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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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HYDRODYNAMIC SIMULATION OF NON-THERMAL PRESSURE PROFILES OF Galaxy Clusters
The Astrophysical Journal, 2014Co-Authors: Kaylea Nelson, Erwin T. Lau, Daisuke NagaiAbstract:Cosmological constraints from X-ray and microwave observations of Galaxy Clusters are subjected to systematic uncertainties. Non-thermal pressure support due to internal gas motions in Galaxy Clusters is one of the major sources of astrophysical uncertainties. Using a mass-limited sample of Galaxy Clusters from a high-resolution hydrodynamical cosmological simulation, we characterize the non-thermal pressure fraction profile and study its dependence on redshift, mass, and mass accretion rate. We find that the non-thermal pressure fraction profile is universal across redshift when Galaxy cluster radii are defined with respect to the mean matter density of the universe instead of the commonly used critical density. We also find that the non-thermal pressure is predominantly radial, and the gas velocity anisotropy profile exhibits strong universality when Galaxy cluster radii are defined with respect to the mean matter density of the universe. However, we find that the non-thermal pressure fraction is strongly dependent on the mass accretion rate of the Galaxy cluster. We provide fitting formulae for the universal non-thermal pressure fraction and velocity anisotropy profiles of gas in Galaxy Clusters, which should be useful in modeling astrophysical uncertainties pertinent to using Galaxy Clusters as cosmological probes.
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Universal Non-thermal Pressure Fraction Profile in Galaxy Clusters
arXiv: Cosmology and Nongalactic Astrophysics, 2014Co-Authors: Kaylea Nelson, Erwin T. Lau, Daisuke NagaiAbstract:Cosmological constraints from X-ray and microwave observations of Galaxy Clusters are subjected to systematic uncertainties. Non-thermal pressure support due to internal gas motions in Galaxy Clusters is one of the major sources of astrophysical uncertainties. Using a mass-limited sample of Galaxy Clusters from a high-resolution hydrodynamical cosmological simulation, we characterize the non-thermal pressure fraction profile and study its dependence on redshift, mass, and mass accretion rate. We find that the non-thermal pressure fraction profile is universal across redshift when Galaxy cluster radii are defined with respect to the mean matter density of the universe instead of the commonly used critical density. We also find that the non-thermal pressure is predominantly radial, and the gas velocity anisotropy profile exhibits strong universality when Galaxy cluster radii are defined with respect to the mean matter density of the universe. However, we find that the non-thermal pressure fraction is strongly dependent on the mass accretion rate of the Galaxy cluster. We provide fitting formulae for the universal non-thermal pressure fraction and velocity anisotropy profiles of gas in Galaxy Clusters, which should be useful in modeling astrophysical uncertainties pertinent to using Galaxy Clusters as cosmological probes.
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Weighing Galaxy Clusters with Gas. II. On the Origin of Hydrostatic Mass Bias in ΛCDM Galaxy Clusters
The Astrophysical Journal, 2014Co-Authors: Kaylea Nelson, Erwin T. Lau, Daisuke Nagai, Douglas H. RuddAbstract:The use of Galaxy Clusters as cosmological probes hinges on our ability to measure their masses accurately and with high precision. Hydrostatic mass is one of the most common methods for estimating the masses of individual Galaxy Clusters, which suffer from biases due to departures from hydrostatic equilibrium. Using a large, mass-limited sample of massive Galaxy Clusters from a high-resolution hydrodynamical cosmological simulation, in this work we show that in addition to turbulent and bulk gas velocities, acceleration of gas introduces biases in the hydrostatic mass estimate of Galaxy Clusters. In unrelaxed Clusters, the acceleration bias is comparable to the bias due to non-thermal pressure associated with merger-induced turbulent and bulk gas motions. In relaxed Clusters, the mean mass bias due to acceleration is small ( 3%), but the scatter in the mass bias can be reduced by accounting for gas acceleration. Additionally, this acceleration bias is greater in the outskirts of higher redshift Clusters where mergers are more frequent and Clusters are accreting more rapidly. Since gas acceleration cannot be observed directly, it introduces an irreducible bias for hydrostatic mass estimates. This acceleration bias places limits on how well we can recover cluster masses from future X-ray and microwave observations. We discuss implications for cluster mass estimates based on X-ray, Sunyaev-Zel'dovich effect, and gravitational lensing observations and their impact on cluster cosmology.
