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PGC 43296
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NGC 4696: The Arrhythmic Beating of a Black Hole Heart

At the center of the Centaurus galaxy cluster, there is a large elliptical galaxy called NGC 4696. Deeper still, there is a supermassive black hole buried within the core of this galaxy.
New data from NASA's Chandra X-ray Observatory and other telescopes has revealed details about this giant black hole, located some 145 million light years from Earth. Although the black hole itself is undetected, astronomers are learning about the impact it has on the galaxy it inhabits and the larger cluster around it.
In some ways, this black hole resembles a beating heart that pumps blood outward into the body via the arteries. Likewise, a black hole can inject material and energy into its host galaxy and beyond.

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RE: NGC 4696
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Title: Implications of Coronal Line Emission in NGC 4696
Author: M. Chatzikos (1), R.J.R. Williams (2), G.J. Ferland (1), R.E.A. Canning (3,4), A.C. Fabian (5), J.S. Sanders (6), P.A.M. van Hoof (7), R.M. Johnstone (5), M. Lykins (1), R.L. Porter (8) ((1) University of Kentucky, (2) AWE, (3) KIPAC, (4) Stanford University, (5) University of Cambridge, (6) MPE, (7) Royal Observatory of Belgium, (8) University of Georgia)

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] {\lambda}5303 / [Fe X] {\lambda}6375 luminosity ratio, a critical diagnostic of a cooling plasma, to slightly less than unity. By contrast, our calculations predict a ratio ~3. We revisit recent optical coronal line observations along the X-ray cool arc around NGC 4696 by Canning et al. (2011), which detected [Fe X] {\lambda}6375, but not [Fe XIV] {\lambda}5303. 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 (A_V > 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 solar masses. 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.

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Zooming Into Galaxy NGC 4696

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NGC 4696 (also MCG -7-26-51 and PGC 43296) is a magnitude +10.4 elliptical galaxy located 136 million light-years away in the constellation Centaurus.

The galaxy was discovered by Scottish astronomer James Dunlop using a 22.86 cm (9 inch) f/12 speculum Newtonian reflector in Parramatta, New South Wales, on the 7th May 1826.

Right Ascension 12h 48m 49.3s, Declination -41° 18' 40"

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Centaurus cluster
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Title: Herschel observations of the Centaurus cluster - the dynamics of cold gas in a cool core
Authors: Rupal Mittal, Christopher P. O'Dea, Gary Ferland, Raymond Oonk, Alastair C. Edge, Rebecca E. A. Canning, Helen Russell, Stefi A. Baum, Hans Böhringer, Francoise Combes, Megan Donahue, Andy C. Fabian, Nina A. Hatch, Aaron Hoffer, Roderick Johnstone, Brian R. McNamara, Philippe Salomé, Grant Tremblay

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, CII at 157.74 micron and OI at 63.18 micron, and in addition NII at 121.90 micron. The CII emission is extended over a region of 7 kpc with a similar spatial morphology and kinematics to the optical H-alpha emission. This has the profound implication that the optical hydrogen recombination line, H-alpha, the optical forbidden lines, NII 6583 Angstrom, the soft X-ray filaments and the far-infrared CII 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 black-body function and find a cold 19 K dust component with mass 1.6x10^6 solar mass and a warm 46 K dust component with mass 4.0x10^3 solar mass. The total FIR luminosity between 8 micron and 1000 micron is 7.5x10^8 solar luminosity, which using Kennicutt relation yields a low star formation rate of 0.13 solar mass per yr. This value is consistent with values derived from other tracers, such as ultraviolet emission. Combining the spectroscopic and photometric results together with optical H-alpha, we model emitting clouds consisting of photodissociation regions (PDRs) adjacent to ionised 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 H-alpha and CII filaments.

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NGC 4696
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NGC 4696: a cosmic question mark

Curling around itself like a question mark, the unusual looking galaxy NGC 4696 itself begs many questions. Why is it such a strange shape? What are the odd, capillary-like filaments that stretch out of it? And what is the role of a large black hole in explaining its decidedly odd appearance?
This picture, taken by Hubble's Advanced Camera for Surveys, is not just a beautiful snapshot of NGC 4696, the largest galaxy in the Centaurus Cluster (galaxy cluster Abell 3526). It is also an illustration of the rich variety of objects that astronomers can see with the NASA/ESA Hubble Space Telescope.

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