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On The Accuracy Of Explicit Finite-Volume Schemes For Fluctuating Hydrodynamics, Aleksandar Donev, Eric Vanden-Eijnden, Alejandro Garcia, John B. Bell 2010 Lawrence Livermore National Laboratory

On The Accuracy Of Explicit Finite-Volume Schemes For Fluctuating Hydrodynamics, Aleksandar Donev, Eric Vanden-Eijnden, Alejandro Garcia, John B. Bell

Alejandro Garcia

This paper describes the development and analysis of finite-volume methods for the Landau–Lifshitz Navier–Stokes (LLNS) equations and related stochastic partial differential equations in fluid dynamics. The LLNS equations incorporate thermal fluctuations into macroscopic hydrodynamics by the addition of white noise fluxes whose magnitudes are set by a fluctuation-dissipation relation. Originally derived for equilibrium fluctuations, the LLNS equations have also been shown to be accurate for nonequilibrium systems. Previous studies of numerical methods for the LLNS equations focused primarily on measuring variances and correlations computed at equilibrium and for selected nonequilibrium flows. In this paper, we introduce a more ...


The Dynamic X-Ray Sky Of The Local Universe, S. Boggs, C. Wunderer, P. von Ballmoos, T. Takahashi, N. Gehrels, J. Tueller, M. Baring, J. Beacom, R. Diehl, Dieter H. Hartmann 2010 Space Sciences Laboratory, University of California, Berkeley

The Dynamic X-Ray Sky Of The Local Universe, S. Boggs, C. Wunderer, P. Von Ballmoos, T. Takahashi, N. Gehrels, J. Tueller, M. Baring, J. Beacom, R. Diehl, Dieter H. Hartmann

Publications

Over the next decade, we can expect time domain astronomy to flourish at optical and radio wavelengths. In parallel with these efforts, a dedicated transient "machine" operating at higher energies (X-ray band through soft gamma-rays) is required to reveal the unique subset of events with variable emission predominantly visible above 100 eV. Here we focus on the transient phase space never yet sampled due to the lack of a sensitive, wide-field and triggering facility dedicated exclusively to catching high energy transients and enabling rapid coordinated multi-wavelength follow-up. We first describe the advancements in our understanding of known X-ray transients that ...


Detection Of Diffuse Neutral Intragroup Medium In Hickson Compact Groups, S Borthakur, Min Yun, L Verdes-Montenegro 2010 University of Massachusetts - Amherst

Detection Of Diffuse Neutral Intragroup Medium In Hickson Compact Groups, S Borthakur, Min Yun, L Verdes-Montenegro

Astronomy Department Faculty Publication Series

We present new Green Bank Telescope (GBT) 21 cm neutral hydrogen (H I) observations of a complete distance-limited sample of 22 Hickson Compact Groups (HCGs) with at least four true members. We detected an average H I mass of 8 × 109 M (median = 6 × 109 M ), which is significantly larger than previous single-dish measurements. Consequently, the H I deficiencies for these HCGs have been reduced, although not completely eliminated. Spectral comparison of the GBT data with complementary Very Large Array data shows significant H I excess in the GBT spectra. The observed excess is primarily due to the ...


The Agn Fraction Of Submm-Selected Galaxies And Contributions To The Submm/Mm-Wave Extragalactic Background Light, S Serjeant, M Negrello, C Pearson, A Mortier, J Austermann, I Aretxaga, D Clements, S Chapman, S Dye, J Dunlop, L Dunne, D Farrah, D Hughes, HM Lee, H Matsuhara, E Ibar, M Im, WS Jeong, S Kim, S Oyabu, T Takagi, T Wada, G Wilson, M Vaccari, Min Yun 2010 University of Massachusetts - Amherst

The Agn Fraction Of Submm-Selected Galaxies And Contributions To The Submm/Mm-Wave Extragalactic Background Light, S Serjeant, M Negrello, C Pearson, A Mortier, J Austermann, I Aretxaga, D Clements, S Chapman, S Dye, J Dunlop, L Dunne, D Farrah, D Hughes, Hm Lee, H Matsuhara, E Ibar, M Im, Ws Jeong, S Kim, S Oyabu, T Takagi, T Wada, G Wilson, M Vaccari, Min Yun

Astronomy Department Faculty Publication Series

We present a comparison of the SCUBA half degree extragalactic survey (SHADES) at 450 μm, 850 μm and 1100 μm with deep guaranteed time 15 μm AKARI FU-HYU survey data and Spitzer guaranteed time data at 3.6-24 μm in the Lockman hole east. The AKARI data was analysed using bespoke software based in part on the drizzling and minimum-variance matched filtering developed for SHADES, and was cross-calibrated against ISO fluxes. Our stacking analyses find AKARI 15 μm galaxies with 200 μJy contribute >10% of the 450 μm background, but only <4 ...


