Strong Lensing Clusters Research Articles

A Strong Lensing Model of RCS1 J0224−0002.5

We present the details of a strong lensing model of RCS1 J0224−0002.5, a strong lensing cluster at z = 0.773, based on data from Hubble Space Telescope/WFC3, Advanced Camera for Surveys, and WFC2. Of particular interest in this field is a z = 4.8786 Lyα emitter (LAE), 15″ from the brightest cluster galaxy (BCG) that stretches northwest to west of the BCG in three different images, with a fourth counter-image ∼4″ southeast of the BCG. Using methods consistent with those used in studying five other LAEs in A. Navarre et al., we find that the cluster is best modeled by two cluster-scale dark matter halos aligned nearly perpendicular to each other at the center of the cluster. A z = 2.396 source is also lensed with six images, providing several constraints that were instrumental in producing this model.

The detection and characterization of highly magnified stars with JWST: Prospects of finding Population III

Abstract Gravitational lensing may render individual high-mass stars detectable out to cosmological distances, and several extremely magnified stars have in recent years been detected out to redshifts z ≈ 6. Here, we present Muspelheim, a model for the evolving spectral energy distributions of both metal-enriched and metal-free stars at high redshifts. Using this model, we argue that lensed stars will form a highly biased sample of the intrinsic distribution of stars across the Hertzsprung-Russell diagram, and that this bias will typically tend to favour the detection of lensed stars in evolved stages characterized by low effective temperatures, even though stars only spend a minor fraction of their lifetimes in such states. We also explore the prospects of detecting individual, lensed metal-free (Population III) stars at high redshifts using the James Webb Space Telescope (JWST). We find that very massive (≳ 100 M⊙) Population III stars at z ≳ 6 may potentially be detected by JWST in surveys covering large numbers of strong lensing clusters, provided that the Population III stellar initial mass function is sufficiently top-heavy, that these stars evolve to effective temperatures ≤15000 K, and that the cosmic star formation rate density of Pop III stars reaches ≳ 10−4 M⊙ cMpc−3 yr−1 at z ≈ 6–10. Various ways to distinguish metal-free lensed stars from metal-enriched ones are also discussed.

COOL-LAMPS. VI. Lens Model and New Constraints on the Properties of COOL J1241+2219, a Bright z = 5 Lyman Break Galaxy and its z = 1 Cluster Lens

We present a strong lensing analysis of COOL J1241+2219, the brightest known gravitationally lensed galaxy at z ≥ 5, based on new multiband Hubble Space Telescope (HST) imaging data. The lensed galaxy has a redshift of z = 5.043, placing it shortly after the end of the “Epoch of Reionization,” and an AB magnitude z AB = 20.47 mag (Khullar et al.). As such, it serves as a touchstone for future research of that epoch. The high spatial resolution of HST reveals internal structure in the giant arc, from which we identify 15 constraints and construct a robust lens model. We use the lens model to extract the cluster mass and lensing magnification. We find that the mass enclosed within the Einstein radius of the z = 1.001 cluster lens is M(<5.″77)=1.079−0.007+0.023×1013M☉ , significantly lower than other known strong lensing clusters at its redshift. The average magnification of the giant arc is 〈μ arc〉 = 76−20+40 , a factor of 2.4−0.7+1.4 greater than previously estimated from ground-based data; the flux-weighted average magnification is 〈μ arc〉 = 92−31+37 . We update the current measurements of the stellar mass and star formation rate (SFR) of the source for the revised magnification to log(M⋆/M⊙)= 9.7 ± 0.3 and SFR = 10.3−4.4+7.0 M ⊙ yr−1, respectively. The powerful lensing magnification acting upon COOL J1241+2219 resolves the source and enables future studies of the properties of its star formation on a clump-by-clump basis. The lensing analysis presented here will support upcoming multiwavelength characterization with HST and JWST data of the stellar mass assembly and physical properties of this high-redshift lensed galaxy.

A high black-hole-to-host mass ratio in a lensed AGN in the early Universe.

