Lensing Galaxy Research Articles

Constraints on S8 from a full-scale and full-shape analysis of redshift-space clustering and galaxy–galaxy lensing in BOSS

ABSTRACT We present a novel simulation-based cosmological analysis of galaxy–galaxy lensing and galaxy redshift-space clustering. Compared to analysis methods based on perturbation theory, our simulation-based approach allows us to probe a much wider range of scales, $0.4 \, h^{-1} \, \mathrm{Mpc}$ to $63 \, h^{-1} \, \mathrm{Mpc}$, including highly non-linear scales, and marginalizes over astrophysical effects such as assembly bias. We apply this framework to data from the Baryon Oscillation Spectroscopic Survey LOWZ sample cross-correlated with state-of-the-art gravitational lensing catalogues from the Kilo Degree Survey and the Dark Energy Survey. We show that gravitational lensing and redshift-space clustering when analysed over a large range of scales place tight constraints on the growth-of-structure parameter $S_8 = \sigma _8 \sqrt{\Omega _{\rm m} / 0.3}$. Overall, we infer S8 = 0.792 ± 0.022 when analysing the combination of galaxy–galaxy lensing and projected galaxy clustering and S8 = 0.771 ± 0.027 for galaxy redshift-space clustering. These findings highlight the potential constraining power of full-scale studies over studies analysing only large scales and also showcase the benefits of analysing multiple large-scale structure surveys jointly. Our inferred values for S8 fall below the value inferred from the CMB, S8 = 0.834 ± 0.016. While this difference is not statistically significant by itself, our results mirror other findings in the literature whereby low-redshift large-scale structure probes infer lower values for S8 than the CMB, the so-called S8-tension.

Euclid: Forecasts from the void-lensing cross-correlation

The Euclid space telescope will survey a large dataset of cosmic voids traced by dense samples of galaxies. In this work we estimate its expected performance when exploiting angular photometric void clustering, galaxy weak lensing, and their cross-correlation. To this aim, we implemented a Fisher matrix approach tailored for voids from the Euclid photometric dataset and we present the first forecasts on cosmological parameters that include the void-lensing correlation. We examined two different probe settings, pessimistic and optimistic, both for void clustering and galaxy lensing. We carried out forecast analyses in four model cosmologies, accounting for a varying total neutrino mass, Mν, and a dynamical dark energy (DE) equation of state, w(z), described by the popular Chevallier-Polarski-Linder parametrization. We find that void clustering constraints on h and Ωb are competitive with galaxy lensing alone, while errors on ns decrease thanks to the orthogonality of the two probes in the 2D-projected parameter space. We also note that, as a whole, with respect to assuming the two probes as independent, the inclusion of the void-lensing cross-correlation signal improves parameter constraints by 10 − 15%, and enhances the joint void clustering and galaxy lensing figure of merit (FoM) by 10% and 25%, in the pessimistic and optimistic scenarios, respectively. Finally, when further combining with the spectroscopic galaxy clustering, assumed as an independent probe, we find that, in the most competitive case, the FoM increases by a factor of 4 with respect to the combination of weak lensing and spectroscopic galaxy clustering taken as independent probes. The forecasts presented in this work show that photometric void clustering and its cross-correlation with galaxy lensing deserve to be exploited in the data analysis of the Euclid galaxy survey and promise to improve its constraining power, especially on h, Ωb, the neutrino mass, and the DE evolution.

