The conventional cold-particle interpretation of dark matter (known as 'cold dark matter', or CDM) still lacks laboratory support and struggles with the basic properties of common dwarf galaxies, ...which have surprisingly uniform central masses and shallow density profiles1, 2, 3, 4, 5. In contrast, galaxies predicted by CDM extend to much lower masses, with steeper, singular profiles6, 7, 8, 9. This tension motivates cold, wavelike dark matter (ψDM) composed of a non-relativistic Bose-Einstein condensate, so the uncertainty principle counters gravity below a Jeans scale10, 11, 12. Here we achieve cosmological simulations of this quantum state at unprecedentedly high resolution capable of resolving dwarf galaxies, with only one free parameter, mB, the boson mass. We demonstrate the large-scale structure is indistinguishable from CDM, as desired, but differs radically inside galaxies where quantum interference forms solitonic cores surrounded by extended haloes of fluctuating density granules. These results allow us to determine eV using stellar phase-space distributions in dwarf spheroidal galaxies. Denser, more massive solitons are predicted for Milky Way sized galaxies, providing a substantial seed to help explain early spheroid formation. The onset of galaxy formation is substantially delayed relative to CDM, appearing at redshift z <, ~ 13 in our simulations.
Simulations of ultralight, ∼10−22 eV, bosonic dark matter exhibit rich wavelike structure, including a soliton core within a surrounding halo that continuously self-interferes on the de Broglie ...scale. We show here that as an inherent consequence, the soliton undergoes a confined random walk at the base of the halo potential. This is significant for the fate of the ancient central star cluster in Eridanus II, as the agitated soliton gravitationally shakes the star cluster in and out of the soliton on a timescale of ∼100 Myr, so complete tidal disruption of the star cluster can occur within ∼1 Gyr. This destructive effect can be mitigated by tidal stripping of the halo of Eridanus II, thereby reducing the agitation, depending on its orbit around the Milky Way. Our simulations show the Milky Way tide affects the halo much more than the soliton, so the star cluster in Eridanus II can survive for over 5 Gyr within the soliton if it formed after significant halo stripping.
The recent discovery of fast transient events near critical curves of massive galaxy clusters, which are interpreted as highly magnified individual stars in giant arcs due to caustic crossing, opens ...up the possibility of using such microlensing events to constrain a range of dark matter models such as primordial black holes and scalar field dark matter. Based on a simple analytic model, we study lensing properties of a point mass lens embedded in a high magnification region, and we derive the dependence of the peak brightness, microlensing time scales, and event rates on the mass of the point mass lens, as well as the radius of a source star that is magnified. We find that the lens mass and source radius of the first event MACS J1149 Lensed Star 1 (LS1) are constrained, with the lens mass range of 0.1 M⊙≲M≲4×103 M⊙ and the source radius range of 40R⊙≲R≲260R⊙. In the most plausible case with M≈0.3 M⊙ and R≈180R⊙, the source star should have been magnified by a factor of ≈4300 at the peak. The derived lens properties are fully consistent with the interpretation that MACS J1149 LS1 is a microlensing event produced by a star that contributes to the intracluster light. We argue that compact dark matter models with high fractional mass densities for the mass range 10−5 M⊙≲M≲102 M⊙ are inconsistent with the observation of MACS J1149 LS1 because such models predict too low magnifications. Our work demonstrates a potential use of caustic crossing events in giant arcs to constrain compact dark matter.
