Recursos de colección

Caltech Authors (142.336 recursos)

Repository of works by Caltech published authors.

Group = TAPIR

Mostrando recursos 1 - 20 de 766

  1. The impact of stellar feedback on hot gas in galaxy haloes: the Sunyaev–Zel'dovich effect and soft X-ray emission

    van de Voort, Freeke; Quataert, Eliot; Hopkins, Philip F.; Faucher-Giguère, Claude-André; Feldmann, Robert; Kereš, Dušan; Chan, T. K.; Hafen, Zachary
    The thermal Sunyaev–Zel'dovich (SZ) effect and soft X-ray emission are routinely observed around massive galaxies and in galaxy groups and clusters. We study these observational diagnostics of galaxy haloes for a suite of cosmological ‘zoom-in’ simulations from the ‘Feedback In Realistic Environments’ project, which spans a large range in halo mass (10^(10–13) M_⊙). We explore the effect of stellar feedback on the hot gas observables. The properties of our simulated groups, such as baryon fractions, SZ flux, and X-ray luminosities (LX), are broadly consistent with existing observations, even though feedback from active galactic nuclei is not included. We make predictions for...

  2. On the equal-mass limit of precessing black-hole binaries

    Gerosa, Davide; Sperhake, Ulrich; Vošmera, Jakub
    We analyze the inspiral dynamics of equal-mass precessing black-hole binaries using multi-timescale techniques. The orbit-averaged post-Newtonian evolutionary equations admit two constants of motion in the equal-mass limit, namely the magnitude of the total spin S and the effective spin ξ. This feature makes the entire dynamics qualitatively different compared to the generic unequal-mass case, where only ξ is constant while the variable S parametrizes the precession dynamics. For fixed individual masses and spin magnitudes, an equal-mass black-hole inspiral is uniquely characterized by the two parameters (S, ξ): these two numbers completely determine the entire evolution under the effect of radiation...

  3. Physics of black holes

    Thorne, Kip S.
    The activity at the galactic center might be fuelled by energy release near a large black hole. In this talk I describe some relativistic effects which may be relevant to this process. I use Newtonian language so far as possible and illustrate the effects with simple  analogies. Specifically, I describe the gravitational field near a black hole, Lens‐Thirring and geodetic precession, electro‐magnetic energy extraction of the spin energy of a black hole and the structure of accretion tori around black holes.

  4. Probing Sagittarius A* accretion with ALMA

    Murchikova, Elena
    The submm Hydrogen recombination line technique can be used as a probe of the Galactic Center. We present the results of our H30α observations of ionized gas from within 0.015 pc around SgrA*. The observations were obtained on ALMA in cycle 3. The line was not detected, but we were able to set a limit on the mass of the cool gas (T~ 10^4 K) at 2 × 10^(-3)M⊙. This is the unique probe of gas cooler than T ~10^6 K traced by X-ray emission. The total amount of gas near SgrA* gives us clues to understanding the accretion rate...

  5. Near Infrared Imaging of the Hubble Deep Field with the Keck Telescope

    Hogg, David W.; Neugebauer, G.; Armus, Lee; Matthews, K.; Pahre, Michael A.; Soifer, B. T.; Weinberger, A. J.
    Two deep K-band (2.2 ¡im) images, with point-source detection limits of K=25.2 mag (one sigma), taken with the Keck Telescope in subfields of the Hubble Deep Field, are presented and analyzed. A sample of objects to K=24 mag is constructed and V_(606)—I_(814) and I_(814)-K colors are measured. By stacking visually selected objects, mean I_(814)—K colors can be measured to very faint levels; the mean I_(814)—K color is constant with apparent magnitude down to V_(606) = 28 mag.

