The Experts below are selected from a list of 57 Experts worldwide ranked by ideXlab platform
Volker Gaibler - One of the best experts on this subject based on the ideXlab platform.
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external pressure triggering of star formation in a disc galaxy a template for positive feedback
Monthly Notices of the Royal Astronomical Society, 2016Co-Authors: Rebekka Bieri, Yohan Dubois, Joseph Silk, G A Mamon, Volker GaiblerAbstract:Feedback from active galactic nuclei (AGN) has often been invoked both in simulations and in interpreting observations for regulating star formation and Quenching Cooling flows in massive galaxies. AGN activity can, however, also over-pressurise the dense star-forming regions of galaxies and thus enhance star formation, leading to a positive feedback effect. To understand this pressurisation better, we investigate the effect of an ambient external pressure on gas fragmentation and triggering of starburst activity by means of hydrodynamical simulations. We find that moderate levels of over-pressurisation of the galaxy boost the global star formation rate of the galaxy by an order of magnitude, turn stable discs unstable, and lead to significant fragmentation of the gas content of the galaxy, similar to what is observed in high redshift galaxies.
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jet induced star formation in gas rich galaxies
Monthly Notices of the Royal Astronomical Society, 2012Co-Authors: Sadegh Khochfar, Volker Gaibler, Martin Krause, Joseph SilkAbstract:Feedback from active galactic nuclei (AGN) has become a major component in simulations of galaxy evolution, in particular for massive galaxies. AGN jets have been shown to provide a large amount of energy and are capable of Quenching Cooling flows. Their impact on the host galaxy, however, is still not understood. Subgrid models of AGN activity in a galaxy evolution context so far have been mostly focused on the Quenching of star formation. To shed more light on the actual physics of the ‘radio mode' part of AGN activity, we have performed simulations of the interaction of a powerful AGN jet with the massive gaseous disc () of a high-redshift galaxy. We spatially resolve both the jet and the clumpy, multi-phase interstellar medium (ISM) and include an explicit star formation model in the simulation. Following the system over more than 107 yr, we find that the jet activity excavates the central region, but overall causes a significant change to the shape of the density probability distribution function and hence the star formation rate due to the formation of a blast wave with strong compression and Cooling in the ISM. This results in a ring- or disc-shaped population of young stars. At later times, the increase in star formation rate also occurs in the disc regions further out since the jet cocoon pressurizes the ISM. The total mass of the additionally formed stars may be up to for one duty cycle. We discuss the details of this jet-induced star formation (positive feedback) and its potential consequences for galaxy evolution and observable signatures.
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jet induced star formation in gas rich galaxies
arXiv: Cosmology and Nongalactic Astrophysics, 2011Co-Authors: Sadegh Khochfar, Volker Gaibler, Martin Krause, Joseph SilkAbstract:Feedback from active galactic nuclei (AGN) has become a major component in simulations of galaxy evolution, in particular for massive galaxies. AGN jets have been shown to provide a large amount of energy and are capable of Quenching Cooling flows. Their impact on the host galaxy, however, is still not understood. Subgrid models of AGN activity in a galaxy evolution context so far have been mostly focused on the Quenching of star formation. To shed more light on the actual physics of the "radio mode" part of AGN activity, we have performed simulations of the interaction of a powerful AGN jet with the massive gaseous disc (10^11 solar masses) of a high-redshift galaxy. We spatially resolve both the jet and the clumpy, multi-phase interstellar medium (ISM) and include an explicit star formation model in the simulation. Following the system over more than 10^7 years, we find that the jet activity excavates the central region, but overall causes a significant change to the shape of the density probability distribution function and hence the star formation rate due to the formation of a blast wave with strong compression and Cooling in the ISM. This results in a ring- or disc-shaped population of young stars. At later times, the increase in star formation rate also occurs in the disc regions further out since the jet cocoon pressurizes the ISM. The total mass of the additionally formed stars may be up to 10^10 solar masses for one duty cycle. We discuss the details of this jet-induced star formation (positive feedback) and its potential consequences for galaxy evolution and observable signatures.
Joseph Silk - One of the best experts on this subject based on the ideXlab platform.
