On the disappearance of a cold molecular torus around the low-luminosity active galactic nucleus of NGC 1097

We used the Atacama Large Millimeter/submillimeter Array (ALMA) to map the CO(3-2) and the underlying continuum emissions around the type 1 low-luminosity active galactic nucleus (LLAGN; bolometric luminosity $\lesssim 10^{42}$ erg~s$^{-1}$) of NGC 1097 at $\sim 10$ pc resolution. These observations revealed a detailed cold gas distribution within a $\sim 100$ pc of this LLAGN. In contrast to the luminous Seyfert galaxy NGC 1068, where a $\sim 7$ pc cold molecular torus was recently revealed, a distinctively dense and compact torus is missing in our CO(3-2) integrated intensity map of NGC 1097. Based on the CO(3-2) flux, the gas mass of the torus of NGC 1097 would be a factor of $\gtrsim 2-3$ less than that found for NGC 1068 by using the same CO-to-H$_2$ conversion factor, which implies less active nuclear star formation and/or inflows in NGC 1097. Our dynamical modeling of the CO(3-2) velocity field implies that the cold molecular gas is concentrated in a thin layer as compared to the hot gas traced by the 2.12 $\mu$m H$_2$ emission in and around the torus. Furthermore, we suggest that NGC 1097 hosts a geometrically thinner torus than NGC 1068. Although the physical origin of the torus thickness remains unclear, our observations support a theoretical prediction that geometrically thick tori with high opacity will become deficient as AGNs evolve from luminous Seyferts to LLAGNs.Comment: 9 pages, 5 figures. Accepted for publication in ApJ

A diversity of dusty AGN tori: Data release for the VLTI/MIDI AGN Large Program and first results for 23 galaxies

The AGN-heated dust distribution (the "torus") is increasingly recognized not only as the absorber required in unifying models, but as a tracer for the reservoir that feeds the nuclear Super-Massive Black Hole. Yet, even its most basic structural properties (such as its extent, geometry and elongation) are unknown for all but a few archetypal objects. Since most AGNs are unresolved in the mid-infrared, we utilize the MID-infrared interferometric Instrument (MIDI) at the Very Large Telescope Interferometer (VLTI) that is sensitive to structures as small as a few milli-arcseconds (mas). We present here an extensive amount of new interferometric observations from the MIDI AGN Large Program (2009 - 2011) and add data from the archive to give a complete view of the existing MIDI observations of AGNs. Additionally, we have obtained high-quality mid-infrared spectra from VLT/VISIR. We present correlated and total flux spectra for 23 AGNs and derive flux and size estimates at 12 micron using simple axisymmetric geometrical models. Perhaps the most surprising result is the relatively high level of unresolved flux and its large scatter: The median "point source fraction" is 70 % for type 1 and 47 % for type 2 AGNs meaning that a large part of the flux is concentrated on scales smaller than about 5 mas (0.1 - 10 pc). Among sources observed with similar spatial resolution, it varies from 20 % - 100 %. For 18 of the sources, two nuclear components can be distinguished in the radial fits. While these models provide good fits to all but the brightest sources, significant elongations are detected in eight sources. The half-light radii of the fainter sources are smaller than expected from the size ~ L^0.5 scaling of the bright sources and show a large scatter, especially when compared to the relatively tight size--luminosity relation in the near-infrared.Comment: A&A in press; 93 pages, 63 figures, 39 tables; data available only via CD

