Jeremiah P. Ostriker

Princeton University, Princeton, New Jersey, United States

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Publications (373)2089.46 Total impact

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    ABSTRACT: We investigate the evolution of stellar population gradients from $z=2$ to $z=0$ in massive galaxies at large radii ($r > 2R_{\mathrm{eff}}$) using ten cosmological zoom simulations of halos with $6 \times 10^{12} M_{\odot} < M_{\mathrm{halo}} < 2 \times 10^{13}M_{\odot}$. The simulations follow metal cooling and enrichment from SNII, SNIa and AGB winds. We explore the differential impact of an empirical model for galactic winds that reproduces the mass-metallicity relation and its evolution with redshift. At larger radii the galaxies, for both models, become more dominated by stars accreted from satellite galaxies in major and minor mergers. In the wind model, fewer stars are accreted, but they are significantly more metal poor resulting in steep global metallicity ($\langle \nabla Z_{\mathrm{stars}} \rangle= -0.35$ dex/dex) and color (e.g. $\langle \nabla g-r \rangle = -0.13$ dex/dex) gradients in agreement with observations. In contrast, colour and metallicity gradients of the models without winds are inconsistent with observations. Age gradients are in general mildly positive at $z=0$ ($\langle \nabla Age_{\mathrm{stars}} \rangle= 0.04$ dex/dex) with significant differences between the models at higher redshift. We demonstrate that for the wind model, stellar accretion is steepening existing in-situ metallicity gradients by about 0.2 dex by the present day and helps to match observed gradients of massive early-type galaxies at large radii. Colour and metallicity gradients are significantly steeper for systems which have accreted stars in minor mergers, while galaxies with major mergers have relatively flat gradients, confirming previous results. This study highlights the importance of stellar accretion for stellar population properties of massive galaxies at large radii, which can provide important constraints for formation models.
    10/2014;
  • Brandon S. Hensley, Jeremiah P. Ostriker, Luca Ciotti
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    ABSTRACT: We study the effects of a detailed dust treatment on the properties and evolution of early-type galaxies containing central black holes, as determined by active galactic nucleus (AGN) feedback. We find that during cooling flow episodes, radiation pressure on the dust in and interior to infalling shells of cold gas can greatly impact the amount of gas able to be accreted and therefore the frequency of AGN bursts. However, the overall hydrodynamic evolution of all models, including mass budget, is relatively robust to the assumptions on dust. We find that IR re-emission from hot dust can dominate the bolometric luminosity of the galaxy during the early stages of an AGN burst, reaching values in excess of 1046 erg s–1. The AGN-emitted UV is largely absorbed, but the optical depth in the IR does not exceed unity, so the radiation momentum input never exceeds L BH/c. We constrain the viability of our models by comparing the AGN duty cycle, broadband luminosities, dust mass, black hole mass, and other model predictions to current observations. These constraints force us towards models wherein the dust to metals ratios are 1% of the Galactic value, and only models with a dynamic dust to gas ratio are able to produce both quiescent galaxies consistent with observations and high obscured fractions during AGN "on" phases. During AGN outbursts, we predict that a large fraction of the FIR luminosity can be attributed to warm dust emission ( 100 K) from dense dusty gas within ≤1 kpc reradiating the AGN UV emission.
