The Effects of X-Ray Feedback from AGN on Host Galaxy Evolution

Hydrodynamic simulations of galaxies with active galactic nuclei (AGN) have typically employed feedback that is purely local: i.e., an injection of energy to the immediate neighborhood of the black hole. We perform GADGET-2 simulations of massive elliptical galaxies with an additional feedback component: an observationally calibrated X-ray radiation field which emanates from the black hole and heats gas out to large radii from the galaxy center. We find that including the heating and radiation pressure associated with this X-ray flux in our simulations enhances the effects which are commonly reported from AGN feedback. This new feedback model is twice as effective as traditional feedback at suppressing star formation, produces 3 times less star formation in the last 6 Gyr, and modestly lowers the final BH mass (30%). It is also significantly more effective than an X-ray background in reducing the number of satellite galaxies.Comment: 9 emulateapj pages, 8 figures; accepted to Ap

Calibration for IR measurements of OH in apatite

abstract In this work, we have calibrated the infrared (IR) method for determining OH concentrations in apatite with absolute concentrations obtained through elastic recoil detection (ERD) analysis. IR spectra were collected on oriented, single-crystal apatite samples using polarized transmission infrared spectroscopy. The weight percent H 2 O is 0.001199 ± 0.000029 (the error is given at 1σ level hereafter) times A/d, where A is the linear absorbance peak height measured using polarized IR when the light vector E is parallel to the c-axis of the apatite crystal, and d is the sample thickness in centimeters. This corresponds to a linear molar absorptivity, ε = 470 ± 11 L/mol/cm -1 . The calibration using linear absorbance can be applied when there is only one dominant peak at 3540 cm -1 . If other peaks are significant, then the integrated molar absorptivity, ε = (2.31 ± 0.06) ×10 4 L/mol/cm 2 , should be used. The detection limit of H 2 O concentration in apatite by IR approaches parts per million level for wafers of 0.1 mm thickness. The accuracy based on our calibration is 5-10% relative

X-ray diffraction studies of GaN p-i-n structures for high power electronics

We have investigated the influence of the ambient exposure and/or ICP etching on the structure and properties of GaN p-i-n structures for high power electronics. To quantify the concentration of various native and extrinsic point defects, we utilize a combination of ion beam analyses in conjunction with x-ray diffraction. The full width at half max (FWHM) of phi and omega scans were used to quantify the mosaicity and threading dislocation (TD) densities at the p-i interfaces. The lowest densities of c-type and highest densities a-type TD components are observed for the “in-situ” GaN structure, which also produces the highest interfacial donor-acceptor pair (DAP) cathodoluminescence (CL) emissions. Interestingly, elastic recoil detection analysis (ERDA) and Rutherford backscattering spectroscopy reveal the lowest interfacial [H] but the highest fraction of displaced Ga atoms, suggesting efficient incorporation of MgGa in the in-situ structure. On the other hand, for the ex-situ structures, minimal interfacial [H] is also observed, but the lowest interfacial NBE and DAP CL emission is apparent as well as the highest density of c-type TD components. The relationship between interfacial [H], displaced Ga, CL emission features, and c- and a-type dislocation densities will be discussed.http://deepblue.lib.umich.edu/bitstream/2027.42/169564/1/zimmerman-alex-capstone-report.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/169564/2/Zimmerman-Alex-Honors-Capstone-Poster.pd

Shallow Dark Matter Cusps in Galaxy Clusters

We study the evolution of the stellar and dark matter components in a galaxy cluster of $10^{15} \, \rm{M_{\odot}}$ from $z=3$ to the present epoch using the high-resolution collisionless simulations of Ruszkowski & Springel (2009). At $z=3$ the dominant progenitor halos were populated with spherical model galaxies with and without accounting for adiabatic contraction. We apply a weighting scheme which allows us to change the relative amount of dark and stellar material assigned to each simulation particle in order to produce luminous properties which agree better with abundance matching arguments and observed bulge sizes at $z=3$. This permits the study of the effect of initial compactness on the evolution of the mass-size relation. We find that for more compact initial stellar distributions the size of the final Brightest Cluster Galaxy grows with mass according to $r\propto M^{2}$, whereas for more extended initial distributions, $r\propto M$. Our results show that collisionless mergers in a cosmological context can reduce the strength of inner dark matter cusps with changes in logarithmic slope of 0.3 to 0.5 at fixed radius. Shallow cusps such as those found recently in several strong lensing clusters thus do not necessarily conflict with CDM, but may rather reflect on the initial structure of the progenitor galaxies, which was shaped at high redshift by their formation process.Comment: 8 pages, 4 figures, submitted to MNRA