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external pressure triggering of star formation in a disc galaxy a template for positive feedback
Monthly Notices of the Royal Astronomical Society, 2016Co-Authors: Rebekka Bieri, Yohan Dubois, Joseph Silk, G A Mamon, Volker GaiblerAbstract:Feedback from active galactic nuclei (AGN) has often been invoked both in simulations and in interpreting observations for regulating star formation and Quenching Cooling flows in massive galaxies. AGN activity can, however, also over-pressurise the dense star-forming regions of galaxies and thus enhance star formation, leading to a positive feedback effect. To understand this pressurisation better, we investigate the effect of an ambient external pressure on gas fragmentation and triggering of starburst activity by means of hydrodynamical simulations. We find that moderate levels of over-pressurisation of the galaxy boost the global star formation rate of the galaxy by an order of magnitude, turn stable discs unstable, and lead to significant fragmentation of the gas content of the galaxy, similar to what is observed in high redshift galaxies.
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jet induced star formation in gas rich galaxies
Monthly Notices of the Royal Astronomical Society, 2012Co-Authors: Sadegh Khochfar, Volker Gaibler, Martin Krause, Joseph SilkAbstract:Feedback from active galactic nuclei (AGN) has become a major component in simulations of galaxy evolution, in particular for massive galaxies. AGN jets have been shown to provide a large amount of energy and are capable of Quenching Cooling flows. Their impact on the host galaxy, however, is still not understood. Subgrid models of AGN activity in a galaxy evolution context so far have been mostly focused on the Quenching of star formation. To shed more light on the actual physics of the ‘radio mode' part of AGN activity, we have performed simulations of the interaction of a powerful AGN jet with the massive gaseous disc () of a high-redshift galaxy. We spatially resolve both the jet and the clumpy, multi-phase interstellar medium (ISM) and include an explicit star formation model in the simulation. Following the system over more than 107 yr, we find that the jet activity excavates the central region, but overall causes a significant change to the shape of the density probability distribution function and hence the star formation rate due to the formation of a blast wave with strong compression and Cooling in the ISM. This results in a ring- or disc-shaped population of young stars. At later times, the increase in star formation rate also occurs in the disc regions further out since the jet cocoon pressurizes the ISM. The total mass of the additionally formed stars may be up to for one duty cycle. We discuss the details of this jet-induced star formation (positive feedback) and its potential consequences for galaxy evolution and observable signatures.
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jet induced star formation in gas rich galaxies
arXiv: Cosmology and Nongalactic Astrophysics, 2011Co-Authors: Sadegh Khochfar, Volker Gaibler, Martin Krause, Joseph SilkAbstract:Feedback from active galactic nuclei (AGN) has become a major component in simulations of galaxy evolution, in particular for massive galaxies. AGN jets have been shown to provide a large amount of energy and are capable of Quenching Cooling flows. Their impact on the host galaxy, however, is still not understood. Subgrid models of AGN activity in a galaxy evolution context so far have been mostly focused on the Quenching of star formation. To shed more light on the actual physics of the "radio mode" part of AGN activity, we have performed simulations of the interaction of a powerful AGN jet with the massive gaseous disc (10^11 solar masses) of a high-redshift galaxy. We spatially resolve both the jet and the clumpy, multi-phase interstellar medium (ISM) and include an explicit star formation model in the simulation. Following the system over more than 10^7 years, we find that the jet activity excavates the central region, but overall causes a significant change to the shape of the density probability distribution function and hence the star formation rate due to the formation of a blast wave with strong compression and Cooling in the ISM. This results in a ring- or disc-shaped population of young stars. At later times, the increase in star formation rate also occurs in the disc regions further out since the jet cocoon pressurizes the ISM. The total mass of the additionally formed stars may be up to 10^10 solar masses for one duty cycle. We discuss the details of this jet-induced star formation (positive feedback) and its potential consequences for galaxy evolution and observable signatures.
Martin Krause - One of the best experts on this subject based on the ideXlab platform.
