The impact of the SZ effect on cm-wavelength (1-30 GHz) observation of galaxy cluster radio relics

(Abridged) Radio relics in galaxy clusters are believed to be associated with powerful shock fronts that originate during cluster mergers, and are a testbed for the acceleration of relativistic particles in the intracluster medium. Recently, radio relic observations have pushed into the cm-wavelength domain (1-30 GHz) where a break from the standard synchrotron power-law spectrum has been found, most noticeably in the famous 'Sausage' relic. In this paper, we point to an important effect that has been ignored or considered insignificant while interpreting these new high-frequency radio data, namely the contamination due to the Sunyaev-Zel'dovich (SZ) effect that changes the observed synchrotron flux. Even though the radio relics reside in the cluster outskirts, the shock-driven pressure boost increases the SZ signal locally by roughly an order of magnitude. The resulting flux contamination for some well-known relics are non-negligible already at 10 GHz, and at 30 GHz the observed synchrotron fluxes can be diminished by a factor of several from their true values. Interferometric observations are not immune to this contamination, since the change in the SZ signal occurs roughly at the same length scale as the synchrotron emission, although there the flux loss is less severe than single-dish observations. We present a simple analytical approximation for the synchrotron-to-SZ flux ratio, based on a theoretical radio relic model that connects the non-thermal emission to the thermal gas properties, and show that by measuring this ratio one can potentially estimate the relic magnetic fields or the particle acceleration efficiency.Comment: Updated to the accepted version. Includes major text modifications and a correction to the numerical coefficient in Eq. 15. Results and conclusions are unchange

CMB observations and the metal enrichment history of the universe

The main purpose of the work presented in this thesis is to investigate the phenomenon of resonant scattering of the Cosmic Microwave Background (CMB) photons by atoms and molecules. The fine-structure transitions of the various atoms and ions of Carbon, Nitrogen, Oxygen and other common metals have wavelengths in the far-infrared regions, which are particularly suitable for scattering the CMB photons at high redshifts ($2 \lesssim z \lesssim 30$). Since the CMB photons are released at redshifts $z\simeq 1100$, they must interact with all the intervening matter before reaching us at $z=0$. Therefore scattering of these photons in the far-IR fine-structure lines of various atoms and ions provide a plausible way to couple the radiation with the matter at those redshifts and to study the enrichment and ionization history of the universe. Moreover, rotational transitions of diatomic molecules like the CO have wavelengths extending into the sub-millimeter wavebands, and hence they can scatter the CMB photons at very low redshifts. Studying the very low density gas of nearby galaxies in CO lines can yield a definitive signature of resonant scattering of the CMB photons through a decrement in the background intensity of the microwave sky. Observation of this scattering signal from any object in the sky will tell us about its radial velocity in the CMB rest frame. In this work we first derive the detailed formalism for the scattering effect in presence of the peculiar motion of the scatterer. Then we investigate the possibility to detect individual objects at different redshifts through scattering and try to find applications for this effect. Our main example is the possibility to find the peculiar motions of nearby galaxies in the CMB rest frame through observation of the scattering signal, which we explore in detail. Next we discuss the density limits in which scattering effect can dominate over the line emission in individual objects. We describe three types of critical densities, and show that detection of single objects through scattering requires very low density, whereas observation of the integrated scattering signal coming from many unresolved objects in the sky will permit us to probe higher densities. We discuss this effect subsequently, as we compute the change in the angular fluctuations of the CMB sky temperature through resonant scattering. We found that the scattering signal gets strong enhancement due to a non-zero correlation existing between the density perturbations at the last scattering surface, where CMB anisotropies are generated, and at the epoch of scattering. This opens up a new way to study the ionization and enrichment history of the universe, and we investigate various enrichment scenarios and the temperature fluctuations that might be caused by them. The resulting signal is already within the sensitivity limits of some upcoming space- and ground-based CMB experiments, and we show upto what extent they shall be able to put constraints on different enrichment histories. Finally we analyze the effect of line and dust emission in the same frequency range that we used for the detection of scattering signal. These emissions are coming from very high density objects where active star formation is taking place, and due to the compactness of their size as well as absence of any velocity dependence the emission signal is significantly suppressed at large angular scales, where scattering will be dominant. We present some detailed analytic expressions for the scattering signal and also a method to solve for the detailed statistical balance equations in a multi-level system in the appendix

