Cold Dark Matter Model Research Articles

Dark Energy Survey Year 3 results: Constraints on extensions to ΛCDM with weak lensing and galaxy clustering

We constrain six possible extensions to the Λ cold dark matter (CDM) model using measurements from the Dark Energy Survey’s first three years of observations, alone and in combination with external cosmological probes. The DES data are the two-point correlation functions of weak gravitational lensing, galaxy clustering, and their cross-correlation. We use simulated data vectors and blind analyses of real data to validate the robustness of our results to astrophysical and modeling systematic errors. In many cases, constraining power is limited by the absence of theoretical predictions beyond the linear regime that are reliable at our required precision. The ΛCDM extensions are dark energy with a time-dependent equation of state, nonzero spatial curvature, additional relativistic degrees of freedom, sterile neutrinos with eV-scale mass, modifications of gravitational physics, and a binned σ8(z) model which serves as a phenomenological probe of structure growth. For the time-varying dark energy equation of state evaluated at the pivot redshift we find (wp,wa)=(−0.99−0.17+0.28,−0.9±1.2) at 68% confidence with zp=0.24 from the DES measurements alone, and (wp,wa)=(−1.03−0.03+0.04,−0.4−0.3+0.4) with zp=0.21 for the combination of all data considered. Curvature constraints of Ωk=0.0009±0.0017 and effective relativistic species Neff=3.10−0.16+0.15 are dominated by external data, though adding DES information to external low-redshift probes tightens the Ωk constraints that can be made without cosmic microwave background observables by 20%. For massive sterile neutrinos, DES combined with external data improves the upper bound on the mass meff by a factor of 3 compared to previous analyses, giving 95% limits of (ΔNeff,meff)≤(0.28,0.20 eV) when using priors matching a comparable Planck analysis. For modified gravity, we constrain changes to the lensing and Poisson equations controlled by functions Σ(k,z)=Σ0ΩΛ(z)/ΩΛ,0 and μ(k,z)=μ0ΩΛ(z)/ΩΛ,0, respectively, to Σ0=0.6−0.5+0.4 from DES alone and (Σ0,μ0)=(0.04±0.05,0.08−0.19+0.21) for the combination of all data, both at 68% confidence. Overall, we find no significant evidence for physics beyond ΛCDM.18 MoreReceived 18 July 2022Accepted 28 November 2022DOI:https://doi.org/10.1103/PhysRevD.107.083504© 2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCosmological constantCosmological parametersCosmologyDark energyDark matterPhysical SystemsGalaxiesLarge scale structure of the UniverseTechniquesTelescopesGravitation, Cosmology & Astrophysics

Dynamical friction due to fuzzy dark matter on satellites described by axisymmetric logarithmic potentials

A plausible dark matter candidate is an ultralight bosonic particle referred to as fuzzy dark matter. The equivalent mass-energy of the fuzzy dark matter boson is ∼ 10-22 eV and has a corresponding de Broglie wavelength of kiloparsec scale, thus exhibiting wave behaviour in scales comparable to a galactic core, which could not appear in conventional cold dark matter models. The presence of fuzzy dark matter in galactic clusters will impact the motion of their members through dynamical friction. In this work, we present simulations of the dynamical friction on satellites traversing an initially uniform fuzzy dark matter halo. We focus on the satellites whose shapes are beyond spherical symmetry described by ellipsoidal and logarithmic potentials. We find that the wakes created on the fuzzy dark matter halo due to the passage of such satellites are qualitatively different from those generated by spherically symmetric ones. Furthermore, we quantify the dynamical friction coefficient for such systems, finding that the same satellite may experience a drag differing by a factor of 5 depending on its ellipticity and the direction of motion. Finally, we find that the dynamical friction time-scale is close to Hubble time, assuming a satellite of 1011 M ⊙ traversing at 103 km/s a FDM halo whose mean density is ∼ 106 M ⊙ kpc-3.

