Implications of coronal line emission in NGC 4696

M. Chatzikos, R. J.R. Williams, G. J. Ferland, R. E.A. Canning, A. C. Fabian, J. S. Sanders, P. A.M. van Hoof, R. M. Johnstone, M. Lykins, R. L. Porter

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


We announce a new facility in the spectral code CLOUDY that enables tracking the evolution of a cooling parcel of gas with time. For gas cooling from temperatures relevant to galaxy clusters, earlier calculations estimated the [Fe XIV] λ5303/[Fe X] λ6375 luminosity ratio, a critical diagnostic of a cooling plasma, to slightly less than unity. By contrast, our calculations predict a ratio of ~3. We revisit recent optical coronal line observations along the X-ray cool arc around NGC 4696 by Canning et al., which detected [Fe X] λ6375, but not [Fe XIV] λ5303. We show that these observations are not consistent with predictions of cooling flow models. Differential extinction could in principle account for the observations, but it requires extinction levels (AV > 3.625) incompatible with previous observations. The non-detection of [Fe XIV] implies a temperature ceiling of 2.1 million K. Assuming cylindrical geometry and transonic turbulent pressure support, we estimate the gas mass at ~1 million M. The coronal gas is cooling isochorically. We propose that the coronal gas has not condensed out of the intracluster medium, but instead is the conductive or mixing interface between the X-ray plume and the optical filaments. We present a number of emission lines that may be pursued to test this hypothesis and constrain the amount of intermediate-temperature gas in the system.

Original languageEnglish
Pages (from-to)1234-1244
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
StatePublished - Jan 11 2015

Bibliographical note

Publisher Copyright:
© 2014 The Authors.


  • Galaxies: clusters: general
  • Galaxies: clusters: individual: Centaurus
  • Galaxies: clusters: intracluster medium
  • Galaxies: individual: NGC 4696
  • Methods: numerical

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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