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3.2. X-Ray Properties of Clusters

Some of the main properties of the X-ray emission from rich clusters of galaxies are summarized in Table 6.

Table 6. X-Ray Properties of Rich Clusters.

Property Typical value of range Notes

Lx (2-10 keV) ~ (1042.5-1045)h-2 erg s-1 a
Ix(r) Ix(r) propto [1+(r / Rc)2]-3beta+1/2 b
<beta> ~ 0.7 c
rhogas(r) rhogas(r) propto [1+(r / Rc)2]-3beta/2
propto [1+(r / Rc)2]-1 d
kTx ~ 2-14 keV e
Tx ~ 2 × 107-108 K e
betaspect = sigmar2 / kTx / µ mp ~ 1 f
Rc(x) ~ (0.1-0.3)h-1 Mpc g
ne ~ 3 × 10-3h1/2 cm-3 h
curlyMgas (ltapprox 1.5h-1 Mpc) ~ 1013.5 curlyModot [range: (1013-1014) curlyModot h-2.5] i
curlyMgas / curlyMcl (ltapprox 1.5 h-1 Mpc) ~ 0.07 (range: 0.03-0.15 h-1.5) i
Iron abundance ~ 0.3 solar (range: 0.2-0.5) j

a The X-ray luminosity of clusters (2-10 keV band). < Lx > increases with cluster richness and with cluster type (toward compact, elliptical-rich clusters) (Bahcall 1977a, b; Sarazin 1986; Edge et al. 1990; Jones and Forman 1992; David et al. 1993; Burg et al. 1994).
b X-ray surface brightness distribution, Ix(r); Rc is the cluster core radius.
c Mean < beta > from observations of X-ray brightness profiles (Jones and Forman 1984; Sarazin 1986).
d Implied spatial density profile of the hot gas in the cluster [from Ix(r); isothermal].
e Range of observed X-ray gas temperature in rich clusters (Edge et al. 1990; Henry and Arnaud 1991; Arnaud et al. 1992).
f betaspect is the ratio of galaxy to gas velocity dispersion: µ is mean molecular weight in amu (µ appeq 0.6), mp is mass of the proton, sigmar is radial velocity dispersion of galaxies in the cluster, and Tx is the X-ray temperature of the gas (Lubin and Bahcall 1993).
g Cluster core radius determined from the X-ray distribution in the cluster (Jones and Forman 1992).
h Typical intracluster gas density in rich cluster cores (Jones and Forman 1992).
i Typical mass (and range of masses) of hot gas in rich clusters and its fraction of the total (virial) cluster mass (curlyMgas / curlyMcl) within r ltapprox 1.5h-1 Mpc of the cluster center (Edge and Stewart 1991; Jones and Forman 1992; White and Fabian 1995; Lubin et al. 1996).
j Typical iron abundance (and range) of the intracluster gas (in solar units) (Edge and Stewart 1991; Jones and Forman 1992).

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