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G. R. Tremblay,
C. P. O'Dea,
S. A. Baum,
T. E. Clarke,
C. L. Sarazin,
J. N. Bregman,
F. Combes,
M. Donahue,
A. C. Edge,
A. C. Fabian, [......],
B. R. McNamara,
R. Mittal,
J. B. R. Oonk,
A. C. Quillen,
H. R. Russell,
J. S. Sanders, P. Salomé,
G. M. Voit,
R. J. Wilman,
M. W. Wise
[show abstract]
[hide abstract]
ABSTRACT: We present new Chandra X-ray observations of the brightest cluster galaxy
(BCG) in the cool core cluster Abell 2597. The data reveal an extensive
kpc-scale X-ray cavity network as well as a 15 kpc filament of soft-excess gas
exhibiting strong spatial correlation with archival VLA radio data. In addition
to several possible scenarios, multiwavelength evidence may suggest that the
filament is associated with multiphase (10^3 - 10^7 K) gas that has been
entrained and dredged-up by the propagating radio source. Stemming from a full
spectral analysis, we also present profiles and 2D spectral maps of modeled
X-ray temperature, entropy, pressure, and metal abundance. The maps reveal an
arc of hot gas which in projection borders the inner edge of a large X-ray
cavity. Although limited by strong caveats, we suggest that the hot arc may be
(a) due to a compressed rim of cold gas pushed outward by the radio bubble or
(b) morphologically and energetically consistent with cavity-driven active
galactic nucleus (AGN) heating models invoked to quench cooling flows, in which
the enthalpy of a buoyant X-ray cavity is locally thermalized as ambient gas
rushes to refill its wake. If confirmed, this would be the first observational
evidence for this model.
05/2012;
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G. R. Tremblay,
C. P. O'Dea,
S. A. Baum,
T. E. Clarke,
C. L. Sarazin,
J. N. Bregman,
F. Combes,
M. Donahue,
A. C. Edge,
A. C. Fabian, [......],
B. R. McNamara,
R. Mittal,
J. B. R. Oonk,
A. C. Quillen,
H. R. Russell,
J. S. Sanders, P. Salomé,
G. M. Voit,
R. J. Wilman,
M. W. Wise
[show abstract]
[hide abstract]
ABSTRACT: New Chandra X-ray and Herschel FIR observations enable a multiwavelength
study of active galactic nucleus (AGN) heating and intracluster medium (ICM)
cooling in the brightest cluster galaxy of Abell 2597. The new Chandra
observations reveal the central < 30 kiloparsec X-ray cavity network to be more
extensive than previously thought, and associated with enough enthalpy to
theoretically inhibit the inferred classical cooling flow. Nevertheless, we
present new evidence, consistent with previous results, that a moderately
strong residual cooling flow is persisting at 4%-8% of the classically
predicted rates in a spatially structured manner amid the feedback-driven
excavation of the X-ray cavity network. New Herschel observations are used to
estimate warm and cold dust masses, a lower-limit gas-to-dust ratio, and a star
formation rate consistent with previous measurements. The cooling time profile
of the ambient X-ray atmosphere is used to map the locations of the
observational star formation entropy threshold as well as the theoretical
thermal instability threshold. Both lie just outside the < 30 kpc central
region permeated by X-ray cavities, and star formation as well as ionized and
molecular gas lie interior to both. The young stars are distributed in an
elongated region that is aligned with the radio lobes, and their estimated ages
are both younger and older than the X-ray cavity network, suggesting both
jet-triggered as well as persistent star formation over the current AGN
feedback episode. Bright X-ray knots that are coincident with extended Ly-alpha
and FUV continuum filaments motivate a discussion of structured cooling from
the ambient hot atmosphere along a projected axis that is perpendicular to
X-ray cavity and radio axis. We conclude that the cooling ICM is the dominant
contributor of the cold gas reservoir fueling star formation and AGN activity
in the Abell 2597 BCG.
05/2012;
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R. Mittal,
C. P. O’Dea,
G. Ferland,
J. B. R. Oonk,
A. C. Edge,
R. E. A. Canning,
H. Russell,
S. A. Baum,
H. Böhringer,
F. Combes,
M. Donahue,
A. C. Fabian,
N. A. Hatch,
A. Hoffer,
R. Johnstone,
B. R. McNamara, P. Salomé,
G. Tremblay
[show abstract]
[hide abstract]
ABSTRACT: 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.
