We have performed a multi-wavelength analysis of two galaxy cluster systems selected with the thermal Sunyaev-Zel’dovich (tSZ) effect and composed of cluster pairs and an inter-cluster filament. We ...have focused on one pair of particular interest: A399-A401 at redshift z ~ 0.073 seperated by 3 Mpc. We have also performed the first analysis of one lower-significance newly associated pair: A21-PSZ2 G114.09-34.34 at z ~ 0.094, separated by 4.2 Mpc. We have characterised the intra-cluster gas using the tSZ signal from Planck and, when possible, the galaxy optical and infrared (IR) properties based on two photometric redshift catalogues: 2MPZ and WISExSCOS. From the tSZ data, we measured the gas pressure in the clusters and in the inter-cluster filaments. In the case of A399-A401, the results are in perfect agreement with previous studies and, using the temperature measured from the X-rays, we further estimate the gas density in the filament and find n0 = (4.3 ± 0.7) × 10-4 cm-3. The optical and IR colour–colour and colour–magnitude analyses of the galaxies selected in the cluster system, together with their star formation rate, show no segregation between galaxy populations, both in the clusters and in the filament of A399-A401. Galaxies are all passive, early type, and red and dead. The gas and galaxy properties of this system suggest that the whole system formed at the same time and corresponds to a pre-merger, with a cosmic filament gas heated by the collapse. For the other cluster system, the tSZ analysis was performed and the pressure in the clusters and in the inter-cluster filament was constrained. However, the limited or nonexistent optical and IR data prevent us from concluding on the presence of an actual cosmic filament or from proposing a scenario.
The reionisation of the Universe is a process that is thought to have ended around z ~ 6, as inferred from spectroscopy of distant bright background sources, such as quasars (QSO) and gamma-ray burst ...(GRB) after glows. We aim to measure the degree of ionisation of the intergalactic medium (1GM) between z = 5.02-5.84 and to study the chemical abundance pattern and dust content of its host galaxy. We estimated the UV continuum of the GRB afterglow using a power-law extrapolation, then measured the flux decrement due to absorption at Lyalpha, beta, and gamma wavelength regions. Our measurements confirm that the Universe is already predominantly ionised over the redshift range probed in this work, but was slightly more neutral at z > 5.6. GRBs are useful probes of the ionisation state of the 1GM in the early Universe, but because of internal scatter we need a larger statistical sample to draw robust conclusions.
The thermal Sunyaev-Zel’dovich (tSZ) effect and X-ray emission from galaxy clusters have been used extensively to constrain cosmological parameters. These constraints are highly sensitive to the ...relations between cluster masses and observables (tSZ and X-ray fluxes). The cross-correlation of tSZ and X-ray data is thus a powerful tool, in addition of tSZ and X-ray based analysis, for testing our modeling of both tSZ and X-ray emission from galaxy clusters. We chose to explore this cross-correlation because both emissions trace the hot gas in galaxy clusters and thus constitute one of the easiest correlations that can be studied. We present a complete modeling of the cross-correlation between tSZ effect and X-ray emission from galaxy clusters and focus on the dependencies with cluster scaling laws and cosmological parameters. We show that current knowledge of cosmological parameters and scaling-law parameters leads to uncertainties of 48% on the overall normalization of the tSZ-X cross-correlation power spectrum. We present the expected signal-to-noise ratio for the tSZ-X cross-correlation angular power spectrum and consider the sensitivity of actual tSZ and X-ray surveys from Planck-like data and ROSAT. We demonstrate that this signal-to-noise can reach 31.5 in a realistic situation, leading to a constraint on the amplitude of tSZ-X cross-correlation up to 3.2%, which is ten times better than actual modeling limitations. Consequently, using it in addition to other probes of cosmological parameters and scaling relations, we show that the tSZ-X is a powerful probe that constrains the cosmological parameters of scaling relations.
Aims. The Planck catalogues of Sunyaev –Zeldovich (SZ) sources, PSZ1 and PSZ2, are the largest catalogues of galaxy clusters selected through their SZ signature in the full sky. In 2013, we started a ...long-term observational programme at Canary Island observatories with the aim of validating ∼500 unconfirmed SZ sources. In this work we present results of the initial pre-screening of possible cluster counterparts using photometric and spectroscopic data of the Sloan Digital Sky Survey DR12. Our main aim is to identify previously unconfirmed PSZ2 cluster candidates and to contribute in the determination of the actual purity and completeness of Planck SZ source sample. Methods. Using the latest version of the PSZ2 catalogue, we selected all sources overlapping with the SDSS DR12 footprint and without redshift information. We validated these cluster fields following optical criteria (mainly distance with respect to the Planck pointing, magnitude of the brightest cluster galaxy, and cluster richness), and combined these criteria with the profiles of the Planck Compton y-maps. This combined procedure allows for a more robust identification of optical counterparts compared to simply cross-matching with existing SDSS cluster catalogues that have been constructed from earlier SDSS data releases. Results. The sample contains new redshifts for 37 Planck galaxy clusters that were not included in the original release of PSZ2 Planck catalogue. We detect three cases as possible multiple counterparts. We show that a combination of all available information (optical images and profile of SZ signal) can provide correct associations between the observed Planck SZ source and the optically identified cluster. We also show that Planck SZ detection is very sensitive even to high-z (z > 0.5) clusters. In addition, we also present updated spectroscopic information for 34 Planck PSZ1 sources (33 previously photometrically confirmed and 1 new identification).