JWST high-redshift galaxy constraints on warm and cold dark matter models

Context. Warm dark matter is a possible alternative to cold dark matter to explain cosmological structure formation. Aims. We study the implications of the latest JWST data on the nature of dark matter. Methods. We compare properties of high-redshift galaxies observed by JWST with hydrodynamical simulations, in the standard cold dark matter model and in warm dark matter models with a suppressed linear matter power spectrum Results. We find that current data are neither in tension with cold dark matter nor with warm dark matter models with mWDM > 2 keV, since they probe bright and rare objects whose physical properties are similar in the different scenarios. Conclusions. We also show how two observables, the galaxy luminosity functions and the galaxy correlation function at small scales of faint objects, can be promising tools for discriminating between the different dark-matter scenarios. Further hints may come from early stellar-mass statistics and galaxy CO emission.

On the dearth of C-enhanced metal-poor stars in the galactic bulge

ABSTRACTThe chemical fingerprints of the first stars are retained within the photospheres of ancient unevolved metal-poor stars. A significant fraction of these stellar fossils is represented by stars known as Carbon-Enhanced Metal-Poor (CEMP), $\mathrm{[C/Fe]} \gt +0.7$ and $\mathrm{[Fe/H]} \lt -2$, which are likely imprinted by low-energy primordial supernovae. These CEMP stars are largely observed in the Galactic halo and ultrafaint dwarf galaxies, with values reaching $\rm [C/Fe]=+4.5$. The Galactic bulge is predicted to host the oldest stars, but it shows a striking dearth of CEMP stars with $\rm [C/Fe]\gtrsim +2.0$. Here, we explore the possible reasons for this anomaly by performing a statistical analysis of the observations of metal-poor stars in combination with the predictions of Lambda cold dark matter models. We suggest that the dearth of CEMP stars with high $\mathrm{[C/Fe]}$ is not due to the low statistics of observed metal-poor stars but is the result of the different formation process of the bulge. N-body simulations show that the first star-forming haloes which end up in the bulge are characterized by the highest star formation rates. These rates enable the formation of rare massive first stars exploding as pair-instability supernovae (PISNe), which wash out the signature of primordial faint supernovae. We demonstrate that the mean $\mathrm{[C/Fe]}$ of first stars polluted environments decreases with the increasing contribution of PISNe. We conclude that the dearth of CEMP stars in the Galactic bulge indirectly probes the existence of elusive PISNe, and propose a novel method which exploits this lack to constrain the mass distribution of the first stars.

Testing dark energy models with gamma-ray bursts calibrated from the observationalH(z) data through a Gaussian process

ABSTRACTWe use a cosmology-independent method to calibrate gamma-ray burst (GRB) from the observational Hubble data (OHD) with the cosmic chronometer method. By using Gaussian process to reconstruct OHD, we calibrate the Amati relation (Ep–Eiso) to construct a GRB Hubble diagram with the A118 data set, and constrain dark energy models in a flat space with the Markov chain Monte Carlo numerical method. With the cosmology-independent GRBs at 1.4 < z ≤ 8.2 in the A118 data set and the Pantheon sample of Type Ia supernovae at 0.01 < z ≤ 2.3, we obtained Ωm = $0.379^{+0.033}_{-0.024}$, h = $0.701^{+0.0035}_{-0.0035}$, w = $-1.25^{+0.14}_{-0.12}$, and wa = $-0.84^{+0.81}_{-0.38}$ for the flat Chevallier–Polarski–Linder model at the 1σ confidence level. We find no significant evidence supporting deviations from the standard Lambda cold dark matter model.

