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Daisuke Nagai - One of the best experts on this subject based on the ideXlab platform.
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The Physics of Galaxy Cluster Outskirts
Space Science Reviews, 2019Co-Authors: Stephen Walker, Daisuke Nagai, Nobuhiro Okabe, S Ettori, Aurora Simionescu, Dominique Eckert, Tony Mroczkowski, Hiroki Akamatsu, Vittorio GhirardiniAbstract:As the largest virialized structures in the universe, galaxy clusters continue to grow and accrete matter from the cosmic web. Due to the low gas density in the Outskirts of clusters, measurements are very challenging, requiring extremely sensitive telescopes across the entire electromagnetic spectrum. Observations using X-rays, the Sunyaev–Zeldovich effect, and weak lensing and galaxy distributions from the optical band, have over the last decade helped to unravel this exciting new frontier of cluster astrophysics, where the infall and virialization of matter takes place. Here, we review the current state of the art in our observational and theoretical understanding of cluster Outskirts, and discuss future prospects for exploration using newly planned and proposed observatories.
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quenching of satellite galaxies at the Outskirts of galaxy clusters
Monthly Notices of the Royal Astronomical Society, 2018Co-Authors: Elad Zinger, Avishai Dekel, Andrey V Kravtsov, Daisuke NagaiAbstract:We find, using cosmological simulations of galaxy clusters, that the hot X-ray emitting intra-cluster medium (ICM) enclosed within the outer accretion shock extends out to $R_{\rm shock}\sim(2 - 3) R_{\rm vir}$, where $R_{\rm vir}$ is the standard virial radius of the halo. Using a simple analytic model for satellite galaxies in the cluster, we evaluate the effect of ram pressure stripping on the gas in the inner discs and in the haloes at different distances from the cluster centre. We find that significant removal of star-forming disc gas occurs only at $r \lesssim 0.5 R_{\rm vir}$, while gas removal from the satellite halo is more effective and can occur when the satellite is found between $ R_{\rm vir}$ and $R_{\rm shock}$. Removal of halo gas sets the stage for quenching of the star formation by starvation over $2\textrm{--}3\,\mathrm{Gyr}$, prior to the satellite entry to the inner cluster halo. This scenario explains the presence of quenched galaxies, preferentially discs, at the Outskirts of galaxy clusters, and the delayed quenching of satellites compared to central galaxies.
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STIRRED, NOT CLUMPED: EVOLUTION OF TEMPERATURE PROFILES IN THE Outskirts OF GALAXY CLUSTERS
The Astrophysical Journal, 2016Co-Authors: Camille Avestruz, Daisuke Nagai, Erwin T. LauAbstract:Recent statistical X-ray measurements of the intracluster medium (ICM) indicate that gas temperature profiles in the Outskirts of galaxy clusters deviate from self-similar evolution. Using a mass-limited sample of galaxy clusters from cosmological hydrodynamical simulations, we show that the departure from self-similarity can be explained by non-thermal gas motions driven by mergers and accretion. Contrary to previous claims, gaseous substructures only play a minor role in the temperature evolution in cluster Outskirts. A careful choice of halo overdensity definition in self-similar scaling mitigates these departures. Our work highlights the importance of non-thermal gas motions in ICM evolution and the use of galaxy clusters as cosmological probes.
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the xmm cluster Outskirts project x cop physical conditions to the virial radius of abell 2142
arXiv: Cosmology and Nongalactic Astrophysics, 2016Co-Authors: C Tchernin, Erwin T. Lau, S Molendi, E Pointecouteau, D Eckert, S Ettori, S Paltani, G Hurier, F Gastaldello, Daisuke NagaiAbstract:Context. Galaxy clusters are continuously growing through the accretion of matter in their Outskirts. This process induces inhomogeneities in the gas density distribution (clumping) which need to be taken into account to recover the physical properties of the intracluster medium (ICM) at large radii. Aims. We studied the thermodynamic properties in the Outskirts (R > R500) of the massive galaxy cluster Abell 2142 by combining the Sunyaev Zel'dovich (SZ) effect with the X-ray signal. Methods. We combined the SZ pressure profile measured by Planck with the XMM-Newton gas density profile to recover radial profiles of temperature, entropy and hydrostatic mass out to 2R500. We used a method that is insensitive to clumping to recover the gas density, and we compared the results with traditional X-ray measurement techniques. Results. When taking clumping into account, our joint SZ/X-ray entropy profile is consistent with the predictions from pure gravitational collapse, whereas a significant entropy flattening is found when the effect of clumping is neglected. The hydrostatic mass profile recovered using joint X-ray/SZ data agrees with that obtained from spectroscopic X-ray measurements and with mass reconstructions obtained through weak lensing and galaxy kinematics. Conclusions. We found that clumping can explain the entropy flattening observed by Suzaku in the Outskirts of several clusters. When using a method insensitive to clumping for the reconstruction of the gas density, the thermodynamic properties of Abell 2142 are compatible with the assumption that the thermal gas pressure sustains gravity and that the entropy is injected at accretion shocks, with no need to evoke more exotic physics. Our results highlight the need for X-ray observations with sufficient spatial resolution, and large collecting area, to understand the processes at work in cluster outer regions.
