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Search Results: 1 - 10 of 191340 matches for " D. Cunnama "
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The velocity--shape alignment of clusters and the kinetic Sunyaev--Zeldovich effect
D. Cunnama,A. Faltenbacher,C. Cress,S. Passmoor
Physics , 2009, DOI: 10.1111/j.1745-3933.2009.00680.x
Abstract: We use the Millennium simulation to probe the correlation between cluster velocities and their shapes and the consequences for measurements of the kinetic Sunyaev-Zeldovich (kSZ) effect. Halos are generally prolate ellipsoids with orientations that are correlated with those of nearby halos. We measure the mean streaming velocities of halos along the lines that separate them, demonstrating that the peculiar velocities and the long axes of halos tend to be somewhat aligned, especially for the most massive halos. Since the kSZ effect is proportional to the line-of-sight velocity and the optical depth of the cluster, the alignment results in a strong enhancement of the kSZ signature in clusters moving along the line of sight. This effect has not been taken into account in many analyses of kSZ signatures.
Gas and Metal Distributions within Simulated Disk Galaxies
B. K. Gibson,S. Courty,D. Cunnama,M. Molla
Physics , 2012,
Abstract: We highlight two research strands related to our ongoing chemodynamical Galactic Archaeology efforts: (i) the spatio-temporal infall rate of gas onto the disk, drawing analogies with the infall behaviour imposed by classical galactic chemical evolution models of inside-out disk growth; (ii) the radial age gradient predicted by spectrophometric models of disk galaxies. In relation to (i), at low-redshift, we find that half of the infall onto the disk is gas associated with the corona, while half can be associated with cooler gas streams; we also find that gas enters the disk preferentially orthogonal to the system, rather than in-plane. In relation to (ii), we recover age gradient troughs/inflections consistent with those observed in nature, without recourse to radial migrations.
The environmental dependence of neutral hydrogen in the GIMIC simulations
D. Cunnama,S. Andrianomena,C. M. Cress,A. Faltenbacher,B. K. Gibson,T. Theuns
Physics , 2013, DOI: 10.1093/mnras/stt2380
Abstract: We use the Galaxies-Intergalactic Medium Interaction Calculation (GIMIC) cosmological hydrodynamic simulation at z=0 to study the distribution and environmental dependence of neutral hydrogen (HI) gas in the outskirts of simulated galaxies. This gas can currently be probed directly in, for example, Ly$\alpha$ absorption via the observation of background quasars. Radio facilities, such as the Square Kilometre Array, will provide a complementary probe of the diffuse HI in emission and will constrain the physics underpinning the complex interplay between accretion and feedback mechanisms which affect the intergalactic medium. We extract a sample of 488 galaxies from a re-simulation of the average cosmic density GIMIC region. We estimate the neutral hydrogen content of these galaxies and the surrounding intergalactic medium within which they reside. We investigate the average HI radial profiles by stacking the individual profiles according to both mass and environment. We find high HI column densities at large impact parameters in group environments and markedly lower HI densities for non-group galaxies. We suggest that these results likely arise from the combined effects of ram pressure stripping and tidal interactions present in group environments.
The Cold Gas Content of Bulgeless Dwarf Galaxies
K. Pilkington,B. K. Gibson,F. Calura,A. M. Brooks,L. Mayer,C. B. Brook,G. S. Stinson,R. J. Thacker,C. G. Few,D. Cunnama,J. Wadsley
Physics , 2011, DOI: 10.1111/j.1365-2966.2011.19450.x
Abstract: We present an analysis of the neutral hydrogen (HI) properties of a fully cosmological hydrodynamical dwarf galaxy, run with varying simulation parameters. As reported by Governato et al. (2010), the high resolution, high star formation density threshold version of this galaxy is the first simulation to result in the successful reproduction of a (dwarf) spiral galaxy without any associated stellar bulge. We have set out to compare in detail the HI distribution and kinematics of this simulated bulgeless disk with what is observed in a sample of nearby dwarfs. To do so, we extracted the radial gas density profiles, velocity dispersion (e.g., velocity ellipsoid, turbulence), and the power spectrum of structure within the cold interstellar medium from the simulations. The highest resolution dwarf, when using a high density star formation threshold comparable to densities of giant molecular clouds, possesses bulk characteristics consistent with those observed in nature, though the cold gas is not as radially extended as that observed in nearby dwarfs, resulting in somewhat excessive surface densities. The lines-of-sight velocity dispersion radial profiles have values that are in good agreement with observed dwarf galaxies, but due to the fact that only the streaming velocities of particles are tracked, a correction to include the thermal velocities can lead to profiles that are quite flat. The ISM power spectra of the simulations appear to possess more power on smaller spatial scales than that of the SMC. We conclude that unavoidable limitations remain due to the unresolved physics of star formation and feedback within pc-scale molecular clouds.
