Jeremiah P. Ostriker

Princeton University, Princeton, New Jersey, United States

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Publications (270)1371.25 Total impact

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    Min-Su Shin, Jeremiah P. Ostriker, Luca Ciotti
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    ABSTRACT: By using high-resolution 1D hydrodynamical simulations, we investigate the effects of purely mechanical feedback from super massive black holes (SMBHs) in the evolution of elliptical galaxies for a broad range of feedback efficiencies and compare the results to four major observational constraints. In particular, we focus on 1) the central black hole to stellar mass ratio of the host galaxy, 2) the lifetime of the luminous quasar phase, 3) the mass of stars formed in the host galaxy within the last Gyr, and 4) the X-ray luminosity of the hot diffuse gas. As a result, we try to pin down the most successful range of mechanical feedback efficiencies. We find that while low feedback efficiencies result in too much growth of the SMBH, high efficiencies totally blow out the hot interstellar gas, and the models are characterized by very low thermal X-ray luminosity well below the observed range. The net lifetime of the quasar phase is strongly coupled to the mass ratio between SMBH and its host galaxy, while the X-ray luminosity is generally correlated to the recent star formation within the last Gyr. When considering the popularly adopted model of the constant feedback efficiency, the feedback energy deposited into the ambient medium should be more than 0.01% of the SMBH accretion energy to be consistent with the SMBH mass to stellar mass ratio in the local universe. Yet, the X-ray luminosity of the hot gas favors about 0.005% of the accretion energy as the mechanical AGN feedback energy. We conclude that the purely mechanical feedback mode is unlikely to be simultaneously compatible with all four observable tests, even allowing a broad range of feedback efficiencies, and that including both radiative and mechanical feedback together may be a solution to comply the observational constraints. [abridged]
    The Astrophysical Journal 05/2009; 711(1). · 6.73 Impact Factor
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    Paul Bode, Jeremiah P. Ostriker, Alexey Vikhlinin
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    ABSTRACT: The state of the hot gas in clusters of galaxies is investigated with a set of model clusters, created by assuming a polytropic equation of state (Gamma=1.2) and hydrostatic equilibrium inside gravitational potential wells drawn from a dark matter simulation. Star formation, energy input, and nonthermal pressure support are included. To match the gas fractions seen in non-radiative hydrodynamical simulations, roughly 5% of the binding energy of the dark matter must be transferred to the gas during cluster formation; the presence of nonthermal pressure support increases this value. In order to match X-ray observations, scale-free behavior must be broken. This can be due to either variation of the efficiency of star formation with cluster mass M_500, or the input of additional energy proportional to the formed stellar mass M_F. These two processes have similar effects on X-ray scalings. If 9% of the gas is converted into stars, independent of cluster mass, then feedback energy input of 1.2e-5*M_Fc^2 (or ~1.0 keV per particle) is required to match observed clusters. Alternatively, if the stellar mass fraction varies as M_500^-0.26 then a lower feedback of 4e-6*M_Fc^2 is needed, and if the stellar fraction varies as steeply as M_500^-0.49 then no additional feedback is necessary. The model clusters reproduce the observed trends of gas temperature and gas mass fraction with cluster mass, as well as observed entropy and pressure profiles; thus they provide a calibrated basis with which to interpret upcoming SZ surveys. One consequence of the increased gas energy is that the baryon fraction inside the virial radius is less than roughly 90% of the cosmic mean, even for the most massive clusters. Comment: Accepted by ApJ; 28 pages, 12 figures
    The Astrophysical Journal 05/2009; · 6.73 Impact Factor
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    S. Pellegrini, L. Ciotti, J.P. Ostriker
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    ABSTRACT: The centers of elliptical galaxies host supermassive black holes that significantly affect the surrounding interstellar medium through feedback resulting from the accretion process. The evolution of this gas and of the nuclear emission during the galaxies’ lifetime has been studied recently with high-resolution hydrodynamical simulations. These included gas cooling and heating specific for an average AGN spectral energy distribution, a radiative efficiency declining at low mass accretion rates, and mechanical coupling between the hot gas and AGN winds. Here, we present a short summary of the observational properties resulting from the simulations, focussing on (1) the nuclear luminosity; (2) the global luminosity and temperature of the hot gas; (3) its temperature profile and X-ray brightness profile. These properties are compared with those of galaxies of the local universe, pointing out the successes of the adopted feedback and the needs for new input in the simulations.
