Gravitational imaging through a triple source plane lens: revisiting the $\Lambda$CDM-defying dark subhalo in SDSSJ0946+1006

Abstract

The $\Lambda$CDM paradigm successfully explains the large-scale structure of the Universe, but is less well constrained on sub-galactic scales. Gravitational lens modelling has been used to measure the imprints of dark substructures on lensed arcs, testing the small-scale predictions of $\Lambda$CDM. 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 $\Lambda$CDM 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 $5.9\sigma$ confidence level with mass ${\log }_{10}(M_{\mathrm{sub}}/M_{\odot })=9.2_{-0.1}^{+0.4}$ and concentration ${\log }_{10}c=2.4_{-0.3}^{+0.5}$. The concentration is more consistent with CDM subhalos 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 ${\log }_{10}(M_{\mathrm{BH}}/M_{\odot })=8.9_{-0.1}^{+0.2}$ 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 $\ge 5\sigma$ level. However, the detection significance can be altered substantially (up to $11.3\sigma$) by alternative choices for the source regularisation scheme.

24 pages, 16 figures, 5 appendices

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• A million-solar-mass object detected at cosmological distance using gravitational imaging
• SIDM Concerto: Compilation and Data Release of Self-interacting Dark Matter Zoom-in Simulations
• SHARP -- IX. The dense, low-mass perturbers in B1938+666 and J0946+1006: implications for cold and self-interacting dark matter
• Elliptical multipoles for gravitational lenses
• Cosmography from accurate mass modeling of the lens group SDSS J0100+1818: five sources at three different redshifts
• The "Little Dark Dot": Evidence for Self-interacting Dark Matter in the Strong Lens SDSS J0946+1006?
• The revolution in strong lensing discoveries from Euclid
• Macromodel-free flux-ratio prediction in quadruply imaged quasars with local constraints from lensed arcs
• Line-of-sight effects on double source plane lenses
• Measuring the Stellar-to-Halo Mass Relation at $\sim 10^{10}$ Solar masses, using forthcoming space-based imaging of galaxy-galaxy strong lenses
• Investigation of mass substructure in gravitational lens system SDP.81 with ALMA long-baseline observations
• Self-Interacting Dark Matter with Mass Segregation: A Unified Explanation of Dwarf Cores and Small-Scale Lenses
• A Salpeter IMF and an NFW halo: Disentangling the dark and stellar mass of an elliptical galaxy through precise lens modelling of a double-source-plane system
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