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Physics and Astronomy Faculty Publications

2011

Articles 1 - 20 of 20

Full-Text Articles in Physical Sciences and Mathematics

Fabrication Of All-Inorganic Nanocrystal Solids Through Matrix Encapsulation Of Nanocrystal Arrays, Erich Kinder, Pavel Moroz, Geoffrey Diederich, Alexa Johnson, Maria Kirsanova, Alexander Nemchinov, Timothy O’Connor, Dan Roth, Mikhail Zamkov Dec 2011

Fabrication Of All-Inorganic Nanocrystal Solids Through Matrix Encapsulation Of Nanocrystal Arrays, Erich Kinder, Pavel Moroz, Geoffrey Diederich, Alexa Johnson, Maria Kirsanova, Alexander Nemchinov, Timothy O’Connor, Dan Roth, Mikhail Zamkov

Physics and Astronomy Faculty Publications

A general strategy for low-temperature processing of colloidal nanocrystals into all-inorganic films is reported. The present methodology goes beyond the traditional ligand-interlinking scheme and relies on encapsulation of morphologically defined nanocrystal arrays into a matrix of a wide-band gap semiconductor, which preserves optoelectronic properties of individual nanoparticles while rendering the nanocrystal film photoconductive. Fabricated solids exhibit excellent thermal stability, which is attributed to the heteroepitaxial structure of nanocrystal matrix interfaces, and show compelling light-harvesting performance in prototype solar cells.

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Dipole-Dipole Interaction Between Rubidium Rydberg Atoms, Emily Altiere, Donald P. Fahey, Michael W. Noel, Rachel J. Smith, Thomas J. Carroll Nov 2011

Dipole-Dipole Interaction Between Rubidium Rydberg Atoms, Emily Altiere, Donald P. Fahey, Michael W. Noel, Rachel J. Smith, Thomas J. Carroll

Physics and Astronomy Faculty Publications

Ultracold Rydberg atoms in a static electric field can exchange energy via the dipole-dipole interaction. The Stark effect shifts the energy levels of the atoms which tunes the energy exchange into resonance at specific values of the electric field (F¨orster resonances). We excite rubidium atoms to Rydberg states by focusing either a 480 nm beam from a tunable dye laser or a pair of diode lasers into a magneto-optical trap. The trap lies at the center of a configuration of electrodes. We scan the electric field by controlling the voltage on the electrodes while measuring the fraction of atoms that …

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Critical Differences And Clues In Eta Car's 2009 Event, Andrea Mehner, Kris Davidson, John C. Martin, Roberta M. Humphreys, Kazunori Ishibashi, Gary J. Ferland Oct 2011

Critical Differences And Clues In Eta Car's 2009 Event, Andrea Mehner, Kris Davidson, John C. Martin, Roberta M. Humphreys, Kazunori Ishibashi, Gary J. Ferland

Physics and Astronomy Faculty Publications

We monitored Eta Carinae with the Hubble Space Telescope WFPC2 and Gemini GMOS throughout the 2009 spectroscopic event, which was expected to differ from its predecessor in 2003. Here we report major observed differences between events and their implications. Some of these results were quite unexpected. (1) The UV brightness minimum was much deeper in 2009. This suggests that physical conditions in the early stages of an event depend on different parameters than the "normal" inter-event wind. Extra mass ejection from the primary star is one possible cause. (2) The expected He II λ4687 brightness maximum was followed several weeks …

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Star Formation In Self-Gravitating Disks In Active Galactic Nuclei. I. Metallicity Gradients In Broad-Line Regions, Jian-Min Wang, Jun-Qiang Ge, Chen Hu, Jack A. Baldwin, Yan-Rong Li, Gary J. Ferland, Fei Xiang, Chang-Shuo Yan, Shu Zhang Aug 2011

Star Formation In Self-Gravitating Disks In Active Galactic Nuclei. I. Metallicity Gradients In Broad-Line Regions, Jian-Min Wang, Jun-Qiang Ge, Chen Hu, Jack A. Baldwin, Yan-Rong Li, Gary J. Ferland, Fei Xiang, Chang-Shuo Yan, Shu Zhang

Physics and Astronomy Faculty Publications

It has been suggested that the high metallicity generally observed in active galactic nuclei (AGNs) and quasars originates from ongoing star formation in the self-gravitating part of accretion disks around supermassive black holes (SMBHs). We designate this region as the star-forming (SF) disk, in which metals are produced from supernova explosions (SNexp) while at the same time inflows are driven by SNexp-excited turbulent viscosity to accrete onto the SMBHs. In this paper, an equation of metallicity governed by SNexp and radial advection is established to describe the metal distribution and evolution in the SF disk. We find that the metal …

