摘要：Aims. This study aims to probe the thermodynamic properties of the hot
intragroup medium (IGM) plasma in the core regions of the NGC 4636 galaxy group by
detailed measurements of several emission lines and their relative intensities.
Methods. We analyzed deep XMM-Newton Reflection Grating
Spectrometer (RGS) data in five adjacent spectral regions in the central parts of the NGC
4636 galaxy group. We examined the suppression of the Fe xvii resonance line
(15.01 Å) as compared to the forbidden lines of the same ion (17.05 Å and 17.10 Å). The
presence and radial dependence of the cooling flow was investigated through spectral
modeling. Parallel analysis with deep Chandra Advances CCD Imaging
Spectrometer (ACIS) data was conducted to gain additional information about the
thermodynamical properties of the IGM.
Results. The plasma at the group center to the north shows efficient
Fe xvii ion resonant scattering, yielding (Iλ17.05 +
Iλ17.10)
/Iλ15.01 line ratios
up to 2.9 ± 0.4, corresponding
toabout twice the predicted
line ratio. In contrast, no resonant scattering was detected at the south side. The
regions featuring resonant scattering coincide with those embodying large amounts of cool
(kT ≲ 0.4
keV) gas phases, and the spectral imprints of cooling gas with a total
mass deposition rate of ~0.8 M⊙ yr-1 within the examined region of
2.4′ × 5.0′.
Conclusions. We interpret the results as possible evidence of asymmetric
turbulence distribution in the NGC 4636 IGM: turbulence dominates the gas dynamics to the
south, while collective gas motions characterize the dynamics to the north. X-ray images
show imprints of energetic AGN at both sides, yet we find evidence of turbulence heating
at the south and gas cooling at the north of the core. We infer that the observed
asymmetry may be the result of the specific observation angle to the source, or arise from
the turbulence driven by core sloshing at south side.
关键词：X-rays: galaxies: clusters;galaxies: groups: individual: NGC 4636;galaxies: clusters: intracluster medium