On the kinetics of the removal of ligands from films of colloidal nanocrystals by plasmas

This paper describes the kinetic limitations of etching ligands from colloidal nanocrystal assemblies (CNAs) by plasma processing. We measured the etching kinetics of ligands from a CNA model system (spherical ZrO2 nanocrystals, 2.5–3.5 nm diameter, capped with trioctylphosphine oxide) with inductively coupled plasmas (He and O2 feed gases, powers ranging from 7 to 30 W, at pressures ranging from 100 to 2000 mTorr and exposure times ranging between 6 and 168 h). The etching rate slows down by about one order of magnitude in the first minutes of etching, after which the rate of carbon removal becomes proportional to the third power of the carbon concentration in the CNA. Pressure oscillations in the plasma chamber significantly accelerate the overall rate of etching. These results indicate that the rate of etching is mostly affected by two main factors: (i) the crosslinking of the ligands in the first stage of plasma exposure, and (ii) the formation of a boundary layer at the surface of the CNA. Optimized conditions of plasma processing allow for a 60-fold improvement in etching rates compared to the previous state of the art and make the timeframes of plasma processing comparable to those of calcination

Calcination does not remove all carbon from colloidal nanocrystal assemblies

Removing organics from hybrid nanostructures is a crucial step in many bottom-up materials fabrication approaches. It is usually assumed that calcination is an effective solution to this problem, especially for thin films. This assumption has led to its application in thousands of papers. We here show that this general assumption is incorrect by using a relevant and highly controlled model system consisting of thin films of ligand-capped ZrO2 nanocrystals. After calcination at 800 °C for 12 h, while Raman spectroscopy fails to detect the ligands after calcination, elastic backscattering spectrometry characterization demonstrates that ~18% of the original carbon atoms are still present in the film. By comparison plasma processing successfully removes the ligands. Our growth kinetic analysis shows that the calcined materials have significantly different interfacial properties than the plasma-processed counterparts. Calcination is not a reliable strategy for the production of single-phase all-inorganic materials from colloidal nanoparticles

Flow-Driven Cloud Formation and Fragmentation: Results From Eulerian and Lagrangian Simulations

The fragmentation of shocked flows in a thermally bistable medium provides a natural mechanism to form turbulent cold clouds as precursors to molecular clouds. Yet because of the large density and temperature differences and the range of dynamical scales involved, following this process with numerical simulations is challenging. We compare two-dimensional simulations of flow-driven cloud formation without self-gravity, using the Lagrangian Smoothed Particle Hydrodynamics (SPH) code VINE and the Eulerian grid code Proteus. Results are qualitatively similar for both methods, yet the variable spatial resolution of the SPH method leads to smaller fragments and thinner filaments, rendering the overall morphologies different. Thermal and hydro-dynamical instabilities lead to rapid cooling and fragmentation into cold clumps with temperatures below 300K. For clumps more massive than 1 Msun/pc, the clump mass function has an average slope of -0.8. The internal velocity dispersion of the clumps is nearly an order of magnitude smaller than their relative motion, rendering it subsonic with respect to the internal sound speed of the clumps, but supersonic as seen by an external observer. For the SPH simulations most of the cold gas resides at temperatures below 100K, while the grid-based models show an additional, substantial component between 100 and 300K. Independently of the numerical method our models confirm that converging flows of warm neutral gas fragment rapidly and form high-density, low-temperature clumps as possible seeds for star formation.Comment: 9 pages, 8 figures, MNRAS accepte

Driving Turbulence and Triggering Star Formation by Ionizing Radiation

We present high resolution simulations on the impact of ionizing radiation of massive O-stars on the surrounding turbulent interstellar medium (ISM). The simulations are performed with the newly developed software iVINE which combines ionization with smoothed particle hydrodynamics (SPH) and gravitational forces. We show that radiation from hot stars penetrates the ISM, efficiently heats cold low density gas and amplifies over-densities seeded by the initial turbulence. The formation of observed pillar-like structures in star forming regions (e.g. in M16) can be explained by this scenario. At the tip of the pillars gravitational collapse can be induced, eventually leading to the formation of low mass stars. Detailed analysis of the evolution of the turbulent spectra shows that UV-radiation of O-stars indeed provides an excellent mechanism to sustain and even drive turbulence in the parental molecular cloud.Comment: 5 pages, 2 figures, accepted by ApJ Letter

Ion Beam Analyses of Carbon Nanotubes

This article discusses ion beam analyses of carbon nanotubes