    The Astrophysical Journal 06/2014; 789(1):78. · 6.73 Impact Factor
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    ABSTRACT: We employ cosmological hydrodynamical simulations to investigate the effects of AGN feedback on the formation of massive galaxies with present-day stellar masses of $M_{stel} > 8.9 \times 10^{10} M_{sun}$. Using smoothed particle hydrodynamics simulations with a pressure-entropy formulation that allows an improved treatment of contact discontinuities and fluid mixing, we run three sets of simulations of 20 halos with different AGN feedback models: (1) no feedback, (2) thermal feedback, and (3) mechanical and radiation feedback. We assume that seed black holes are present at early cosmic epochs at the centre of emerging dark matter halos and trace their mass growth via gas accretion and mergers with other black holes. Both feedback models successfully recover the observed M_BH - sigma relation and black hole-to-stellar mass ratio for simulated central early-type galaxies. The baryonic conversion efficiencies are reduced by a factor of two compared to models without any AGN feedback at all halo masses. However, massive galaxies simulated with thermal AGN feedback show a factor of ~ 10-100 higher X-ray luminosities than observed. The mechanical and radiation feedback model reproduces the observed correlation between X-ray luminosities and velocity dispersion, e.g. for galaxies with sigma=200 km/s, the X-ray luminosity is reduced from $10^{42}$ erg/s to $10^{40}$ erg/s. It also efficiently suppresses late time star formation, reducing the specific star formation rate from $10^{-10.5}$ $\rm yr^{-1}$ to $10^{-14}$ $\rm yr^{-1}$ on average and resulting in quiescent galaxies since z=2, whereas the thermal feedback model shows higher late time in-situ star formation rates than observed.
    03/2014;
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    ABSTRACT: Based on two-dimensional high resolution hydrodynamic numerical simulation, we study the mechanical and radiative feedback effects from the central AGN on the cosmological evolution of an isolated elliptical galaxy. Physical processes such as star formation and supernovae are considered. The inner boundary of the simulation domain is carefully chosen so that the fiducial Bondi radius is resolved and the accretion rate of the black hole is determined self-consistently. In analogy to previous works, we assume that the specific angular momentum of the galaxy is low. It is well-known that when the accretion rates are high and low, the central AGNs will be in cold and hot accretion modes, which correspond to the radiative and kinetic feedback modes, respectively. The emitted spectrum from the hot accretion flows is harder than that from the cold accretion flows, which results in a higher Compton temperature accompanied by a more efficient radiative heating. Such a difference of the Compton temperature between the two feedback modes, the focus of this study, has been neglected in previous works. Significant differences in the kinetic feedback mode are found as a result of the stronger Compton heating and accretion becomes more chaotic. More importantly, if we constrain models to correctly predict black hole growth and AGN duty cycle after cosmological evolution, we find that the favored model parameters are constrained: mechanical feedback efficiency diminishes with decreasing luminosity (the maximum efficiency being $\simeq 10^{-3.5}$) and X-ray Compton temperature increases with decreasing luminosity, although models with fixed mechanical efficiency and Compton temperature can be found that are satisfactory as well. We conclude that radiative feedback in the kinetic mode is much more important than previously thought.
    The Astrophysical Journal 03/2014; 789(2). · 6.73 Impact Factor
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    Brandon S. Hensley, Jeremiah P. Ostriker, Luca Ciotti
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    ABSTRACT: We study the effects of a detailed treatment of dust physics on the properties and evolution of early-type galaxies containing central black holes, as determined by AGN feedback. We find that during cooling flow episodes, radiation pressure on the dust in and interior to infalling shells of cold gas can greatly impact the amount of gas able to be accreted and therefore the frequency of AGN bursts. However, the overall hydrodynamic evolution of all models, including mass budget, is relatively robust to the assumptions on dust. Our most detailed models find that the dust to metals ratio is reduced by factors of $10^{-1}-10^{-2}$ relative to Milky Way abundances, and in quiescent phases the dust content of the galaxy would result in ~0.03 magnitudes of extinction to the center of the galaxy. We find that IR re-emission from hot dust can dominate the bolometric luminosity of the galaxy during the early stages of an AGN burst, reaching values in excess of $10^{46}$ erg/s. The AGN-emitted UV is largely absorbed, but the optical depth in the IR does not exceed unity, so the radiation momentum input never exceeds $L_{\rm BH}/c$. We constrain the viability of our models by comparing the energy output in each band, AGN duty cycle, FIR emission, dust mass and opacity, black hole mass, and other model predictions to current observations. These constraints force us to models wherein the destruction of dust in hot gas by sputtering and the competing growth of dust in cold gas results in depletion at the $\simeq10^{-2}$ level, and only models with a dynamic dust to gas ratio are able to produce both quiescent galaxies consistent with observations and high obscured fractions during AGN "on" phases. During AGN outbursts, we predict that a large fraction of the FIR luminosity can be attributed to warm dust emission ($\simeq100$ K) from dense dusty gas within $\leq$1 kpc reradiating the AGN UV emission.