Monthly Notices of the Royal Astronomical Society 12/2011; 418(4):2386 - 2402. · 4.90 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We used K-band spectra to measure the H2 excitation temperatures in six
molecular knots associated with the filaments in the Crab Nebula. The
temperatures are quite high - in the range T ~ 2000-3000K, just below the H2
dissociation temperature. This is the temperature range over which the H2 1-0
S(1) line at 2.121\mum has its maximum emissivity per unit mass, so there may
be many additional H2 cores with lower temperatures that are too faint to
detect. We also measured the electron density in adjacent ionized gas, which on
the assumption of gas pressure balance indicates densities in the molecular
region n_mol ~ 20,000 H baryons cm-3, although this really is just a lower
limit since the H2 gas may be confined by other means. The excited region may
be just a thin skin on a much more extensive blob of molecular gas that does
not have the correct temperature and density to be as easily detectable. At the
opposite extreme, the observed knots could consist of a fine mist of molecular
gas in which we are detecting essentially all of the H2. Future CO observations
could distinguish between these two cases. The Crab filaments serve as the
nearby laboratories for understanding the very much larger filamentary
structures that have formed in the intracluster medium of cool-core galaxy
clusters.
12/2011;
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[show abstract]
[hide abstract]
ABSTRACT: We present the first detection of CO emission lines in the Halpha filaments
at distances as far as 50 kpc from the centre of the galaxy NGC 1275. This gas
is probably dense (>=10E3 cm-3). However, it is not possible to accurately
determine the density and the kinetic temperature of this relatively warm gas
(Tkin~20-500K) with the current data only. The amount of molecular gas in the
filaments is large 10E9 Msun (assuming a Galactic N(H2)/Ico ratio). This is 10%
of the total mass of molecular gas detected in this cD galaxy. This gas has
large-scale velocities comparable to those seen in Halpha. The origin of the
filaments is still unclear, but their formation is very likely linked to the
AGN positive feedback (Revaz et al., 2008) that regulates the cooling of the
surrounding X-ray-emitting gas as suggested by numerical simulations. We also
present high-resolution spectra of the galaxy core. The spatial characteristics
of the double-peaked profile suggest that the molecular web of filaments and
streamers penetrates down to radii of less than 2 kpc from the central AGN and
eventually feed the galaxy nucleus. The mass of gas inside the very central
region is ~10E^9 Msun, and is similar to the mass of molecular gas found in the
filaments.
05/2011;
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[show abstract]
[hide abstract]
ABSTRACT: We report CO observations towards MS0735.6+7421 a distant cooling core galaxy, and towards M87, the nearest cooling core in the center of the Virgo cluster. Both galaxies contain radio cavities that are thought to be responsible for the heating that can regulate or stop the cooling of the surrounding gas. In this feedback process, there could still be some gas cooling along filaments, along the borders of the radio cavities. Molecular gas is known to exist in clusters with cooling cores, in long and thin filaments that can be formed behind the rising bubbles inflated by the central AGN. CO emission was searched for at several locations along the radio lobes of those two galaxies, but only upper limits were found. These correspond to cold gas mass limits of a few 10^9 Msol for each pointing in MS0735.6+7421, and a few 10^6 Msol in M87. This non detection means that either the cooling is strongly reduced by the AGN feedback or that the gas is cooling in very localized places like thin filaments, possibly diluted in the large beam for MS0735.6+7421. For M87, the AGN heating appears to have stopped the cooling completely. Comment: 10 pages, 5 figures, accepted in A&A
06/2008;
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[show abstract]
[hide abstract]
ABSTRACT: We have recently detected CO lines in the well-known filaments around NGC 1275, the galaxy at the centre of the Perseus cluster of galaxies. These previous observations, with the HERA multi-beam array at the IRAM 30m telescope enabled us to make a large map of the CO(2-1) line and to see hints of molecular gas far away from the cluster centre. To confirm the presence of CO emission lines in the outer filaments and to study the CO(2-1)/CO(1-0) line ratio, we observed seven regions of interest again with the 30m telescope in both CO(1-0) and CO(2-1). The regions we observed were: the eastern filament, the horseshoe, the northern filament and a southern extension, all selected from Halpha emission line mapping. Molecular gas is detected in all the observed regions. This result confirms the large extent of the cold molecular gas filaments. We discuss the CO(2-1)/CO(1-0) ratios in the filaments. The eastern filament has optically thick gas, whereas further away, the line ratio increases close to values expected for a warmer optically thin medium. We also show CO(1-0) and CO(2-1) lines in 9 regions closer to the centre. The kinematics of the CO is studied here in more detail and confirms that it follows the motions of the warm H_2 gas found in the near-infrared. Finally, we searched for dense gas tracers around 3C84 and claim here the first detection of HCN(3-2). Comment: 10 pages, 6 figures, A&A in press