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non equilibrium electrons in the Outskirts of galaxy clusters
The Astrophysical Journal, 2015Co-Authors: Camille Avestruz, Erwin T. Lau, Daisuke Nagai, Kaylea NelsonAbstract:The analysis of X-ray and Sunyaev–Zel’dovich measurements of the intracluster medium (ICM) assumes that electrons are in thermal equilibrium with ions in the plasma. However, in the Outskirts of galaxy clusters, the electron–ion equilibration timescale can become comparable to the Hubble time, leading to systematic biases in cluster mass estimates and mass-observable scaling relations. To quantify an upper limit of the impact of non-equilibrium electrons, we use a mass-limited sample of simulated galaxy clusters taken from a cosmological simulation with a two-temperature model that assumes the Spitzer equilibration time for the electrons and ions. We show that the temperature bias is more pronounced in more massive and rapidly accreting clusters. For the most extreme case, we find that the bias is of the order of 10% at half of the cluster virial radius and increases to 40% at the edge of the cluster. Gas in filaments is less susceptible to the non-equilibrium effect, leading to azimuthal variations in the temperature bias at large cluster-centric radii. Using mock Chandra observations of simulated clusters, we show that the bias manifests in ultra-deep X-ray observations of cluster Outskirts and quantify the resulting biases in hydrostatic mass and cluster temperature derived from these observations. We provide a mass-dependent fitting function for the temperature bias profile, which can be useful for modeling the effect of electron-ion equilibration in galaxy clusters.
Erwin T. Lau - One of the best experts on this subject based on the ideXlab platform.
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STIRRED, NOT CLUMPED: EVOLUTION OF TEMPERATURE PROFILES IN THE Outskirts OF GALAXY CLUSTERS
The Astrophysical Journal, 2016Co-Authors: Camille Avestruz, Daisuke Nagai, Erwin T. LauAbstract:Recent statistical X-ray measurements of the intracluster medium (ICM) indicate that gas temperature profiles in the Outskirts of galaxy clusters deviate from self-similar evolution. Using a mass-limited sample of galaxy clusters from cosmological hydrodynamical simulations, we show that the departure from self-similarity can be explained by non-thermal gas motions driven by mergers and accretion. Contrary to previous claims, gaseous substructures only play a minor role in the temperature evolution in cluster Outskirts. A careful choice of halo overdensity definition in self-similar scaling mitigates these departures. Our work highlights the importance of non-thermal gas motions in ICM evolution and the use of galaxy clusters as cosmological probes.
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the xmm cluster Outskirts project x cop physical conditions to the virial radius of abell 2142
arXiv: Cosmology and Nongalactic Astrophysics, 2016Co-Authors: C Tchernin, Erwin T. Lau, S Molendi, E Pointecouteau, D Eckert, S Ettori, S Paltani, G Hurier, F Gastaldello, Daisuke NagaiAbstract:Context. Galaxy clusters are continuously growing through the accretion of matter in their Outskirts. This process induces inhomogeneities in the gas density distribution (clumping) which need to be taken into account to recover the physical properties of the intracluster medium (ICM) at large radii. Aims. We studied the thermodynamic properties in the Outskirts (R > R500) of the massive galaxy cluster Abell 2142 by combining the Sunyaev Zel'dovich (SZ) effect with the X-ray signal. Methods. We combined the SZ pressure profile measured by Planck with the XMM-Newton gas density profile to recover radial profiles of temperature, entropy and hydrostatic mass out to 2R500. We used a method that is insensitive to clumping to recover the gas density, and we compared the results with traditional X-ray measurement techniques. Results. When taking clumping into account, our joint SZ/X-ray entropy profile is consistent with the predictions from pure gravitational collapse, whereas a significant entropy flattening is found when the effect of clumping is neglected. The hydrostatic mass profile recovered using joint X-ray/SZ data agrees with that obtained from spectroscopic X-ray measurements and with mass reconstructions obtained through weak lensing and galaxy kinematics. Conclusions. We found that clumping can explain the entropy flattening observed by Suzaku in the Outskirts of several clusters. When using a method insensitive to clumping for the reconstruction of the gas density, the thermodynamic properties of Abell 2142 are compatible with the assumption that the thermal gas pressure sustains gravity and that the entropy is injected at accretion shocks, with no need to evoke more exotic physics. Our results highlight the need for X-ray observations with sufficient spatial resolution, and large collecting area, to understand the processes at work in cluster outer regions.