ALMA Resolves the First Strongly Lensed Optical/Near-IR-dark Galaxy

We present high-resolution (≲0.″1) Atacama Large Millimeter/submillimeter Array observations of the strongly lensed galaxy HATLASJ113526.2-01460 at redshift z ∼ 3.1, discovered in the GAMA 12th field of the Herschel-ATLAS survey. This gravitationally lensed system is remarkably peculiar, in that neither the background source nor the foreground lens show a clearly detected optical/near-IR Hubble Space Telescope-J band emission. We perform accurate lens modeling and source morphology reconstruction in three different (sub)millimeter continuum bands and in the C[ii] and CO(8−7) spectral lines. The modeling indicates a foreground lensing (likely elliptical) galaxy with mass ≳1011 M ⊙ at z ≳ 1.5, while the source (sub)millimeter continuum and line emissions are amplified by factors μ ∼ 6–13. We estimate extremely compact sizes—≲0.5 kpc for the star-forming region and ≲1 kpc for the gas component—with no clear evidence of rotation or ongoing merging events. We perform broadband SED fitting and retrieve the intrinsic demagnified physical properties of the source, which is found to feature a very high star formation rate, ≳103 M ⊙ yr−1, which, given the compact sizes, is on the verge of the Eddington limit for starbursts; the radio luminosity at 6 cm from the available EVLA observations is consistent with star formation activity. The galaxy is found to be extremely rich in gas ∼1011 M ⊙ and dust ≳109 M ⊙. The stellar content ≲1011 M ⊙ places the source well above the main sequence of star-forming galaxies, indicating that the starburst is rather young, with an estimated age ∼108 yr. Our results indicate that the overall properties of HATLASJ113526.2-01460 are consistently explained by in situ galaxy formation and evolution scenarios.

Constraining gravity with synergies between radio and optical cosmological surveys

In this work we present updated forecasts on parameterised modifications of gravity that can capture deviations of the behaviour of cosmological density perturbations beyond ΛCDM. For these forecasts we adopt the SKA Observatory (SKAO) as a benchmark for future cosmological surveys at radio frequencies, combining a continuum survey for weak lensing and angular galaxy clustering with an Hi galaxy survey for spectroscopic galaxy clustering that can detect baryon acoustic oscillations and redshift space distortions. Moreover, we also add 21 cm Hi intensity mapping, which provides invaluable information at higher redshifts, and can complement tomographic resolution, thus allowing us to probe redshift-dependent deviations of modified gravity models. For some of these cases, we combine the probes with other optical surveys, such as the Dark Energy Spectroscopic Instrument (DESI) and the Vera C. Rubin Observatory (VRO). We show that such synergies are powerful tools to remove systematic effects and degeneracies in the non-linear and small-scale modelling of the observables. Overall, we find that the combination of all SKAO radio probes will have the ability to constrain the present value of the functions parameterising deviations from ΛCDM (μ and Σ) with a precision of 2.7% and 1.8% respectively, competitive with the constraints expected from optical surveys and with constraints we have on gravitational interactions in the standard model. Exploring the radio-optical synergies, we find that the combination of VRO with SKAO can yield extremely tight constraints on μ and Σ (0.9% and 0.7% respectively), which are further improved when the cross-correlation between intensity mapping and DESI galaxies is included.

Photometric Objects Around Cosmic Webs (PAC) Delineated in a Spectroscopic Survey. IV. High-precision Constraints on the Evolution of the Stellar–Halo Mass Relation at Redshift z < 0.7

Taking advantage of the Photometric objects Around Cosmic webs method developed in Paper I, we measure the excess surface density of the photometric objects around spectroscopic objects down to stellar masses 108.0 M ⊙, 109.2 M ⊙, and 109.8 M ⊙ in the redshift ranges of z s < 0.2, 0.2 < z s < 0.4, and 0.5 < z s < 0.7, respectively, using data from the DESI Legacy Imaging Surveys and spectroscopic samples from the Sloan Digital Sky Survey (i.e., the Main, LOWZ, and CMASS samples). We model the measured in an N-body simulation, using the abundance matching method, and we constrain the stellar–halo mass relations (SHMRs) in the three redshift ranges to percent levels. With the accurate modeling, we demonstrate that the stellar mass scatter for a given halo mass is nearly a constant, and that the empirical form of Behroozi et al. describes the SHMR better than the double-power-law form at low mass. Our SHMR accurately captures the downsizing of massive galaxies from z s = 0.7, while it also indicates that small galaxies are still growing faster than their host halos. The galaxy stellar mass functions (GSMFs) from our modeling are in perfect agreement with the model-independent measurements in Paper III, although the current work extends the GSMFs to a much smaller stellar mass. Based on the GSMFs and the SHMRs, we derive the stellar mass completeness and halo occupation distributions for the LOWZ and CMASS samples, which are useful for correctly interpreting their cosmological measurements, such as galaxy–galaxy lensing and redshift space distortion.