The Radio Properties And Magnetic Field Configuration In The Crab-Like Pulsar Wind Nebula G54.1+0.3, CC Lang, QD Wang, F Lu, KI Clubb 2010 University of Massachusetts - Amherst

The Radio Properties And Magnetic Field Configuration In The Crab-Like Pulsar Wind Nebula G54.1+0.3, Cc Lang, Qd Wang, F Lu, Ki Clubb

Astronomy Department Faculty Publication Series

We present a multifrequency radio investigation of the Crab-like pulsar wind nebula (PWN) G54.1+0.3 using the Very Large Array. The high resolution of the observations reveals that G54.1+0.3 has a complex radio structure which includes filamentary and loop-like structures that are magnetized, a diffuse extent similar to the associated diffuse X-ray emission. But the radio and X-ray structures in the central region differ strikingly, indicating that they trace very different forms of particle injection from the pulsar and/or particle acceleration in the nebula. No spectral index gradient is detected in the radio emission ...


The Pulsar B2224+65 And Its Jets: A Two Epoch X-Ray Analysis, SP Johnson, QD Wang 2010 University of Massachusetts - Amherst

The Pulsar B2224+65 And Its Jets: A Two Epoch X-Ray Analysis, Sp Johnson, Qd Wang

Astronomy Department Faculty Publication Series

We present an X-ray morphological and spectroscopic study of the pulsar B2224+65 and its apparent jet-like X-ray features based on two epoch Chandra observations. The main X-ray feature, which shows a large directional offset from the ram-pressure confined pulsar wind nebula (Guitar nebula), is broader in apparent width and shows evidence for spectral hardening (at 95 per cent confidence) in the second epoch compared to the first. Furthermore, the sharp leading edge of the feature is found to have a proper motion consistent with that of the pulsar (∼180 mas yr−1). The combined data set also provides evidence ...


Aztec/Aste 1.1-Mm Survey Of The Akari Deep Field South: Source Catalogue And Number Counts, B Hatsukade, K Kohno, I Aretxaga, JE Austermann, H Ezawa, DH Hughes, S Ikarashi, D Iono, R Kawabe, S Khan, H Matsuo, S Matsuura, K Nakanishi, T Oshima, T Perera, KS Scott, M Shirahata, TT Takeuchi, Y Yamura, K Tanaka, T Tosaki, GW Wilson, Min Yun 2010 University of Massachusetts - Amherst

Aztec/Aste 1.1-Mm Survey Of The Akari Deep Field South: Source Catalogue And Number Counts, B Hatsukade, K Kohno, I Aretxaga, Je Austermann, H Ezawa, Dh Hughes, S Ikarashi, D Iono, R Kawabe, S Khan, H Matsuo, S Matsuura, K Nakanishi, T Oshima, T Perera, Ks Scott, M Shirahata, Tt Takeuchi, Y Yamura, K Tanaka, T Tosaki, Gw Wilson, Min Yun

Astronomy Department Faculty Publication Series

We present results of a 1.1-mm deep survey of the AKARI Deep Field South (ADF-S) with AzTEC mounted on the Atacama Submillimetre Telescope Experiment (ASTE). We obtained a map of 0.25-deg2 area with an rms noise level of 0.32–0.71 mJy. This is one of the deepest and widest maps thus far at millimetre and submillimetre wavelengths. We uncovered 198 sources with a significance of 3.5σ–15.6σ, providing the largest catalogue of 1.1-mm sources in a contiguous region. Most of the sources are not detected in the far-infrared bands of the AKARI ...


