Inflow Generated X-ray Corona Around Supermassive Black Holes and Unified Model for X-ray Emission

Three-dimensional hydrodynamic simulations, covering the spatial domain from hundreds of Schwarzschild radii to $2\ \mathrm{pc}$ around the central supermassive black hole of mass $10^8 M_\odot$, with detailed radiative cooling processes, are performed. Generically found is the existence of a significant amount of shock heated, high temperature ($\geq 10^8\ \mathrm{K}$) coronal gas in the inner ($\leq 10^4 r_\mathrm{sch}$) region. It is shown that the composite bremsstrahlung emission spectrum due to coronal gas of various temperatures are in reasonable agreement with the overall ensemble spectrum of AGNs and hard X-ray background. Taking into account inverse Compton processes, in the context of the simulation-produced coronal gas, our model can readily account for the wide variety of AGN spectral shape, which can now be understood physically. The distinguishing feature of our model is that X-ray coronal gas is, for the first time, an integral part of the inflow gas and its observable characteristics are physically coupled to the concomitant inflow gas. One natural prediction of our model is the anti-correlation between accretion disk luminosity and spectral hardness: as the luminosity of SMBH accretion disk decreases, the hard X-ray luminosity increases relative to the UV/optical luminosity.Comment: 37 pages, 12 figures; to appear on Ap

Wind-driven Accretion in Transitional Protostellar Disks

Transitional protostellar disks have inner cavities heavily depleted in dust and gas, yet most show signs of ongoing accretion, often at rates comparable to full disks. We show that recent constraints on the gas surface density in a few well-studied disk cavities imply that the accretion speed is at least transsonic. We propose that this is the natural result of accretion driven by magnetized winds. Typical physical conditions of the gas inside such cavities are estimated for plausible X-ray and FUV radiation fields. The gas is molecular and predominantly neutral, with a dimensionless ambipolar parameter in the right general range for wind solutions of the type developed by K\"onigl, Wardle, and others. That is to say, the density of ions and electrons is sufficient for moderately good coupling to the magnetic field, but not so good that the magnetic flux need be dragged inward by the accreting neutrals.Comment: 7 pages, 2 figures; submitted to Ap

An analytic model for redshift-space distortions

Understanding the formation and evolution of large-scale structure is a central problem in cosmology and enables precise tests of General Relativity on cosmological scales and constraints on dark energy. An essential ingredient is an accurate description of the pairwise velocities of biased tracers of the matter field. In this paper we compute the first and second moments of the pairwise velocity distribution by extending the Convolution Lagrangian Perturbation theory (CLPT) formalism of Carlson et al. (2012). Our predictions outperform standard perturbation theory calculations in many cases when compared to statistics measured in N-body simulations. We combine the CLPT predictions of real-space clustering and velocity statistics in the Gaussian streaming model of Reid & White (2011) to obtain predictions for the monopole and quadrupole correlation functions accurate to 2 and 4 per cent respectively down to <25Mpc/h for halos hosting the massive galaxies observed by SDSS-III BOSS. We also discuss contours of the 2D correlation function and clustering "wedges". We generalize the scheme to cross-correlation functions.Comment: 12 pages, 12 figures. Minor modifications to match version accepted by MNRA

Global Simulations of Protoplanetary Disk Outflows with Coupled Non-ideal Magnetohydrodynamics and Consistent Thermochemistry

Magnetized winds may be important in dispersing protoplanetary disks and influencing planet formation. We carry out global full magnetohydrodynamic simulations in axisymmetry, coupled with ray-tracing radiative transfer, consistent thermochemistry, and non-ideal MHD diffusivities. Magnetized models lacking EUV photons ($h\nu>13.6\ \mathrm{eV}$) feature warm molecular outflows that have typical poloidal speeds $\gtrsim 4\ \mathrm{km\ s}^{-1}$. When the magnetization is sufficient to drive accretion rates $\sim 10^{-8}\ M_\odot\ \mathrm{yr}^{-1}$, the wind mass-loss rate is comparable. Such outflows are driven not centrifugally but by the pressure of toroidal magnetic fields produced by bending the poloidal field. Both the accretion and outflow rates increase with the poloidal field energy density, the former almost linearly. The mass-loss rate is also strongly affected by ionization due to UV and X-ray radiation near the wind base. Adding EUV irradiation to the system heats, ionizes, and accelerates the part of the outflow nearest the symmetry axis, but reduces the overall mass-loss rate by exerting pressure on the wind base. Most of our models are non-turbulent, but some with reduced dust abundance and therefore higher ionization fractions exhibit magnetorotational instabilities near the base of the wind.Comment: 25 pages, 16 figures; submitted to Ap

