scholarly journals Double dark matter vision: twice the number of compact-source lenses with narrow-line lensing and the WFC3 grism

2019 ◽  
Vol 492 (4) ◽  
pp. 5314-5335 ◽  
Author(s):  
A M Nierenberg ◽  
D Gilman ◽  
T Treu ◽  
G Brammer ◽  
S Birrer ◽  
...  
Keyword(s):  
Dark Matter ◽  
Gravitational Lensing ◽  
Line Emission ◽  
Companion Paper ◽  
Small Scale ◽  
Gravitational Lenses ◽  
Narrow Line ◽  
Entire Sample ◽  
Compact Source ◽  
Low Mass

ABSTRACT The magnifications of compact-source lenses are extremely sensitive to the presence of low-mass dark matter haloes along the entire sightline from the source to the observer. Traditionally, the study of dark matter structure in compact-source strong gravitational lenses has been limited to radio-loud systems, as the radio emission is extended and thus unaffected by microlensing which can mimic the signal of dark matter structure. An alternate approach is to measure quasar nuclear-narrow-line emission, which is free from microlensing and present in virtually all quasar lenses. In this paper, we double the number of systems which can be used for gravitational lensing analyses by presenting measurements of narrow-line emission from a sample of eight quadruply imaged quasar lens systems, WGD J0405−3308, HS 0810+2554, RX J0911+0551, SDSS J1330+1810, PS J1606−2333, WFI 2026−4536, WFI 2033−4723, and WGD J2038−4008. We describe our updated grism spectral modelling pipeline, which we use to measure narrow-line fluxes with uncertainties of 2–10 per cent, presented here. We fit the lensed image positions with smooth mass models and demonstrate that these models fail to produce the observed distribution of image fluxes over the entire sample of lenses. Furthermore, typical deviations are larger than those expected from macromodel uncertainties. This discrepancy indicates the presence of perturbations caused by small-scale dark matter structure. The interpretation of this result in terms of dark matter models is presented in a companion paper.

scholarly journals An excess of small-scale gravitational lenses observed in galaxy clusters

Science ◽  
2020 ◽  
Vol 369 (6509) ◽  
pp. 1347-1351 ◽  
Author(s):  
Massimo Meneghetti ◽  
Guido Davoli ◽  
Pietro Bergamini ◽  
Piero Rosati ◽  
Priyamvada Natarajan ◽  
...  
Keyword(s):  
Dark Matter ◽  
Galaxy Clusters ◽  
Gravitational Lensing ◽  
Cold Dark Matter ◽  
Small Scale ◽  
Gravitational Lenses ◽  
Strong Lensing ◽  
Luminous Matter ◽  
Order Of Magnitude ◽  
The Universe

Cold dark matter (CDM) constitutes most of the matter in the Universe. The interplay between dark and luminous matter in dense cosmic environments, such as galaxy clusters, is studied theoretically using cosmological simulations. Observations of gravitational lensing are used to characterize the properties of substructures—the small-scale distribution of dark matter—in clusters. We derive a metric, the probability of strong lensing events produced by dark-matter substructure, and compute it for 11 galaxy clusters. The observed cluster substructures are more efficient lenses than predicted by CDM simulations, by more than an order of magnitude. We suggest that systematic issues with simulations or incorrect assumptions about the properties of dark matter could explain our results.

scholarly journals Understanding the large inferred Einstein radii of observed low-mass galaxy clusters

2020 ◽  
Vol 494 (4) ◽  
pp. 4706-4712 ◽  
Author(s):  
Andrew Robertson ◽  
Richard Massey ◽  
Vincent Eke
Keyword(s):  
Dark Matter ◽  
Galaxy Clusters ◽  
Gravitational Lensing ◽  
Cold Dark Matter ◽  
Baryonic Matter ◽  
Analysis Method ◽  
Critical Curves ◽  
Hydrodynamical Simulation ◽  
Low Mass ◽  
Main Effects

ABSTRACT We assess a claim that observed galaxy clusters with mass ${\sim}10^{14} \mathrm{\, M_\odot }$ are more centrally concentrated than predicted in lambda cold dark matter (ΛCDM). We generate mock strong gravitational lensing observations, taking the lenses from a cosmological hydrodynamical simulation, and analyse them in the same way as the real Universe. The observed and simulated lensing arcs are consistent with one another, with three main effects responsible for the previously claimed inconsistency. First, galaxy clusters containing baryonic matter have higher central densities than their counterparts simulated with only dark matter. Secondly, a sample of clusters selected because of the presence of pronounced gravitational lensing arcs preferentially finds centrally concentrated clusters with large Einstein radii. Thirdly, lensed arcs are usually straighter than critical curves, and the chosen image analysis method (fitting circles through the arcs) overestimates the Einstein radii. After accounting for these three effects, ΛCDM predicts that galaxy clusters should produce giant lensing arcs that match those in the observed Universe.

scholarly journals Simulating the complexity of the dark matter sheet I: numerical algorithms