Early JWST observations have uncovered a population of red sources that might represent a previously overlooked phase of supermassive black hole growth1-3. One of the most intriguing examples is an extremely red, point-like object that was found to be triply imaged by the strong lensing cluster Abell 2744 (ref. 4). Here we present deep JWST/NIRSpec observations of this object, Abell2744-QSO1. The spectroscopy confirms that the three images are of the same object, and that it is a highly reddened (AV ≃ 3) broad emission line active galactic nucleus at a redshift of zspec = 7.0451 ± 0.0005. From the width of Hβ (full width at half-maximum = 2,800 ± 250 km s-1), we derive a black hole mass of . We infer a very high ratio of black-hole-to-galaxy mass of at least 3%, an order of magnitude more than that seen in local galaxies5 and possibly as high as 100%. The lack of strong metal lines in the spectrum together with the high bolometric luminosity (Lbol = (1.1 ± 0.3) × 1045 erg s-1) indicate that we are seeing the black hole in a phase of rapid growth, accreting at 30% of the Eddington limit. The rapid growth and high black-hole-to-galaxy mass ratio of Abell2744-QSO1 suggest that it may represent the missing link between black hole seeds6 and one of the first luminous quasars7.

A full reconstruction of two galaxy clusters intra-cluster medium with strong gravitational lensing

ABSTRACT Whilst X-rays and Sunyaev–Zel’dovich observations allow to study the properties of the intra-cluster medium (ICM) of galaxy clusters, their gravitational potential may be constrained using strong gravitational lensing. Although being physically related, these two components are often described with different physical models. Here, we present a unified technique to derive the ICM properties from strong lensing for clusters in hydrostatic equilibrium. In order to derive this model, we present a new universal and self-similar polytropic temperature profile, which we fit using the X-COP sample of clusters. We subsequently derive an analytical model for the electron density, which we apply to strong lensing clusters MACS J0242.5-2132 and MACS J0949.8+1708. We confront the inferred ICM reconstructions to XMM-Newton and ACT observations. We contrast our analytical electron density reconstructions with the best canonical β-model. The ICM reconstructions obtained prove to be compatible with observations. However they appear to be very sensitive to various dark matter halo parameters constrained through strong lensing (such as the core radius), and to the halo scale radius (fixed in the lensing optimizations). With respect to the important baryonic effects, we make the sensitivity on the scale radius of the reconstruction an asset, and use the inferred potential to constrain the dark matter density profile using ICM observations. The technique here developed should allow to take a new, and more holistic path to constrain the content of galaxy clusters.

On the gravitational lensing interpretation of three gravitational wave detections in the mass gap by LIGO and Virgo

ABSTRACT We search for gravitational wave (GW) events from LIGO-Virgo’s third run that may have been affected by gravitational lensing. Gravitational lensing delays the arrival of GWs, and alters their amplitude – thus biasing the inferred progenitor masses. This would provide a physically well-understood interpretation of GW detections in the ‘mass gap’ between neutron stars and black holes, as gravitationally lensed binary neutron star (BNS) mergers. We selected three GW detections in LIGO-Virgo’s third run for which the probability of at least one of the constituent compact objects being in the mass gap was reported as high with low latency – i.e. candidate lensed BNS mergers. Our observations of powerful strong lensing clusters located adjacent to the peak of their sky localization error maps reached a sensitivity $\rm AB\simeq 25.5$ in the z′ band with the GMOS instruments on the Gemini telescopes, and detected no candidate lensed optical counterparts. We combine recent kilonova light-curve models with recent predictions of the lensed BNS population and the properties of the objects that we followed up to show that realistic optical counterparts were detectable in our observations. Further detailed analysis of two of the candidates suggests that they are a plausible pair of images of the same low-mass binary black hole merger, lensed by a local galaxy or small group of galaxies. This further underlines that access to accurate mass information with low latency would improve the efficiency of candidate lensed BNS selection.