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The gas distribution in the outer regions of Galaxy Clusters
Astronomy & Astrophysics, 2012Co-Authors: Dominique Eckert, Erwin T. Lau, Daisuke Nagai, Stefano Ettori, Franco Vazza, Silvano Molendi, Mauro Roncarelli, Mariachiara Rossetti, Steven L. Snowden, Fabio GastaldelloAbstract:Aims. We present our analysis of a local (z = 0.04-0.2) sample of 31 Galaxy Clusters with the aim of measuring the density of the X-ray emitting gas in cluster outskirts. We compare our results with numerical simulations to set constraints on the azimuthal symmetry and gas clumping in the outer regions of Galaxy Clusters.
Daisuke Nagai - 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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HYDRODYNAMIC SIMULATION OF NON-THERMAL PRESSURE PROFILES OF Galaxy Clusters
The Astrophysical Journal, 2014Co-Authors: Kaylea Nelson, Erwin T. Lau, Daisuke NagaiAbstract:Cosmological constraints from X-ray and microwave observations of Galaxy Clusters are subjected to systematic uncertainties. Non-thermal pressure support due to internal gas motions in Galaxy Clusters is one of the major sources of astrophysical uncertainties. Using a mass-limited sample of Galaxy Clusters from a high-resolution hydrodynamical cosmological simulation, we characterize the non-thermal pressure fraction profile and study its dependence on redshift, mass, and mass accretion rate. We find that the non-thermal pressure fraction profile is universal across redshift when Galaxy cluster radii are defined with respect to the mean matter density of the universe instead of the commonly used critical density. We also find that the non-thermal pressure is predominantly radial, and the gas velocity anisotropy profile exhibits strong universality when Galaxy cluster radii are defined with respect to the mean matter density of the universe. However, we find that the non-thermal pressure fraction is strongly dependent on the mass accretion rate of the Galaxy cluster. We provide fitting formulae for the universal non-thermal pressure fraction and velocity anisotropy profiles of gas in Galaxy Clusters, which should be useful in modeling astrophysical uncertainties pertinent to using Galaxy Clusters as cosmological probes.
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Universal Non-thermal Pressure Fraction Profile in Galaxy Clusters
arXiv: Cosmology and Nongalactic Astrophysics, 2014Co-Authors: Kaylea Nelson, Erwin T. Lau, Daisuke NagaiAbstract:Cosmological constraints from X-ray and microwave observations of Galaxy Clusters are subjected to systematic uncertainties. Non-thermal pressure support due to internal gas motions in Galaxy Clusters is one of the major sources of astrophysical uncertainties. Using a mass-limited sample of Galaxy Clusters from a high-resolution hydrodynamical cosmological simulation, we characterize the non-thermal pressure fraction profile and study its dependence on redshift, mass, and mass accretion rate. We find that the non-thermal pressure fraction profile is universal across redshift when Galaxy cluster radii are defined with respect to the mean matter density of the universe instead of the commonly used critical density. We also find that the non-thermal pressure is predominantly radial, and the gas velocity anisotropy profile exhibits strong universality when Galaxy cluster radii are defined with respect to the mean matter density of the universe. However, we find that the non-thermal pressure fraction is strongly dependent on the mass accretion rate of the Galaxy cluster. We provide fitting formulae for the universal non-thermal pressure fraction and velocity anisotropy profiles of gas in Galaxy Clusters, which should be useful in modeling astrophysical uncertainties pertinent to using Galaxy Clusters as cosmological probes.
