Non-gravitational interactions between dark matter particles with strong scattering, but relatively small annihilation and dissipation, has been proposed to match various observables on cluster and ...group scales. In this paper, we present the results from large cosmological simulations which include the effects of different self-interaction scenarios. In particular we explore a model with the differential cross section that can depend on both the relative velocity of the interacting particles and the angle of scattering. We focus on how quantities, such as the stacked density profiles, subhalo counts and the splashback radius change as a function of different forms of self-interaction. We find that self-interactions not only affect the central region of the cluster, the effect well known from previous studies, but also significantly alter the distribution of subhalos and the density of particles out to the splashback radius. Therefore, our results suggest that current weak lensing data can already put constraints on the self-interaction cross-section that are only slightly weaker than the Bullet Cluster constraints (σ/m ≲ 2 cm2/g), and future lensing surveys should be able to tighten them even further making halo profiles on cluster scales a competitive probe for DM physics.
ABSTRACT We show that the projected number density profiles of Sloan Digital Sky Survey photometric galaxies around galaxy clusters display strong evidence for the splashback radius, a sharp halo ...edge corresponding to the location of the first orbital apocenter of satellite galaxies after their infall. We split the clusters into two subsamples with different mean projected radial distances of their members, , at fixed richness and redshift. The sample with smaller has a smaller ratio of the splashback radius to the traditional halo boundary than the subsample with larger , indicative of different mass accretion rates for these subsamples. The same subsamples were recently used by Miyatake et al. to show that their large-scale clustering differs despite their similar weak lensing masses, demonstrating strong evidence for halo assembly bias. We expand on this result by presenting a 6.6 difference in the clustering amplitudes of these samples using cluster-photometric galaxy cross-correlations. This measurement is a clear indication that halo clustering depends on parameters other than halo mass. If is related to the mass assembly history of halos, the measurement is a manifestation of the halo assembly bias. However, our measured splashback radii are smaller, while the strength of the assembly bias signal is stronger, than the predictions of collisionless Λ cold dark matter simulations. We show that dynamical friction, cluster mis-centering, or projection effects are not likely to be the sole source of these discrepancies. However, further investigations regarding unknown catastrophic weak lensing or cluster identification systematics are warranted.
Abstract
We study how tidal streams from globular clusters may be
used to constrain the mass of ultra-light dark matter particles,
called `fuzzy' dark matter (FDM). A general feature of FDM models
is ...the presence of ubiquitous density fluctuations in bound,
virialized dark matter structures, on the scale of the de Broglie
wavelength, arising from wave interference in the evolving dark
matter distribution. These time-varying fluctuations can disturb
the motions of stars, leading to potentially observable signatures
in cold thin tidal streams in our own Galaxy. The study of this
effect has been hindered by the difficulty in simulating the FDM
wavefunction in Milky Way-sized systems. We present a simple method
to evolve realistic wavefunctions in nearly static potentials, that
should provide an accurate estimate of this granulation effect. We
quantify the impact of FDM perturbations on tidal streams, and show
that initially, while stream perturbations are small in amplitude,
their power spectra exhibit a sharp cutoff corresponding to the de
Broglie wavelength of the FDM potential fluctuations. Eventually,
when stream perturbations become nonlinear, fold caustics
generically arise that lead to density fluctuations with universal
behavior. This erases the signature of the de Broglie wavelength in
the stream density power spectrum, but we show that it will still be
possible to determine the FDM mass in this regime, by considering
the fluctuations in quantities like angular momenta or actions.
We present evidence of anisotropic galaxy assembly bias in the Baryon Oscillation Spectroscopic Survey Data Release 12 galaxy sample at a level exceeding 5σ. We use measurements of the line-of-sight ...velocity dispersion σ☆ and stellar mass M☆ to perform a simple split into subsamples of galaxies. We show that the amplitude of the monopole and quadrupole moments of the power spectrum depend differently on σ☆ and M☆, allowing us to split the galaxy sample into subsets with matching monopoles but significantly different quadrupoles on all scales. Combining data from the LOWZ and CMASS NGC galaxy samples, we find >5σ evidence for anisotropic bias on scales k<0.15hMpc−1. We also examine splits using other observed properties. For galaxy samples split using M☆ and projected size R0, we find no significant evidence of anisotropic bias. Galaxy samples selected using additional properties exhibit strongly varying degrees of anisotropic assembly bias, depending on which combination of properties is used to split into subsets. This may explain why previous searches for this effect using the Fundamental Plane found inconsistent results. We conclude that any selection of a galaxy sample that depends on σ☆ can give biased and incorrect Redshift Space Distortion measurements.
The splashback radius is a physical scale in dark matter halos that is set by the gravitational dynamics of recently accreted shells. We use analytical models and N-body simulations to study the ...dependence of splashback on dark energy and screened modified gravity theories. In modified gravity models, the transition from screened to unscreened regions typically occurs in the cluster outskirts, suggesting potentially observable signatures in the splashback feature. We investigate the location of splashback in both chameleon and Vainshtein screened models and find significant differences compared with ΛCDM predictions. We also observe an interesting interplay between dynamical friction and modified gravity, providing a distinctive signature for modified gravity models in the behavior of the splashback feature as a function of galaxy luminosity.