Structural Behavior of Inflatable, Reinforced, Braided, Tubular Members

The Hypersonic Inflatable Aerodynamic Decelerator (HIAD) system being developed by the National Aeronautics and Space Administration (NASA) is an inflatable structure composed of multiple, concentric, pressurized tori, load straps, and a thermal protection system. The HIAD overcomes limitations inherent with the use of rigid decelerators since the deployed diameter is much larger than the packed size, which makes it an enabling technology for new opportunities in space exploration. The HIAD is designed to decelerate and protect spacecraft during atmospheric re-entry. The objective of this research was to improve understanding of structural behavior of HIAD components through material testing, structural testing of components, and numerical models. The mechanics of inflatable, reinforced braided tubes have been reviewed from a geometric standpoint. Exploratory experimental efforts were performed to quantify the stiffness of the reinforcing cords, which drive axial and bending stiffness of the inflatable tubes. Benchtop inflation tests were performed to quantify longitudinal stiffness and examine instrumentation methods. The constitutive properties of the braided fabric shell of tori were determined as a function of braid angle and inflation pressure. The shear modulus is highly dependent on braid angle and pressure. Independent testing of extracted fiber tow bundles allowed the effect of de-crimping to be examined with straight tow thickness measured as an upper limit. Beam bending tests of straight beams with highly controlled loading and boundary conditions were performed for tubes with five different braid angles over a range of inflation pressures. These data sets are ideal for finite element validation due to the highly controlled conditions. Structural testing of individual tori was performed via radial compression loading. Many improvements were made to the single torus test setup using fixtures provided by NASA. Methods were developed to quantify the 3D shape of the tori and displacements using non-contact photogrammetry methods. The effect of load-control versus displacement-control experiments was investigated and found to result in different response. Finite-element models using three-dimensional shell-elements were developed and compared to the torus experiments. These modeling efforts proved to be challenging and no firm conclusions could be drawn

Stellar masers, circumstellar envelopes, and supernova remnants

This paper reviews recent advances in the study or circumstellar masers and masers found toward supernova remnants. The review is organized by science focus area, including the astrophysics of extended stellar atmospheres, stellar mass-loss processes and outflows, late-type evolved stellar evolution, stellar maser excitation and chemistry, and the use of stellar masers as independent distance estimators. Masers toward supernova remnants are covered separately. Recent advances and open future questions in this field are explored.Comment: 16 pages, 2 figures, 2 tables: based on a review talk presented at IAU Symposium 242: Astrophysical masers and their environments, held at Alice Springs (Australia), March 12-16, 200

Nonlinear Hamiltonian dynamics of Lagrangian transport and mixing in the ocean

Methods of dynamical system's theory are used for numerical study of transport and mixing of passive particles (water masses, temperature, salinity, pollutants, etc.) in simple kinematic ocean models composed with the main Eulerian coherent structures in a randomly fluctuating ocean -- a jet-like current and an eddy. Advection of passive tracers in a periodically-driven flow consisting of a background stream and an eddy (the model inspired by the phenomenon of topographic eddies over mountains in the ocean and atmosphere) is analyzed as an example of chaotic particle's scattering and transport. A numerical analysis reveals a nonattracting chaotic invariant set $\Lambda$ that determines scattering and trapping of particles from the incoming flow. It is shown that both the trapping time for particles in the mixing region and the number of times their trajectories wind around the vortex have hierarchical fractal structure as functions of the initial particle's coordinates. Scattering functions are singular on a Cantor set of initial conditions, and this property should manifest itself by strong fluctuations of quantities measured in experiments. The Lagrangian structures in our numerical experiments are shown to be similar to those found in a recent laboratory dye experiment at Woods Hole. Transport and mixing of passive particles is studied in the kinematic model inspired by the interaction of a jet current (like the Gulf Stream or the Kuroshio) with an eddy in a noisy environment. We demonstrate a non-trivial phenomenon of noise-induced clustering of passive particles and propose a method to find such clusters in numerical experiments. These clusters are patches of advected particles which can move together in a random velocity field for comparatively long time