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non equilibrium electrons in the Outskirts of galaxy clusters
The Astrophysical Journal, 2015Co-Authors: Camille Avestruz, Erwin T. Lau, Daisuke Nagai, Kaylea NelsonAbstract:The analysis of X-ray and Sunyaev–Zel’dovich measurements of the intracluster medium (ICM) assumes that electrons are in thermal equilibrium with ions in the plasma. However, in the Outskirts of galaxy clusters, the electron–ion equilibration timescale can become comparable to the Hubble time, leading to systematic biases in cluster mass estimates and mass-observable scaling relations. To quantify an upper limit of the impact of non-equilibrium electrons, we use a mass-limited sample of simulated galaxy clusters taken from a cosmological simulation with a two-temperature model that assumes the Spitzer equilibration time for the electrons and ions. We show that the temperature bias is more pronounced in more massive and rapidly accreting clusters. For the most extreme case, we find that the bias is of the order of 10% at half of the cluster virial radius and increases to 40% at the edge of the cluster. Gas in filaments is less susceptible to the non-equilibrium effect, leading to azimuthal variations in the temperature bias at large cluster-centric radii. Using mock Chandra observations of simulated clusters, we show that the bias manifests in ultra-deep X-ray observations of cluster Outskirts and quantify the resulting biases in hydrostatic mass and cluster temperature derived from these observations. We provide a mass-dependent fitting function for the temperature bias profile, which can be useful for modeling the effect of electron-ion equilibration in galaxy clusters.
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mass accretion and its effects on the self similarity of gas profiles in the Outskirts of galaxy clusters
The Astrophysical Journal, 2015Co-Authors: Erwin T. Lau, Daisuke Nagai, Camille Avestruz, Kaylea Nelson, A VikhlininAbstract:Galaxy clusters exhibit remarkable self-similar behavior which allows us to establish simple scaling relationships between observable quantities and cluster masses, making galaxy clusters useful cosmological probes. Recent X-ray observations suggested that self-similarity may be broken in the Outskirts of galaxy clusters. In this work, we analyze a mass-limited sample of massive galaxy clusters from the Omega500 cosmological hydrodynamic simulation to investigate the self-similarity of the diffuse X-ray emitting intracluster medium (ICM) in the Outskirts of galaxy clusters. We find that the self-similarity of the outer ICM profiles is better preserved if they are normalized with respect to the mean density of the universe, while the inner profiles are more self-similar when normalized using the critical density. However, the outer ICM profiles as well as the location of accretion shock around clusters are sensitive to their mass accretion rate, which causes the apparent breaking of self-similarity in cluster Outskirts. We also find that the collisional gas does not follow the distribution of collisionless dark matter (DM) perfectly in the infall regions of galaxy clusters, leading to 10% departures in the gas-to-DM density ratio from the cosmic mean value. Our results have a number implications for interpreting observations of galaxy clusters in X-ray and through the Sunyaev?Zel?dovich effect, and their applications to cosmology.
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mass accretion and its effects on the self similarity of gas profiles in the Outskirts of galaxy clusters
arXiv: Cosmology and Nongalactic Astrophysics, 2014Co-Authors: Erwin T. Lau, Daisuke Nagai, Camille Avestruz, Kaylea Nelson, A VikhlininAbstract:Galaxy clusters exhibit remarkable self-similar behavior which allows us to establish simple scaling relationships between observable quantities and cluster masses, making galaxy clusters useful cosmological probes. Recent X-ray observations suggest that self-similarity may be broken in the Outskirts of galaxy clusters. In this work, we analyze a mass-limited sample of massive galaxy clusters from the Omega500 cosmological hydrodynamic simulation to investigate the self-similarity of the diffuse X-ray emitting intracluster medium (ICM) in the Outskirts of galaxy clusters. We find that the self-similarity of the outer ICM profiles is better preserved if they are normalized with respect to the mean density of the universe, while the inner profiles are more self-similar when normalized using the critical density. However, the outer ICM profiles as well as the location of accretion shock around clusters are sensitive to their mass accretion rate, which causes the apparent breaking of self-similarity in cluster Outskirts. We also find that the collisional gas does not follow the distribution of collisionless dark matter perfectly in the infall regions of galaxy clusters, leading to 10% departures in the gas-to-dark matter density ratio from the cosmic mean value. Our results have a number implications for interpreting observations of galaxy clusters in X-ray and through the Sunyaev-Zel'dovich effect and their application to cluster cosmology.