Holographic energy density, dark energy sound speed, and tensions in cosmological parameters: H0 and S8

Interesting discrepancies in cosmological parameters are challenging the success of the ΛCDM model. Direct measurements of the Hubble constant H 0 using Cepheid variables and supernovae turn out to be higher than inferred from the Cosmic Microwave Background (CMB). Weak galaxy lensing surveys consistently report values of the strength of matter clustering σ 8 lower than values derived from the CMB in the context of ΛCDM. In this paper we address these discrepancies in cosmological parameters by considering Dark Energy (DE) as a fluid with evolving equation of state w de(z), constant sound speed squared ĉ s 2, and vanishing anisotropic stress σ. Our w de(z) is derived from the Holographic Principle and can consecutively exhibit radiation-like, matter-like, and DE-like behaviour, thus affecting the sound horizon and the comoving angular diameter distance, hence H 0. Here we show DE sound speed plays a part in the matter clustering behaviour through its effect on the evolution of the gravitational potential. We compute cosmological constraints using several data set combinations including primary CMB, CMB lensing, redshift-space-distortions, local distance-ladder, supernovae, and baryon acoustic oscillations. In our analysis we marginalise over ĉ s 2 and find ĉ s 2 = 1 is excluded at ≳ 3σ. For our baseline result including the whole data set we found H 0 and σ 8 in good agreement (within ≈ 2σ) with low redshift probes. Our constraint for the baryon energy density ω b is however in ≈ 3σ tension with BBN constraints. We conclude evolving DE also having non-standard clustering properties [e.g., ĉ s 2(z,k)] might be relevant for the solution of current discrepancies in cosmological parameters.

Joint analysis of Dark Energy Survey Year 3 data and CMB lensing from SPT and Planck . III. Combined cosmological constraints

We present cosmological constraints from the analysis of two-point correlation functions between galaxy positions and galaxy lensing measured in Dark Energy Survey (DES) Year 3 data and measurements of cosmic microwave background (CMB) lensing from the South Pole Telescope (SPT) and Planck. When jointly analyzing the DES-only two-point functions and the DES cross-correlations with SPT+Planck CMB lensing, we find Ωm=0.344±0.030 and S8≡σ8(Ωm/0.3)0.5=0.773±0.016, assuming ΛCDM. When additionally combining with measurements of the CMB lensing autospectrum, we find Ωm=0.306−0.021+0.018 and S8=0.792±0.012. The high signal-to-noise of the CMB lensing cross-correlations enables several powerful consistency tests of these results, including comparisons with constraints derived from cross-correlations only, and comparisons designed to test the robustness of the galaxy lensing and clustering measurements from DES. Applying these tests to our measurements, we find no evidence of significant biases in the baseline cosmological constraints from the DES-only analyses or from the joint analyses with CMB lensing cross-correlations. However, the CMB lensing cross-correlations suggest possible problems with the correlation function measurements using alternative lens galaxy samples, in particular the redmagic galaxies and high-redshift maglim galaxies, consistent with the findings of previous studies. We use the CMB lensing cross-correlations to identify directions for further investigating these problems.8 MoreReceived 27 June 2022Accepted 15 November 2022DOI:https://doi.org/10.1103/PhysRevD.107.023531© 2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCosmic microwave backgroundCosmological constantCosmological parametersDark energyDark matterEvolution of the UniverseLarge scale structure of the UniverseOptical, UV, & IR astronomyPhysical SystemsNormal galaxiesGravitation, Cosmology & Astrophysics

Joint analysis of Dark Energy Survey Year 3 data and CMB lensing from SPT andPlanck. I. Construction of CMB lensing maps and modeling choices