    02/2014;
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    Adam S Burrows, Jeremiah P Ostriker
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    ABSTRACT: Using basic physical arguments, we derive by dimensional and physical analysis the characteristic masses and sizes of important objects in the universe in terms of just a few fundamental constants. This exercise illustrates the unifying power of physics and the profound connections between the small and the large in the cosmos we inhabit. We focus on the minimum and maximum masses of normal stars, the corresponding quantities for neutron stars, the maximum mass of a rocky planet, the maximum mass of a white dwarf, and the mass of a typical galaxy. To zeroth order, we show that all these masses can be expressed in terms of either the Planck mass or the Chandrasekar mass, in combination with various dimensionless quantities. With these examples, we expose the deep interrelationships imposed by nature between disparate realms of the universe and the amazing consequences of the unifying character of physical law.
    Proceedings of the National Academy of Sciences 01/2014; · 9.81 Impact Factor
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    ABSTRACT: We investigate the differential effects of metal cooling and galactic stellar winds on the cosmological formation of individual galaxies with three sets of cosmological, hydrodynamical zoom simulations of 45 halos in the mass range 10^11<M_halo<10^13M_sun. Models including both galactic winds and metal cooling (i) suppress early star formation at z>1 and predict reasonable star formation histories, (ii) produce galaxies with high cold gas fractions (30-60 per cent) at high redshift, (iii) significantly reduce the galaxy formation efficiencies for halos (M_halo<10^12M_sun) at all redshifts in agreement with observational and abundance matching constraints, (iv) result in high-redshift galaxies with reduced circular velocities matching the observed Tully-Fisher relation at z~2, and (v) significantly increase the sizes of low-mass galaxies (M_stellar<3x10^10M_sun) at high redshift resulting in a weak size evolution - a trend in agreement with observations. However, the low redshift (z<0.5) star formation rates of massive galaxies are higher than observed (up to ten times). No tested model predicts the observed size evolution for low-mass and high-mass galaxies simultaneously. Due to the delayed onset of star formation in the wind models, the metal enrichment of gas and stars is delayed and agrees well with observational constraints. Metal cooling and stellar winds are both found to increase the ratio of in situ formed to accreted stars - the relative importance of dissipative vs. dissipationless assembly. For halo masses below ~10^12M_sun, this is mainly caused by less stellar accretion and compares well to predictions from semi-analytical models but still differs from abundance matching models. For higher masses, the fraction of in situ stars is over-predicted due to the unrealistically high star formation rates at low redshifts.
    Monthly Notices of the Royal Astronomical Society 09/2013; 436(4). · 5.52 Impact Factor
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    ABSTRACT: We employ hydrodynamical simulations to study the effect of AGN mechanical and radiation feedback on the formation of bulge dominated galaxies via mergers of disk galaxies. The merging galaxies have mass-ratios of 1:1 to 6:1 and include pre-existing hot gaseous halos to properly account for the global impact of AGN feedback. We compare three models: (1) no black hole and no AGN feedback; (2) thermal AGN feedback; and (3) mechanical and radiative AGN feedback. The last model is motivated by observations of broad absorption line quasars which show winds with initial velocities of v_w ~ 10,000 km/s and also heating associated with the central AGN X-ray radiation. The primary changes in gas properties due to mechanical AGN feedback are lower thermal X-ray luminosity from the final galaxy - in better agreement with observations - and galactic outflows with higher velocity ~ 1000 km/s similar to recent direct observations of nearby merger remnants. The kinetic energy of the outflowing gas is a factor of ~ 20 higher than in the thermal feedback case. All merger remnants with momentum-based AGN feedback, independent of their progenitor mass-ratios, follow the observed relations between stellar velocity dispersion and black hole mass (M_BH-\sigma) as well as X-ray luminosity (L_X-\sigma) with 10^37.5 < L_X (0.3-8 keV) < 10^39.2 for velocity dispersions in the range of 120 km/s < \sigma < 190 km/s. In addition, the mechanical feedback produces a much greater AGN variability. We also show that gas is more rapidly and impulsively stripped from the galactic centres driving a moderate increase in galaxy size and decrease in central density with the mechanical AGN feedback model. However, the black hole mass growth required to produce the observed galaxy size and central density evolution is inconsistent with the observed M_BH-{\sigma} relation.
