Thermal Sunyaev-Zeldovich Effect Research Articles

Multiwavelength view of SPT-CL J2106-5844

Context. SPT-CL J2106-5844 is among the most massive galaxy clusters at z > 1 yet discovered. While initially used in cosmological tests to assess the compatibility with Λ Cold Dark Matter cosmology of such a massive virialized object at this redshift, more recent studies indicate SPT-CL J2106-5844 is undergoing a major merger and is not an isolated system with a singular, well-defined halo. Aims. We use sensitive, high spatial resolution measurements from the Atacama Large Millimeter/Submillimeter Array (ALMA) and Atacama Compact Array (ACA) of the thermal Sunyaev-Zeldovich (SZ) effect to reconstruct the pressure distribution of the intracluster medium in this system. These measurements are coupled with radio observations from the pilot survey for the Evolutionary Map of the Universe, using the Australian Square Kilometre Array Pathfinder (ASKAP), and the Australia Telescope Compact Array (ATCA) to search for diffuse nonthermal emission. Further, to better constrain the thermodynamic structure of the cluster, we complement our analysis with reprocessed archival Chandra observations. Methods. We jointly fit the ALMA and ACA SZ data in uv-space using a Bayesian forward modeling technique. The ASKAP and low-frequency ATCA data are processed and imaged to specifically highlight any potential diffuse radio emission. Results. In the ALMA and ACA SZ data, we reliably identify at high significance two main gas components associated with the mass clumps inferred from weak lensing. Our statistical test excludes at the ∼9.9σ level the possibility of describing the system with a single SZ component. While the components had been more difficult to identify in the X-ray data alone, we find that the bimodal gas distribution is supported by the X-ray hardness distribution. The EMU radio observations reveal a diffuse radio structure ∼400 kpc in projected extent along the northwest-southeast direction, indicative of strong activity from the active galactic nucleus within the brightest cluster galaxy. Interestingly, a putative optical star-forming filamentary structure detected in the HST image is in an excellent alignment with the radio structure, albeit on a smaller scale.

Breaking degeneracies with the Sunyaev-Zeldovich full bispectrum

Non-Gaussian (NG) statistics of the thermal Sunyaev-Zeldovich (tSZ) effect carry significant information which is not contained in the power spectrum. Here, we perform a joint Fisher analysis of the tSZ power spectrum and bispectrum to verify how much the full bispectrum can contribute to improve parameter constraints. We go beyond similar studies of this kind in several respects: first of all, we include the complete power spectrum and bispectrum (auto- and cross-) covariance in the analysis, computing all NG contributions; furthermore we consider a multi-component foreground scenario and model the effects of component separation in the forecasts; finally, we consider an extended set of both cosmological and intra-cluster medium parameters. We show that the tSZ bispectrum is very efficient at breaking parameter degeneracies, making it able to produce even stronger cosmological constraints than the tSZ power spectrum: e.g. the standard deviation on σ8 shrinks from σPS(σ8)=0.35 to σBS(σ8)=0.065 when we consider a multi-parameter analysis. We find that this is mostly due to the different response of separate triangle types (e.g. equilateral and squeezed) to changes in model parameters. While weak, this shape dependence is clearly non-negligible for cosmological parameters, and it is even stronger, as expected, for intra-cluster medium parameters.

Non-thermal Sunyaev–Zeldovich signal from radio galaxy lobes

ABSTRACT Energetic electrons in the lobes of radio galaxies make them potential sources for not only radio and X-rays but also Sunyaev–Zeldovich (SZ) distortions in the cosmic microwave background (CMB) radiation. Previous works have discussed the energetics of radio galaxy lobes, but assuming thermal SZ effect, coming from the non-thermal electron population. We use an improved evolutionary model for radio galaxy lobes to estimate the observed parameters such as the radio luminosity and intensity of SZ-distortions at the redshifts of observation. We, further, quantify the effects of various relevant physical parameters of the radio galaxies, such as the jet power, the time-scale over which the jet is active, the evolutionary time-scale for the lobe, etc. on the observed parameters. For current SZ observations towards galaxy clusters, we find that the non-thermal SZ distortions from radio lobes embedded in galaxy clusters can be non-negligible compared to the amount of thermal SZ distortion from the intracluster medium and, hence, cannot be neglected. We show that small and young (and preferably residing in a cluster environment) radio galaxies offer better prospects for the detection of the non-thermal SZ signal from these sources. We further discuss the limits on different physical parameters for some sources for which SZ effect has been either detected or upper limits are available. The evolutionary models enable us to obtain limits, previously unavailable, on the low energy cut-off of electron spectrum (pmin ∼ 1–2) in order to explain the recent non-thermal SZ detection. Finally, we discuss how future CMB experiments, which would cover higher frequency bands (>400 GHz), may provide clear signatures for non-thermal SZ effect.