Parsec-Scale Images of Flat-Spectrum Radio Sources in Seyfert Galaxies

We present high angular resolution (~2 mas) radio continuum observations of five Seyfert galaxies with flat-spectrum radio nuclei, using the VLBA at 8.4 GHz. The goal of the project is to test whether these flat-spectrum cores represent thermal emission from the accretion disk, as inferred previously by Gallimore et al. for NGC 1068, or non-thermal, synchrotron self-absorbed emission, which is believed to be responsible for more powerful, flat-spectrum nuclear sources in radio galaxies and quasars. In four sources (T0109-383, NGC 2110, NGC 5252, Mrk 926), the nuclear source is detected but unresolved by the VLBA, indicating brightness temperatures in excess of 10^8 K and sizes, on average, less than 1 pc. We argue that the radio emission is non-thermal and synchrotron self-absorbed in these galaxies, but Doppler boosting by relativistic outflows is not required. Synchrotron self-absorption brightness temperatures suggest intrinsic source sizes smaller than ~0.05-0.2 pc, for these four galaxies, the smallest of which corresponds to a light-crossing time of ~60 light days or 10^4 gravitational radii for a 10^8 M_sun black hole. We also present MERLIN and VLA observations of NGC 4388, which was undetected by the VLBA, and argue that the observed, flat-spectrum, nuclear radio emission in this galaxy represents optically thin, free-free radiation from dense thermal gas on scales ~0.4 to a few pc. It is notable that the two Seyfert galaxies with detected thermal nuclear radio emission (NGC 1068 and NGC 4388) both have large X-ray absorbing columns, suggesting that columns in excess of \~10^{24} cm^{-2} are needed for such disks to be detectable. (Abridged)Comment: 36 pages including 5 tables and 4 figures; accepted for publication in Ap

The SKA and "High-Resolution" Science

"High-resolution", or "long-baseline", science with the SKA and its precursors covers a broad range of topics in astrophysics. In several research areas, the coupling between improved brightness sensitivity of the SKA and a sub-arcsecond resolution would uncover truly unique avenues and opportunities for studying extreme states of matter, vicinity of compact relativistic objects, and complex processes in astrophysical plasmas. At the same time, long baselines would secure excellent positional and astrometric measurements with the SKA and critically enhance SKA image fidelity at all scales. The latter aspect may also have a substantial impact on the survey speed of the SKA, thus affecting several key science projects of the instrument.Comment: JENAM-2010: Invited talk at JENAM session S7: The Square Kilometre Array: Paving the way for the new 21st century radio astronomy paradigm; 9 page

Signatures of the disk-jet coupling in the Broad-line Radio Quasar 4C+74.26

Here we explore the disk-jet connection in the broad-line radio quasar 4C+74.26, utilizing the results of the multiwavelength monitoring of the source. The target is unique in that its radiative output at radio wavelengths is dominated by a moderately-beamed nuclear jet, at optical frequencies by the accretion disk, and in the hard X-ray range by the disk corona. Our analysis reveals a correlation (local and global significance of 96\% and 98\%, respectively) between the optical and radio bands, with the disk lagging behind the jet by $250 \pm 42$ days. We discuss the possible explanation for this, speculating that the observed disk and the jet flux changes are generated by magnetic fluctuations originating within the innermost parts of a truncated disk, and that the lag is related to a delayed radiative response of the disk when compared with the propagation timescale of magnetic perturbations along relativistic outflow. This scenario is supported by the re-analysis of the NuSTAR data, modelled in terms of a relativistic reflection from the disk illuminated by the coronal emission, which returns the inner disk radius $R_{\rm in}/R_{\rm ISCO} =35^{+40}_{-16}$. We discuss the global energetics in the system, arguing that while the accretion proceeds at the Eddington rate, with the accretion-related bolometric luminosity $L_{\rm bol} \sim 9 \times 10^{46}$ erg s$^{-1}$ $\sim 0.2 L_{\rm Edd}$, the jet total kinetic energy $L_\textrm{j} \sim 4 \times 10^{44}$ erg s$^{-1}$, inferred from the dynamical modelling of the giant radio lobes in the source, constitutes only a small fraction of the available accretion power.Comment: 9 pages and 6 figures, ApJ accepte

Intraspecific and interspecific variation in the xylem functional traits of Callitris species growing along an aridity gradient