Camille Avestruz - One of the best experts on this subject based on the ideXlab platform.
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STIRRED, NOT CLUMPED: EVOLUTION OF TEMPERATURE PROFILES IN THE Outskirts OF GALAXY CLUSTERS
The Astrophysical Journal, 2016Co-Authors: Camille Avestruz, Daisuke Nagai, Erwin T. LauAbstract:Recent statistical X-ray measurements of the intracluster medium (ICM) indicate that gas temperature profiles in the Outskirts of galaxy clusters deviate from self-similar evolution. Using a mass-limited sample of galaxy clusters from cosmological hydrodynamical simulations, we show that the departure from self-similarity can be explained by non-thermal gas motions driven by mergers and accretion. Contrary to previous claims, gaseous substructures only play a minor role in the temperature evolution in cluster Outskirts. A careful choice of halo overdensity definition in self-similar scaling mitigates these departures. Our work highlights the importance of non-thermal gas motions in ICM evolution and the use of galaxy clusters as cosmological probes.
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non equilibrium electrons in the Outskirts of galaxy clusters
The Astrophysical Journal, 2015Co-Authors: Camille Avestruz, Erwin T. Lau, Daisuke Nagai, Kaylea NelsonAbstract:The analysis of X-ray and Sunyaev–Zel’dovich measurements of the intracluster medium (ICM) assumes that electrons are in thermal equilibrium with ions in the plasma. However, in the Outskirts of galaxy clusters, the electron–ion equilibration timescale can become comparable to the Hubble time, leading to systematic biases in cluster mass estimates and mass-observable scaling relations. To quantify an upper limit of the impact of non-equilibrium electrons, we use a mass-limited sample of simulated galaxy clusters taken from a cosmological simulation with a two-temperature model that assumes the Spitzer equilibration time for the electrons and ions. We show that the temperature bias is more pronounced in more massive and rapidly accreting clusters. For the most extreme case, we find that the bias is of the order of 10% at half of the cluster virial radius and increases to 40% at the edge of the cluster. Gas in filaments is less susceptible to the non-equilibrium effect, leading to azimuthal variations in the temperature bias at large cluster-centric radii. Using mock Chandra observations of simulated clusters, we show that the bias manifests in ultra-deep X-ray observations of cluster Outskirts and quantify the resulting biases in hydrostatic mass and cluster temperature derived from these observations. We provide a mass-dependent fitting function for the temperature bias profile, which can be useful for modeling the effect of electron-ion equilibration in galaxy clusters.
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mass accretion and its effects on the self similarity of gas profiles in the Outskirts of galaxy clusters
The Astrophysical Journal, 2015Co-Authors: Erwin T. Lau, Daisuke Nagai, Camille Avestruz, Kaylea Nelson, A VikhlininAbstract:Galaxy clusters exhibit remarkable self-similar behavior which allows us to establish simple scaling relationships between observable quantities and cluster masses, making galaxy clusters useful cosmological probes. Recent X-ray observations suggested that self-similarity may be broken in the Outskirts of galaxy clusters. In this work, we analyze a mass-limited sample of massive galaxy clusters from the Omega500 cosmological hydrodynamic simulation to investigate the self-similarity of the diffuse X-ray emitting intracluster medium (ICM) in the Outskirts of galaxy clusters. We find that the self-similarity of the outer ICM profiles is better preserved if they are normalized with respect to the mean density of the universe, while the inner profiles are more self-similar when normalized using the critical density. However, the outer ICM profiles as well as the location of accretion shock around clusters are sensitive to their mass accretion rate, which causes the apparent breaking of self-similarity in cluster Outskirts. We also find that the collisional gas does not follow the distribution of collisionless dark matter (DM) perfectly in the infall regions of galaxy clusters, leading to 10% departures in the gas-to-DM density ratio from the cosmic mean value. Our results have a number implications for interpreting observations of galaxy clusters in X-ray and through the Sunyaev?Zel?dovich effect, and their applications to cosmology.