Planck intermediate results

The largest temperature anisotropy in the cosmic microwave background (CMB) is the dipole, which has been measured with increasing accuracy for more than three decades, particularly with the Planck satellite. The simplest interpretation of the dipole is that it is due to our motion with respect to the rest frame of the CMB. Since current CMB experiments infer temperature anisotropies from angular intensity variations, the dipole modulates the temperature anisotropies with the same frequency dependence as the thermal Sunyaev-Zeldovich (tSZ) effect. We present the first, and significant, detection of this signal in the tSZ maps and find that it is consistent with direct measurements of the CMB dipole, as expected. The signal contributes power in the tSZ maps, which is modulated in a quadrupolar pattern, and we estimate its contribution to the tSZ bispectrum, noting that it contributes negligible noise to the bispectrum at relevant scales.

Turbulent density and pressure fluctuations in the stratified intracluster medium

ABSTRACT Turbulent gas motions are observed in the intracluster medium (ICM). The ICM is density-stratified, with the gas density being highest at the centre of the cluster and decreasing radially outwards. As a result of this, Kolmogorov (homogeneous, isotropic) turbulence theory does not apply to the ICM. The gas motions are instead explained by anisotropic stratified turbulence, with the stratification quantified by the perpendicular Froude number (Fr⊥). These turbulent motions are associated with density and pressure fluctuations, which manifest as perturbations in X-ray surface brightness maps of the ICM and as thermal Sunyaev–Zeldovich effect (SZ) fluctuations, respectively. In order to advance our understanding of the relations between these fluctuations and the turbulent gas velocities, we have conducted 100 high-resolution hydrodynamic simulations of stratified turbulence (2562 × 384–10242 × 1536 resolution elements), in which we scan the parameter space of subsonic rms Mach number ($\mathcal {M}$), Fr⊥, and the ratio of entropy and pressure scale heights (RPS = HP/HS), relevant to the ICM. We develop a new scaling relation between the standard deviation of logarithmic density fluctuations (σs, where s = ln (ρ/$\langle$ρ$\rangle$)), $\mathcal {M}$, and Fr⊥, which covers both the strongly stratified (Fr⊥ ≪ 1) and weakly stratified (Fr⊥ ≫ 1) turbulence regimes: $\sigma _{\rm s}^2=\ln (1+b^2\mathcal {M}^4+0.10/(\mathrm{Fr}_\perp +0.25/\sqrt{\mathrm{Fr}_\perp })^2\mathcal {M}^2R_{\rm PS})$, where b ∼ 1/3 for solenoidal turbulence driving studied here. We further find that logarithmic pressure fluctuations σ(ln P/ < P >) are independent of stratification and scale according to the relation $\sigma _{(\ln {\bar{P}})}^2=\ln (1+b^2\gamma ^2\mathcal {M}^4)$, where $\bar{P}=P/\left\langle P \right\rangle $ and γ is the adiabatic index of the gas. We have tested these scaling relations to be valid over the parameter ranges $\mathcal {M} = 0.01$–0.40, Fr⊥ = 0.04–10.0, and RPS = 0.33–2.33.

