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Register a new userDiscovery of a pseudobulge galaxy launching powerful relativistic jets
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Supermassive black holes launching plasma jets at close to speed of light, producing gamma-rays, have ubiquitously been found to be hosted by massive elliptical galaxies. Since elliptical galaxies are generally believed to be built through galaxy mergers, active galactic nuclei (AGN) launching relativistic jets are associated to the latest stages of galaxy evolution. We have discovered a pseudo-bulge morphology in the host galaxy of the gamma-ray AGN PKS 2004-447. This is the first gamma-ray emitter radio loud AGN found to be launched from a system where both black hole and host galaxy have been actively growing via secular processes. This is evidence for an alternative black hole-galaxy co-evolutionary path to develop powerful relativistic jets that is not merger-driven.
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Velocities close to the speed of light are a robust observational property of the jets observed in microquasars and AGNs, and are expected to be behind much of the phenomenology of GRBs. Yet, the mechanism boosting relativistic jets to such large Lorentz factors is still essentially unknown. Building on recent general-relativistic, multidimensional simulations of progenitors of short GRBs, we discuss a new effect in relativistic hydrodynamics which can act as an efficient booster in jets. This effect is purely hydrodynamical and occurs when large velocities tangential to a discontinuity are present in the flow, yielding Lorentz factors $Gamma sim 10^2-10^3$ or larger in flows with moderate initial Lorentz factors. Although without a Newtonian counterpart, this effect can be explained easily through the most elementary hydrodynamical flow: i.e., a relativistic Riemann problem.
We present deep Near-infrared (NIR) images of a sample of 19 intermediate-redshift ($0.3<z<1.0$) radio-loud active galactic nuclei (AGN) with powerful relativistic jets ($L_{1.4GHz} >10^{27}$ WHz$^{-1}$), previously classified as flat-spectrum radio quasars. We also compile host galaxy and nuclear magnitudes for blazars from literature. The combined sample (this work and compilation) contains 100 radio-loud AGN with host galaxy detections and a broad range of radio luminosities $L_{1.4GHz} sim 10^{23.7} - 10^{28.3}$~WHz$^{-1}$, allowing us to divide our sample into high-luminosity blazars (HLBs) and low-luminosity blazars (LLBs). The host galaxies of our sample are bright and seem to follow the $mu_{e}$-$R_{eff}$ relation for ellipticals and bulges. The two populations of blazars show different behaviours in the mnuc - mbulge plane, where a statistically significant correlation is observed for HLBs. Although it may be affected by selection effects, this correlation suggests a close coupling between the accretion mode of the central supermassive black hole and its host galaxy, that could be interpreted in terms of AGN feedback. Our findings are consistent with semi--analytical models where low--luminosity AGN emit the bulk of their energy in the form of radio jets, producing a strong feedback mechanism, and high--luminosity AGN are affected by galaxy mergers and interactions, which provide a common supply of cold gas to feed both nuclear activity and star formation episodes.
We present a model for launching relativistic jets in active galactic nuclei (AGN) from an accreting Kerr black hole (BH) as an effect of the rotation of the space-time, where the gravitational energy of the accretion disc inside the ergosphere, which can be increased by the BH rotational energy transferred to the disc via closed magnetic field lines that connect the BH to the disc (BH-disc magnetic connection), is converted into jet energy. The main role of the BH-disc magnetic connection is to provide the source of energy for the jets when the mass accretion rate is very low. We assume that the jets are launched from the disc inside the BH ergosphere, where the rotational effects of the space-time become much stronger, being further accelerated by magnetic processes. The rotation of the space-time channels a fraction of the disc energy (i.e., the gravitational energy of the disc plus the rotational energy of the BH which is deposited into the disc by magnetic connection) into a population of particles that escape from the disc surfaces, carrying away mass, energy and angular momentum in the form of jets, allowing the remaining disc gas to accrete. In the limit of the spin-down power regime, the model proposed here can be regarded as a variant of the Blandford-Znajek mechanism, where the BH rotational energy is transferred to the disc inside the ergosphere and then used to drive the jets. We use general-relativistic conservation laws to calculate the mass flow rate into the jets, the launching power of the jets and the angular momentum transported by the jets for BHs with a spin parameter $a_* geqslant 0.95$. We found that a stationary state of the BH ($a_* = $ const) can be reached if the mass accretion rate is larger than $dot{m} sim 0.001$. In addition, the maximum AGN lifetime can be much longer than $sim 10^{7}$ yr when using the BH spin-down power.
We report the results of the Australia Telescope Compact Array (ATCA) 15 mm observation of the Phoenix galaxy cluster possessing an extreme star-burst brightest cluster galaxy (BCG) at the cluster center. We spatially resolved radio emission around the BCG, and found diffuse bipolar and bar-shape structures extending from the active galactic nucleus (AGN) of the BCG. They are likely radio jets/lobes, whose sizes are ~10-20 kpc and locations are aligned with X-ray cavities. If we assume that the radio jets/lobes expand with the sound velocity, their ages are estimated to be ~10 Myr. We also found compact radio emissions near the center and suggest that they are another young bipolar jets with ~1 Myr of age. Moreover, we found extended radio emission surrounding the AGN and discussed the possibility that the component is a product of the cooling flow, by considering synchrotron radiation partially absorbed by molecular clumps, free-free emission from the warm ionized gas, and the spinning dust emission from dusty circum-galactic medium.
We present ~103 ks of Chandra observations of the galaxy cluster SPT-CLJ0528-5300 (SPT0528, z=0.768). This cluster harbors the most radio-loud (L_1.4GHz = 1.01 x 10^33 erg/s/Hz) central AGN of any cluster in the South Pole Telescope (SPT) SZ survey with available X-ray data. We find evidence of AGN-inflated cavities in the X-ray emission, which are consistent with the orientation of the jet direction revealed by ATCA radio data. The combined probability that two such depressions -- each at ~1.4-1.8sigma significance, oriented ~180 degrees apart and aligned with the jet axis -- would occur by chance is 0.1%. At >10^61 erg, the outburst in SPT0528 is among the most energetic known in the universe, and certainly the most powerful known at z>0.25. This work demonstrates that such powerful outbursts can be detected even in shallow X-ray exposures out to relatively high redshifts (z~0.8), providing an avenue for studying the evolution of extreme AGN feedback. The ratio of the cavity power (P_cav = 9.4+/-5.8 x 10^45 erg/s) to the cooling luminosity (L_cool = 1.5+/-0.5 x 10^44 erg/s) for SPT0528 is among the highest measured to date. If, in the future, additional systems are discovered at similar redshifts with equally high P_cav/L_cool ratios, it would imply that the feedback/cooling cycle was not as gentle at high redshifts as in the low-redshift universe.
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