Gas Corona Research Articles

X-Ray Constraints on the Hot Gaseous Corona of Edge-on Late-type Galaxies in Virgo

We present a systematic study of the putative hot gas corona around late-type galaxies (LTGs) residing in the Virgo cluster, based on archival Chandra observations. Our sample consists of 21 nearly edge-on galaxies representing a range of star formation rate (SFR) of 0.2–3 M ⊙ yr−1 and a range of stellar mass (M *) of (0.2–10) × 1010 M ⊙, the majority of which have not been explored with high-sensitivity X-ray observations so far. Significant extraplanar diffuse X-ray (0.5–2 keV) emission is detected in only three LTGs, which are also the three galaxies with the highest SFR. A stacking analysis is performed for the remaining galaxies without individual detection, dividing the whole sample into two subsets based on SFR, stellar mass, or specific SFR. Only the high-SFR bin yields a significant detection, which has a value of L X ∼ 3 × 1038 erg s−1 per galaxy. The stacked extraplanar X-ray signals of the Virgo LTGs are consistent with the empirical L X–SFR and L X–M * relations found among highly inclined disk galaxies in the field, but appear to be systematically lower than those of a comparison sample of simulated star-forming galaxies in clusters identified from the Illustris-TNG100 simulation. The apparent paucity of hot gas coronae in the sampled Virgo LTGs might be understood as the net outcome of the long-lasting effect of ram pressure stripping exerted by the hot intracluster medium and in-disk star-forming activity acting on shorter timescales. A better understanding of the roles of environmental effects in regulating the hot gas content of cluster galaxies invites sensitive X-ray observations for a large sample of galaxies.

STUDY OF THE DEPENDENCE OF THE CHARACTERISTICS OF THE PULSE NEGATIVE CORONA ON THE PARAMETERS OF THE COMBINED HIGH VOLTAGE POWER SUPPLY

Numerical simulations of the negative corona in oxygen-containing gases under varying voltage are carried out. It is shown that by changing the values of constant voltage and duration of its application, between high voltage pulses, it is possible to control the electric field strength near the cathode, during the pulse. Quantitative characteristics of the ozone generation process are experimentally investigated. It is found that the agreed choice of the values of the constant component of the applied voltage and the frequency of the high voltage pulses can significantly increase the productivity and energy efficiency of ozone generators.

Experimental study of heat transfer enhancement with point-to-ring corona discharge

In this study, we experimentally inquire into the mechanism of the electric field for heat transfer enhancement by a point-to-ring corona gas discharge with either positive or negative applied voltage. We use a self-assembly 2D2C particle imaging velocimetry system to visualize and record the flow field. Results show that in our configuration the onset voltage of positive corona discharge is only slightly higher than that of the negative corona as a relatively large ring electrode is used. The current-voltage relationship follows Townsend's quadratic equation. The electrode distance has a slight effect on the current-voltage relationship. The time-averaged velocity demonstrates that the positive corona produces a faster and thinner jet compared to the negative one, and the region of the ionic wind is limited at low corona voltage. In addition, it is observed that the ionic wind can dramatically enhance heat transfer by ∼ 200%, and the enhancement effect of the positive discharge is more significant than that of the negative one. Furthermore, the proposed ionic wind generator has low power consumption, and therefore it is energy efficient.

Earthquake precursors in the light of peroxy defects theory: Critical review of systematic observations