Probing the cluster pressure profile with thermal Sunyaev–Zeldovich effect and weak lensing cross-correlation

ABSTRACT We confront the universal pressure profile (UPP) proposed. with the recent measurement of the cross-correlation function of the thermal Sunyaev–Zeldovich (tSZ) effect from Planck and weak gravitational lensing measurement from the Red Cluster Sequence Lensing Survey. By using the halo model, we calculate the prediction of ξy−κ (lensing convergence and Compton-y parameter) and $\xi ^{y-\gamma _{\rm t}}$ (lensing shear and Compton-y parameter) and fit the UPP parameters by using the observational data. We find consistent UPP parameters when fixing the cosmology to either WMAP 9-yr or Planck 2018 best-fitting values. The best constrained parameter is the pressure profile concentration c500 = r500/rs, for which we find $c_{500} = 2.68^{+1.46}_{-0.96}$ (WMAP-9) and $c_{500} = 1.91^{+1.07}_{-0.65}$ (Planck-2018) for the $\xi ^{y-\gamma _t}$ estimator. The shape index for the intermediate radius region α parameter is constrained to $\alpha =1.75^{+1.29}_{-0.77}$ and $\alpha = 1.65^{+0.74}_{-0.5}$ for WMAP-9 and Planck-2018 cosmologies, respectively. Propagating the uncertainties of the UPP parameters to pressure profiles results in a factor of 3 uncertainty in the shape and magnitude. Further investigation shows that most of the signal of the cross-correlation comes from the low-redshift, inner halo profile (r ≤ rvir/2) with halo mass in the range of 1014–$10^{15}{\, {\rm M}_{\odot }}$, suggesting that this is the major regime that constitutes the cross-correlation signal between weak lensing and tSZ.

Detection of WHIM in the Planck data using Stack First approach

We detect the diffuse thermal Sunyaev-Zeldovich (tSZ) effect from the gas filaments between the Luminous Red Galaxy (LRG) pairs using a new approach relying on stacking the individual frequency maps. We apply and demonstrate our method on 08800 LRG pairs in the SDSS DR12 catalogue selected with an improved selection criterion that ensures minimal contamination by the Galactic CO emission as well as the tSZ signal from the clusters of galaxies. We first stack the Planck channel maps and then perform the Internal Linear Combination method to extract the diffuse ysz signal. Our Stack First approach makes the component separation a lot easier as the stacking greatly suppresses the noise and CMB contributions while the dust foreground becomes homogeneous in spectral-domain across the stacked patch. Thus one component, the CMB, is removed while the rest of the foregrounds are made simpler even before component separation algorithm is applied. We obtain the WHIM signal of ywhim=(3.78± 0.37)× 10−8 in the gas filaments, accounting for the electron overdensity of ∼ 13. We estimate the detection significance to be ≳ 10.2σ. This excess ysz signal is tracing the warm-hot intergalactic medium and it could account for most of the missing baryons of the Universe. We show that the Stack First approach is more robust to systematics and produces a cleaner signal compared to the methods relying on stacking the y-maps to detect weak tSZ signal currently being used by the cosmology community.

JoXSZ: Joint X-SZ fitting code for galaxy clusters

The thermal Sunyaev-Zeldovich (SZ) effect and the X-ray emission offer separate and highly complementary probes of the thermodynamics of the intracluster medium. We presentJoXSZ, the first publicly available code designed to jointly fit SZ and X-ray data coming from various instruments to derive the thermodynamic profiles of galaxy clusters.JoXSZfollows a fully Bayesian forward-modelling approach, accounts for the SZ calibration uncertainty, and for the X-ray background level systematic. It improves upon most current and not publicly available analyses because it adopts the correct Poisson-Gauss expression for the joint likelihood, makes full use of the information contained in the observations, even in the case of missing values within the datasets, has a more inclusive error budget, and adopts a consistent temperature in the various parts of the code, allowing for differences between X-ray and SZ gas-mass weighted temperatures when required by the user.JoXSZaccounts for beam smearing and data analysis transfer function, accounts for the temperature and metallicity dependencies of the SZ and X-ray conversion factors, adopts flexible parametrisation for the thermodynamic profiles, and on user request, allows either adopting or relaxing the assumption of hydrostatic equilibrium (HE). When HE holds,JoXSZuses a physical (positive) prior on the radial derivative of the enclosed mass and derives the mass profile and overdensity radiirΔ. For these reasons,JoXSZgoes beyond simple SZ and electron density fits. We illustrate the use ofJoXSZby combining Chandra and NIKA data of the high-redshift cluster CL J1226.9+3332. The code is written in Python, it is fully documented, and the users are free to customise their analysis in accordance with their needs and requirements.JoXSZis publicly available on GitHub.

