Deprojection of X-ray data in galaxy clusters: confronting simulations with observations

Kartick C Sarkar; Arjun Dey; Prateek Sharma

doi:10.1093/mnras/stac2296

paper

Deprojection of X-ray data in galaxy clusters: confronting simulations with observations

arXiv:2110.12447 · doi:10.1093/mnras/stac2296

Abstract

Numerical simulations with varying realism indicate an emergent principle -- multiphase condensation and large cavity power occur when the ratio of the cooling time to the free-fall time ( $t_{cool} / t_{ff}$ ) falls below a threshold value close to 10. Observations indeed show cool-core signatures when this ratio falls below 20-30, but the prevalence of cores with $t_{cool} / t_{ff}$ ratio below 10 is rare as compared to simulations. In X-ray observations, we obtain projected spectra from which we have to infer radial gas density and temperature profiles. Using idealized models of X-ray cavities and multiphase gas in the core and 3-D hydro jet-ICM simulations, we quantify the biases introduced by deprojection based on the assumption of spherical symmetry in determining $t_{cool} / t_{ff}$ . We show that while the used methods are able to recover the $t_{cool} / t_{ff}$ ratio for relaxed clusters, they have an uncertainty of a factor of $2 - 3$ in systems containing large cavities ( $≳ 20$ kpc). We also show that the mass estimates from these methods, in the absence of X-ray spectra close to the virial radius, suffer from a degeneracy between the virial mass ( $M_{200}$ ) and the concentration parameter ( $c$ ) in the form of $M_{200} c^{2} \approx$ constant. Additionally, lack of soft-X-ray ( $≲ 0.5$ keV) coverage and poor spatial resolution make us overestimate min( $t_{cool} / t_{ff}$ ) by a factor of few in clusters with min( $t_{cool} / t_{ff}$ ) $≲ 5$ . This bias can largely explain the lack of cool-core clusters with min( $t_{cool} / t_{ff}$ ) $≲ 5$ .

arXiv commentAccepted for publication in MNRAS. Comments are welcome

Deprojection of X-ray data in galaxy clusters: confronting simulations with observations

Abstract

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