Possible depletion of metals into dust grains in the core of the Centaurus cluster of galaxies

K. Lakhchaura, F. Mernier, N. Werner

Published 2018-12-01Version 1

We present azimuthally-averaged metal abundance profiles from a full, comprehensive, and conservative re-analysis of the deep ($\sim$800 ks total net exposure) Chandra/ACIS-S observation of the Centaurus cluster core (NGC 4696). After carefully checking various sources of systematic uncertainties, including the choice of the spectral deprojection method, assumptions about the temperature structure of the gas and uncertainties in the continuum modelling, we confirm the existence of a central drop in the abundances of the `reactive' elements Fe, Si, S, Mg and Ca, within $r\lesssim$10 kpc. The same drops are also found when analyzing the XMM-Newton/EPIC data ($\sim$150 ks). Adopting our most conservative approach, we find that, unlike the central drops seen for Fe, Si, S, Mg and Ca, the abundance of the `non-reactive' element Ar is fully consistent with showing no central drop. This is further confirmed by the significant ($>3\sigma$) central radial increase of the Ar/Fe ratio. Our results corroborate the `dust depletion scenario', previously proposed by Panagoulia et al. (2013, 2015), in which central metal abundance drops are explained by the deposition of a significant fraction of centrally cooled reactive metals into dust grains present in the central regions of the Centaurus cluster. This is also supported by the previous findings that the extent of the metal abundance drops in NGC 4696 broadly coincides with the infrared dust emission.