Forecasting earthquakes implies that there are time-varying processes, which depend on the changing conditions deep in the Earth's crust prior to major seismic activity. These processes may be linearly or non-linearly correlated. In seismology, the research has traditionally focused on mechanical variables, including precursory ground deformation (revealing the build-up of stress deep below) and on prior seismic events (past earthquakes may be related to or even trigger future earthquakes). Since the results have been less than convincing, there is a general consensus in the seismology community that earthquake forecasting on time scales comparable to meteorological forecasts is still quite far in the future, if ever attainable. The starting point of the present review is to acknowledge that there are innumerable reports of other types of precursory phenomena observable on the ground or in near-Earth space ranging from the emission of electromagnetic waves from ultralow frequency (ULF) to near-infrared (NIR) and visible (VIS) light, electric field and magnetic field anomalies of various kinds (see below), all the way to widely reported but never fully understood unusual animal behavior. These precursory signals are intermittent and seem not to occur systematically before every major earthquake. As a result they are not widely accepted, because no one could fully explain their origins. In addition, the diversity of these signals makes them look unrelatable, hampering any progress. In the first part, we review evidence for a solid-state mechanism based on decades of research bridging semi-conductor physics, solid state chemistry and rock physics, that is capable of providing explanations for the diversity of reported pre-earthquake phenomena. In fact, it appears that all pre-earthquake phenomena might be traceable to a single fundamental process on the atomic scale: the rupture of peroxy bonds via activation of electronic charges, electrons and positive holes, in rocks subjected to tectonic stresses prior to seismic activity. The positive holes are defect electrons in the O2- sublattice. They are unusual inasmuch as they are able to flow out of the stressed rock volume, into and through the surrounding unstressed or less stressed rocks. They form electric currents that travel fast and far, causing along the way a wide range of physical and chemical follow-on processes: electrical ground potentials, stimulated infrared emission, massive air ionization, radon emanation, increased levels of ozone, toxic levels of carbon monoxide (CO) and more. In the second part, we critically examine satellite and ground station data, recorded before a selection of past large earthquakes. Some of the phenomena can be directly related to the peroxy defect theory, namely, radon gas emanations, corona discharges, thermal infrared emissions, air ionization, ion and electron content in the ionosphere, and electro-magnetic anomalies. Of course there is a need for further systematic investigations, continuing statistical examination of the relevance and confidence levels of the observable precursors. Only then will the scientific community be able to assess and eventually improve the performance of earthquake forecasts.

Effect of gas type on insulation recovery performance and repetitive breakdown stability of a corona-stabilized plasma closing switch

The corona-stabilized plasma closing switch, which utilizes the stabilization effect resulted from the movement and accumulation of corona-generated space charge to improve the repetitive performance, has a great potential in repetitive pulsed power systems. In this paper, the influence of gas type on the recovery performance and repetitive breakdown stability of a corona-stabilized plasma closing switch is investigated. The results are analyzed from the memory effect of residual plasma, the development and propagation characteristics of streamer corona, and the thermo-hydrodynamic process of discharge channel. The enhancement effect of residual plasma on corona stabilization of the subsequent breakdown in the repetitive operation of the gas gap with highly inhomogeneous electric field and strong electronegative gas is proposed. The development and propagation characteristics of streamer corona in different gases that can lead to significant differences in the corona stabilization effect of breakdown are clarified. It is also found that the gas with small molecular mass and higher gas velocity exhibits excellent insulation recovery in the gas switch with uniform fields, but displays poor repetitive performance in the corona-stabilized switch with a rod-plate electrode.

Research on fuze microswitch based on corona discharge effect

Abnormal voltages such as electrostatic, constant current, and strong electromagnetic signals can erroneously trigger operation of MEMS pyrotechnics and control systems in a fuze, which may result in casualties. This study designs a solid-state micro-scale switch by combining the corona gas discharge theory of asymmetric electric fields and Peek’s Law. The MEMS switch can be transferred from “off” to “on” through the gas breakdown between the corona electrodes. In the model, one of the two electrodes is spherical and the other flat, so a non-uniform electric field is formed around the electrodes. The theoretical work is as follows. First, the relation among the radius of curvature of the spherical electrode, the discharge gap, and the air breakdown voltage is obtained; to meet the low voltage (30–60 V) required to drive the MEMS switch, the radius of curvature of the spherical electrode needs to be 10–50 μm and the discharge gap between the two electrodes needs to be 9–11 μm. Second, the optimal ratio ε is introduced to parameterize the model. Finally, the corona discharge structural parameters are determined by comparing the theoretical and electric field simulation results. The switch is then fabricated via MEMS processing. A hardware test platform is built and the performing chip tested. It is found that when the electrode gap is 9 μm, the electrostatic voltage is at least 37.3 V, with an error of 2.6% between the actual and theoretical air breakdown voltages. When the electrode gap is 11 μm, the electrostatic voltage is at least 42.3 V, with an error of 10.5% between the actual and theoretical air breakdown voltages. Both cases meet the design requirements.

