Context. The fundamental properties of the photon have a deep impact on the astrophysical processes that involve it, such as the inverse Compton scattering of CMB photon by energetic electrons ...residing within galaxy cluster atmospheres. This is usually referred to as the Sunyaev-Zel’dovich effect (SZE). Aims. We calculate the combined constraints on the photon decay time and mass by studying the impact of the modified CMB spectrum on the SZE of galaxy clusters. Methods. We analyze the modifications of the SZE as produced by photon decay effects. We study the frequency ranges where these modifications are large and where the constraints derived from the SZE are stronger than those already obtained from the CMB spectrum. Results. We show that the SZE can set limits on the photon decay time and mass, or on E∗ = (t0/τγ)mγc2 , which are stronger than those obtained from the CMB. The main constraints come from the low-frequency range ν ≈ 10−50 GHz where the modified SZE ΔImod is greater than the standard one ΔI, with the difference |(ΔImod − ΔI)| increasing with the frequency for increasing values of E∗. Additional constraints can be set in the range 120−180 GHz where there is an increase in the frequency position of the minimum of ΔImod with respect to the standard one with increasing values of E∗. Conclusions. We demonstrated that the effect of photon decay can be measured or constrained by the Square Kilometer Array in the optimal range ≈ 10−30 GHz setting limits of E∗ ≲ 1.4 × 10-9 eV and 5 × 10-10 eV for 30- and 260-h integration for A2163, respectively. These limits are tighter than those obtained with the COBE-FIRAS spectral measurements of the CMB.
This work presents an analytical approach for studying the cosmological 21cm background signal from the Dark Ages (DA) and subsequent Epoch of Reionization (EoR). We simulate differential ...observations of a galaxy cluster to demonstrate how these epochs can be studied with a specific form of the Sunyaev-Zel’dovich Effect called the SZE-21cm. This work produces simulated maps of the SZE-21cm and shows that the SZE-21cm can be extracted from future observations with low-frequency radio interferometers such as the Hydrogen Epoch of Reionization Array (HERA) and the Square Kilometre Array (SKA). In order to simulate near realistic scenarios, we look into cosmic variance noise, incorporate and take into account the effects of foregrounds, thermal noise, and angular resolution for our simulated observations. We further extend this exploration by averaging over a sample of galaxy clusters to mitigate the effects of cosmic variance and instrumental noise. The impact of point source contamination is also studied. Lastly, we apply this technique to the results of the EDGES collaboration, which in 2018 reported an absorption feature of the global 21cm background signal centred at 78 MHz. The challenges to be addressed in order to achieve the objectives of this work include errors that arise due to cosmic variation, instrumental noise and point source contamination. Our approach demonstrates the potential of the SZE-21cm as an indirect probe for the DA and EoR, and we conclude that the spectral features of the SZE-21cm from our simulated observations yield results that are close to prior theoretical predictions and that the SZE-21cm can be used to test the validity of the EDGES detection.
Aims. 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.
ABSTRACT
We present deep total intensity and polarization observations of the Coma cluster at 1.4 and 6.6 GHz performed with the Sardinia Radio Telescope. By combining the single-dish 1.4 GHz data ...with archival Very Large Array observations, we obtain new images of the central radio halo and of the peripheral radio relic where we properly recover the brightness from the large-scale structures. At 6.6 GHz, we detect both the relic and the central part of the halo in total intensity and polarization. These are the highest frequency images available to date for these radio sources in this galaxy cluster. In the halo, we find a localized spot of polarized signal, with fractional polarization of about 45 per cent. The polarized emission possibly extends along the north-east side of the diffuse emission. The relic is highly polarized, up to 55 per cent, as usually found for these sources. We confirm the halo spectrum is curved, in agreement with previous single-dish results. The spectral index is α = 1.48 ± 0.07 at a reference frequency of 1 GHz and varies from α ≃ 1.1, at 0.1 GHz, up to α ≃ 1.8, at 10 GHz. We compare the Coma radio halo surface brightness profile at 1.4 GHz (central brightness and e-folding radius) with the same properties of the other haloes, and we find that it has one of the lowest emissivities observed so far. Reanalysing the relic’s spectrum in the light of the new data, we obtain a refined radio Mach number of M = 2.9 ± 0.1.