  6. Planet-induced Stellar Pulsations in HAT-P-2's Eccentric System

    De Wit, Julien; Lewis, Nikole K.; Knutson, Heather A.; Fuller, Jim; Antoci, Victoria; Fulton, Benjamin J.; Laughlin, Gregory; Deming, Drake; Shporer, Avi; Batygin, Konstantin; Cowan, Nicolas B.; Agol, Eric; Burrows, Adam S.; Fortney, Jonathan J.; Langton, Jonathan; Showman, Adam P.
    Extrasolar planets on eccentric short-period orbits provide a laboratory in which to study radiative and tidal interactions between a planet and its host star under extreme forcing conditions. Studying such systems probes how the planet's atmosphere redistributes the time-varying heat flux from its host and how the host star responds to transient tidal distortion. Here, we report the insights into the planet–star interactions in HAT-P-2's eccentric planetary system gained from the analysis of ~350 hr of 4.5 μm observations with the Spitzer Space Telescope. The observations show no sign of orbit-to-orbit variability nor of orbital evolution of the eccentric planetary...

  7. An architecture for efficient multimodal gravitational wave parameter estimation with linear surrogate models

    O'Shaughnessy, Richard; Blackman, Jonathan; Field, Scott E.
    The recent direct detection of gravitational waves has further emphasized the need for fast, low-cost, and accurate methods to infer the parameters of gravitational wave sources. The performance of these calculations is limited by the cost of evaluating the likelihood function, due to expense in data handling and waveform generation. Building on recently developed surrogate models and a novel parameter estimation pipeline, we show how to quickly generate the likelihood function as a simple, analytic closed-form expression. Using a simple variant of a production-scale parameter estimation code, we demonstrate our method using surrogate models of effective-one-body and numerical relativity waveforms. Our study is the first time these models have...

  8. An architecture for efficient multimodal gravitational wave parameter estimation with linear surrogate models

    O'Shaughnessy, Richard; Blackman, Jonathan; Field, Scott E.
    The recent direct detection of gravitational waves has further emphasized the need for fast, low-cost, and accurate methods to infer the parameters of gravitational wave sources. The performance of these calculations is limited by the cost of evaluating the likelihood function, due to expense in data handling and waveform generation. Building on recently developed surrogate models and a novel parameter estimation pipeline, we show how to quickly generate the likelihood function as a simple, analytic closed-form expression. Using a simple variant of a production-scale parameter estimation code, we demonstrate our method using surrogate models of effective-one-body and numerical relativity waveforms. Our study is the first time these models have...

  9. Equation of State Effects on Gravitational Waves from Rotating Core Collapse

    Richers, S.; Ott, C. D.; Abdikamalov, E.; O'Connor, E.; Sullivan, C.
    Gravitational waves (GWs) generated by axisymmetric rotating collapse, bounce, and early postbounce phases of a galactic core-collapse supernova will be detectable by current-generation gravitational wave observatories. Since these GWs are emitted from the quadrupole-deformed nuclear-density core, they may encode information on the uncertain nuclear equation of state (EOS). We examine the effects of the nuclear EOS on GWs from rotating core collapse and carry out 1824 axisymmetric general-relativistic hydrodynamic simulations that cover a parameter space of 98 different rotation profiles and 18 different EOS. We show that the bounce GW signal is largely independent of the EOS and sensitive primarily to the ratio of rotational to gravitational energy, and...

  10. Are the Formation and Abundances of Metal-poor Stars the Result of Dust Dynamics?

    Hopkins, Philip F.; Conroy, Charlie
    Large dust grains can fluctuate dramatically in their local density, relative to the gas, in neutral turbulent disks. Small, high-redshift galaxies (before reionization) represent ideal environments for this process. We show via simple arguments and simulations that order-of-magnitude fluctuations are expected in local abundances of large grains (>100 Å) under these conditions. This can have important consequences for star formation and stellar metal abundances in extremely metal-poor stars. Low-mass stars can form in dust-enhanced regions almost immediately after some dust forms even if the galaxy-average metallicity is too low for fragmentation to occur. We argue that the metal abundances of...

  11. Dynamical ejecta from precessing neutron star-black hole mergers with a hot, nuclear-theory based equation of state

    Foucart, F.; Desai, D.; Brege, W.; Duez, M. D.; Kasen, D.; Hemberger, D. A.; Kidder, L. E.; Pfeiffer, H. P.; Scheel, M. A.
    Neutron star-black hole binaries are among the strongest sources of gravitational waves detectable by current observatories. They can also power bright electromagnetic signals (gamma-ray bursts, kilonovae), and may be a significant source of production of r-process nuclei. A misalignment of the black hole spin with respect to the orbital angular momentum leads to precession of that spin and of the orbital plane, and has a significant effect on the properties of the post-merger remnant and of the material ejected by the merger. We present a first set of simulations of precessing neutron star-black hole mergers using a hot, composition dependent,...