    08/2013;
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    Oleg Y. Gnedin, Jeremiah P. Ostriker, Scott Tremaine
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    ABSTRACT: We revisit the hypothesis that dense galactic nuclei are formed from inspiraling globular clusters. Recent advances in understanding of the continuous formation of globular clusters over cosmic time and the concurrent evolution of the galaxy stellar distribution allow us to construct a simple model that matches the observed spatial and mass distributions of clusters in the Galaxy and the giant elliptical galaxy M87. In order to compare with observations, we model the effects of dynamical friction and dynamical evolution, including stellar mass loss, tidal stripping of stars, and tidal disruption of clusters by the growing galactic nucleus. We find that inspiraling globular clusters form a dense central stellar cluster with an effective radius of several pc, with mass and radius comparable to the typical values in observed nuclear star clusters in late-type and low-mass early-type galaxies. The density contrast associated with the nuclear star cluster is less pronounced in giant elliptical galaxies. Thus disrupted globular clusters may contribute most of the mass of nuclear star clusters (NSCs) in galaxies with stellar mass below 10^{11} Msun. Our results indicate that the NSC mass as a fraction of mass of the galaxy stellar spheroid scales as M_{NSC}/M_{sph} ~ 0.0025 M_{sph,11}^{-0.5}. However, some fraction of the accumulated stellar debris may seed the growth of a central black hole via stellar dynamical core collapse, thereby relieving the problem of how to form luminous quasars at high redshift. Both the formation time of NSC and the core collapse time are less than 1 Gyr for galaxies more massive than the Milky Way.
    The Astrophysical Journal 07/2013; 785(1). · 6.73 Impact Factor
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    ABSTRACT: We (the CAGE team) present a possible solution to the scaling problem that is inherent to cosmological simulations of structure formation. With an increasing number of computational nodes the resources that are lost due to communication overhead and load balancing is growing and thereby limiting the problem sizes and/or resolution level that can be computed in a reasonable amount of time. To alleviate this problem, we propose the HECA (Hierarchical Ensemble Computing Algorithm). Instead of running a full-box cosmological simulation, we perform multiple (only limited by the number of processing nodes) zoom-in simulations concurrently that are independent of each other and thereby providing a perfect scaling to large core counts. In these simulations we can reach a much higher resolution level that would be unfeasible to achieve in a full-box simulation. We show that with the help of HECA we are able to efficiently use the ressources provided by modern petascale supercomputers to simulate a statistically significant sample of galaxies.