Galaxy Formation & Dark Matter Modelling in the Era of the Square Kilometre Array
C. Power,C. D. P. Lagos,B. Qin,C. M. Baugh,D. Cunnama,J. Fu,H. S. Kim,C. G. Lacey,L. Li,D. Obreschkow,J. Wang,Y. Wang,M. Zhu
Physics , 2015,
Abstract: Theoretical galaxy formation models are an established and powerful tool for interpreting the astrophysical significance of observational data, particularly galaxy surveys. Such models have been utilised with great success by optical surveys such as 2dFGRS and SDSS, but their application to radio surveys of cold gas in galaxies has been limited. In this chapter we describe recent developments in the modelling of the cold gas properties in the models, and how these developments are essential if they are to be applied to cold gas surveys of the kind that will be carried out with the SKA. By linking explicitly a galaxy's star formation rate to the abundance of molecular hydrogen in the galaxy rather than cold gas abundance, as was assumed previously, the latest models reproduce naturally many of the global atomic and molecular hydrogen properties of observed galaxies. We review some of the key results of the latest models and highlight areas where further developments are necessary. We discuss also how model predictions can be most accurately compared with observational data, what challenges we expect when creating synthetic galaxy surveys in the SKA era, and how the SKA can be used to test models of dark matter.
nIFTy galaxy cluster simulations II: radiative models
Federico Sembolini,Pascal Jahan Elahi,Frazer R. Pearce,Chris Power,Alexander Knebe,Scott T. Kay,Weiguang Cui,Gustavo Yepes,Alexander M. Beck,Stefano Borgani,Daniel Cunnama,Romeel Davé,Sean February,Shuiyao Huang,Neal Katz,Ian G. McCarthy,Giuseppe Murante,Richard D. A. Newton,Valentin Perret,Alexandro Saro,Joop Schaye,Romain Teyssier
Physics , 2015,
Abstract: We have simulated the formation of a massive galaxy cluster (M$_{200}^{\rm crit}$ = 1.1$\times$10$^{15}h^{-1}M_{\odot}$) in a $\Lambda$CDM universe using 10 different codes (RAMSES, 2 incarnations of AREPO and 7 of GADGET), modeling hydrodynamics with full radiative subgrid physics. These codes include Smoothed-Particle Hydrodynamics (SPH), spanning traditional and advanced SPH schemes, adaptive mesh and moving mesh codes. Our goal is to study the consistency between simulated clusters modeled with different radiative physical implementations - such as cooling, star formation and AGN feedback. We compare images of the cluster at $z=0$, global properties such as mass, and radial profiles of various dynamical and thermodynamical quantities. We find that, with respect to non-radiative simulations, dark matter is more centrally concentrated, the extent not simply depending on the presence/absence of AGN feedback. The scatter in global quantities is substantially higher than for non-radiative runs. Intriguingly, adding radiative physics seems to have washed away the marked code-based differences present in the entropy profile seen for non-radiative simulations in Sembolini et al. (2015): radiative physics + classic SPH can produce entropy cores. Furthermore, the inclusion/absence of AGN feedback is not the dividing line -as in the case of describing the stellar content- for whether a code produces an unrealistic temperature inversion and a falling central entropy profile. However, AGN feedback does strongly affect the overall stellar distribution, limiting the effect of overcooling and reducing sensibly the stellar fraction.
