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Register a new userPowerful AGN jets and unbalanced cooling in the hot atmosphere of IC 4296
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We present new Karl G. Jansky Very Large Array (VLA, 1.5 GHz) radio data for the giant elliptical galaxy IC 4296, supported by archival radio, X-ray (Chandra, XMM-Newton) and optical (SOAR, HST) observations. The galaxy hosts powerful radio jets piercing through the inner hot X-ray emitting atmosphere, depositing most of the energy into the ambient intra-cluster medium (ICM). Whereas the radio surface brightness of the A configuration image is consistent with a Fanaroff-Riley Class I (FR I) system, the D configuration image shows two bright, relative to the central region, large (~160 kpc diameter), well-defined lobes, previously reported by Killeen et al., at a projected distance r~>230 kpc. The XMM-Newton image reveals an X-ray cavity associated with one of the radio lobes. The total enthalpy of the radio lobes is ~7x10^59 erg and the mechanical power output of the jets is ~10^44 erg/s. The jets are mildly curved and possibly re-brightened by the relative motion of the galaxy and the ICM. The lobes display sharp edges, suggesting the presence of bow shocks, which would indicate that they are expanding supersonically. The central entropy and cooling time of the X-ray gas are unusually low and the nucleus hosts a warm Halpha+[NII] nebula and a cold molecular CO disk. Because most of the energy of the jets is deposited far from the nucleus, the atmosphere of the galaxy continues to cool, apparently feeding the central supermassive black hole and powering the jet activity.
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The nearby elliptical galaxy IC4296 has produced a large (510 kpc) low-luminosity radio source with typical FR I core/jet/lobe morphology. The unprecedented combination of brightness sensitivity, dynamic range, and angular resolution of a new 1.28 GHz MeerKAT continuum image reveals striking new morphological features which we call threads, ribbons, and rings. The threads are faint narrow emission features originating where helical Kelvin-Helmholtz instabilities disrupt the main radio jets. The ribbons are smooth regions between the jets and the lobes, and they appear to be relics of jets powered by earlier activity that have since come into pressure equilibrium. Vortex rings in the outer portions of the lobes and their backflows indicate that the straight outer jets and ribbons are inclined by $i = 60 pm 5^circ$ from the line-of-sight, in agreement with photometric, geometric, and gas-dynamical estimates of inclination angles near the nucleus.
We present an analysis of deep Chandra X-ray observations of the galaxy cluster MS 0735.6+7421, which hosts the most energetic radio AGN known. Our analysis has revealed two cavities in its hot atmosphere with diameters of 200-240 kpc. The total cavity enthalpy, mean age, and mean jet power are $9times 10^{61}$ erg, $1.6times 10^{8}$ yr, and $1.7times 10^{46}$ erg/s, respectively. The cavities are surrounded by nearly continuous temperature and surface brightness discontinuities associated with an elliptical shock front of Mach number 1.26 (1.17-1.30) and age of $1.1times 10^{8}$ yr. The shock has injected at least $4times 10^{61}$ erg into the hot atmosphere at a rate of $1.1times 10^{46}$ erg/s. A second pair of cavities and possibly a second shock front are located along the radio jets, indicating that the AGN power has declined by a factor of 30 over the past 100 Myr. The multiphase atmosphere surrounding the central galaxy is cooling at a rate of 36 Msun/yr, but does not fuel star formation at an appreciable rate. In addition to heating, entrainment in the radio jet may be depleting the nucleus of fuel and preventing gas from condensing out of the intracluster medium. Finally, we examine the mean time intervals between AGN outbursts in systems with multiple generations of X-ray cavities. We find that, like MS0735, their AGN rejuvenate on a timescale that is approximately 1/3 of their mean central cooling timescales, indicating that jet heating is outpacing cooling in these systems.
Several galaxy clusters are known to present multiple and misaligned pairs of cavities seen in X-rays, as well as twisted kiloparsec-scale jets at radio wavelengths. It suggests that the AGN precessing jets play a role in the formation of the misaligned bubbles. Also, X-ray spectra reveal that typically these systems are also able to supress cooling flows, predicted theoretically. The absence of cooling flows in galaxy clusters has been a mistery for many years since numerical simulations and analytical studies suggest that AGN jets are highly energetic, but are unable to redistribute it at all directions. We performed 3D hydrodynamical simulations of the interaction between a precessing AGN jet and the warm intracluster medium plasma, which dynamics is coupled to a NFW dark matter gravitational potential. Radiative cooling has been taken into account and the cooling flow problem was studied. We found that precession is responsible for multiple pairs of bubbles, as observed. The misaligned bubbles rise up to scales of tens of kiloparsecs, where the thermal energy released by the jets are redistributed. After $sim 150$ Myrs, the temperature of the gas within the cavities is kept of order of $sim 10^7$ K, while the denser plasma of the intracluster medium at the central regions reaches $T sim 10^5$ K. The existence of multiple bubbles, at diferent directions, result in an integrated temperature along the line of sight much larger than the simulations of non-precessing jets. This result is in agreement with the observations. The simulations reveal that the cooling flows cessed $sim 50 - 70$ Myr after the AGN jets are started.
Synchrotron self-absorption in active galactic nuclei (AGN) jets manifests itself as a time delay between flares observed at high and low radio frequencies. It is also responsible for the observing frequency dependent change in size and position of the apparent base of the jet, aka the core shift effect, detected with very long baseline interferometry (VLBI). We measure the time delays and the core shifts in 11 radio-loud AGN to estimate the speed of their jets without relying on multi-epoch VLBI kinematics analysis. The 15$-$8 GHz total flux density time lags are obtained using Gaussian process regression, the core shift values are measured using VLBI observations and adopted from the literature. A strong correlation is found between the apparent core shift and the observed time delay. Our estimate of the jet speed is higher than the apparent speed of the fastest VLBI components by the median coefficient of 1.4. The coefficient ranges for individual sources from 0.5 to 20. We derive Doppler factors, Lorentz factors and viewing angles of the jets, as well as the corresponding de-projected distance from the jet base to the core. The results support evidence for acceleration of the jets with bulk motion Lorentz factor $Gammapropto R^{0.52pm0.03}$ on de-projected scales $R$ of 0.5$-$500 parsecs.
We aim to determine the properties of the central region of NGC 1052 using X-ray and radio data. NGC 1052 (z=0.005) has been investigated for decades in different energy bands and shows radio lobes and a low luminosity active galactic nucleus (LLAGN). We use X-ray images from Chandra and radio images from Very Large Array (VLA) to explore the morphology of the central area. We also study the spectra of the nucleus and the surrounding region using observations from Chandra and XMM-Newton. We find diffuse soft X-ray radiation and hotspots along the radio lobes. The spectrum of the circum-nuclear region is well described by a thermal plasma (T~0.6 keV) and a power law with photon index Gamma~2.3. The nucleus shows a hard power law (Gamma~1.4) modified by complex absorption. A narrow iron K-alpha line is also clearly detected in all observations, but there is no evidence for relativistic reflection. The extended emission is consistent with originating from extended jets and from jet-triggered shocks in the surrounding medium. The hard power-law emission from the nucleus and the lack of relativistic reflection supports the scenario of inefficient accretion in an Advection Dominated Accretion Flow (ADAF).
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