Systematics in the X-ray cluster mass estimators

By E. Rasia, S. Ettori, L. Moscardini, P. Mazzotta, Stefano Borgani, Klaus Dolag, G. Tormen, L. M. Cheng, A. Diaferio. 2006

251 citations recorded by the source corpus.

We examine the systematics affecting the X-ray mass estimators applied to a set of five galaxy clusters resolved at high resolution in hydrodynamic simulations, including cooling, star formation and feedback processes. These simulated objects are processed through the X-ray Map Simulator, X-MAS, to provide Chandra-like long exposures that are analysed to reconstruct the gas temperature, density and mass profiles used as input. These clusters have different dynamic state: we consider a hot cluster with temperature T = 11.4 keV, a perturbed cluster with T = 3.9 keV, a merging object with T = 3.6 keV, and two relaxed systems with T = 3.3 keV and T = 2.7 keV, respectively. These systems are located at z = 0.175 so that their emission fits within the Chandra ACIS-S3 chip between 0.6 and 1.2 R-500. We find that the mass profile obtained via a direct application of the hydrostatic equilibrium ( HE) equation is dependent upon the measured temperature profile. An irregular radial distribution of the temperature values, with associated large errors, induces a significant scatter on the reconstructed mass measurements. At R-2500, the actual mass is recovered within 1 sigma, although we notice this estimator shows high statistical errors due to high level of Chandra background. Instead, the poorness of the beta-model in describing the gas density profile makes the evaluated masses to be underestimated by similar to 40 per cent with respect to the true mass, both with an isothermal and a polytropic temperature profile. We also test ways to recover the mass by adopting an analytic mass model, such as those proposed by Nvarro, Frenk & White and Rasia, Tormen & Moscardini, and fitting the temperature profile expected from the HE equation to the observed one. We conclude that the methods of the HE equation and those of the analytic fits provide a more robust mass estimation than the ones based on the beta-model. In the present work, the main limitation for a precise mass reconstruction is to ascribe to the relatively high level of the background chosen to reproduce the Chandra one. After artificially reducing the total background by a factor of 100, we find that the estimated mass significantly underestimates the true mass profiles. This is manly due (i) to the neglected contribution of the gas bulk motions to the total energy budget and (ii) to the bias towards lower values of the X-ray temperature measurements because of the complex thermal structure of the emitting plasma.