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Galaxy Formation In Heavily Overdense Regions At Z ~ 10: The Prevalence Of Disks In Massive Halos, Emilio Romano-Díaz, Jun-Hwan Choi, Isaac Shlosman, Michele Trenti Aug 2011

Galaxy Formation In Heavily Overdense Regions At Z ~ 10: The Prevalence Of Disks In Massive Halos, Emilio Romano-Díaz, Jun-Hwan Choi, Isaac Shlosman, Michele Trenti

Physics and Astronomy Faculty Publications

Using a high-resolution cosmological numerical simulation, we have analyzed the evolution of galaxies at z ~ 10 in a highly overdense region of the universe. These objects could represent the high-redshift galaxies recently observed by the Hubble's Wide Field Camera 3 and could as well be possible precursors of QSOs at z ~ 6-7. To overcome the sampling and resolution problems in cosmological simulations of these rare regions, we have used the constrained realizations method. Our main result for z ~ 10 shows the high-resolution central region of 3.5 h–1 Mpc radius in comoving coordinates being completely dominated by …

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Structure And Feedback In 30 Doradus. Ii. Structure And Chemical Abundances, E. W. Pellegrini, J. A. Baldwin, Gary J. Ferland Aug 2011

Structure And Feedback In 30 Doradus. Ii. Structure And Chemical Abundances, E. W. Pellegrini, J. A. Baldwin, Gary J. Ferland

Physics and Astronomy Faculty Publications

We use our new optical-imaging and spectrophotometric survey of key diagnostic emission lines in 30 Doradus, together with CLOUDY photoionization models, to study the physical conditions and ionization mechanisms along over 4000 individual lines of sight at points spread across the face of the extended nebula, out to a projected radius 75 pc from R136 at the center of the ionizing cluster NGC 2070. We focus on the physical conditions, geometry, and importance of radiation pressure on a point-by-point basis, with the aim of setting observational constraints on important feedback processes. We find that the dynamics and large-scale structure of …

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N Ii Λλ5668−5712: A New Class Of Spectral Features In Eta Carinae, Andrea Mehner, Kris Davidson, Gary J. Ferland Aug 2011

N Ii Λλ5668−5712: A New Class Of Spectral Features In Eta Carinae, Andrea Mehner, Kris Davidson, Gary J. Ferland

Physics and Astronomy Faculty Publications

We report on the N II λλ5668-5712 emission and absorption lines in the spectrum of η Carinae. Spectral lines of the stellar wind regions can be classified into four physically distinct categories: (1) low-excitation emission such as H I and Fe II, (2) higher-excitation He I features, (3) the N II lines discussed in this paper, and (4) He II emission. These categories have different combinations of radial velocity behavior, excitation processes, and dependences on the secondary star. The N II lines are the only known features that originate in "normal" undisturbed zones of the primary wind but depend primarily …

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Torus And Active Galactic Nucleus Properties Of Nearby Seyfert Galaxies: Results From Fitting Infrared Spectral Energy Distributions And Spectroscopy, Almudena Alonso-Herrero, Almeida Cristina Ramos, Rachel Mason, Ramos Andrés Asensio, Patrick F. Roche, Nancy A. Levenson, Moshe Elitzur, Christopher Packham, José Miguel Rodríguez Espinosa, Stuart Young, Tanio Díaz-Santos, Ana M. Pérez-García Jul 2011

Torus And Active Galactic Nucleus Properties Of Nearby Seyfert Galaxies: Results From Fitting Infrared Spectral Energy Distributions And Spectroscopy, Almudena Alonso-Herrero, Almeida Cristina Ramos, Rachel Mason, Ramos Andrés Asensio, Patrick F. Roche, Nancy A. Levenson, Moshe Elitzur, Christopher Packham, José Miguel Rodríguez Espinosa, Stuart Young, Tanio Díaz-Santos, Ana M. Pérez-García

Physics and Astronomy Faculty Publications

We used the CLUMPY torus models and a Bayesian approach to fit the infrared spectral energy distributions and ground-based high angular resolution mid-infrared spectroscopy of 13 nearby Seyfert galaxies. This allowed us to put tight constraints on torus model parameters such as the viewing angle i, the radial thickness of the torus Y, the angular size of the cloud distribution σtorus, and the average number of clouds along radial equatorial rays N0. We found that the viewing angle i is not the only parameter controlling the classification of a galaxy into type 1 or …