    Advances in Space Research 05/2009; · 1.18 Impact Factor
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    ABSTRACT: This paper describes the Seventh Data Release of the Sloan Digital Sky Survey (SDSS), marking the completion of the original goals of the SDSS and the end of the phase known as SDSS-II. It includes 11,663 deg^2 of imaging data, with most of the ~2000 deg^2 increment over the previous data release lying in regions of low Galactic latitude. The catalog contains five-band photometry for 357 million distinct objects. The survey also includes repeat photometry on a 120° long, 2°.5 wide stripe along the celestial equator in the Southern Galactic Cap, with some regions covered by as many as 90 individual imaging runs. We include a co-addition of the best of these data, going roughly 2 mag fainter than the main survey over 250 deg^2. The survey has completed spectroscopy over 9380 deg^2; the spectroscopy is now complete over a large contiguous area of the Northern Galactic Cap, closing the gap that was present in previous data releases. There are over 1.6 million spectra in total, including 930,000 galaxies, 120,000 quasars, and 460,000 stars. The data release includes improved stellar photometry at low Galactic latitude. The astrometry has all been recalibrated with the second version of the USNO CCD Astrograph Catalog, reducing the rms statistical errors at the bright end to 45 milliarcseconds per coordinate. We further quantify a systematic error in bright galaxy photometry due to poor sky determination; this problem is less severe than previously reported for the majority of galaxies. Finally, we describe a series of improvements to the spectroscopic reductions, including better flat fielding and improved wavelength calibration at the blue end, better processing of objects with extremely strong narrow emission lines, and an improved determination of stellar metallicities.
    The Astrophysical Journal Supplement Series 05/2009; 182(2):543. · 16.24 Impact Factor
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    Yen-Ting Lin, Jeremiah P. Ostriker, Christopher J. Miller
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    ABSTRACT: A novel statistic is proposed to examine the hypothesis that all cluster galaxies are drawn from the same luminosity distribution (LD). In such a "statistical model" of galaxy LD, the brightest cluster galaxies (BCGs) are simply the statistical extreme of the galaxy population. Using a large sample of nearby clusters, we show that BCGs in high luminosity clusters (e.g., L_tot > 4x10^11 L_sun) are unlikely (probability <3x10^-4) to be drawn from the LD defined by all red cluster galaxies more luminous than M_r=-20. On the other hand, BCGs in less luminous clusters are consistent with being the statistical extreme. Applying our method to the second brightest galaxies, we show that they are consistent with being the statistical extreme, which implies that the BCGs are also distinct from non-BCG luminous, red, cluster galaxies. We point out some issues with the interpretation of the classical tests proposed by Tremaine & Richstone (1977) that are designed to examine the statistical nature of BCGs, investigate the robustness of both our statistical test and those of TR against difficulties in photometry of galaxies of large angular size, and discuss the implication of our findings on surveys that use the luminous red galaxies to measure the baryon acoustic oscillation features in the galaxy power spectrum. Comment: 12 pages, 8 figures, 4 tables; published in ApJ
    The Astrophysical Journal 04/2009; · 6.73 Impact Factor
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    ABSTRACT: Great strides have been made in the last two decades in determining how galaxies evolve from their initial dark matter seeds to the complex structures we observe at z=0. The role of mergers has been documented through both observations and simulations, numerous satellites that may represent these initial dark matter seeds have been discovered in the Local Group, high redshift galaxies have been revealed with monstrous star formation rates, and the gaseous cosmic web has been mapped through absorption line experiments. Despite these efforts, the dark matter simulations that include baryons are still unable to accurately reproduce galaxies. One of the major problems is our incomplete understanding of how a galaxy accretes its baryons and subsequently forms stars. Galaxy formation simulations have been unable to accurately represent the required gas physics on cosmological timescales, and observations have only just begun to detect the star formation fuel over a range of redshifts and environments. How galaxies obtain gas and subsequently form stars is a major unsolved, yet tractable problem in contemporary extragalactic astrophysics. In this paper we outline how progress can be made in this area in the next decade.
    03/2009;
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    Peter H. Johansson, Thorsten Naab, Jeremiah P. Ostriker
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    ABSTRACT: We study the thermal formation history of four simulated galaxies that were shown in Naab et al. (2007) to reproduce a number of observed properties of elliptical galaxies. The temperature of the gas in the galaxies is steadily increasing with decreasing redshift, although much of the gas has a cooling time shorter than the Hubble time. The gas is being heated and kept hot by gravitational heating processes through the release of potential energy from infalling stellar clumps. The energy is dissipated in supersonic collisions of infalling gas lumps with the ambient gas and through the dynamical capturing of satellite systems causing gravitational wakes that transfer energy to the surrounding gas. Furthermore dynamical friction from the infalling clumps pushes out dark matter, lowering the central dark matter density by up to a factor of two from z=3 to z=0. In galaxies in which the late formation history (z<2) is dominated by minor merging and accretion the energy released (E~5x10^{59} ergs) from gravitational feedback is sufficient to form red and dead elliptical galaxies by z~1 even in the absence of supernova and AGN feedback.
