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Diffuse radio emission has been detected in a considerable number of galaxy clusters and groups, revealing the presence of pervasive cosmic magnetic fields, and of relativistic particles in the large scale structure of the Universe. Since the radio emission in galaxy systems is faint and its spectrum is steep, its observations are largely limited by the instrument sensitivity and frequency of observation, leading to a dearth of information, more so for lower-mass systems. The recent commissioning or upgrade of several large radio telescope arrays, particularly at the low frequency bands (

We consider the dynamics of and emission from growing superbubbles in a stratified interstellar gaseous disc driven by energy release from supernovae explosions in stellar clusters with masses Mcl = 105 − 1.6 × 106 M⊙. Supernovae are spread randomly within a sphere of rc = 60 pc, and inject energy episodically with a specific rate |$1/130~\mathrm{M}_\odot ^{-1}$| proportional to the star formation rate (SFR) in the cluster. Models are run for several values of SFR in the range 0.01 to 0.1 M⊙ yr−1, with the corresponding average surface energy input rate ∼0.04–0.4 erg cm−2 s−1. We find that the discrete energy injection by isolated SNe are more efficient in blowing superbubbles: Asymptotically they reach heights of up to 3 to 16 kpc for Mcl = 105 − 1.6 × 105 M⊙, correspondingly, and stay filled with a hot and dilute plasma for at least 30 Myr. During this time, they emit X-ray, Hα and dust infrared emission. X-ray luminosities LX ∝SFR3/5 that we derive here are consistent with observations in star-forming galaxies. Even though dust particles of small sizes a ≤ 0.03 μm are sputtered in the interior of bubbles, larger grains still contribute considerably ensuring the bubble luminosity |$L_{\rm IR}/{\rm SFR}\sim 5\times 10^7 \, \mathrm{L}_\odot \, \mathrm{M}_\odot ^{-1} ~{\rm yr}$|⁠. It is shown that the origin of the North Polar Spur in the Milky Way can be connected with activity of a cluster with the stellar mass of ∼105 M⊙ and the SFR ∼ 0.1 M⊙ yr−1 some 25–30 Myr ago. Extended luminous haloes observed in edge-on galaxies (NGC 891 as an example) can be maintained by disc spread stellar clusters of smaller masses M * ≲ 105 M⊙. [ABSTRACT FROM AUTHOR]

Current and upcoming high angular resolution and multifrequency experiments are well poised to explore the rich landscape of secondary cosmic microwave background (CMB) anisotropies. In this context, we compute, for the first time, the power spectrum of CMB fluctuations from a cosmological distribution of evolving lobes of giant radio galaxies. We also explicitly take into account the non-thermal electron distribution, which has important implications for the inference of the CMB angular power spectrum. We calculate the mean global non-thermal y -distortion, 〈 y 〉NT. For observationally reasonable distribution of the jet luminosities in the range of 1045–1047 erg s−1, we find 〈 y 〉NT to be less than 10−5, and hence not violating the cosmic background explorer limit as previously claimed. Using the unique spectral dependence of the non-thermal Sunyaev–Zeldovich (SZ), we show that a detection of 〈 y 〉NT can be within reach at the level of ≳5σ from a future Primordial Inflation Explorer (PIXIE)-like experiment provided we understand the foregrounds precisely. The total non-thermal SZ power spectrum, |$C^{\mathrm{ NT}}_\ell$|⁠ , from the radio lobes peaks at ℓ ∼ 3000 with an amplitude |$\sim 1{{\ \rm per\ cent}}$| of thermal SZ power spectrum from galaxy clusters. A detection of the |$C^{\mathrm{ NT}}_\ell$|⁠ , with a PIXIE-like sensitivity experiment, can lead to ∼5σ constraint on the mass dependence of the jet luminosity with the constraint becoming at least ten times better for the proposed more ambitious CMB-HD survey. This will further lead to the tightest constraint on the central black hole mass-to-host halo mass scaling relations. [ABSTRACT FROM AUTHOR]