We detect a new suspected giant radio galaxy (GRG) discovered by KAT-7. The GRG core is identified with the Wide-field Infrared Survey Explorer source J013313.50-130330.5, an extragalactic source ...based on its infrared colours and consistent with a misaligned active galactic nuclei-type spectrum at z ≈ 0.3. The multi-ν spectral energy distribution (SED) of the object associated with the GRG core shows a synchrotron peak at ν ≈ 1014 Hz consistent with the SED of a radio galaxy blazar-like core. The angular size of the lobes are ∼4 arcmin for the NW lobe and ∼1.2 arcmin for the SE lobe, corresponding to projected linear distances of ∼1078 kpc and ∼324 kpc, respectively. The best-fitting parameters for the SED of the GRG core and the value of jet boosting parameter δ = 2, indicate that the GRG jet has maximum inclination θ ≈ 30 deg with respect to the line of sight, a value obtained for δ = Γ, while the minimum value of θ is not constrained due to the degeneracy existing with the value of Lorentz factor Γ. Given the photometric redshift z ≈ 0.3, this GRG shows a core luminosity of P
1.4 GHz ≈ 5.52 × 1024 W Hz−1, and a luminosity P
1.4 GHz ≈ 1.29 × 1025 W Hz−1 for the NW lobe and P
1.4 GHz ≈ 0.46 × 1025 W Hz−1 for the SE lobe, consistent with the typical GRG luminosities. The radio lobes show a fractional linear polarization ≈9 per cent consistent with typical values found in other GRG lobes.
Context. The origin of radio halos in galaxy clusters is still unknown and is the subject of a vibrant debate from both observational and theoretical points of view. In particular, the amount and the ...nature of nonthermal plasma and of the magnetic field energy density in clusters hosting radio halos is still unclear. Aims. The aim of this paper is to derive an estimate of the pressure ratio X = Pnon − th/Pth between the nonthermal and thermal plasma in radio halo clusters that have combined radio, X-ray and Sunyaev-Zel’dovich (SZ) effect observations. Methods. From the simultaneous P1.4 − LX and P1,4 − YSZ correlations for a sample of clusters observed with Planck, we derive a correlation between YSZ and LX that we use to derive a value for X. This is possible since the Compton parameter YSZ is proportional to the total plasma pressure in the cluster, which we characterize as the sum of the thermal and nonthermal pressure, while the X-ray luminosity LX is proportional only to the thermal pressure of the intracluster plasma. Results. Our results indicate that the average (best-fit) value of the pressure ratio in a self-similar cluster formation model is X = 0.55 ± 0.05 in the case of an isothermal β-model with β = 2/3 and a core radius rc = 0.3·R500, holding on average for the cluster sample. We also show that the theoretical prediction for the YSZ − LX correlation in this model has a slope that is steeper than the best-fit value for the available data. The agreement with the data can be recovered if the pressure ratio X decreases with increasing X-ray luminosity as LX-0.96. Conclusions. We conclude that the available data on radio halo clusters indicate a substantial amount of nonthermal pressure in cluster atmospheres whose value must decrease with increasing X-ray luminosity or increasing cluster mass (temperature). This is in agreement with the idea that nonthermal pressure is related to nonthermal sources of cosmic rays that live in cluster cores and inject nonthermal plasma in the cluster atmospheres, which is subsequently diluted by the intracluster medium acquired during cluster collapse, and has relevant impact for further studies of high-energy phenomena in galaxy clusters.