Joint analyses of cross-correlations between measurements of galaxy positions, galaxy lensing, and lensing of the cosmic microwave background (CMB) offer powerful constraints on the large-scale structure of the Universe. In a forthcoming analysis, we will present cosmological constraints from the analysis of such cross-correlations measured using Year 3 data from the Dark Energy Survey (DES), and CMB data from the South Pole Telescope (SPT) and Planck. Here we present two key ingredients of this analysis: (1) an improved CMB lensing map in the SPT-SZ survey footprint and (2) the analysis methodology that will be used to extract cosmological information from the cross-correlation measurements. Relative to previous lensing maps made from the same CMB observations, we have implemented techniques to remove contamination from the thermal Sunyaev Zel’dovich effect, enabling the extraction of cosmological information from smaller angular scales of the cross-correlation measurements than in previous analyses with DES Year 1 data. We describe our model for the cross-correlations between these maps and DES data, and validate our modeling choices to demonstrate the robustness of our analysis. We then forecast the expected cosmological constraints from the galaxy survey-CMB lensing auto and cross-correlations. We find that the galaxy-CMB lensing and galaxy shear-CMB lensing correlations will on their own provide a constraint on S8=σ8Ωm/0.3 at the few percent level, providing a powerful consistency check for the DES-only constraints. We explore scenarios where external priors on shear calibration are removed, finding that the joint analysis of CMB lensing cross-correlations can provide constraints on the shear calibration amplitude at the 5% to 10% level.13 MoreReceived 31 March 2022Accepted 12 December 2022DOI:https://doi.org/10.1103/PhysRevD.107.023529© 2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCosmic microwave backgroundCosmological parametersDark matterEvolution of the UniverseGravitational lensesLarge scale structure of the UniverseGravitation, Cosmology & Astrophysics

Joint analysis of Dark Energy Survey Year 3 data and CMB lensing from SPT andPlanck. II. Cross-correlation measurements and cosmological constraints

Cross-correlations of galaxy positions and galaxy shears with maps of gravitational lensing of the cosmic microwave background (CMB) are sensitive to the distribution of large-scale structure in the Universe. Such cross-correlations are also expected to be immune to some of the systematic effects that complicate correlation measurements internal to galaxy surveys. We present measurements and modeling of the cross-correlations between galaxy positions and galaxy lensing measured in the first three years of data from the Dark Energy Survey with CMB lensing maps derived from a combination of data from the 2500 deg2 SPT-SZ survey conducted with the South Pole Telescope and full-sky data from the Planck satellite. The CMB lensing maps used in this analysis have been constructed in a way that minimizes biases from the thermal Sunyaev Zel’dovich effect, making them well suited for cross-correlation studies. The total signal-to-noise of the cross-correlation measurements is 23.9 (25.7) when using a choice of angular scales optimized for a linear (nonlinear) galaxy bias model. We use the cross-correlation measurements to obtain constraints on cosmological parameters. For our fiducial galaxy sample, which consist of four bins of magnitude-selected galaxies, we find constraints of Ωm=0.272−0.052+0.032 and S8≡σ8Ωm/0.3=0.736−0.028+0.032 (Ωm=0.245−0.044+0.026 and S8=0.734−0.028+0.035) when assuming linear (nonlinear) galaxy bias in our modeling. Considering only the cross-correlation of galaxy shear with CMB lensing, we find Ωm=0.270−0.061+0.043 and S8=0.740−0.029+0.034. Our constraints on S8 are consistent with recent cosmic shear measurements, but lower than the values preferred by primary CMB measurements from Planck.12 MoreReceived 4 April 2022Accepted 30 September 2022DOI:https://doi.org/10.1103/PhysRevD.107.023530© 2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCosmic microwave backgroundCosmological parametersLarge scale structure of the UniverseGravitation, Cosmology & Astrophysics

