Dark matter contraction and stellar-mass-to-light ratio gradients in massive early-type galaxies. Issue 1 (10th January 2018)

• Record Type: Journal Article
• Authors: Oldham, Lindsay J; Auger, Matthew W
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 476:Issue 1(2018)
• Page Start: 133
• Page End: 150
• Publication Date: 2018-01-10
• Subjects: gravitational lensing: strong -- galaxies: elliptical and lenticular, cD -- galaxies: evolution -- galaxies: kinematics and dynamics -- galaxies: structure; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/sty065
• Languages: English
• ISSNs: 0035-8711

Abstract

Abstract: We present models for the dark and luminous mass structure of 12 strong lensing early-type galaxies. We combine pixel-based modelling of multiband Hubble Space Telescope imaging with Jeans modelling of kinematics obtained from Keck/ESI spectra to disentangle the dark and luminous contributions to the mass. Assuming a generalised NFW (gNFW) profile for the dark matter halo and a spatially constant stellar-mass-to-light ratio ϒ⋆ for the baryonic mass, we infer distributions for ϒ⋆ consistent with initial mass functions (IMFs) that are heavier than the Milky Way's (with a global mean mismatch parameter relative to a Chabrier IMF μα c = 1.80 ± 0.14) and halo inner density slopes that span a large range but are generally cuspier than the dark-matter-only prediction ($\mu _{\gamma ^{\prime }} = 2.01_{-0.22}^{+0.19}$ ). We investigate possible reasons for overestimating the halo slope, including the neglect of spatially varying stellar-mass-to-light ratios and/or stellar orbital anisotropy, and find that a quarter of the systems prefer radially declining stellar-mass-to-light ratio gradients, but that the overall effect on our inference on the halo slope is small. We suggest a coherent explanation of these results in the context of inside-out galaxy growth, and that the relative importance of different baryonic processes in shaping the dark halo may depend on halo environment.