Gas Mass Fraction Profiles Research Articles

The X-ray invisible Universe. A look into the haloes undetected by eROSITA

ABSTRACT The paper presents the analysis of optically selected GAMA groups and clusters in the SRG/eROSITA X-ray map of eROSITA Final Equatorial Depth Survey, in the halo mass range 1013−5 × 1014 M⊙ and at z < 0.2. All X-ray detections have a clear GAMA counterpart, but most of the GAMA groups in the halo mass range 1013−1014 M⊙ remain undetected. We compare the X-ray surface brightness profiles of the eROSITA detected groups with the mean stacked profile of the undetected low-mass haloes at fixed halo mass. Overall, we find that the undetected groups exhibit less concentrated X-ray surface brightness, dark matter, and galaxy distributions with respect to the X-ray-detected haloes. The mean gas mass fraction profiles are consistent in the two samples within 1.5σ, indicating that the gas follows the dark matter profile. The low-mass concentration and the magnitude gap indicate that these systems are young. They reside with a higher probability in filaments while X-ray-detected groups favour the nodes of the Cosmic Web. Because of the lower central emission, the undetected systems tend to be X-ray underluminous at fixed halo mass and to lie below the LX−Mhalo relation. Interestingly, the X-ray-detected systems inhabiting the nodes scatter the less around the relation, while those in filaments tend to lie below it. We do not observe any strong relationship between the system X-ray appearance and the active galactic nucleus (AGN) activity. We cannot exclude the role of the past AGN feedback in affecting the gas distribution over the halo lifetime. However, the data suggests that the observed differences might be related to the halo assembly bias.

Cosmological implications of a modified galaxy cluster pressure profile using the Planck tSZ power spectrum

The mean pressure profile of the cluster population is a key element in cosmological analyses based on surveys of galaxy clusters observed through the Sunyaev-Zel’dovich (SZ) effect. A variation of both the shape and the amplitude of this profile could explain part of the discrepancy currently observed between the cosmological constraints obtained from the analyses of the CMB primary anisotropies and those from cluster abundance in SZ surveys for a fixed mass bias parameter. We study the cosmological implications of a modification of the mean pressure profile through the analysis of the SZ power spectrum measured by Planck. We define two mean pressure profiles on either side of the one obtained from the observation of nearby clusters by Planck. The parameters of these profiles are chosen to ensure their compatibility with the distributions of pressure and gas mass fraction profiles observed at low redshift. We find significant differences between the cosmological parameters obtained by using these two profiles to fit the Planck SZ power spectrum and those found in previous analyses. We conclude that a ∼15% decrease of the amplitude of the mean normalized pressure profile is sufficient to alleviate the discrepancy observed between the constraints of σ8 and Ωm from the CMB and cluster analyses.

Impact of the mean pressure profile of galaxy clusters on the cosmological constraints from the Planck tSZ power spectrum

ABSTRACTCosmological analyses based on surveys of galaxy clusters observed through the Sunyaev–Zel’dovich (SZ) effect strongly rely on the mean pressure profile of the cluster population. A tension is currently observed between the cosmological constraints obtained from the analyses of the CMB primary anisotropies and those from cluster abundance in SZ surveys. This discrepancy may be explained by a wrong estimate of the hydrostatic bias parameter that links the hydrostatic mass to the true mass of galaxy clusters. However, a variation of both the amplitude and the shape of the mean pressure profile could also explain part of this tension. We analyse the effects of a modification of this profile on the constraints of the σ8 and Ωm parameters through the analysis of the SZ power spectrum measured by the Planck collaboration. We choose two mean pressure profiles that are respectively lower and higher than the one obtained from the observation of nearby clusters by Planck. The selection of the parameters of these two profiles is based on the current estimates of the pressure and gas mass fraction profile distributions at low redshift. The cosmological parameters found for these two profiles are significantly different from the ones obtained with the Planck pressure profile. We conclude that an ${\sim }15{{\ \rm per\ cent}}$ decrease of the amplitude of the mean normalized pressure profile would alleviate the tension observed between the constraints of σ8 and Ωm from the CMB and cluster analyses without requiring extreme values of the mass bias parameter.

