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Caltech Authors (147.820 recursos)

Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 797

  1. Neutrino-heated winds from millisecond protomagnetars as sources of the weak r-process

    Vlasov, Andrey D.; Metzger, Brian D.; Lippuner, Jonas; Roberts, Luke F.; Thompson, Todd A.
    We explore heavy element nucleosynthesis in neutrino-driven winds from rapidly rotating, stronglymagnetized protoneutron stars (‘millisecond protomagnetars’) forwhich themagnetic dipole is aligned with the rotation axis, and the field is assumed to be a static force-free configuration. We process the protomagnetar wind trajectories calculated by Vlasov, Metzger & Thompson through the r-process nuclear reaction network SkyNet using contemporary models for the evolution of the wind electron fraction during the protoneutron star cooling phase. Although we do not find a successful second or third-peak r-process for any rotation period P, we show that protomagnetars with P ∼ 1–5 ms produce heavy element abundance distributions that extend to higher nuclear mass...

  2. Simulating the dust content of galaxies: successes and failures

    McKinnon, Ryan; Torrey, Paul; Vogelsberger, Mark; Hayward, Christopher C.; Marinacci, Federico
    We present full-volume cosmological simulations, using the moving-mesh code AREPO to study the coevolution of dust and galaxies. We extend the dust model in AREPO to include thermal sputtering of grains and investigate the evolution of the dust mass function, the cosmic distribution of dust beyond the interstellar medium and the dependence of dust-to-stellar mass ratio on galactic properties. The simulated dust mass function is well described by a Schechter fit and lies closest to observations at z = 0. The radial scaling of projected dust surface density out to distances of 10 Mpc around galaxies with magnitudes 17 < i < 21 is similar to...

  3. Tidal dissipation and evolution of white dwarfs around massive black holes: an eccentric path to tidal disruption

    Vick, Michelle; Lai, Dong; Fuller, Jim
    Awhite dwarf (WD)captured into a high-eccentricity orbit around amassive black hole (MBH) may undergo many pericentre passages before tidal disruption. During these passages, the tidal potential of the MBH excites internal oscillations or waves in the WD, and the dissipation of these oscillations can significantly influence the physical properties of the WD prior to its disruption. We calculate the amplitude of the tidally excited gravity (buoyancy) waves in the WD as a function of the pericentre distance and eccentricity for realistic WD models, under the assumption that these outgoing gravity waves are efficiently dissipated in the outer layers of the WD by non-linear effects or radiative damping....

  4. A Surrogate model of gravitational waveforms from numerical relativity simulations of precessing binary black hole mergers

    Blackman, Jonathan; Field, Scott E.; Scheel, Mark A.; Galley, Chad R.; Hemberger, Daniel A.; Schmidt, Patricia; Smith, Rory
    We present the first surrogate model for gravitational waveforms from the coalescence of precessing binary black holes. We call this surrogate model NRSur4d2s. Our methodology significantly extends recently introduced reduced-order and surrogate modeling techniques, and is capable of directly modeling numerical relativity waveforms without introducing phenomenological assumptions or approximations to general relativity. Motivated by GW150914, LIGO’s first detection of gravitational waves from merging black holes, the model is built from a set of 276 numerical relativity (NR) simulations with mass ratios q ≤ 2, dimensionless spin magnitudes up to 0.8, and the restriction that the initial spin of the smaller...

  5. Radiative transfer effects in primordial hydrogen recombination

    Ali-Haïmoud, Yacine; Grin, Daniel; Hirata, Christopher M.
    The calculation of a highly accurate cosmological recombination history has been the object of particular attention recently, as it constitutes the major theoretical uncertainty when predicting the angular power spectrum of cosmic microwave background anisotropies. Lyman transitions, in particular the Lyman-α line, have long been recognized as one of the bottlenecks of recombination, due to their very low escape probabilities. The Sobolev approximation does not describe radiative transfer in the vicinity of Lyman lines to a sufficient degree of accuracy, and several corrections have already been computed in other works. In this paper, we compute the impact of some radiative...