Equality scale-based and sound horizon-based analysis of the Hubble tension

The Hubble horizon at matter-radiation equality (${k}_{\mathrm{eq}}^{\ensuremath{-}1}$) and the sound horizon at the last scattering surface [${r}_{s}({z}_{*})$] provides an interesting consistency check for the standard $\mathrm{\ensuremath{\Lambda}}$ Cold Dark Matter ($\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$) model and its extensions. It is well known that the reduction of ${r}_{s}$ can be compensated by the increase of ${H}_{0}$, while the same is true for the standard rulers ${k}_{\mathrm{eq}}$. Adding extra radiational component to the early Universe can reduce ${k}_{\mathrm{eq}}$. The addition of early dark energy (EDE), however, tends to increase ${k}_{\mathrm{eq}}$. We perform ${k}_{\mathrm{eq}}$- and ${r}_{s}$-based analyses in both the EDE model and the Wess-Zumino dark radiation (WZDR) model. In the latter case, we find $\mathrm{\ensuremath{\Delta}}{H}_{0}=0.4$ between the ${r}_{s}$- and ${k}_{\mathrm{eq}}$-based datasets, while in the former case, we find $\mathrm{\ensuremath{\Delta}}{H}_{0}=1.2$. This result suggests that the dark radiation scenario is more consistent in the fit of the two standard rulers (${k}_{\mathrm{eq}}$ and ${r}_{s}$). As a forecast analyses, we fit the two models with a mock ${k}_{\mathrm{eq}}$ prior derived from Planck best-fit $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model. Compared with the best-fit ${H}_{0}$ in baseline $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model, we find $\mathrm{\ensuremath{\Delta}}{H}_{0}=1.1$ for the WZDR model and $\mathrm{\ensuremath{\Delta}}{H}_{0}=\ensuremath{-}2.4$ for EDE model.

Beyond – ΛCDM constraints from the full shape clustering measurements from BOSS and eBOSS

ABSTRACT We analyse the full shape of anisotropic clustering measurements from the extended Baryon Oscillation Spectroscopic Survey quasar sample together with the combined galaxy sample from the Baryon Oscillation Spectroscopic Survey. We obtain constraints on the cosmological parameters independent of the Hubble parameter h for the extensions of the Lambda cold dark matter (ΛCDM) models, focusing on cosmologies with free dark energy equation of state parameter w. We combine the clustering constraints with those from the latest cosmic microwave background data from Planck to obtain joint constraints for these cosmologies for w and the additional extension parameters – its time evolution wa, the physical curvature density ωK and the neutrino mass sum ∑mν. Our joint constraints are consistent with a flat ΛCDM cosmological model within 68 per cent confidence limits. We demonstrate that the Planck data are able to place tight constraints on the clustering amplitude today, σ12, in cosmologies with varying w and present the first constraints for the clustering amplitude for such cosmologies, which is found to be slightly higher than the ΛCDM value. Additionally, we show that when we vary w and allow for non-flat cosmologies and the physical curvature density is used, Planck prefers a curved universe at 4σ significance, which is ∼2σ higher than when using the relative curvature density ΩK. Finally, when w is varied freely, clustering provides only a modest improvement (of 0.021 eV) on the upper limit of ∑mν.

Gamma-ray bursts, quasars, baryonic acoustic oscillations, and supernovae Ia: new statistical insights and cosmological constraints

ABSTRACTThe recent $\sim 4 \, \sigma$ Hubble constant, H0, tension is observed between the value of H0 from the cosmic microwave background (CMB) and Type Ia supernovae (SNe Ia). It is a decade since this tension is excruciating the modern astrophysical community. To shed light on this problem is key to consider probes at intermediate redshifts between SNe Ia and CMB and reduce the uncertainty on H0. Toward these goals, we fill the redshift gap by employing gamma-ray bursts (GRBs) and quasars (QSOs), reaching z = 9.4 and z = 7.6, respectively, combined with baryonic acoustic oscillations (BAO), and SNe Ia. To this end, we employ the ‘Dainotti GRB 3D relation’ among the rest-frame end time of the X-ray plateau emission, its corresponding luminosity, and the peak prompt luminosity, and the ‘Risaliti–Lusso’ QSO relation between ultraviolet and X-ray luminosities. We inquire the commonly adopted Gaussianity assumption on GRBs, QSOs, and BAO. With the joint sample, we fit the flat Λ Cold Dark Matter model with both the Gaussian and the newly discovered likelihoods. We also investigate the impact of the calibration assumed for Pantheon and Pantheon + SNe Ia on this analysis. Remarkably, we show that only GRBs fulfil the Gaussianity assumption. We achieve small uncertainties on the matter-density parameter ΩM and H0. We find H0 values compatible within 2σ with the one from the Tip of the Red Giant Branch. Finally, we show that the cosmological results are heavily biased against the arbitrary calibration choice for SNe Ia.