Shapes and Centroids of 39 Strong Lensing Galaxy Clusters from the Sloan Giant Arcs Survey

AbstractStrong lensing galaxy clusters provide a powerful observational test of Cold Dark Matter (CDM) structure predictions derived from simulation. Specifically, the shape and relative alignments of the dark matter halo, stars, and hot intracluster gas tells us the extent to which theoretical structure predictions hold for clusters in various dynamical states. We measure the position angles, ellipticities, and locations/centroids of the brightest cluster galaxy (BCG), intracluster light (ICL), the hot intracluster medium (ICM), and the core lensing mass for a sample of strong lensing galaxy clusters from the SDSS Giant Arcs Survey (SGAS). We use iterative elliptical isophote fitting methods and GALFIT modeling on HST WFC3/IR imaging data to extract ICL and BCG information and use CIAO’s Sherpa modeling on Chandra ACIS-I X-ray data to make measurements of the ICM. Using this multicomponent approach, we attempt to constrain the physical state of these strong lensing clusters and evaluate the different observable components in terms of their ability to trace out the gravitational potential of the cluster.

A Submillimeter Survey of Faint Galaxies behind 10 Strong Lensing Clusters

We present deep SCUBA-2 450 μm and 850 μm imaging of 10 strong lensing clusters. We provide a >4σ SCUBA-2 850 μm catalog of the 404 sources lying within a radius of from the cluster centers. We also provide catalogs of the >4.5σ Atacama Large Millimeter/submillimeter Array (ALMA) 850 μm detections in the clusters A370, MACSJ1149.5+2223, and MACSJ0717.5+3745 from our targeted ALMA observations, along with catalogs of all other >4.5σ ALMA (mostly 1.2 mm) detections in any of our cluster fields from archival ALMA observations. For the ALMA detections, we give spectroscopic or photometric redshifts, where available, from our own Keck observations or from the literature. We confirm the use of the 450–850 μm flux ratio for estimating redshifts. We use lens models to determine magnifications, most of which are in the 1.5–4 range. After supplementing the ALMA cluster sample with Chandra Deep Field ALMA and Submillimeter Array samples, we find no evidence for evolution in the redshift distribution of submillimeter galaxies down to demagnified 850 μm fluxes of 0.5 mJy. Given this result, we conclude that our observed trend of increasing F160W to 850 μm flux ratio from brighter to fainter demagnified 850 μm flux results from the fainter submillimeter galaxies having less extinction. However, there is wide spread in this relation, including the presence of some optical/near-infrared dark galaxies down to fluxes below 1 mJy. Finally, with insights from our ALMA analysis, we analyze our SCUBA-2 sample and present 55 850 μm bright z > 4 candidates.

Impact of the turnover in the high-z galaxy luminosity function on the 21-cm signal during Cosmic Dawn and Epoch of Reionization

ABSTRACT The shape of the faint-end of the high-z galaxy luminosity function (LF) informs early star formation and reionization physics during the Cosmic Dawn and Epoch of Reionization. Until recently, based on the strong gravitational lensing cluster deep surveys, the Hubble Frontier Fields (HFF) has found a potential turnover in the ultraviolet (UV) LF at $\mathit{ z}$ ∼ 6. In this paper, we analyse the contribution of extremely faint galaxies with the magnitude larger than the turnover magnitude in LF to cosmic reionization. We apply the measurement from HFF to our suppressed star formation efficiency model, including three free parameters: halo mass threshold Mt, curvature parameter β, and a UV conversion factor lUV. According to our fit of 68 per cent confidence level, the high-redshift star formation in haloes smaller than $M_t=1.82^{+2.86}_{-1.08}\times 10^{10} \, \rm M_{\odot }$ is found to be dampened. The turnover magnitude $\rm \gtrsim -13.99-2.45$, correspondingly the halo mass $\lesssim (4.57+20.03)\times 10^{9} \, \rm M_{\odot }$. We find that the absorption trough in the global 21-cm signal is sensitive to our SFE model parameters. Together with (β, lUV) = ($2.17^{+2.42}_{-1.72}$, $9.33^{+0.43}_{-0.42} \, \rm ~erg~yr ~s^{-1}\, M_{\odot }^{-1})$, the trough locates at ∼$134^{+10}_{-17}$$\rm MHz$ with an amplitude of ∼$-237^{-6}_{+7}$$\rm mK$, compared to (106 MHz, -212 mK) in the absence of turnover. Besides, we find that the star formation of faint galaxies has also an impact on the 21-cm power spectra. The best-fitting peak power decreases by$\sim 4{{\ \rm per\ cent}}$ and shifts towards smaller scales from $0.88 \, h\, \rm Mpc^{-1}$ to $0.91 \, h\, \rm Mpc^{-1}$. According to our calculation, such impact is distinguishable with the forthcoming Square Kilometre Array.