Probing general relativity in galactic scales at z ∼ 0.3

ABSTRACT General Relativity (GR) has been successfully tested mainly at Solar system scales; however, galaxy-scale tests have become popular in the last few decades. In this work, we investigate the ηPPN parameter, which is commonly defined by the ratio of two scalar potentials that appears in the cosmological linearly perturbed metric. Under the assumption of GR and a vanish anisotropic stress tensor, ηPPN = 1. Using ALMA, HST, and VLT/MUSE data, we combine mass measurements, using gravitational lensing and galactic dynamics, for the SDP.81 lens galaxy (z = 0.299) to constrain ηPPN. By using a flexible and self-consistent mass profile, our fiducial model takes into account the contribution of the stellar mass and a dark matter halo to reconstruct the lensed galaxy and the spatially resolved stellar kinematics. We infer, after accounting for systematic uncertainties related to the mass model, cosmology, and kinematics, $\eta _{\text{PPN}} = 1.13^{+0.03}_{-0.03}\pm 0.20\, (\text{sys})$, which is in accordance with GR predictions. Better spectroscopy data are needed to push the systematics down and bring the uncertainty to the percentage level since our analysis shows that the main source of the systematics is related to kinematics, which heavily depends on the signal-to-noise ratio of the spectra.

Consistent and simultaneous modelling of galaxy clustering and galaxy–galaxy lensing with subhalo abundance matching

ABSTRACT The spatial distribution of galaxies and their gravitational lensing signal offer complementary tests of galaxy formation physics and cosmology. However, their synergy can only be fully exploited if both probes are modelled accurately and consistently. In this paper, we demonstrate that this can be achieved using an extension of Sub-Halo Abundance Matching extended model (SHAMe), dubbed SHAMe. Specifically, we use mock catalogues built from the TNG300 hydrodynamical simulation to show that SHAMe can simultaneously model the multipoles of the redshift–space galaxy correlation function and galaxy–galaxy lensing, without noticeable bias within the statistical sampling uncertainties of a SDSS volume and on scales r ∈ [0.6 − 30]h−1 Mpc. Modelling the baryonic processes in galaxy–galaxy lensing with a baryonification scheme allows SHAMe’s range of validity to be extended to r ∈ [0.1 − 30] h−1 Mpc. Remarkably, our model achieves this level of precision with just five free parameters beyond those describing the baryonification model. At fixed cosmology, we find that galaxy–galaxy lensing provides a general consistency test but little additional information on galaxy modelling parameters beyond that encoded in the redshift-space multipoles. It does, however, improve constraints if only the projected correlation function is available, as in surveys with only photometric redshifts. We expect SHAMe to have a higher fidelity across a wider range of scales than more traditional methods such as Halo Occupation Distribution modelling. Thus it should provide a significantly more powerful and more robust tool for analysing next-generation large-scale surveys.

RELICS: Small-scale Star Formation in Lensed Galaxies at z = 6–10

Detailed observations of star-forming galaxies at high redshift are critical to understanding the formation and evolution of the earliest galaxies. Gravitational lensing provides an important boost, allowing observations at physical scales unreachable in unlensed galaxies. We present three lensed galaxies from the RELICS survey at z phot = 6–10, including the most highly magnified galaxy at z phot ∼ 6 (WHL 0137–zD1, dubbed the Sunrise Arc), the brightest known lensed galaxy at z phot ∼ 6 (MACS 0308–zD1), and the only spatially resolved galaxy currently known at z phot ∼ 10 (SPT 0615–JD). The Sunrise Arc contains seven star-forming clumps with delensed radii as small as 3 pc, the smallest spatial scales yet observed in a z > 6 galaxy, while SPT 0615–JD contains features measuring a few tens of parsecs. MACS 0308–zD1 contains an r ∼ 30 pc clump with a star formation rate (SFR) of ∼3 M ⊙ yr−1, giving it an SFR surface density of ΣSFR ∼ 103 M ⊙ yr−1 kpc−2. These galaxies provide a unique window into small-scale star formation during the epoch of reionization. They will be excellent targets for future observations with JWST, including one approved program targeting the Sunrise Arc.