    Proceedings of the Conference on Extreme Science and Engineering Discovery Environment: Gateway to Discovery; 07/2013
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    ABSTRACT: Accretion and merger triggered accretion episodes are thought to primarily contribute to the mass accumulation history of supermassive black holes throughout cosmic time. While this might be the dominant growth mode at high redshifts, at lower redshifts and for the most massive black holes, mergers themselves might add significantly to the mass budget. In this paper, we use merger trees derived from hydrodynamical cosmological simulations of a cluster and void region to examine the growth of SMBHs from 4 > z > 0. Mass gains from gas accretion and BH-BH mergers are tracked as are black holes that remain unmerged and "orbiting" due to insufficient dynamical friction in a merger remnant, as well as those that are ejected due to gravitational recoil. We find that gas accretion remains the dominant source of mass accumulation in almost all of the SMBHs produced; mergers contribute an average of 3.3 +/- 0.2% for all SMBHs in the cluster, and 1.3 +/- 0.2% in the void from z = 4 to 0. However, mergers are significant for massive SMBHs, with the contribution from mergers reaching a maximum of 20% in the cluster for black holes with mass around 10^9 M_sun. We also find that the total mass in orbiting SMBHs is generally negligible in the void, but significant in the cluster, with a median value of M_orbiting >~ 10^7 M_sun per galaxy for galaxies with stellar mass M_{*} > 10^11.5 M_sun. We find that 40% of SMBHs and approximately 14% of the total SMBH mass is found orbiting in the cluster region at z = 0. We estimate the correction to the Soltan argument due to such orbiting SMBHs as well as SMBHs ejected via gravitational slingshot effects to be in the range 1.6 - 15%, with a mean value of 7.4 +/- 3.7% in the estimate of the inventory of the integrated accreted mass density of SMBHs. We also calculate the total energy output and strain due to gravitational waves emitted by merging SMBHs.
    07/2013;
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    Chao Liu, Feng Yuan, Jeremiah P. Ostriker, Zhaoming Gan, Xiaohong Yang
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    ABSTRACT: We perform time-dependent, 2DHD numerical simulations to study the dynamics of a slowly rotating accretion flow from sub-pc to pc scales under the irradiation from the central AGN. Compared to previous work, we improve the calculation of the radiative force due to X-rays. More importantly, in addition to radiative pressure and radiative heating/cooling directly from the central AGN, in the momentum equation we also include the force due to the scattered and reprocessed photons. We find that the accretion flow properties change significantly due to this "re-radiation" effect. The inflow rate at the inner boundary is reduced, while the outflow rate at the outer boundary is enhanced by about one order of magnitude. This effect is more significant when the density at the outer boundary is higher. The properties of outflows such as velocity, momentum and energy fluxes, and the ratio of outflow rate and the accretion rate, are calculated. We find that the efficiency of transferring the radiation power into the kinetic power of outflow is typically $10^{-3}$, far below the value of $\sim 0.05$ which is assumed in some cosmological simulations. The effect of the temperature of the gas at the outer boundary ($T_0$) is investigated. When $T_0$ is high, the emitted luminosity of the accretion flow oscillates. This is because in this case the gas around the Bondi radius can be more easily heated to be above the virial temperature due to its high internal energy. Another question we hope to address is the so-called "sub-Eddington" puzzle. Observationally, the luminosity of almost all AGNs are sub-Eddington, while theoretically the luminosity of an accretion flow can easily be super-Eddington. We find that even when the re-radiation effect is included and outflow does become much stronger, the luminosity, while reduced, can still be super-Eddington.
    Monthly Notices of the Royal Astronomical Society 04/2013; 434(2). · 5.52 Impact Factor
  • G. S. Novak, J. P. Ostriker, L. Ciotti
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    ABSTRACT: To facilitate the study of black hole fuelling, star formation and feedback in galaxies, we outline a method for treating the radial forces on interstellar gas due to absorption of photons by dust grains. The method gives the correct behaviour in all of the relevant limits [dominated by the central point source; dominated by the distributed isotropic source; optically thin; optically thick to ultraviolet (UV)/optical; optically thick to infrared (IR)] and reasonably interpolates between the limits when necessary. The method is explicitly energy conserving so that UV/optical photons that are absorbed are not lost, but are rather redistributed to the IR where they may scatter out of the galaxy. We implement the radiative transfer algorithm in a two-dimensional hydrodynamical code designed to study feedback processes in the context of early-type galaxies. We find that the dynamics and final state of simulations are measurably but only moderately affected by radiative forces on dust, even when assumptions about the dust-to-gas ratio are varied from zero to a value appropriate for the Milky Way. In simulations with high gas densities designed to mimic ultraluminous IR galaxies with a star formation rate of several hundred solar masses per year, dust makes a more substantial contribution to the dynamics and outcome of the simulation. We find that, despite the large opacity of dust to UV radiation, the momentum input to the flow from radiation very rarely exceeds L/c due to two factors: the low opacity of dust to the re-radiated IR and the tendency for dust to be destroyed by sputtering in hot gas environments. We also develop a simplification of our radiative transfer algorithm that respects the essential physics but is much easier to implement and requires a fraction of the computational cost.
