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Search Results: 1 - 10 of 11124 matches for " Joseph Silk "
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Reionization and the Cosmic Microwave Background
Joseph Silk
Physics , 1994, DOI: 10.1007/3-540-57755-6_44
Abstract: If the COBE detection of CMB fluctuations is used to normalize the power spectrum of primordial density fluctuations in a cold dark matter--dominated universe, early reionization is likely to result in a substantial diminution of primordial temperature fluctuations on degree scales. I argue that the reionization may be non--Gaussian because of feedback effects. Secondary fluctuations on arc--minute scales provide an important probe of the efficiency of rescattering.
Feedback, Disk Self-regulation and Galaxy Formation
Joseph Silk
Physics , 1996, DOI: 10.1086/304073
Abstract: Self-regulation of star formation in disks is controlled by two dimensionless parameters: the Toomre parameter for gravitational instability and the porosity of the interstellar medium to supernova remnant-heated gas. An interplay between these leads to expressions for the gas fraction and star formation efficiency in disks, and to a possible explanation of the Tully-Fisher relation. I further develop feedback arguments that arise from the impact of massive star formation and death on protogalaxies in order to account for the characteristic luminosity of a galaxy and for early winds from forming spheroids.
Baryonic Dark Matter
Joseph Silk
Physics , 1994,
Abstract: In the first two of these lectures, I present the evidence for baryonic dark matter and describe possible forms that it may take. The final lecture discusses formation of baryonic dark matter, and sets the cosmological context.
A New Prescription for Protogalactic Feedback and Outflows: Where Have All the Baryons Gone?
Joseph Silk
Physics , 2002, DOI: 10.1046/j.1365-8711.2003.06674.x
Abstract: Up to half of the baryons inferred to once have been in our galaxy have not yet been detected. Ejection would seem to provide the most attractive explanation. Previous numerical studies may have underestimated the role of winds. I propose a solution involving a multiphase model of the protogalactic interstellar medium and the possibility of driving a superwind. Simulations do not yet incorporate the small-scale physics that, I argue, drives mass-loading of the cold phase gas and enhances the porosity, thereby ensuring that winds are driven at a rate that depends primarily on the star formation rate. The occurrence of hypernovae, as claimed for metal-poor and possibly also for starburst environments, and the possibility of a top-heavy primordial stellar initial mass function are likely to have played important roles in allowing winds to prevail in massive gas-rich starbursting protogalaxies as well as in dwarfs. I discuss why such outflows are generically of order the rate of star formation and may have been a common occurrence in the past.
The Cosmic Microwave Background
Joseph Silk
Physics , 2002, DOI: 10.1007/s00023-003-0922-1
Abstract: I review the discovery of the temperature fluctuations in the cosmic microwave background radiation. The underlying theory and the implications for cosmology are reviewed, and I describe the prospects for future progress.
Feedback in Galaxy Formation
Joseph Silk
Physics , 2011, DOI: 10.1017/S1743921311022939
Abstract: I review the outstanding problems in galaxy formation theory, and the role of feedback in resolving them. I address the efficiency of star formation, the galactic star formation rate, and the roles of supernovae and supermassive black holes.
Unleashing Positive Feedback: Linking the Rates of Star Formation, Supermassive Black Hole Accretion and Outflows in Distant Galaxies
Joseph Silk
Physics , 2013, DOI: 10.1088/0004-637X/772/2/112
Abstract: Pressure-regulated star formation is a simple variant on the usual supernova-regulated star formation efficiency that controls the global star formation rate as a function of cold gas content in star-forming galaxies, and accounts for the Schmidt-Kennicutt law in both nearby and distant galaxies. Inclusion of AGN-induced pressure, by jets and/or winds that flow back onto a gas-rich disk, can lead under some circumstances to significantly enhanced star formation rates, especially at high redshift and most likely followed by the more widely accepted phase of star formation quenching. Simple expressions are derived that relate supermassive black hole growth, star formation and outflow rates. The ratios of black hole to spheroid mass and of both black hole accretion and outflow rates to star formation rate are predicted as a function of time. I suggest various tests of the AGN-triggered star formation hypothesis.
Aspects of Galaxy Formation
Joseph Silk
Physics , 2001,
Abstract: I describe some of the current challenges in galaxy formation theory with applications to formation of disks and of spheroids. Forthcoming deep surveys of galaxies with Keck and VLT will provide high quality spectra of $\sim 10^5$ galaxies that will probe stellar populations and star formation rates at redshift unity. This will help refine our phenomenological knowledge of galaxy evolution and enable robust predictions to be developed for future breakthroughs in understanding galaxy formation at high redshift that are anticipated with NGST and with the proposed new generation of 30 metre-class telescopes.
The Formation of Galaxy Disks
Joseph Silk
Physics , 2000, DOI: 10.1046/j.1365-8711.2001.04197.x
Abstract: Galaxy disk formation must incorporate the multiphase nature of the interstellar medium. The resulting two-phase structure is generated and maintained by gravitational instability and supernova energy input, which yield a source of turbulent viscosity that is able to effectively compete in the protodisk phase with early angular momentum loss of the baryonic component via dynamical friction in the dark halo. Provided that star formation occurs on the viscous drag time-scale, this mechanism provides a means of accounting for disk sizes and radial profiles. The star formation feedback is self-regulated by turbulent gas pressure-limited percolation of the supernova remnant-heated hot phase, but can run away in gas-rich protodisks to generate compact starbursts. A simple analytic model is derived for a Schmidt-like global star formation law in terms of the cold gas volume density.
The Dark Side of the Universe
Joseph Silk
Physics , 2001, DOI: 10.1142/S0217751X02013101
Abstract: Most of the matter in the universe is invisible. I review the status of dark matter and describe how both the theory of galaxy formation and novel types of experimental searches are revitalizing attempts to find non-baryonic dark matter.
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