Photometric redshift estimation of strongly lensed galaxies

Context.Around 105strongly lensed galaxies are expected to be discovered with upcoming wide-field surveys such asEuclidand the LSST. Utilising these large samples to study the inner structure of lens galaxies requires source redshifts, which are needed to turn lens models into mass measurements. However, obtaining spectroscopic source redshifts for large samples of strong lenses is prohibitive with the current capacity of spectroscopic facilities.Aims.As an alternative to spectroscopy, we study the possibility of obtaining source photometric redshifts (photo-zs) for large samples of strong lenses. We pay particular attention to the problem of blending between the lens and the source light.Methods.Our strategy consists of deblending the source and lens light by simultaneously modelling the lens galaxy and the background source in all available photometric bands, and then feeding the derived source colours to a template-fitting photo-zalgorithm. We describe the lens and the source light with a Sérsic profile, and the lens mass with a singular isothermal ellipsoid. We first test our approach on a simulated sample of lenses. Then, we apply it to 23 real systems with broad-band photometry from the Hyper Suprime-Cam survey.Results.We identify the deviations of the lens light from a Sérsic profile and the contrast between the lens and source image as the main drivers of the source colour measurement error. Although the former is challenging to measure directly for real lenses, we find the latter to be sufficient for evaluating the accuracy of a measured source colour. We split the real sample based on the ratio Λ of the lens to source surface brightness measured at the image locations. In the Λ &lt; 1 regime, the photo-zoutlier fraction is 20%, and the accuracy of photo-zestimation is limited by the performance of the template-fitting process. In the opposite regime, the photo-zoutlier fraction is 75%, and the errors from the source colour measurements dominate the photo-zuncertainty.Conclusions.Measuring source photo-zs for lenses with Λ &lt; 1 poses no particular challenges compared to the isolated galaxy case. For systems with significant lens light contamination, however, improvements in the description of the surface brightness distribution of the lens are required: a single Sérsic model is not sufficiently accurate.

Gravitationally lensed quasars in Gaia – IV. 150 new lenses, quasar pairs, and projected quasars

ABSTRACT We report the spectroscopic follow-up of 175 lensed quasar candidates selected using Gaia Data Release 2 observations following Paper III of this series. Systems include 86 confirmed lensed quasars and a further 17 likely lensed quasars based on imaging and/or similar spectra. We also confirm 11 projected quasar pairs and 11 physical quasar pairs, while 25 systems are left as unclassified quasar pairs – pairs of quasars at the same redshift, which could be either distinct quasars or potential lensed quasars. Especially interesting objects include eight quadruply imaged quasars of which two have BAL sources, an apparent triple, and a doubly lensed LoBaL quasar. The source redshifts and image separations of these new lenses range between 0.65–3.59 and 0.78–6.23 arcsec, respectively. We compare the known population of lensed quasars to an updated mock catalogue at image separations between 1 and 4 arcsec, showing a very good match at z &amp;lt; 1.5. At z &amp;gt; 1.5, only 47 per cent of the predicted number are known, with 56 per cent of these missing lenses at image separations below 1.5 arcsec. The missing higher redshift, small-separation systems will have fainter lensing galaxies, and are partially explained by the unclassified quasar pairs and likely lenses presented in this work, which require deeper imaging. Of the 11 new reported projected quasar pairs, 5 have impact parameters below 10 kpc, almost tripling the number of such systems, which can probe the innermost regions of quasar host galaxies through absorption studies. We also report four new lensed galaxies discovered through our searches, with source redshifts ranging from 0.62 to 2.79.