Relativistic SZ temperature scaling relations of groups and clusters derived from the BAHAMAS and MACSIS simulations

ABSTRACT The Sunyaev–Zeldovich (SZ) effect has long been recognized as a powerful cosmological probe. Using the BAHAMAS and MACSIS simulations to obtain ${\gt }10\, 000$ simulated galaxy groups and clusters, we compute three temperature measures and quantify the differences between them. The first measure is related to the X-ray emission of the cluster, while the second describes the non-relativistic thermal SZ (tSZ) effect. The third measure determines the lowest order relativistic correction to the tSZ signal, which is seeing increased observational relevance. Our procedure allows us to accurately model the relativistic SZ (rSZ) contribution and we show that a ${\gtrsim}10\!-\!40{{\ \rm per\ cent}}$ underestimation of this rSZ cluster temperature is expected when applying standard X-ray relations. The correction also exhibits significant mass and redshift evolution, as we demonstrate here. We present the mass dependence of each temperature measure alongside their profiles and a short analysis of the temperature dispersion as derived from the aforementioned simulations. We also discuss a new relation connecting the temperature and Compton-y parameter, which can be directly used for rSZ modelling. Simple fits to the obtained scaling relations and profiles are provided. These should be useful for future studies of the rSZ effect and its relevance to cluster cosmology.

New constraints on the mass bias of galaxy clusters from the power spectra of the thermal Sunyaev–Zeldovich effect and cosmic shear

Abstract The thermal Sunyaev–Zeldovich (tSZ) power spectrum is a powerful probe of the present-day amplitude of matter density fluctuations, and has been measured up to $\ell \approx 10^3$ from the Planck data. The largest systematic uncertainty in the interpretation of this data is the so-called “mass bias” parameter B, which relates the true halo mass to the mass proxy used by the Planck team as $M\,_{\rm 500c}^{\rm Planck}=M\,_{\rm 500c}^{\rm true}/B$. Since the power spectrum of the cosmic weak lensing shear is also sensitive to the amplitude of matter density fluctuations via $S_8\equiv \sigma _8 \Omega _{\rm m}^{\alpha }$ with $\alpha \sim 0.5$, we can break the degeneracy between the mass bias and the cosmological parameters by combining the tSZ and cosmic shear power spectra. In this paper, we perform a joint likelihood analysis of the tSZ power spectrum from Planck and the cosmic shear power spectrum from Subaru Hyper Suprime-Cam. Our analysis does not use the primordial cosmic microwave background (CMB) information. We obtain a new constraint on the mass bias as $B = 1.37 ^{+0.15}_{-0.23}$ or $(1-b) = B^{-1}=0.73^{+0.08}_{-0.13}$ ($68\%$ confidence limit), for $\sigma _8 < 0.9$. This value of B is lower than that needed to reconcile the tSZ data with the primordial CMB and CMB lensing data, i.e., $B = 1.64 \pm 0.19$, but is consistent with the mass bias expected from hydrodynamical simulations, $B = 1.28 \pm 0.20$. Thus our results indicate that the mass bias is consistent with the non-thermal pressure support from mass accretion of galaxy clusters via the cosmic structure formation, and that the cosmologies inferred from the tSZ and the cosmic shear are consistent with each other.

Improving constraints on fundamental physics parameters with the clustering of Sunyaev-Zeldovich selected galaxy clusters

