We find that the power of jets that inflate bubble pairs in cooling flow clusters of galaxies correlates with the size of the inner region where the entropy profile is flat, as well as with the gas mass in that region and the entropy floor (the entropy value at the center of the cluster). These correlations strengthen the cold feedback mechanism that is thought to operate in cooling flow clusters and during galaxy formation. In the cold feedback mechanism the central super-massive black hole (SMBH) is fed with cold clumps that originate in an extended region of the cooling flow volume, in particular from the inner region that has a flat entropy profile. Such a process ensures a tight feedback between radiative cooling and heating by the SMBH (the AGN). The derived expressions should be used instead of the Bondi accretion rate when studying AGN feedback. We find that the mass of molecular gas also correlates with the entropy profile parameters, despite that the jet power does not correlate with the molecular gas mass. This further suggests that the entropy profile is a fundamental parameter determining cooling and feedback in cooling flow clusters.
I suggest that the main process that amplifies magnetic fields in cooling flows in clusters and group of galaxies is a jet-driven dynamo (JEDD). The main processes that are behind the JEDD is the turbulence that is formed by the many vortices formed in the inflation processes of bubbles, and the large scale shear formed by the propagating jet. It is sufficient that a strong turbulence exits in the vicinity of the jets and bubbles, just where the shear is large. The typical amplification time of magnetic fields by the JEDD near the jets and bubbles is approximately hundred million years. The am…
Cool-Core Destruction in Merging Clusters with AGN Feedback and Radiative Cooling
National Taiwan University（台湾大学）；California Institute of Technology（加州理工学院）；National Tsing Hua University（清华大学）；National Center for Theoretical Sciences（国家理论科学中心）；Harvard-Smithsonian Center for Astrophysics（哈佛-史密松天体物理中心）；University of Modena and Reggio Emilia（摩德纳和雷焦艾米利亚大学）
Cosmic reionization put an end to the dark ages that came after the recombination era. Observations seem to favor the scenario where massive stars generating photons in low-mass galaxies were responsible for the bulk of reionization. Even though a possible contribution from accretion disks of active galactic nuclei (AGN) has been widely considered, they are currently thought to have had a minor role in reionization. Our aim is to study the possibility that AGN contributed to reionization not only through their accretion disks, but also through ionizing photons coming from the AGN jets interact…
The group velocity of light in material around the AGN jet is acquiescently one (c as a unit), but this is only a hypothesis. Here, we re-derive apparent superluminal and Doppler formulas for the general case (it is assumed that the group velocity of light in the uniform and isotropic medium around a jet (a beaming model) is not necessarily equal to one, e.g., Araudo et al. (2010) thought that there may be dense clouds around AGN jet base), and show that the group velocity of light close to one could seriously affect apparent superluminal phenomena and Doppler effect in the AGN jet (when the v…
We study how jets driven by active galactic nuclei influence the cooling flow in Perseus-like galaxy cluster cores with idealised, non-relativistic, hydrodynamical simulations performed with the Eulerian code ATHENA using high-resolution Godunov methods with low numerical diffusion. We use novel analysis methods to measure the cooling rate, the heating rate associated to multiple mechanisms, and the power associated with adiabatic compression/expansion. A significant reduction of the cooling rate and cooling flow within 20 kpc from the centre can be achieved with kinetic jets. However, at larg…
Detection of the copious amount of X-ray emission from the dilute hot plasma in galaxy clusters suggests that a substantial fraction of the central intracluster medium (ICM) is cooling radiatively on a time scale much faster than the Hubble time. Theoretical models predict the cooling rate as high as about few hundred to few thousand solar mass per year, which would be then made available for the formation of new stars in the core of these clusters. However, systematic studies of the cores of such clusters failed to detect the expected reservoirs of cooled gas. Thus, the gas in the cores of ga…
We have used the broadband backend available at the ATCA to study the fast interstellar scintillation of quasar PKS 1257-326, resolving the core shift as a function of frequency on scales less than 10 microarcseconds. In this short paper we discuss the jet direction implied from the microarcsecond-scale core shift in PKS 1257-326.
The jet production efficiency of radio galaxies can be quantified by comparison of their kinetic jet powers P_jet and Bondi accretion powers P_B. These two parameters are known to be related linearly, with the jet power resulting from the Bondi power by multiplication with an efficiency factor of order 1%. Using a recently published (Nemmen + Tchekhovskoy 2014) high-quality sample of 27 radio galaxies, I construct a P_B-P_jet diagram that includes information on optical AGN types as far as available. This diagram indicates that the jet production efficiency is a function of AGN type: Seyfert 2…
This paper presents the first measurement of the radio luminosity function of 'jet-mode' (radiatively-inefficient) radio-AGN out to z=1, in order to investigate the cosmic evolution of radio-AGN feedback. Eight radio source samples are combined to produce a catalogue of 211 radio-loud AGN with 0.5<z<1.0, which are spectroscopically classified into jet-mode and radiative-mode (radiatively-efficient) AGN classes. Comparing with large samples of local radio-AGN from the Sloan Digital Sky Survey, the cosmic evolution of the radio luminosity function of each radio-AGN class is independently derived…
We present a multi-wavelength analysis of the galaxy cluster SPT-CL J0607-4448 (SPT0607), which is one of the most distant clusters discovered by the South Pole Telescope (SPT) at $z=1.4010\pm0.0028$. The high-redshift cluster shows clear signs of being relaxed with well-regulated feedback from the active galactic nucleus (AGN) in the brightest cluster galaxy (BCG). Using Chandra X-ray data, we construct thermodynamic profiles and determine the properties of the intracluster medium. The cool core nature of the cluster is supported by a centrally-peaked density profile and low central entropy (…