We examine the nonlinear structure of gravitationally collapsed objects that form in our simulations of wavelike cold dark matter, described by the Schrödinger-Poisson (SP) equation with a particle ...mass ∼10(-22) eV. A distinct gravitationally self-bound solitonic core is found at the center of every halo, with a profile quite different from cores modeled in the warm or self-interacting dark matter scenarios. Furthermore, we show that each solitonic core is surrounded by an extended halo composed of large fluctuating dark matter granules which modulate the halo density on a scale comparable to the diameter of the solitonic core. The scaling symmetry of the SP equation and the uncertainty principle tightly relate the core mass to the halo specific energy, which, in the context of cosmological structure formation, leads to a simple scaling between core mass (Mc) and halo mass (Mh), Mc∝a(-1/2)Mh(1/3), where a is the cosmic scale factor. We verify this scaling relation by (i) examining the internal structure of a statistical sample of virialized halos that form in our 3D cosmological simulations and by (ii) merging multiple solitons to create individual virialized objects. Sufficient simulation resolution is achieved by adaptive mesh refinement and graphic processing units acceleration. From this scaling relation, present dwarf satellite galaxies are predicted to have kiloparsec-sized cores and a minimum mass of ∼10(8)M⊙, capable of solving the small-scale controversies in the cold dark matter model. Moreover, galaxies of 2×10(12)M⊙ at z=8 should have massive solitonic cores of ∼2×10(9)M⊙ within ∼60 pc. Such cores can provide a favorable local environment for funneling the gas that leads to the prompt formation of early stellar spheroids and quasars.
We derive a projected 2D mass map of the well-studied galaxy cluster A1689 based on an entropy-regularized maximum likelihood combination of the lens magnification and distortion of red background ...galaxies registered in deep Subaru images. The method is not restricted to the weak regime but applies to the whole area outside the tangential critical curve, where nonlinearity between the surface mass density and the observables extends to a radius of a few arcminutes. The known strong-lensing information is also readily incorporated in this approach, represented as a central pixel with a mean surface density close to the critical value. We also utilize the distortion measurements to locally downweight the intrinsic clustering noise, which otherwise perturbs the depletion signal. The projected mass profile continuously steepens with radius and is well fitted by the Navarro-Frenk- White model, but with a surprisingly large concentration image, lying far from the predicted value of image, corresponding to the measured virial mass, image, posing a challenge to the standard assumptions defining the Lambda CDM model. We examine the consistency of our results with estimates derived with the standard weak-lensing estimators and by comparison with the inner mass profile obtained from strong lensing. All the reconstructions tested here imply a virial mass in the range image, and the combined ACS and Subaru 2D mass reconstruction yields a tight constraint on the concentration parameter, image, improving upon the statistical accuracy of our earlier 1D analysis. Importantly, our best-fitting profile properly reproduces the observed Einstein radius of image, in contrast to other weak-lensing work, reporting lower concentration profiles, which underestimate the observed Einstein radius.
Abstract
Fuzzy dark matter (FDM), a scalar particle coupled to the gravitational field without self-interaction, whose mass range is
m
∼ 10
−24
–10
−20
eV, is one of the promising alternative dark ...matter candidates to cold dark matter. The quantum interference pattern, which is a unique structure of FDM, can be seen in halos in cosmological FDM simulations. In this paper, we first provide an analytic model of the subgalactic matter power spectrum originating from quantum clumps in FDM halos, in which the density distribution of the FDM is expressed by a superposition of quantum clumps whose size corresponds to the de Broglie wavelength of the FDM. These clumps are assumed to be distributed randomly, such that the ensemble average density follows a halo profile such as the Navarro–Frenk–White profile. We then compare the convergence power spectrum projected along the line of sight around the Einstein radius, which is converted from the subgalactic matter power spectrum, to that measured in the strong lens system SDSS J0252 + 0039. While we find that the current observation provides no useful constraint on the FDM mass, we show that future deep, high spatial resolution observations of strong lens systems can tightly constrain FDM with a mass around 10
−22
eV.