Upcoming millimeter experiments that probe the cosmic microwave background (CMB) will observe tens of thousands of galaxy clusters through the thermal Sunyaev-Zeldovich (tSZ) effect. tSZ selected clusters are powerful probes of cosmological models, as they trace the late-time growth of structure. Late-time structure growth is highly sensitive to extensions to the standard cosmological model ($\Lambda$CDM), such as the sum of the neutrino masses, the dark energy equation of state, and modifications to general relativity. The nominal statistic used for cluster observations is their abundances as a function of redshift. We investigate what additional cosmological information is gained after including the clustering signal of clusters, the cluster power spectrum. We forecast the cluster power spectra for the upcoming Simons Observatory and a CMB Stage-4-like experiment and find that the cluster power spectrum reduces marginalized constraints on the dark energy equation of state by $3$--$12\%$ and the growth index by $5$--$8\%$, for example. We present the constraints using a generalized figure of merit and find improvements ranging from $12$--$18\%$ for extensions, $12$--$19\%$ for the astrophysical nuisance parameters, and $14$--$25\%$ for $\Lambda$CDM parameters. We also find that if the bias of clusters as a tracer of the matter density can be measured to within $3\%$ or better, these improvements can be increased by up to a factor of $6$. We discuss the possibility of utilizing the clustering signal to address specific systematic uncertainties present in cluster abundance measurements.

Sloshing of Galaxy Cluster Core Plasma in the Presence of Self-interacting Dark Matter

Abstract The “sloshing” of the cold gas in the cores of relaxed clusters of galaxies is a widespread phenomenon evidenced by the presence of spiral-shaped “cold fronts” in X-ray observations of these systems. In simulations, these flows of cold gas readily form via interactions of the cluster core with small subclusters, due to a separation of the cold gas from the dark matter (DM), due to their markedly different collisionalities. In this work, we use numerical simulations to investigate the effects of increasing the DM collisionality on sloshing cold fronts in a cool-core cluster. For clusters in isolation, the formation of a flat DM core via self-interactions results in modest adiabatic expansion and cooling of the core gas. In merger simulations, cold fronts form in the same manner as in previous simulations, but the flattened potential in the core region enables the gas to expand to larger radii in the initial stages. Upon infall, the subclusters DM mass decreases via collisions, reducing its influence on the core. Thus, the sloshing gas moves slower, inhibiting the growth of fluid instabilities relative to simulations where the DM cross section is zero. This also inhibits turbulent mixing and the increase in entropy that would otherwise result. For values of the cross section σ/m ≳ 1, subclusters do not survive as self-gravitating structures for more than two core passages. Additionally, separations between the peaks in the X-ray emissivity and thermal Sunyaev–Zeldovich effect signals during sloshing may place constraints on DM self-interactions.

An ALMA+ACA measurement of the shock in the Bullet Cluster

Context. The thermal Sunyaev-Zeldovich (SZ) effect presents a relatively new tool for characterizing galaxy cluster merger shocks, traditionally studied through X-ray observations. Widely regarded as the “textbook example” of a cluster merger bow shock, the western, most-prominent shock front in the Bullet Cluster (1E0657-56) represents the ideal test case for such an SZ study. Aims. We aim to characterize the shock properties using deep, high-resolution interferometric SZ effect observations in combination with priors from an independent X-ray analysis. Methods. Our analysis technique relies on the reconstruction of a parametric model for the SZ signal by directly and jointly fitting data from the Atacama Large Millimeter/submillimeter Array (ALMA) and Atacama Compact Array (ACA) in Fourier space. Results. The ALMA+ACA data are primarily sensitive to the electron pressure difference across the shock front. To estimate the shock Mach number ℳ, this difference can be combined with the value for the upstream electron pressure derived from an independent Chandra X-ray analysis. In the case of instantaneous electron-ion temperature equilibration, we find ℳ = 2.08−0.12+0.12, in ≈ 2.4σ tension with the independent constraint from Chandra, MX = 2.74 ± 0.25. The assumption of purely adiabatic electron temperature change across the shock leads to ℳ = 2.53−0.25+0.33, in better agreement with the X-ray estimate ℳX = 2.57 ± 0.23 derived for the same heating scenario. Conclusion. We have demonstrated that interferometric observations of the thermal SZ effect provide constraints on the properties of the shock in the Bullet Cluster that are highly complementary to X-ray observations. The combination of X-ray and SZ data yields a powerful probe of the shock properties, capable of measuring ℳ and addressing the question of electron-ion equilibration in cluster shocks. Our analysis is however limited by systematics related to the overall cluster geometry and the complexity of the post-shock gas distribution. To overcome these limitations, a simultaneous, joint-likelihood analysis of SZ and X-ray data is needed.

