On the Origin of Intracluster Entropy

By G. Mark Voit, M. Balogh, Richard G. Bower, C. Lacey, Greg L. Bryan. 2003

133 citations recorded by the source corpus.

The entropy distribution of the intracluster medium and the shape of its confining potential well completely determine the X-ray properties of a relaxed cluster of galaxies, motivating us to explore the origin of intracluster entropy and to describe how it develops in terms of some simple models. We present an analytical model for smooth accretion, including both preheating and radiative cooling, that links a cluster's entropy distribution to its mass accretion history and shows that smooth accretion overproduces the entropy observed in massive clusters by a factor of ~2-3, depending on the mass accretion rate. Any inhomogeneity in the accreting gas reduces entropy production at the accretion shock; thus, smoothing of the gas accreting onto a cluster raises its entropy level. Because smooth accretion produces more entropy than hierarchical accretion, we suggest that some of the observed differences between clusters and groups may arise because preheating smooths the smaller scale lumps of gas accreting onto groups more effectively than it smooths the larger scale lumps accreting onto clusters. This effect may explain why entropy levels at the outskirts of groups are ~2-3 times larger than expected from self-similar scaling arguments. The details of how the density distribution of accreting gas affects the entropy distribution of a cluster are complex, and we suggest how to explore the relevant physics with numerical simulations.

Subfields: Astronomy and Astrophysics, Global and Planetary Change, Instrumentation

View Paper: https://www.semanticscholar.org/paper/25026fd1a014bca9a8987108b76df9db14a28c47

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

In Global and Planetary Change

In Instrumentation

Citations in the corpus

The impact of mergers on relaxed X-ray clusters – I. Dynamical evolution and emergent transient structures (2006, result): “We note that our choice for the form of the initial density profile conforms not only with these observations but also with the results of high-resolution cluster simulations (Lewis et al. 2000; Voit et al. 2003).”
X‐ray properties of galaxy clusters and groups from a cosmological hydrodynamical simulation (2003, background): “Possible explanations for this global violation of self–similarity have been proposed by Ponman et al. (2003) and Voit et al. (2003), and are based on a differential entropy amplification by shocks in the presence of pre–heating.”
The representative XMM-Newton cluster structure survey (REXCESS) of an X-ray luminosity selected galaxy cluster sample (2007, background): “…relations as a consequence of energy input from other sources, related to galaxy and star formation processes and the cooling of dense intracluster gas regions (e.g. Kaiser 1991; Bower 1997; Ponman et al. 1999, 2003; Voit & Bryan 2000; Voit et al. 2003; Pratt & Arnaud 2005; Pratt et al. 2006).”
CHANDRA STUDIES OF THE X-RAY GAS PROPERTIES OF GALAXY GROUPS (2008, background): “The first idea relies on modification of accretion, without extra non-gravitational processes (Ponman et al. 2003; Voit et al. 2003; Voit & Ponman 2003).”
X-ray Spectroscopy of Cooling Clusters (2005, background): “The simplest explanation for this result is that the gas has had additional heating of 2–3 keV per particle (Wu et al. 2000; Voit et al. 2003).”
Formation of Galaxy Clusters (2012, methodology): “3 UNDERSTANDING THE FORMATION OF GALAXY CLUSTERS Both analytical models (e.g. Babul et al. 2002, Tozzi & Norman 2001, Voit et al. 2003) and hydrodynamical simulations (e.g. Bialek, Evrard & Mohr2001; Borgani et al. 2002; Muanwong et al. 2002) have demonstrated that with a suitablepre-heating…”
The case for AGN feedback in galaxy groups (2009, background): “Therefore, unlike the temperature or density, which may be raised/lowered by any processes that compress/expand the gas, the entropy will maintain a record of the thermodynamic history of the gas (see Voit et al. 2003; Voit 2005).”
X-ray spectroscopy of galaxy clusters: studying astrophysical processes in the largest celestial laboratories (2009, background): “…the entropy profiles, the scaling relations, and the amount of baryons that are converted into stars in the cluster volume and efforts to obtain a completely consistent and satisfying modelar still ongoing (e.g. Borgani et al. 2004, 2005; Voit et al. 2003; Voit 2005; McCarthy et al. 2008).”
X-ray coronae in simulations of disc galaxy formation (2010, background): “Entropy therefore maintains a record of the thermodynamic history of the gas (e.g. Voit et al. 2003; Voit 2005).”
Planck intermediate results: V. Pressure profiles of galaxy clusters from the Sunyaev-Zeldovich effect (2012, unknown): “In the cluster surroundings, accretion along ﬁlaments is three-dimensional and non-spherical (Tozzi & Norman 2001) and the initial conditions of the accretion shock are driven by the thermodynamical state of the (pre-shocked) in-falling material (Voit et al. 2002, 2003).”
Gas expulsion by quasar-driven winds as a solution to the overcooling problem in galaxy groups and clusters (2010, methodology): “The entropy1 of the IGrM is perhaps the best tool for studying the impact of non-gravitational physics, since it maintains a record of the thermal history of the gas (see Voit et al. 2003; Voit 2005 for further discussion).”
Galaxy formation theory (2010, background): “Models of accretion shocks have been presented by several authors (Bertschinger 1985; Tozzi and Norman 2001; Voit et al. 2003; Book and Benson 2010) with the general conclusion that the shock occurs at a rdius comparable to (or perhaps slightly larger than) the virial radius when cooling times are…”
Hydrodynamical simulations of cluster formation with central AGN heating (2005, background): “…invoked some sort of nongravitational heating to explain the cluster scaling relations (e.g. Kaiser 1991; Navarro, Frenk & White 1995; Bower 1997; Tozzi & Norman 2001; Voit & Bryan 2001; Borgani et al. 2001, 2004; Babul et al. 2002; Voit et al. 2002, 2003; Oh & Benson 2003; Tornatore et al. 2003).”