    The Astrophysical Journal 03/2009; 697(1). · 6.73 Impact Factor
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    Thorsten Naab, Peter H. Johansson, Jeremiah P. Ostriker
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    ABSTRACT: Using a high resolution hydrodynamical cosmological simulation of the formation of a massive spheroidal galaxy we show that elliptical galaxies can be very compact and massive at high redshift in agreement with recent observations. Accretion of stripped in-falling stellar material increases the size of the system with time and the central concentration is reduced by dynamical friction of the surviving stellar cores. In a specific case of a spheroidal galaxy with a final stellar mass of $1.5 \times 10^{11} M_{\odot}$ we find that the effective radius $r_e$ increases from $0.7 \pm 0.2 \rm kpc$ at z = 3 to $r_e = 2.4 \pm 0.4 \rm kpc$ at z = 0 with a concomitant decrease in the effective density of an order of magnitude and a decrease of the central velocity dispersion by approximately 20% over this time interval. A simple argument based on the virial theorem shows that during the accretion of weakly bound material (minor mergers) the radius can increase as the square of the mass in contrast to the usual linear rate of increase for major mergers. By undergoing minor mergers compact high redshift spheroids can evolve into present-day systems with sizes and concentrations similar to observed local ellipticals. This indicates that minor mergers may be the main driver for the late evolution of sizes and densities of early-type galaxies.
    The Astrophysical Journal 03/2009; 699. · 6.73 Impact Factor
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    ABSTRACT: We use an Eulerian hydrodynamic cosmological simulation to model the Lyα forest in a spatially flat, COBE-normalized, cold dark matter model with) Ω = 0.4. We find that the intergalactic, photoionized gas is predicted to collapse into sheetlike and filamentary structures which give rise to absorption lines having characteristics similar to the observed Lyα forest. A typical filament is ~500 h–1 kpc long with thickness ~50 h–1 kpc (in proper units), and baryonic mass ~ 1010 h−1 M. In comparison our cell size is (2.5, 9) h−1 kpc in the two simulations we perform, with true resolution perhaps a factor of 2.5 worse than this. The gas temperature is in the range 104-105 K, and it increases with time as structures with larger velocities collapse gravitationally. We show that the predicted distributions of column densities, b-parameters, and equivalent widths of the Lyα forest clouds agree reasonably with observations, and that their evolution is consistent with the observed evolution, if the ionizing background has an approximately constant intensity between z = 2 and z = 4. A new method of identifying lines as contiguous regions in the spectrum below a fixed flux threshold is suggested to analyze the absorption lines, given that the Lyα spectra arise from a continuous density field of neutral hydrogen rather than discrete clouds. We also predict the distribution of transmitted flux and its correlation along a spectrum and on parallel spectra, and the He ii flux decrement as a function of redshift. We predict a correlation length of ~80 h−1 kpc perpendicular to the line of sight for features in the Lyα forest. In order to reproduce the observed number of lines and average flux transmission, the baryon content of the clouds may need to be significantly higher than in previous models because of the low densities and large volume-filling factors we predict. If the background intensity JH I is at least that predicted from the observed quasars, Ωb needs to be as high as ~0.25 h−2. The model also predicts that most of the baryons at z > 2 are in Lyα clouds, and that the rate at which the baryons move to more overdense regions is slow. A large fraction of the baryons which are not observed at present in galaxies might be intergalactic gas in the currently collapsing structures, with T ~ 105–106 K. All our results on the statistical properties of the simulated spectra are predictions that can be directly tested by applying the same methods to observed spectra. We are making the simulated spectra electronically available.