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Weighing Galaxy Clusters with Gas. II. On the Origin of Hydrostatic Mass Bias in ΛCDM Galaxy Clusters
The Astrophysical Journal, 2014Co-Authors: Kaylea Nelson, Erwin T. Lau, Daisuke Nagai, Douglas H. RuddAbstract:The use of Galaxy Clusters as cosmological probes hinges on our ability to measure their masses accurately and with high precision. Hydrostatic mass is one of the most common methods for estimating the masses of individual Galaxy Clusters, which suffer from biases due to departures from hydrostatic equilibrium. Using a large, mass-limited sample of massive Galaxy Clusters from a high-resolution hydrodynamical cosmological simulation, in this work we show that in addition to turbulent and bulk gas velocities, acceleration of gas introduces biases in the hydrostatic mass estimate of Galaxy Clusters. In unrelaxed Clusters, the acceleration bias is comparable to the bias due to non-thermal pressure associated with merger-induced turbulent and bulk gas motions. In relaxed Clusters, the mean mass bias due to acceleration is small ( 3%), but the scatter in the mass bias can be reduced by accounting for gas acceleration. Additionally, this acceleration bias is greater in the outskirts of higher redshift Clusters where mergers are more frequent and Clusters are accreting more rapidly. Since gas acceleration cannot be observed directly, it introduces an irreducible bias for hydrostatic mass estimates. This acceleration bias places limits on how well we can recover cluster masses from future X-ray and microwave observations. We discuss implications for cluster mass estimates based on X-ray, Sunyaev-Zel'dovich effect, and gravitational lensing observations and their impact on cluster cosmology.
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Cosmology and astrophysics with Galaxy Clusters
2014Co-Authors: Daisuke NagaiAbstract:Galaxy Clusters are the largest gravitationally bound objects in the universe, whose formation is driven by dark energy and dark matter. The majority of the baryonic mass in Clusters resides in the hot X-ray emitting plasma, which also leaves imprints in the cosmic microwave background radiation. Recent X-ray and microwave observations have revealed detailed thermodynamic structure of the hot X-ray emitting plasma from their cores to the virial radii, making comparisons of baryonic component in simulations to observations a strong cosmological probe. However, the statistical power of these future surveys can only be exploited for cosmology if and only if we are able to measure the cluster mass with a very high precision. I will discuss recent progress and future challenges for the use of Galaxy Clusters as precise cosmological probes, with highlights on (1) the importance of understanding thermodynamics and plasma physics in the outskirts of Galaxy Clusters and (2) prospects for improving the power of cluster-based cosmological measurements using numerical simulations and multi-wavelength observations.
Asantha Cooray - One of the best experts on this subject based on the ideXlab platform.
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Galaxy Clusters: oblate or prolate?
Monthly Notices of the Royal Astronomical Society, 2000Co-Authors: Asantha CoorayAbstract:ABSTRA C T It is now well known that a combined analysis of the Sunyaev‐Zel’dovich (SZ) effect and the X-ray emission observations can be used to determine the angular diameter distance to Galaxy Clusters, from which the Hubble constant is derived. Given that the SZ/X-ray Hubble constant is determined through a geometrical description of Clusters, the accuracy to which such distance measurements can be made depends on how well one can describe intrinsic cluster shapes. Using the observed X-ray isophotal axial ratio distribution for a sample of Galaxy Clusters, we discuss intrinsic cluster shapes and, in particular, if Clusters can be described by axisymmetric models, such as oblate and prolate ellipsoids. These models are currently favoured when determining the SZ/X-ray Hubble constant. We show that the current observational data on the asphericity of Galaxy Clusters suggest that Clusters are more consistent with a prolate than with an oblate distribution. We address the possibility that Clusters are intrinsically triaxial by viewing triaxial ellipsoids at random angles with the intrinsic axial ratios following an isotropic Gaussian distribution. We discuss implications of our results on current attempts at measuring the Hubble constant using Galaxy Clusters and suggest that an unbiased estimate of the Hubble constant, not fundamentally limited by projection effects, would eventually be possible with the SZ/X-ray method.
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Sunyaev-Zel’dovich effect in Galaxy Clusters
The 9th astrophysics conference: After the dark ages when galaxies were young (the Universe at 2, 1999Co-Authors: Asantha Cooray, Laura Grego, W. L. Holzapfel, Marshall Joy, John E. Carlstrom, Gilbert Holder, Sandeep K. Patel, Erik D. ReeseAbstract:We review recent results of Sunyaev-Zel’dovich-effect (SZE) observations toward Galaxy Clusters. Using cm-wave receivers mounted on the OVRO and BIMA mm-wave arrays, we have obtained high signal-to-noise images of the effect for more than 25 Clusters. Over 90% of these Clusters are scheduled to be observed with AXAF during the first year of its observations. We present current estimates of cosmological parameters H0 and Ωm based on the SZE in Galaxy Clusters.
