39 research outputs found
Not all subhaloes are created equal: modelling the diversity of subhalo density profiles in TNG50
In this work, we analyse the density profiles of subhaloes with masses Msh ≥ 1.4 × 108 M in the TNG50 simulation, with the aim of including baryonic effects. We evaluate the performance of frequently used models, such as the standard Navarro–Frenk–White (NFW), the Einasto, and a smoothly truncated version of the NFW profile. We find that these models do not perform well for the majority of subhaloes, with the NFW profile giving the worst fit in most cases. This is primarily due to mismatches in the inner and outer logarithmic slopes, which are significantly steeper for a large number of subhaloes in the presence of baryons. To address this issue, we propose new three-parameter models and show that they significantly improve the goodness of fit independently of the subhalo’s specific properties. Our best-performing model is a modified version of the NFW profile with an inner log-slope of −2 and a variable truncation that is sharper and steeper than the slope transition in the standard NFW profile. Additionally, we investigate how both the parameter values of the best density profile model and the average density profiles vary with subhalo mass, Vmax, distance from the host halo centre, baryon content, and infall time, and we also present explicit scaling relations for the mean parameters of the individual profiles. The newly proposed fit and the scaling relations are useful to predict the properties of realistic subhaloes in the mass range 108 M ≤Msh ≤ 1013 M that can be influenced by the presence of baryons
Constraining SIDM with halo shapes: Revisited predictions from realistic simulations of early-type galaxies
We study the effect of self-interacting dark matter (SIDM) and baryons on the shape of early-type galaxies (ETGs) and their dark matter haloes, comparing them to the predictions of the cold dark matter (CDM) scenario. We use five hydrodynamical zoom-in simulations of haloes hosting ETGs (Mvir sim 10 13 , M ⊙ and M ∗ ∼ 10 11 , M ⊙), simulated in CDM and a SIDM model with constant cross-section of σT/mχ = 1 cm2g-1. We measure the 3D and projected shapes of the dark matter haloes and their baryonic content using the inertia tensor and compare our measurements to the results of three HST samples of gravitational lenses and Chandra and XMM-Newton X-ray observations. We find that the inclusion of baryons greatly reduces the differences between CDM and a SIDM, together with the ability to draw constraints based on shapes. Lensing measurements reject the predictions of CDM dark-matter-only simulations and prefer one of the hydro scenarios. When we consider the total sample of lenses, observational data prefer the CDM hydro scenario. The shapes of the X-ray emitting gas are compatible with observational results in both hydro runs, with CDM predicting higher elongations only in the very centre. Contrary to previous claims at the scale of elliptical galaxies, we conclude that both CDM and our SIDM model can still explain observed shapes once we include baryons in the simulations. Our results demonstrate that this is essential to derive realistic constraints and that new simulations are needed to confirm and extend our findings
The lensing properties of subhaloes in massive elliptical galaxies in sterile neutrino cosmologies
We use high-resolution hydrodynamical simulations run with the EAGLE model of galaxy formation to study the differences between the properties of - and subsequently the lensing signal from - subhaloes of massive elliptical galaxies at redshift 0.2, in Cold and Sterile Neutrino (SN) Dark Matter models. We focus on the two 7 keV SN models that bracket the range of matter power spectra compatible with resonantly produced SN as the source of the observed 3.5 keV line. We derive an accurate parametrization for the subhalo mass function in these two SN models relative to cold dark matter (CDM), as well as the subhalo spatial distribution, density profile, and projected number density and the dark matter fraction in subhaloes. We create mock lensing maps from the simulated haloes to study the differences in the lensing signal in the framework of subhalo detection. We find that subhalo convergence is well described by a lognormal distribution and that signal of subhaloes in the power spectrum is lower in SN models with respect to CDM, at a level of 10-80 per cent, depending on the scale. However, the scatter between different projections is large and might make the use of power spectrum studies on the typical scales of current lensing images very difficult. Moreover, in the framework of individual detections through gravitational imaging a sample of ≃30 lenses with an average sensitivity of Msub = 5 × 107 M☉ would be required to discriminate between CDM and the considered sterile neutrino models
Systematic errors in strong gravitational lensing reconstructions, a numerical simulation perspective
We present the analysis of a sample of twenty-four SLACS-like galaxy-galaxy
strong gravitational lens systems with a background source and deflectors from
the Illustris-1 simulation. We study the degeneracy between the complex mass
distribution of the lenses, substructures, the surface brightness distribution
of the sources, and the time delays. Using a novel inference framework based on
Approximate Bayesian Computation, we find that for all the considered lens
systems, an elliptical and cored power-law mass density distribution provides a
good fit to the data. However, the presence of cores in the simulated lenses
affects most reconstructions in the form of a Source Position Transformation.