The cosmological surveys that are planned for the current decade will provide us with unparalleled observations of the distribution of galaxies on cosmic scales, by means of which we can probe the ...underlying large-scale structure (LSS) of the Universe. This will allow us to test the concordance cosmological model and its extensions. However, precision pushes us to high levels of accuracy in the theoretical modelling of the LSS observables so that no biases are introduced into the estimation of the cosmological parameters. In particular, effects such as redshift-space distortions (RSD) can become relevant in the computation of harmonic-space power spectra even for the clustering of the photometrically selected galaxies, as has previously been shown in literature. In this work, we investigate the contribution of linear RSD, as formulated in the Limber approximation by a previous work, in forecast cosmological analyses with the photometric galaxy sample of the survey. We aim to assess their impact and to quantify the bias on the measurement of cosmological parameters that would be caused if this effect were neglected. We performed this task by producing mock power spectra for photometric galaxy clustering and weak lensing as is expected to be obtained from the survey. We then used a Markov chain Monte Carlo approach to obtain the posterior distributions of cosmological parameters from these simulated observations. When the linear RSD is neglected, significant biases are caused when galaxy correlations are used alone and when they are combined with cosmic shear in the so-called 3times 2pt approach. These biases can be equivalent to as much as $5\ when an underlying Lambda CDM cosmology is assumed When the cosmological model is extended to include the equation-of-state parameters of dark energy, the extension parameters can be shifted by more than $1\ sigma$.
If dark energy introduces an acceleration in the universal expansion then large-scale gravitational potential wells should be shrinking, causing a blueshift in the cosmic microwave background (CMB) ...photons that cross such structures integrated Sachs-Wolfe (ISW) effect. Galaxy clusters are known to probe those potential wells. In these objects, CMB photons also experience inverse Compton scattering off the hot electrons of the intracluster medium and this results in a distortion with a characteristic spectral signature of the CMB spectrum the so-called thermal Sunyaev-Zel'dovich (tSZ) effect. Since both the ISW and the tSZ effects take place in the same potential wells, they must be spatially correlated. We present how this cross-ISW-tSZ signal can be detected in a CMB data contained way by using the frequency dependence of the tSZ effect in multifrequency CMB experiments like Planck, without requiring the use of external large-scale structure tracers data. We find that by masking low-redshift clusters, the shot noise level decreases significantly, boosting the signal-to-noise ratio of the ISW-tSZ cross-correlation. Nevertheless, in a more realistic case in which we only mask the clusters that could be detected by Planck, detection of the ISW-tSZ cross-signal is expected to reach only low significance (1.5σ) unless external cluster catalogues are used to mask the tSZ signal coming from lower mass clusters at low z that do not significantly contribute to the signal but to the shot noise. We also find that galactic and extragalactic dust residuals must be kept at or below the level of ∼0.04 (μK)2 at ℓ= 10, a limit that is a factor of a few below Planck's expectations for foreground subtraction. If this is achieved, CMB observations of the ISW-tSZ cross-correlation should also provide an independent probe for the existence of dark energy and the amplitude of density perturbations.
We present the first detection of the cross-correlation angular power spectrum between the thermal Sunyaev-Zel’dovich (tSZ) effect and the X-ray emission over the full sky. The tSZ effect and X-rays ...are produced by the same hot gas within groups and clusters of galaxies, which creates a naturally strong correlation between them that can be used to boost the joint signal and derive cosmological parameters. We computed the correlation between the ROSAT All Sky Survey in the 0.5−2 keV energy band and the tSZ effect reconstructed from six Planck all-sky frequency maps between 70 and 545 GHz. We detect a significant correlation over a wide range of angular scales. In the range 50 <ℓ< 2000, the cross-correlation of X-rays to tSZ is detected at an overall significance of 28σ. As part of our systematic study, we performed a multi-frequency modelling of the AGN contamination and the correlation between cosmic infra-red background and X-rays. Taking advantage of the strong dependence of the cross-correlation signal on the amplitude of the power spectrum, we constrained σ8 = 0.804 ± 0.037, where modelling uncertainties dominate statistical and systematic uncertainties. We also derived constraints on the mass indices of scaling relations between the halo mass and X-ray luminosity, L500 − M500, and SZ signal, Y500 − M500, asz + ax = 3.37 ± 0.09, and on the indices of the extra-redshift evolution, \hbox{$\beta_{\rm sz} + \beta_{\rm x} = 0.4^{+0.4}_{-0.5}$}βsz+βx=0.4-0.5+0.4.