Pilot-WINGS: An extended MUSE view of the structure of Abell 370

ABSTRACT We investigate the strong-lensing cluster Abell 370 (A370) using a wide Integral Field Unit (IFU) spectroscopic mosaic from the Multi-Unit Spectroscopic Explorer (MUSE). IFU spectroscopy provides significant insight into the structure and mass content of galaxy clusters, yet IFU-based cluster studies focus almost exclusively on the central Einstein-radius region. Covering over 14 arcmin2, the new MUSE mosaic extends significantly beyond the A370 Einstein radius, providing, for the first time, a detailed look at the cluster outskirts. Combining these data with wide-field, multi-band Hubble Space Telescope (HST) imaging from the BUFFALO project, we analyse the distribution of objects within the cluster and along the line of sight. Identifying 416 cluster galaxies, we use kinematics to trace the radial mass profile of the halo, providing a mass estimate independent from the lens model. We also measure radially averaged properties of the cluster members, tracking their evolution as a function of infall. Thanks to the high spatial resolution of our data, we identify six cluster members acting as galaxy–galaxy lenses, which constrain localized mass distributions beyond the Einstein radius. Finally, taking advantage of MUSE’s 3D capabilities, we detect and analyse multiple spatially extended overdensities outside of the cluster that influence lensing-derived halo mass estimates. We stress that much of this work is only possible thanks to the robust, extended IFU coverage, highlighting its importance even in less optically dense cluster regions. Overall, this work showcases the power of combining HST + MUSE, and serves as the initial step towards a larger and wider program targeting several clusters.

A Spectroscopic View of the JWST/GTO Strong Lensing Cluster A1489

We discuss a spectroscopic survey of the strong lensing cluster A1489 that includes redshifts for 195 cluster members along with central velocity dispersions for 188 cluster members. The caustic technique applied to the redshift survey gives the dynamical parameters M 200 = (1.25 ± 0.09) × 1015 M ⊙, R 200 = 1.97 ± 0.05 Mpc, and a cluster line-of-sight velocity dispersion of 1150 ± 72 km s−1 within R 200. These parameters are very similar to those of other strong lensing systems with comparably large Einstein radii. We use the spectroscopy and deep photometry to demonstrate that A1489 is probably dynamically active; its four brightest cluster galaxies have remarkably different rest-frame radial velocities. Like other massive strong lensing clusters, the velocity dispersion function for members of A1489 shows an excess for dispersions ≳250 km s−1. The central dispersions also provide enhanced constraints on future lensing models.

Spectroscopic confirmation of a gravitationally lensed Lyman-break galaxy at z[C ii] = 6.827 using NOEMA