2020 ◽  
Vol 495 (4) ◽  
pp. 4943-4964
Author(s):  
Jens Stücker ◽  
Oliver Hahn ◽  
Raul E Angulo ◽  
Simon D M White
Keyword(s):  
Dark Matter ◽  
Numerical Algorithms ◽  
Linear Structure ◽  
Small Scale ◽  
Deviation Equation ◽  
Unknown Amplitude ◽  
Low Mass ◽  
Force Resolution ◽  
Force Calculation ◽  
Matter Phase

ABSTRACT At early times, dark matter has a thermal velocity dispersion of unknown amplitude which, for warm dark matter (WDM) models, can influence the formation of non-linear structure on observable scales. We propose a new scheme to simulate cosmologies with a small-scale suppression of perturbations that combines two previous methods in a way that avoids the numerical artefacts which have so far prevented either from producing fully reliable results. At low densities and throughout most of the cosmological volume, we represent the dark matter phase sheet directly using high-accuracy interpolation, thereby avoiding the artificial fragmentation which afflicts particle-based methods in this regime. Such phase-sheet methods are, however, unable to follow the rapidly increasing complexity of the denser regions of dark matter haloes, so for these we switch to an N-body scheme which uses the geodesic deviation equation to track phase-sheet properties local to each particle. In addition, we present a novel high-resolution force calculation scheme based on an oct-tree of cubic force resolution elements which is well suited to approximate the force field of our combined sheet+particle distribution. Our hybrid simulation scheme enables the first reliable simulations of the internal structure of low-mass haloes in a WDM cosmology.

scholarly journals Small-scale Substructure in Dark Matter Haloes: Where Does Galaxy Formation Come to an End?

2004 ◽  
Vol 220 ◽  
pp. 91-98 ◽  
Author(s):  
J. E. Taylor ◽  
J. Silk ◽  
A. Babul
Keyword(s):  
Dark Matter ◽  
Power Spectrum ◽  
Structure Formation ◽  
Galaxy Formation ◽  
Cold Dark Matter ◽  
High Redshift ◽  
Small Scale ◽  
Analytic Model ◽  
Model Predictions ◽  
Low Mass

Models of structure formation based on cold dark matter predict that most of the small dark matter haloes that first formed at high redshift would have merged into larger systems by the present epoch. Substructure in present-day haloes preserves the remains of these ancient systems, providing the only direct information we may ever have about the low-mass end of the power spectrum. We describe some recent attempts to model halo substructure down to very small masses, using a semi-analytic model of halo formation. We make a preliminary comparison between the model predictions, observations of substructure in lensed systems, and the properties of local satellite galaxies.

scholarly journals Gravitational lenses as probes of the distribution of dark matter in the universe

1986 ◽  
Vol 119 ◽  
pp. 545-546
Author(s):  
R. Cowsik ◽  
P. Ghosh
Keyword(s):  
Dark Matter ◽  
Gravitational Lensing ◽  
Clusters Of Galaxies ◽  
Gravitational Lenses ◽  
The Universe ◽  
Individual Galaxies

Studies of the characteristic properties of gravitational lensing by clusters of galaxies suggest that the dark matter in them is probably smoothly distributed on the scale of the cluster itself, rather than being clumped into halos around individual galaxies.

scholarly journals Quantifying the power spectrum of small-scale structure in semi-analytic galaxies

2019 ◽  
Vol 488 (4) ◽  
pp. 5085-5092 ◽  
Author(s):  
Sean Brennan ◽  
Andrew J Benson ◽  
Francis-Yan Cyr-Racine ◽  
Charles R Keeton ◽  
Leonidas A Moustakas ◽  
...  
Keyword(s):  
Dark Matter ◽  
Power Spectrum ◽  
Gravitational Lensing ◽  
Cold Dark Matter ◽  
Scale Structure ◽  
Small Scale ◽  
Small Scale Structure ◽  
Mass Distributions ◽  
Theoretical Predictions ◽  
Spectrum Distribution

Abstract In the cold dark matter (CDM) picture of structure formation, galaxy mass distributions are predicted to have a considerable amount of structure on small scales. Strong gravitational lensing has proven to be a useful tool for studying this small-scale structure. Much of the attention has been given to detecting individual dark matter subhaloes through lens modelling, but recent work has suggested that the full population of subhaloes could be probed using a power spectrum analysis. In this paper, we quantify the power spectrum of small-scale structure in simulated galaxies, with the goal of understanding theoretical predictions and setting the stage for using measurements of the power spectrum to test dark matter models. We use a sample of simulated galaxies generated from the galacticus semi-analytic model to determine the power spectrum distribution first in the CDM paradigm and then in a warm dark matter scenario. We find that a measurement of the slope and amplitude of the power spectrum on galaxy strong lensing scales (k ∼ 1 kpc−1) could be used to distinguish between CDM and alternate dark matter models, especially if the most massive subhaloes can be directly detected via gravitational imaging.

