Implications of Halo Inside‐Out Growth for the X‐Ray Properties of Nearby Galaxy Systems within the Preheating Scenario

Abstract

We present an entirely analytic model for a preheated, polytropic intergalactic medium in hydrostatic equilibrium within a NFW dark halo potential in which the evolution of the halo structure between major merger events proceeds inside-out by accretion. This model is used to explain, within a standard ΛCDM cosmogony, the observed X-ray properties of nearby relaxed, non-cooling flow groups and clusters of galaxies. We find that our preferred solution to the equilibrium equations produces scaling relations in excellent agreement with observations, while simultaneously accounting for the typical structural characteristics of the distribution of the diffuse baryons. In the class of preheating models, ours stands out because it offers a unified description of the intrahalo medium for galaxy systems with total masses above ∼ 2 × 10 13 M ⊙ , does not produce baryonic configurations with large isentropic cores, and reproduces faithfully the observed behavior of the gas entropy at large radii. All this is achieved with a moderate level of energy injection of about half a keV, which can be easily accommodated within the limits of the total energy released by the most commonly invoked feedback mechanisms, as well as with a polytropic index of 1.2, consistent with both many observational determinations and predictions from high-resolution gas-dynamical simulations of non-cooling flow clusters. More interestingly, our scheme offers a physical motivation for the adoption of this specific value of the polytropic index, as it is the one that best ensures the conservation after halo virialization of the balance between the total specific energies of the gas and dark matter components for the full range of masses investigated.

A Simple and Accurate Model for Intracluster Gas

“…This result holds for both adiabatic and radiative simulations (but see Kay et al 2004) and agrees well with the effective À derived from observed clusters by Finoguenov et al (2001). Solanes et al (2005) find that À ¼ 1:2 offers the best consistency with the assumption that the specific energy of the hot gas equals that of the dark matter. Interestingly, the purely adiabatic, spherical, and self-similar collapse solution of Bertschinger (1985) was also polytropic with À % 1:17.…”

“…Aside from the innermost region, the model with a À of 1.2-1.4 satisfactorily represents the T falloff in the outer regions, which contain most of the gas mass. À ¼ 1:2 1:4, corresponding to polytropes with index n ¼ 2:5 5, provides adequate fits to the outer parts of the clusters, within which resides most of the gaseous mass (see also the discussion in Solanes et al 2005). Ascasibar et al (2003) have shown that a À ¼ 1:18 model is a good fit to the average temperature profile measured by Markevitch et al (1998); this latter measurement has been confirmed by De Grandi & Molendi (2002), Piffaretti et al (2005), and Vikhlinin et al (2005).…”

“…Kaiser (1991) proposed that nongravitational energy injection could lead to the observed relations. This possibility has been explored in the type of analytic model described here using an NFW profile for the dark matter Wu et al 2000;Shimizu et al 2004;Lapi et al 2005;Afshordi et al 2005;Solanes et al 2005) and with other profiles (Balogh et al 1999;Babul et al 2002). The breaking of self-similarity can also be cast as the modification of the initial gas entropy by thermal and nonthermal processes, as explored in NFW-like potentials by Tozzi & Norman (2001), Komatsu & Seljak (2001), Voit et al (2002), and Dos Santos & Doré (2002); on the other hand, Roychowdhury & Nath (2003) argue that the entropy imparted to the gas from gravitational processes alone is larger than previously thought.…”

CONSTRAINING THE EPOCH OF REIONIZATION FROM THE OBSERVED PROPERTIES OF THE HIGH-z UNIVERSE

“…AMIGA follows this growth in a well-contrasted analytic manner with no free parameters (Salvador-Solé et al 1998, 2007Raig et al 2001). This allows us to accurately calculate, at any given moment, their abundance (Juan et al 2014a(Juan et al , 2014b and inner structure and kinematics (Salvador-Solé et al 2012a, which in turn sets the structure and temperature of their hot gas (Solanes et al 2005). The amount and metallicity of such a hot gas and the properties of the central galaxy and its satellites are monitored in AMIGA from the individual halo aggregation history.…”

Semi-analytical predictions of density profiles for ΛCDM haloes

“…This gives a rough estimation of the slope at the virial radius in the range 2.64 to 2.36, which is in satisfactory agreement with the models based on the results of N-body simulations as those described in the introduction. For ∆ vir , we use the model ∆ vir (a) = 178Ω 0.45 m (a) resulting in ∆ vir ≈ 100 at present epoch (a = 1) (see Solanes et al 2005).…”