ABSTRACT We present the spectroscopic confirmation of the brightest known gravitationally lensed Lyman-break galaxy in the Epoch of Reionization (EoR), A1703-zD1, through the detection of [C ii] 158 $\mu$m at a redshift of z = 6.8269 ± 0.0004. This source was selected behind the strong lensing cluster Abell 1703, with an intrinsic luminosity and a very blue Spitzer/Infrared Array Camera (IRAC) [3.6]–[4.5] colour, implying high equivalent width line emission of [O iii] + Hβ. [C ii] is reliably detected at 6.1σ cospatial with the rest-frame ultraviolet (UV) counterpart, showing similar spatial extent. Correcting for the lensing magnification, the [C ii] luminosity in A1703-zD1 is broadly consistent with the local $L_{\rm [C\, {\small II}]}$–star formation rate (SFR) relation. We find a clear velocity gradient of 103 ± 22 km $\rm s^{-1}$ across the source that possibly indicates rotation or an ongoing merger. We furthermore present spectral scans with no detected [C ii] above 4.6σ in two unlensed Lyman-break galaxies in the Extended Groth Strip (EGS)-Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) field at z ∼ 6.6–6.9. This is the first time that the Northern Extended Millimeter Array (NOEMA) has been successfully used to observe [C ii] in a ‘normal’ star-forming galaxy at z &amp;gt; 6, and our results demonstrate its capability to complement the Atacama Large Millimeter/submillimeter Array (ALMA) in confirming galaxies in the EoR.

Core Mass Estimates in Strong Lensing Galaxy Clusters: A Comparison between Masses Obtained from Detailed Lens Models, Single-halo Lens Models, and Einstein Radii

Abstract The core mass of galaxy clusters is both an important anchor of the radial mass distribution profile and a probe of structure formation. With thousands of strong lensing galaxy clusters being discovered by current and upcoming surveys, timely, efficient, and accurate core mass estimates are needed. We assess the results of two efficient methods to estimate the core mass of strong lensing clusters: the mass enclosed by the Einstein radius (M(&lt;θ E), where θ E is approximated from arc positions, and a single-halo lens model (M SHM), compared with measurements from publicly available detailed lens models (M DLM) of the same clusters. We use data from the Sloan Giant Arc Survey, the Reionization Lensing Cluster Survey, the Hubble Frontier Fields, and the Cluster Lensing and Supernova Survey with Hubble. We find a scatter of 18.1% (8.2%) with a bias of −7.1% (1.0%) between M corr &lt; θ arcs (M SHM) and M DLM. Last, we compare the statistical uncertainties measured in this work to those from simulations. This work demonstrates the successful application of these methods to observational data. As the effort to efficiently model the mass distribution of strong lensing galaxy clusters continues, we need fast, reliable methods to advance the field.

Core Mass Estimates in Strong Lensing Galaxy Clusters Using a Single-halo Lens Model

Abstract The core mass of galaxy clusters is an important probe of structure formation. Here we evaluate the use of a single-halo model (SHM) as an efficient method to estimate the strong lensing cluster core mass, testing it with ray-traced images from the Outer Rim simulation. Unlike detailed lens models, the SHM represents the cluster mass distribution with a single halo and can be automatically generated from the measured lensing constraints. We find that the projected core mass estimated with this method, M SHM, has a scatter of 8.52% and a bias of 0.90% compared to the “true” mass within the same aperture. Our analysis shows no systematic correlation between the scatter or bias and the lens-source system properties. The bias and scatter can be reduced to 3.26% and 0.34%, respectively, by excluding models that fail a visual inspection test. We find that the SHM success depends on the lensing geometry, with single giant arc configurations accounting for most of the failed cases due to their limiting constraining power. When excluding such cases, we measure a scatter and bias of 3.88% and 0.84%, respectively. Finally, we find that when the source redshift is unknown, the model-predicted redshifts are overestimated, and the M SHM is underestimated by a few percent, highlighting the importance of securing spectroscopic redshifts of background sources. Our analysis provides a quantitative characterization of M SHM, enabling its efficient use as a tool to estimate the strong lensing cluster core masses in the large samples, expected from current and future surveys.

