Beyond the bulge-halo conspiracy? Density profiles of Early-type galaxies from extended-source strong lensing

Amy Etherington, James W. Nightingale, Richard Massey, Andrew Robertson, XiaoYue Cao, Aristeidis Amvrosiadis, Shaun Cole, Carlos S. Frenk, Qiuhan He, David J. Lagattuta, Samuel Lange, Ran Li

Submitted on 8 July 2022


Observations suggest the dark matter and stars in early-type galaxies `conspire' to produce an unexpectedly simple distribution of total mass ρ(r)ργ with γ2. We measure the distribution of mass in 48 early-type galaxies that gravitationally lens a resolved background source. By fitting the source light in every pixel of images from the Hubble Space Telescope, we find mean γ=2.0750.024+0.023 with intrinsic scatter between galaxies σγ=0.1720.032+0.022. This is consistent with, and has similar precision to, traditional techniques that also require deep spectroscopic observations to measure stellar dynamics. At fixed surface mass density, we measure redshift dependence γ/z=0.3450.296+0.322 that is consistent with traditional techniques for the same sample of SLACS and GALLERY lenses. Interestingly, the consistency breaks down when we measure the dependence of γ on a lens galaxy's surface mass density. We argue that this is tentative evidence for an inflection point in the total-mass density profile at a few times a galaxy's effective radius -- breaking the conspiracy.


Comment: 14 pages, 11 figures, 5 tables, submitted to MNRAS

Subject: Astrophysics - Astrophysics of Galaxies