The latter leads to a systematic underestimation of the source sizes by 50 per
cent on average, and a fractional error in of around
per cent. The analysis of a control sample of twenty-four lens systems, for
which we have perfect knowledge about the shape of the lensing potential, leads
to a fractional error on of per cent. We find no
degeneracy between complexity in the lensing potential and the inferred amount
of substructures. We recover an average total projected mass fraction in
substructures of at the 68 per cent
confidence level in agreement with zero and the fact that all substructures had
been removed from the simulation. Our work highlights the need for
higher-resolution simulations to quantify the lensing effect of more realistic
galactic potentials better, and that additional observational constraint may be
required to break existing degeneracies.Comment: Accepted by MNRA
Detecting low-mass haloes with strong gravitational lensing I: the effect of data quality and lensing configuration
This paper aims to quantify how the lowest halo mass that can be detected with galaxy-galaxy strong gravitational lensing depends on the quality of the observations and the characteristics of the observed lens systems. Using simulated data, we measure the lowest detectable NFW mass at each location of the lens plane, in the form of detailed sensitivity maps. In summary, we find that: (i) the lowest detectable mass Mlow decreases linearly as the signal-to-noise ratio (SNR) increases and the sensitive area is larger when we decrease the noise; (ii) a moderate increase in angular resolution (0.07′′ versus 0.09′′) and pixel scale (0.01′′ versus 0.04′′) improves the sensitivity by on average 0.25 dex in halo mass, with more significant improvement around the most sensitive regions; (iii) the sensitivity to low-mass objects is largest for bright and complex lensed galaxies located inside the caustic curves and lensed into larger Einstein rings (i.e rE ≥ 1.0′′). We find that for the sensitive mock images considered in this work, the minimum mass that we can detect at the redshift of the lens lies between 1.5 × 108 and 3 × 109 M☉. We derive analytic relations between Mlow, the SNR and resolution and discuss the impact of the lensing configuration and source structure. Our results start to fill the gap between approximate predictions and real data and demonstrate the challenging nature of calculating precise forecasts for gravitational imaging. In light of our findings, we discuss possible strategies for designing strong lensing surveys and the prospects for HST, Keck, ALMA, Euclid and other future observations
Sharp - VII. New constraints on the dark matter free-streaming properties and substructure abundance from gravitationally lensed quasars
We present an analysis of seven strongly gravitationally lensed quasars and the corresponding constraints on the properties of dark matter. Our results are derived by modelling the lensed image positions and flux-ratios using a combination of smooth macro-models and a population of low-mass haloes within the mass range of 106-109 M☉. Our lens models explicitly include higher order complexity in the form of stellar discs and luminous satellites, as well as low-mass haloes located along the observed lines of sight for the first time. Assuming a cold dark matter (CDM) cosmology, we infer an average total mass fraction in substructure of fsub = 0.012+−00007004 (68 per cent confidence limits), which is in agreement with the predictions from CDM hydrodynamical simulations to within 1σ. This result is closer to the predictions than those from previous studies that did not include line-of-sight haloes. Under the assumption of a thermal relic dark matter model, we derive a lower limit on the particle relic mass of mth > 5.58 keV (95 per cent confidence limits), which is consistent with a value of mth > 5.3 keV from the recent analysis of the Ly α forest. We also identify two main sources of possible systematic errors and conclude that deeper investigations in the complex structure of lens galaxies as well as the size of the background sources should be a priority for this field
A New Era in the Quest for Dark Matter
There is a growing sense of `crisis' in the dark matter community, due to the
absence of evidence for the most popular candidates such as weakly interacting
massive particles, axions, and sterile neutrinos, despite the enormous effort
that has gone into searching for these particles. Here, we discuss what we have
learned about the nature of dark matter from past experiments, and the
implications for planned dark matter searches in the next decade. We argue that
diversifying the experimental effort, incorporating astronomical surveys and
gravitational wave observations, is our best hope to make progress on the dark
matter problem.Comment: Published in Nature, online on 04 Oct 2018. 13 pages, 1 figur
Time Delay Lens Modelling Challenge
In recent years, breakthroughs in methods and data have enabled gravitational
time delays to emerge as a very powerful tool to measure the Hubble constant
. However, published state-of-the-art analyses require of order 1 year of
expert investigator time and up to a million hours of computing time per
system. Furthermore, as precision improves, it is crucial to identify and
mitigate systematic uncertainties. With this time delay lens modelling
challenge we aim to assess the level of precision and accuracy of the modelling
techniques that are currently fast enough to handle of order 50 lenses, via the
blind analysis of simulated datasets. The results in Rung 1 and Rung 2 show
that methods that use only the point source positions tend to have lower
precision () while remaining accurate. In Rung 2, the methods that
exploit the full information of the imaging and kinematic datasets can recover
within the target accuracy () and precision ( per
system), even in the presence of poorly known point spread function and complex
source morphology. A post-unblinding analysis of Rung 3 showed the numerical
precision of the ray-traced cosmological simulations to be insufficient to test
lens modelling methodology at the percent level, making the results difficult
to interpret. A new challenge with improved simulations is needed to make
further progress in the investigation of systematic uncertainties. For
completeness, we present the Rung 3 results in an appendix, and use them to
discuss various approaches to mitigating against similar subtle data generation
effects in future blind challenges.Comment: 23 pages, 12 figures, 6 tables, MNRAS accepte