X-Ray Cavities, Filaments, and Cold Fronts in the Core of the Galaxy Group NGC 5044 (original) (raw)
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Hard X-Ray Emission from the NGC 5044 Group
The Astrophysical Journal, 2011
Observations made with the Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA) to constrain the hard X-ray emission in the NGC 5044 group are reported here. Modeling a combined PCA and ROSAT position sensitive proportional counter (PSPC) spectrum with a 0.5 -15 keV energy range shows excess hard emission above 4 keV. Addition of a powerlaw component with spectral index of 2.6 -2.8 and luminosity of 2.6×10 42 ergs s −1 within 700 kpc in the observed energy band removes these residuals. Thus, there is a detection of a significant non-thermal component that is 32% of the total X-ray emission. Point source emission makes up at most 14% of the non-thermal emission from the NGC 5044 group. Therefore, the diffuse, point source subtracted, non-thermal component is 2.2 -3.0×10 42 ergs s −1 . The cosmic-ray electron energy density is 3.6×10 −12 ergs cm −3 and the average magnetic field is 0.034 µGauss in the largest radio emitting region. The ratio of cosmic-ray electron energy density to magnetic field energy density, ∼2.5×10 4 , is significantly out of equipartition and is therefore atypical of radio lobes. In addition, the group's small size and low non-thermal energy density strongly contradicts the size-energy relationship found for radio lobes. Thus, it is unlikely to be related to the active galaxy and is most likely a relic of the merger. The energy in cosmic-rays and magnetic field is consistent with simulations of cosmic-ray acceleration by merger shocks.
A Deep X‐Ray Observation of NGC 4258 and Its Surrounding Field
The Astrophysical Journal, 2000
We present a deep X-ray observation of the low-luminosity active galactic nucleus (AGN) in NGC 4258 (M106) using the Advanced Satellite for Cosmology and Astrophysics (ASCA). ConÐrming previous results, we Ðnd that the X-ray spectrum of this source possesses several components. The soft X-ray spectrum (\2 keV) is dominated by thermal emission from optically thin plasma with kT D 0.5 keV. The hard X-ray emission is clearly due to a power-law component with photon index ! B 1.8 absorbed by a column density of cm~2. The power law is readily identiÐed with primary X-ray N H
Accretion and Outflow in the Active Galactic Nucleus and Starburst of NGC 5135
2004
Observations of the Seyfert 2 and starburst galaxy NGC 5135 with the Chandra X-ray Observatory demonstrate that both of these phenomena contribute significantly to its X-ray emission. We spatially isolate the active galactic nucleus (AGN) and demonstrate that it is entirely obscured by column density N H > 10 24 cm −2 , detectable in the Chandra bandpass only as a strongly reprocessed, weak continuum and a prominent iron Kα emission line with equivalent width of 2.4 keV. Most of the soft Xray emission, both near the AGN and extending over several-kpc spatial scales, is collisionally-excited plasma. We attribute this thermal emission to stellar processes. The AGN dominates the X-ray emission only at energies above 4 keV. In the spectral energy distribution that extends to far-infrared wavelengths, nearly all of the emergent luminosity below 10 keV is attributable to star formation, not the AGN.
Accretion and Outflow in the AGN and Starburst of NGC 5135
2003
Observations of the Seyfert 2 and starburst galaxy NGC 5135 with the Chandra X-ray Observatory demonstrate that both of these phenomena contribute significantly to its X-ray emission. We spatially isolate the active galactic nucleus (AGN) and demonstrate that it is entirely obscured by column density N_H > 10^{24} cm^{-2}, detectable in the Chandra bandpass only as a strongly reprocessed, weak continuum and a prominent iron K alpha emission line with equivalent width of 2.4 keV. Most of the soft X-ray emission, both near the AGN and extending over several-kpc spatial scales, is collisionally-excited plasma. We attribute this thermal emission to stellar processes. The AGN dominates the X-ray emission only at energies above 4 keV. In the spectral energy distribution that extends to far-infrared wavelengths, nearly all of the emergent luminosity below 10 keV is attributable to star formation, not the AGN.