    Monthly Notices of the Royal Astronomical Society 12/2012; 427(4):2734-2756. · 5.52 Impact Factor
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    Sean T. McWilliams, Jeremiah P. Ostriker, Frans Pretorius
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    ABSTRACT: We present a model for merger-driven evolution of the mass function for massive galaxies and their central supermassive black holes at late times. We discuss the current observational evidence in favor of merger-driven massive galaxy evolution during this epoch, and demonstrate that the observed evolution of the mass function can be reproduced by evolving an initial mass function under the assumption of negligible star formation. We calculate the stochastic gravitational wave signal from the resulting black-hole binary mergers in the low redshift universe (z <= 1) implied by this model, and find that this population has a signal-to-noise ratio as much as ~5x larger than previous estimates for pulsar timing arrays, with an expectation value for the characteristic strain h_c (f=1 yr^{-1}) = 4.1 x 10^{-15} that may already be in tension with observational constraints, and a {2-sigma, 3-sigma} lower limit within this model of h_c (f=1 yr^{-1}) = {1.1 x 10^{-15}, 6.8 x 10^{-16}}. The strength of this signal is sufficient to make it detectable with high probability under conservative assumptions within the next several years, if the principle assumption of merger-driven galaxy evolution since z = 1 holds true. For cases where a galaxy merger fails to lead to a black hole merger, we estimate the probability for a given number of satellite unmerged black holes to remain within a massive host galaxy, and interpret the result in light of ULX observations. In particular, we find that the brightest cluster galaxies should have 1-2 such sources with luminosities above 10^{39} erg/s, which is consistent with the statistics of observed ULXs.
    The Astrophysical Journal 11/2012; · 6.73 Impact Factor
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    Sean T. McWilliams, Jeremiah P. Ostriker, Frans Pretorius
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    ABSTRACT: Recent observations of massive galaxies indicate that they double in mass and quintuple in size between redshift z = 1 and the present, despite undergoing very little star formation, suggesting that galaxy mergers drive the evolution. Since these galaxies will contain supermassive black holes, this suggests a larger black hole merger rate, and therefore a larger gravitational-wave signal, than previously expected. We calculate the merger-driven evolution of the mass function, and find that merger rates are 10 to 30 times higher and gravitational waves are 3 to 5 times stronger than previously estimated, so that the gravitational-wave signal may already be detectable with existing data from pulsar timing arrays. We also provide an explanation for the disagreement with past estimates that were based on dark matter halo simulations.
    11/2012;
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    Ena Choi, Jeremiah P. Ostriker, Thorsten Naab, Peter H. Johansson
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    ABSTRACT: We study the growth of black holes (BHs) in galaxies using three-dimensional smoothed particle hydrodynamic simulations with new implementations of the momentum mechanical feedback, and restriction of accreted elements to those that are gravitationally bound to the BH. We also include the feedback from the X-ray radiation emitted by the BH, which heats the surrounding gas in the host galaxies, and adds radial momentum to the fluid. We perform simulations of isolated galaxies and merging galaxies and test various feedback models with the new treatment of the Bondi radius criterion. We find that overall the BH growth is similar to what has been obtained by earlier works using the Springel, Di Matteo, and Hernquist algorithms. However, the outflowing wind velocities and mechanical energy emitted by winds are considerably higher (v{sub w} {approx} 1000-3000 km s{sup -1}) compared to the standard thermal feedback model (v{sub w} {approx} 50-100 km s{sup -1}). While the thermal feedback model emits only 0.1% of BH released energy in winds, the momentum feedback model emits more than 30% of the total energy released by the BH in winds. In the momentum feedback model, the degree of fluctuation in both radiant and wind output is considerably larger than in standard treatments. We check that the new model of BH mass accretion agrees with analytic results for the standard Bondi problem.