  6. Proposal for gravitational-wave detection beyond the standard quantum limit through EPR entanglement

    Ma, Yiqiu; Miao, Haixing; Pang, Belinda Heyun; Evans, Matthew; Zhao, Chunnong; Harms, Jan; Schnabel, Roman; Chen, Yanbei
    In continuously monitored systems the standard quantum limit is given by the trade-off between shot noise and back-action noise. In gravitational-wave detectors, such as Advanced LIGO, both contributions can be simultaneously squeezed in a broad frequency band by injecting a spectrum of squeezed vacuum states with a frequency-dependent squeeze angle. This approach requires setting up an additional long baseline, low-loss filter cavity in a vacuum system at the detector’s site. Here, we show that the need for such a filter cavity can be eliminated, by exploiting Einstein–Podolsky–Rosen (EPR)-entangled signals and idler beams. By harnessing their mutual quantum correlations and the...

  7. Mufasa: Galaxy star formation, gas, and metal properties across cosmic time

    Davé, Romeel; Rafieferantsoa, Mika H.; Thompson, Robert J.; Hopkins, Philip F.
    We examine galaxy star formation rates (SFRs), metallicities and gas contents predicted by the Mufasa cosmological hydrodynamic simulations, which employ meshless hydrodynamics and novel feedback prescriptions that yield a good match to observed galaxy stellar mass assembly. We combine 50, 25 and 12.5 h^(−1) Mpc boxes with a quarter billion particles each to show that Mufasa broadly reproduces a wide range of relevant observations, including SFR and specific SFR functions, the mass–metallicity relation, H i and H2 fractions, H i (21 cm) and CO luminosity functions, and cosmic gas density evolution. There are mild but significant discrepancies, such as perhaps too many high-SFR galaxies,...

  8. Calculating the Gravitational Self-Force in Schwarzschild Spacetime

    Barack, Leor; Mino, Yasushi; Nakano, Hiroyuki; Ori, Amos; Sasaki, Misao
    We present a practical method for calculating the local gravitational self-force (often called “radiation-reaction force”) for a pointlike particle orbiting a Schwarzschild black hole. This is an implementation of the method of mode-sum regularization, in which one first calculates the (finite) contribution to the force due to each individual multipole mode of the perturbation, and then applies a certain regularization procedure to the mode sum. Here we give the values of all the “regularization parameters” required for implementing this regularization procedure, for any geodesic orbit in Schwarzschild spacetime.

  9. Forward and backward galaxy evolution in comoving cumulative number density space

    Torrey, Paul; Wellons, Sarah; Ma, Chung-Pei; Hopkins, Philip F.; Vogelsberger, Mark
    Galaxy cumulative comoving number density is commonly used to forge progenitor/descendant links between observed galaxy populations at different epochs. However, this method breaks down in the presence of galaxy mergers, or when galaxies experience stochastic growth rates. We present a simple analytic framework to treat the physical processes that drive the evolution and diffusion of galaxies within comoving number density space. The evolution in mass rank order of a galaxy population with time is influenced by (1) the non-conservative nature of total galaxy number density driven by galaxies combining in mergers (which we tabulate as a galaxy ‘coagulation’ rate) and...

  10. Eccentricity and spin-orbit misalignment in short-period stellar binaries as a signpost of hidden tertiary companions

    Anderson, Kassandra R.; Lai, Dong; Storch, Natalia I.
    Eclipsing binaries are observed to have a range of eccentricities and spin-orbit misalignments (stellar obliquities). Whether such properties are primordial or arise from post-formation dynamical interactions remains uncertain. This paper considers the scenario in which the binary is the inner component of a hierarchical triple stellar system, and derives the requirements that the tertiary companion must satisfy in order to raise the eccentricity and obliquity of the inner binary. Through numerical integrations of the secular octupole-order equations of motion of stellar triples, coupled with the spin precession of the oblate primary star due to the torque from the secondary, we...

