arXiv subjects

Assaf Sternberg

Publications and source records attributed to Assaf Sternberg.

23 records · Page 2Linked to original sources

arXiv2009

Explaining the Energetic AGN Outburst of MS0735+7421 with Massive Slow Jets

By conducting axisymmetrical hydrodynamical numerical simulations (2.5 dimensional code) we show that slow, massive, wide jets can reproduce the morphology of the huge X-ray deficient bubble pair in the cluster of galaxies MS0735+7421. The total energy of the jets, composed of the energy in the bubble pair and in the shock wave, is constraint by observations conducted by McNamara et al. (2009) to be ~10^{62}erg. We show that two opposite jets that are active for ~100Myr, each with a launching half opening angle of ~70 degrees, an initial velocity of ~0.1c, and a total mass loss rate of the two jets of ~100 Mo/year, can account for the observed morphology. Rapidly precessing narrow jets can be used instead of wide jets. In our model the cluster suffered from a cooling catastrophe ~100Myr ago. Most of the mass that cooled, ~10^{10} Mo, was expelled back to the intracluster medium (ICM) by the AGN activity and is inside the bubbles now, ~10% formed stars, and ~10% of the cold gas was accreted by the central black hole and was the source of the outburst energy. This type of activity is similar to that expected to occur in galaxy formation.

astro-ph.CO↗

arXiv2008

Sound Waves Excitation by Jet-Inflated Bubbles in Clusters of Galaxies

We show that repeated sound waves in the intracluster medium (ICM) can be excited by a single inflation episode of an opposite bubble pair. To reproduce this behavior in numerical simulations the bubbles should be inflated by jets, rather than being injected artificially. The multiple sound waves are excited by the motion of the bubble-ICM boundary that is caused by vortices inside the inflated bubbles and the backflow (`cocoon') of the ICM around the bubble. These sound waves form a structure that can account for the ripples observed in the Perseus cooling flow cluster. We inflate the bubbles using slow massive jets, with either a wide opening angle or that are precessing. The jets are slow in the sense that they are highly sub-relativistic, $v_j \sim 0.01c-0.1c$, and they are massive in the sense that the pair of bubbles carry back to the ICM a large fraction of the cooling mass, i.e., $\sim 1-50 M_\odot \yr^{-1}$. We use a two-dimensional axisymmetric (referred to as 2.5D) hydrodynamical numerical code (VH-1).

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arXiv2008

Rising Jet-Inflated Bubbles in Clusters of Galaxies

We conduct two-dimensional axisymmetric (referred to as 2.5D) hydrodynamical numerical simulations of bubble evolution in clusters of galaxies. We inflate bubbles using slow, massive jets with a wide opening angle, and follow their evolution as they rise through the intra-cluster medium (ICM). We find that these jet-inflated bubbles are quite stable, and can reach large distances in the cluster while still maintaining their basic structure. The stability of the jet-inflated bubble comes mainly from the dense shell that forms around it during it's inflation stage, and from the outward momentum of the bubble and the shell. On the contrary, bubbles that are inserted by hand onto the grid and not inflated by a jet, i.e., an artificial bubble, lack these stabilizing factors, therefore, they are rapidly destroyed. The stability of the jet-inflated bubble removes the demand for stabilizing magnetic fields in the bubble.

astro-ph↗

arXiv2008

Inflating Fat Bubbles in Clusters of Galaxies by Precessing Massive Slow Jets

We conduct hydrodynamical numerical simulations and find that precessing massive slow jets can inflate fat bubbles, i.e., more or less spherical bubbles, that are attached to the center of clusters of galaxies. To inflate a fat bubble the jet should precess fast. The precessing angle $θ$ should be large, or change over a large range $ 0 \le θ\le θ_{\max} \sim 30-70 ^\circ$ (depending also on other parameters), where $θ=0$ is the symmetry axis. The constraints on the velocity and mass outflow rate are similar to those on wide jets to inflate fat bubbles. The velocity should be $v_j \sim 10^4 \kms$, and the mass loss rate of the two jets should be $ 2 \dot M_j \simeq 1-50 \dot M_\odot \yr^{-1} $. These results, and our results from a previous paper dealing with slow wide jets, support the claim that a large fraction of the feedback heating in cooling flow clusters and in the processes of galaxy formation is done by slow massive jets.

astro-ph↗

arXiv2006

Inflating Fat Bubbles in Clusters of Galaxies by Wide Jets

We conduct two-dimensional hydrodynamical simulations of jets expanding in the intra-cluster medium (ICM). We find that for a fat, i.e. more or less spherical, bubble attached to the center to be formed the jet should have high momentum flux and a large opening angle. Typically, the half opening angle should be >50 degrees, and the large momentum flux requires a jet speed of \~10,000 km/sec. The inflation process involves vortices and local instabilities which mix some ICM with the hot bubble. These results predict that most of the gas inside the bubble has a temperature of 3x10^8<T<3x10^9 K, and that large quantities of the cooling gas in cooling flow clusters are expelled back to the intra-cluster medium, and heated up. The magnetic fields and relativistic electrons that produce the synchrotron radio emission might be formed in the shock wave of the jet.

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