Nuclear Wind Research Articles

A NEW PERSPECTIVE OF THE RADIO BRIGHT ZONE AT THE GALACTIC CENTER: FEEDBACK FROM NUCLEAR ACTIVITIES

ABSTRACT New observations of Sgr A have been carried out with the Jansky VLA in the B and C arrays using the broadband (2 GHz) continuum mode at 5.5 GHz. The field of view covers the central 13′ (30 pc) region of the radio-bright zone at the Galactic center. Using the multi-scale and multi-frequency-synthesis (MS-MFS) algorithms in CASA, we have imaged Sgr A with a resolution of 1″, achieving an rms noise of 8 μJy beam−1, and a dynamic range of 100,000:1. Both previously known and newly identified radio features in this region are revealed, including numerous filamentary sources. The radio continuum image is compared with Chandra X-ray images, with a CN emission-line image obtained with the Submillimeter Array and with detailed Paschen-α images obtained with Hubble Space Telescope/NICMOS. We discuss several prominent features in the radio image. The “Sgr A west Wings” extend 2′ (5 pc) from the NW and SE tips of the Sgr A west H ii region (the “Mini-spiral”) to positions located 2.9 and 2.4 arcmin to the northwest and southeast of Sgr A*, respectively. The NW wing, along with several other prominent features, including the previously identified “NW Streamers,” form an elongated radio lobe (NW lobe), oriented nearly perpendicular to the Galactic plane. This radio lobe, with a size of 6.′3 × 3.′2 (14.4 pc × 7.3 pc), has a known X-ray counterpart. In the outer region of the NW lobe, a row of three thermally emitting rings is observed. A field containing numerous amorphous radio blobs extends for a distance of ∼2 arcmin beyond the tip of the SE wing; these newly recognized features coincide with the SE X-ray lobe. Most of the amorphous radio blobs in the NW and SE lobes have Paschen-α counterparts. We propose that they have been produced by shock interaction of ambient gas concentrations with a collimated nuclear wind or an outflow that originated from within the circumnuclear disk (CND). We also discuss the possibility that the ionized wind or outflow has been launched by radiation force produced by the central star cluster. Finally, we remark on the detailed structure of a prominent radio emission feature located within the shell of the Sgr A east supernova remnant. Because this feature—the “Sigma Front”—correlates well in shape and orientation with the nearby edge of the CND, we propose that it is a reflected shock wave resulting from the impact of the Sgr A east blast wave on the CND.

The multi-phase winds of Markarian 231: from the hot, nuclear, ultra-fast wind to the galaxy-scale, molecular outflow

We present the best sensitivity and angular resolution maps of the molecular disk and outflow of Mrk 231, as traced by CO observations obtained with IRAM/PdBI, and we analyze archival Chandra and NuSTAR observations. We constrain the physical properties of both the molecular disk and outflow, the presence of a highly-ionized ultra-fast nuclear wind, and their connection. The molecular outflow has a size of ~1 kpc, and extends in all directions around the nucleus, being more prominent along the south-west to north-east direction, suggesting a wide-angle biconical geometry. The maximum projected velocity of the outflow is nearly constant out to ~1 kpc, thus implying that the density of the outflowing material decreases from the nucleus outwards as $r^{-2}$. This suggests that either a large part of the gas leaves the flow during its expansion or that the bulk of the outflow has not yet reached out to ~1 kpc, thus implying a limit on its age of ~1 Myr. We find $\dot M_{OF}=[ 500-1000]~ M_{\odot}~yr^{-1}$ and $\dot E_{kin,OF}=[7-10]\times 10^{43}$ erg s$^{-1}$. Remarkably, our analysis of the X-ray data reveals a nuclear ultra-fast outflow (UFO) with velocity -20000 km s$^{-1}$, $\dot M_{UFO}=[0.3- 2.1] ~M_\odot yr^{-1}$, and momentum load $\dot P_{UFO}/\dot P_{rad}=[0.2-1.6]$.We find $\dot E_{kin,UFO}\sim \dot E_{kin,OF}$ as predicted for outflows undergoing an energy conserving expansion. This suggests that most of the UFO kinetic energy is transferred to mechanical energy of the kpc-scale outflow, strongly supporting that the energy released during accretion of matter onto super-massive black holes is the ultimate driver of giant massive outflows. We estimate a momentum boost $\dot P_{OF}/\dot P_{UFO}\approx [30-60]$. The ratios $\dot E_{kin, UFO}/L_{bol,AGN} =[ 1-5]\%$ and $\dot E_{kin,OF}/L_{bol,AGN} = [1-3]\%$ agree with the requirements of the most popular models of AGN feedback.