    The Astrophysical Journal 01/2009; 471(2):582. · 6.73 Impact Factor
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    ABSTRACT: We have simulated the formation of an X-ray cluster in a cold dark matter universe using 12 different codes. The codes span the range of numerical techniques and implementations currently in use, including smoothed particle hydrodynamics (SPH) and grid methods with fixed, deformable, or multilevel meshes. The goal of this comparison is to assess the reliability of cosmological gasdynamical simulations of clusters in the simplest astrophysically relevant case, that in which the gas is assumed to be nonradiative. We compare images of the cluster at different epochs, global properties such as mass, temperature and X-ray luminosity, and radial profiles of various dynamical and thermodynamical quantities. On the whole, the agreement among the various simulations is gratifying, although a number of discrepancies exist. Agreement is best for properties of the dark matter and worst for the total X-ray luminosity. Even in this case, simulations that adequately resolve the core radius of the gas distribution predict total X-ray luminosities that agree to within a factor of 2. Other quantities are reproduced to much higher accuracy. For example, the temperature and gas mass fraction within the virial radius agree to within about 10%, and the ratio of specific dark matter kinetic to gas thermal energies agree to within about 5%. Various factors, including differences in the internal timing of the simulations, contribute to the spread in calculated cluster properties. Based on the overall consistency of results, we discuss a number of general properties of the cluster we have modeled.
    The Astrophysical Journal 01/2009; 525(2):554. · 6.73 Impact Factor
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    L. Ciotti, J. P. Ostriker, D. Proga
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    ABSTRACT: The importance of the radiative feedback from SMBHs at the centers of elliptical galaxies is not in doubt, given the well established relations among electromagnetic output, black hole mass and galaxy optical luminosity. In addition, feedback due to mechanical and thermal deposition of energy from jets and winds emitted by the accretion disk around the central SMBH is also expected to occur. In this paper we improve and extend the accretion and feedback physics explored in our previous papers to include also a physically motivated mechanical feedback. We study the evolution of an isolated elliptical galaxy with the aid of a high-resolution 1-D hydrodynamical code, where the cooling and heating functions include photoionization and Compton effects, and restricting to models which include only radiative or only mechanical feedback. We confirm that for Eddington ratios above 0.01 both the accretion and radiative output are forced by feedback effects to be in burst mode, so that strong intermittencies are expected at early times, while at low redshift the explored models are characterized by smooth, very sub-Eddington mass accretion rates punctuated by rare outbursts. However, the explored models always fail some observational tests. If we assume the high mechanical efficiency of 10^{-2.3}, we find that most of the gas is ejected from the galaxy, the resulting X-ray luminosity is far less than is typically observed and little SMBH growth occurs. But models with low enough mechanical efficiency to accomodate satisfactory SMBH growth tend to allow too strong cooling flows and leave galaxies at z=0 with E+A spectra more frequently than is observed. We conclude that both types of feedback are required. Models with combined feedback are explored in a forthcoming paper [abridged] Comment: 42 pages, 4 figures (low resolution), ApJ accepted
    The Astrophysical Journal 01/2009; · 6.73 Impact Factor
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    ABSTRACT: What breakthrough advances will petascale computing bring to various science and engineering fields? Experts in everything from astronomy to seismology envision the opportunities ahead and the impact they'll have on advancing our understanding of the world.
    Computing in Science and Engineering 01/2009; 11(5):28-37. · 1.73 Impact Factor
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    Laurie D. Shaw, Jochen Weller, Jeremiah P Ostriker, and Paul Bode
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    ABSTRACT: We have identified over 2000 well-resolved cluster halos, and also their associated bound subhalos, from the output of a 10243 particle cosmological N-body simulation (of box size 320 h-1 Mpc and softening length 3.2 h-1 kpc). This has allowed us to measure halo quantities in a statistically meaningful way, and for the first time analyze their distribution for a large and well-resolved sample. We characterize each halo in terms of its morphology, concentration, spin, circular velocity, and the fraction of their mass in substructure. We also identify those halos that have not yet reached a state of dynamical equilibrium, using the virial theorem with an additional correction to account for the surface pressure at the boundary. These amount to 3.4% of our initial sample. For the virialized halos, we find a median of 5.6% of halo mass is contained within substructure, with the distribution ranging between no identified subhalos to 65%. The fraction of mass in substructure increases with halo mass with logarithmic slope of 0.44 ± 0.06. Halos tend to have a prolate morphology, becoming more so with increasing mass. Subhalos have a greater orbital angular momentum per unit mass than their host halo. Furthermore, their orbital angular momentum is typically well aligned with that of their host. Overall, we find that dimensionless properties of dark matter halos do depend on their mass, thereby demonstrating a lack of self-similarity.