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mass accretion and its effects on the self similarity of gas profiles in the Outskirts of galaxy clusters
arXiv: Cosmology and Nongalactic Astrophysics, 2014Co-Authors: Erwin T. Lau, Daisuke Nagai, Camille Avestruz, Kaylea Nelson, A VikhlininAbstract:Galaxy clusters exhibit remarkable self-similar behavior which allows us to establish simple scaling relationships between observable quantities and cluster masses, making galaxy clusters useful cosmological probes. Recent X-ray observations suggest that self-similarity may be broken in the Outskirts of galaxy clusters. In this work, we analyze a mass-limited sample of massive galaxy clusters from the Omega500 cosmological hydrodynamic simulation to investigate the self-similarity of the diffuse X-ray emitting intracluster medium (ICM) in the Outskirts of galaxy clusters. We find that the self-similarity of the outer ICM profiles is better preserved if they are normalized with respect to the mean density of the universe, while the inner profiles are more self-similar when normalized using the critical density. However, the outer ICM profiles as well as the location of accretion shock around clusters are sensitive to their mass accretion rate, which causes the apparent breaking of self-similarity in cluster Outskirts. We also find that the collisional gas does not follow the distribution of collisionless dark matter perfectly in the infall regions of galaxy clusters, leading to 10% departures in the gas-to-dark matter density ratio from the cosmic mean value. Our results have a number implications for interpreting observations of galaxy clusters in X-ray and through the Sunyaev-Zel'dovich effect and their application to cluster cosmology.
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non equilibrium electrons in the Outskirts of galaxy clusters
arXiv: Cosmology and Nongalactic Astrophysics, 2014Co-Authors: Camille Avestruz, Erwin T. Lau, Daisuke Nagai, Kaylea NelsonAbstract:The analysis of X-ray and Sunyaev-Zeldovich measurements of the intracluster medium (ICM) assumes that electrons are in thermal equilibrium with ions in the plasma. However, electron-ion equilibration timescales can be comparable to the Hubble time in the low density galaxy cluster Outskirts, leading to differences between the electron and ion temperatures. This temperature difference can lead to systematic biases in cluster mass estimates and mass-observable scaling relations. To quantify the impact of non-equilibrium electrons on the ICM profiles in cluster Outskirts, we use a high resolution cosmological simulation with a two-temperature model assuming the Spitzer equilibration timescale for the electrons. First, we show how the radial profile of this temperature bias depends on both the mass and mass accretion rate of the cluster; the bias is most pronounced in the most massive and most rapidly accreting clusters. For the most extreme case in our sample, we find that the bias is of order 10% at half of the cluster virial radius and increases to 40% at the edge of the cluster. We also find that gas in filaments is less susceptible to the non-equilibrium effect, leading to azimuthal variations at large cluster-centric radii. By analyzing mock Chandra observations of simulated clusters, we show that such azimuthal variations can be probed with deep X-ray observations. Finally, the mass-dependent temperature bias introduces biases in hydrostatic mass and cluster temperature, which has implications for cluster-based cosmological inferences. We provide a mass-dependent model for the temperature bias profile which can be useful for modeling the effect of electron-ion equilibration in galaxy clusters.
A Vikhlinin - One of the best experts on this subject based on the ideXlab platform.
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mass accretion and its effects on the self similarity of gas profiles in the Outskirts of galaxy clusters
The Astrophysical Journal, 2015Co-Authors: Erwin T. Lau, Daisuke Nagai, Camille Avestruz, Kaylea Nelson, A VikhlininAbstract:Galaxy clusters exhibit remarkable self-similar behavior which allows us to establish simple scaling relationships between observable quantities and cluster masses, making galaxy clusters useful cosmological probes. Recent X-ray observations suggested that self-similarity may be broken in the Outskirts of galaxy clusters. In this work, we analyze a mass-limited sample of massive galaxy clusters from the Omega500 cosmological hydrodynamic simulation to investigate the self-similarity of the diffuse X-ray emitting intracluster medium (ICM) in the Outskirts of galaxy clusters. We find that the self-similarity of the outer ICM profiles is better preserved if they are normalized with respect to the mean density of the universe, while the inner profiles are more self-similar when normalized using the critical density. However, the outer ICM profiles as well as the location of accretion shock around clusters are sensitive to their mass accretion rate, which causes the apparent breaking of self-similarity in cluster Outskirts. We also find that the collisional gas does not follow the distribution of collisionless dark matter (DM) perfectly in the infall regions of galaxy clusters, leading to 10% departures in the gas-to-DM density ratio from the cosmic mean value. Our results have a number implications for interpreting observations of galaxy clusters in X-ray and through the Sunyaev?Zel?dovich effect, and their applications to cosmology.
