49 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
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
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
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
Real-Time Detection and Rapid Multiwavelength Follow-up Observations of a Highly Subluminous Type II-P Supernova from the Palomar Transient Factory Survey
The Palomar Transient Factory (PTF) is an optical wide-field variability
survey carried out using a camera with a 7.8 square degree field of view
mounted on the 48-in Oschin Schmidt telescope at Palomar Observatory. One of
the key goals of this survey is to conduct high-cadence monitoring of the sky
in order to detect optical transient sources shortly after they occur. Here, we
describe the real-time capabilities of the PTF and our related rapid
multiwavelength follow-up programs, extending from the radio to the gamma-ray
bands. We present as a case study observations of the optical transient
PTF10vdl (SN 2010id), revealed to be a very young core-collapse (Type II-P)
supernova having a remarkably low luminosity. Our results demonstrate that the
PTF now provides for optical transients the real-time discovery and
rapid-response follow-up capabilities previously reserved only for high-energy
transients like gamma-ray bursts.Comment: ApJ, in press; all spectroscopic data available from the Weizmann
Institute of Science Experimental Astrophysics Spectroscopy System (WISEASS;
http://www.weizmann.ac.il/astrophysics/wiseass/