    The Astrophysical Journal 08/2012; 754(2). · 6.73 Impact Factor
  • Ludwig Oser, Thorsten Naab, Jeremiah P. Ostriker, Peter H. Johansson
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    ABSTRACT: We use a large sample of cosmological re-simulations of individual massive galaxies to investigate the origin of the strong increase in sizes and weak decrease of the stellar velocity dispersions since z = 2. At the end of a rapid early phase of star-formation, where stars are created from infalling cold gas, our simulated galaxies are all compact with projected half-mass radii of ≲ 1 kpc and central line-of-sight velocity dispersions of ≈ 262 km s−1. At lower redshifts (z < 2) those galaxies grow predominantly by the accretion of smaller stellar systems and evolve towards the observed local mass-size and mass-velocity dispersion relations. This loss of compactness is accompanied with an increase of central dark matter fractions. We find that the structural evolution of massive galaxies can be explained by frequent minor stellar mergers, which is the dominant mode of accretion for our simulated galaxies.
    Proceedings of the International Astronomical Union 08/2012; 8(S295).
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    ABSTRACT: We (the CAGE team) present a possible solution to the scaling problem that is inherent to cosmological simulations of structure formation. With an increasing number of computational nodes the resources that are lost due to communication overhead and load balancing is growing and thereby limiting the problem sizes and/or resolution level that can be computed in a reasonable amount of time. To alleviate this problem, we propose the HECA (Hierarchical Ensemble Computing Algorithm). Instead of running a full-box cosmological simulation, we perform multiple (only limited by the number of processing nodes) zoom-in simulations concurrently that are independent of each other and thereby providing a perfect scaling to large core counts. In these simulations we can reach a much higher resolution level that would be unfeasible to achieve in a full-box simulation.
    Proceedings of the Extreme Scaling Workshop; 07/2012
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    Michael Hilz, Thorsten Naab, Jeremiah P. Ostriker
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    ABSTRACT: There is observational evidence for inside-out growth of elliptical galaxies since $z \gtrsim 2-3$, which is not driven by in-situ star formation. Many systems at high redshift have small sizes $\sim 1kpc$ and surface brightness profiles with low Sersic indices n. The most likely descendants have, on average, grown by a factor of two in mass and a factor of four in size, indicating $r \propto M^{\alpha}$ with $\alpha \gtrsim 2$. They also have surface brightness profiles with $n \gtrsim 5$. This evolution can be qualitatively explained on the basis of two assumptions: compact ellipticals predominantly grow by collisionless minor or intermediate 'dry' mergers, and they are embedded in massive dark matter halos. We draw these conclusions from idealized collisionless mergers spheroidal galaxies - with and without dark matter - with mass ratios of 1:1, 1:5, and 1:10. The sizes evolve as $r \propto M^{\alpha}$ with $\alpha < 2$ for mass-ratios of 1:1. For minor mergers of galaxies embedded in dark matter halos, the sizes grow significantly faster and the profile shapes change more rapidly. Mergers with moderate mass-ratios of 1:5 give $\alpha \sim 2.3$ and a final Sersic index of $n = 9.5$ after doubling the stellar mass. This is accompanied by a significant increase of the dark matter fraction within the stellar half-mass radius, driven by the strong size increase probing larger, dark matter dominated regions. Only a few intermediate mass-ratio mergers of galaxies embedded in massive dark matter halos can result in the observed concurrent inside-out growth and the rapid evolution in profile shapes. Apart from negative stellar metallicity gradients such a 'minor' merger scenario also predicts significantly lower dark matter fractions for $z \sim 2$ compact quiescent galaxies and their rare present day analogues (abbreviated).