The two z ∼ 13 galaxy candidates HD1 and HD2 are likely not lensed

ABSTRACT The discovery of two ultraviolet (UV)-bright galaxy candidates at z ∼ 13, HD1 and HD2, laid the foundation for a new race to study the early Universe. Previous investigations suggested that they are powered either by a supermassive black hole or by an extreme, transient burst of star formation. Given their uncertain nature, we investigate whether these sources could be lensed by a hitherto undetected, faint foreground galaxy. We find that at the current limiting magnitude with which HD1 and HD2 were imaged, there is only a $7.39{{\ \rm per\ cent}}$ probability they are strongly lensed by spherical deflectors and that the hypothetical lensing galaxy was too faint to be detected. Meanwhile, with the limiting magnitudes of the Hubble Space Telescope (HST) and JWST, the theoretical probability would drop precipitously to 0.058 and $0.0012{{\ \rm per\ cent}}$, respectively. We further find it unlikely that the luminosities of both sources can be accounted for by lensing that produces a single, resolved image with sufficiently high magnification. Alternatively, in the unlikely event that their brightness results from lensing by an elliptical isothermal galaxy, there is a $30.9 {{\ \rm per\ cent}}$ probability that the lensing galaxy is too faint to be observable at the current limiting magnitude. Future HST (JWST) imaging will drop this probability to $0.245 {{\ \rm per\ cent}}$ ($0.0025 {{\ \rm per\ cent}}$). In summary, while deep imaging with HST and JWST is required to discard the lensing hypothesis entirely, it is unlikely that the exceptional luminosity of the two z ∼ 13 sources can be accounted for by gravitational lensing.

Cosmological constraint precision of photometric and spectroscopic multi-probe surveys of China Space Station Telescope (CSST)

ABSTRACT As a Stage IV space-based telescope, the China Space Station Telescope (CSST) can perform photometric and spectroscopic surveys simultaneously to explore the Universe efficiently in extreme precision. In this work, we investigate several powerful CSST cosmological probes, including cosmic shear, galaxy–galaxy lensing, photometric and spectroscopic galaxy clustering, and number counts of galaxy clusters, and study the capability of these probes by forecasting the results of joint constraints on the cosmological parameters. By referring to real observational results, we generate mock data and estimate the measured errors based on CSST observational and instrumental designs. To study systematic effects on the results, we also consider a number of systematics in CSST photometric and spectroscopic surveys, such as the intrinsic alignment, shear calibration uncertainties, photometric redshift uncertainties, galaxy bias, non-linear effects, instrumental effects, etc. The Fisher matrix method is used to derive the constraint results on the cosmological and systematic parameters from individual or joint surveys. We find that the joint constraints achieved by including all these CSST cosmological probes can significantly improve the results from current observations by one order of magnitude at least, which gives Ωm and σ8 &amp;lt;1 per cent accuracy and w0 and wa &amp;lt;5 and 20 per cent accuracy, respectively. This indicates that CSST photometric and spectroscopic multi-probe surveys could provide powerful tools with which to explore the Universe and greatly improve the studies of relevant cosmological problems.

Clumpiness of lens galaxies as a window on dark matter

AbstractWhile the direct detection of the dark-matter particle remains very challenging, the physical properties of dark matter could potentially be constrained indirectly – by comparing the population characteristics of substructures in real galaxies with predictions from the phenomenological dark-matter models, such as cold, warm or self-interacting dark matter. Whereas these models are practically indistinguishable with respect to the expected abundance and statistical properties of massive galactic substructures, the critical difference lies in the low-mass regime ≲ 108M⊙. Galaxy-galaxy strong gravitational lensing provides a unique opportunity to search for gravitational signatures of such low-mass substructures in galaxies acting as a strong gravitational lens on a more distant background galaxy, serendipitously located along the same line of sight. In [Bayer et∼al.(2023)Bayer, Chatterjee, Koopmans, Vegetti, McKean, Treu, Fassnacht, and Glazebrook, Bayer et∼al.(2023)Bayer, Koopmans, McKean, Vegetti, Treu, Fassnacht, and Glazebrook, Bayer et∼al.(2023)Bayer, Vernardos, and Koopmans], we have recently introduced a novel approach to investigate the collective perturbative effect of low-mass substructures in the inner regions of massive elliptical lens galaxies and observationally constrain their power spectrum (on 1-10 kpc scales) based on the Fourier analysis of the associated surface-brightness anomalies in the lensed images (i.e., Einstein rings and gravitational arcs) observed with the Hubble Space Telescope. Here, we present a concise summary of the methodology, the encountered modelling challenges and the inferred observational constraints on the sub-galactic matter power spectrum. The future comparison of these results with predictions from hydrodynamical simulations might either verify the cold-dark-matter paradigm or require its substantial revision. Moreover, we demonstrate that the grid-based smooth lens modelling might model away surface-brightness anomalies caused by the presence of substructures in the lens galaxy and incorrectly interpret them as surface-brightness structure in the lensed background galaxy itself. If not properly understood and accounted for, such signal suppression might lead to severely biased constraints on the properties of substructures in galactic haloes.

