Gravitational imaging through a triple source plane lens: revisiting the ΛCDM-defying dark subhalo in SDSSJ0946+1006

Daniel J. Ballard, Wolfgang J. R. Enzi, Thomas E. Collett, Hannah C. Turner, Russell J. Smith

Research output: Contribution to journalArticlepeer-review

2 Downloads (Pure)


The ΛCDM paradigm successfully explains the large-scale structure of the Universe, but is less well constrained on subgalactic scales. Gravitational lens modelling has been used to measure the imprints of dark substructures on lensed arcs, testing the small-scale predictions of ΛCDM. However, the methods required for these tests are subject to degeneracies among the lens mass model and the source light profile. We present a case study of the unique compound gravitational lens SDSSJ0946+1006, wherein a dark, massive substructure has been detected, whose reported high concentration would be unlikely in a ΛCDM universe. For the first time, we model the first two background sources in both I- and U-band HST imaging, as well as VLT-MUSE emission line data for the most distant source. We recover a lensing perturber at a 5.9σ confidence level with mass log10(Msub/M) = 9.2+0.4 and concentration log10 c = 2.4+0.5 −0.1. The concentration is more consistent with CDM subhaloes than previously reported, and the mass is compatible with that of a dwarf satellite galaxy whose flux is undetectable in the data at the location of the perturber. A wandering black hole with mass log10(MBH/M) = 8.9+0.2 −0.1 is a viable alternative model. We systematically investigate alternative assumptions about the complexity of the mass distribution and source reconstruction; in all cases the subhalo is detected at around the ≥5σ level. However, the detection significance can be altered substantially (up to 11.3σ) by alternative choices for the source regularization scheme.
Original languageEnglish
Pages (from-to)7564–7586
Number of pages23
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Early online date20 Feb 2024
Publication statusPublished - 1 Mar 2024


  • gravitational lensing: strong
  • dark matter
  • UKRI
  • STFC
  • ST/T000244/1
  • ST/X001075/1
  • ST/R002452/1
  • ST/R00689X/1
  • ST/P002293/1
  • ST/R002371/1
  • ST/R000832/1

Cite this