M87 at 90 Centimeters: A Different Picture

view Abstract Citations (86) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radio studies of the ionized gas in the nucleus of M 82. Seaquist, E. R. ; Bell, M. B. ; Bignell, R. C. Abstract Continuum and recombination-line radio observations of M82, obtained at 4.87 and 1.48 GHz using the VLA during July 1981 and January and September 1982 are reported. The data are presented in tables, graphs, maps and analyzed in combination with published radio and IR observations. A seven-layer model of the nuclear region is proposed, and the vertical gradient seen in the spectral index is attributed to an age gradient for the radiating particles and the 2000-km/s transport of relativistic particles out of the plane. The ionized gas in the central synchrotron-emission region is found to have maximum density 30/cu cm and to almost entirely fill the nuclear volume, while the molecular gas remains in small isolated clouds in pressure equilibrium with the ionized gas. The nature of the second component of M82, a compact H II complex apparently identical with the VLBI source 41.9 + 58 and objects seen in CO and the forbidden O I line at 63 microns, is briefly considered. Publication: The Astrophysical Journal Pub Date: July 1985 DOI: 10.1086/163322 Bibcode: 1985ApJ...294..546S Keywords: Galactic Nuclei; Galactic Structure; Hydrogen Clouds; Interstellar Gas; Ionized Gases; Radio Galaxies; Radio Spectra; Astronomical Models; Continuous Spectra; Infrared Astronomy; Line Spectra; Relativistic Electron Beams; Stellar Evolution; Synchrotron Radiation; Astrophysics full text sources ADS | data products SIMBAD (1) NED (1)

I study non-radiative cooling of X-ray emitting gas via heat conduction along magnetic field lines inside magnetic flux loops in cooling flow clusters of galaxies. I find that such heat conduction can reduce the fraction of energy radiated in the X-ray band by a factor of 1.5-2. This non-radiative cooling joins two other proposed non-radiative cooling processes, which can be more efficient. These are mixing of cold and hot gas, and heat conduction initiated by magnetic fields reconnection between hot and cold gas. These processes when incorporated into the moderate cooling flow model lead to a general cooling flow model with the following ingredients. (1) Cooling flow does occur, but with a mass cooling rate about 10 times lower than in old versions of the cooling flow model. Namely, heating occurs such that the effective age of the cooling flow is much below the cluster age, but the heating can't prevent cooling altogether. (2) The cooling flow region is in a non-steady state evolution. (3) Non-radiative cooling of X-ray emitting gas can bring the model to a much better agreement with observations. (4) The general behavior of the cooling flow gas, and in particular the role played by magnetic fields, make the intracluster medium in cooling flow clusters similar in some aspects to the active solar corona.

A supersynthesis radio map of the 8085 MHz emission in M82 is presented. The radio structure is complex, and is dominated by a bright unresolved source which is unpolarized ( 5 K exist in the galaxy but outside the main radio source. An upper limit of 5 mJy can be set to any 8085 MHz radio emission from remnants, the brightest of which (source 41.9+58) is very recent (approximately-less-than150 years) and has brightness and size limits which are consistent with the $Sigma$-D relationship for known supernova remnants. The absence of a detectable linear polarization on all angular scales approximately-greater-than1'' suggests that the magnetic field in the M82 nucleus is highly tangled on all size scales down to approximately-less- than20 pc. (AIP)

view Abstract Citations (64) References (39) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Physical Conditions in the Nucleus of M82 Peimbert, Manuel ; Spinrad, Hyron Abstract Narrow-band photoelectric photometry of the nucleus and a bright region northeast of the center of M82 was carried out with the 120-inch telescope at Lick Observatory. The intensity of several emission lines in the nucleus, as well as of the continuum in both regions at different wavelengths, was obtained. From the Balmer and Paschen emission lines of hydrogen, an interstellar absorption of 4.23 mag at Hfl was derived for the nucleus. Collisions by thermal electrons are not responsible for the ionization in the nuclear region: this result and the observed Balmer decrement led to the adoption of radiation as the principal mechanism of ionization. The thermal contribution to the radio flux is smaller than 10 percent in the most favorable wavelengths. By extrapolating the radio spectrum to below the Lyman limit on the basis of a model of a single electron reservoir, synchrotron radiation fails by at least two orders of magnitude for the excitation of Ha in the nucleus; furthermore, the synchrotron contribution to the visible region of the spectrum is negligible. The N(He+)/N(H+) ratio is 0.065; however, a large fraction of the helium atoms is neutral, and the N(He)/N(H) ratio is about 0.13. The observed Balmer jump is smaller in the nucleus than in the region northeast of it. It is found that the spectral type of the galaxy becomes progressively later from the center outward. Publication: The Astrophysical Journal Pub Date: May 1970 DOI: 10.1086/150444 Bibcode: 1970ApJ...160..429P full text sources ADS | data products SIMBAD (7) NED (1)