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mass accretion and its effects on the self similarity of gas profiles in the Outskirts of galaxy clusters
arXiv: Cosmology and Nongalactic Astrophysics, 2014Co-Authors: Erwin T. Lau, Daisuke Nagai, Camille Avestruz, Kaylea Nelson, A VikhlininAbstract:Galaxy clusters exhibit remarkable self-similar behavior which allows us to establish simple scaling relationships between observable quantities and cluster masses, making galaxy clusters useful cosmological probes. Recent X-ray observations suggest that self-similarity may be broken in the Outskirts of galaxy clusters. In this work, we analyze a mass-limited sample of massive galaxy clusters from the Omega500 cosmological hydrodynamic simulation to investigate the self-similarity of the diffuse X-ray emitting intracluster medium (ICM) in the Outskirts of galaxy clusters. We find that the self-similarity of the outer ICM profiles is better preserved if they are normalized with respect to the mean density of the universe, while the inner profiles are more self-similar when normalized using the critical density. However, the outer ICM profiles as well as the location of accretion shock around clusters are sensitive to their mass accretion rate, which causes the apparent breaking of self-similarity in cluster Outskirts. We also find that the collisional gas does not follow the distribution of collisionless dark matter perfectly in the infall regions of galaxy clusters, leading to 10% departures in the gas-to-dark matter density ratio from the cosmic mean value. Our results have a number implications for interpreting observations of galaxy clusters in X-ray and through the Sunyaev-Zel'dovich effect and their application to cluster cosmology.
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testing x ray measurements of galaxy cluster Outskirts with cosmological simulations
The Astrophysical Journal, 2014Co-Authors: Erwin T. Lau, Daisuke Nagai, Camille Avestruz, A VikhlininAbstract:The study of galaxy cluster Outskirts has emerged as one of the new frontiers in extragalactic astrophysics and cosmology with the advent of new observations in X-ray and microwave. However, the thermodynamic properties and chemical enrichment of this diffuse and azimuthally asymmetric component of the intracluster medium (ICM) are still not well understood. This work, for the first time, systematically explores potential observational biases in these regions. To assess X-ray measurements of galaxy cluster properties at large radii (>R 500c ), we use mock Chandra analyses of cosmological galaxy cluster simulations. The pipeline is identical to that used for Chandra observations, but the biases discussed in this paper are relevant for all X-ray observations outside of R 500c . We find the following from our analysis: (1) filament regions can contribute as much as 50% at R 200c to the emission measure; (2) X-ray temperatures and metal abundances from model fitted mock X-ray spectra in a multi-temperature ICM respectively vary to the level of 10% and 50%; (3) resulting density profiles vary to within 10% out to R 200c , and gas mass, total mass, and baryon fractions all vary to within a few percent; (4) the bias from a metal abundance extrapolated a factor of five higher than the true metal abundance results in total mass measurements biased high by 20% and total gas measurements biased low by 10%; and (5) differences in projection and dynamical state of a cluster can lead to gas density slope measurements that differ by a factor of 15% and 30%, respectively. The presented results can partially account for some of the recent gas profile measurements in cluster Outskirts by, e.g., Suzaku. Our findings are pertinent to future X-ray cosmological constraints from cluster Outskirts, which are least affected by non-gravitational gas physics, as well as to measurements probing gas properties in filamentary structures.
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testing x ray measurements of galaxy cluster Outskirts with cosmological simulations
arXiv: Cosmology and Nongalactic Astrophysics, 2014Co-Authors: Erwin T. Lau, Daisuke Nagai, Camille Avestruz, A VikhlininAbstract:The study of galaxy cluster Outskirts has emerged as one of the new frontiers in extragalactic astrophysics and cosmology with the advent of new observations in X-ray and microwave. However, the thermodynamic properties and chemical enrichment of this diffuse and azimuthally asymmetric component of the intracluster medium (ICM) are still not well understood. This work, for the first time, systematically explores potential observational biases in these regions. To assess X-ray measurements of galaxy cluster properties at large radii ($>{R}_{500c}$), we use mock Chandra analyses of cosmological galaxy cluster simulations. The pipeline is identical to that used for Chandra observations, but the biases discussed in this paper are relevant for all X-ray observations outside of ${R}_{500c}$. We find the following from our analysis: (1) filament regions can contribute as much as $50\%$ at $R_{200c}$ to the emission measure; (2) X-ray temperatures and metal abundances from model fitted mock X-ray spectra in a multi-temperature ICM respectively vary to the level of $10\%$ and $50\%$; (3) resulting density profiles vary to within $10\%$ out to $R_{200c}$, and gas mass, total mass, and baryon fractions all vary to within a few percent; (4) the bias from a metal abundance extrapolated a factor of five higher than the true metal abundance results in total mass measurements biased high by $20\%$ and total gas measurements biased low by $10\%$; and (5) differences in projection and dynamical state of a cluster can lead to gas density slope measurements that differ by a factor of $15\%$ and $30\%$, respectively. The presented results can partially account for some of the recent gas profile measurements in cluster Outskirts by, e.g., Suzaku. Our findings are pertinent to future X-ray cosmological constraints from cluster Outskirts.
Nobuhiro Okabe - One of the best experts on this subject based on the ideXlab platform.