WHIM-hunting through cross-correlation of optical and SZ effect data in the Virgo cluster filaments

Context. The physical state of most of the baryonic matter in the local universe is unknown, which is commonly referred to as the ``missing baryon problem". It is theorized that at least half of these missing baryons are in a warm-hot, low-density phase outside of the virialized dark-matter halos. Aims. We make an attempt to find the signature of this warm-hot intergalactic medium (WHIM) phase in the filaments of the nearby Virgo cluster by using optical and Sunyaev-Zeldovich effect data. Methods. Specifically, we use a filament-galaxy catalog created from the HyperLeda database and an all-sky Compton-y map extracted from the Planck satellite data for 2-dimensional cross-correlation analysis by applying spherical harmonics transform. Significance test is based on the null-test simulations which exploits advanced cut-sky analysis tools for a proper map reconstruction. To place upper limits on the WHIM density in the Virgo filaments, realistic baryonic density modelling within the cosmic filaments is done based on state-of-the-art hydro-simulations, and it's done within the signal-boosting routine. Results. The cross-correlation signal is found to be too dim compared to the noise level in the Planck y-map. At 3$\sigma$ confidence level, the upper limit on volume-average WHIM density turns out to be $\left\langle n_e \right\rangle \lt 4\times10^{-4} cm^{-3}$, which is indeed consistent with the WHIM parameter space as predicted from simulations.Comment: Currently under the revision process to be published in the journal of Astronomy & Astrophysic

ALMA-SZ Detection of a Galaxy Cluster Merger Shock at Half the Age of the Universe

We present ALMA measurements of a merger shock using the thermal Sunyaev-Zel'dovich (SZ) effect signal, at the location of a radio relic in the famous El Gordo galaxy cluster at $z \approx 0.9$. Multi-wavelength analysis in combination with the archival Chandra data and a high-resolution radio image provides a consistent picture of the thermal and non-thermal signal variation across the shock front and helps to put robust constraints on the shock Mach number as well as the relic magnetic field. We employ a Bayesian analysis technique for modeling the SZ and X-ray data self-consistently, illustrating respective parameter degeneracies. Combined results indicate a shock with Mach number ${\cal M} = 2.4^{+1.3}_{-0.6}$, which in turn suggests a high value of the magnetic field (of the order of $4-10 ~\mu$G) to account for the observed relic width at 2 GHz. At roughly half the current age of the universe, this is the highest-redshift direct detection of a cluster shock to date, and one of the first instances of an ALMA-SZ observation in a galaxy cluster. It shows the tremendous potential for future ALMA-SZ observations to detect merger shocks and other cluster substructures out to the highest redshifts.Comment: Matched to the ApJL published version (2016 September 22), minor grammar and typo fixe

Regional differences in the expression of K⁺–Cl⁻ 2 cotransporter in the developing rat cortex

The type 2 potassium–chloride cotransporter (KCC2) is the main regulator of intracellular chloride concentration in CNS neurons, and plays a crucial role in spine development that is independent of its ion cotransport function. The expression pattern of KCC2 is upregulated during postnatal development showing area and layer-specific differences in distinct brain areas. We examined the regional and ultrastructural localisation of KCC2 in various areas of developing neocortex and paleocortex during the first two postnatal weeks. Light-microscopy examination revealed diffuse neuropil and discrete funnel-shaped dendritic labelling in the piriform and entorhinal cortices at birth. Subsequently, during the beginning of the first postnatal week, diffuse KCC2 labelling gradually started to appear in the superficial layers of the neocortex while the punctate-like labelling of dendrites in the piriform, entorhinal and perirhinal cortices become more pronounced. By the end of the first postnatal week, discrete dendritic expression of KCC2 was visible in all neocortical and paleocortical areas. The expression level did not change during the second postnatal week suggesting that, in contrast to hippocampus, adult pattern of KCC2 in the cortical cells is already established by the end of the first postnatal week. Quantitative electron microscopy examination revealed that in superficial layers of both neo- and paleocortex, the majority of KCC2 signal was plasma membrane associated but the number of transport vesicle-associated immunosignal increased with development. In deep layers, KCC2 immunolabeling was evenly distributed in plasma membrane and transport vesicles showing no obvious change with maturation. The number of KCC2 immunogold particles increased in dendritic spines with no association with synapses. This observation points to the dual role of KCC2 in spine genesis and ion cotransport