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jet induced star formation in gas rich galaxies
Monthly Notices of the Royal Astronomical Society, 2012Co-Authors: Sadegh Khochfar, Volker Gaibler, Martin Krause, Joseph SilkAbstract:Feedback from active galactic nuclei (AGN) has become a major component in simulations of galaxy evolution, in particular for massive galaxies. AGN jets have been shown to provide a large amount of energy and are capable of Quenching Cooling flows. Their impact on the host galaxy, however, is still not understood. Subgrid models of AGN activity in a galaxy evolution context so far have been mostly focused on the Quenching of star formation. To shed more light on the actual physics of the ‘radio mode' part of AGN activity, we have performed simulations of the interaction of a powerful AGN jet with the massive gaseous disc () of a high-redshift galaxy. We spatially resolve both the jet and the clumpy, multi-phase interstellar medium (ISM) and include an explicit star formation model in the simulation. Following the system over more than 107 yr, we find that the jet activity excavates the central region, but overall causes a significant change to the shape of the density probability distribution function and hence the star formation rate due to the formation of a blast wave with strong compression and Cooling in the ISM. This results in a ring- or disc-shaped population of young stars. At later times, the increase in star formation rate also occurs in the disc regions further out since the jet cocoon pressurizes the ISM. The total mass of the additionally formed stars may be up to for one duty cycle. We discuss the details of this jet-induced star formation (positive feedback) and its potential consequences for galaxy evolution and observable signatures.
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jet induced star formation in gas rich galaxies
arXiv: Cosmology and Nongalactic Astrophysics, 2011Co-Authors: Sadegh Khochfar, Volker Gaibler, Martin Krause, Joseph SilkAbstract:Feedback from active galactic nuclei (AGN) has become a major component in simulations of galaxy evolution, in particular for massive galaxies. AGN jets have been shown to provide a large amount of energy and are capable of Quenching Cooling flows. Their impact on the host galaxy, however, is still not understood. Subgrid models of AGN activity in a galaxy evolution context so far have been mostly focused on the Quenching of star formation. To shed more light on the actual physics of the "radio mode" part of AGN activity, we have performed simulations of the interaction of a powerful AGN jet with the massive gaseous disc (10^11 solar masses) of a high-redshift galaxy. We spatially resolve both the jet and the clumpy, multi-phase interstellar medium (ISM) and include an explicit star formation model in the simulation. Following the system over more than 10^7 years, we find that the jet activity excavates the central region, but overall causes a significant change to the shape of the density probability distribution function and hence the star formation rate due to the formation of a blast wave with strong compression and Cooling in the ISM. This results in a ring- or disc-shaped population of young stars. At later times, the increase in star formation rate also occurs in the disc regions further out since the jet cocoon pressurizes the ISM. The total mass of the additionally formed stars may be up to 10^10 solar masses for one duty cycle. We discuss the details of this jet-induced star formation (positive feedback) and its potential consequences for galaxy evolution and observable signatures.
Sadegh Khochfar - One of the best experts on this subject based on the ideXlab platform.
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jet induced star formation in gas rich galaxies
Monthly Notices of the Royal Astronomical Society, 2012Co-Authors: Sadegh Khochfar, Volker Gaibler, Martin Krause, Joseph SilkAbstract:Feedback from active galactic nuclei (AGN) has become a major component in simulations of galaxy evolution, in particular for massive galaxies. AGN jets have been shown to provide a large amount of energy and are capable of Quenching Cooling flows. Their impact on the host galaxy, however, is still not understood. Subgrid models of AGN activity in a galaxy evolution context so far have been mostly focused on the Quenching of star formation. To shed more light on the actual physics of the ‘radio mode' part of AGN activity, we have performed simulations of the interaction of a powerful AGN jet with the massive gaseous disc () of a high-redshift galaxy. We spatially resolve both the jet and the clumpy, multi-phase interstellar medium (ISM) and include an explicit star formation model in the simulation. Following the system over more than 107 yr, we find that the jet activity excavates the central region, but overall causes a significant change to the shape of the density probability distribution function and hence the star formation rate due to the formation of a blast wave with strong compression and Cooling in the ISM. This results in a ring- or disc-shaped population of young stars. At later times, the increase in star formation rate also occurs in the disc regions further out since the jet cocoon pressurizes the ISM. The total mass of the additionally formed stars may be up to for one duty cycle. We discuss the details of this jet-induced star formation (positive feedback) and its potential consequences for galaxy evolution and observable signatures.