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The Dark Side Of Qso Formation At High Redshifts, Emilio Romano-Díaz, Isaac Shlosman, Michele Trenti, Yehuda Hoffman Jul 2011

The Dark Side Of Qso Formation At High Redshifts, Emilio Romano-Díaz, Isaac Shlosman, Michele Trenti, Yehuda Hoffman

Physics and Astronomy Faculty Publications

Observed high-redshift QSOs, at z ~ 6, may reside in massive dark matter (DM) halos of more than 1012 M☉ and are thus expected to be surrounded by overdense regions. In a series of 10 constrained simulations, we have tested the environment of such QSOs. The usage of constrained realizations has enabled us to address the issue of cosmic variance and to study the statistical properties of the QSO host halos. Comparing the computed overdensities with respect to the unconstrained simulations of regions empty of QSOs, assuming there is no bias between the DM and baryon distributions, and …

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The Role Of Hole Localization In Sacrificial Hydrogen Production By Semiconductor-Metal Heterostructured Nanocrystals, Krishna P. Acharya, Rony S. Khnayzer, Timothy O’Connor, Geoffrey Diederich, Maria Kirsanova, Anna Klinkova, Daniel Roth, Erich Kinder, Martene Imboden, Mikhail Zamkov Jul 2011

The Role Of Hole Localization In Sacrificial Hydrogen Production By Semiconductor-Metal Heterostructured Nanocrystals, Krishna P. Acharya, Rony S. Khnayzer, Timothy O’Connor, Geoffrey Diederich, Maria Kirsanova, Anna Klinkova, Daniel Roth, Erich Kinder, Martene Imboden, Mikhail Zamkov

Physics and Astronomy Faculty Publications

The effect of hole localization on photocatalytic activity of Pt-tipped semiconductor nanocrystals is investigated. By tuning the energy balance at the semiconductor-ligand interface, we demonstrate that hydrogen production on Pt sites is efficient only when electron-donating molecules are used for stabilizing semiconductor surfaces. These surfactants play an important role in enabling an efficient and stable reduction of water by heterostructured nanocrystals as they fill vacancies in the valence band of the semiconductor domain, preventing its degradation. In particular, we show that the energy of oxidizing holes can be efficiently transferred to a ligand moiety, leaving the semiconductor domain intact. This …

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A Survey Of Molecular Hydrogen In The Crab Nebula, E. D. Loh, J. A. Baldwin, Z. K. Curtis, Gary J. Ferland, C. R. O'Dell, A. C. Fabian, Philippe Salomé May 2011

A Survey Of Molecular Hydrogen In The Crab Nebula, E. D. Loh, J. A. Baldwin, Z. K. Curtis, Gary J. Ferland, C. R. O'Dell, A. C. Fabian, Philippe Salomé

Physics and Astronomy Faculty Publications

We have carried out a near-infrared, narrowband imaging survey of the Crab Nebula, in the H2 2.12 μm and Brγ 2.17 μm lines, using the Spartan Infrared camera on the SOAR Telescope. Over a 2.8 × 5'.1 area that encompasses about 2/3 of the full visible extent of the Crab, we detect 55 knots that emit strongly in the H2 line. We catalog the observed properties of these knots. We show that they are in or next to the filaments that are seen in optical-passband emission lines. Comparison to Hubble Space Telescope [S …

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Physical Conditions In Barnard's Loop, Components Of The Orion-Eridanus Bubble, And Implications For The Warm Ionized Medium Component Of The Interstellar Medium, C. R. O'Dell, Gary J. Ferland, R. L. Porter, P. A. M. Vanhoof Apr 2011

Physical Conditions In Barnard's Loop, Components Of The Orion-Eridanus Bubble, And Implications For The Warm Ionized Medium Component Of The Interstellar Medium, C. R. O'Dell, Gary J. Ferland, R. L. Porter, P. A. M. Vanhoof

Physics and Astronomy Faculty Publications

We have supplemented existing spectra of Barnard's Loop with high accuracy spectrophotometry of one new position. Cloudy photoionization models were calculated for a variety of ionization parameters and stellar temperatures and compared with the observations. After testing the procedure with recent observations of M43, we establish that Barnard's Loop is photoionized by four candidate ionizing stars, but agreement between the models and observations is only possible if Barnard's Loop is enhanced in heavy elements by about a factor of 1.4. Barnard's Loop is very similar in properties to the brightest components of the Orion-Eridanus Bubble and the warm ionized medium …

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Emission From Hot Dust In The Infrared Spectra Of Gamma-Ray Bright Blazars, Michael P. Malmrose, Alan P. Marscher, Svetlana G. Jorstad, Robert Nikutta, Moshe Elitzur Apr 2011