Dark Matter

2018 ◽  
pp. 169-174
Author(s):  
Alvaro De Rújula
Keyword(s):  
General Relativity ◽  
Dark Matter ◽  
Solar Eclipse ◽  
Gravitational Lensing ◽  
Virial Theorem ◽  
Dark Matter Halos ◽  
Gravitational Lenses ◽  
Coma Cluster ◽  
Cluster Of Galaxies ◽  
Galactic Dark Matter

What we know or do not know about dark matter. The evidence for its existence, first found by Fritz Zwicky. The “virial theorem” and the Coma cluster. The rotation curves of galaxies. Galactic dark-matter halos. Gravitational lensing and the May 1919 solar eclipse, a thiumph of General Relativity that propelled Einstein to his fame. The deflection of starlight by the eclipsed Sun. Gravitational lenses, Einstein rings, and Smilie. Gravitational-lensing and evidence for dark matter in the Bullet cluster of galaxies.

scholarly journals Gaia white dwarfs within 40 pc – I. Spectroscopic observations of new candidates

2020 ◽  
Vol 497 (1) ◽  
pp. 130-145 ◽  
Author(s):  
P-E Tremblay ◽  
M A Hollands ◽  
N P Gentile Fusillo ◽  
J McCleery ◽  
P Izquierdo ◽  
...  
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Line Emission ◽  
Companion Paper ◽  
Metal Species ◽  
Balmer Line ◽  
Infrared Excess ◽  
Balmer Lines ◽  
Low Mass ◽  
Almost All

ABSTRACT We present a spectroscopic survey of 230 white dwarf candidates within 40 pc of the Sun from the William Herschel Telescope and Gran Telescopio Canarias. All candidates were selected from Gaia Data Release 2 (DR2) and in almost all cases, had no prior spectroscopic classifications. We find a total of 191 confirmed white dwarfs and 39 main-sequence star contaminants. The majority of stellar remnants in the sample are relatively cool (〈Teff〉 = 6200 K), showing either hydrogen Balmer lines or a featureless spectrum, corresponding to 89 DA and 76 DC white dwarfs, respectively. We also recover two DBA white dwarfs and 9–10 magnetic remnants. We find two carbon-bearing DQ stars and 14 new metal-rich white dwarfs. This includes the possible detection of the first ultra-cool white dwarf with metal lines. We describe three DZ stars for which we find at least four different metal species, including one that is strongly Fe- and Ni-rich, indicative of the accretion of a planetesimal with core-Earth composition. We find one extremely massive (1.31 ± 0.01 M⊙) DA white dwarf showing weak Balmer lines, possibly indicating stellar magnetism. Another white dwarf shows strong Balmer line emission but no infrared excess, suggesting a low-mass sub-stellar companion. A high spectroscopic completeness (>99 per cent) has now been reached for Gaia DR2 sources within 40-pc sample, in the Northern hemisphere (δ > 0°) and located on the white dwarf cooling track in the Hertzsprung–Russell diagram. A statistical study of the full northern sample is presented in a companion paper.

scholarly journals Seeking Observable Imprints of Small-Scale Structure on the Properties of Dark Matter Haloes

2013 ◽  
Vol 30 ◽  
Author(s):  
C. Power
Keyword(s):  
Dark Matter ◽  
Angular Momentum ◽  
Spatial Clustering ◽  
Scale Structure ◽  
Small Scale ◽  
Halo Formation ◽  
Potential Wells ◽  
Massive Galaxies ◽  
Small Scale Structure ◽  
Low Mass

AbstractThe characteristic prediction of the Cold Dark Matter (CDM) model of cosmological structure formation is that the Universe should contain a wealth of small-scale structure—low-mass dark matter haloes and subhaloes. However, galaxy formation is inefficient in their shallow potential wells and so we expect these low-mass haloes and subhaloes to be dark. Can we tell the difference between a Universe in which these low-mass haloes are present but dark and one in which they never formed, thereby providing a robust test of the CDM model? We address this question using cosmological N-body simulations to examine how properties of low-mass haloes that are potentially accessible to observation, such as their spatial clustering, rate of accretions and mergers onto massive galaxies, and the angular momentum content of massive galaxies, differ between a fiducial ΛCDM model and dark matter models in which low-mass halo formation is suppressed. Adopting an effective cut-off mass scale Mcut below which small-scale power is suppressed in the initial conditions, we study dark matter models in which Mcut varies between 5×109h−1M⊙ and 1011h−1M⊙, equivalent to the host haloes of dwarf and low-mass galaxies. Our results show that both the clustering strength of low-mass haloes around galaxy-mass primaries and the rate at which they merge with these primaries are sensitive to the assumed value of Mcut; in contrast, suppressing low-mass halo formation has little influence on the angular momentum content of galaxy-mass haloes—it is the quiescence or violence of a halo's assembly history that has a more marked effect. However, we expect that measuring the effect on spatial clustering or the merger rate is likely to be observationally difficult for realistic values of Mcut, and so isolating the effect of this small-scale structure would appear to be remarkably difficult to detect, at least in the present day Universe.

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