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jet induced star formation in gas rich galaxies
arXiv: Cosmology and Nongalactic Astrophysics, 2011Co-Authors: Sadegh Khochfar, Volker Gaibler, Martin Krause, Joseph SilkAbstract:Feedback from active galactic nuclei (AGN) has become a major component in simulations of galaxy evolution, in particular for massive galaxies. AGN jets have been shown to provide a large amount of energy and are capable of Quenching Cooling flows. Their impact on the host galaxy, however, is still not understood. Subgrid models of AGN activity in a galaxy evolution context so far have been mostly focused on the Quenching of star formation. To shed more light on the actual physics of the "radio mode" part of AGN activity, we have performed simulations of the interaction of a powerful AGN jet with the massive gaseous disc (10^11 solar masses) of a high-redshift galaxy. We spatially resolve both the jet and the clumpy, multi-phase interstellar medium (ISM) and include an explicit star formation model in the simulation. Following the system over more than 10^7 years, we find that the jet activity excavates the central region, but overall causes a significant change to the shape of the density probability distribution function and hence the star formation rate due to the formation of a blast wave with strong compression and Cooling in the ISM. This results in a ring- or disc-shaped population of young stars. At later times, the increase in star formation rate also occurs in the disc regions further out since the jet cocoon pressurizes the ISM. The total mass of the additionally formed stars may be up to 10^10 solar masses for one duty cycle. We discuss the details of this jet-induced star formation (positive feedback) and its potential consequences for galaxy evolution and observable signatures.
Shiquan Huang - One of the best experts on this subject based on the ideXlab platform.
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investigation of quench sensitivity of high strength 2219 aluminum alloy by ttp and ttt diagrams
Journal of Alloys and Compounds, 2017Co-Authors: Huimin Wang, Youping Yi, Shiquan HuangAbstract:Abstract The time-temperature-transformation (TTT) curve and time-temperature-property (TTP) curve of 2219 aluminum alloy were determined by an interrupted quench technique. The results show that the quench sensitivity temperature range of 2219 aluminum alloy is from 300 °C to 480 °C and the nose temperature is about 440 °C. The transmission electron microscopy (TEM) observation indicated that, during isothermal holding at 440 °C, a number of coarse equilibrium rod-shaped θ particles precipitated and grew fast, resulting in loss of solutes and decrease of subsequent ageing hardening effect. In the quench sensitive range, primary precipitating reasons of rod-shaped θ particles are high diffusion rate of solute atoms and large phase transformation driving force. Therefore, for large 2219 aluminum alloy forgings, the Quenching Cooling rate should be increased as high as possible in the Quenching sensitive range (300–480 °C) to obtain high mechanical properties, and decreased properly from the solution temperature to 480°Cin order to reduce the residual stress.
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influence of Quenching Cooling rate on residual stress and tensile properties of 2a14 aluminum alloy forgings
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2016Co-Authors: Yuxun Zhang, Youping Yi, Shiquan Huang, Fei DongAbstract:Abstract To balance the Quenching residual stress and the mechanical properties of aluminum alloys, the influence of Cooling rate on the residual stress and tensile properties was investigated by numerical simulation and Quenching experiments. During the Quenching experiments, 2A14 aluminum alloy samples were treated with different water temperatures (20 °C, 70 °C, 100 °C) and a step Quenching process. X-ray diffraction (XRD) was used to measure the residual stress. Prior to them, the Quenching sensitivity was studied. For this purpose, the time-temperature-properties (TTP) curves were measured and the alloy microstructure was observed using transmission electron microscopy (TEM). The results indicated that the mechanical properties of 2A14 aluminum alloys were mainly determined by the Cooling rate within the Quenching sensitive temperature range from 300 to 400 °C. Lower Cooling rates reduced the tensile strength and yield strength due to a decrease amount of fine precipitates, and reduced the residual stress with the reduction of plastic strain and the degree of inhomogeneous plastic deformation. In addition, the residual stress changed faster than the tensile properties with decreasing Cooling rate. Therefore, warm water (70 °C) was used to balance the residual stress and tensile properties of 140-mm-thick 2A14 aluminum alloy forgings, since it can achieve low Cooling rates. Furthermore, by combining this characteristic and the material Quenching sensitivity, step Quenching produced similar tensile properties and lower residual stress, compared with the sample quenched in warm water (70 °C), by increasing Cooling rate within Quenching sensitivity range and reducing it in other ranges.
