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We study the mass of quasar-hosting dark matter halos at z ∼ 6 and further constrain the fraction of dark matter halos hosting active quasars fon and the quasar opening angle imax using observations of C ii lines in the literature. We make assumptions that (1) on average more massive halos host quasars with higher peak brightness, (2) cold gas in galaxies has rotational velocity Vcirc = αVmax, where Vmax is the maximum circular velocity of dark matter particles obtained from DM-only simulation and α ∼ 1 is a free parameter, (3) a fraction fon of the halos host active quasars with a certain opening angle imax, and that (4) quasars point randomly on the sky. We find that for a choice of specific α ≳ 1, the most likely solution has fon < 0.01, corresponding to a small duty cycle of quasar activity. We also apply a bounded flat prior on α and marginalize over it, and we find the most likely fon shift to 1 as the upper-boundary of α decreases below 1. Overall, our constraints are highly sensitive to α and hence inconclusive. Stronger constraints on fon can be made if we better understand the dynamics of cold gas in these galaxies. [ABSTRACT FROM AUTHOR]

The rich galaxy cluster Abell 2204 exhibits edges in its X-ray surface brightness at ∼65 and west and east of its center, respectively. The presence of these edges, which were interpreted as sloshing cold fronts, implies that the intracluster medium (ICM) was recently disturbed. We analyze the properties of the ICM using multiple Chandra observations of Abell 2204. We find a density ratio of and a temperature ratio of (projected, or 1.87 ± 0.56 deprojected) across the western edge, and correspondingly and (projected, or 1.25 ± 0.26 deprojected) across the eastern edge. These values are typical of cold fronts in galaxy clusters. This, together with the spiral pattern observed in the cluster core, supports the sloshing scenario for Abell 2204. No Kelvin–Helmholtz eddies are observed along the cold front surfaces, indicating that they are effectively suppressed by some physical mechanism. We argue that the suppression is likely facilitated by the magnetic fields amplified in the sloshing motion and deduce from the measured gas properties that the magnetic field strength should be greater than 24 ± 6 μG and 32 ± 8 μG along the west and east cold fronts, respectively. [ABSTRACT FROM AUTHOR]