The presence of dust in the intracluster medium (ICM) has been a long-standing problem that is still awaiting elucidation. Direct observational diagnostics are rather challenging (though not impossible) either because of a sparse distribution of dust in the intracluster space that makes extinction measurements difficult or because of a low surface brightness of infrared emission from dust. Complex indirect approaches are currently available that can overcome uncertainties and provide a reasonable understanding of the basic regulations of the physical state of dust in the ICM. Contrary to the common opinion that the hot ICM does not allow dust to survive and manifest, many sparse observational data either directly point out that dust exists in the intracluster space or its presence is consistent with the data. Highly divergent data in direct evidence and highly uncertain indirect indicators are often connected either with dust fragility in a hot environment, the possible compactness of spatial (clumpy) dust distribution in the ICM, or dynamical features of dust transport. The source of dust is obviously connected with galaxies, and it turns out that in most cases, dust is carried from galaxies into the ICM while being thermally and dynamically shielded against the hostile influence of high-energy ions. In this review, we briefly discuss related issues from observational and theoretical points of view, including the transport of dust into the ICM, and the associated destructive and protective mechanisms and their characteristic time scales. [ABSTRACT FROM AUTHOR]

Energetic electrons in the lobes of radio galaxies make them potential sources for not only radio and X-rays but also Sunyaev–Zeldovich (SZ) distortions in the cosmic microwave background (CMB) radiation. Previous works have discussed the energetics of radio galaxy lobes, but assuming thermal SZ effect, coming from the non-thermal electron population. We use an improved evolutionary model for radio galaxy lobes to estimate the observed parameters such as the radio luminosity and intensity of SZ-distortions at the redshifts of observation. We, further, quantify the effects of various relevant physical parameters of the radio galaxies, such as the jet power, the time-scale over which the jet is active, the evolutionary time-scale for the lobe, etc. on the observed parameters. For current SZ observations towards galaxy clusters, we find that the non-thermal SZ distortions from radio lobes embedded in galaxy clusters can be non-negligible compared to the amount of thermal SZ distortion from the intracluster medium and, hence, cannot be neglected. We show that small and young (and preferably residing in a cluster environment) radio galaxies offer better prospects for the detection of the non-thermal SZ signal from these sources. We further discuss the limits on different physical parameters for some sources for which SZ effect has been either detected or upper limits are available. The evolutionary models enable us to obtain limits, previously unavailable, on the low energy cut-off of electron spectrum (p min ∼ 1–2) in order to explain the recent non-thermal SZ detection. Finally, we discuss how future CMB experiments, which would cover higher frequency bands (>400 GHz), may provide clear signatures for non-thermal SZ effect. [ABSTRACT FROM AUTHOR]

We present constraints on a simple analytical model for hot diffuse halo gas, derived from a fit spanning two orders of magnitude in halo mass (⁠|$M_{500} \sim 10^{12.5}\!-\!10^{14.5} \, \mathrm{M}_{\odot }$|⁠). The model is motivated by the observed prevalence of a precipitation limit, and its main free parameter is the central ratio of gas cooling time-scale to free-fall time-scale (t cool/ t ff). We use integrated X-ray and thermal Sunyaev–Zel'dovich observations of the environments around massive galaxies, galaxy groups, and clusters, averaged in halo mass bins, and obtain the best-fitting model parameters. We find t cool/ t ff ∼ 50–110, depending on the model extrapolation beyond the halo virial radius and possibly on biases present in the data sets used in the fitting analysis. The model adequately describes the entire mass range, except for intermediate mass haloes (⁠|$M_{500} \sim 10^{13.5} \, \mathrm{M}_{\odot }$|⁠) that systematically fall below the model predictions. However, the best fits for t cool/ t ff substantially exceed the values typically derived from X-ray observations of individual systems (t cool/ t ff ∼ 10–30). We consider several explanations for those discrepancies, including X-ray selection biases and a potential anticorrelation between X-ray luminosity and the central galaxy's stellar mass. [ABSTRACT FROM AUTHOR]

We study the excess entropy and the corresponding non-gravitational feedback energy (E feedback) in the intra-cluster medium (ICM) by considering a sample of 38 galaxy clusters using Chandra X-ray and NRAO VLA Sky Survey/Giant Metrewave Radio Telescope radio observations. We find moderate correlation of the feedback energy and brightest cluster galaxy (BCG) radio luminosity (L R) with the various cluster thermal properties. We show conclusively that the active galactic nucleus is more effective in transferring feedback energy to the ICM in less massive clusters. We find that within 0.3 r 500, the feedback energy correlates with cluster temperature as |$E_{\rm feedback}\propto T_{\mathrm{ obs}}^{0.98\pm 0.37}$|⁠. Moreover, for radio-detected BCG sample, we find that BCG radio luminosity at 1.4 GHz scales with gas mass as |$L_\mathrm{ R}\propto m_{\mathrm{ g},\mathrm{ obs}}^{ 1.76\pm 0.71}$| and with an X-ray luminosity as |$L_\mathrm{ R}\propto L_{\mathrm{ X},\mathrm{ obs}}^{0.94\pm 0.35}$|⁠. Finally, we discuss the implications of our results with regard to feedback in clusters. [ABSTRACT FROM AUTHOR]