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

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Citations in the corpus

Evidence for non-hydrostatic gas from the cluster X-ray to lensing mass ratio (2007, methodology): “Earlier studies based on simulations (e.g. Evrard 1990; Faltenbacher et al. 2005; Rasia et al. 2006; Hallman et al. 2006) support this conclusion.”
A Catalog of Galaxy Clusters Observed by XMM-Newton (2007, background): “Since the total mass of the cluster is quite sensitive to the measured temperature profile (Rasia et al. 2006), particularly at large radii, these systematic differences lead to significant uncertainties in the cosmological constraints.”
Combining Strong and Weak Gravitational Lensing in Abell 1689 (2006, background): “Rasia et al. (2006) studied a set of five galaxy clusters, resolved at high resolution, in a hydrodynamic simulation, examining the systematics affecting the X-ray mass estimates.”
RESIDUAL GAS MOTIONS IN THE INTRACLUSTER MEDIUM AND BIAS IN HYDROSTATIC MEASUREMENTS OF MASS PROFILES OF CLUSTERS (2009, methodology): “…in very relaxed clusters (Evrard 1990; Norman & Bryan 1999; Nagai et al. 2003; Rasia et al. 2004; Kay et al. 2004; Faltenbacher et al. 2005; Dolag et al. 2005; Rasia et al. 2006; Nagai et al. 2007b; Piffaretti & Valdarnini 2008; Jeltema et al. 2008; Iapichino & Niemeyer 2008; Ameglio et al. 2009).”
Total mass biases in X-ray galaxy clusters (2008, methodology): “Our analysis may be viewed as complementary to those presented in Rasia et al. (2006) and Nagai et al. (2007a).”
Cosmological Parameters from Observations of Galaxy Clusters (2011, background): “Hydrostatic and virial equilibrium assumptions are typically valid to within roughly ten percent for the majority of the cluster population (e.g. Rasia et al. 2006; Nagai, Vikhlinin & Kravtsov 2007).”
CHANDRA CLUSTER COSMOLOGY PROJECT III: COSMOLOGICAL PARAMETER CONSTRAINTS (2008, background): “On the theoretical side, im- proved numerical simulations resulted in better understand- ing of measurement biases in the X-ray data analysis (Nagai et al. 2007; Rasia et al. 2006; Jeltema et al. 2007).”
X-Ray and Sunyaev-Zel’dovich Effect Measurements of the Gas Mass Fraction in Galaxy Clusters (2006, result): “Recent numerical simulations suggest that this provides about 10% of the total pressure support in clusters (Faltenbacher et al. 2005; Rasia et al. 2006; Lau et al. 2006) and similar results are obtained using XMM-Newton observations of the Coma cluster (Schuecker et al. 2004).”
Shock waves in Eulerian cosmological simulations: main properties and acceleration of cosmic rays (2008, background): “Studies concerning the convolution of simulated cosmological shocks into simulated X-ray images (e.g. Gardini et al. 2004; Rasia et al. 2006) have clearly shown that the apparent lack of shocks in the intracluster medium (ICM) may be due to the concourse of projections and mass-weighting effects…”
The dark matter haloes of massive, relaxed galaxy clusters observed with Chandra (2006, background): “However, the relaxed nature of the clusters argues that large, unaccounted for, bulk and/or turbulent motions are unlikely to be present and that the mass measurements should be re- c© 2006 RAS, MNRAS 000, 1–14 covered to better than 10-20 per cent accuracy (Nagai et al. 2007; Rasia et al. 2006).”
Lensing and x-ray mass estimates of clusters (simulations) (2012, background): “Thus, they are ideal for testing data reduction pipelines (Rasia et al. 2006; Mazzotta et al. 2004; Nagai et al. 2007).”
The X-Ray Luminosity-Mass Relation for Local Clusters of Galaxies (2006, background): “…this approach may yield masses that are biased by up to a few tens of percent (Evrard 1990; Schindler 1996; Navarro et al. 1995; Evrard et al. 1996; Rasia et al. 2004, 2006), but the computational expectations are rendered uncertain by incomplete modeling of ICM physics and by systematic errors…”
MASSIVE HALOS IN MILLENNIUM GAS SIMULATIONS: MULTIVARIATE SCALING RELATIONS (2009, background): “The magnitude of this offset is consistent with the level of expected bias from hydrostatic mass estimates, which simulations show tend to underestimate true masses by approximately 20% (Rasia et al. 2006; Nagai et al. 2007).”
Cosmology and astrophysics from relaxed galaxy clusters - II. Cosmological constraints (2014, methodology): “…Weighing the Giants, or WtG) allows us to directly calibrate any bias in the mass measurements from X-ray data, for example due to departures from hydrostatic equilibrium (e.g. Rasia et al. 2006; Nagai et al. 2007; Battaglia et al. 2013) or instrument calibration (Applegate et al., in preparation).”
Improved constraints on dark energy from Chandra X-ray observations of the largest relaxed galaxy clusters (2007, background): “Progress in this area has been made (e.g. Bialek, Evrard & Mohr 2001, Muanwong et al. 2002, Kay S. et al. , 2004, Kravtsov, Nagai & Vikhlinin 2005, Ettori et al. 2004, 2006, Rasia et al. 2006; Nagai et al. 2007a,b), though more work remains.”
Weighing simulated galaxy clusters using lensing and X-ray (2009, methodology): “These objects have already been used in several other studies (Dolag et al. 2005; Puchwein et al. 2005; Meneghetti et al. 2007, 2008; Rasia et al. 2006, 2008).”
Towards a realistic population of simulated galaxy groups and clusters (2013, background): “Consistent with previous sim- ulation studies (e.g. Mathiesen et al. 1999; Rasia et al. 2006; Nagai et al. 2007b; Kay et al. 2012; Nelson et al. 2014), we find a mean bias of ∼ −20 per cent for both groups and clusters.”
Formation of Galaxy Clusters (2012, background): “…practical consideration is that theoretical models should consider observables derived from mock observations of simulated clusters that take into account instrumental eff cts of detectors and projection effects (e.g., Biffi et al. 2011; Nagai, Vikhlinin & Kravtsov 2007; Rasia et al. 2006).”