More severe and prolonged drought events as a result of climate change, have the potential to cause broad scale forest and woodland dieback worldwide. The Australian continent is primarily comprised of arid biomes. However, rapid climate change-induced desertification threatens these surprisingly diverse ecosystems. Callitris is Australia’s most successful conifer genus, yet they remain they remain vulnerable to drought-induced decline. Given Callitris are the primary structural component of vegetation in many Arid-Australian ecosystems, their persistence is the most important factor preventing the collapse of these ecosystems. Resistance to drought-induced xylem cavitation has emerged as a key physiological trait determining the survival of tree species under water-limited conditions. Under the influence of aridity, Callitris have evolved the world’s most cavitation resistant xylem, yet little is known about the xylem anatomy liable to convey this. The main objective of this thesis was to identify the anatomical xylem traits and attributes associated with cavitation resistance in Callitris. The main body of work in this thesis involved analysis of microscopic anatomical traits through the use and development of several microscopy techniques. An inter-specific study produced a complementary dataset of xylem anatomical traits for branches of 15 Callitris and closely related species, building on the physiological dataset by Larter et al. (2017). An intraspecific study among five C. glaucophylla populations required the physiological and anatomical traits measurements. An intraspecific increase in cavitation resistance with aridity was found among the five populations in both the primary branches and roots. To understand whole plant hydraulic function, variability in xylem anatomical traits in the tertiary branches, secondary branches and trunks, of C. glaucophylla, in relation to the primary branches and roots was also explored. A greenhouse experiment tested the plasticity of anatomical traits in C. glaucophylla seedlings grown under contrasting water treatments. Mainly, among seedlings grown under well-watered conditions, height growth and more hydraulically efficient roots are prioritised, while more mechanically reinforced tracheids and safer but less efficient pit traits are favoured among seedling grown under water deficit

Large Payload HIAD Systems: Development of Computationally Efficient Modeling Strategies and Structural Investigations

The hypersonic inflatable aerodynamic decelerator (HIAD) system under development by the National Aeronautics and Space Administration (NASA) has the potential to deliver the size of payloads to the Martian surface that will be necessary for future human-scale missions. An important step in realizing the promise of the HIAD system is to understand the structural behavior of this inflatable, textile, relatively compliant system. This is accomplished through structural testing and the development of structural modeling and analysis methodologies and tools. The structural modeling tools that have been developed to date utilize a continuum, shell-based finite element (FE) analysis approach. This methodology is capable of capturing the structural response of the HIAD system, but the models are time intensive to develop, difficult to parameterize and computationally intensive to run. In this dissertation a computationally efficient, beam-based FE modeling approach is developed. The beam-based modeling methodology addresses the challenges that are encountered in analyzing an inflatable, textile system, such as the effect of internal inflation pressure, nonlinear material response, the loss of pretension due to inflation pressure during loading, and the large deformations that occur as a result of having relatively compliant system. Material models are developed for use with both shell and beam-based FE models. A three-dimensional, corotational, flexibility-based, fiber beam modelling methodology is developed for the inflatable, braided members with axial reinforcing cords. The modeling methodology and tools are applied to the analysis of component level inflatable tubes and the single torus structures that make up the HIAD system. Initial validation of the modeling strategy is accomplished by comparing model predictions and parallel experiments conducted by others at the University of Maine. The modeling tools are then extended to analyze the full HIAD system, composed of multiple, stacked tori with straps. The interactions between tori are accounted for, along with the strap sets that connect tori to each other and to the center-body of the decelerator. The modeling methodology is then further validated by comparison with results from pressure tub testing of a full HIAD system conducted by NASA researchers. Following model development and validation, the analysis methodologies are used to investigate structural response of a full-scale HIAD devices. A number of configurations are investigated, including the influence of strap pretension and non-axisymmetric configurations and loading. The structural modeling tools are then coupled to optimization techniques to better understand the structural response drivers and demonstrate the feasibility of using the tools developed here in optimization studies