repository.worktribe.com/output/1348759
• Related Public URLs: https://arxiv.org/abs/1706.07055