Discordances in Cosmology and the Violation of Slow-Roll Inflationary Dynamics.

We identify examples of single field inflationary trajectories beyond the slow-roll regime that improve the fit to Planck 2018 data compared to a baseline Λ cold dark matter model with power law form of primordial spectrum and at the same time alleviate existing tensions between different datasets in the estimate of cosmological parameters such as H_{0} and S_{8}. A damped oscillation in the first Hubble flow function-or equivalently a feature in the potential-and the corresponding localized oscillations in the primordial power spectrum partially mimic the improvement in the fit of Planck data due to A_{L} or Ω_{K}. Compared to the baseline model, this model can lead simultaneously to a larger value of H_{0} and a smaller value of S_{8}, a trend that can be enhanced when the most recent SH0ES measurement for H_{0} is combined with Planck and BICEP-Keck 2018 data. Large scale structure data and more precise cosmic microwave background polarization measurements will further provide critical tests of this intermediate fast-roll phase.

Cosmological constraints from HSC survey first-year data using deep learning

ABSTRACT We present cosmological constraints from the Subaru Hyper Suprime-Cam (HSC) first-year weak lensing shear catalogue using convolutional neural networks (CNNs) and conventional summary statistics. We crop 19 $3\times 3\, \mathrm{{deg}^2}$ sub-fields from the first-year area, divide the galaxies with redshift 0.3 ≤ z ≤ 1.5 into four equally spaced redshift bins, and perform tomographic analyses. We develop a pipeline to generate simulated convergence maps from cosmological N-body simulations, where we account for effects such as intrinsic alignments (IAs), baryons, photometric redshift errors, and point spread function errors, to match characteristics of the real catalogue. We train CNNs that can predict the underlying parameters from the simulated maps, and we use them to construct likelihood functions for Bayesian analyses. In the Λ cold dark matter model with two free cosmological parameters Ωm and σ8, we find $\Omega _\mathrm{m}=0.278_{-0.035}^{+0.037}$, $S_8\equiv (\Omega _\mathrm{m}/0.3)^{0.5}\sigma _{8}=0.793_{-0.018}^{+0.017}$, and the IA amplitude $A_\mathrm{IA}=0.20_{-0.58}^{+0.55}$. In a model with four additional free baryonic parameters, we find $\Omega _\mathrm{m}=0.268_{-0.036}^{+0.040}$, $S_8=0.819_{-0.024}^{+0.034}$, and $A_\mathrm{IA}=-0.16_{-0.58}^{+0.59}$, with the baryonic parameters not being well-constrained. We also find that statistical uncertainties of the parameters by the CNNs are smaller than those from the power spectrum (5–24 per cent smaller for S8 and a factor of 2.5–3.0 smaller for Ωm), showing the effectiveness of CNNs for uncovering additional cosmological information from the HSC data. With baryons, the S8 discrepancy between HSC first-year data and Planck 2018 is reduced from $\sim 2.2\, \sigma$ to $0.3\!-\!0.5\, \sigma$.