We estimate the 'non-gravitational' entropy-injection profiles, ∼K, and the resultant energy feedback profiles, ▵E, of the intracluster medium for 17 clusters using their Planck Sunyaev-Zel'dovich and ROSAT X-ray observations, spanning a large radial range from 0.2r500 up to r200. The feedback profiles are estimated by comparing the observed entropy, at fixed gas mass shells, with theoretical entropy profiles predicted from non-radiative hydrodynamic simulations. We include non-thermal pressure and gas clumping in our analysis. The inclusion of non-thermal pressure and clumping results in changing the estimates for r500 and r200 by 10-20 per cent. When clumpiness is not considered it leads to an underestimation of ▵ K ≈ 300 keV cm2 at r500 and▵ K≈1100 keV cm2 at r200. On the other hand, neglecting non-thermal pressure results in an overestimation of ▵ K ≈ 100 keV cm2 at r500 and underestimation of ▵ K ≈ 450 keV cm2 at r200. For the estimated feedback energy, we find that ignoring clumping leads to an underestimation of energy per particle ▵E ≈ 1 keV at r500 and ▵E ≈ 1.5 keV at r200. Similarly, neglect of the non-thermal pressure results in an overestimation of ▵E ≈ 0.5 keV at r500 and underestimation of ▵E ≈ 0.25 keV at r200. We find entropy floor of ▵ K ≈ 300 keV cm2 is ruled out at ≈3σ throughout the entire radial range and ▵E ≈ 1 keV at more than 3σ beyond r500, strongly constraining intracluster medium pre-heating scenarios. We also demonstrate robustness of results w.r.t. sample selection, X-ray analysis procedures, entropy modelling, etc. [ABSTRACT FROM AUTHOR]

Non-gravitational feedback affects the nature of the intracluster medium (ICM). X-ray cooling of the ICM and in situ energy feedback from active galactic nuclei (AGNs) and supernovae as well as pre-heating of the gas at epochs preceding the formation of clusters are proposed mechanisms for such feedback. While cooling and AGN feedbacks are dominant in cluster cores, the signatures of a pre-heated ICM are expected to be present even at large radii. To estimate the degree of pre-heating, with minimum confusion from AGN feedback/cooling, we study the excess entropy and non-gravitational energy profiles up to r500 for a sample of 17 galaxy clusters using joint data sets of Planck Sunyaev–Zel'dovich pressure and ROSAT/Position Sensitive Proportional Counter gas density profiles. The canonical value of pre-heating entropy floor of ≳300 keV cm2, needed in order to match cluster scalings, is ruled out at ≈3σ. We also show that the feedback energy of 1 keV particle-1 is ruled out at 5.2σ beyond r500. Our analysis takes both non-thermal pressure and clumping into account which can be important in outer regions. Our results based on the direct probe of the ICM in the outermost regions do not support any significant pre-heating. [ABSTRACT FROM AUTHOR]

We study the Sunyaev-Zel'dovich (SZ) distortion of the cosmic microwave background radiation from extensive circumgalactic gas (CGM) in massive galactic haloes. Recent observations have shown that galactic haloes contain a large amount of X-ray emitting gas at the virial temperature, as well as a significant amount of warm O VI absorbing gas. We consider the SZ distortion from the hot gas in those galactic haloes in which the gas cooling time is longer than the halo destruction time-scale. We show that the SZ distortion signal from the hot gas in these galactic haloes at redshifts z ≈ 1-8 can be significant at small angular scales (ℓ ∼ 104), and dominate over the signal from galaxy clusters. The estimated SZ signal for most massive galaxies (halo mass ≥1012.5 M⊙) is consistent with the marginal detection by Planck at these mass scales. We also consider the SZ effect from warm circumgalactic gas. The integrated Compton distortion from the warm O VI absorbing gas is estimated to be y ∼ 10-8, which could potentially be detected by experiments planned for the near future. Finally, we study the detectability of the SZ signal from circumgalactic gas in two types of surveys, a simple extension of the South Pole Telescope survey and a more futuristic cosmic-variance-limited survey. We find that these surveys can easily detect the kinetic Sunyaev-Zel'dovich signal from CGM. With the help of a Fisher matrix analysis, we find that it will be possible for these surveys to constrain the gas fraction in CGM, after marginalizing over cosmological parameters, to ≤33 per cent, in case of no redshift evolution of the gas fraction. [ABSTRACT FROM AUTHOR]