A Method For Measuring Variations In The Stellar Initial Mass Function, D. Calzetti 2010 University of Massachusetts - Amherst

A Method For Measuring Variations In The Stellar Initial Mass Function, D. Calzetti

Astronomy Department Faculty Publication Series

We present a method for investigating variations in the upper end of the stellar initial mass function (IMF) by probing the production rate of ionizing photons in unresolved, compact star clusters with ages ≤107 yr and with different masses. We test this method by performing a pilot study on the young cluster population in the nearby galaxy NGC5194 (M51a), for which multi-wavelength observations from the Hubble Space Telescope are available. Our results indicate that the proposed method can probe the upper end of the IMF in galaxies located out to at least ~10 Mpc, i.e., a factor 200 further ...


Pacs And Spire Photometer Maps Of M 33: First Results Of The Herschel M 33 Extended Survey (Herm33es), C Kramer, C Buchbender, E Xilouris, M Boquien, J Braine, D Calzetti 2010 University of Massachusetts - Amherst

Pacs And Spire Photometer Maps Of M 33: First Results Of The Herschel M 33 Extended Survey (Herm33es), C Kramer, C Buchbender, E Xilouris, M Boquien, J Braine, D Calzetti

Astronomy Department Faculty Publication Series

Context. Within the framework of the HERM33ES key program, we are studying the star forming interstellar medium in the nearby, metal-poor spiral galaxy M 33, exploiting the high resolution and sensitivity of Herschel. Aims. We use PACS and SPIRE maps at 100, 160, 250, 350, and 500 μm wavelength, to study the variation of the spectral energy distributions (SEDs) with galacto-centric distance. Methods. Detailed SED modeling is performed using azimuthally averaged fluxes in elliptical rings of 2 kpc width, out to 8 kpc galacto-centric distance. Simple isothermal and two-component grey body models, with fixed dust emissivity index, are fitted to ...


Far-Infrared Line Imaging Of The Starburst Ring In Ngc 1097 With The Herschel/Pacs Spectrometer, P Beirão, L Armus, P Appleton, J Smith, K Croxall, E Murphy, D Dale, G Helou, R Kennicutt, D Calzetti 2010 University of Massachusetts Amherst

Far-Infrared Line Imaging Of The Starburst Ring In Ngc 1097 With The Herschel/Pacs Spectrometer, P Beirão, L Armus, P Appleton, J Smith, K Croxall, E Murphy, D Dale, G Helou, R Kennicutt, D Calzetti

Astronomy Department Faculty Publication Series

NGC 1097 is a nearby SBb galaxy with a Seyfert nucleus and a bright starburst ring. We study the physical properties of the interstellar medium (ISM) in the ring using spatially resolved far-infrared spectral maps of the circumnuclear starburst ring of NGC 1097, obtained with the PACS spectrometer on board the Herschel Space Observatory. In particular, we map the important ISM cooling and diagnostic emission lines of [OI] 63 μm, [OIII] 88 μm, [NII] 122 μm, [CII] 158 μm and [NII] 205 μm. We observe that in the [OI] 63 μm, [OIII] 88 μm, and [NII] 122 μm line maps ...


The History Of Star Formation In Galaxies, T Brown, M Postman, D Calzetti 2010 University of Massachusetts - Amherst

The History Of Star Formation In Galaxies, T Brown, M Postman, D Calzetti

Astronomy Department Faculty Publication Series

If we are to develop a comprehensive and predictive theory of galaxy formation and evolution, it is essential that we obtain an accurate assessment of how and when galaxies assemble their stellar populations, and how this assembly varies with environment. There is strong observational support for the hierarchical assembly of galaxies, but by definition the dwarf galaxies we see today are not the same as the dwarf galaxies and proto-galaxies that were disrupted during the assembly. Our only insight into those disrupted building blocks comes from sifting through the resolved field populations of the surviving giant galaxies to reconstruct the ...


An Aromatic Inventory Of The Local Volume, AR Marble, CW Engelbracht, L van Zee, DA Dale, JDT Smith, KD Gordon, Y Wu, JC Lee, RC Kennicutt, ED Skillman, LC Johnson, M Block, D Calzetti, SA Cohen, H Lee, MD Schuster 2010 University of Massachusetts Amherst

An Aromatic Inventory Of The Local Volume, Ar Marble, Cw Engelbracht, L Van Zee, Da Dale, Jdt Smith, Kd Gordon, Y Wu, Jc Lee, Rc Kennicutt, Ed Skillman, Lc Johnson, M Block, D Calzetti, Sa Cohen, H Lee, Md Schuster

Astronomy Department Faculty Publication Series

Using infrared photometry from the Spitzer Space Telescope, we perform the first inventory of aromatic feature emission (also commonly referred to as polycyclic aromatic hydrocarbon emission) for a statistically complete sample of star-forming galaxies in the local volume. The photometric methodology involved is calibrated and demonstrated to recover the aromatic fraction of the Infrared Array Camera 8 μm flux with a standard deviation of 6% for a training set of 40 SINGS galaxies (ranging from stellar to dust dominated) with both suitable mid-infrared Spitzer Infrared Spectrograph spectra and equivalent photometry. A potential factor of 2 improvement could be realized with ...