We show how LIGO is expected to detect coalescing binary black holes at z>1 that are lensed by the intervening galaxy population. Gravitational magnification, μ, strengthens gravitational-wave ...signals by μ without altering their frequencies, which if unrecognized leads to an underestimate of the event redshift and hence an overestimate of the binary mass. High magnifications can be reached for coalescing binaries, because the region of intense gravitational-wave emission during coalescence is so small (∼100 km), permitting very close projections between lensing caustics and gravitational-wave events. Our simulations use the current LIGO event-based mass function and incorporate accurate waveforms convolved with the LIGO power spectral density. Importantly, we include the detection dependence on sky position and orbital orientation, which for the LIGO configuration translates into a wide spread in observed redshifts and chirp masses. Currently, we estimate a detectable rate of lensed events 0.06−0.02+0.02 yr−1 that rises to 5−3+5 yr−1 at LIGO design sensitivity limit, depending on the high redshift rate of black hole coalescence.
ABSTRACT
Strong lensing of gravitational waves (GWs) is more likely for distant sources but predicted event rates are highly uncertain with many astrophysical origins proposed. Here, we open a new ...avenue to estimate the event rate of strongly lensed systems by exploring the amplitude of the stochastic gravitational wave background (SGWB). This method can provide a direct upper bound on the high-redshift binary coalescing rates, which can be translated into an upper bound on the expected rate of strongly lensed systems. We show that from the ongoing analysis of the Laser Interferometer Gravitational-wave Observatory (LIGO)-Virgo and in the future from the LIGO–Virgo design sensitivity stringent bounds on the lensing event rate can be imposed using the SGWB signal. Combining measurements of loud GW events with an unresolved stochastic background detection will improve estimates of the numbers of lensed events at high redshift. The proposed method is going to play a crucial in understanding the population of lensed and unlensed systems from GW observations.
ABSTRACT
The expected event rate of lensed gravitational wave sources scales with the merger rate at redshift z ≥ 1, where the optical depth for lensing is high. It is commonly assumed that the ...merger rate of the astrophysical compact objects is closely connected with the star formation rate, which peaks around redshift z ∼ 2. However, a major source of uncertainty is the delay time between the formation and merger of compact objects. We explore the impact of delay time on the lensing event rate. We show that as the delay time increases, the peak of the merger rate of gravitational wave sources gets deferred to a lower redshift. This leads to a reduction in the event rate of the lensed events which are detectable by the gravitational wave detectors. We show that for a delay time of around 10 Gyr or larger, the lensed event rate can be less than one per year for the design sensitivity of LIGO/Virgo. We also estimate the merger rate for lensed sub-threshold for different delay time scenarios, finding that for larger delay times the number of lensed sub-threshold events is reduced, whereas for small-delay time models they are significantly more frequent. This analysis shows for the first time that lensing is a complementary probe to explore different formation channels of binary systems by exploiting the lensing event rate from the well-detected events and sub-threshold events which are measurable using the network of gravitational wave detectors.
Large Einstein radii: a problem for ΛCDM Broadhurst, Tom J.; Barkana, Rennan
Monthly Notices of the Royal Astronomical Society,
11/2008, Letnik:
390, Številka:
4
Journal Article
Recenzirano
Odprti dostop
The Einstein radius of a cluster provides a relatively model-independent measure of the mass density of a cluster within a projected radius of ∼150 kpc, large enough to be relatively unaffected by ...gas physics. We show that the observed Einstein radii of four well-studied massive clusters, for which reliable virial masses are measured, lie well beyond the predicted distribution of Einstein radii in the standard Λ cold dark matter (ΛCDM) model. Based on large samples of numerically simulated cluster-sized objects with virial masses ∼1015M⊙, the predicted Einstein radii are only 15–25 arcsec, a factor of 2 below the observed Einstein radii of these four clusters. This is because the predicted mass profile is too shallow to exceed the critical surface density for lensing at a sizable projected radius. After carefully accounting for measurement errors as well as the biases inherent in the selection of clusters and the projection of mass measured by lensing, we find that the theoretical predictions are excluded at a 4σ significance. Since most of the free parameters of the ΛCDM model now rest on firm empirical ground, this discrepancy may point to an additional mechanism that promotes the collapse of clusters at an earlier time thereby enhancing their central mass density.
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