The hot gas content of fossil galaxy clusters

We investigate the properties of the hot gas in four fossil galaxy systems detected at high significance in the Planck Sunyaev-Zeldovich (SZ) survey. XMM-Newton observations reveal overall temperatures of kT ~ 5-6 keV and yield hydrostatic masses M500,HE > 3.5 x 10e14 Msun, confirming their nature as bona fide massive clusters. We measure the thermodynamic properties of the hot gas in X-rays (out to beyond R500 in three cases) and derive their individual pressure profiles out to R ~ 2.5 R500 with the SZ data. We combine the X-ray and SZ data to measure hydrostatic mass profiles and to examine the hot gas content and its radial distribution. The average Navarro-Frenk-White (NFW) concentration parameter, c500 = 3.2 +/- 0.4, is the same as that of relaxed `normal' clusters. The gas mass fraction profiles exhibit striking variation in the inner regions, but converge to approximately the cosmic baryon fraction (corrected for depletion) at R500. Beyond R500 the gas mass fraction profiles again diverge, which we interpret as being due to a difference in gas clumping and/or a breakdown of hydrostatic equilibrium in the external regions. Overall our observations point to considerable radial variation in the hot gas content and in the gas clumping and/or hydrostatic equilibrium properties in these fossil clusters, at odds with the interpretation of their being old, evolved and undisturbed. At least some fossil objects appear to be dynamically young.

Planckintermediate results

Taking advantage of the all-sky coverage and broadfrequency range of the Planck satellite, we study the Sunyaev-Zeldovich (SZ) and pressure profiles of 62 nearby massive clusters detected at high significance in the 14-month nominal survey. Careful reconstruction of the SZ signal indicates that most clusters are individually detected at least out to R500. By stacking the radial profiles, we have statistically detected the radial SZ signal out to 3 × R500, i.e., at a density contrast of about 50–100, though the dispersion about the mean profile dominates the statistical errors across the whole radial range. Our measurement is fully consistent with previous Planck results on integrated SZ fluxes, further strengthening the agreement between SZ and X-ray measurements inside R500. Correcting for the effects of the Planck beam, we have calculated the corresponding pressure profiles. This new constraint from SZ measurements is consistent with the X-ray constraints from XMM-Newton in the region in which the profiles overlap (i.e., [0.1–1] R500), and is in fairly good agreement with theoretical predictions within the expected dispersion. At larger radii the average pressure profile is slightly flatter than most predictions from numerical simulations. Combining the SZ and X-ray observed profiles into a joint fit to a generalised pressure profile gives best-fit parameters [P0,c500,γ,α,β ] = [6.41,1.81,0.31,1.33,4.13 ] . Using a reasonable hypothesis for the gas temperature in the cluster outskirts we reconstruct from our stacked pressure profile the gas mass fraction profile out to 3 R500. Within the temperature driven uncertainties, our Planck constraints are compatible with the cosmic baryon fraction and expected gas fraction in halos.

Investigation of CO2 sorption in molten polymers at high pressures using Raman line imaging

CO2 sorption in molten poly(ε-caprolactone) (PCL) has been investigated by temporally resolved Raman line imaging, which is introduced here as a new technology for the direct measurement of gas mass fraction profiles inside polymers during transient sorption experiments. Molten PCL was exposed to pressurized carbon dioxide in an optically accessible pressure cell at 80 °C and pressures up to 7.1 MPa. During sorption, Raman spectra were acquired temporally and spatially resolved across the PCL drop, allowing the evaluation of the PCL/CO2 mutual diffusivity, of the CO2 solubility in PCL, and the determination of temporal evolution of mass fraction profiles of carbon dioxide inside PCL.

