Tests for Substructure in Gravitational Lenses

By C. Kochanek, N. D. C. F. Astrophysics, Institute for Advanced Study. 2003

165 citations recorded by the source corpus.

The flux anomalies in four-image gravitational lenses can be interpreted as evidence for the dark matter substructure predicted by cold dark matter (CDM) halo models. In principle, these flux anomalies could arise from alternate sources, such as absorption, scattering, or scintillation by the interstellar medium (ISM) of the lens galaxy, problems in the ellipsoidal macro models used to fit lens systems, or stellar microlensing. We apply several tests to the data that appear to rule out these alternate explanations. First, the radio flux anomalies show no significant dependence on wavelength, as would be expected for almost any propagation effect in the ISM or microlensing by the stars. Second, the flux anomaly distributions show the characteristic demagnifications of the brightest saddle point relative to the other images expected for low optical depth substructure, which cannot be mimicked by either the ISM or problems in the macro models. Microlensing by stars also cannot reproduce the suppression of the bright saddle points if the radio source sizes are consistent with the Compton limit for their angular sizes. Third, while it is possible to change the smooth lens models to fit the flux anomalies in some systems, we can rule out the necessary changes in all systems where we have additional lens constraints to check the models. Moreover, the parameters of these models are inconsistent with our present observations and expectations for the structure of galaxies. We conclude that low-mass halos remain the best explanation of the phenomenon.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/7ec89e92e811978c7e94d01f434c9fcf3098e031

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Citations in the corpus

Gravitational lensing (2010, background): “The authors of [261] investigated various alternative explanations for the anomalous flux ratios, such as absorption, scattering, scintillation, uncertainties in the macro-model, and stellar microlensing, and arrived again at the conclusion that halo substructures remain as the most likely reason.”
The large-scale structure of the Universe (2006, background): “Gravitational lensing measurements may offer a test of this explanatio”
Bayesian strong gravitational-lens modelling on adaptive grids: objective detection of mass substructure in Galaxies (2008, background): “…addition, for a significant number of cases the observed flux ratio anomalies can be explained by taking into account the luminous dwarf satellite population (Trotter et al. 2000; Ros et al. 2000; Koopmans & Treu 2002; Kochanek & Dalal 2004; Chen et al. 2007; McKean et al. 2007; More et al. 2008).”
Galaxy Masses: A Review (2013, background): “Detailed comparisons with cosmological numerical simulations are challenging, owing to the need for high resolution and approximations related to the implementation of baryonic physics (e.g. Kochanek & Dalal 2004; Mao et al. 2004; Macciò et al. 2006; Xu et al. 2009, 2012).”
Gravitational Lens Time Delays: A Statistical Assessment of Lens Model Dependences and Implications for the Global Hubble Constant (2006, background): “Anomalous flux ratios observed in many gravitational lens systems indicate that substructures are indeed present (Metcalf & Madau 2001; Chiba 2002; Dalal & Kochanek 2002; Bradač et al. 2002; Keeton et al. 2005; Kochanek & Dalal 2004; Metcalf et al. 2004; Chiba et al. 2005).”
THE SIZES OF THE X-RAY AND OPTICAL EMISSION REGIONS OF RXJ 1131–1231 (2009, background): “These offsets can be non-zero due to problems in the macro model or the presence of unrecognized substructures that perturb the magnifications (e.g. Kochanek & Dalal 2004), because of differential absorption due to dust or gas in the lens galaxy (e.g. Falco et al. 1999, Dai & Kochanek 2009), or due…”
DETECTION OF LENSING SUBSTRUCTURE USING ALMA OBSERVATIONS OF THE DUSTY GALAXY SDP.81 (2016, background): “…substructure is completely devoid of baryons (e.g., Mao & Schneider 1998; Metcalf & Madau 2001; Dalal & Kochanek 2002; Moustakas & Metcalf 2003; Kochanek & Dalal 2004; Koopmans 2005; Keeton et al. 2006; Vegetti & Koopmans 2009; Vegetti et al. 2012; Nierenberg et al. 2014; Xu et al. 2015b;…”
SIZES AND TEMPERATURE PROFILES OF QUASAR ACCRETION DISKS FROM CHROMATIC MICROLENSING (2010, background): “For example, differential extinction is unlikely to be a factor in these early-type lens galaxies (Kochanek & Dalal 2004); this is supported by the general lack of strong hydrogen absorption in X-rays (Pooley et al. 2007).”
The Time Delays of Gravitational Lens HE 0435–1223: An Early-Type Galaxy with a Rising Rotation Curve (2005, background): “This provides evidence that the stars represent no more than about 20% of the total surface density of the lens galaxies at the positions of the quasar images (Schechter & Wambsganss 2002; Kochanek & Dalal 2004).”
Detection of a dark substructure through gravitational imaging (2009, unknown): “2002; Chiba 2002; Dalal & Kochanek 2002; Metcalf & Zhao 2002; Keeton et al. 2003; Kochanek & Dalal 2004; Bradač et al. 2004; Keeton et al. 2005; McKean et al. 2007; Chen et al. 2007; More et al. 2009).”