A prediction of the galaxy cluster cooling flow model is that as gas cools from the ambient cluster temperature, emission lines are produced in gas at subsequently decreasing temperatures. Gas passing through 10^5.5 K emits in the lines of OVI 1032,1035, and here we report a FUSE study of these lines in three cooling flow clusters, Abell 426, Abell 1795, and AWM 7. No emission was detected from AWM 7, but OVI is detected from the centers of Abell 426 and Abell 1795, and possibly to the south of the center in Abell 1795, where X-ray and optical emission line filaments lie. In Abell 426, these line luminosities imply a cooling rate of 32+/-6 Msolar/yr within the central r = 6.2 kpc region, while for Abell 1795, the central cooling rate is 26+/-7 Msolar/yr (within r = 22 kpc), and about 42+/-9 Msolar/yr including the southern pointing. Including other studies, three of six clusters have OVI emission, and they also have star formation as well as emission lines from 1E4 K gas. These observations are generally consistent with the cooling flow model but at a rate closer to 30 Msolar/yr than originally suggested values of 100-1000 Msolar/yr.

We analyse the performance of 12 different implementations of Smoothed Particle Hydrodynamics (SPH) using seven tests designed to isolate key hydrodynamic elements of cosmological simulations which are known to cause the SPH algorithm problems. In order, we consider a shock tube, spherical adiabatic collapse, cooling flow model, drag, a cosmological simulation, rotating cloud-collapse and angular momentum transport. In the implementations special attention is given to the way in which force symmetry is enforced in the equations of motion. We study in detail how the hydrodynamics are affected by different implementations of the artificial viscosity including those with a shear-correction modification. We present an improved first-order smoothing-length update algorithm that is designed to remove instabilities that are present in simple forward prediction algorithms. Gravity is calculated using the adaptive particle–particle, particle–mesh algorithm. For all tests we find that the artificial viscosity is the single most important factor distinguishing the results from the various implementations. The shock tube and adiabatic collapse problems show that the artificial viscosity used in the hydra code prior to version 4.0 performs relatively poorly for simulations involving strong shocks when compared to a more standard artificial viscosity. The shear-correction term is shown to reduce the shock-capturing ability of the algorithm and to lead to a spurious increase in angular momentum in the rotating cloud-collapse problem. For the disc stability test, the shear-corrected and previous hydra artificial viscosities are shown to reduce outward angular momentum transport. The cosmological simulations produce comparatively similar results, with the fraction of gas in the hot and cold phases varying by less than 10 per cent amongst the versions. Similarly, the drag test shows little systematic variation amongst versions. The cooling flow tests show that implementations using the force symmetrization of Thomas & Couchman are more prone to accelerate the overcooling instability of SPH, although the problem is generic to SPH. The second most important factor in code performance is the way force symmetry is achieved in the equation of motion. Most results favour a kernel symmetrization approach. The exact method by which SPH pressure forces are included in the equation of motion appears to have comparatively little effect on the results. Combining the equation of motion presented by Thomas & Couchman with a modification of the Monaghan & Gingold artificial viscosity leads to an SPH scheme that is both fast and reliable.