Aftermath

Aftermath Marcia L. Hurlow (bio) for my brother You witness an explosion you calculate in numbers so small their heat shatters into white flame. Subatomic heartbreak rolls into the clouds. A star the reaction lit like a candle snaps in blue above the microscopic field of your narrowing choices. Here, floating above the blast a black thread frays, widens in the nuclear wind like the shadow of a man risen from the fracture. [End Page 71] Marcia L. Hurlow Marcia L. Hurlow, professor of creative writing at Asbury University in Wilmore, Kentucky, is the author of five collections of poetry. Her most recent chapbook, Green Man in Suburbia, won the Backwards City Review Press contest, and her full-length collection, Anomie, won the Edges Prize at WordTech. Her poems have appeared in various journals, including Poetry, Poetry Northwest, Nimrod, Poetry Wales, The Iconoclast, Hawaii Pacific Review, and Malahat Review. Copyright © 2015 Berea College

Evaluate Pumped-Storage Unit in Power System with Multi-Type Units

This paper proposed an approach to evaluate the economics of pumped-storage unit from the perspective of the power system. An MIP-based unit commitment model with multi-type units was established, which integrated thermal, CCGT, hydro, wind, nuclear and pumped-storage units. Based on the model the net present value of pumped-storage per megawatt was calculated and compared with the capital cost per megawatt, which produce the economic result of pumped-storage. The case study proved the feasibility of the above model and approach. Furthermore, the change of economic result of pumped-storage over system variables like nuclear capacity, wind capacity and regulating capacity of thermal unit was analyzed. The case study showed that with the increase of nuclear capacity, wind capacity and minimum output of thermal units, the economics of pumped-storage was improved.

Using real options to compare the economics of nuclear power and wind power with electricity from natural gas

The real options method provides one objective basis for judging when (if at all) it is reasonable to invest in a product in competition with another, the future price of which may exhibit a high degree of uncertainty. This article uses the real options technique to find the economically desirable start-up dates for three carbon-free methods of generating electricity, nuclear, onshore wind, and offshore wind, when facing competition from electricity generated from natural gas. The fact that the same assessment method has been used for each of the three carbon-free options allows intercomparability of the results. Nuclear power is projected to become competitive with gas-based electricity in 2015, even when no benefit is claimed for its carbon-free properties. Using the same yardstick, unaided onshore wind power first becomes competitive with gas in 2032 and unaided offshore wind power in 2040. There is thus a wide disparity among the dates of competiveness for the three methods of generation considered. Judged on a level playing field for carbon-free technologies, nuclear power emerges as a much better investment than onshore wind, while onshore wind is better than offshore wind. The analysis provides an explanation for the significant number of utilities who have declared an interest in New Nuclear Build in the UK in the near future. It shows that these utilities can be expected to make money immediately after their plants start up, even if they are given no credit for the carbon-free nature of nuclear generation. By contrast, the economics of wind power look more problematic. Even given the current level of intervention, £40/MWh, equivalent to £90/t CO2 avoided, onshore wind farms are not expected to become competitive with gas generation for about 15 years. That timescale stretches to over 20 years if no intervention is made. The situation is worse for offshore wind farms, which do not become competitive until 2028 even when given twice the aid offered to onshore wind farms: £80/MWh, equivalent to £180/t CO2 avoided. Without this high level of support, offshore wind farms are not expected to become competitive with gas generation for nearly 30 years even when allowance is made for the improved technology associated with series build. While wind technology is likely eventually to become competitive with gas, the real options analysis suggests that it would require significant cost reductions for a major, early deployment of wind power to become justified. It would appear to be a particularly questionable use of resources to spend money developing offshore wind farms so far in advance of their likely cost-effectiveness. The real options analysis suggests that large-scale construction of offshore wind farms should be delayed until the late 2030s.

Projected Costs of Electricity Generation

This paper describes the outcomes from the joint report between the Nuclear Energy Agency and the International Energy Agency of the OECD on the projected costs of generating electricity. It is the seventh in the series and presents the latest data available on electricity generating costs for a wide variety of fuels and technologies, including coal, gas, nuclear, hydro, onshore and offshore wind, biomass, solar, wave and tidal. The study contains data on electricity generating costs for almost 200 power plants provided by 16 OECD member countries, 4 non-OECD countries and 4 industrial companies or industry organisations. The study presents the projected costs of generating electricity calculated according to common methodological rules on the basis of the data provided by participating countries and organisations. Cost estimates were also provided for combined heat and power (CHP) plants, as well as for coal plants that include carbon capture. As in previous studies of the same series, all costs and benefits were discounted or capitalised to the date of commissioning in order to calculate the levelised costs of electricity (LCOE) per MWh, based on plant operating lifetime data.