Ly Alpha Emission From Cosmic Structure. I. Fluorescence, JA Kollmeier, Z Zheng, R Dave, A Gould, N Katz, J Miralda-Escude, DH Weinberg 2010 University of Massachusetts - Amherst

Ly Alpha Emission From Cosmic Structure. I. Fluorescence, Ja Kollmeier, Z Zheng, R Dave, A Gould, N Katz, J Miralda-Escude, Dh Weinberg

Astronomy Department Faculty Publication Series

We present predictions for the fluorescent Lyα emission signature arising from photoionized, optically thick structures in smoothed particle hydrodynamic cosmological simulations of a ΛCDM universe using a Monte Carlo Lyα radiative transfer code. We calculate the expected Lyα image and two-dimensional spectra for gas exposed to a uniform ultraviolet ionizing background as well as gas exposed additionally to the photoionizing radiation from a local quasar, after correcting for the self-shielding of hydrogen. As a test of our numerical methods and for application to current observations, we examine simplified analytic structures that are uniformly or anisotropically illuminated. We compare these results ...


Spitzer 70 Μm Emission As A Star Formation Rate Indicator For Sub-Galactic Regions, Y Li, D Calzetti 2010 University of Massachusetts - Amherst

Spitzer 70 Μm Emission As A Star Formation Rate Indicator For Sub-Galactic Regions, Y Li, D Calzetti

Astronomy Department Faculty Publication Series

We use Spitzer 24 μm, 70 μm and ground-based Hα data for a sample of 40 SINGS galaxies to establish a star formation rate (SFR) indicator using 70 μm emission for sub-galactic (~0.05-2 kpc) line-emitting regions and to investigate limits in application. A linear correlation between 70 μm and SFR is found and a star formation indicator SFR(70) is proposed for line-emitting sub-galactic regions as Σ(SFR)(M yr-1 kpc–2 ) = 9.4 × 10–44 Σ(70)(erg s-1 kpc–2), for regions with 12 + log(O/H) 8.4 and Σ(SFR) 10–3(M yr-1 kpc ...


On The Algorithms Of Radiative Cooling In Semi-Analytic Models, Yu Lu, Dusan Keres, N Katz, H.J. Mo, Mark Fardal, Martin D. Weinberg 2010 University of Massachusetts - Amherst

On The Algorithms Of Radiative Cooling In Semi-Analytic Models, Yu Lu, Dusan Keres, N Katz, H.J. Mo, Mark Fardal, Martin D. Weinberg

Astronomy Department Faculty Publication Series

We study the behaviour of multiple radiative cooling algorithms implemented in six Semi-Analytic Models (SAMs) of galaxy formation, including a new model we propose in this paper. We use versions of the models without feedback and apply them to dark matter haloes growing in a cosmological context, which have final masses that range from 10^{11}Msun to 10^{14}Msun. First, using simplified smoothly-growing halo models, we demonstrate that the different algorithms predict cooling rates and final cold gas masses that differ by a factor of ~5 for massive haloes (>10^{12}Msun). The algorithms are in better agreement ...


Computing The Bayes Factor From A Markov Chain Monte Carlo Simulation Of The Posterior Distribution, Martin D. Weinberg 2010 University of Massachusetts Amherst

Computing The Bayes Factor From A Markov Chain Monte Carlo Simulation Of The Posterior Distribution, Martin D. Weinberg

Astronomy Department Faculty Publication Series

Computation of the marginal likelihood from a simulated posterior distribution is central to Bayesian model selection but is computationally difficult. I argue that the marginal likelihood can be reliably computed from a posterior sample by careful attention to the numerics of the probability integral. Posing the expression for the marginal likelihood as a Lebesgue integral, we may convert the harmonic mean approximation from a sample statistic to a quadrature rule. As a quadrature, the harmonic mean approximation suffers from enormous truncation error as consequence . In addition, I demonstrate that the integral expression for the harmonic-mean approximation converges slowly at best ...