Lensed radio arcs at milli-arcsecond resolution: Methods, science results, and current status

AbstractStrong gravitational lensing by galaxies provides us with a powerful laboratory for testing dark matter models. Various particle models for dark matter give rise to different small-scale distributions of mass in the lens galaxy, which can be differentiated with sensitive observations. Th. The sensitivity of a gravitational lens observation to the presence (or absence) of low-mass dark structures in the lens galaxy is determined mainly by the angular resolution of the instrument and the spatial structure of the source. Here, I discuss results from the analysis of a global VLBI observation of a gravitationally lensed radio jet. With an angular resolution better than 5 milli-arcseconds and a highly extended, spatially resolved source, we are able to place competitive constraints on the particle mass in fuzzy dark matter models using this single observation. I also discuss preliminary results from our analysis of warm dark matter models using this lens system.

Evidence for a milliparsec-separation supermassive binary black hole with quasar microlensing

We report periodic oscillations in the 15-year-long optical light curve of the gravitationally lensed quasar Q J0158−4325 at zs = 1.29. The signal is enhanced during a high magnification microlensing event of the quasar that the fainter lensed image, B, underwent between 2003 and 2010. We measure a period of Po = 172.6 ± 0.9 days, which translates to 75.4 ± 0.4 days in the quasar frame. The oscillations have a maximum amplitude of 0.26 ± 0.02 mag and decrease concurrently with the smooth microlensing amplitude. We explore four scenarios to explain the origin of the periodicity: (1) the high magnification microlensing event is due to a binary star in the lensing galaxy, (2) Q J0158−4325 contains a supermassive binary black hole system in its final dynamical stage before merging, (3) the quasar accretion disk contains a bright inhomogeneity in Keplerian motion around the black hole, and (4) the accretion disk is in precession. Of these four scenarios, only a supermassive binary black hole can account for both the short observed period and the amplitude of the signal, through the oscillation of the accretion disk towards and away from high-magnification regions of a microlensing caustic. The short measured period implies that the semi-major axis of the orbit is ∼10−3 pc and that and the coalescence timescale is tcoal ∼ 1000 yr, assuming that the decay of the orbit is solely powered by the emission of gravitational waves. The probability of observing a system so close to coalescence, in a sample of only 30 monitored lensed quasars, suggests either a much larger population of supermassive binary black holes than predicted or, more likely, that some other mechanism significantly increases the coalescence timescale. Three tests of the binary black hole hypothesis include: (i) the recurrence of oscillations in photometric monitoring during any future microlensing events in either image, (ii) spectroscopic detection of Doppler shifts (up to ∼0.01c) associated with optical emission in the vicinity of the black holes, and (iii) the detection of gravitational waves through pulsar timing array experiments, such as the Square Kilometre Array, which will have the sensitivity to detect the ∼100 nano-hertz emission.

Impact of Galaxy Dynamics on Modified Gravity Constraints from Strong Lensing Systems

AbstractGalaxy-galaxy strong lensing systems have been used in literature to test General Relativity by constraining the post-Newtonian parameter (γPPN). Nevertheless, these methods are prone to systematic errors, some of which arise from difficulties in modelling the dynamics of the lens galaxy. In this study, we address the systematic error related to the assumption of a constant anisotropy between the radial and tangential components of the velocity dispersion of stars within the lens galaxy, characterised by the parameter β. We considered two radial models for the anisotropy parameter, the Osipkov-Merritt and Mamon &amp; Lokas, as well three Gaussian priors for constant β. Our analysis showed that the choice of β has a strong impact on the value of γPPN, with radial models leading to lower values of this parameter.