Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSHARP - II. Mass structure in strong lenses is not necessarily dark matter substructure: A flux ratio anomaly from an edge-on disc
63
0
0.0
(
0
)
Authors
J.- W. Hsueh
Ask ChatGPT about the research
No Arabic abstract
Gravitational lens flux-ratio anomalies provide a powerful technique for measuring dark matter substructure in distant galaxies. However, before using these flux-ratio anomalies to test galaxy formation models, it is imperative to ascertain that the given anomalies are indeed due to the presence of dark matter substructure and not due to some other component of the lensing galaxy halo or to propagation effects. Here we present the case of CLASS~B1555+375, which has a strong radio-wavelength flux-ratio anomaly. Our high-resolution near-infrared Keck~II adaptive optics imaging and archival Hubble Space Telescope data reveal the lensing galaxy in this system to have a clear edge-on disc component that crosses directly over the pair of images that exhibit the flux-ratio anomaly. We find that simple models that include the disc can reproduce the cm-wavelength flux-ratio anomaly without requiring additional dark matter substructure. Although further studies are required, our results suggest the assumption that all flux-ratio anomalies are due to a population of dark matter sub-haloes may be incorrect, and analyses that do not account for the full complexity of the lens macro-model may overestimate the substructure mass fraction in massive lensing galaxies.
rate research
Read More
Flux ratio anomalies in quasar lenses can be attributed to dark matter substructure surrounding the lensing galaxy and, thus, used to constrain the substructure mass fraction. Previous applications of this approach infer a substructure abundance that potentially in tension with the predictions of a $Lambda$CDM cosmology. However, the assumption that all flux ratio anomalies are due to substructure is a strong one, and alternative explanations have not been fully investigated. Here, we use new high-resolution near-IR Keck~II adaptive optics imaging for the lens system CLASS B0712+472 to perform pixel-based lens modelling for this system and, in combination with new VLBA radio observations, show that the inclusion of the disc in the lens model can explain the flux ratio anomalies without the need for dark matter substructures. The projected disc mass comprises 16% of the total lensing mass within the Einstein radius and the total disc mass is $1.79 times 10^{10} M_{sun}$. The case of B0712+472 adds to the evidence that not all flux ratio anomalies are due to dark subhaloes, and highlights the importance of taking the effects of baryonic structures more fully into account in order to obtain an accurate measure of the substructure mass fraction.
The subtle and unique imprint of dark matter substructure on extended arcs in strong lensing systems contains a wealth of information about the properties and distribution of dark matter on small scales and, consequently, about the underlying particle physics. However, teasing out this effect poses a significant challenge since the likelihood function for realistic simulations of population-level parameters is intractable. We apply recently-developed simulation-based inference techniques to the problem of substructure inference in galaxy-galaxy strong lenses. By leveraging additional information extracted from the simulator, neural networks are efficiently trained to estimate likelihood ratios associated with population-level parameters characterizing substructure. Through proof-of-principle application to simulated data, we show that these methods can provide an efficient and principled way to simultaneously analyze an ensemble of strong lenses, and can be used to mine the large sample of lensing images deliverable by near-future surveys for signatures of dark matter substructure.
I show that the lensing masses of the SLACS sample of strong gravitational lenses are consistent with the stellar masses determined from population synthesis models using the Salpeter IMF. This is true in the context of both General Relativity and modified Newtonian dynamics, and is in agreement with the expectation of MOND that there should be little classical discrepancy within the high surface brightness regions probed by strong gravitational lensing. There is also dynamical evidence from this sample supporting the claim that the mass-to-light ratio of the stellar component increases with the velocity dispersion.
A fundamental prediction of the cold dark matter (CDM) model of structure formation is the existence of a vast population of dark matter haloes extending to subsolar masses. By contrast, other possibilities for the nature of the dark matter, such as a warm thermal relic or a sterile neutrino (WDM) predict a cutoff in the mass function at a mass of $sim 10^8~{rm M}_odot$. We use mock observations to demonstrate the viability of a forward modelling approach to extract information on the cosmological number density of low-mass dark matter haloes along the line-of-sight to galaxy-galaxy strong lenses. This can be used to constrain the mass of a thermal relic dark matter particle, $m_mathrm{DM}$. With 50 strong lenses at Hubble Space Telescope resolution and signal-to-noise (similar to the existing SLACS survey), the expected 2$sigma$ constraint for CDM is $m_mathrm{DM} > 3.7 , mathrm{keV}$. If, however, the dark matter is a warm particle of $m_mathrm{DM}=2.2 , mathrm{keV}$, one could rule out $m_mathrm{DM} > 3.2 , mathrm{keV}$. Our [Approximate Bayesian Computation] method can be extended to the large samples of strong lenses that will be observed by future space telescopes, potentially to rule out the standard CDM model of cosmogony. To aid future survey design, we quantify how these constraints will depend on data quality (spatial resolution and integration time) as well as on the lensing geometry (source and lens redshifts).
We compare subhalo mass and velocity functions obtained from different simulations with different subhalo finders among each other, and with predictions from the new semi-analytical model of Jiang & van den Bosch (2014). We find that subhalo mass functions (SHMFs) obtained using different subhalo finders agree with each other at the level of ~ 20 percent, but only at the low mass end. At the massive end, subhalo finders that identify subhaloes based purely on density in configuration space dramatically underpredict the subhalo abundances by more than an order of magnitude. These problems are much less severe for subhalo velocity functions (SHVFs), indicating that they arise from issues related to assigning masses to the subhaloes, rather than from detecting them. Overall the predictions from the semi-analytical model are in excellent agreement with simulation results obtained using the more advanced subhalo finders that use information in six dimensional phase-space. In particular, the model accurately reproduces the slope and host-mass-dependent normalization of both the subhalo mass and velocity functions. We find that the SHMFs and SHVFs have power-law slopes of 0.82 and 2.6, respectively, significantly shallower than what has been claimed in several studies in the literature.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