We analyse the performance of 12 different implementations of Smoothed Particle Hydrodynamics (SPH) using seven tests designed to isolate key hydrodynamic elements of cosmological simulations which are known to cause the SPH algorithm problems. In order, we consider a shock tube, spherical adiabatic collapse, cooling flow model, drag, a cosmological simulation, rotating cloud-collapse and angular momentum transport. In the implementations special attention is given to the way in which force symmetry is enforced in the equations of motion. We study in detail how the hydrodynamics are affected by different implementations of the artificial viscosity including those with a shear-correction modification. We present an improved first-order smoothing-length update algorithm that is designed to remove instabilities that are present in simple forward prediction algorithms. Gravity is calculated using the adaptive particle–particle, particle–mesh algorithm. For all tests we find that the artificial viscosity is the single most important factor distinguishing the results from the various implementations. The shock tube and adiabatic collapse problems show that the artificial viscosity used in the hydra code prior to version 4.0 performs relatively poorly for simulations involving strong shocks when compared to a more standard artificial viscosity. The shear-correction term is shown to reduce the shock-capturing ability of the algorithm and to lead to a spurious increase in angular momentum in the rotating cloud-collapse problem. For the disc stability test, the shear-corrected and previous hydra artificial viscosities are shown to reduce outward angular momentum transport. The cosmological simulations produce comparatively similar results, with the fraction of gas in the hot and cold phases varying by less than 10 per cent amongst the versions. Similarly, the drag test shows little systematic variation amongst versions. The cooling flow tests show that implementations using the force symmetrization of Thomas & Couchman are more prone to accelerate the overcooling instability of SPH, although the problem is generic to SPH. The second most important factor in code performance is the way force symmetry is achieved in the equation of motion. Most results favour a kernel symmetrization approach. The exact method by which SPH pressure forces are included in the equation of motion appears to have comparatively little effect on the results. Combining the equation of motion presented by Thomas & Couchman with a modification of the Monaghan & Gingold artificial viscosity leads to an SPH scheme that is both fast and reliable.

We present a new 300 ks Chandra observation of M87 that limits pileup to only a few per cent of photon events and maps the hot gas properties closer to the nucleus than has previously been possible. Within the supermassive black hole's gravitational sphere of influence, the hot gas is multiphase and spans temperatures from 0.2 to 1 keV. The radiative cooling time of the lowest temperature gas drops to only 0.1-0.5 Myr, which is comparable to its free fall time. Whilst the temperature structure is remarkably symmetric about the nucleus, the density gradient is steep in sectors to the N and S, with $\rho{\propto}r^{-1.5\pm0.1}$, and significantly shallower along the jet axis to the E, where $\rho{\propto}r^{-0.93\pm0.07}$. The density structure within the Bondi radius is therefore consistent with steady inflows perpendicular to the jet axis and an outflow directed E along the jet axis. By putting limits on the radial flow speed, we rule out Bondi accretion on the scale resolved at the Bondi radius. We show that deprojected spectra extracted within the Bondi radius can be equivalently fit with only a single cooling flow model, where gas cools from 1.5 keV down below 0.1 keV at a rate of 0.03 M$_{\odot}$/yr. For the alternative multi-temperature spectral fits, the emission measures for each temperature component are also consistent with a cooling flow model. The lowest temperature and most rapidly cooling gas in M87 is therefore located at the smallest radii at ~100 pc and may form a mini cooling flow. If this cooling gas has some angular momentum, it will feed into the cold gas disk around the nucleus, which has a radius of ~80 pc and therefore lies just inside the observed transition in the hot gas structure.

Early-type galaxies are luminous sources of X-ray radiation, and contain large amounts of hot, interstellar gas. In the brighter X-ray galaxies, the inferred masses of hot gas are consistent with those expected given the present rates of stellar mass loss. The required rates of heating of the gas are also roughly consistent with those expected from the motions of gas losing stars and supernovae. The X-ray observations suggest a lower rate of Type la supernovae than has been previously thought to apply. In the brightest X-ray galaxies, the cooling times in the gas are short, which suggests that the gas forms steady-state cooling flows. Cooling flow models explain most of the properties of the brighter X-ray galaxies, including their luminosities, the X-ray—optical correlation, their temperatures, and their surface brightness profiles. Homogeneous cooling flow models, in which all the hot gas flows into the central regions of the galaxy, have surface brightness profiles which are too centrally peaked, and which decline too rapidly in the outer parts. On the other hand, if the gas is inhomogeneous and much of the gas cools below X-ray emitting temperature near the point where it is injected, good agreement with the observed X-ray surface brightness profiles is found. Although the optical and X-ray luminosities of early-type galaxies are strongly correlated, there is a large dispersion in this correlation. One suggestion is that this dispersion indicates that early-type galaxies are not generally in steady-state, and that the fainter galaxies are in an earlier hydrodynamical phase in which most of the heating of the gas goes into the kinetic energy in a wind or partial wind, or into the thermal energy of subsonic inflation. Alternatively, the fainter galaxies may have lost much of their gas to ram pressure ablation. At a given optical luminosity, galaxies which are brighter in X-rays are found in less dense regions, which supports this last suggestion.