Efficient Mass Estimate at the Core of Strong Lensing Galaxy Clusters Using the Einstein Radius

Abstract In the era of large surveys, yielding thousands of galaxy clusters, efficient mass proxies at all scales are necessary in order to fully utilize clusters as cosmological probes. At the cores of strong lensing clusters, the Einstein radius can be turned into a mass estimate. This efficient method has been routinely used in literature, in lieu of detailed mass models; however, its scatter, assumed to be , has not yet been quantified. Here, we assess this method by testing it against ray-traced images of cluster-scale halos from the Outer Rim N-body cosmological simulation. We measure a scatter of 13.9% and a positive bias of 8.8% in , with no systematic correlation with total cluster mass, concentration, or lens or source redshifts. We find that increased deviation from spherical symmetry increases the scatter; conversely, where the lens produces arcs that cover a large fraction of its Einstein circle, both the scatter and the bias decrease. While spectroscopic redshifts of the lensed sources are critical for accurate magnifications and time delays, we show that for the purpose of estimating the total enclosed mass, the scatter introduced by source redshift uncertainty is negligible compared to other sources of error. Finally, we derive and apply an empirical correction that eliminates the bias, and reduces the scatter to 10.1% without introducing new correlations with mass, redshifts, or concentration. Our analysis provides the first quantitative assessment of the uncertainties in , and enables its effective use as a core mass estimator of strong lensing galaxy clusters.

Shapes and alignments of dark matter haloes and their brightest cluster galaxies in 39 strong lensing clusters

ABSTRACT We study shapes and alignments of 45 dark matter (DM) haloes and their brightest cluster galaxies (BCGs) using a sample of 39 massive clusters from Hubble Frontier Field (HFF), Cluster Lensing And Supernova survey with Hubble (CLASH), and Reionization Lensing Cluster Survey (RELICS). We measure shapes of the DM haloes by strong gravitational lensing, whereas BCG shapes are derived from their light profiles in Hubble Space Telescope images. Our measurements from a large sample of massive clusters presented here provide new constraints on DM and cluster astrophysics. We find that DM haloes are on average highly elongated with the mean ellipticity of 0.482 ± 0.028, and position angles of major axes of DM haloes and their BCGs tend to be aligned well with the mean value of alignment angles of 22.2 ± 3.9 deg. We find that DM haloes in our sample are on average more elongated than their BCGs with the mean difference of their ellipticities of 0.11 ± 0.03. In contrast, the Horizon-AGN cosmological hydrodynamical simulation predicts on average similar ellipticities between DM haloes and their central galaxies. While such a difference between the observations and the simulation may well be explained by the difference of their halo mass scales, other possibilities include the bias inherent to strong lensing measurements, limited knowledge of baryon physics, or a limitation of cold DM.

On building a cluster watchlist for identifying strongly lensed supernovae, gravitational waves and kilonovae

ABSTRACT Motivated by discovering strongly lensed supernovae, gravitational waves, and kilonovae in the 2020s, we investigate whether to build a watchlist of clusters based on observed cluster properties (i.e. lens-plane selection) or on the detectability of strongly lensed background galaxies (i.e. source-plane selection). First, we estimate the fraction of high-redshift transient progenitors that reside in galaxies that are themselves too faint to be detected as being strongly lensed. We find ∼15–50 per cent of transient progenitors reside in z = 1 − 2 galaxies too faint to be detected in surveys that reach AB ≃ 23, such as the Dark Energy Survey. This falls to ≲10 per cent at depths that will be probed by early data releases of LSST (AB ≃ 25). Secondly, we estimate a conservative lower limit on the fraction of strong-lensing clusters that will be missed by magnitude-limited searches for multiply imaged galaxies and giant arcs due to the faintness of such images. We find that DES-like surveys will miss ∼75 per cent of 1015 M⊙ strong-lensing clusters, rising to ∼100 per cent of 1014 M⊙ clusters. Deeper surveys, such as LSST, will miss ∼40 per cent at 1015 M⊙ and ∼95 per cent at 1014 M⊙. Our results motivate building a cluster watchlist for strongly lensed transients that includes those found by the lens-plane selection.