Observations of asymmetric velocity fields and gas cooling in the NGC 4636 galaxy group X-ray halo
Astronomy & Astrophysics, 2016
Aims. This study aims to probe the thermodynamic properties of the hot intragroup medium (IGM) plasma in the core regions of the NGC 4636 galaxy group by detailed measurements of several emission lines and their relative intensities. Methods. We analyzed deep XMM-Newton Reflection Grating Spectrometer (RGS) data in five adjacent spectral regions in the central parts of the NGC 4636 galaxy group. We examined the suppression of the Fe xvii resonance line (15.01 Å) as compared to the forbidden lines of the same ion (17.05 Å and 17.10 Å). The presence and radial dependence of the cooling flow was investigated through spectral modeling. Parallel analysis with deep Chandra Advances CCD Imaging Spectrometer (ACIS) data was conducted to gain additional information about the thermodynamical properties of the IGM. Results. The plasma at the group center to the north shows efficient Fe xvii ion resonant scattering, yielding (I λ17.05 + I λ17.10)/I λ15.01 line ratios up to 2.9 ± 0.4, corresponding to about twice the predicted line ratio. In contrast, no resonant scattering was detected at the south side. The regions featuring resonant scattering coincide with those embodying large amounts of cool (kT 0.4 keV) gas phases, and the spectral imprints of cooling gas with a total mass deposition rate of ∼0.8 M yr −1 within the examined region of 2.4 × 5.0. Conclusions. We interpret the results as possible evidence of asymmetric turbulence distribution in the NGC 4636 IGM: turbulence dominates the gas dynamics to the south, while collective gas motions characterize the dynamics to the north. X-ray images show imprints of energetic AGN at both sides, yet we find evidence of turbulence heating at the south and gas cooling at the north of the core. We infer that the observed asymmetry may be the result of the specific observation angle to the source, or arise from the turbulence driven by core sloshing at south side.
Publications of the Astronomical Society of Japan, 2013
Based on Suzaku X-ray observations, we study the hot gas around the NGC4839 group of galaxies and the radio relic in the outskirts of the Coma cluster. We find a gradual decline in the gas temperature from 5 keV around NGC4839 to 3.6 keV at the radio relic, across which there is a further, steeper drop down to 1.5 keV. This drop as well as the observed surface brightness profile are consistent with a shock with Mach number M = 2.2 ± 0.5 and velocity v s = (1410 ± 110) km s −1 . A lower limit of B > 0.33 µG is derived on the magnetic field strength around the relic from upper limits to inverse Compton X-ray emission. Although this suggests that the non-thermal electrons responsible for the relic are generated by diffusive shock acceleration (DSA), the relation between the measured Mach number and the electron spectrum inferred from radio observations are inconsistent with that expected from the simplest, test-particle theory of DSA. Nevertheless, DSA is still viable if it is initiated by the injection of a pre-existing population of non-thermal electrons. Combined with previous measurements, the temperature profile of Coma in the southwest direction is shallower outside NGC4839 and also slightly shallower in the outermost region. The metal abundance around NGC4839 is confirmed to be higher than in its vicinity, implying a significant peak in the abundance profile that decreases to 0.2 solar toward the outskirts. We interpret these facts as due to ram pressure stripping of metal-enriched gas from NGC4839 as it falls into Coma. The relic shock may result from the combined interaction of pre-existing intracluster gas, gas associated with NGC 4839, and cooler gas flowing in from the large-scale structure filament in the southwest.
