Planckintermediate results

Abstract

Context. About half of the baryons of the Universe are expected to be in the form of filaments of hot and low-density intergalactic medium. Most of these baryons remain undetected even by the most advanced X-ray observatories, which are limited in sensitivity to the diffuse low-density medium. Aims. The Planck satellite has provided hundreds of detections of the hot gas in clusters of galaxies via the thermal Sunyaev-Zel'dovich (tSZ) effect and is an ideal instrument for studying extended low-density media through the tSZ effect. In this paper we use the Planck data to search for signatures of a fraction of these missing baryons between pairs of galaxy clusters. Methods. Cluster pairs are good candidates for searching for the hotter and denser phase of the intergalactic medium (which is more easily observed through the SZ effect). Using an X-ray catalogue of clusters and the Planck data, we selected physical pairs of clusters as candidates. Using the Planck data, we constructed a local map of the tSZ effect centred on each pair of galaxy clusters. ROSAT data were used to construct X-ray maps of these pairs. After modelling and subtracting the tSZ effect and X-ray emission for each cluster in the pair, we studied the residuals on both the SZ and X-ray maps. Results. For the merging cluster pair A399-A401 we observe a significant tSZ effect signal in the intercluster region beyond the virial radii of the clusters. A joint X-ray SZ analysis allows us to constrain the temperature and density of this intercluster medium. We obtain a temperature of kT = 7.1 ± 0.9 keV (consistent with previous estimates) and a baryon density of (3.7 ± 0.2) × 10 −4 cm −3 . Conclusions. The Planck satellite mission has provided the first SZ detection of the hot and diffuse intercluster gas.

Can HI 21-cm lines trace the missing baryons in the filamentary structures?

“…Recent various cosmological observations strongly support that the ΛCDM (Lambda Cold Dark Matter) model is preferred for describing the evolution of the Universe (Planck Collaboration et al 2016). The present acceleration expansion revealed by observations of type Ia supernovae suggests the existence of dark energy (Perlmutter et al 1997;Riess et al 1998). Furthermore, numerical simulations based on the ΛCDM model succeed in explaining observed galaxy clustering in the large scale structure (Alam et al 2016).…”

Polarized anisotropic spectral distortions of the CMB: galactic and extragalactic constraints on photon-axion conversion

“…Along with the angular fluctuations of the CMB field, we also expect deviations from the blackbody spectrum within the standard cosmological scenario [16][17][18][19][20][21][22][23][24][25][26] and measurement of these would deepen our understanding of both early and late time epoch of the Universe. Only one type of spectral distortion, the Sunyaev-Zeldovich effect or the y-type distortion [16], has so far been detected towards the clusters of galaxies [27][28][29][30][31][32]. Spectral distortions in CMB are also predicted by several high energy physics scenarios which are important particularly in the pre-recombination epoch [33][34][35][36][37][38][39].…”

A new probe of axion-like particles: CMB polarization distortions due to cluster magnetic fields

“…Several CMB experiments have explored the spatially varying part of the blackbody and non-blackbody (particularly y-distortions) over the last three decades from space, balloon -1 -and ground platforms 1 . Along with the unprecedented measurement of the temperature and polarization anisotropy by WMAP [25] and Planck [26], ground-based experiments such as ACT (Atacama Cosmology Telescope) [27] and SPT (South-Pole Telescope) [28] have also explored the y-distortion signals from galaxy clusters [8,[29][30][31][32][33][34]. However, the spatially nonvarying spectrum of the CMB has not been explored after COBE-FIRAS (Cosmic Background Explorer-Far Infrared Absolute Spectrophotometer) experiment [35][36][37][38] which had imposed an upper bound on y-distortions and µ-distortions of 15 × 10 −6 and 9 × 10 −5 respectively at 95% C.L.…”