The standard model for apparent superluminal motion is that of relativistic motion in a jet pointed nearly along the line of sight. Variants of this model give a natural explanation for the extremely asymmetric morphology observed in the radio cores of these sources. Despite this, examination of the large scale structure in superluminal radio sources strongly suggests that large scale symmetrical structure with two large radio lobes placed on either side of the compact emission is a common phenomenon among these objects. When a comparison is done between the large scale structure typically seen in double quasars and that seen in superluminal sources, it is found that the de-projected physical sizes estimated for superluminal quasars are similar to the size scales observed in the double quasars. Large scale radio structure is probably as common among apparent superluminal sources as it is in radio quasars.

Dependence of the efficiency of various emissions on excitation density in BaF 2 crystals

In-situ observation of end crater crack mechanisms in AA7075 during laser beam welding using synchrotron radiation

Existing propulsion technology has not achieved cost effective payload delivery rates to low earth orbit. A fusion based propulsion system, denoted as the Simultaneous Heating and eXpansion (SHX) engine, has been proposed in earlier papers. The SHX couples energy generated by a fusion reactor to the engine flowpath by use of coherent beam emitters. A quasi-one-dimensional flow model was used to quantify the effects of area expansion and energy input on propulsive efficiency for several beam models. Entropy calculations were included to evaluate the lost work in the system.

Under the influence of environmental pollution and energy scarcity, integrated energy systems (IES) have received extensive attention in the field of energy supply due to their ability to consume renewable energy and enhance energy utilization. In the context of low‐carbon scheduling for IES, numerous studies calculate the system's carbon emissions based on the carbon emission coefficients of energy devices. However, IES is a multi‐energy coupling system in which a device's energy input can originate from multiple sources with varying degrees of carbon emissions, making it difficult to accurately calculate the resulting carbon emissions using fixed coefficients. Consequently, a carbon emission flow (CEF) model is constructed for the system to calculate carbon emissions. In addition to the basic input–output CEF model, the CEF model for energy storage devices is considered, and carbon emission constraints during system operation are formulated based on the CEF model. Furthermore, many studies on low‐carbon scheduling of IES overlook the uncertainties associated with load and renewable energy. Therefore, a two‐stage scheduling model consisting of day‐ahead stage and intra‐day stage is developed to achieve reliable energy supply. Finally, through experiments, the low‐carbon performance and reliability of the model are validated.

This book is about the mechanisms of wealth creation, or what we like to think of as evolutionary progress . For the modern economy, natural wealth consists of complex physical structures of condensed ( frozen ) energy mass - maintained in the earth s crust far from thermodynamic equilibrium. However, we usually perceive wealth as created when mutation or invention a change agent - introduces something different, and fitter, and usually after some part of the natural wealth of the planet has been exploited in an episode of creative destruction . Selection out of the resulting diversity is determined by survival in a competitive environment, whether a planet, a habitat, or a market. While human wealth is associated with money and what it can buy, it is ultimately based on natural wealth, both as materials transformed into useful artifacts, and how those artifacts, activated by energy, can create and transmit useful information. Humans have learned how to transform natural wealth into other forms. Can the new immaterial wealth of information and ideas, which makes up the so-called knowledge economy, replace depleted natural wealth? This seemingly simple question is the grand challenge of the 21st century. In this book, you will learn about the three key requirements for wealth creation, and how this process acts at all scales from elementary particles to biological organisms to the human economy according to physical laws. At the planetary level, continuing life on Earth depends on entropy minimization or the circular economy . In the human economy, however, the massive circular flow of goods and services between producers and consumers is not a perpetual motion machine; it has been dependent for the past 150 years on energy inputs from a finite storage of fossil fuels. Knowledge and natural capital, particularly energy, will interact to power the human wealth engine in the future as it has in the past. Will it sputter or continue along the path of evolutionary progress that we have come to expect?