The friends-of-friends algorithm (hereafter FOF) is a percolation algorithm which is routinely used to identify dark matter halos from N-body simulations. We use results from percolation theory to ...show that the boundary of FOF halos does not correspond to a single density threshold but to a range of densities close to a critical value that depends upon the linking length parameter, b. We show that for the commonly used choice of b = 0.2, this critical density is equal to 81.62 times the mean matter density. Consequently, halos identified by the FOF algorithm enclose an average overdensity which depends on their density profile (concentration) and therefore changes with halo mass, contrary to the popular belief that the average overdensity is ~180. We derive an analytical expression for the overdensity as a function of the linking length parameter b and the concentration of the halo. Results of tests carried out using simulated and actual FOF halos identified in cosmological simulations show excellent agreement with our analytical prediction. We also find that the mass of the halo that the FOF algorithm selects crucially depends upon mass resolution. We find a percolation-theory-motivated formula that is able to accurately correct for the dependence on number of particles for the mock realizations of spherical and triaxial Navarro-Frenk-White halos. However, we show that this correction breaks down when applied to the real cosmological FOF halos due to the presence of substructures. Given that abundance of substructure depends on redshift and cosmology, we expect that the resolution effects due to substructure on the FOF mass and halo mass function will also depend on redshift and cosmology and will be difficult to correct for in general. Finally, we discuss the implications of our results for the universality of the mass function.
The Halo Boundary of Galaxy Clusters in the SDSS Baxter, Eric; Chang, Chihway; Jain, Bhuvnesh ...
Astrophysical journal/The Astrophysical journal,
05/2017, Volume:
841, Issue:
1
Journal Article
Peer reviewed
Open access
Analytical models and simulations predict a rapid decline in the halo density profile associated with the transition from the "infalling" regime outside the halo to the "collapsed" regime within the ...halo. Using data from SDSS, we explore evidence for such a feature in the density profiles of galaxy clusters using several different approaches. We first estimate the steepening of the outer galaxy density profile around clusters, finding evidence for truncation of the halo profile. Next, we measure the galaxy density profile around clusters using two sets of galaxies selected on color. We find evidence of an abrupt change in galaxy colors that coincides with the location of the steepening of the density profile. Since galaxies that have completed orbits within the cluster are more likely to be quenched of star formation and thus appear redder, this abrupt change in galaxy color can be associated with the transition from single-stream to multi-stream regimes. We also use a standard model comparison approach to measure evidence for a "splashback"-like feature, but find that this approach is very sensitive to modeling assumptions. Finally, we perform measurements using an independent cluster catalog to test for potential systematic errors associated with cluster selection. We identify several avenues for future work: improved understanding of the small-scale galaxy profile, lensing measurements, identification of proxies for the halo accretion rate, and other tests. With upcoming data from the DES, KiDS, and HSC surveys, we can expect significant improvements in the study of halo boundaries.
ABSTRACT We study the abundance of substructure in the matter density near galaxies using ALMA Science Verification observations of the strong lensing system SDP.81. We present a method to measure ...the abundance of subhalos around galaxies using interferometric observations of gravitational lenses. Using simulated ALMA observations we explore the effects of various systematics, including antenna phase errors and source priors, and show how such errors may be measured or marginalized. We apply our formalism to ALMA observations of SDP.81. We find evidence for the presence of a M = 108.96 0.12M subhalo near one of the images, with a significance of 6.9 in a joint fit to data from bands 6 and 7; the effect of the subhalo is also detected in both bands individually. We also derive constraints on the abundance of dark matter (DM) subhalos down to M ∼ 2 × 107M , pushing down to the mass regime of the smallest detected satellites in the Local Group, where there are significant discrepancies between the observed population of luminous galaxies and predicted DM subhalos. We find hints of additional substructure, warranting further study using the full SDP.81 data set (including, for example, the spectroscopic imaging of the lensed carbon monoxide emission). We compare the results of this search to the predictions of ΛCDM halos, and find that given current uncertainties in the host halo properties of SDP.81, our measurements of substructure are consistent with theoretical expectations. Observations of larger samples of gravitational lenses with ALMA should be able to improve the constraints on the abundance of galactic substructure.
In recent years, it has become possible to detect individual dark matter subhalos near images of strongly lensed extended background galaxies. Typically, only the most massive subhalos in the strong ...lensing region may be detected this way. In this work, we show that strong lenses may also be used to constrain the much more numerous population of lower mass subhalos that are too small to be detected individually. In particular, we show that the power spectrum of projected density fluctuations in galaxy halos can be measured using strong gravitational lensing. We develop the mathematical framework of power spectrum estimation, and test our method on mock observations. We use our results to determine the types of observations required to measure the substructure power spectrum with high significance. We predict that deep observations (∼10 hours on a single target) with current facilities can measure this power spectrum at the 3σ level, with no apparent degeneracy with unknown clumpiness in the background source structure or fluctuations from detector noise. Upcoming ALMA measurements of strong lenses are capable of placing strong constraints on the abundance of dark matter subhalos and the underlying particle nature of dark matter.
Observing dynamical friction in galaxy clusters Adhikari, Susmita; Dalal, Neal; Clampitt, Joseph
Journal of cosmology and astroparticle physics,
07/2016, Volume:
2016, Issue:
7
Journal Article
Peer reviewed
We present a novel method to detect the effects of dynamical friction in observed galaxy clusters. Following accretion into clusters, massive satellite galaxies will backsplash to systematically ...smaller radii than less massive satellites, an effect that may be detected by stacking the number density profiles of galaxies around clusters. We show that this effect may be understood using a simple toy model which reproduces the trends with halo properties observed in simulations. We search for this effect using SDSS redMaPPer clusters with richness 10 < λ < 20, and find that bright ( M {sub i} < −21.5) satellites have smaller splashback radii than fainter ( M {sub i} > −20) satellites at 99% confidence.
PDF