A Bayesian Approach To The Semi-Analytic Model Of Galaxy Formation: Methodology, Yu Lu, H.J. Mo, Martin D. Weinberg, N Katz 2010 University of Massachusetts Amherst

A Bayesian Approach To The Semi-Analytic Model Of Galaxy Formation: Methodology, Yu Lu, H.J. Mo, Martin D. Weinberg, N Katz

Astronomy Department Faculty Publication Series

We believe that a wide range of physical processes conspire to shape the observed galaxy population but we remain unsure of their detailed interactions. The semi-analytic model (SAM) of galaxy formation uses multi-dimensional parameterizations of the physical processes of galaxy formation and provides a tool to constrain these underlying physical interactions. Because of the high dimensionality, the parametric problem of galaxy formation may be profitably tackled with a Bayesian-inference based approach, which allows one to constrain theory with data in a statistically rigorous way. In this paper, we develop a generalized SAM using the framework of Bayesian inference. We show ...


The Evolution Of Stellar Structures In Dwarf Galaxies, N. Bastian, D. R. Weisz, E. D. Skillman, K. B.W. Mc Quinn, A E. Dolphin, R. A. Gutermuth 2010 University of Massachusetts - Amherst

The Evolution Of Stellar Structures In Dwarf Galaxies, N. Bastian, D. R. Weisz, E. D. Skillman, K. B.W. Mc Quinn, A E. Dolphin, R. A. Gutermuth

Astronomy Department Faculty Publication Series

We present a study of the variation of spatial structure of stellar populations within dwarf galaxies as a function of the population age. We use deep Hubble Space Telescope/Advanced Camera for Surveys imaging of nearby dwarf galaxies in order to resolve individual stars and create composite colour-magnitude diagrams (CMDs) for each galaxy. Using the obtained CMDs, we select Blue Helium Burning stars (BHeBs), which can be unambiguously age-dated by comparing the absolute magnitude of individual stars with stellar isochrones. Additionally, we select a very young (<10 >Myr) population of OB stars for a subset of the galaxies based on the ...


The Mass Distribution Of Starless And Protostellar Cores In Gould Belt Clouds, Sarah I. Sadavoy, James Di Francesco, Sylvain Bontemps, S. Thomas Megeath, Luisa M. Rebull, Erin Allgaier, Sean Carey, Robert Gutermuth 2010 University of Massachusetts - Amherst

The Mass Distribution Of Starless And Protostellar Cores In Gould Belt Clouds, Sarah I. Sadavoy, James Di Francesco, Sylvain Bontemps, S. Thomas Megeath, Luisa M. Rebull, Erin Allgaier, Sean Carey, Robert Gutermuth

Astronomy Department Faculty Publication Series

Using data from the SCUBA Legacy Catalogue (850 μm) and Spitzer Space Telescope (3.6-70 μm), we explore dense cores in the Ophiuchus, Taurus, Perseus, Serpens, and Orion molecular clouds. We develop a new method to discriminate submillimeter cores found by Submillimeter Common-User Bolometer Array (SCUBA) as starless or protostellar, using point source photometry from Spitzer wide field surveys. First, we identify infrared sources with red colors associated with embedded young stellar objects (YSOs). Second, we compare the positions of these YSO candidates to our submillimeter cores. With these identifications, we construct new, self-consistent starless and protostellar core mass functions ...


Distance To U Pegasi By The Dde Algorithm, Todd R. Vaccaro, Dirk Terrell, Robert E. Wilson 2010 St. Cloud State University

Distance To U Pegasi By The Dde Algorithm, Todd R. Vaccaro, Dirk Terrell, Robert E. Wilson

Physics and Astronomy Faculty Publications

A distance is found for the W UMa type binary U Pegasi, with a newly modified version of the Wilson-Devinney program (W-D) that makes use of the direct distance estimation (DDE) algorithm. The reported distance of d=123.6pc is an average based on solutions for B and V data and a primary star temperature of 5800K. Standardized light curves (not differential), radial velocities, and a spectroscopic primary star temperature are input to the program. Differential corrections were performed for each light curve band along with the velocities for two primary temperatures that span 100K. Log10d is a ...


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