Investigation of mass substructure in gravitational lens system SDP.81 with ALMA long-baseline observations

Abstract

The prevalence and properties of low-mass dark matter haloes serve as a crucial test for understanding the nature of dark matter, and may be constrained through the gravitational deflection of strongly lensed arcs. Previous studies found evidence for the presence of low-mass dark matter haloes in observations of the gravitationally lensed, dusty star-forming galaxy SDP.81, using the Atacama Large Millimetre/sub-millimetre Array (ALMA). In this work, we analyse these observations to assess the robustness of these reported results. While our analysis indicates that the data support additional angular structure in the lensing mass distribution beyond an elliptical power-law density profile, we do not find evidence for two previously reported sub-halo detections. However, we verify with realistic mock data that we could have found evidence in favour of a previously reported $\approx 10^9{\mathrm{M}}_{\odot }$ sub-halo with a log Bayes factor of 29, should it exist in the real data. After testing various systematics, we find that this previous sub-halo inference was most likely spurious and resulted from an inadequate smooth model, specifically, poorly fitting multipoles. While we do not find evidence in favour of any individual sub-halo, we find evidence for similarity in the lensing signatures of multipoles ($m=3,4$) and single massive sub-haloes, consistent with other recent work. We suggest that future searches for low-mass haloes in lensed arcs include lens angular structure in the form of multipoles up to 4th order and require a good-fitting smooth model as a prerequisite. Overall, our findings demonstrate the suitability of ALMA data of this quality to simultaneously constrain the abundance of low-mass haloes and lens angular structure.

Accepted for publication in A&A

References in corpus (20)

• Array Programming with NumPy
• First Dark Matter Search Results from the LUX-ZEPLIN (LZ) Experiment
• Dark matter and cosmic structure
• Bayesian Strong Gravitational-Lens Modeling on Adaptive Grids: Objective Detection of Mass Substructure in Galaxies
• Search for "Invisible" Axion Dark Matter in the $3.3\text{-}4.2\mu$eV Mass Range
• Inference of the Cold Dark Matter substructure mass function at z=0.2 using strong gravitational lenses
• A lensed radio jet at milli-arcsecond resolution II: Constraints on fuzzy dark matter from an extended gravitational arc
• A Self-interacting Dark Matter Solution to the Extreme Diversity of Low-mass Halo Properties
• Substructure Detection Reanalyzed: Dark Perturber shown to be a Line-of-Sight Halo
• A lensed radio jet at milli-arcsecond resolution I: Bayesian comparison of parametric lens models
• On the density profile of dark matter substructure in gravitational lens galaxies
• Gravitational imaging through a triple source plane lens: revisiting the $\Lambda$CDM-defying dark subhalo in SDSSJ0946+1006
• Detecting low-mass haloes with strong gravitational lensing II: constraints on the density profiles of two detected subhaloes
• Complex angular structure of three elliptical galaxies from high-resolution ALMA observations of strong gravitational lenses
• Not All Subhaloes Are Created Equal: Modelling the Diversity of Subhalo Density Profiles in TNG50
• Probing sub-galactic mass structure with the power spectrum of surface-brightness anomalies in high-resolution observations of galaxy-galaxy strong gravitational lenses. I. Power-spectrum measurement and feasibility study
• Inferring subhalo effective density slopes from strong lensing observations with neural likelihood-ratio estimation
• A nuclear spiral in a dusty star-forming galaxy at $z=2.78$
• SHARP -- IX. The dense, low-mass perturbers in B1938+666 and J0946+1006: implications for cold and self-interacting dark matter
• Dark Matter Substructure or Source Model Systematics? A Case Study of Cluster Lens Abell S1063

Cited by in corpus (1)

• Using Strong Lensing to Detect Subhalos with Steep Inner Density Profiles