THE HIGHEST RESOLUTIONCHANDRAVIEW OF PHOTOIONIZATION AND JET–CLOUD INTERACTION IN THE NUCLEAR REGION OF NGC 4151

We report high resolution imaging of the nucleus of the Seyfert 1 galaxy NGC 4151 obtained with a 50 ks Chandra HRC observation. The HRC image resolves the emission on spatial scales of 0.5", ~30 pc, showing an extended X-ray morphology overall consistent with the narrow line region (NLR) seen in optical line emission. Removal of the bright point-like nuclear source and image deconvolution techniques both reveal X-ray enhancements that closely match the substructures seen in the Hubble Space Telescope [OIII] image and prominent knots in the radio jet. We find that most of the NLR clouds in NGC 4151 have [OIII] to soft X-ray ratio ~10, despite the distance of the clouds from the nucleus. This ratio is consistent with the values observed in NLRs of some Seyfert 2 galaxies, which indicates a uniform ionization parameter even at large radii and a density decreasing as $r^{-2}$ as expected for a nuclear wind scenario. The [OIII]/X-ray ratios at the location of radio knots show an excess of X-ray emission, suggesting shock heating in addition to photoionization. We examine various mechanisms for the X-ray emission and find that, in contrast to jet-related X-ray emission in more powerful AGN, the observed jet parameters in NGC 4151 are inconsistent with synchrotron emission, synchrotron self-Compton, inverse Compton of CMB photons or galaxy optical light. Instead, our results favor thermal emission from the interaction between radio outflow and NLR gas clouds as the origin for the X-ray emission associated with the jet. This supports previous claims that frequent jet-ISM interaction may explain why jets in Seyfert galaxies appear small, slow, and thermally dominated, distinct from those kpc scale jets in the radio galaxies.

Hydrogen storage for mixed wind–nuclear power plants in the context of a Hydrogen Economy

A novel methodology for the economic evaluation of hydrogen production and storage for a mixed wind–nuclear power plant considering some new aspects such as residual heat and oxygen utilization is applied in this work. This analysis is completed in the context of a Hydrogen Economy and competitive electricity markets. The simulation of the operation of a combined nuclear–wind–hydrogen system is discussed first, where the selling and buying of electricity, the selling of excess hydrogen and oxygen, and the selling of heat are optimized to maximize profit to the energy producer. The simulation is performed in two phases: in a pre-dispatch phase, the system model is optimized to obtain optimal hydrogen charge levels for the given operational horizons. In the second phase, a real-time dispatch is carried out on an hourly basis to optimize the operation of the system as to maximize profits, following the hydrogen storage levels of the pre-dispatch phase. Based on the operation planning and dispatch results, an economic evaluation is performed to determine the feasibility of the proposed scheme for investment purposes; this evaluation is based on calculations of modified internal rates of return and net present values for a realistic scenario. The results of the present studies demonstrate the feasibility of a hydrogen storage and production system with oxygen and heat utilization for existent nuclear and wind power generation facilities.

The High‐Velocity Gas toward Messier 5: Tracing Feedback Flows in the Inner Galaxy

We present Far Ultraviolet Spectroscopic Explorer (FUSE) and Space Telescope Imaging Spectrograph (STIS E140M) observations of the post-asymptotic giant branch star ZNG 1 in the globular cluster Messier 5 (l=3.9, b=+47.7; d=7.5 kpc, z=+5.3 kpc). High velocity absorption is seen in C IV, Si IV, O VI, and lower ionization species at LSR velocities of -140 and -110 km/s. We conclude that this gas is not circumstellar on the basis of photoionization models and path length arguments. Thus, the high velocity gas along the ZNG 1 sight line is the first evidence that highly-ionized HVCs can be found near the Galactic disk. We measure the metallicity of these HVCs to be [O/H]=+0.22\pm0.10, the highest of any known HVC. Given the clouds' metallicity and distance constraints, we conclude that these HVCs have a Galactic origin. This sight line probes gas toward the inner Galaxy, and we discuss the possibility that these HVCs may be related to a Galactic nuclear wind or Galactic fountain circulation in the inner regions of the Milky Way.