We make the first estimate of non-gravitational energy profiles in galaxy cluster cores (and beyond) based on observational data. Comparing the observed entropy profiles within r500, from the Representative XMM-Newton Cluster Structure Survey to simulated base entropy profiles without feedback from both adaptive mesh refinement (AMR) and smoothed particle hydrodynamic (SPH) non-radiative simulations, we estimate the amount of additional non-gravitational energy, EICM, contained in the intracluster medium (ICM), as well as the total energy feedback, EFeedback, from active galactic nuclei (AGNs; the central AGNs in most cases) into the clusters. The total feedback energy scales with the mean spectroscopic temperature as and for the SPH and AMR baseline profiles. The mean non-gravitational energy per particle within r500 remaining in the ICM after energy lost during cooling is εICM = 2.8 ± 0.8 keV for the SPH theoretical relation and εICM = 1.7 ± 0.9 keV for the AMR theoretical relation. We use the NRAO/VLA Sky Survey source catalog to determine the radio luminosity, LR, at 1.4 GHz of the central source(s) of our sample. For Tsp > 3 keV, the EFeedback correlates with LR, although with different normalization for cool-core and non-cool-core clusters. We show that AGNs could provide a significant portion of the feedback. [ABSTRACT FROM AUTHOR]

ABSTRACT We study the effect of entropy injection in the intracluster medium (ICM) in light of the recent observationally determined universal pressure profile of the ICM. Beginning with a power-law entropy profile that is expected in the absence of any feedback, we show that a simple universal prescription of entropy injection results in the final, observed universal pressure profile. This simple prescription has two components, one associated with an overall increase in entropy and another associated with injection in the central parts of the cluster. Importantly, both the components of entropy injection are needed to produce the final universal pressure profile. This is indicative of a need of both pre-heating the ICM as well in situ active galactic nuclei/supernovae heating. We demonstrate the usefulness of the method by extending the calculations to clusters at high redshift, and predict redshift evolution of cluster scaling relations that can be tested against data. We show that the self-similar evolution of the universal pressure profile is equivalent to a negative evolution of entropy injection with redshift, with a scaling Sinj∝ (1 + z)−0.8 Sinj( z = 0). We also show the current observational data are indicative of the entropy injection decreasing with redshift. [ABSTRACT FROM AUTHOR]

We study the X-ray cluster gas density distribution in hydrostatic equilibrium using the universal temperature profile obtained from recent simulations involving only gravitational processes. If this temperature profile is an indicator of the influence of gravitational processes alone on the intracluster medium (ICM), then the comparison of various X-ray parameters expected from this profile and the observed data would point towards any additional physics that may be required. We compare the entropy at and , the scaled entropy profile, the gas fraction at and the gas fraction profile with recent observations and we discuss the implications of this temperature profile in light of these data. We find that the entropy imparted to the gas from gravitational processes alone is larger than previously thought. The entropy at for rich clusters is consistent with the data, whereas the entropy at is still less than the observed values. We also find that the gas fraction in the inner region of clusters, expected from gravitational processes alone, is smaller than previously thought but larger than the observed data. It does show a trend with the emission-weighted temperature (〈 T〉) as shown by the data. We therefore find that the role of any additional non-gravitational process influencing the physical state of ICM would have to be revised in light of these findings. [ABSTRACT FROM AUTHOR]

The distribution of luminous radio galaxies in galaxy clusters has been observed to be concentrated in the inner region. We consider the role of dynamical friction of massive galaxies , assuming them to be hosts of luminous radio galaxies, and show that beginning with a Navarro–Frenk–White density profile of a cluster of mass of concentration c∼ 5 and collapsing at z∼ 1, the density profile of radio galaxies evolves to a profile of concentration c∼ 25, as observed, in a time-scale of t∼ 3–5 Gyr. [ABSTRACT FROM AUTHOR]