Further X-ray observations of the galaxy cluster PKS 0745−191 to the virial radius and beyond

We use new Suzaku observations of PKS 0745-191 to measure the thermodynamic properties of its ICM out to and beyond r_{200} (reaching 1.25r_{200}) with better accuracy than previously achieved, owing to a more accurate and better understood background model. We investigate and resolve the tensions between the previous Suzaku and ROSAT results for PKS 0745-191, which are found to be principally caused by incorrect background modelling in the previous Suzaku analysis. We investigate in depth the systematic errors affecting this observation, and present temperature, density, entropy and gas mass fraction profiles reaching out to and beyond the virial radius. We find that the entropy profile flattens in the outskirts as originally observed in the previous Suzaku analysis, but that the flattening starts at larger radius. The flattening of the entropy profile and our mass analysis suggests that outside ~17' (~1.9 Mpc) the ICM is out of hydrostatic equilibrium or the presence of significant non-thermal pressure support.

JOINT ANALYSIS OF X-RAY AND SUNYAEV–ZEL'DOVICH OBSERVATIONS OF GALAXY CLUSTERS USING AN ANALYTIC MODEL OF THE INTRACLUSTER MEDIUM

ABSTRACT We perform a joint analysis of X-ray and Sunyaev–Zel'dovich effect data using an analytic model that describes the gas properties of galaxy clusters. The joint analysis allows the measurement of the cluster gas mass fraction profile and Hubble constant independent of cosmological parameters. Weak cosmological priors are used to calculate the overdensity radius within which the gas mass fractions are reported. Such an analysis can provide direct constraints on the evolution of the cluster gas mass fraction with redshift. We validate the model and the joint analysis on high signal-to-noise data from the Chandra X-ray Observatory and the Sunyaev–Zel'dovich Array for two clusters, A2631 and A2204.

Gas entropy in a representative sample of nearby X-ray galaxy clusters (REXCESS): relationship to gas mass fraction

(Abridged) We examine the radial entropy distribution and its scaling using 31 nearby galaxy clusters from the Representative XMM-Newton Cluster Structure Survey (REXCESS). The entropy profiles are robustly measured at least out to R_1000 in all systems and out to R_500 in 13 systems. Compared to theoretical expectations, the observed distributions show a radial and mass-dependent excess entropy that is greater and extends to larger radii in lower mass systems. At R_500, the mass dependence and entropy excess are both negligible within the uncertainties. Mirroring this behaviour, the scaling of gas entropy is shallower than self-similar in the inner regions, but steepens with radius, becoming consistent with self-similar at R_500. The dispersion in scaled entropy in the inner regions is linked to the presence of cool cores and dynamical activity; at larger radii the dispersion decreases by a factor of two and the dichotomy between subsamples disappears. Parameterising the profiles with a power law plus constant model, there are two peaks in central entropy K_0; however, we cannot distinguish between a bimodal or a left-skewed distribution. The outer slopes are correlated with system temperature; their distribution is unimodal with a median value of 0.98. Renormalising the dimensionless entropy profiles by the gas mass fraction profile f_gas(< R), leads to a remarkable reduction in the scatter, implying that gas mass fraction variations with radius and mass are the cause of the observed entropy properties. We discuss a tentative scenario to explain the behaviour of the entropy and gas mass fraction in the REXCESS sample, in which extra heating and merger mixing maintains an elevated central entropy level in the majority of the population, and a smaller fraction of systems develops a cool core.

X-ray observations of the galaxy cluster PKS 0745−191: to the virial radius, and beyond

We use new Suzaku observations of PKS 0745−191 to measure the thermodynamic properties of its intracluster medium (ICM) out to and beyond r200 (reaching 1.25r200) with better accuracy than previously achieved, owing to a more accurate and better understood background model. We investigate and resolve the tensions between the previous Suzaku and ROSAT results for PKS 0745−191, which are found to be principally caused by incorrect background modelling in the previous Suzaku analysis. We investigate in depth the systematic errors affecting this observation, and present temperature, density, entropy and gas mass fraction profiles reaching out to and beyond the virial radius. We find that the entropy profile flattens in the outskirts as originally observed in the previous Suzaku analysis, but that the flattening starts at larger radius. The flattening of the entropy profile and our mass analysis suggest that outside ∼17 arcmin (∼1.9 Mpc) the ICM is out of hydrostatic equilibrium or the presence of significant non-thermal pressure support.