nIFTy Cosmology: Comparison of Galaxy Formation Models
Alexander Knebe,Frazer R. Pearce,Peter A. Thomas,Andrew Benson,Jeremy Blaizot,Richard Bower,Jorge Carretero,Francisco J. Castander,Andrea Cattaneo,Sofia A. Cora,Darren J. Croton,Weiguang Cui,Daniel Cunnama,Gabriella De Lucia,Julien E. Devriendt,Pascal J. Elahi,Andreea Font,Fabio Fontanot,Juan Garcia-Bellido,Ignacio D. Gargiulo,Violeta Gonzalez-Perez,John Helly,Bruno Henriques,Michaela Hirschmann,Jaehyun Lee,Gary A. Mamon,Pierluigi Monaco,Julian Onions,Nelson D. Padilla,Chris Power,Arnau Pujol,Ramin A. Skibba,Rachel S. Somerville,Chaichalit Srisawat,Cristian A. Vega-Martinez,Sukyoung K. Yi
Physics , 2015,
Abstract: We present a comparison of 14 galaxy formation models: 12 different semi-analytical models and 2 halo-occupation distribution models for galaxy formation based upon the same cosmological simulation and merger tree information derived from it. The participating codes have proven to be very successful in their own right but they have all been calibrated independently using various observational data sets, stellar models, and merger trees. In this paper we apply them without recalibration and this leads to a wide variety of predictions for the stellar mass function, specific star formation rates, stellar-to- halo mass ratios, and the abundance of orphan galaxies. The scatter is much larger than seen in previous comparison studies primarily because the codes have been used outside of their native environment within which they are well tested and calibrated. The purpose of the `nIFTy comparison of galaxy formation models' is to bring together as many different galaxy formation modellers as possible and to investigate a common approach to model calibration. This paper provides a unified description for all participating models and presents the initial, uncalibrated comparison as a baseline for our future studies where we will develop a common calibration framework and address the extent to which that reduces the scatter in the model predictions seen here.
nIFTY galaxy cluster simulations III: The Similarity & Diversity of Galaxies & Subhaloes
Pascal J. Elahi,Alexander Knebe,Frazer R. Pearce,Chris Power,Gustavo Yepes,Weiguang Cui,Daniel Cunnama,Scott T. Kay,Federico Sembolini,Alexander M. Beck,Romeel Davé,Sean February,Shuiyao Huang,Neal Katz,Ian G. McCarthy,Giuseppe Murante,Valentin Perret,Ewald Puchwein,Alexandro Saro,Romain Teyssier
Physics , 2015,
Abstract: We examine subhaloes and galaxies residing in a simulated LCDM galaxy cluster ($M^{\rm crit}_{200}=1.1\times10^{15}M_\odot/h$) produced by hydrodynamical codes ranging from classic Smooth Particle Hydrodynamics (SPH), newer SPH codes, an adaptive mesh code and a moving mesh scheme. These codes use subgrid models to capture galaxy formation physics. We compare how well these codes reproduce the same subhaloes/galaxies in gravity only, non-radiative hydrodynamics and full radiative physics runs by looking at the overall subhalo/galaxy distribution and on an individual objects basis. We find the subhalo population is reproduced to within $\lesssim10\%$ for both dark matter only and non-radiative runs, with individual objects showing code-to-code scatter of $\lesssim0.1$ dex, although the gas in non-radiative simulations shows significant scatter. Including radiative physics significantly increases the diversity seen. The subhalo mass and $V_{max}$ distributions vary by $\approx20\%$, a result of feedback moving significant baryonic mass around. Galaxies also show striking code-to-code variations. Although the Tully-Fisher relation is similar in almost all codes, the number of galaxies with $10^{9}M_\odot/h\lesssim M_*\lesssim 10^{12}M_\odot/h$ can differ by a factor of 4. Individual galaxies show code-to-code scatter of $\sim0.5$ dex in stellar mass. Moreover, strong systematic differences exist, with some codes producing galaxies $70\%$ smaller than others. The diversity partially arises from the inclusion/absence of AGN feedback. Our results combined with our companion papers, Sembolini et al. (2015a,b), demonstrate that subgrid physics is not just subject to fine-tuning, but the complexity of building galaxies in all environments remains a challenge. We argue that even basic galaxy properties, such as the stellar mass to halo mass, should be treated with errors bars of $\sim0.2-0.5$ dex.
Electrical Conductivity of Collapsed Multilayer Graphene Tubes  [PDF]
D. Mendoza
World Journal of Nano Science and Engineering (WJNSE) , 2012, DOI: 10.4236/wjnse.2012.22009
Abstract: Synthesis of multilayer graphene on copper wires by a chemical vapor deposition method is reported. After copper etching, the multilayer tube collapses forming stripes of graphitic films, their electrical conductance as a function of temperature indicate a semiconductor-like behavior. Using the multilayer graphene stripes, a cross junction is built and owing to its electrical behavior we propose that a tunneling process exists in the device.
Porous Carbon Grown by Chemical Vapor Deposition on Copper Substrates  [PDF]
D. Mendoza
Journal of Materials Science and Chemical Engineering (MSCE) , 2015, DOI: 10.4236/msce.2015.38003
Abstract: Amorphous porous carbon was synthesized by chemical vapor deposition on copper substrates. The average size of the pores is around 1.2 microns with some small pores decorating the big ones. Lamellar samples of this carbonaceous material can be separated from the copper support and may be useful as electrode due to its low electrical resistivity of the order of 0.4 Ωcm.
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