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Herschel observations of the Centaurus cluster - the dynamics of cold gas in a cool core.

Mittal, R. and O'Dea, C.P. and Ferland, G. and Oonk, J.B.R. and Edge, A.C. and Canning, R.E.A. and Russell, H. and Baum, S.A. and Böhringer, H. and Combes, F. and Donahue, M. and Fabian, A.C. and Hatch, N.A. and Hoffer, A. and Johnstone, R. and McNamara, B.R. and Salomé, P. and Tremblay, G. (2011) 'Herschel observations of the Centaurus cluster - the dynamics of cold gas in a cool core.', Monthly notices of the Royal Astronomical Society., 418 (4). pp. 2386-2402.


Brightest cluster galaxies (BCGs) in the cores of galaxy clusters have distinctly different properties from other low-redshift massive ellipticals. The majority of the BCGs in cool-core clusters show signs of active star formation. We present observations of NGC 4696, the BCG of the Centaurus galaxy cluster, at far-infrared (FIR) wavelengths with the Herschel space telescope. Using the PACS spectrometer, we detect the two strongest coolants of the interstellar medium, [C ii] at 157.74 μm and [O i] at 63.18 μm, and in addition [N ii] at 121.90 μm. The [C ii] emission is extended over a region of 7 kpc with a similar spatial morphology and kinematics to the optical Hα emission. This has the profound implication that the optical hydrogen recombination line, Hα, the optical forbidden lines, [N ii] λ6583 Å, the soft X-ray filaments and the FIR [C ii] line all have the same energy source. We also detect dust emission using the PACS and SPIRE photometers at all six wavebands. We perform a detailed spectral energy distribution fitting using a two-component modified blackbody function and find a cold 19-K dust component with mass 1.6 × 106 M⊙ and a warm 46-K dust component with mass 4.0 × 103 M⊙. The total FIR luminosity between 8 and 1000 μm is 7.5 × 108 L⊙, which using Kennicutt relation yields a low star formation rate of 0.13 M⊙ yr−1. This value is consistent with values derived from other tracers, such as ultraviolet emission. Combining the spectroscopic and photometric results together with optical Hα, we model emitting clouds consisting of photodissociation regions adjacent to ionized regions. We show that in addition to old and young stellar populations, there is another source of energy, such as cosmic rays, shocks or reconnection diffusion, required to excite the Hα and [C ii] filaments.

Item Type:Article
Keywords:Photodissociation region (PDR), Galaxies, Active, Clusters, Intracluster medium, Kinematics and dynamics, Star formation, Infrared, ISM.
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Publisher statement:This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS Published by Oxford University Press on behalf of The Royal Astronomical Society. All rights reserved.
Date accepted:No date available
Date deposited:03 January 2014
Date of first online publication:December 2011
Date first made open access:No date available

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