Emission From Hot Dust In The Infrared Spectra Of Gamma-Ray Bright Blazars, Michael P. Malmrose, Alan P. Marscher, Svetlana G. Jorstad, Robert Nikutta, Moshe Elitzur

Physics and Astronomy Faculty Publications

A possible source of γ-ray photons observed from the jets of blazars is inverse Compton scattering by relativistic electrons of infrared seed photons from a hot, dusty torus in the nucleus. We use observations from the Spitzer Space Telescope to search for signatures of such dust in the infrared spectra of four γ-ray bright blazars, the quasars 4C 21.35, CTA102, and PKS 1510-089, and the BL Lacertae object ON231. The spectral energy distribution (SED) of 4C 21.35 contains a prominent infrared excess indicative of dust emission. After subtracting a non-thermal component with a power-law spectrum, we fit a …

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Local Origins Of Volume Fraction Fluctuations In Dense Granular Materials, James G. Puckett, Frederic Lechenault, Karen E. Daniels Apr 2011

Local Origins Of Volume Fraction Fluctuations In Dense Granular Materials, James G. Puckett, Frederic Lechenault, Karen E. Daniels

Physics and Astronomy Faculty Publications

Fluctuations of the local volume fraction within granular materials have previously been observed to decrease as the system approaches jamming.We experimentally examine the role of boundary conditions and interparticle friction μ on this relationship for a dense granular material of bidisperse particles driven under either constant volume or constant pressure.Using a radicalVorono¨ı tessellation, we find the variance of the local volume fraction φ monotonically decreases as the system becomes more dense, independent of boundary condition and μ. We examine the universality and origins of this trend using experiments and the recent granocentric model, modified to draw particle locations from an …

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Dusty Tori Of Luminous Type 1 Quasars At Z ~ 2, Rajesh P. Deo, Gordon T. Richards, Robert Nikutta, Moshe Elitzur, Sarah C. Gallagher, Željko Ivezić, Dean Hines Feb 2011

Dusty Tori Of Luminous Type 1 Quasars At Z ~ 2, Rajesh P. Deo, Gordon T. Richards, Robert Nikutta, Moshe Elitzur, Sarah C. Gallagher, Željko Ivezić, Dean Hines

Physics and Astronomy Faculty Publications

We present Spitzer infrared (IR) spectra and ultraviolet (UV) to mid-IR spectral energy distributions (SEDs) of 25 luminous type 1 quasars at z ~ 2. In general, the spectra show a bump peaking around 3 μm and the 10 μm silicate emission feature. The 3 μm emission is identified with hot dust emission at its sublimation temperature. We explore two approaches to modeling the SED: (1) using the CLUMPY model SED from Nenkova et al. and (2) the CLUMPY model SED and an additional blackbody component to represent the 3 μm emission. In the first case, …

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Spitzer Reveals What Is Behind Orion's Bar, Robert H. Rubin, Janet P. Simpson, C. R. O'Dell, Ian A. Mcnabb, Sean W. J. Colgan, Scott Y. Zhuge, Gary J. Ferland, Sergio A. Hidalgo Jan 2011

Spitzer Reveals What Is Behind Orion's Bar, Robert H. Rubin, Janet P. Simpson, C. R. O'Dell, Ian A. Mcnabb, Sean W. J. Colgan, Scott Y. Zhuge, Gary J. Ferland, Sergio A. Hidalgo

Physics and Astronomy Faculty Publications

We present Spitzer Space Telescope observations of 11 regions south-east (SE) of the Bright Bar in the Orion Nebula, along a radial from the exciting star θ1 Ori C, extending from 2.6 to 12.1 arcmin. Our Cycle 5 programme obtained deep spectra with matching Infrared Spectrograph (IRS) short-high (SH) and long-high (LH) aperture grid patterns. Most previous IR missions observed only the inner few arcmin (the ‘Huygens’ Region). The extreme sensitivity of Spitzer in the 10–37 μm spectral range permitted us to measure many lines of interest to much larger distances from θ1 Ori C. Orion is the …

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A Deep Spectroscopic Study Of The Filamentary Nebulosity In Ngc 4696, The Brightest Cluster Galaxy In The Centaurus Cluster, R. E. A. Canning, A. C. Fabian, R. M. Johnstone, J. S. Sanders, C. S. Crawford, Gary J. Ferland, N. A. Hatch Jan 2011

