Impact of stochastic gas motions on galaxy cluster abundance profiles

Abstract

The impact of stochastic gas motions on the metal distribution in cluster core is evaluated. Peaked abundance profiles are a characteristic feature of clusters with cool cores and abundance peaks are likely associated with the brightest cluster galaxies (BCGs) which dwell in cluster cores. The width of the abundance peaks is however significantly broader than the BCG light distribution, suggesting that some gas motions are transporting metals originating from within the BCG. Assuming that this process can be treated as diffusive and using the brightest X-ray cluster A426 (Perseus) as an example, we estimate that a diffusion coefficient of the order of $2 10^{29} {\rm cm^2 s^{-1}}$ is needed to explain the width of the observed abundance profiles. Much lower (higher) diffusion coefficients would result in too peaked (too shallow) profiles. Such diffusion could be produced by stochastic gas motions and our analysis provides constraints on the product of their characteristic velocity and their spatial coherence scale. We speculate that the activity of the supermassive black hole of the BCG is driving the stochastic gas motions in cluster cores. When combined with the assumption that the dissipation of the same motions is a key gas heating mechanism, one can estimate both the velocity and the spatial scale of such a diffusive processes.Comment: 9 pages, 9 figures, submitted to MNRAS typos corrected, references update

Fast growth of magnetic fields in galaxy clusters: a self‐accelerating dynamo

“…Various indirect observational estimates (e.g., Schuecker et al, 2004;Rebusco et al, 2005;Fujita, 2005) appear to converge in expecting random flows with velocity fluctuations U ∼ 10 2 − 10 3 km/s at the outer scale L ∼ 10 2 − 10 3 kpc (a direct detection may be achieved in the near future; see Inogamov & Sunyaev, 2003). Similar numbers are obtained in numerical simulations of cluster formation (Norman & Bryan, 1999;Sunyaev, Norman & Bryan, 2003;Ricker & Sarazin, 2001;Takizawa, 2005).…”

The Chemical Enrichment of the ICM from Hydrodynamical Simulations

“…While a number of studies have been performed so far to infer the IMF shape from the enrichment pattern of the ICM, no general consensus has been reached. For instance, Renzini (1997Renzini ( , 2004 and Pipino et al (2002) As we shall discuss in the following, a similar conclusion was also reached by Nagashima et al (2005), who used semi-analytical models of galaxy formation to trace the production of heavy elements, and by Romeo et al (2005), who used hydrodynamical simulations including chemical enrichment. Saro et al (2006) analysed the galaxy population from simulations of galaxy clusters and concluded that a Salpeter IMF produces a colour-magnitude relation that, with the exception of the BCGs, is in reasonable agreement with observations.…”

“…Therefore, the evolution of the ICM metallicity is expected to be quite sensitive to the enrichment level of the recently accreted gas. On the other hand, as noted by Renzini (1997), if ram-pressure stripping plays a dominant role in determining the ICM enrichment, one should then expect to observe more massive clusters, whose ICM has a higher pressure, to be more metal rich than poorer systems. In fact, observations do not show this trend and, if any, suggest a decrease of the iron abundance with the ICM temperature (e.g., Baumgartner et al 2005).…”

“…Spatially resolved X-ray spectroscopy permits to measure the equivalent width of emission lines associated to transitions of heavily ionised elements and, therefore, to trace the pattern of chemical enrichment (e.g., Mushotzky 2004 for a review). In turn, this information is inextricably linked to the history of formation and evolution of the galaxy population (e.g., Renzini 1997 and references therein), as inferred from observations in the optical/near-IR band. For instance, De Grandi et al (2004) have first shown that cool core clusters are characterised by a significant central enhancement of the iron abundance, which closely correlates with the magnitude of the Brightest Cluster Galaxies (BCGs).…”

Observations of Metals in the Intra-Cluster Medium

“…The observed metal profiles are much less steep than the light profiles, which suggests that the injected metals are mixed and they diffuse to larger radii. Rebusco et al (2005Rebusco et al ( , 2006 model the diffusion of metals by stochastic gas motions after they were ejected by the brightest galaxy and compare their results with the peaked Fe abundance profiles of 8 groups and clusters. They suggest that the AGN/ICM interaction makes an important contribution to the gas motion in the cluster cores.…”