04/2008;
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[show abstract]
[hide abstract]
ABSTRACT: We recently found extended CO(2-1) emission from cold molecular gas embedded in the network of Halpha filaments surrounding the galaxy NGC 1275 (Salome et al. 2006). We now present CO(2-1) interferometer maps of the eastern filaments, at high spatial and spectral resolutions. The cold molecular gas is detected by the Plateau de Bure Interferometer along the eastern filaments over an extent of 15'', or with a projected length of 5kpc. In our 2.5'' beam, the main CO filament is mostly unresolved along its minor axis. The multiple peaks along the CO filaments and the low values of the observed CO brightness temperatures imply further unresolved structures that may be giant molecular clouds. These clouds have very narrow line-width emission lines (~30 km/s). The CO emission is optically thick. It very likely traces cold clouds bound under their own self-gravity that may be falling back in the gravitational potential well of the galaxy. Such a picture would agree with current models of ``positive feedback'' in which some of the hot gas around NGC 1275 (a) is trapped by buoyantly rising bubbles inflated by the energy input of the 3C84 AGN, (b) subsequently cools efficiently at a larger radius around the edges of the hot bubbles, and (c) then falls back in self-gravitating clouds of molecular gas toward the center of the galaxy. Comment: 7 pages, 5 figures, A&A in press
04/2008;
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09/2007: pages 324-329;
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[show abstract]
[hide abstract]
ABSTRACT: A CO emission line survey in central cluster galaxies with cooling flows
had been performed with the IRAM 30m telescope. We have detected cold
molecular gas in 6 cluster cores leading to Mgas up to a few
1010 Msun \citepSalo03a, in agreement with
previous detections claimed by Edge (2001). We focus here on one of
these detections, the cluster of galaxies Abell 1795, which shows a
remarkable filamentary structure, seen both in X-ray and Hα. We
report IRAM interferometer maps of CO(1-0) and CO(2-1) rotational lines
of the cluster center. The cold gas morphology is shown and appear to be
associated with a cooling wake. The total cold gas mass derived with the
30m telescope was 4.3×109Msun and is
likely to be even higher since the ICM metallicity is 0.2-0.3 solar. We
find now that most of the emission is extended, as only 25% of the
single dish flux detected is retrieved by the interferometer.
Position-velocity maps are also presented and reveal a velocity
gradient. The cold gas kinematics and morphology is very similar to what
was found through Hα, supporting the association between the cold
gas and the optical filament. The optical nebulosities, aligned with the
cD orbit, are intimately related to the radio jets and lobes and the
material detected here is certainly fueling the star formation (also
aligned with the lobes). Even if some heating mechanisms are present,
these millimetric CO maps show an effective cooling to very low
temperatures indeed occurs.
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[show abstract]
[hide abstract]
ABSTRACT: Cold molecular gas has recently been detected in several cooling flow clusters of galaxies containing huge optical nebula. These optical filaments are tightly linked to cooling flows and related phenomena, such as rising bubbles of relativistic plasma fed by radio jets. We present here a map, in the CO(2–1) rotational line, of the cold molecular gas associated with some of the H$\alpha$ filaments surrounding the central galaxy of the Perseus cluster: NGC 1275. The map, extending to about 50 kpc (135 arcsec) from the center of the galaxy, has been made with the 18-receiver array HERA at the focus of the IRAM 30 m telescope. Although most of the cold gas is concentrated to the center of the galaxy, the CO emission is also clearly associated with the extended filaments conspicuous in ionised gas, and could trace a possible reservoir fueling the star formation there. Some of the CO emission is also found where the X-ray gas could cool down more efficiently at the rims of the central X-ray cavities (where the hot gas is thought to have been pushed out and compressed by the expanding radio lobes of the central AGN). The CO global kinematics do not show any rotation in NGC 1275. The cold gas is probably a mixture of gas falling down on the central galaxy and of uplifted gas dragged out by a rising bubble in the intracluster medium. As recently suggested in other cluster cores, the cold gas peculiar morphology and kinematics argue for the picture of an intermittent cooling flow scenario where the central AGN plays an important role.
http://dx.doi.org/10.1051/0004-6361:20054745.
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A. C. Edge,
J. B. R. Oonk,
R. Mittal,
S. W. Allen,
S. A. Baum,
H. Böhringer,
J. N. Bregman,
M. N. Bremer,
F. Combes,
C. S. Crawford, [......],
R. M. Johnstone,
B. R. McNamara,
C. P. O'Dea,
P. Popesso,
A. C. Quillen, P. Salomé,
C. L. Sarazin,
G. M. Voit,
R. J. Wilman,
M. W. Wise
http://dx.doi.org/10.1051/0004-6361/201014572.
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A. C. Edge,
J. B. R. Oonk,
R. Mittal,
S. W. Allen,
S. A. Baum,
H. Böhringer,
J. N. Bregman,
M. N. Bremer,
F. Combes,
C. S. Crawford, [......],
R. M. Johnstone,
B. R. McNamara,
C. P. O'Dea,
P. Popesso,
A. C. Quillen, P. Salomé,
C. L. Sarazin,
G. M. Voit,
R. J. Wilman,
M. W. Wise
http://dx.doi.org/10.1051/0004-6361/201014569.