The Planck catalogue of SZ sources limits itself to a significance threshold of 4.5 to ensure a low contamination rate by false cluster candidates. This means that only the most massive clusters at ...redshift z> 0.5, and in particular z> 0.7, are expected to enter into the catalogue, with a large number of systems in that redshift regime being expected around and just below that threshold. In this paper, we follow-up a sample of SZ sources from the Planck SZ catalogues from 2013 and 2015. In the latter maps, we consider detections around and at lower significance than the threshold adopted by the Planck Collaboration. To keep the contamination rate low, our 28 candidates are chosen to have significant WISE detections, in combination with non-detections in SDSS/DSS, which effectively selects galaxy cluster candidates at redshifts z ≳ 0.5. By taking r- and z-band imaging with MegaCam at CFHT, we bridge the 4000 Å rest-frame break over a significant redshift range, thus allowing accurate redshift estimates of red-sequence cluster galaxies up to z ~ 0.8. After discussing the possibility that an overdensity of galaxies coincides -by chance- with a Planck SZ detection, we confirm that 16 of the candidates have likely optical counterparts to their SZ signals, 13 (6) of which have an estimated redshift z> 0.5 (z> 0.7). The richnesses of these systems are generally lower than expected given the halo masses estimated from the Planck maps. However, when we follow a simplistic model to correct for Eddington bias in the SZ halo mass proxy, the richnesses are consistent with a reference mass-richness relation established for clusters detected at higher significance. This illustrates the benefit of an optical follow-up, not only to obtain redshift estimates, but also to provide an independent mass proxy that is not based on the same data the clusters are detected with, and thus not subject to Eddington bias.
Matter distribution around clusters is highly anisotropic because clusters are the nodes of the cosmic web. The shape of the clusters and the number of filaments to which they are connected, that is, ...their connectivity, is thought to reflect their level of anisotropic matter distribution and must in principle be related to their physical properties. We investigate the effect of the dynamical state and the formation history on both the morphology and local connectivity of about 2400 groups and clusters of galaxies from the large hydrodynamical simulation IllustrisTNG at
z
= 0. We find that the mass of groups and clusters mainly affects the geometry of the matter distribution: Massive halos are significantly more elliptical and are more strongly connected to the cosmic web than low-mass halos. Beyond the mass-driven effect, ellipticity and connectivity are correlated and are imprints of the growth rate of groups and clusters. Both anisotropy measures appear to trace different dynamical states, such that unrelaxed groups and clusters are more elliptical and more connected than relaxed ones. This relation between matter anisotropies and dynamical state is the sign of different accretion histories. Relaxed groups and clusters have mostly been formed a long time ago and are slowly accreting matter at the present time. They are highly spherical and weakly connected to their environment, mostly because they had enough time to relax and thus lost the connection with their preferential directions of accretion and merging. In contrast, late-formed unrelaxed objects are highly anisotropic with strong connectivities and ellipticities. These groups and clusters are in their formation phase and must be strongly affected by the infalling of materials from filaments.
PACT Aghanim, N.; Douspis, M.; Hurier, G. ...
Astronomy and astrophysics (Berlin),
12/2019, Letnik:
632
Journal Article
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We present the optimal reconstruction of the thermal Sunyaev–Zel’dovich (tSZ) effect signal based on the combination of a heterogeneous dataset consisting of Atacama Cosmology Telescope (ACT) and ...Planck data, with different numbers of channels, angular resolutions, and noise levels. We combine both datasets using two different approaches, a matched multifilter (MMF) technique and an optimized internal linear combination (ILC). We show that when applying the MMF to the combination of ACT and Planck data, the size-flux degeneracy is reduced and the signal-to-noise of clusters detected with their Sunyaev–Zel’dovich (SZ) signal improves by up to a factor of three. In the case of the optimized ILC method, we show that the tSZ map is reconstructed with a resolution of ∼1.5 arcmin. This is more than a factor two improvement compared with the Planck resolution, and with a very good control of noise, meaning that it is limited only by the intrinsic noise of the individual experiments. The combination of ACT and Planck data offers a unique opportunity to improve on the study of the pressure profiles and to study substructure in clusters through their tSZ.
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