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Radio Sources in Galaxy Clusters at 28.5 GHz
The Astronomical Journal, 1998Co-Authors: Asantha Cooray, Laura Grego, W. L. Holzapfel, Marshall Joy, John E. CarlstromAbstract:We present serendipitous detections of radio sources at 28.5 GHz (1 cm), which resulted from our program to image the thermal Sunyaev-Zeldovich (SZ) effect in 56 Galaxy Clusters. In a total area of ~0.8 deg2, we find 64 radio sources with fluxes down to ~0.4 mJy (greater than 4 σ) and within 250'' from the pointing centers. The spectral indices (S ∝ ν-α) of 54 sources with published low-frequency flux densities lie in the range -0.6 α 2, with a mean of 0.77 ± 0.06 and a median of 0.84. Extending low-frequency surveys of radio sources toward the Galaxy Clusters Cl 0016+16, Abell 665, and Abell 2218 to 28.5 GHz and selecting sources with S1.4 GHz ≥ 7 mJy to form an unbiased sample, we find a mean spectral index of 0.71 ± 0.08 and a median of 0.71. We find 4 to 7 times more sources than predicted from a low-frequency survey in areas without Galaxy Clusters. This excess cannot be accounted for by gravitational lensing of a background radio population by cluster potentials, indicating that most of the detected sources are associated with Galaxy Clusters. The differential source count slope, γ ~ 1.96 (dN/dS ∝ S-γ), is flatter than what is expected for a nonevolving Euclidean population (γ = 2.5). For the cluster Abell 2218, the presence of unsubtracted radio sources with S28.5 GHz ≤ 0.5 mJy (~5 σ) can reduce the observed SZ temperature decrement by ΔT ~ 10 to 25 μK. The corresponding overestimation of the Hubble constant derived through a combined analysis of 28.5 GHz SZ images and X-ray emission observations is less than 6%.
Dmitry Prokhorov - One of the best experts on this subject based on the ideXlab platform.
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Unveiling the 3D temperature structure of Galaxy Clusters by means of the thermal Sunyaev–Zel’dovich effect
Monthly Notices of the Royal Astronomical Society, 2011Co-Authors: Dmitry Prokhorov, Y. Dubois, Shigehiro Nagataki, Takuya Akahori, Kohji YoshikawaAbstract:The Sunyaev-Zel'dovich (hereafter SZ) effect is a promising tool to derive the gas temperature of Galaxy Clusters. The approximation of a spherically symmetric gas distribution is usually used to determine the temperature structure of Galaxy Clusters, but this approximation cannot properly describe merging Galaxy Clusters. The methods used so far, which do not assume the spherically symmetric distribution, permit us to derive 2D temperature maps of merging Galaxy Clusters. In this paper, we propose a method to derive the standard temperature deviation and temperature variance along the line-of-sight, which permits us to analyze the 3D temperature structure of Galaxy Clusters by means of the thermal SZ effect. We also propose a method to reveal merger shock waves in Galaxy Clusters by analyzing the presence of temperature inhomogeneities along the line-of-sight.Comment: 8 pages, 3 figures, accepted for publication in MNRA
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Unveiling the 3D temperature structure of Galaxy Clusters by means of the thermal SZ effect
Monthly Notices of the Royal Astronomical Society, 2011Co-Authors: Dmitry Prokhorov, Y. Dubois, Shigehiro Nagataki, Takuya Akahori, Kohji YoshikawaAbstract:The Sunyaev-Zel'dovich (hereafter SZ) effect is a promising tool to derive the gas temperature of Galaxy Clusters. The approximation of a spherically symmetric gas distribution is usually used to determine the temperature structure of Galaxy Clusters, but this approximation cannot properly describe merging Galaxy Clusters. The methods used so far, which do not assume the spherically symmetric distribution, permit us to derive 2D temperature maps of merging Galaxy Clusters. In this paper, we propose a method to derive the standard temperature deviation and temperature variance along the line-of-sight, which permits us to analyze the 3D temperature structure of Galaxy Clusters by means of the thermal SZ effect. We also propose a method to reveal merger shock waves in Galaxy Clusters by analyzing the presence of temperature inhomogeneities along the line-of-sight.