  11. The structure and dynamical evolution of the stellar disc of a simulated Milky Way-mass galaxy

    Ma, Xiangcheng; Hopkins, Philip F.; Wetzel, Andrew R.; Kirby, Evan N.; Anglés-Alcázar, Daniel; Faucher-Giguère, Claude-André; Kereš, Dušan; Quataert, Eliot
    We study the structure, age and metallicity gradients, and dynamical evolution using a cosmological zoom-in simulation of a Milky Way-mass galaxy from the Feedback in Realistic Environments project. In the simulation, stars older than 6 Gyr were formed in a chaotic, bursty mode and have the largest vertical scaleheights (1.5–2.5 kpc) by z = 0, while stars younger than 6 Gyr were formed in a relatively calm, stable disc. The vertical scaleheight increases with stellar age at all radii, because (1) stars that formed earlier were thicker ‘at birth’, and (2) stars were kinematically heated to an even thicker distribution...

  12. The IRX–β Relation: Insights from Simulations

    Safarzadeh, Mohammadtaher; Hayward, Christopher C.; Ferguson, Henry C.
    We study the relationship between the UV continuum slope and infrared excess (IRX ≡ L_(IR)/L_(FUV)) predicted by performing dust radiative transfer on a suite of hydrodynamical simulations of galaxies. Our suite includes both isolated disk galaxies and mergers intended to be representative of galaxies at both z ~ 0 and z ~ 2-3. Our low-redshift systems often populate a region around the locally calibrated Meurer et al. relation but move above the relation during merger-induced starbursts. Our high-redshift systems are blue and IR luminous and therefore lie above the Meurer et al. relation. The value of β strongly depends on...

  13. (Star)bursts of FIRE: observational signatures of bursty star formation in galaxies

    Sparre, Martin; Hayward, Christopher C.; Feldmann, Robert; Faucher-Giguère, Claude-André; Muratov, Alexander L.; Kereš, Dušan; Hopkins, Philip F.
    Galaxy formation models are now able to reproduce observed relations such as the relation between galaxies’ star formation rates (SFRs) and stellar masses (M^*) and the stellar-mass–halo-mass relation. We demonstrate that comparisons of the short-time-scale variability in galaxy SFRs with observational data provide an additional useful constraint on the physics of galaxy formation feedback. We apply SFR indicators with different sensitivity time-scales to galaxies from the Feedback in Realistic Environments (FIRE) simulations. We find that the SFR–M* relation has a significantly greater scatter when the Hα-derived SFR is considered compared with when the far-ultraviolet (FUV)-based SFR is used. This difference...

  14. Joint constraints on the Galactic dark matter halo and GC from hypervelocity stars

    Rossi, E. M.; Marchetti, T.; Cacciato, M.; Kuiack, M.; Sari, R.
    The mass assembly history of the Milky Way can inform both theory of galaxy formation and the underlying cosmological model. Thus, observational constraints on the properties of both its baryonic and dark matter contents are sought. Here, we show that hypervelocity stars (HVSs) can in principle provide such constraints. We model the observed velocity distribution of HVSs, produced by tidal break-up of stellar binaries caused by Sgr A*. Considering a Galactic Centre (GC) binary population consistent with that inferred in more observationally accessible regions, a fit to current HVS data with significance level >5 per cent can only be obtained if the...

  15. The most massive heartbeat: an in-depth analysis of ι Orionis

    Pablo, Herbert; Richardson, N. D.; Fuller, J.; Rowe, J.; Moffatt, A. F. J.; Kuschnig, R.; Popowicz, A.; Handler, G.; Neiner, C.; Pigulski, A.; Wade, G. A.; Weiss, W.; Buysschaert, B.; Ramiaramanantsoa, T.; Bratcher, A. D.; Gerhartz, C. J.; Greco, J. J.; Hardegree-Ullman, K.; Lembryk, L.; Oswald, W. L.
    ι Ori is a well-studied massive binary consisting of an O9 III + B1 III/IV star. Due to its high eccentricity (e = 0.764) and short orbital period (Porb = 29.133 76 d), it has been considered to be a good candidate to show evidence of tidal effects; however, none have previously been identified. Using photometry from the BRIght Target Explorer (BRITE)-Constellation space photometry mission, we have confirmed the existence of tidal distortions through the presence of a heartbeat signal at periastron. We combine spectroscopic and light-curve analyses to measure the masses and radii of the components, revealing ι Ori...