A Deep Spectroscopic Study Of The Filamentary Nebulosity In Ngc 4696, The Brightest Cluster Galaxy In The Centaurus Cluster, R. E. A. Canning, A. C. Fabian, R. M. Johnstone, J. S. Sanders, C. S. Crawford, Gary J. Ferland, N. A. Hatch

Physics and Astronomy Faculty Publications

We present results of deep integral-field spectroscopy observations using high-resolution optical (4150–7200 Å) VLT VIsible MultiObject Spectrograph spectra of NGC 4696, the dominant galaxy in the Centaurus cluster (Abell 3526). After the Virgo cluster, this is the second nearest (z= 0.0104) example of a cool-core cluster. NGC 4696 is surrounded by a vast, luminous Hα emission-line nebula (LHα= 2.2 × 1040 erg s−1). We explore the origin and excitation of the emission-line filaments and find their origin consistent with being drawn out, under rising radio bubbles, into the intracluster medium as in …

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Detection Of Optical Coronal Emission From 106-K Gas In The Core Of The Centaurus Cluster, R. E. A. Canning, A. C. Fabian, R. M. Johnstone, J. S. Sanders, C. S. Crawford, N. A. Hatch, Gary J. Ferland Jan 2011

Detection Of Optical Coronal Emission From 106-K Gas In The Core Of The Centaurus Cluster, R. E. A. Canning, A. C. Fabian, R. M. Johnstone, J. S. Sanders, C. S. Crawford, N. A. Hatch, Gary J. Ferland

Physics and Astronomy Faculty Publications

We report a detection (3.5 × 1037± 5.6 × 1036 erg s−1) of the optical coronal emission line [Fe X] λ6374 and upper limits of four other coronal lines using high-resolution VIMOS spectra centred on NGC 4696, the brightest cluster galaxy in the Centaurus cluster. Emission from these lines is indicative of gas at temperatures between 1 × 106−5 × 106 K, so traces the interstellar gas in NGC 4696. The rate of cooling derived from the upper limits is consistent with the cooling rate from X-ray observations (∼10 M⊙ yr …

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Herschel Observations Of The Centaurus Oluster - The Dynamics Of Cold Gas In A Cool Core, R. Mittal, C. P. O'Dea, Gary J. Ferland, J. B. R. Oonk, A. C. Edge, R. E. A. Canning, H. Russell, S. A. Baum, H. Böhringer, F. Combes, M. Donahue, A. C. Fabian, N. A. Hatch, A. Hoffer, R. Johnstone, B. R. Mcnamara, P. Salomé, G. Tremblay Jan 2011

Herschel Observations Of The Centaurus Oluster - The Dynamics Of Cold Gas In A Cool Core, R. Mittal, C. P. O'Dea, Gary J. Ferland, J. B. R. Oonk, A. C. Edge, R. E. A. Canning, H. Russell, S. A. Baum, H. Böhringer, F. Combes, M. Donahue, A. C. Fabian, N. A. Hatch, A. Hoffer, R. Johnstone, B. R. Mcnamara, P. Salomé, G. Tremblay

Physics and Astronomy Faculty Publications

Brightest cluster galaxies (BCGs) in the cores of galaxy clusters have distinctly different properties from other low-redshift massive ellipticals. The majority of the BCGs in cool-core clusters show signs of active star formation. We present observations of NGC 4696, the BCG of the Centaurus galaxy cluster, at far-infrared (FIR) wavelengths with theHerschel space telescope. Using the PACS spectrometer, we detect the two strongest coolants of the interstellar medium, [C II] at 157.74 μm and [O I] at 63.18 μm, and in addition [N II] at 121.90 μm. The [C II] emission is extended over a region of 7 kpc …

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The Energy Source Of The Filaments Around The Giant Galaxy Ngc 1275, A. C. Fabian, J. S. Sanders, R. J. R. Williams, A. Lazarian, Gary J. Ferland, R. M. Johnstone Jan 2011

The Energy Source Of The Filaments Around The Giant Galaxy Ngc 1275, A. C. Fabian, J. S. Sanders, R. J. R. Williams, A. Lazarian, Gary J. Ferland, R. M. Johnstone

Physics and Astronomy Faculty Publications

The brightest galaxy in the nearby Perseus cluster, NGC 1275, is surrounded by a network of filaments. These were first observed through their Hα emission but are now known to have a large molecular component with a total mass approaching 1011 M⊙ of gas. The filaments are embedded in hot intracluster gas and stretch over 80 kpc. They have an unusually low excitation spectrum which is well modelled by collisional heating and ionization by secondary electrons. Here we note that the surface radiative flux from the outer filaments is close to the energy flux impacting on them from …

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