The Astrophysical Journal, 2014
We have obtained a deep, sub-arcsecond resolution X-ray image of the nuclear region of the luminous galaxy merger NGC 6240 with Chandra, which resolves the X-ray emission from the pair of active nuclei and the diffuse hot gas in great detail. We detect extended hard X-ray emission from kT ∼ 6 keV (∼70 million K) hot gas over a spatial scale of 5 kpc, indicating the presence of fast shocks with velocity of ∼2200 km s −1. For the first time we obtain the spatial distribution of this highly ionized gas emitting Fe XXV, which shows a remarkable correspondence to the large scale morphology of H 2 (1-0) S(1) line emission and Hα filaments. Propagation of fast shocks originated in the starburst driven wind into the ambient dense gas can account for this morphological correspondence. With an observed L 0.5−8keV = 5.3 × 10 41 erg s −1 , the diffuse hard X-ray emission is ∼100 times more luminous than that observed in the classic starburst galaxy
The Astrophysical Journal, 2013
We present a combined X-ray, optical, and radio analysis of the galaxy group IC 1860 using the currently available Chandra and XMM data, literature multi-object spectroscopy data and GMRT data. The Chandra and XMM imaging and spectroscopy reveal two surface brightness discontinuities at 45 and 76 kpc shown to be consistent with a pair of cold fronts. These features are interpreted as due to sloshing of the central gas induced by an off-axis minor merger with a perturber. This scenario is further supported by the presence of a peculiar velocity of the central galaxy IC 1860 and the identification of a possible perturber in the optically disturbed spiral galaxy IC 1859. The identification of the perturber is consistent with the comparison with numerical simulations of sloshing. The GMRT observation at 325 MHz shows faint, extended radio emission contained within the inner cold front, as seen in some galaxy clusters hosting diffuse radio mini-halos. However, unlike mini-halos, no particle reacceleration is needed to explain the extended radio emission, which is consistent with aged radio plasma redistributed by the sloshing. There is strong analogy of the X-ray and optical phenomenology of the IC 1860 group with two other groups, NGC 5044 and NGC 5846, showing cold fronts. The evidence presented in this paper is among the strongest supporting the currently favored model of cold-front formation in relaxed objects and establishes the group scale as a chief environment to study this phenomenon.
Insights into the location and dynamics of the coolest X-ray emitting gas in clusters of galaxies
Monthly Notices of the Royal Astronomical Society
We extend our previous study of the cool gas responsible for the emission of O VII X-ray lines in the cores of clusters and groups of galaxies. This is the coolest X-ray emitting phase and connects the 10 000 K H α emitting gas to the million degree phase, providing a useful tool to understand cooling in these objects. We study the location of the O VII gas and its connection to the intermediate Fe XVII and hotter O VIII phases. We use high-resolution X-ray grating spectra of elliptical galaxies with strong Fe XVII line emission and detect O VII in 11 of 24 objects. Comparing the O VII detection level and resonant scattering, which is sensitive to turbulence and temperature, suggests that O VII is preferably found in cooler objects, where the Fe XVII resonant line is suppressed due to resonant scattering, indicating subsonic turbulence. Although a larger sample of sources and further observations is needed to distinguish between effects from temperature and turbulence, our results are consistent with cooling being suppressed at high turbulence as predicted by models of active galactic nuclei feedback, gas sloshing and galactic mergers. In some objects, the O VII resonant-to-forbidden line ratio is decreased by either resonant scattering or charge exchange boosting the forbidden line, as we show for NGC 4636. Charge exchange indicates interaction between neutral and ionized gas phases. The Perseus cluster also shows a high Fe XVII forbidden-to-resonance line ratio, which can be explained with resonant scattering by low-turbulence cool gas in the line of sight.
The Astrophysical Journal, 2002
Using Chandra and HST we show that X-ray and Hα filaments that form the 1.3-kpc diameter superbubble of NGC 3079 have strikingly similar patterns at ∼0. ′′ 8 resolution. This tight optical line/X-ray match seems to arise from cool disk gas that has been driven by the wind, with X-rays being emitted from upstream, stand-off bowshocks or by conductive cooling at the cloud/wind interfaces. We find that the soft X-ray plasma has thermal and kinetic energies E TH ∼ 2 × 10 56 η 0.5