Finding the missing baryons with fast radio bursts and Sunyaev-Zeldovich maps

Almost a third of the cosmic baryons are "missing" at low redshifts, as they reside in the invisible warm-hot intergalactic medium (WHIM). The thermal Sunyaev-Zeldovich (tSZ) effect, which measures the line-of-sight integral of the plasma pressure, can potentially detect this WHIM, although its expected signal is hidden below the noise. Extragalactic dispersion measures (DMs)---obtained through observations of fast radio bursts (FRBs)---are excellent tracers of the WHIM, as they measure the column density of plasma, regardless of its temperature. Here we propose cross correlating DMs and tSZ maps as a new way to find and characterize the missing baryons in the WHIM. Our method relies on the precise ($\sim$ arcminute) angular localization of FRBs to assign each burst a DM and a $y$ parameter. We forecast that the signal from the WHIM should be confidently detected in a cross-correlation analysis of $\sim10^4$ FRBs, expected to be gathered in a year of operation of the upcoming CHIME and HIRAX radio arrays, confirming the recent tentative detections of filamentary WHIM. Using this technique, future CMB probes (which might lower the tSZ noise) could determine both the temperature of the WHIM and its evolution to within tens of percent. Altogether, DM-tSZ cross correlations hold great promise for studying the baryons in the local Universe.

Non-Gaussianity of secondary anisotropies from ACTPol and Planck

Most secondary sources of cosmic microwave background anisotropy (radio sources, dusty galaxies, thermal Sunyaev Zel'dovich distortions from hot gas, and gravitational lensing) are highly non-Gaussian. Statistics beyond the power spectrum are therefore potentially important sources of information about the physics of these processes. We combine data from the Atacama Cosmology Telescope and with data from the Planck satellite (only using Planck data in the overlapping region) to constrain the amplitudes of a set of theoretical bispectrum templates from the thermal Sunyaev-Zeldovich (tSZ) effect, dusty star-forming galaxies (DSFGs), gravitational lensing, and radio galaxies. We make a strong detection of radio galaxies (>5σ) and have hints of non-Gaussianity arising from the tSZ effect, DSFGs, from cross-correlations between the tSZ effect and DSFGs and from cross-correlations among the tSZ effect, DSFGs and radio galaxies. These results suggest that the same halos host radio sources, DSFGs, and have tSZ signal. We present a new method to calculate the non-Gaussian contributions to the template covariances. Using this method we find significant non-Gaussian contributions to the variance and covariance of our templates, with templates involving the tSZ effect most effected. Strong degeneracies exist between the various sources at the current noise levels. In light of these degeneracies, combined with theoretical uncertainty in the templates, these results are a demonstration of this technique. With these caveats, we demonstrate the utility of future bispectrum measurements by using the tSZ bispectrum measurement to constrain a combination of the amplitude of matter fluctuations and the matter density to be σ8 Ωm0.17=0.65+0.05−0.06. Improvements in signal to noise from upcoming Advanced ACT, SPT-3G, Simons Observatory, and CMB-S4 observations will enable the separation of bispectrum components and robust constraints on cosmological parameters.

Exploring the thermal energy contents of the intergalactic mediumwith the Sunyaev–Zeldovich effect

We examine the thermal energy contents of the intergalactic medium (IGM) over three orders of magnitude in both mass density and gas temperature using thermal Sunyaev–Zeldovich effect (tSZE). The analysis is based on Planck tSZE map and the cosmic density field, reconstructed in the Sloan Digital Sky Survey Data Release 7 volume and sampled on a grid of cubic cells of |$(1\, h^{-1}{\rm Mpc})^3$|⁠, together with a matched filter technique employed to maximize the signal to noise. Our results show that the pressure–density relation of the IGM is roughly a power law given by an adiabatic equation of state, with an indication of steepening at densities higher than about 10 times the mean density of the Universe. The implied average gas temperature is |$\sim$|104 K in regions of mean density, |$\rho _{\rm m} \sim {\overline{\rho }}_{\rm m}$|⁠, increasing to about |$10^5\, {\rm K}$| for |$\rho _{\rm m} \sim 10\, {\overline{\rho }}_{\rm m}$|⁠, and to |$\gt$|106 K for |$\rho _{\rm m} \sim 100\, {\overline{\rho }}_{\rm m}$|⁠. At a given density, the thermal energy content of the IGM is also found to be higher in regions of stronger tidal fields, likely due to shock heating by the formation of large-scale structure and/or feedback from galaxies and active galactic nuclei. A comparison of the results with hydrodynamic simulations suggests that the current data can already provide interesting constraints on galaxy formation.