ChandraSample of Nearby Relaxed Galaxy Clusters: Mass, Gas Fraction, and Mass‐Temperature Relation

We present gas and total mass profiles for 13 low-redshift, relaxed clusters spanning a temperature range 0.7-9 keV, derived from all available Chandra data of sufficient quality. In all clusters, gas temperature profiles are measured to large radii (Vikhlinin et al.) so that direct hydrostatic mass estimates are possible to nearly r_500 or beyond. The gas density was accurately traced to larger radii; its profile is not described well by a beta-model, showing continuous steepening with radius. The derived rho_tot profiles and their scaling with mass generally follow the Navarro-Frenk-White model with concentration expected for dark matter halos in LambdaCDM cosmology. In the inner region (r<0.1r_500), the gas density and temperature profiles exhibit significant scatter and trends with mass, but they become nearly self-similar at larger radii. Correspondingly, we find that the slope of the mass-temperature relation for these relaxed clusters is in good agreement with the simple self-similar behavior, M_500 ~ T^alpha, where alpha=(1.5-1.6)+-0.1, if the gas temperatures are measured excluding the central cool cores. The normalization of this M-T relation is significantly, by =~ 30%, higher than most previous X-ray determinations. We derive accurate gas mass fraction profiles, which show increase both with radius and cluster mass. The enclosed f_gas profiles within r_2500 =~ 0.4 r_500 have not yet reached any asymptotic value and are still far (by a factor of 1.5-2) from the Universal baryon fraction according to the CMB observations. The f_gas trends become weaker and its values closer to Universal at larger radii, in particular, in spherical shells r_2500<r<r_500.

X-ray spectroscopy of the cluster of galaxies PKS 0745-191 with XMM-Newton

We present the results from XMM-Newton observations of the cluster of galaxies PKS 0745-191. The spatially resolved spectra from the European Photon Imaging Cameras ( both EPN and EMOS) can be fitted with a single temperature thermal plasma model when the interstellar column density is closer to the lower limit of the range allowed by observations. Alternatively, a two-component model can be fitted to the spectra from the inner region for slightly higher values of N-H. The temperature profile shows a drop in the center of the cluster, from about 8 keV at radii larger than similar to350 kpc to about 4 keV at the center, indicating that the gas in the central region is cooling. The total cooling flow rate inferred from the spectral data is only 364(-94)(+97) M-circle dot yr(-1), however, much smaller than the previously obtained value. The metal abundance is found to decrease from 0.5 in solar units at the center to about 0.2 at a radius of similar to300 kpc. Deprojected spectra are also presented, which show a result similar to the projected spectra. The location of the X-ray emission peak is also the site of extended radio emission. Inspection of the higher resolution Chandra image of the cluster shows enhanced X-ray emission about 3 west of the center where also the radio emission is elongated. We explore possible implications on the interaction between the radio lobes and the intracluster plasma. Assuming that the gas is in hydrostatic equilibrium with the cluster potential, we find a total mass of about 1.18 +/- 0.04 x 10(13) M-circle dot within the critical radius of the observed gravitational arc, which is a factor similar to2 lower, however, than that from optical lensing. We also calculated the gas mass fraction profile up to 0.63 r(vir) and obtained a mean gas mass fraction f(gas) = 0.22 +/- 0.02.

A two-phase model for laminar film condensation from steam-air mixtures in vertical parallel-plate channels

Detailed results are presented for laminar film condensation from steam-air mixtures flowing downward in vertical flat-plate channels. The mixture flow is laminar and saturation conditions prevail at the inlet. A fully coupled implicit numerical approach is used that achieves excellent convergence behavior, even for high inlet gas mass fractions. The detailed results include velocity, temperature, and gas mass fraction profiles, as well as axial variations of film thickness, pressure gradient and Nusselt number. The effects of a wide range of changes in the four independent variables (the inlet-to-wall temperature difference and the inlet values of gas concentration, Reynolds number, and pressure) on the film thickness, axial pressure gradient, and the local and average Nusselt numbers are carefully examined. It was found that increases in inlet concentration of noncondensable gas caused significant decreases in the film thickness, local Nusselt number, and axial pressure gradient. An analytical solution for the film thickness and velocity field at the end of condensation path was developed and shown to be the asymptotic value of the numerical results for large distances along the channel.