Collisional heating as the origin of filament emission in galaxy clusters

By G. Ferland, A. C. Fabian, N. Hatch, R. Johnstone, R. Porter, P. V. Hoof, R. Williams. 2008

141 citations recorded by the source corpus.

It has long been known that photoionization, whether by starlight or other sources, has difficulty in accounting for the observed spectra of the optical filaments that often surround central galaxies in large clusters. This paper builds on the first of this series in which we examined whether heating by energetic particles or dissipative magnetohydrodynamic (MHD) wave can account for the observations. The first paper focused on the molecular regions which produce strong H2 and CO lines. Here we extend the calculations to include atomic and low-ionization regions. Two major improvements to the previous calculations have been made. The model of the hydrogen atom, along with all elements of the H-like iso-electronic sequence, is now fully nl-resolved. This allows us to predict the hydrogen emission-line spectrum including excitation by suprathermal secondary electrons and thermal electrons or nuclei. We show how the predicted H i spectrum differs from the pure-recombination case. The second update is to the rates for H0–H2 inelastic collisions. We now use the values computed by Wrathmall et al. The rates are often much larger and allow the ro–vibrational H2 level populations to achieve a thermal distribution at substantially lower densities than previously thought. We calculate the chemistry, ionization, temperature, gas pressure and emission-line spectrum for a wide range of gas densities and collisional heating rates. We assume that the filaments are magnetically confined. The gas is free to move along field lines so that the gas pressure is equal to that of the surrounding hot gas. A mix of clouds, some being dense and cold and others hot and tenuous, can exist. The observed spectrum will be the integrated emission from clouds with different densities and temperatures but the same pressure P/k=nT. We assume that the gas filling factor is given by a power law in density. The power-law index, the only free parameter in this theory, is set by matching the observed intensities of infrared H2 lines relative to optical H i lines. We conclude that the filaments are heated by ionizing particles, either conducted in from surrounding regions or produced in situ by processes related to MHD waves.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/1f5cfe818906f16c2791286ed06764548826ef78

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In Astronomy and Astrophysics

1. M. Cappellari
2. M. Sarzi
3. Roger Davies
4. M. Bureau
5. Eric Emsellem
6. P. de Zeeuw
7. D. Krajnovi'c
8. R. McDermid

In Instrumentation

1. M. Cappellari
2. M. Sarzi
3. M. Bureau
4. Eric Emsellem
5. P. de Zeeuw
6. D. Krajnovi'c
7. Roger Davies
8. R. McDermid

Citations in the corpus

• ON THE ORIGIN OF THE EXTENDED Hα FILAMENTS IN COOLING FLOW CLUSTERS (2010, background): “Once sufficiently cool, the gas in these filaments can be re-ionized via star formation, collisional heating (e.g., Ferland et al. 2009), or drag heating (e.g., Pope et al. 2008).”
• Jet-induced star formation in gas-rich galaxies (2011, background): “…heat the cold molecular gas and keep it warm during the lifetime of the jet although the cooling times are much shorter than the jet lifetime – potentially due to the action of shocks, turbulent dissipation or cosmic rays (Ferland et al. 2008, 2009; Guillard et al. 2009; Papadopoulos et al. 2010).”
• The fast molecular outflow in the Seyfert galaxy IC 5063 as seen by ALMA (2015, background): “…excited by a variety of physical processes, such as shocks A1, page 4 of 11 (e.g. Hollenbach & McKee 1989), cosmic rays (e.g. Sternberg et al. 1997; Ferland et al. 2009; Meijerink et al. 2011; Bayet et al. 2011), mechanical heating (Loenen et al. 2008; Meijerink et al. 2011) and photodissociation…”
• The SAURON project - XVI. On the sources of ionization for the gas in elliptical and lenticular galaxies (2009, background): “…from heat conduction is sufficient to explain the nebular emission, whereas Donahue & Voit (1991) found that the X-ray gas radiation could explain also the typical line ratios observed in the optical filaments of cooling flows clusters (see also Ferland et al. 2009, for a recent investigation).”
• Thermal instability and the feedback regulation of hot haloes in clusters, groups and galaxies (2011, background): “In reality magnetic fields, cosmic rays, and thermal conduction along magnetic field lines strongly influence c© 2011 RAS, MNRAS 000, 1–26 the geometry and energy balance in filaments (e.g., Ferland et al. 2009; Sharma, Parrish, & Quataert 2010).”