90 research outputs found
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 (). Since the CMB photons are released at redshifts , they must
interact with all the intervening matter before reaching us at .
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 confidence level, the upper limit
on volume-average WHIM density turns out to be , 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 . 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 , which in turn suggests a high value of
the magnetic field (of the order of 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<sup>+</sup>âCl<sup>â</sup> 2 cotransporter in the developing rat cortex
The type 2 potassiumâchloride 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
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