    Monthly Notices of the Royal Astronomical Society 06/2012; 429(4). · 5.52 Impact Factor
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    Jason Li, Jeremiah Ostriker, Rashid Sunyaev
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    ABSTRACT: Accretion onto a supermassive black hole of a rotating inflow is a particularly difficult problem to study because of the wide range of length scales involved. There have been broadly utilized analytic and numerical treatments of the global properties of accretion flows, but detailed numerical simulations are required to address certain critical aspects. We use the ZEUS code to run hydrodynamical simulations of rotating, axisymmetric accretion flows with Bremsstrahlung cooling, considering solutions for which the centrifugal balance radius significantly exceeds the Schwarzschild radius, with and without viscous angular momentum transport. Infalling gas is followed from well beyond the Bondi radius down to the vicinity of the black hole. We produce a continuum of solutions with respect to the single parameter Mdot_Bondi/Mdot_Edd, and there is a sharp transition between two general classes of solutions at an Eddington ratio of Mdot_Bondi/Mdot_Edd ~ few x 10^(-2). Our high inflow solutions are very similar to the standard Shakura & Sunyaev (1973) results. But our low inflow results are to zeroth order the stationary Papaloizou and Pringle (1984) solution, which has no accretion. To next order in the small, assumed viscosity they show circulation, with disk and conical wind outflows almost balancing inflow. These solutions are characterized by hot, vertically extended disks, and net accretion proceeds at an extremely low rate, only of order alpha times the inflow rate. Our simulations have converged with respect to spatial resolution and temporal duration, and they do not depend strongly on our choice of boundary conditions.
    The Astrophysical Journal 06/2012; 767(2). · 6.73 Impact Factor

Publication Stats

19k Citations
2,089.46 Total Impact Points

Institutions

  • 1975–2014
    • Princeton University
      • • Department of Astrophysical Sciences
      • • Department of Physics
      Princeton, New Jersey, United States
  • 2012
    • West Virginia University
      Morgantown, West Virginia, United States
  • 2009
    • California Institute of Technology
      • Department of Astronomy
      Pasadena, California, United States
    • Pontifical Catholic University of Chile
      • Departamento de Astronomía y Astrofísica
      CiudadSantiago, Santiago, Chile
    • University of Bologna
      • Department of Physics and Astronomy DIFA
      Bolonia, Emilia-Romagna, Italy
  • 2008
    • Chinese Academy of Sciences
      • Shanghai Astronomical Observatory
      Peping, Beijing, China
  • 1977–2008
    • University of Cambridge
      • Institute of Astronomy
      Cambridge, ENG, United Kingdom
  • 2007
    • Los Alamos National Laboratory
      • Theoretical Division
      Los Alamos, California, United States
  • 1993–2007
    • TRI/Princeton
      Princeton, New Jersey, United States
  • 2003
    • Università degli Studi di Siena
      Siena, Tuscany, Italy
  • 2002
    • Cancer Research UK Cambridge Institute
      Cambridge, England, United Kingdom
    • Fermi National Accelerator Laboratory (Fermilab)
      Batavia, Illinois, United States
  • 1997–2000
    • The Astronomical Observatory of Brera
      Merate, Lombardy, Italy
  • 1998
    • The University of Tokyo
      Edo, Tōkyō, Japan
    • Seoul National University
      • Department of Physics and Astronomy
      Sŏul, Seoul, South Korea
  • 1996
    • University of Washington Seattle
      • Department of Astronomy
      Seattle, Washington, United States
  • 1995
    • University of Illinois, Urbana-Champaign
      • Department of Astronomy
      Urbana, IL, United States
  • 1974
    • Tel Aviv University
      Tell Afif, Tel Aviv, Israel