Aims. Sunyaev-Zel’dovich effect (SZE) observation of galaxy clusters at high frequency are able to set relevant constraints on intracluster plasma physics because of the strong dependence from the ...electron distribution function. Methods. We used the multifrequency SZE observation that are available for the first time up to very high frequencies of ~850 GHz to set contraints on the structure of the Bullet cluster atmosphere. In this context we explore the predictions of five different plasma models with single or multiple temperatures, as well as a model with the coexistence of a thermal background plasma and an additional nonthermal one. Results. The statistical analysis of the SZE spectrum for the Bullet cluster excludes single temperature models and instead favors a more complex structure of the cluster atmosphere consisting of either two temperature plasma or – more preferably – a thermal plasma at a temperature of ~13.9 keV coexisting with a second plasma component, either at higher temperature or, more preferably, of nonthermal origin, confirming the preliminary, but not conclusive, indications of the hard X-ray observations of the Bullet cluster. Conclusions. The multifrequency study of the SZE signal in the range ~150−850 GHz observed in the Bullet cluster indicates that there is a complex plasma distribution with a combination of a thermal plus a nonthermal electron distribution consistently with the theoretical expectation for a powerful merging in the Bullet cluster.
Warming rays in cluster cool cores Colafrancesco, S.; Marchegiani, P.
Astronomy and astrophysics (Berlin),
06/2008, Letnik:
484, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Context. Cosmic rays are confined in the atmospheres of galaxy clusters and, therefore, they can play a crucial role in the heating of their cool cores. Aims. We discuss here the thermal and ...non-thermal features of a model of cosmic ray heating of cluster cores that can provide a solution to the cooling-flow problems. To this aim, we generalize a model originally proposed by Colafrancesco, Dar & DeRujula (2004) and we show that our model predicts specific correlations between the thermal and non-thermal properties of galaxy clusters and enables various observational tests. Methods. The model reproduces the observed temperature distribution in clusters by using an energy balance condition in which the X-ray energy emitted by clusters is supplied, in a quasi-steady state, by the hadronic cosmic rays, which act as “warming rays” (WRs). The temperature profile of the intracluster (IC) gas is strictly correlated with the pressure distribution of the WRs and, consequently, with the non-thermal emission (radio, hard X-ray and gamma-ray) induced by the interaction of the WRs with the IC gas and the IC magnetic field. Results. The temperature distribution of the IC gas in both cool-core and non cool-core clusters is successfully predicted from the measured IC plasma density distribution. Under this contraint, the WR model is also able to reproduce the thermal and non-thermal pressure distribution in clusters, as well as their radial entropy distribution, as shown by the analysis of three clusters studied in detail: Perseus, A2199 and Hydra. The WR model provides other observable features of galaxy clusters: a correlation of the pressure ratio (WRs to thermal IC gas) with the inner cluster temperature $(P_{\rm WR}/P_{\rm th}) \sim (kT_{\rm inner})^{-2/3}$, a correlation of the gamma-ray luminosity with the inner cluster temperature $L_{\gamma} \sim (kT_{\rm inner})^{4/3}$, a substantial number of cool-core clusters observable with the GLAST-LAT experiment, a surface brightness of radio halos in cool-core clusters that recovers the observed one, a hard X-ray ICS emission from cool-core clusters that is systematically lower than the observed limits and yet observable with the next generation high-sensitivity and spatial resolution HXR experiments like Simbol-X. Conclusions. The specific theoretical properties and the multi-frequency distribution of the e.m. signals predicted in the WR model render it quite different from the other models so far proposed for the heating of clusters' cool-cores. Such differences make it possible to prove or disprove our model as an explanation for the cooling-flow problems on the basis of multi-frequency observations of galaxy clusters.
