1,721,451 research outputs found
Is the radio emission in the Bullet cluster due to dark matter annihilation?
Full text linkWe study the complex structure of the Bullet cluster radio halo to determine the Dark Matter (DM) contribution to the emission observed in the different subhaloes corresponding to the DM- and baryonic-dominated regions. We use different non-thermal models to study the different regions, and we compare our results with the available observations in the radio, X-ray and gamma-ray bands, and the Sunyaev–Zel'dovich effect (SZE) data. We find that the radio emission coming from the main DM subhalo can be produced by secondary electrons produced by DM annihilations. In this scenario, there are however some open issues, like the difficulty to explain the observed flux at 8.8 GHz, the high value of the required annihilation cross-section, and the lack of observed emission coming from the minor DM subhalo. We also find that part of the radio emission originated by DM annihilation could be associated with a slightly extended radio source present near the main DM subhalo. Regarding the baryonic subhaloes, the radio measurements do not allow to discriminate between a primary or secondary origin of the electrons, while the SZE data point towards a primary origin for the non-thermal electrons in the Main subcluster. We conclude that in order to better constrain the properties of the DM subhaloes, it is important to perform detailed measurements of the radio emission in the regions where the DM haloes have their peaks, and that the separation of the complex radio halo in different subhaloes is a promising technique to understand the properties of each specific subhalo.National Research Foundation (South Africa
Effect of the non-thermal Sunyaev–Zel’dovich effect on the temperature determination of galaxy clusters
Full text linkA recent stacking analysis of Planck HFI data of galaxy clusters led to the derivation of the cluster temperatures using the relativistic corrections to the Sunyaev-Zel'dovich effect (SZE). However, the temperatures of high-temperature clusters, as derived from this analysis, were basically higher than the temperatures derived from X-ray measurements, at a moderate statistical significance of 1.5 sigma. This discrepancy has been attributed by Hurier to calibration issues. In this paper, we discuss an alternative explanation for this discrepancy in terms of a non-thermal SZE astrophysical component. We find that this explanation can work if non-thermal electrons in galaxy clusters have a low minimum momentum (p(1) similar to 0.5-1), and if their pressure is of the order of 20-30 per cent of the thermal gas pressure. Both these conditions are hard to obtain if the non-thermal electrons are mixed with the hot gas in the intracluster medium, but can be possibly obtained if the non-thermal electrons are mainly confined in bubbles with a high amount of non-thermal plasma and a low amount of thermal plasma, or are in giant radio lobes/relics in the outskirts of the clusters. To derive more precise results on the properties of the non-thermal electrons in clusters, and in view of more solid detections of a discrepancy between X-ray- and SZE-derived cluster temperatures that cannot be explained in other ways, it would be necessary to reproduce the full analysis done by Hurier by systematically adding the non-thermal component of the SZE.EM201
Multi-frequency analysis of neutralino dark matter annihilations in the Coma cluster
Full text linkWe study the astrophysical implications of neutralino dark matter annihilations in galaxy clusters, with a specific application to the Coma cluster. We first address the determination of the dark halo models for Coma, starting from structure formation models and observational data, and we discuss in detail the role of sub-halos. We then perform a thorough analysis of the transport and diffusion properties of neutralino annihilation products, and investigate the resulting multi-frequency signals, from radio to gamma-ray frequencies. We also study other relevant astrophysical effects of neutralino annihilations, like the DM-induced Sunyaev-Zel'dovich effect and the intracluster gas heating. As for the particle physics setup, we adopt a two-fold approach, resorting both to model-independent bottom-up scenarios and to benchmark, GUT-motivated frameworks. We show that the Coma radio-halo data ( the spectrum and the surface brightness) can be nicely fitted by the neutralino-induced signal for peculiar particle physics models and for magnetic field values, which we outline in detail. Fitting the radio data and moving to higher frequencies, we find that the multi-frequency spectral energy distributions are typically dim at EUV and X-ray frequencies ( with respect to the data), but show a non-negligible gamma-ray emission, depending on the amplitude of the Coma magnetic field. A simultaneous fit to the radio, EUV and HXR data is not possible without violating the gamma-ray EGRET upper limit. The best-fit particle physics models yields substantial heating of the intracluster gas, but not sufficient energy injection as to explain the quenching of cooling flows in the innermost region of clusters. Due to the specific multi-frequency features of the DM-induced spectral energy distribution in Coma, we find that supersymmetric models can be significantly and optimally constrained either in the gamma-rays or at radio and microwave frequencies
Autoimmune/Inflammatory Syndrome Induced by Adjuvants and Sjogren's Syndrome
No full textSjogren's syndrome (SS), a chronic systemic autoimmune inflammatory condition involving the exocrine glands, has been suggested to be part of the spectrum of the Autoimmune/inflammatory Syndrome Induced by Adjuvants (ASIA). ASIA incorporates an umbrella of clinical conditions including siliconosis, macrophage myofasciitis syndrome, and post, vaccination phenomena that occur after the exposure to a substance, namely the adjuvant. Interestingly, SS and ASIA share several common features. Firstly, a shared pathogenic mechanism involving a disruption of the immune system balance, with B cell proliferation, cytokine production and tissue infiltration, has been proposed. Patients with ASIA often present clinical features resembling those of SS; dry mouth and dry eyes have also been included in the proposed classification criteria for ASIA. Finally, several case reports have suggested that both vaccines and silicone may trigger the development of SS. Unveiling these common pathways will contribute considerably to our understanding and management of both conditions
Disentangling the gamma-ray emission of NGC 1275 and that of the Perseus cluster
No full textContext. The Gamma-ray emission from galaxy clusters hosting active galaxies is a complex combination of diffuse and point-like emission features with different spectral and spatial properties.