Exhaust Dynamics of PM by Gas Mixture Fuel and Corona Dischargeand

Exhaust Dynamics of PM by Gas Mixture Fuel and Corona Dischargeand

The escape velocity curve of the Milky Way in modified Newtonian dynamics

We determine the escape velocity from the Milky Way (MW) at a range of Galactocentric radii in the context of Modified Newtonian Dynamics (MOND). Due to its non-linear nature, escape is possible if the MW is considered embedded in a constant external gravitational field (EF) from distant objects. We model this situation using a fully self-consistent method based on a direct solution of the governing equations out to several thousand disk scale lengths. We try out a range of EF strengths and mass models for the MW in an attempt to match the escape velocity measurements of Williams et al. (2017). A reasonable match is found if the EF on the MW is ${\sim 0.03 a_{_0}}$, towards the higher end of the range considered. Our models include a hot gas corona surrounding the MW, but our results suggest that this should have a very low mass of ${\sim 2 \times 10^{10} M_\odot}$ to avoid pushing the escape velocity too high. Our analysis favours a slightly lower baryonic disk mass than the ${\sim 7 \times 10^{10} M_\odot}$ required to explain its rotation curve in MOND. However, given the uncertainties, MOND is consistent with both the locally measured amplitude of the MW rotation curve and its escape velocity over Galactocentric distances of 8$-$50 kpc.

Stellar streams as gravitational experiments

Tidal streams of disrupting dwarf galaxies orbiting around their host galaxy offer a unique way to constrain the shape of galactic gravitational potentials. Such streams can be used as “leaning tower” gravitational experiments on galactic scales. The most well-motivated modification of gravity proposed as an alternative to dark matter on galactic scales is Milgromian dynamics (MOND), and we present here the first ever N-body simulations of the dynamical evolution of the disrupting Sagittarius dwarf galaxy in this framework. Using a realistic baryonic mass model for the Milky Way, we attempt to reproduce the present-day spatial and kinematic structure of the Sagittarius dwarf and its immense tidal stream that wraps around the Milky Way. With very little freedom on the original structure of the progenitor, constrained by the total luminosity of the Sagittarius structure and by the observed stellar mass-size relation for isolated dwarf galaxies, we find reasonable agreement between our simulations and observations of this system. The observed stellar velocities in the leading arm can be reproduced if we include a massive hot gas corona around the Milky Way that is flattened in the direction of the principal plane of its satellites. This is the first time that tidal dissolution in MOND has been tested rigorously at these mass and acceleration scales.

The Evaporation and Survival of Cluster Galaxy Coronae. I. The Effectiveness of Isotropic Thermal Conduction Including Saturation

Abstract We simulate the evolution of cluster galaxy hot interstellar medium (ISM) gas that is a result of the effects of ram pressure and thermal conduction in the intracluster medium (ICM). At the density and temperature of the ICM, the mean free paths of ICM electrons are comparable to the sizes of galaxies, therefore electrons can efficiently transport heat that is due to thermal conduction from the hot ICM to the cooler ISM. Galaxies consisting of dark matter halos and hot gas coronae are embedded in an ICM-like “wind tunnel” in our simulations. In this paper, we assume that thermal conduction is isotropic and include the effects of saturation. We find that as heat is transferred from the ICM to the ISM, the cooler denser ISM expands and evaporates. This process is significantly faster than gas loss due to ram pressure stripping; for our standard model galaxy, the evaporation time is 160 Myr, while the ram pressure stripping timescale is 2.5 Gyr. Thermal conduction also suppresses the formation of shear instabilities, and there are no stripped ISM tails since the ISM evaporates before tails can form. Observations of long-lived X-ray emitting coronae and ram pressure stripped X-ray tails in galaxies in group and cluster environments therefore require that thermal conduction is suppressed or offset by some additional physical process. The most likely process is anisotropic thermal conduction that is due to magnetic fields in the ISM and ICM, which we simulate and study in the next paper in this series.

The tilting rate of the Milky Way's disc

We present tilting rates for galaxies comparable to the Milky Way (MW) in a $\Lambda$ cold dark matter cosmological hydrodynamical simulation, and compare these with the predicted tilting rate detection limit of the {\it Gaia} satellite $0.28\degrees$Gyr$^{-1}$. We first identify galaxies with mass comparable to the MW ($9 \times 10^{11} \le M_{200} \le 1.2 \times 10^{12} \Msun $) and consider the tilting rates between $z=0.3$ and $0$. This sample yields a tilting rate of $7.6\degrees \pm 4.5\degrees$Gyr$^{-1}$. We constrain our sample further to exclude any galaxies that have high stellar accretion during the same time. We still find significant tilting, with an average rate of $6.3\degrees$Gyr$^{-1}$. Both subsamples tilt with rates significantly above {\it Gaia}'s predicted detection limit. We show that our sample of galaxies covers a wide range of environments, including some similar to the MW's. We find galaxies in denser regions tilt with higher rates then galaxies in less dense regions. We also find correlations between the angular misalignment of the hot gas corona, and the tilting rate. {\it Gaia} is likely to be able to directly measure tilting in the MW. Such a detection will provide an important constraint on the environment of the MW, including the rate of gas cooling onto the disc, the shape and orientation of its dark matter halo, and the mass of the Large Magellanic Cloud. Conversely, failure to detect tilting may suggest the MW is in a very quiet configuration.