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The Physics of Galaxy Cluster Outskirts
Space Science Reviews, 2019Co-Authors: Stephen Walker, Daisuke Nagai, Nobuhiro Okabe, S Ettori, Aurora Simionescu, Dominique Eckert, Tony Mroczkowski, Hiroki Akamatsu, Vittorio GhirardiniAbstract:As the largest virialized structures in the universe, galaxy clusters continue to grow and accrete matter from the cosmic web. Due to the low gas density in the Outskirts of clusters, measurements are very challenging, requiring extremely sensitive telescopes across the entire electromagnetic spectrum. Observations using X-rays, the Sunyaev–Zeldovich effect, and weak lensing and galaxy distributions from the optical band, have over the last decade helped to unravel this exciting new frontier of cluster astrophysics, where the infall and virialization of matter takes place. Here, we review the current state of the art in our observational and theoretical understanding of cluster Outskirts, and discuss future prospects for exploration using newly planned and proposed observatories.
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suzaku observations of the Outskirts of a1835 deviation from hydrostatic equilibrium
The Astrophysical Journal, 2013Co-Authors: Kazuya Ichikawa, Nobuhiro Okabe, Kyoko Matsushita, Y Fukazawa, Kosuke Sato, Y Y Zhang, A Finoguenov, Yutaka Fujita, Madoka KawaharadaAbstract:We present results of four-pointing Suzaku X-ray observations (total ~200 ks) of the intracluster medium (ICM) in the A1835 galaxy cluster (kT ~ 8 keV, z = 0.253) out to the virial radius (r vir ~ 2.9 Mpc) and beyond. Faint X-ray emission from the ICM out to r vir is detected. The temperature gradually decreases with radius from ~8 keV in the inner region to ~2 keV at r vir. The entropy profile is shown to flatten beyond r 500, in disagreement with the r 1.1 dependence predicted from the accretion shock heating model. The thermal pressure profile in the range 0.3r 500 r r vir agrees well with that obtained from the stacked Sunyaev-Zel'dovich effect observations with the Planck satellite. The hydrostatic mass profile in the cluster Outskirts (r 500 r r vir) falls well short of the weak-lensing one derived from Subaru/Suprime-Cam observations, showing an unphysical decrease with radius. The gas mass fraction at r vir defined with the lensing total mass agrees with the cosmic baryon fraction from the Wilkinson Microwave Anisotropy Probe seven-year data. All these results indicate, rather than the gas-clumping effect, that the bulk of the ICM in the cluster Outskirts is far from hydrostatic equilibrium and infalling matter retained some of its kinetic energy. Finally, combining with our recent Suzaku and lensing analysis of A1689, a cluster of similar mass, temperature, and redshift, we show that the cluster temperature distribution in the Outskirts is significantly correlated with the galaxy density field in the surrounding large-scale environment at (1-2)r vir.
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suzaku observations of abell 1835 Outskirts deviation from hydrostatic equilibrium
arXiv: Cosmology and Nongalactic Astrophysics, 2013Co-Authors: Kazuya Ichikawa, Madoka Kawaharada, Nobuhiro Okabe, Kyoko Matsushita, Y Fukazawa, Kosuke Sato, Y Y Zhang, A Finoguenov, Yutaka Fujita, Kazuhiro NakazawaAbstract:We present results of four-pointing Suzaku X-ray observations (total ~200 ks) of the intracluster medium (ICM) in the Abell 1835 galaxy cluster (kT ~ 8 keV, z = 0.253) out to the virial radius (r_vir ~ 2.9 Mpc) and beyond. Faint X-ray emission from the ICM out to r_vir is detected. The temperature gradually decreases with radius from ~8 keV in the inner region to ~2 keV at r_vir. The entropy profile is shown to flatten beyond r_500, in disagreement with the r_1.1 dependence predicted from the accretion shock heating model. The thermal pressure profile in the range 0.3r_500 < r < r_vir agrees well with that obtained from the stacked Sunyaev-Zel'dovich effect observations with the Planck satellite. The hydrostatic mass profile in the cluster Outskirts (r_500 < r < r_vir) falls well short of the weak lensing one derived from Subaru/Suprime-Cam observations, showing an unphysical decrease with radius. The gas mass fraction at r_vir defined with the lensing total mass agrees with the cosmic baryon fraction from the WMAP 7-year data. All these results indicate, rather than the gas-clumping effect, that the bulk of the ICM in the cluster Outskirts is far from hydrostatic equilibrium and infalling matter retained some of its kinetic energy. Finally, combining with our recent Suzaku and lensing analysis of Abell 1689, a cluster of similar mass, temperature, and redshift, we show that the cluster temperature distribution in the Outskirts is significantly correlated with the galaxy density field in the surrounding large-scale environment at (1-2)r_vir.
