Molecular tracers of filamentary CO emission regions surrounding the central galaxies of clusters

¹ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK e-mail: [eb;daw]@star.ucl.ac.uk
² School of Physics and Astronomy University of Leeds, Leeds LS2 9JT, UK e-mail: twh@ast.leeds.ac.uk
³ Department of Astronomy, California Institute of Technology, Pasadena, CA 91125, USA e-mail: tab@phobos.caltech.edu

Received: 26 August 2009
Accepted: 9 July 2010

Abstract

Context. Optical emission is detected from filaments around the central galaxies of clusters of galaxies. These filaments have lengths of tens of kiloparsecs. The emission is possibly due to heating caused by the dissipation of mechanical energy and by cosmic ray induced ionisation. CO millimeter and submillimeter line emissions as well as H₂ infrared emission originating in such filaments surrounding NGC 1275, the central galaxy of the Perseus cluster, have been detected.

Aims. Our aim is to identify those molecular species, other than CO, that may emit detectable millimeter and submillimeter line features arising in these filaments, and to determine which of those species will produce emissions that might serve as diagnostics of the dissipation and cosmic ray induced ionisation.

Methods. The time-dependent UCL photon-dominated region modelling code was used in the construction of steady-state models of molecular filamentary emission regions at appropriate pressures, for a range of dissipation and cosmic ray induced ionisation rates and incident radiation fields.

Results. HCO⁺ and C₂H emissions will potentially provide information about the cosmic ray induced ionisation rates in the filaments. HCN and, in particular, CN are species with millimeter and submillimeter lines that remain abundant in the warmest regions containing molecules.

Conclusions. Detections of the galaxy cluster filaments in HCO⁺, C₂H, and CN emissions and further detections of them in HCN emissions would provide significant constraints on the dissipation and cosmic ray induced ionisation rates.