Joint analysis of the thermal Sunyaev–Zeldovich effect and 2MASS galaxies: probing gas physics in the local Universe and beyond

We present a first joint analysis of the power spectra of the thermal Sunyaev-Zeldovich (tSZ) effect measured by the Planck and the number density fluctuations of galaxies in the 2MASS redshift survey (2MRS) catalog, including their cross-correlation. Combining these measurements with the cosmic microwave background (CMB) data and CMB lensing of Planck assuming a flat $\Lambda$CDM model, we constrain the mass bias parameter as $B = 1.54 \pm 0.098\;(1\sigma)$ [$(1-b) = 0.649 \pm 0.041$, where $(1-b) \equiv B^{-1}$], i.e., the Planck cluster mass should be $35\%$ lower than the true mass. The mass bias determined by the 2MRS-tSZ cross-power spectrum alone is consistent with that determined by the tSZ auto-power spectrum alone, suggesting that this large mass bias is not due to obvious systematics in the tSZ data. We find that the 2MRS-tSZ cross-power spectrum is more sensitive to less massive halos than the tSZ auto-power spectrum and it significantly improves a constraint on the mass dependence of the mass bias. The redshift dependence is not strongly constrained since the multipole range in which high redshift clusters mainly contribute to the tSZ auto is dominated by the contaminating sources. We conclude that no strong mass or redshift evolution of the mass bias is needed to explain the data.

Impact of SZ cluster residuals in CMB maps and CMB–LSS cross-correlations

Residual foreground contamination in cosmic microwave background (CMB) maps, such as the residual contamination from thermal Sunyaev-Zeldovich (SZ) effect in the direction of galaxy clusters, can bias the cross-correlation measurements between CMB and large-scale structure optical surveys. It is thus essential to quantify those residuals and, if possible, to null out SZ cluster residuals in CMB maps. We quantify for the first time the amount of SZ cluster contamination in the released Planck 2015 CMB maps through (i) the stacking of CMB maps in the direction of the clusters, and (ii) the computation of cross-correlation power spectra between CMB maps and the SDSS-IV large-scale structure data. Our cross-power spectrum analysis yields a $30\sigma$ detection at the cluster scale ($\ell=1500-2500$) and a $39\sigma$ detection on larger scales ($\ell=500-1500$) due to clustering of SZ clusters, giving an overall $54\sigma$ detection of SZ cluster residuals in the Planck CMB maps. The Planck 2015 NILC CMB map is shown to have $44\pm4\%$ of thermal SZ foreground emission left in it. Using the 'Constrained ILC' component separation technique, we construct an alternative Planck CMB map, the 2D-ILC map, which is shown to have negligible SZ contamination, at the cost of being slightly more contaminated by Galactic foregrounds and noise. We also discuss the impact of the SZ residuals in CMB maps on the measurement of the ISW effect, which is shown to be negligible based on our analysis.

Extracting foreground-obscured μ-distortion anisotropies to constrain primordial non-Gaussianity