MIFAL: fully automated Multiple-Image Finder ALgorithm for strong-lens modelling – proof of concept

ABSTRACT We outline a simple procedure designed for automatically finding sets of multiple images in strong lensing (SL) clusters. We show that by combining (a) an arc-finding (or source extracting) program, (b) photometric redshift measurements, and (c) a preliminary light-traces-mass lens model, multiple-image systems can be identified in a fully automated (‘blind’) manner. The presented procedure yields an assessment of the likelihood of each arc to belong to one of the multiple-image systems, as well as the preferred redshift for the different systems. These could be then used to automatically constrain and refine the initial lens model for an accurate mass distribution. We apply this procedure to Cluster Lensing And Supernova with Hubble observations of three galaxy clusters, MACS J0329.6-0211, MACS J1720.2 + 3536, and MACS J1931.8-2635, comparing the results to published SL analyses where multiple images were verified by eye on a particular basis. In the first cluster all originally identified systems are recovered by the automated procedure, and in the second and third clusters about half are recovered. Other known systems are not picked up, in part due to a crude choice of parameters, ambiguous photometric redshifts, or inaccuracy of the initial lens model. On top of real systems recovered, some false images are also mistakenly identified by the procedure, depending on the thresholds used. While further improvements to the procedure and a more thorough scrutinization of its performance are warranted, the work constitutes another important step toward fully automatizing SL analyses for studying mass distributions of large cluster samples.

Cosmology from the Chinese Space Station Optical Survey (CSS-OS)

Abstract The Chinese Space Station Optical Survey (CSS-OS) is a planned full sky survey operated by the Chinese Space Station Telescope (CSST). It can simultaneously perform the photometric imaging and spectroscopic slitless surveys, and will probe weak and strong gravitational lensing, galaxy clustering, individual galaxies and galaxy clusters, active galactic nucleus, and so on. It aims to explore the properties of dark matter and dark energy and other important cosmological problems. In this work, we focus on two main CSS-OS scientific goals, i.e., the weak gravitational lensing (WL) and galaxy clustering surveys. We generate the mock CSS-OS data based on the observational COSMOS and zCOSMOS catalogs. We investigate the constraints on the cosmological parameters from the CSS-OS using the Markov Chain Monte Carlo method. The intrinsic alignments, galaxy bias, velocity dispersion, and systematics from instrumental effects in the CSST WL and galaxy clustering surveys are also included, and their impacts on the constraint results are discussed. We find that the CSS-OS can improve the constraints on the cosmological parameters by a factor of a few (even one order of magnitude in the optimistic case), compared to the current WL and galaxy clustering surveys. The constraints can be further enhanced when performing joint analysis with the WL, galaxy clustering, and galaxy–galaxy lensing data. Therefore, the CSS-OS is expected to be a powerful survey for exploring the universe. Since some assumptions may be still optimistic and simple, it is possible that the results from the real survey could be worse. We will study these issues in detail with the help of simulations in the future.

What if LIGO’s gravitational wave detections are strongly lensed by massive galaxy clusters?

Motivated by the preponderance of so-called "heavy black holes" in the binary black hole (BBH) gravitational wave (GW) detections to date, and the role that gravitational lensing continues to play in discovering new galaxy populations, we explore the possibility that the GWs are strongly-lensed by massive galaxy clusters. For example, if one of the GW sources were actually located at $z=1$, then the rest-frame mass of the associated BHs would be reduced by a factor $\sim2$. Based on the known populations of BBH GW sources and strong-lensing clusters, we estimate a conservative lower limit on the number of BBH mergers detected per detector year at LIGO/Virgo's current sensitivity that are multiply-imaged, of $R_{\rm detect}\simeq10^{-5}{\rm yr}^{-1}$. This is equivalent to rejecting the hypothesis that one of the BBH GWs detected to date was multiply-imaged at $<\sim4\sigma$. It is therefore unlikely but not impossible that one of the GWs is multiply-imaged. We identify three spectroscopically confirmed strong-lensing clusters with well constrained mass models within the $90\%$ credible sky localisations of the BBH GWs from LIGO's first observing run. In the event that one of these clusters multiply-imaged one of the BBH GWs, we predict that $20-60\%$ of the putative next appearances of the GWs would be detectable by LIGO, and that they would arrive at Earth within three years of first detection.