Aims. We discuss in details the case of the Perseus cluster containing the radio-galaxy NGC 1275 that has been recently detected as a bright gamma-ray source by the Fermi-LAT experiment, in order to disentangle the sources of emission.
Methods. We provide a detailed study of the gamma-ray emission coming from the core of Perseus by modeling the central AGN emission with a multiple plasma blob model, and the emission from the extended cluster atmosphere with both a warming ray (WR) model and dark matter (DM) neutralino annihilation models. We set constraints on both the central galaxy and cluster SED models by using both archival multi-frequency data and the recent very high energy observations obtained by Fermi and MAGIC.
Results. We find that: i) in all the viable models for the cluster gamma-ray emission, the emission detected recently by Fermi from the center of the Perseus cluster is dominated by the active galaxy NGC 1275, that is found in a high-emission state; ii) the diffuse gamma-ray emission of the cluster, in the WR model and in the DM models with the highest allowed normalization, could be detected by Fermi if the central emission from NGC 1275 is in a low-emission state; iii) Fermi can have the possibility to resolve and detect the diffuse gamma-ray flux (predicted by the WR model) coming from the outer corona of the Perseus cluster atmosphere at distances r greater than or similar to 800 kpc. These results are consistent with the evidence that in the other frequency bands, the diffuse cluster emission dominates on the central galaxy one at low radio frequencies with. v less than or similar to 1 GHz and at X-ray energies of order of E similar to keV.
Conclusions. Our results show that a simultaneous study of the various emission mechanisms that produce diffuse gamma-rays from galaxy clusters and the study of the emission mechanisms that produce gamma-rays from active galaxies residing in the cluster atmospheres is absolutely crucial first to disentangle the spectral and spatial characteristics of the gamma-ray emission and secondly to assess the optimal observational strategy in the attempt to reveal the still elusive diffuse gamma-ray emission widely predicted for the atmospheres of large-scale structures
The hepatitis B vaccine and autoimmune/inflammatory syndrome induced by adjuvants: Relationship with Saccharomyces cerevisiae
No full text
Polarization of the Sunyaev-Zel'dovich effect: relativistic imprint of thermal and non-thermal plasma
Full text linkAbridged] Inverse Compton scattering of CMB fluctuations off cosmic electron plasma generates a polarization of the associated Sunyaev-Zel'dovich (SZ) effect. This signal has been studied so far mostly in the non-relativistic regime and for a thermal electron population and, as such, has limited astrophysical applications. Partial attempts to extend this calculation for a thermal electron plasma in the relativistic regime have been done but cannot be applied to a general relativistic electron distribution. Here we derive a general form of the SZ effect polarization valid in the full relativistic approach for both thermal and non-thermal electron plasmas, as well as for a generic combination of various electron population co-spatially distributed in the environments of galaxy clusters or radiogalaxy lobes. We derive the spectral shape of the Stokes parameters induced by the IC scattering of every CMB multipole, focusing on the CMB quadrupole and octupole that provide the largest detectable signals in galaxy clusters. We found that the CMB quadrupole induced Stoke parameter Q is always positive with a maximum amplitude at 216 GHz which increases slightly with increasing cluster temperature. The CMB octupole induced Q spectrum shows, instead, a cross-over frequency which depends on the cluster electron temperature, or on the minimum momentum p_1 as well as on the power-law spectral index of a non-thermal electron population. We discuss some possibilities to disentangle the quadrupole-induced Q spectrum from the octupole-induced one which allow to measure these quantities through the SZ effect polarization. We finally apply our model to the realistic case of the Bullet cluster and derive the visibility windows of the total, quandrupole-induced and octupole-induced Stoke parameter Q in the frequency ranges accessible to SKA, ALMA, MILLIMETRON and CORE++ experiments.National Research Foundation (South Africa
On the ability of the spectroscopic Sunyaev-Zeldovich effect measurements to determine the temperature structure of galaxy clusters
No full textAims.
We explore the ability of spatially resolved spectroscopic measurements
of the SZ effect (SZE) to determine the temperature profile of galaxy clusters. We
derive a general formalism for the thermal SZE in galaxy clusters
with a non-uniform temperature profile that can be applied to
both cool-core clusters and non-cool-core clusters with an isothermal
or non-isothermal temperature structure.
Methods.
We develop an inversion technique by means of which the electron distribution function
can be extracted from spectroscopic SZE observations over a wide frequency
range. We study the fitting procedure to extract the cluster temperature
from a set of simulated spatially resolved spectroscopic SZE observations in
different bands of the spectrum from 100 to 450 GHz.
Results.
We present our analysis results for three different cluster prototypes:
A2199 with a low-temperature cool core, Perseus with a relatively
high-temperature cool core, and Ophiuchus with an isothermal temperature distribution.
These results indicate both the precision of the SZE observations and the optimal frequency
bands required to determine the cluster temperature with similar or better accuracy than that
obtainable from X-ray observations. The precision of SZE-derived temperature
is also discussed for the outer regions of clusters.
Using our method, we also study the possibility of extracting the
parameters characterizing the non-thermal SZE spectrum of the relativistic plasma
contained in the lobes of radio galaxies as well as the spectrum of relativistic
electrons cospatially distributed with the thermal plasma in clusters that exhibit non-thermal phenomena.
Conclusions. We find that the next generation SZE experiments, which will have both
spectroscopic capabilities with moderate resolution of a few to tens GHz
and imaging capabilities with spatial resolution of tens of arcsec up to arcmin,
can provide precise temperature distribution measurements over a wide range of radial
distances for galaxy clusters even out to high redshift
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