Four Measures of the Intracluster Medium Temperature and Their Relation to a Cluster’s Dynamical State

By B. Mathiesen, August E. Evrard. 2000

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We employ an ensemble of 24 hydrodynamic cluster simulations to create spatially and spectrally resolved images of quality comparable to Chandra's expected performance. Emission from simulation mass elements is represented using the XSPEC "MEKAL" program assuming 0.3 solar metallicity and the resulting spectra are fitted with a single-temperature model. Despite significant departures from isothermality in the cluster gas, single-temperature models produce acceptable fits to 20,000 source photon spectra. The spectral fit temperature Ts is generally lower than the mass-weighted average temperature Tm due to the influence of soft line emission from cooler gas being accreted as part of the hierarchical clustering process. The nature of this deviation depends on the bandpass used for spectral fitting. In a Chandra-like bandpass of 0.5 to 9.5 keV we find a nearly uniform fractional bias of (Tm - Ts)/Ts ≃ 20%, although smaller clusters sometimes demonstrate much greater deviations. If the minimum energy threshold is raised to 2 keV, however, the effect of line emission on the spectrum is greatly decreased and Ts becomes a nearly unbiased estimator of Tm for smaller clusters. The fractional deviation in Ts relative to Tm is scale-dependent in this bandpass and follows the approximate relation (Tm - Ts)/Ts = 0.2 log10 Tm. This results in an observed MICM-Ts relationship for the simulations with slope of about 1.6, intermediate between the virial relation M ∝ T and the observed relation MICM ∝ T2. Tracking each cluster in the ensemble at 16 epochs in its evolutionary history, we catalog merger events with mass ratios exceeding 10% in order to investigate the relationship between spectral temperature and proximity to a major merger event. Clusters that are very cool relative to the mean mass-temperature relationship lie preferentially close to a major merger, suggesting a viable observational method to cull a subset of dynamically young clusters from the general population.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/9ab2ee14f90a36e0fcdafcf844f1e840eed23f5a