  16. Gravitational waves from hot young rapidly rotating neutron stars

    Owen, Benjamin; Lindblom, Lee; Cutler, Curt; Schutz, Bernard; Vecchio, Alberto; Andersson, Nils
    Gravitational radiation drives an instability in the r-modes of young rapidly rotating neutron stars. This instability is expected to carry away most of the angular momentum of the star by gravitational radiation emission, leaving a star rotating at about 100 Hz. In this paper we model in a simple way the development of the instability and evolution of the neutron star during the year-long spindown phase. This allows us to predict the general features of the resulting gravitational waveform. We show that a neutron star formed in the Virgo cluster could be detected by the LIGO and VIRGO gravitational wave...

  17. Three-dimensional Boltzmann-Hydro Code for Core-collapse in Massive Stars. II. The Implementation of Moving-mesh for Neutron Star Kicks

    Nagakura, Hiroki; Iwakami, Wakana; Furusawa, Shun; Sumiyoshi, Kohsuke; Yamada, Shoichi; Matsufuru, Hideo; Imakura, Akira
    We present a newly developed moving-mesh technique for the multi-dimensional Boltzmann-Hydro code for the simulation of core-collapse supernovae (CCSNe). What makes this technique different from others is the fact that it treats not only hydrodynamics but also neutrino transfer in the language of the 3 + 1 formalism of general relativity (GR), making use of the shift vector to specify the time evolution of the coordinate system. This means that the transport part of our code is essentially general relativistic, although in this paper it is applied only to the moving curvilinear coordinates in the flat Minknowski spacetime, since the...

  18. Black Hole Spectroscopy with Coherent Mode Stacking

    Yang, Huan; Yagi, Kent; Blackman, Jonathan; Lehner, Luis; Paschalidis, Vasileios; Pretorius, Frans; Yunes, Nicolás
    The measurement of multiple ringdown modes in gravitational waves from binary black hole mergers will allow for testing the fundamental properties of black holes in general relativity and to constrain modified theories of gravity. To enhance the ability of Advanced LIGO/Virgo to perform such tasks, we propose a coherent mode stacking method to search for a chosen target mode within a collection of multiple merger events. We first rescale each signal so that the target mode in each of them has the same frequency and then sum the waveforms constructively. A crucial element to realize this coherent superposition is to...

  19. Magnetocentrifugal Launching of Jets from Accretion Disks. I. Cold Axisymmetric Flows

    Krasnopolsky, Ruben; Li, Zhi-Yun; Blandford, Roger
    We present time-dependent, numerical simulations of the magnetocentrifugal model for jet formation, in an axisymmetric geometry, using a modification of the ZEUS3D code adapted to parallel computers. The gas is supposed cold with negligible thermal pressure throughout. The number of boundary conditions imposed on the disk surface is that necessary and sufficient to take into account information propagating upstream from the fast and Alfvén critical surfaces, avoiding overdetermination of the flow and unphysical effects, such as numerical "boundary layers" that otherwise isolate the disk from the flow and produce impulsive accelerations. It is known that open magnetic field lines can...

  20. Simulating galaxy formation with black hole driven thermal and kinetic feedback

    Weinberger, Rainer; Springel, Volker; Hernquist, Lars; Pillepich, Annalisa; Marinacci, Federico; Pakmor, Rüdiger; Nelson, Dylan; Genel, Shy; Vogelsberger, Mark; Naiman, Jill; Torrey, Paul
    The inefficiency of star formation in massive elliptical galaxies is widely believed to be caused by the interactions of an active galactic nucleus (AGN) with the surrounding gas. Achieving a sufficiently rapid reddening of moderately massive galaxies without expelling too many baryons has however proven difficult for hydrodynamical simulations of galaxy formation, prompting us to explore a new model for the accretion and feedback effects of supermassive black holes. For high-accretion rates relative to the Eddington limit, we assume that a fraction of the accreted rest mass energy heats the surrounding gas thermally, similar to the ‘quasar mode’ in previous...

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