The condensation of the corona for the correlation between the hard X-ray photon index Γ and the reflection scaling factor ℜ in active galactic nuclei

Observationally, it is found that there is a strong correlation between the hard X-ray photon index $\Gamma$ and the Compton reflection scaling factor $\Re$ in active galactic nuclei. In this paper, we propose that the $\Gamma-\Re$ correlation can be explained within the framework of the condensation of the hot corona onto the cold accretion disc around a supermassive black hole. In the model, it is presumed that, initially, a vertically extended hot gas (corona) is supplied to the central supermassive black hole by capturing the interstellar medium and stellar wind. In this scenario, when the initial mass accretion rate $\dot M/ \dot M_{\rm Edd} \gtrsim 0.01$, at a critical radius $r_{\rm d}$, part of the hot gas begins to condense onto the equatorial disc plane of the black hole, forming an inner cold accretion disc. Then the matter is accreted in the form of the disc-corona structure extending down to the innermost stable circular orbits of the black hole. The size of the inner disc is determined by the initial mass accretion rate. With the increase of the initial mass accretion rate, the size of the inner disc increases, which results in both the increase of the Compton reflection scaling factor $\Re$ and the increase of the hard X-ray photon index $\Gamma$. By comparing with a sample of Seyfert galaxies with well-fitted X-ray spectra, it is found that our model can roughly explain the observations. Finally, we discuss the possibility to apply our model to high mass X-ray binaries, which are believed to be fueled by the hot wind from the companion star.

The angular momentum of cosmological coronae and the inside-out growth of spiral galaxies

Massive and diffuse haloes of hot gas (coronae) are important intermediaries between cosmology and galaxy evolution, storing mass and angular momentum acquired from the cosmic web until eventual accretion on to star-forming discs. We introduce a method to reconstruct the rotation of a galactic corona, based on its angular momentum distribution (AMD). This allows us to investigate in what conditions the angular momentum acquired from tidal torques can be transferred to star forming discs and explain observed galaxy-scale processes, such as inside-out growth and the build-up of abundance gradients. We find that a simple model of an isothermal corona with a temperature slightly smaller than virial and a cosmologically motivated AMD is in good agreement with galaxy evolution requirements, supporting hot-mode accretion as a viable driver for the evolution of spiral galaxies in a cosmological context. We predict moderately sub-centrifugal rotation close to the disc and slow rotation close to the virial radius. Motivated by the observation that the Milky Way has a relatively hot corona (T ~ 2 x 10^6 K), we also explore models with a temperature larger than virial. To be able to drive inside-out growth, these models must be significantly affected by feedback, either mechanical (ejection of low angular momentum material) or thermal (heating of the central regions). However, the agreement with galaxy evolution constraints becomes, in these cases, only marginal, suggesting that our first and simpler model may apply to a larger fraction of galaxy evolution history.

Fluxes of diffuse gamma rays and neutrinos from cosmic-ray interactions with the circumgalactic gas

The Milky Way is surrounded by a gravitationally bound gas corona extending up to the Galaxy's virial radius. Interactions of cosmic-ray particles with this gas give rise to energetic secondary gamma rays and neutrinos. We present a quantitative analysis of the neutrino and gamma-ray fluxes from the corona of the Milky Way together with a combined contribution of coronae of other galaxies. The high-energy neutrino flux is insufficient to explain the IceCube results, while the contribution to the FERMI-LAT diffuse gamma-ray flux is not negligible.