In this paper we provide a general derivation of the non-thermal Sunyaev-Zel'dovich (SZ) effect in galaxy clusters which is exact in the Thomson limit to any approximation order in the optical depth ...τ. The general approach we use also allows us to obtain an exact derivation of the thermal SZ effect in a self-consistent framework. Such a general derivation is obtained using the full relativistic formalism and overcoming the limitations of the Kompaneets and of the single scattering approximations. We compare our exact results with those obtained at different approximation orders in τ and we give estimates of the precision fit. We verified that the third order approximation yields a quite good description of the spectral distortion induced by the Comptonization of CMB photons in the cluster atmosphere. In our general derivation, we show that the spectral shape of the thermal and non-thermal SZ effect depends not only on the frequency but also on the cluster parameters, like the electron pressure and optical depth and from the energy spectrum of the electron population. We also show that the spatial distribution of the thermal and non-thermal SZ effect in clusters depends on a combination of the cluster parameters and on the spectral features of the effect. To have a consistent description of the SZ effect in clusters containing non-thermal phenomena, we also evaluate in a consistent way – for the first time – the total SZ effect produced by a combination of thermal and non-thermal electron population residing in the same environment, like is the case in radio-halo clusters. In this context, we show that the location of the zero of the total SZ effect increases non-linearly with increasing values of the pressure ratio between the non-thermal and thermal electron populations and its determination provides a unique way to determine the pressure of the relativistic particles residing in the cluster atmosphere. We discuss in detail both the spectral and the spatial features of the total (thermal plus non-thermal) SZ effect and we provide specific predictions for a well studied radio-halo cluster like A2163. Our general derivation allows also to discuss the overall SZ effect produced by a combination of different thermal populations residing in the cluster atmosphere. Such a general derivation of the SZ effect allows to consider also the CMB Comptonization induced by several electron populations. In this context, we discuss how the combined observations of the thermal and non-thermal SZ effect and of the other non-thermal emission features occurring in clusters (radio-halo, hard X-ray and EUV excesses) provide relevant constraints of the spectrum of the relativistic electron population and, in turn, on the presence and on the origin of non-thermal phenomena in galaxy clusters. We finally discuss how SZ experiments with high sensitivity and narrow-band spectral coverage, beyond the coming PLANCK satellite, can definitely probe the presence of a non-thermal SZ effect in galaxy clusters and disentangle this source of bias from the cosmologically relevant thermal SZ effect.
Context. Radio galaxy (RG) lobes contain relativistic electrons embedded in a tangled magnetic field that produce, in addition to low-frequency synchrotron radio emission, inverse-Compton scattering ...(ICS) of the cosmic microwave background (CMB) photons. This produces a relativistic, non-thermal Sunyaev-Zel’dovich effect (SZE). Aims. We study the spectral and spatial properties of the non-thermal SZE in a sample of radio galaxies and make predictions for their detectability in both the negative and the positive part of the SZE, with space experiments like Planck, OLIMPO, and Herschel-SPIRE. These cover a wide range of frequencies, from radio to sub-mm. Methods. We model the SZE in a general formalism that is equivalent to the relativistic covariant one and describe the electron population contained in the lobes of the radio galaxies with parameters derived from their radio observations, namely, flux, spectral index, and spatial extension. We further constrain the electron spectrum and the magnetic field of the RG lobes using X-ray, gamma-ray, and microwave archival observations. Results. We determine the main spectral features of the SZE in RG lobes, namely, the minimum, the crossover, and the maximum of the SZE. We show that these typical spectral features fall in the frequency ranges probed by the available space experiments. We provide the most reliable predictions for the amplitude and spectral shape of the SZE in a sample of selected RGs with extended lobes. In three of these objects, we also derive an estimate of the magnetic field in the lobe at the ~μG level by combining radio (synchrotron) observations and X-ray (ICS) observations. These data, together with the WMAP upper limits, set constraints on the minimum momentum of the electrons residing in the RG lobes and allow realistic predictions for the visibility of their SZE to be derived with Planck, OLIMPO, and Herschel-SPIRE. Conclusions. We show that the SZE from several RG lobes can be observed with mm and sub-mm experiments like Planck, OLIMPO, and Herschel-SPIRE, as well as with ground-based telescopes that have ≲ mJy sensitivity and sub-arcmin spatial resolution. These measurements will be crucial to disentangle the relativistic electron distribution from that of the magnetic field in RG lobes and to constrain the properties of their ICS emission, which is also visible at very high X-ray and gamma-ray energies.
PDF