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suzaku observation of a1689 anisotropic temperature and entropy distributions associated with the large scale structure
The Astrophysical Journal, 2010Co-Authors: Madoka Kawaharada, Nobuhiro Okabe, Keiichi Umetsu, Motokazu Takizawa, Kyoko Matsushita, Y Fukazawa, Takashi Hamana, Satoshi Miyazaki, Kazuhiro NakazawaAbstract:We present results of new, deep Suzaku X-ray observations (160 ks) of the intracluster medium (ICM) in A1689 out to its virial radius, combined with complementary data sets of the projected galaxy distribution obtained from the SDSS catalog and the projected mass distribution from our recent comprehensive weak and strong lensing analysis of Subaru/Suprime-Cam and Hubble Space Telescope/Advanced Camera for Surveys observations. Faint X-ray emission from the ICM around the virial radius (r vir ~ 156) is detected at 4.0σ significance, thanks to the low and stable particle background of Suzaku. The Suzaku observations reveal anisotropic gas temperature and entropy distributions in cluster Outskirts of r 500 r r vir correlated with large-scale structure of galaxies in a photometric redshift slice around the cluster. The high temperature (~5.4 keV) and entropy region in the northeastern (NE) Outskirts is apparently connected to an overdense filamentary structure of galaxies outside the cluster. The gas temperature and entropy profiles in the NE direction are in good agreement, out to the virial radius, with that expected from a recent XMM-Newton statistical study and with an accretion shock heating model of the ICM, respectively. On the contrary, the other outskirt regions in contact with low-density void environments have low gas temperatures (~1.7 keV) and entropies, deviating from hydrostatic equilibrium. These anisotropic ICM features associated with large-scale structure environments suggest that the thermalization of the ICM occurs faster along overdense filamentary structures than along low-density void regions. We find that the ICM density distribution is fairly isotropic, with a three-dimensional density slope of –2.29 ± 0.18 in the radial range of r 2500 r r 500, and with –1.24+0.23 –0.56 in r 500 r r vir, which, however, is significantly shallower than the Navarro, Frenk, and White universal matter density profile in the Outskirts, ρ r –3. A joint X-ray and lensing analysis shows that the hydrostatic mass is lower than the spherical-lensing one (~60%-90%), but comparable to a triaxial halo mass within errors, at intermediate radii of 0.6r 2500 r 0.8r 500. On the other hand, the hydrostatic mass within 0.4r 2500 is significantly biased as low as 60%, irrespective of mass models. The thermal gas pressure within r 500 is, at most, ~50%-60% of the total pressure to balance fully the gravity of the spherical-lensing mass, and ~30%-40% around the virial radius. Although these constitute lower limits when one considers the possible halo triaxiality, these small relative contributions of thermal pressure would require additional sources of pressure, such as bulk and/or turbulent motions.
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suzaku observation of abell 1689 anisotropic temperature and entropy distributions associated with the large scale structure
arXiv: Cosmology and Nongalactic Astrophysics, 2010Co-Authors: Madoka Kawaharada, Nobuhiro Okabe, Keiichi Umetsu, Motokazu Takizawa, Kyoko Matsushita, Y Fukazawa, Takashi Hamana, Satoshi Miyazaki, Kazuhiro Nakazawa, Takaya OhashiAbstract:(Abridged) We present results of Suzaku observations of the intracluster medium (ICM) in Abell 1689, combined with complementary analysis of the SDSS data and weak and strong lensing analysis of Subaru/Suprime-Cam and HST/ACS observations. Faint X-ray emission from the ICM around the virial radius is detected at 4.0 sigma significance. We find anisotropic gas temperature and entropy distributions in cluster Outskirts correlated with large-scale structure of galaxies. The high temperature and entropy region in the northeastern (NE) Outskirts is connected to an overdense filamentary structure. The outskirt regions in contact with low density void environments have low gas temperatures and entropies, deviating from hydrostatic equilibrium. These results suggest that thermalization of the ICM occurs faster along the filamentary structures than the void regions. A joint X-ray and lensing analysis shows that the hydrostatic mass is $\sim60-90%$ of spherical lensing one but comparable to a triaxial halo mass within errors in $0.6r_{2500} \simlt r \simlt 0.8r_{500}$, and that it is significantly biased as low as $\simlt60%$ within $0.4r_{2500}$, irrespective of mass models. The thermal gas pressure within $r_{500}$ is, at most, $\sim50$--60% of the total pressure to balance fully the gravity of the spherical lensing mass, and $\sim30$--40% around the virial radius. Although these constitute lower limits when one considers the possible halo triaxiality, these small relative contributions of thermal pressure would require additional sources of pressure, such as bulk and/or turbulent motions.