UK subscribes to nuclear and offshore wind

UK subscribes to nuclear and offshore wind

Indicators of the impact of environmental factors on UK construction law: developments in the new millennium

In examining the impact of environmental issues on construction law, recent construction‐related legislation and litigation can be seen as indicators of the growing importance of specific property‐related environmental issues. Through reference to relevant literature and law reports, several recent legal developments can be identified relating to energy production and consumption, water inundation, the physical qualities of buildings, excluded materials, noise and disability discrimination and, finally, waste disposal and contamination. Recent law relating to energy consumption in buildings is evidence of the ever‐widening set of legal obligations regarding energy efficiency. Similarly, recent litigation relating to nuclear waste and wind farms may be more typical of future energy cases than those relating to traditional fossil fuel production processes. Noise represents another form of environmental pollution and has been seen in a number of cases. The impact of the built environment on people with disabilities is now recognized in Part M of the Building Regulations which places additional disabled access requirements on all building owners, landlords, employers and service providers. Property professionals, local authorities and statutory authorities need, more than ever before, to be aware of their current legal obligations while remaining constrained by resource and financial management regulation.

Stepping on the gas [hydrogen based fuel economy

This article looks at the technological and economical challenges in changing to a hydrogen based fuel economy. It discusses the use of hydrogen as fuel in vehicles, and in fuel cells to generate electricity. The main obstacle to a hydrogen economy is the production technology. Hydrogen generation by electrolysis using nuclear power, wind power and other renewable resources is examined. Also considered are the considerable storage and distribution networks that would be required.

Does the Milky Way produce a starburst wind?

We present new FUSE and HST/STIS observations of two high Galactic latitude AGN that we use to measure the nuclear wind velocity of the Milky Way for the first time. We find high velocity C III & O VI at a heliocentric velocity of , respectively. Thus, we have detected both infalling and bound outflowing gas from the Galactic Centre, indicating that the Milky Way does not produce a starburst wind, but a bound Galactic “fountain” instead.

Stellar envelopes as sources of broad line region emission: New possibilities allowed

In Active Galactic Nuclei (AGNs) the presence of a star cluster around the central black hole can have several effects on the dynamics and the emission of the global system. In this paper we analyze the interaction of stellar atmospheres with a wind outflowing from the central region of the AGN nucleus. Even a small mass loss from stars, as well as possible star collisions, can give a non-negligible contribution in feeding matter into the AGN nuclear wind. Moreover, stellar mass loss can produce envelopes surrounding stars that turn out to be suitable for reproducing the observed emission from the Broad Line Region (BLR). In this framework, the envelope can be confined by the bow shock arising from the interaction between the expanding stellar atmosphere and the AGN nuclear wind.

Accretion discs with accreting coronae in active galactic nuclei - II. The nuclear wind

We study an accretion disc with a hot continuous corona. We assume that the corona itself accretes and therefore it is powered directly by the release of the gravitational energy and cooled by radiative interaction with the disc. We consider the vertical structure of such a corona and show that the radial infall is accompanied by strong vertical outflow. Such a model has two important consequences: (i) at a given radius the corona forms only for accretion rate larger than a limiting value and the fraction of energy dissipated in the corona decreases with increasing accretion rate, and (ii) the disc spectra are significantly softer in the optical/UV band in comparison with the predictions of standard accretion discs due to the mass loss and the decrease of internal dissipation in the disc. Both trends correspond well to the mean spectra of radio quiet AGN and observed luminosity states in galactic black hole candidates.

The nature of the dense obscuring material in the nucleus of NGC 1068

High spatial and spectral resolution observations of the distribution, physical parameters, and kinematics of the molecular interstellar medium toward the nucleus of the Seyfert 2 galaxy NGC 1068 are reported. The data consist of 2.4 by 3.4 arcseconds resolution interferometry of the 88.6 GHz HCN J = 1 towards 0 line at 17 km/s spectral resolution, single dish observations of several mm/submm isotopic lines of CO and HCN, and 0.85 arcseconds imaging spectroscopy of the 2.12 micron H2 S(1) line at a velocity resolution of 110 km/s. The central few hundred parsecs of NGC 1068 contain a system of dense (N(H2) approximately 10(exp 5) cm(exp -3)), warm (T greater than or equal to 70 K) molecular cloud cores. The low density molecular envelopes have probably been stripped by the nuclear wind and radiation. The molecular gas layer is located in the plane of NGC 1068's large scale disk (inclination approximately 35 deg) and orbits in elliptical streamlines in response to the central stellar bar. The spatial distribution of the 2 micron H2 emission suggests that gas is shocked at the leading edge of the bar, probably resulting in gas influx into the central 100 pc at a rate of a few solar mass per year. In addition to large scale streaming (with a solid body rotation curve), the HCN velocity field requires the presence of random motions of order 100 km/s. We interpret these large random motions as implying the nuclear gas disk to be very thick (scale height/radius approximately 1), probably as the result of the impact of nuclear radiation and wind on orbiting molecular clouds. Geometry and column density of the molecular cloud layer between approximately 30 pc to 300 pc from the nucleus can plausibly account for the nuclear obscuration and anisotropy of the radiation field in the visible and UV.

