Detection of a dark matter subhalo in the strongly lensed system PJ011646
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arXiv
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| Natura: | Preprint |
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2026
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| _version_ | 1866910240964870144 |
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| author | Amvrosiadis, Aristeidis Nightingale, James W. He, Qiuhan Robertson, Andrew Cole, Shaun Frenk, Carlos S. Lange, Samuel Massey, Richard von Wietersheim-Kramsta, Maximilian Cao, Xiaoyue Li, Ran Li, Shubo Wang, Kaihao Ma, Xianghao Fung, Leo W. H. |
| author_facet | Amvrosiadis, Aristeidis Nightingale, James W. He, Qiuhan Robertson, Andrew Cole, Shaun Frenk, Carlos S. Lange, Samuel Massey, Richard von Wietersheim-Kramsta, Maximilian Cao, Xiaoyue Li, Ran Li, Shubo Wang, Kaihao Ma, Xianghao Fung, Leo W. H. |
| contents | We present a strong lensing analysis of the system PJ011646 using high-resolution ($\sim$0.1 arcsec) Atacama Large Millimeter/submillimeter Array (ALMA) dust-continuum observations to test for the presence of dark matter substructures. The lens mass distribution is modelled with an elliptical power law and third- and fourth-order multipoles (PL+MP; $m=3,4$), plus external shear. The multipoles have amplitudes of $\simeq$1.5 per cent of the convergence, consistent with nearby early-type galaxies, and improve the fit by $Δ\ln Z = 52.1$ relative to a pure PL model. Using this best-fitting macromodel, we perform a grid-based subhalo search in the image plane, parametrising the perturber as a spherical NFW. A subhalo in two locations in the image plane improves the fit by $Δ\ln Z>10$. Both correspond to the same location in the source plane, so they are partially degenerate; follow-up analysis suggests that only one is physically real. This is a subhalo of mass $M_{200} = {2.78}_{-0.66}^{+0.43} \times 10^{10} \, M_\odot$ and concentration $c_{200} = 30_{-7}^{+5}$, detected at $\sim$5.8$σ$ significance (relative to the PL+MP). This concentration is consistent with that expected for a typical tidally stripped Navarro-Frenk-White subhalo. The enclosed projected mass is most tightly constrained within a radius of 2 kpc, where we infer $M_{\rm sub} = {3.57}_{-0.14}^{+0.16}\times 10^9 \, M_\odot$. From grid cells consistent with no detection ($Δ\ln Z < 10$), we derive limits on the minimum subhalo mass that could have been detected at $3σ$ significance, finding $M_{200} \approx 8 \times 10^{8} \, M_\odot$ in the most sensitive regions of the lensed arcs. This demonstrates that ALMA continuum imaging at sub-arcsecond resolution can probe dark matter substructure in a mass regime where cold and warm dark matter models predict different abundances of subhalos. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2605_21212 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Detection of a dark matter subhalo in the strongly lensed system PJ011646 Amvrosiadis, Aristeidis Nightingale, James W. He, Qiuhan Robertson, Andrew Cole, Shaun Frenk, Carlos S. Lange, Samuel Massey, Richard von Wietersheim-Kramsta, Maximilian Cao, Xiaoyue Li, Ran Li, Shubo Wang, Kaihao Ma, Xianghao Fung, Leo W. H. Astrophysics of Galaxies Cosmology and Nongalactic Astrophysics We present a strong lensing analysis of the system PJ011646 using high-resolution ($\sim$0.1 arcsec) Atacama Large Millimeter/submillimeter Array (ALMA) dust-continuum observations to test for the presence of dark matter substructures. The lens mass distribution is modelled with an elliptical power law and third- and fourth-order multipoles (PL+MP; $m=3,4$), plus external shear. The multipoles have amplitudes of $\simeq$1.5 per cent of the convergence, consistent with nearby early-type galaxies, and improve the fit by $Δ\ln Z = 52.1$ relative to a pure PL model. Using this best-fitting macromodel, we perform a grid-based subhalo search in the image plane, parametrising the perturber as a spherical NFW. A subhalo in two locations in the image plane improves the fit by $Δ\ln Z>10$. Both correspond to the same location in the source plane, so they are partially degenerate; follow-up analysis suggests that only one is physically real. This is a subhalo of mass $M_{200} = {2.78}_{-0.66}^{+0.43} \times 10^{10} \, M_\odot$ and concentration $c_{200} = 30_{-7}^{+5}$, detected at $\sim$5.8$σ$ significance (relative to the PL+MP). This concentration is consistent with that expected for a typical tidally stripped Navarro-Frenk-White subhalo. The enclosed projected mass is most tightly constrained within a radius of 2 kpc, where we infer $M_{\rm sub} = {3.57}_{-0.14}^{+0.16}\times 10^9 \, M_\odot$. From grid cells consistent with no detection ($Δ\ln Z < 10$), we derive limits on the minimum subhalo mass that could have been detected at $3σ$ significance, finding $M_{200} \approx 8 \times 10^{8} \, M_\odot$ in the most sensitive regions of the lensed arcs. This demonstrates that ALMA continuum imaging at sub-arcsecond resolution can probe dark matter substructure in a mass regime where cold and warm dark matter models predict different abundances of subhalos. |
| title | Detection of a dark matter subhalo in the strongly lensed system PJ011646 |
| topic | Astrophysics of Galaxies Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2605.21212 |