Поляризация и рекомбинация в электрически активных центрах захвата носителей заряда в кабельных полимерных диэлектриках и слюде

The study of electrically active centers EATSZ capture in polar and non-polar dielectric and mica was studied by polarimetry electret in an electric gas corona EGKR and method of thermally stimulated depolarization current TSD. It is shown that uncompensated permanent dipoles C-H bonds, CF endings in non-polar molecules, PE, PTFE, and C-H, C = O at the ends and within the polar molecules of PET and PC are EATSZ polar and non-polar polymeric cable and capacitor dielectrics. It is shown that EATSZ mica crystals are radiative vacancy defects OH K + ion crystal sublattice slyud.

Влияние плотности и концентрации центров захвата на подвижность носителей заряда в полимерных диэлектриках

The study of electrically active centers EATSZ capture in polar and non-polar dielectric and mica was studied by polarimetry electret in an electric gas corona EGKR and method of thermally stimulated depolarization current TSD. It is shown that uncompensated permanent dipoles C-H bonds, CF endings in non-polar molecules, PE, PTFE, and C-H, C = O at the ends and within the polar molecules of PET and PC are EATSZ polar and non-polar polymeric cable and capacitor dielectrics.

Электретный эффект и подвижность носителей заряда в электроизоляционных полимерных кабельных и конденсаторных диэлектриках

Research mobility of charge carriers in the polar and nonpolar dielektrikah (LDPE, HDPE, PET and PC) carried by an electret polarimetry in the electric gas corona and method of thermally stimulated depolarization current TSD. It is shown that the measurement of spectra of TSD at linear heating rate of current 1 °C/min and 10 °C/min, and the method of electret polarimetry can be measured by the value of mobility of electrons and holes in LDPE, HDPE, PET and PC.

Mobility of Charge Carriers in Polymer and Mica Electrets

Ionizing radiation of an electric corona gas discharge (ECGD) and electric barrier gas discharge (EBGD) creates a radiation thickness gradient of recombination center concentration N rec = f(h) near the surface of polymer and mica electrets. The mobility of charge carriers in polymer and mica electrets and the stability of the electret potential difference U el = f(t) are obtained by the method of experimental measurements of the x-ray radiation half-absorption depth δ 1/2ECGD, EBGD .

Coronal accretion: the power of X-ray emission in AGN

AbstractThe optical/UV and X-ray emissions in luminous AGN are commonly believed to be produced in an accretion disk and an embedded hot corona respectively. We explore the possibility that a geometrically thick coronal gas flow, which is supplied by gravitational capture of interstellar medium or stellar wind, condenses partially to a geometrically thin cold disk and accretes via a thin disk and a corona onto the supermassive black hole. We found that for mass supply rates less than about 0.01 (expressed in Eddington units), condensation does not occur and the accretion flow takes the form of a corona/ADAF. For higher mass supply rates, corona gas condenses to the disk. As a consequence, the coronal mass flow rate decreases and the cool mass flow rate increases towards the black hole. Here the thin disk is characterized by the condensation rate of hot gas as it flows towards the black hole. With increase of mass supply rate, condensation becomes more efficient, while the mass flow rate of the coronal gas attains values of order 0.02 in the innermost regions of the disk, which can help to elucidate the production of strong X-ray with respect to the optical and ultraviolet radiation in high luminosity AGN.

Thermal instabilities in cooling galactic coronae: fuelling star formation in galactic discs

We investigate the means by which cold gas can accrete onto Milky Way mass galaxies from a hot corona of gas, using a new smoothed particle hydrodynamics code, 'SPHS'. We find that the 'cold clumps' seen in many classic SPH simulations in the literature are not present in our SPHS simulations. Instead, cold gas condenses from the halo along filaments that form at the intersection of supernovae-driven bubbles from previous phases of star formation. This positive feedback feeds cold gas to the galactic disc directly, fuelling further star formation. The resulting galaxies in the SPH and SPHS simulations differ greatly in their morphology, gas phase diagrams, and stellar content. We show that the classic SPH cold clumps owe to a numerical thermal instability caused by an inability for cold gas to mix in the hot halo. The improved treatment of mixing in SPHS suppresses this instability leading to a dramatically different physical outcome. In our highest resolution SPHS simulation, we find that the cold filaments break up into bound clumps that form stars. The filaments are overdense by a factor of 10-100 compared to the surrounding gas, suggesting that the fragmentation results from a physical non-linear instability driven by the overdensity. This 'fragmenting filament' mode of disc growth has important implications for galaxy formation, in particular the role of star formation in bringing cold gas into disc galaxies.