Euclid: Testing the Copernican principle with next-generation surveys

Context.The Copernican principle, the notion that we are not at a special location in the Universe, is one of the cornerstones of modern cosmology. Its violation would invalidate the Friedmann-Lemaître-Robertson-Walker metric, causing a major change in our understanding of the Universe. Thus, it is of fundamental importance to perform observational tests of this principle.Aims.We determine the precision with which future surveys will be able to test the Copernican principle and their ability to detect any possible violations.Methods.We forecast constraints on the inhomogeneous Lemaître-Tolman-Bondi (LTB) model with a cosmological constant Λ, basically a cosmological constant Λ and cold dark matter (CDM) model but endowed with a spherical inhomogeneity. We consider combinations of currently available data and simulatedEucliddata, together with external data products, based on both ΛCDM and ΛLTB fiducial models. These constraints are compared to the expectations from the Copernican principle.Results.When considering the ΛCDM fiducial model, we find thatEucliddata, in combination with other current and forthcoming surveys, will improve the constraints on the Copernican principle by about 30%, with ±10% variations depending on the observables and scales considered. On the other hand, when considering a ΛLTB fiducial model, we find that futureEucliddata, combined with other current and forthcoming datasets, will be able to detect gigaparsec-scale inhomogeneities of contrast −0.1.Conclusions.Next-generation surveys, such asEuclid, will thoroughly test homogeneity at large scales, tightening the constraints on possible violations of the Copernican principle.

The investigation of dark matter density profiles on the neutralino mass and cross-section annihilation ([formula omitted]) constraint lines of selected galaxy clusters by considering their synchrotron emission

We investigated the indirect detection of neutralino dark matter using radio observation. By looking at the energy spectrum of relativistic positron–electron, this method may provide us with the upper limit of neutralino dark matter emission. Neutralino dark matter can emit synchrotron emissions due to the interaction of relativistic positron–electron spectrum energy with the intracluster magnetic field. The synchrotron emission of dark matter highly depends on the dark matter density at the centre of the cluster. By using the cold dark matter model, the density of dark matter can be obtained using Navarro–Frenk–White (NFW), Einasto, Diemer and Kravtsov 2014 (DK14) and Hernquist profiles. Using the observed radio halo emission as the maximum emission (from dark matter and other sources), we constrained the neutralino mass (mχ) and neutralino cross-section annihilation 〈σv〉 as mχ−〈σv〉 constraint lines. We investigated the effect of different profiles on the mχ−〈σv〉 constraint lines. We also used all the basic annihilation channels for better and stronger constraint lines. Our findings demonstrated the NFW profiles provided us with a good constraint line similarly with previous study. Our results also confirmed that the τ+τ− and tt̄ channels provide us with a stronger constraint at mχ = 100 GeV and 1000 GeV, respectively. Overall, our findings are consistent for the constraint lines of all the chosen galaxy clusters namely A119, A2199, A2142, A2744, A478 and A2029.

Aspects of cosmologies with complete scenario

We consider a flat Friedmann–Robertson–Walker (FRW) universe with expansion history based on a Hubble parameter. The Hubble parameter ansatz, by construction, yields de Sitter-like evolution at early and late-times. The phase transition from accelerated to decelerated era during early times and decelerated to accelerated era in the recent past provide the complete cosmological history of the universe in a natural way. In order to exhibit the dynamical evolution of universe, we explore the inflationary dynamics along with graceful exit, behaviors of cosmological parameters, energy conditions along with behavior in ω − ω ′ plane to identify the thawing and freezing regions. Statefinder diagnostic highlights that the universe will evolve to Λ cold dark matter model during late-times. We also find the scalar field description for the considered Hubble parameter ansatz. • The FRW model having expansion history based on the Hubble parameter is studied. • Cosmic parameters illustrate physically realistic cases of the universe evolution. • Model exhibits graceful exit from inflation during early era. • The model explains late-time accelerating evolution of the universe. • The model possess potential having polynomial form with field.

Eliminating the Hubble Tension in the Presence of the Interconnection between Dark Energy and Matter in the Modern Universe