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Citations in the corpus

Chandra Observations of A2029: The Dark Matter Profile Down to below 0.01rvir in an Unusually Relaxed Cluster (2002, background): “[9]), normalized to the 2.0–9.5 keV band mass-temperature relation given by Mathiesen & Evrard (2001), which we convert to our cosmology.”
Galaxy Clusters in Hubble Volume Simulations: Cosmological Constraints from Sky Survey Populations (2001, methodology): “This approach has the advantage of naturally building in scatter between T and M at a fractional amplitude ∼10% that is consistent with expectations from direct, gas dynamic modeling (e.g., Mathiesen & Evrard 2001; Thomas et al. 2001).”
Scaling laws in X-ray galaxy clusters at redshift between 0.4 and 1.3 (2003, background): “…(e.g., Horner et al. 1999; Nevalainen et al. 2000; Finoguenov et al. 2001; Ettori et al. 2002) is known to have a normalization lower by about 30 per cent than that obtained from hydrodynamical simulations (e.g. Mathiesen & Evrard 2001; cf. also Muanwong et al. 2002; Borgani et al. in preparation).”
The X‐ray virial relations for relaxed lensing clusters observed with Chandra (2001, methodology): “2a,b show the predicted (zero-redshift) relations for the SCDM [E(z)M2500 = 9.9 ± 1.5 × 1014kT 1.5] and ΛCDM [E(z)M2500 = 7.7 ± 0.6 × 1014kT 1.52±0.03] cosmologies from the hydrodynamical simulations of Evrard et al. (1996) and Mathiesen & Evrard (2001), respectively.”
Comparing the temperatures of galaxy clusters from hydrodynamical N-body simulations to Chandra and XMM-Newton observations (2004, methodology): “Consistent with what was found by Mathiesen & Evrard (2001), whenever the lower-temperature component is at T > 2 keV, then almost any twotemperature spectrum can be well-fitted by a single-temperature model.”
MASSIVE HALOS IN MILLENNIUM GAS SIMULATIONS: MULTIVARIATE SCALING RELATIONS (2009, methodology): “The distribution of the gas in the GO models contains cool, low entropy cores of accreted sub-halos (Mathiesen & Evrard 2001), and these cool, dense clumps pull down the Tsl measure relative to the PH simulation.”
Cosmological constraints from the local X-ray luminosity function of the most X-ray-luminous galaxy clusters (2002, background): “The evolution parameter E(z) = (1 + z) √ (1 + zΩm + ΩΛ/(1 + z)2 − ΩΛ) (11) accounts for the expected cosmological scaling of the relationship (e.g. Bryan & Norman 1998; Mathiesen & Evrard 2001).”
X-Ray and Sunyaev-Zel’dovich Effect Measurements of the Gas Mass Fraction in Galaxy Clusters (2006, background): “Second, cluster substructure can bias the average spectroscopic temperature of the cluster as a whole (e.g., Mathiesen & Evrard 2001; Mazzotta et al. 2004).”
The universal galaxy cluster pressure profile from a representative sample of nearby systems (REXCESS) and the Y-SZ-M-500 relation (2009, background): “By contrast, temperatures derived from X-ray spectra, by fitting an isothermal model to a multi-temperature plasma emission along the line of sight, are likely to be biased (Mathiesen & Evrard 2001).”
Modified Entropy Models for the Intracluster Medium (2002, unknown): “Furthermore, the luminosity-weighted temperature derived from theoretical modeling is not necessarily identical to the spectral fit temperature derived from observations (Mathiesen & Evrard 2001).”
X‐ray properties of galaxy clusters and groups from a cosmological hydrodynamical simulation (2003, background): “While all this is true under the assumption of vanishing metallicity, including metals has the effect of biasing temper- atures towards lower values (Mathiesen & Evrard 2001).”
The X-Ray Luminosity-Mass Relation for Local Clusters of Galaxies (2006, methodology): “…are rendered uncertain by incomplete modeling of ICM physics and by systematic errors associated with determining the spectral temperature derived from the thermally complex intracluster medium of simulated clusters (Mathiesen & Evrard 2001b; Mazzotta et al. 2003; Vikhlinin et al. 2005).”
CHANDRA CLUSTER COSMOLOGY PROJECT. II. SAMPLES AND X-RAY DATA REDUCTION (2008, background): “Relation (4) also generally describes the ICM temperatures found in the cosmological numerical simulations (Evrard et al. 1996; Mathiesen & Evrard 2001; Borgani et al. 2004, KVN).”
X-ray spectroscopy of galaxy clusters: studying astrophysical processes in the largest celestial laboratories (2009, background): “A first intuitive guess is to assume that it isan average of the temperatures weighted by the radiative emission contributions of the different phases, the so-called emission weighted temperature,Tew (e.g. Mathiesen & Evrard 2001).”
Power-spectrum normalization from the local abundance of rich clusters of galaxies (2001, background): “However, the spectrally measured cluster temperatures may not coincide with the mass or emission weighted temperature estimated from the simulations, due to the influence of soft line emission (Mathiesen & Evrard 2001).”
Total mass biases in X-ray galaxy clusters (2008, background): “This is motivated by the presence of complex thermal structures in the ICM, which bias the (measured) spectral fit temperatures towards lower values than the average emission weighted cluster temperatures defined theoretically (Mathiesen & Evrard 2001; Mazzotta et al. 2004; Valdarnini 2006).”
Systematics in the X-ray cluster mass estimators (2006, methodology): “We find that, while |A| 3 up to R500 for all the objects, B indicates that the spectroscopic temperature is within 20 per cent of T mw, with implications on the mass estimates (Mathiesen & Evrard 2001; Vikhlinin et al. 2006; see Section 5.1).”
ERRATUM: “CHANDRA SAMPLE OF NEARBY RELAXED GALAXY CLUSTERS: MASS, GAS FRACTION, AND MASS–TEMPERATURE RELATION” (2006, ApJ, 640, 691) (2005, methodology): “T relation is expected to follow (e.g., Mathiesen & Evrard 2001) M T3=2 / E(z) 1; E(z) ¼ H(z) H0 : ð10Þ Although the effect of evolution is small within our redshift interval, we applied the corresponding corrections by multiplying the measured masses by E(z) computed for our preferred cosmology,…”