55 research outputs found
The Moderate Cooling Flow Model and Feedback in Galaxy Formation
For the recent four years we have been studying feedback heating in cooling
flow (CF) clusters by AGN activity that inflate bubbles by jets; this short
contribution to a meeting summarizes our main results. To achieve our results
we had to self-consistently inflate the bubbles with jets, rather than inject
them artificially. Our main results are as follows
(1) Feedback mechanisms that are based on Bondi accretion fail. Instead, the
accretion to the central super-massive black hole (SMBH) is in the form of cold
dense blobs that fall-in from an extended region. (2) Slow massive wide (SMW)
jets, or rapidly precessing jets, can inflate bubbles similar to those observed
in CF clusters. (3) Contrary to some claims in the literature, the inflated
bubbles are stable for a relatively long time, becoming unstable only at later
times. (4) A single bubble inflation episode excites multiple sound waves and
shocks. These can then heat the intracluster medium (ICM). (5) Mixing of the
bubble material to the ICM is efficient, and can serve as a main heating
channel. (6) The heating processes work in all directions, and can explain the
heating of the ICM in CF in clusters and in galaxies.Comment: To appear in proceedings of "The Monster's Fiery Breath", Eds.
Sebastian Heinz & Eric Wilcots (AIP conference series
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 should be
large, or change over a large range (depending also on other parameters), where 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.Comment: Accepted for publication in MNRA
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.Comment: Accepted by MNRA
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, ,
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).Comment: submitted to MNRA
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.Comment: Submitted to ApJ Letter
Controlled sumoylation of the mevalonate pathway enzyme HMGS-1 regulates metabolism during aging
Many metabolic pathways are critically regulated during development and aging but little is known about the molecular mechanisms underlying this regulation. One key metabolic cascade in eukaryotes is the mevalonate pathway. It catalyzes the synthesis of sterol and nonsterol isoprenoids, such as cholesterol and ubiquinone, as well as other metabolites. In humans, an age-dependent decrease in ubiquinone levels and changes in cholesterol homeostasis suggest that mevalonate pathway activity changes with age. However, our knowledge of the mechanistic basis of these changes remains rudimentary. We have identified a regulatory circuit controlling the sumoylation state of Caenorhabditis elegans HMG-CoA synthase (HMGS-1). This protein is the ortholog of human HMGCS1 enzyme, which mediates the first committed step of the mevalonate pathway. In vivo, HMGS-1 undergoes an age-dependent sumoylation that is balanced by the activity of ULP-4 small ubiquitin-like modifier protease. ULP-4 exhibits an age-regulated expression pattern and a dynamic cytoplasm-to-mitochondria translocation. Thus, spatiotemporal ULP-4 activity controls the HMGS-1 sumoylation state in a mechanism that orchestrates mevalonate pathway activity with the age of the organism. To expand the HMGS-1 regulatory network, we combined proteomic analyses with knockout studies and found that the HMGS-1 level is also governed by the ubiquitin–proteasome pathway. We propose that these conserved molecular circuits have evolved to govern the level of mevalonate pathway flux during aging, a flux whose dysregulation is associated with numerous age-dependent cardiovascular and cancer pathologies
Multi-epoch high-spectral-resolution observations of neutral sodium in 14 Type Ia supernovae
One of the main questions concerning Type Ia supernovae is the nature of the binary companion of the exploding white dwarf. A major discriminant between different suggested models is the presence and physical properties of circumstellar material at the time of explosion. If present, this material will be ionized by the ultraviolet radiation of the explosion and later recombine. This ionization-recombination should manifest itself as time-variable absorption features that can be detected via multi-epoch high-spectral-resolution observations. Previous studies have shown that the strongest effect is seen in the neutral sodium D lines. We report on observations of neutral sodium absorption features observed in multi-epoch high-resolution spectra of 14 Type Ia supernova events. This is the first multi-epoch high-resolution study to include multiple SNe. No variability in line strength that can be associated with circumstellar material is detected in the events presented in this paper. If we include previously published events, we find that ~18 per cent of the events in the extended sample exhibit time-variable sodium features associated with circumstellar material. We explore the implication of this study on our understanding of the progenitor systems of Type Ia supernovae via the current Type Ia supernova multi-epoch high-spectral-resolution sample
Slow-Speed Supernovae from the Palomar Transient Factory: Two Channels
Since the discovery of the unusual prototype SN 2002cx, the eponymous class
of low-velocity, hydrogen-poor supernovae has grown to include at most another
two dozen members identified from several heterogeneous surveys, in some cases
ambiguously. Here we present the results of a systematic study of 1077
hydrogen-poor supernovae discovered by the Palomar Transient Factory, leading
to nine new members of this peculiar class. Moreover we find there are two
distinct subclasses based on their spectroscopic, photometric, and host galaxy
properties: The "SN 2002cx-like" supernovae tend to be in later-type or more
irregular hosts, have more varied and generally dimmer luminosities, have
longer rise times, and lack a Ti II trough when compared to the "SN
2002es-like" supernovae. None of our objects show helium, and we counter a
previous claim of two such events. We also find that these transients comprise
5.6+17-3.7% (90% confidence) of all SNe Ia, lower compared to earlier
estimates. Combining our objects with the literature sample, we propose that
these subclasses have two distinct physical origins.Comment: 49 pages, 36 figures, submitted to Ap
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