It is accepted in modern cosmology that the scalar field responsible for the inflationary stage of the early Universe is completely transformed into matter. It is assumed that the accelerated expansion is currently driven by dark energy (DE), which is likely determined by Einstein’s cosmological constant, unrelated to the scalar field responsible for inflation. We consider a cosmological model in which DE can currently have two components, one of which is Einstein’s constant (Λ) and the other, smaller dark energy variable component DEV (ΛV), is associated with the remnant of the scalar field that caused inflation after the main part of the scalar field has turned into matter. We consider only the stages of evolution of the Universe after recombination (z=1100), where dark matter (DM) is the predominant component of matter. It is assumed that the transformation of the scalar field into matter continues at the present time and is accompanied by the reverse process of the transformation of DM into a scalar field. The interconnection between DM and DEV, which leads to a linear relationship between the energy densities of these components after recombination ρDM=αρDEV, is considered. Variants with a dependence of the coefficient α(z) on the redshift z are also considered. One of the problems that have arisen in modern cosmology, called Hubble Tension (HT), is the discrepancy between the present values of the Hubble constant (H0) measured from observations of the Universe at small redshifts (z≲1) and the values found from fluctuations of the cosmic microwave background in the Universe at large redshifts (z≈1100). In the model under consideration, this discrepancy can be explained by the deviation of the existing cosmological model from the conventional Λ cold dark matter (CDM) model of the flat Universe by the action of the additional dark energy component DEV at the stages after recombination. Within this extended model, we consider various α(z) functions that can eliminate the HT. To maintain the ratio of DEV and DM energy densities close to constant over the interval 0⩽z≲1100, it is necessary to assume the existence of a wide spectrum of dark matter particle masses.

Eliminating the Hubble Tension in the Presence of the Interconnection between Dark Energy and Matter in the Modern Universe

It is accepted in modern cosmology that the scalar field responsible for the inflationary stage of the early Universe is completely transformed into matter. It is assumed that the accelerated expansion is currently driven by dark energy (DE), which is likely determined by Einstein’s cosmological constant, unrelated to the scalar field responsible for inflation. We consider a cosmological model in which DE can currently have two components, one of which is Einstein’s constant ( $$\Lambda $$ ) and the other, smaller dark energy variable component DEV ( $${{\Lambda }_{V}}$$ ), is associated with the remnant of the scalar field that caused inflation after the main part of the scalar field has turned into matter. We consider only the stages of evolution of the Universe after recombination ( $$z \lesssim 1100$$ ), where dark matter (DM) is the predominant component of matter. It is assumed that the transformation of the scalar field into matter continues at the present time and is accompanied by the reverse process of the transformation of DM into a scalar field. The interconnection between DM and DEV, which leads to a linear relationship between the energy densities of these components after recombination $${{\rho }_{{{\text{DM}}}}} = \alpha {\kern 1pt} {{\rho }_{{{\text{DEV}}}}}$$ , is considered. Variants with a dependence of the coefficient $$\alpha (z)$$ on the redshift $$z$$ are also considered. One of the problems that have arisen in modern cosmology, called Hubble Tension (HT), is the discrepancy between the present values of the Hubble constant ( $${{H}_{0}}$$ ) measured from observations of the Universe at small redshifts ( $$z \lesssim 1$$ ) and the values found from fluctuations of the cosmic microwave background in the Universe at large redshifts ( $$z \approx 1100$$ ). In the model under consideration, this discrepancy can be explained by the deviation of the existing cosmological model from the conventional $$\Lambda $$ cold dark matter (CDM) model of the flat Universe by the action of the additional dark energy component DEV at the stages after recombination. Within this extended model, we consider various $$\alpha {\kern 1pt} (z)$$ functions that can eliminate the HT. To maintain the ratio of DEV and DM energy densities close to constant over the interval $$0 \leqslant z \lesssim 1100$$ , it is necessary to assume the existence of a wide spectrum of dark matter particle masses.

High-redshift JWST Observations and Primordial Non-Gaussianity

Several bright and massive galaxy candidates at high redshifts have been recently observed by the James Webb Space Telescope. Such early massive galaxies seem difficult to reconcile with standard Λ cold dark matter model predictions. We discuss under which circumstances such observed massive galaxy candidates can be explained by introducing primordial non-Gaussianity in the initial conditions of cosmological perturbations.