  12. Extraction of gravitational-wave energy in higher dimensional numerical relativity using the Weyl tensor

    Cook, William G.; Sperhake, Ulrich
    Gravitational waves are one of the most important diagnostic tools in the analysis of strong-gravity dynamics and have been turned into an observational channel with LIGO's detection of GW150914. Aside from their importance in astrophysics, black holes and compact matter distributions have also assumed a central role in many other branches of physics. These applications often involve spacetimes with D  >  4 dimensions where the calculation of gravitational waves is more involved than in the four dimensional case, but has now become possible thanks to substantial progress in the theoretical study of general relativity in D  >  4. Here, we develop a numerical implementation...

  13. Tidally Induced Pulsations in Kepler Eclipsing Binary KIC 3230227

    Guo, Zhao; Gies, Douglas R.; Fuller, Jim
    KIC 3230227 is a short period (P ≈ 7.0 days) eclipsing binary with a very eccentric orbit (e = 0.6). From combined analysis of radial velocities and Kepler light curves, this system is found to be composed of two A-type stars, with masses of M_1 = 1.84 ± 0.18 M_⊙, M_2 = 1.73 ± 0.17 M_⊙ and radii of R_1 = 2.01 ± 0.09 R_⊙, R_2 = 1.68 ± 0.08 R_⊙ for the primary and secondary, respectively. In addition to an eclipse, the binary light curve shows a brightening and dimming near periastron, making this a somewhat rare eclipsing heartbeat...

  14. Post-outburst Radio Observations of the High Magnetic Field Pulsar PSR J1119-6127

    Majid, Walid A.; Pearlman, Aaron B.; Dobreva, Tatyana; Horiuchi, Shinji; Kocz, Jonathon; Lippuner, Jonas; Prince, Thomas A.
    We have carried out high-frequency radio observations of the high magnetic field pulsar PSR J1119-6127 following its recent X-ray outburst. While initial observations showed no evidence of significant radio emission, subsequent observations detected pulsed emission across a large frequency band. In this Letter, we report on the initial disappearance of the pulsed emission and its prompt reactivation and dramatic evolution over several months of observation. The periodic pulse profile at S-band (2.3 GHz) after reactivation exhibits a multi-component emission structure, while the simultaneous X-band (8.4 GHz) profile shows a single emission peak. Single pulses were also detected at S-band near...

  15. Under pressure: quenching star formation in low-mass satellite galaxies via stripping

    Fillingham, Sean P.; Cooper, Michael C.; Pace, Andrew B.; Boylan-Kolchin, Michael; Bullock, James S.; Garrison-Kimmel, Shea; Wheeler, Coral
    Recent studies of galaxies in the local Universe, including those in the Local Group, find that the efficiency of environmental (or satellite) quenching increases dramatically at satellite stellar masses below ∼10^8 M⊙. This suggest a physical scale where quenching transitions from a slow ‘starvation’ mode to a rapid ‘stripping’ mode at low masses. We investigate the plausibility of this scenario using observed H I surface density profiles for a sample of 66 nearby galaxies as inputs to analytic calculations of ram-pressure and turbulent viscous stripping. Across a broad range of host properties, we find that stripping becomes increasingly effective at M* ≲...

  16. Feedback first: the surprisingly weak effects of magnetic fields, viscosity, conduction, and metal diffusion on galaxy formation

    Su, Kung-Yi; Hopkins, Philip F.; Hayward, Christopher C.; Faucher-Giguère, Claude-André; Kereš, Dušan; Ma, Xiangcheng; Robles, Victor H.
    Using high-resolution simulations with explicit treatment of stellar feedback physics based on the FIRE (Feedback in Realistic Environments) project, we study how galaxy formation and the interstellar medium (ISM) are affected by magnetic fields, anisotropic Spitzer-Braginskii conduction and viscosity, and sub-grid turbulent metal diffusion. We consider controlled simulations of isolated (non-cosmological) galaxies but also a limited set of cosmological "zoom-in" simulations. Although simulations have shown significant effects from these physics with weak or absent stellar feedback, the effects are much weaker than those of stellar feedback when the latter is modeled explicitly. The additional physics have no systematic effect on...