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Non-equilibrium ionization states in Galaxy Clusters
Astronomy and Astrophysics, 2009Co-Authors: Dmitry ProkhorovAbstract:Context. X-ray imaging observatories have revealed hydrodynamic structures with linear scales of ∼10 kpc in Clusters of galaxies, such as shock waves in the 1E0657-56 and A520 Galaxy Clusters and the hot plasma bubble in the MKW 3s cluster. The future X-ray observatory IXO will for the first time resolve the metal distribution in Galaxy Clusters at the these scales. Aims. Heating of plasmas by shocks and AGN activities can result in non-equilibrium ionization states of metal ions. We study the effect of the non-equilibrium ionization at linear scales of 50 kpc in Galaxy Clusters. Methods. A condition for non-equilibrium ionization is derived by comparing the ionization time-scale with the age of hydrodynamic structures. Modeling of non-equilibrium ionization is performed at a point in time when the plasma temperature suddenly changes. An analysis of the relaxation processes of the FeXXV and FeXXVI ions by means of eigenvectors of the transition matrix is given. Results. We conclude that the non-equilibrium ionization of iron can occur in Galaxy Clusters if the baryonic overdensity δ is smaller than 11.0/τ ,w hereτ � 1 is the ratio of the hydrodynamic structure age to the Hubble time. Our modeling indicates that the emissivity in the helium-like emission lines of iron increases as a result of the deviation from the ionization equilibrium. A slow process of helium-like ionic fraction relaxation was analyzed. A new way to determine a shock velocity is proposed.
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Missing baryons in shells around Galaxy Clusters
Astronomy & Astrophysics, 2008Co-Authors: Dmitry ProkhorovAbstract:Aims. The cluster baryon fraction is estimated from the CMB-scattering leptonic component of the intracluster medium (ICM); however, the observed cluster baryon fraction is less than t he cosmic one. Understanding the origin of this discrepancy is necessary for correctly describing the structure of the ICM. Methods. We estimate the baryonic mass in the outskirts of Galaxy Clusters which is diffi cult to observe because of low electron temperature and density in these regions. Results. The time scale for the electrons and protons to reach equipartition in the outskirts is longer than the cluster age. Since thermal equilibrium is not achieved, a significant fraction of the IC M baryons may be hidden in shells around Galaxy Clusters. We derive the necessary condition on the cluster mass for the concealment of missing baryons in an outer baryon shell and show that this condition is fulfilled because cluster masses are comparable to the est imated characteristic mass M = e 4 /(m 3G 2 ) = 1.3x10 15 solar masses. The existence of extreme-ultraviolet emission haloes around Galaxy Clusters is predicted.
S. Andreon - One of the best experts on this subject based on the ideXlab platform.
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PreProFit: Pressure Profile Fitter for Galaxy Clusters
Astronomy & Astrophysics, 2019Co-Authors: Fabio Castagna, S. AndreonAbstract:Galaxy cluster analyses based on high-resolution observations of the Sunyaev-Zeldovich (SZ) effect have become common in the last decade. We present PreProFit, the first publicly available code designed to fit the pressure profile of Galaxy Clusters from SZ data. PreProFit is based on a Bayesian forward-modelling approach, allows the analysis of data coming from different sources, adopts a flexible parametrization for the pressure profile, and fits the model to the data accounting for Abel integral, beam smearing, and transfer function filtering. PreProFit is computationally efficient, is extensively documented, has been released as an open source Python project, and was developed to be part of a joint analysis of X-ray and SZ data on Galaxy Clusters. PreProFit returns $\chi^2$, model parameters and uncertainties, marginal and joint probability contours, diagnostic plots, and surface brightness radial profiles. PreProFit also allows the use of analytic approximations for the beam and transfer functions useful for feasibility studies.