Assessing the Constraints and Opportunities for Private Sector Participation in Activities Implemented Jointly: Two Case Studies From the U.S. Initiative for Joint Implementation

This paper assesses the constraints and opportunities for private-sector participation in Activities Implemented Jointly under the United Nations Framework Convention on Climate Change. After some initial background, the discussion turns to the United States Initiative on Joint Implementation (USIJI)—its objectives, proposal review and evaluation criteria, and a classification of project proposals by project type and stage of development. Two USIJI projects are developed as case studies. One case is an energy end use project that has gained formal acceptance and financing. The other case is an energy production project proposal that has not secured acceptance or financing. In both cases, transaction costs were substantial, and project proponents regarded gaining formal host country acceptance as the principal impediment to project development. The cases illustrate how the host country JI project approval process can become entangled in broader struggles over economic reforms. The cases also suggest that JI project proponents may have divergent perspectives on the speculative value of greenhouse gas (GHG) credits. An enforceable cap on GHG emissions in the project funders’ countries, which is a prerequisite to establishing any market for the credits, is contrary to the position of energy and power suppliers who promote voluntary emissions reductions. For emissions reduction technology firms, however, establishing a value for GHG credits would help generate demand for the firms’ stock in trade. Finally, the study underscores that notwithstanding transaction costs associated with JI proposal development and acceptance, financing remains the ultimate hurdle to project implementation.

Implementing the Clean Development Mechanism: Lessons from U.S. Private-Sector Participation in Activities Implemented Jointly

The "Clean Development Mechanism" (CDM) contained in the December 1997 Kyoto Protocol to the United Nations Framework Convention on Climate Change provides, for the first time, the capacity for industrialized countries to claim credits for greenhouse gas (GHG) emissions reductions or offsets undertaken in cooperation with host developing countries. However, the Protocol provides no guidance on how these cooperative activities for GHG reduction and sustainable development would be undertaken in practice, including the particularly important issue of the relationship of the private sector vis-à-vis government institutions in designing, financing, and securing approval for jointly implemented GHG abatement projects. The pilot program for "Activities Implemented Jointly" under the Framework Convention provides an opportunity to better understand the practical constraints and opportunities for successful private sector participation in the CDM. This paper highlights some of the lessons for establishing a successful CDM by examining a small number of cases from the United States Initiative on Joint Implementation (USIJI). The authors first review the objectives, proposal review and evaluation criteria of this program, and provide some overall information on project proposals by project type and stage of development. They then develop case studies of two energy-related USIJI projects from the earlier phase of the program. These cases illustrate several potential problems that can arise in establishing CDM transactions. Further investigation of more recent cases sheds some light on the extent to which these problems change over time. To be successful, the CDM must be based on a solid institutional footing, with clear incentives for all parties involved. The cases examined here illustrate how transactions can become entangled in the same kinds of problems that bedevil other transactions in developing and transitional economies. In both early cases, "transaction costs" were substantial. The latter projects indicated that while the nature of transactions costs changed over time, they still remained somewhat substantial. Project proponents regarded gaining USIJI acceptance as one of the principal impediments to JI project development. The cases also illustrate the need for clear and widely understood goals and procedures for investor country approval. In addition, the analysis underscores how attitudes of different project proponents regarding the value of GHG credits can affect their perspective on the transaction. Finally, the study underscores that financing remains the ultimate hurdle to project implementation, and that the expectation of a clear financial return on investment is a prerequisite to a successful project.

Hydrodynamic Photoevaporation of Protoplanetary Disks with Consistent Thermochemistry

Photoevaporation is an important dispersal mechanism for protoplanetary disks. We conduct hydrodynamic simulations coupled with ray-tracing radiative transfer and consistent thermochemistry to study photoevaporative winds driven by ultraviolet and X-ray radiation from the host star. Most models have a three-layer structure: a cold midplane, warm intermediate layer, and hot wind, the last having typical speeds $\sim 30~\mathrm{km\ s}^{-1}$ and mass-loss rates $\sim 10^{-9}~M_\odot~\mathrm{yr}^{-1}$ when driven primarily by ionizing UV radiation. Observable molecules including CO, OH and H2O re-form in the intermediate layer and survive at relatively high wind temperatures due to reactions being out of equilibrium. Mass-loss rates are sensitive to the intensity of radiation in energy bands that interact directly with hydrogen. Comparison with previous works shows that mass loss rates are also sensitive to the treatment of both the hydrodynamics and the thermochemistry. Divergent results concerning the efficiency of X-ray photoevaporation are traced in part to differing assumptions about dust and other coolants.Comment: 15 pages, 9 figures, submitted to Ap