We estimate the 'non-gravitational' entropy-injection profiles, ∼K, and the resultant energy feedback profiles, ▵E, of the intracluster medium for 17 clusters using their Planck Sunyaev-Zel'dovich and ROSAT X-ray observations, spanning a large radial range from 0.2r500 up to r200. The feedback profiles are estimated by comparing the observed entropy, at fixed gas mass shells, with theoretical entropy profiles predicted from non-radiative hydrodynamic simulations. We include non-thermal pressure and gas clumping in our analysis. The inclusion of non-thermal pressure and clumping results in changing the estimates for r500 and r200 by 10-20 per cent. When clumpiness is not considered it leads to an underestimation of ▵ K ≈ 300 keV cm2 at r500 and▵ K≈1100 keV cm2 at r200. On the other hand, neglecting non-thermal pressure results in an overestimation of ▵ K ≈ 100 keV cm2 at r500 and underestimation of ▵ K ≈ 450 keV cm2 at r200. For the estimated feedback energy, we find that ignoring clumping leads to an underestimation of energy per particle ▵E ≈ 1 keV at r500 and ▵E ≈ 1.5 keV at r200. Similarly, neglect of the non-thermal pressure results in an overestimation of ▵E ≈ 0.5 keV at r500 and underestimation of ▵E ≈ 0.25 keV at r200. We find entropy floor of ▵ K ≈ 300 keV cm2 is ruled out at ≈3σ throughout the entire radial range and ▵E ≈ 1 keV at more than 3σ beyond r500, strongly constraining intracluster medium pre-heating scenarios. We also demonstrate robustness of results w.r.t. sample selection, X-ray analysis procedures, entropy modelling, etc. [ABSTRACT FROM AUTHOR]

We report the results of our study of fractional entropy enhancement in the intracluster medium (ICM) of the clusters from the representative XMM-Newton cluster structure survey. We compare the observed entropy profile of these clusters with that expected for the ICM without any feedback, as well as with the introduction of preheating and cooling. We make the first estimate of the total, as well as radial, non-gravitational energy deposition up to r500 for this large, nearly flux-limited, sample of clusters. We find that the total energy deposition corresponding to the entropy enhancement is proportional to the cluster temperature (and hence cluster mass). The energy deposition per particle scaled by Tsp, ΔE/Tsp has a similar profile in all clusters, and is more pronounced in the central regions. Our results support models of entropy enhancement through active galactic nucleus feedback. [ABSTRACT FROM AUTHOR]

We consider the production of 6Li in spallation reactions by cosmic rays in order to explain the observed abundance in halo metal-poor stars. We show that heating of ambient gas by cosmic rays is an inevitable consequence of this process, and estimate the energy input required to reproduce the observed abundance of to be of the order of a few hundred eV per particle. We draw attention to the possibility that this could explain the excess entropy in gas in galaxy groups and clusters. The evolution of 6Li and the accompanying heating of gas are calculated for structures collapsing at the present epoch with injection of cosmic rays at high redshift. We determine the energy required to explain the abundance of 6Li at corresponding to the formation epoch of halo metal-poor stars, and also an increased entropy level of ∼300 keV cm2 necessary to explain X-ray observations of clusters. The energy budget for this process is consistent with the expected energy output of radio-loud active galactic nuclei, and the diffusion length-scale of cosmic ray protons responsible for heating is comparable to the size of regions with excess entropy. We also discuss the constraints imposed by the extragalactic gamma-ray background. [ABSTRACT FROM AUTHOR]

Recent X-ray observations have revealed a universal temperature profile for the intracluster gas of non-cooling flow clusters which is flat for r ≤ 0.2r[sub 180]. Numerical simulations, however, obtain a steeper temperature profile in the inner region. We study the effect of thermal conduction on the intracluster gas in non-cooling flow clusters in light of these observations, using the steep temperature profiles obtained by numerical simulations. We find that, given 10[sup 10] yr for the intracluster gas to evolve, thermal conduction should be suppressed from the classical value by a factor of ∼10[sup -3] in order to explain the observations. [ABSTRACT FROM AUTHOR]