  17. ALMA Resolves the Nuclear Disks of Arp 220

    Scoville, Nick; Murchikova, Lena; Walter, Fabian; Vlahakis, Catherine; Koda, Jin; Vanden Bout, Paul; Barnes, Joshua; Henrquist, Lars; Sheth, Kartik; Yun, Min; Sanders, David; Armus, Lee; Cox, Pierre; Thompson, Todd; Robertson, Brant; Zschaechner, Laura; Tacconi, Linda; Torrey, Paul; Hayward, Christopher C.; Genzel, Reinhard; Hopkins, Phil; van der Werf, Paul; Decarli, Roberto
    We present 90 mas (37 pc) resolution ALMA imaging of Arp 220 in the CO (1-0) line and continuum at λ = 2.6 mm. The internal gas distribution and kinematics of both galactic nuclei are well resolved for the first time. In the west nucleus, the major gas and dust emission extends out to 0.”2 radius (74 pc); the central resolution element shows a strong peak in the dust emission but a factor of 3 dip in the CO line emission. In this nucleus, the dust is apparently optically thick (τ_(2.6 mm) ~ 1) at λ = 2.6 mm with...

  18. Dynamics of Stellar Spin Driven by Planets Undergoing Lidov-Kozai Migration: Paths to Spin-Orbit Misalignment

    Storch, Natalia I.; Lai, Dong; Anderson, Kassandra R.
    Many exoplanetary systems containing hot Jupiters (HJs) exhibit significant misalignment between the spin axes of the host stars and the orbital angular momentum axes of the planets (“spin-orbit misalignment”). High-eccentricity migration involving Lidov-Kozai oscillations of the planet’s orbit induced by a distant perturber is a possible channel for producing such misaligned HJ systems. Previous works have shown that the dynamical evolution of the stellar spin axis during the high-e migration plays a dominant role in generating the observed spin-orbit misalignment. Numerical studies have also revealed various patterns of the evolution of the stellar spin axis leading to the final misalignment....

  19. Stream-subhalo interactions in the Aquarius simulations

    Sanderson, R. E.; Vera-Ciro, C.; Helmi, A.; Heit, J.
    Aims. We perform the first self-consistent measurement of the rate of interactions between stellar tidal streams created by disrupting satellites and dark subhalos in a cosmological simulation of a Milky-Way-mass galaxy. Methods. Using a retagged version of the Aquarius A dark-matter-only simulation, we selected 18 streams of tagged star particles that appear thin at the present day and followed them from the point their progenitors accrete onto the main halo, recording in each snapshot the characteristics of all dark-matter subhalos passing within several distance thresholds of any tagged star particle in each stream. We considered distance thresholds corresponding to constant impact...

  20. Modeling the source of GW150914 with targeted numerical-relativity simulations

    Lovelace, Geoffrey; Lousto, Carlos O.; Healy, James; Scheel, Mark A.; Garcia, Alyssa; O’Shaughnessy, Richard; Boyle, Michael; Campanelli, Manuela; Hemberger, Daniel A.; Kidder, Lawrence E.; Pfeiffer, Harald P.; Szilágyi, Béla; Teukolsky, Saul A.; Zlochower, Yosef
    In fall of 2015, the two LIGO detectors measured the gravitational wave signal GW150914, which originated from a pair of merging black holes (Abbott et al Virgo, LIGO Scientific 2016 Phys. Rev. Lett. 116 061102). In the final 0.2 s (about 8 gravitational-wave cycles) before the amplitude reached its maximum, the observed signal swept up in amplitude and frequency, from 35 Hz to 150 Hz. The theoretical gravitational-wave signal for merging black holes, as predicted by general relativity, can be computed only by full numerical relativity, because analytic approximations fail near the time of merger. Moreover, the nearly-equal masses, moderate spins,...

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