Nuclear winds in active elliptical galaxies. I - Interaction

view Abstract Citations (7) References (58) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Nuclear Winds in Active Elliptical Galaxies. I. Interaction Smith, Steven J. ; Kennel, C. F. ; Coroniti, F. V. Abstract The interaction of a supersonic wind generated by an active nucleus, a nuclear wind, with the hot interstellar medium of an elliptical host galaxy is investigated. We survey the basic time and spatial scales of this interaction through a study covering the range of probable wind and galaxy parameters. The evolving wind/ISM interaction is detailed, with the conclusion that a true equilibrium state is never possible due to long cooling times. Alteration of the wind by mass loading is considered, and a relationship between nuclear winds and central stellar clusters in this context is outlined. The nuclear wind will fundamentally alter the interstellar medium of the host galaxy. Powerful radio galaxies and quasars can evacuate the entire ISM of their host galaxy. In an isolated elliptical galaxy, winds from moderately powerful radio galaxies will either be confined to within about a kpc or evacuate the entire hot ISM. Even in the relatively high pressure ISM of elliptical galaxies winds containing only 1%-10% of the radiant luminosity of the active nucleus will extend to the narrow-line region. Therefore, nuclear winds are likely to control the properties of the narrow-line emission. Publication: The Astrophysical Journal Pub Date: July 1993 DOI: 10.1086/172860 Bibcode: 1993ApJ...411..581S Keywords: Active Galactic Nuclei; Active Galaxies; Elliptical Galaxies; Galactic Radiation; Interacting Galaxies; Supersonic Speed; Interstellar Matter; Seyfert Galaxies; Shock Wave Interaction; Star Clusters; Astrophysics; GALAXIES: NUCLEI; GALAXIES: SEYFERT; GALAXIES: ACTIVE; GALAXIES: ELLIPTICAL AND LENTICULAR; CD; SHOCK WAVES full text sources ADS | data products SIMBAD (2) Related Materials (1) Part 2: 1993ApJ...412...82S

H I streamers around M82 - Tidally disrupted outer gas disk

Our new VLA observations of M82 reveals a triangular central concentration of neutral atomic gas (1.9×10 8 M ○. ) and several ≥10 kpc long tidal streamers originating from M82 itself. The coincidence of the beginning of the tidal streamer with the flaring of the optical disk as well as the smooth continuation of the disk velocity field into the H I streamer strongly suggest the tidal disruption of the disk of M82, contrary to the widely proposed scenario of tidal stripping and gas accretion from its neighbor M81. The velocity characteristics of H I within M82 are that of disk rotation as seen in CO. The gas kinematics appear complex because of large velocity dispersions that may be due to a tidally induced bar potential and the interaction between the disk gas and the nuclear wind

Nuclear winds in active elliptical galaxies. II - Observational signatures

We discuss the possible observational signatures resulting from the interaction of a nuclear wind with an elliptical host galaxy. The ionization parameter in emission-line gas, deduced from spatially resolved spectral observations, will be a strong indicator of the nuclear wind as well as the possible pickup of stellar mass loss by the wind. If the wind is sufficiently luminous, galactic X-ray profiles will exhibit an extended flattening. Detailed study of individual objects will be necessary for conclusive evidence of nuclear winds. We find that nuclear winds are unlikely to cause the disruption of the radio jets in wide-angle tail radio galaxies. Previously proposed mechanisms whereby nuclear winds cause the formation of narrow absorption line systems or stellar shells are not likely to occur if the interstellar medium of the host elliptical galaxy is hot.

Nuclear winds and the narrow-line emission from active galaxies

This paper discusses active galaxy narrow-line emission in the context of a supersonic wind generated by the active nucleus, a nuclear wind. Wind acceleration can naturally produce the inferred narrow-line cloud velocities as well as those of the broad-line and broad absorption line clouds with only a weak dependence on the parameters of the active nucleus. The primary obstacle to wind acceleration of emission-line clouds is the destructive effect of instabilities; however, the stability and structure of wind-confined clouds remain areas of future research. Observations, particularly of the Seyfert galaxy NGC 1068, are interpreted in the context of nuclear winds.