A preference for cold dark matter over Superfluid Dark Matter in local Milky Way data

There are many well-known correlations between dark matter and baryons that exist on galactic scales. These correlations can essentially be encompassed by a simple scaling relation between observed and baryonic accelerations, historically known as the Mass Discrepancy Acceleration Relation (MDAR). The existence of such a relation has prompted many theories that attempt to explain the correlations by invoking additional fundamental forces on baryons. The standard lore has been that a theory that reduces to the MDAR on galaxy scales but behaves like cold dark matter (CDM) on larger scales provides an excellent fit to data, since CDM is desirable on scales of clusters and above. However, this statement should be revised in light of recent results showing that a fundamental force that reproduces the MDAR is challenged by local Milky Way dynamics and rotation curve data between 5-18 kpc. In this study, we test this claim on the example of Superfluid Dark Matter. We find that a standard CDM model is preferred over a static superfluid profile assuming a steady-state Galactic disk and discuss the robustness of this conclusion to disequilibrium effects. This preference is due to the fact that the superfluid model over-predicts vertical accelerations, even while reproducing galactic rotation curves. Our results establish an important criterion that any dark matter model must satisfy within the Milky Way.

Spatial and orbital planes of the Milky Way satellites: unusual but consistent with ΛCDM

ABSTRACT We examine the spatial distribution and orbital pole correlations of satellites in a suite of zoom-in high-resolution dissipationless simulations of Milky Way (MW)-sized haloes. We use the measured distribution to estimate the incidence of satellite configurations as flattened and as correlated in their orbital pole distribution as the satellite system of the MW. We confirm that this incidence is sensitive to the radial distribution of subhaloes and thereby to the processes that affect it, such as artificial disruption due to numerical effects and disruption due to the central disc. Controlling for the resolution effects and bracketing the effects of the disc, we find that the MW satellite system is somewhat unusual (at the ≈2–3σ level) but is statistically consistent with the Lambda cold dark matter model, in general agreement with results and conclusions of other recent studies.

Estimating the feasibility of ‘standard speed-gun’ distances

ABSTRACT In a previous paper, we demonstrated a single-rung method for measuring cosmological distances in active galactic nuclei (AGNs) that can be used from low redshift (z < 0.1) to high redshift (z > 3). This method relies on the assumption that the variability seen in AGNs is constrained by the speed of light during a flare event and can therefore be used to estimate the size of an emitting region. A limitation of this method is that previously, the Doppler factor was required to be known. In this paper, we derive an extension of the ‘standard speed-gun’ method for measuring cosmological distances that depends on the maximum intrinsic brightness temperature that a source can reach, rather than the Doppler factor. If the precise value of the intrinsic brightness temperature does not evolve with redshift, and flares are statistically independent, we can in principle improve the errors on measurements of the matter content of the Universe (in a flat Lambda cold dark matter model) statistically. We then explored how well a future observing programme would constrain cosmological parameters. We found that recovering the input cosmology depends critically on the uncertainty of the intrinsic brightness temperature and the number of flares observed.

Classifying the satellite plane membership of Centaurus A’s dwarf galaxies using orbital alignment constraints

ABSTRACT The flattened, possibly co-rotating plane of satellite galaxies around Centaurus A, if more than a fortuitous alignment, adds to the pre-existing tension between the well-studied Milky Way and M31 planes and the Lambda cold dark matter model of structure formation. It was recently reported that the Centaurus A satellite plane (CASP) may be rotationally supported, but a further understanding of the system’s kinematics is elusive in the absence of full 3D velocities. We constrain the transverse velocities of 27 satellites that would rotationally stabilize the Centaurus A plane, and classify the satellites by whether their possible orbits are consistent with the CASP. Five satellites are identified to be unlikely to participate in the plane, two of which are clearly non-members. Despite their previously reported line-of-sight velocity trend suggestive of a common co-rotating motion, 17 out of 22 potential CASP members are consistent with either orbital direction within both the full range of possible kinematics as well as when limiting orbits to those within the plane. On the other hand, disregarding the 5 off-plane satellites found to be inconsistent with CASP membership enhances the significance of the CASP’s line-of-sight velocity trend fivefold. Our results are robust with different mass estimates of the Centaurus A halo, and the adoption of either spherical or triaxial NFW potentials.