Correlations between cosmic microwave background (CMB) temperature, polarization and spectral distortion anisotropies can be used as a probe of primordial non-Gaussianity. Here, we perform a reconstruction of $\mu$-distortion anisotropies in the presence of Galactic and extragalactic foregrounds, applying the so-called Constrained ILC component separation method to simulations of proposed CMB space missions (PIXIE, LiteBIRD, CORE, PICO). Our sky simulations include Galactic dust, Galactic synchrotron, Galactic free-free, thermal Sunyaev-Zeldovich effect, as well as primary CMB temperature and $\mu$-distortion anisotropies, the latter being added as correlated field. The Constrained ILC method allows us to null the CMB temperature anisotropies in the reconstructed $\mu$-map (and vice versa), in addition to mitigating the contaminations from astrophysical foregrounds and instrumental noise. We compute the cross-power spectrum between the reconstructed (CMB-free) $\mu$-distortion map and the ($\mu$-free) CMB temperature map, after foreground removal and component separation. Since the cross-power spectrum is proportional to the primordial non-Gaussianity parameter, $f_{\rm NL}$, on scales $k\simeq 740$ Mpc$^{-1}$, this allows us to derive $f_{\rm NL}$-detection limits for the aforementioned future CMB experiments. Our analysis shows that foregrounds degrade the theoretical detection limits (based mostly on instrumental noise) by more than one order of magnitude, with PICO standing the best chance at placing upper limits on scale-dependent non-Gaussianity. We also discuss the dependence of the constraints on the channel sensitivities and chosen bands. Like for $B$-mode polarization measurements, extended coverage at frequencies $\nu\lesssim 40\,{\rm GHz}$ and $\nu\gtrsim 400\,{\rm GHz}$ provides more leverage than increased channel sensitivity.

Exploring cosmic origins with CORE: Cluster science

We examine the cosmological constraints that can be achieved with a galaxy cluster survey with the future CORE space mission. Using realistic simulations of the millimeter sky, produced with the latest version of the Planck Sky Model, we characterize the CORE cluster catalogues as a function of the main mission performance parameters. We pay particular attention to telescope size, key to improved angular resolution, and discuss the comparison and the complementarity of CORE with ambitious future ground-based CMB experiments that could be deployed in the next decade. A possible CORE mission concept with a 150 cm diameter primary mirror can detect of the order of 50,000 clusters through the thermal Sunyaev-Zeldovich effect (SZE). The total yield increases (decreases) by 25% when increasing (decreasing) the mirror diameter by 30 cm. The 150 cm telescope configuration will detect the most massive clusters (>1014 M⊙) at redshift z>1.5 over the whole sky, although the exact number above this redshift is tied to the uncertain evolution of the cluster SZE flux-mass relation; assuming self-similar evolution, CORE will detect 0∼ 50 clusters at redshift z>1.5. This changes to 800 (200) when increasing (decreasing) the mirror size by 30 cm. CORE will be able to measure individual cluster halo masses through lensing of the cosmic microwave background anisotropies with a 1-σ sensitivity of 4×1014 M⊙, for a 120 cm aperture telescope, and 1014 M⊙ for a 180 cm one. From the ground, we estimate that, for example, a survey with about 150,000 detectors at the focus of 350 cm telescopes observing 65% of the sky would be shallower than CORE and detect about 11,000 clusters, while a survey with the same number of detectors observing 25% of sky with a 10 m telescope is expected to be deeper and to detect about 70,000 clusters. When combined with the latter, CORE would reach a limiting mass of M500 ∼ 2−3 × 1013 M⊙ and detect 220,000 clusters (5 sigma detection limit). Cosmological constraints from CORE cluster counts alone are competitive with other scheduled large scale structure surveys in the 2020's for measuring the dark energy equation-of-state parameters w0 and wa (σw0=0.28, σwa=0.31). In combination with primary CMB constraints, CORE cluster counts can further reduce these error bars on w0 and wa to 0.05 and 0.13 respectively, and constrain the sum of the neutrino masses, Σ mν, to 39 meV (1 sigma). The wide frequency coverage of CORE, 60–600 GHz, will enable measurement of the relativistic thermal SZE by stacking clusters. Contamination by dust emission from the clusters, however, makes constraining the temperature of the intracluster medium difficult. The kinetic SZE pairwise momentum will be extracted with 0S/N=7 in the foreground-cleaned CMB map. Measurements of TCMB(z) using CORE clusters will establish competitive constraints on the evolution of the CMB temperature: (1+z)1−β, with an uncertainty of σβ ≲ 2.7× 10−3 at low redshift (z ≲ 1). The wide frequency coverage also enables clean extraction of a map of the diffuse SZE signal over the sky, substantially reducing contamination by foregrounds compared to the Planck SZE map extraction. Our analysis of the one-dimensional distribution of Compton-y values in the simulated map finds an order of magnitude improvement in constraints on σ8 over the Planck result, demonstrating the potential of this cosmological probe with CORE.