    The Astrophysical Journal 12/2008; 646(2):815. · 6.73 Impact Factor
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    ABSTRACT: Approximately 30%-40% of all baryons in the present-day universe reside in a warm-hot intergalactic medium (WHIM), with temperatures in the range 105 < T < 107 K. This is a generic prediction from six hydrodynamic simulations of currently favored structure formation models having a wide variety of numerical methods, input physics, volumes, and spatial resolutions. Most of these warm-hot baryons reside in diffuse large-scale structures with a median overdensity around 10-30, not in virialized objects such as galaxy groups or galactic halos. The evolution of the WHIM is primarily driven by shock heating from gravitational perturbations breaking on mildly nonlinear, nonequilibrium structures such as filaments. Supernova feedback energy and radiative cooling play lesser roles in its evolution. WHIM gas may be consistent with observations of the 0.25 keV X-ray background without being significantly heated by nongravitational processes because the emitting gas is very diffuse. Our results confirm and extend previous work by Cen & Ostriker and Davé et al.
    The Astrophysical Journal 12/2008; 552(2):473. · 6.73 Impact Factor
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    ABSTRACT: The mass function of clusters of galaxies is determined from 400 deg2 of early commissioning imaging data of the Sloan Digital Sky Survey using ~300 clusters in the redshift range z = 0.1-0.2. Clusters are selected using two independent selection methods: a matched filter and a red-sequence color-magnitude technique. The two methods yield consistent results. The cluster mass function is compared with large-scale cosmological simulations. We find a best-fit cluster normalization relation of σ8Ω = 0.33 ± 0.03 (for 0.1 Ωm 0.4) or, equivalently, σ8 = (0.16/Ωm)0.6. The amplitude of this relation is significantly lower than the previous canonical value, implying that either Ωm is lower than previously expected (Ωm = 0.16 if σ8 = 1) or σ8 is lower than expected (σ8 = 0.7 if Ωm = 0.3). The shape of the cluster mass function partially breaks this classic degeneracy. We find best-fit parameters of Ωm = 0.19 ± and σ8 = 0.9 ±. High values of Ωm (0.4) and low σ8 (0.6) are excluded at 2 σ.
    The Astrophysical Journal 12/2008; 585(1):182. · 6.73 Impact Factor
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    Weihsueh A. Chiu, Jeremiah P. Ostriker
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    ABSTRACT: We present a semianalytic model for the thermal and ionization history of the universe at 1000 z 3. This model incorporates much of the essential physics included in full-scale hydrodynamical simulations, such as (1) gravitational collapse and virialization; (2) star/quasar formation and subsequent ionizing radiation; (3) heating and cooling; (4) atomic and molecular physics of hydrogen; and (5) the feedback relationships between these processes. In addition, we model the process of reheating and reionization using two separate phases, self-consistently calculating the filling factor of each phase. Thus, radiative transfer is treated more accurately than simulations published to date have done: we allow to lowest order for the inhomogeneity of the sources and the sinks of radiation. After calibrating and checking the results of this model against a hydrodynamical simulation, we apply our model to a variety of Gaussian (adiabatic power spectra) and non-Gaussian (texture and isocurvature) cold dark matter (CDM)-dominated cosmologies normalized to cluster abundances. Our model is also normalized to observations of the ionizing UV intensity J21 ≈ 1 at redshift z = 4. Our major conclusions include: (1) the epoch of reheating (starting late at z ~ 30 or early at z ~ 80) depends most strongly on the power spectrum (late: adiabatic; early: texture or isocurvature); (2) because of the effects of gas clumping, full reionization occurs at z ~ 10 in all models; (3) the cosmic microwave background radiation (CMBR) polarization anisotropy will be a strong discriminant between late and early reheating models; (4) the fraction of baryons sequestered in stars and quasars in early reheating models appears to be greater than the observational limit, while the fraction in late reheating models is well below it; (5) the average degree of nonlinearity for collapsing baryons remains roughly constant during reheating, a possible explanation of which is feedback, which regulates the pace of reheating through the Jeans criterion; and (6) the evolution of the bias of luminous objects can potentially discriminate strongly between Gaussian and non-Gaussian probability density functions.
    The Astrophysical Journal 12/2008; 534(2):507. · 6.73 Impact Factor
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    ABSTRACT: We study the evolution of the global stellar mass density in a Λ cold dark matter (ΛCDM) universe using two different types of hydrodynamic simulations (Eulerian total variation diminishing and smoothed particle hydrodynamics) and the analytical model of Hernquist & Springel. We find that the theoretical calculations all predict both a higher stellar mass density at z ~ 3 than indicated by current observations and that the peak of the cosmic star formation rate history should lie at z 5. Such a star formation history implies that as much as (70%, 30%) of the total stellar mass density today must already have formed by z = (1, 3). Our results suggest that current observations at z ~ 3 are missing as much as 50% of the total stellar mass density in the universe, perhaps because of an inadequate allowance for dust obscuration in star-forming galaxies, limited sample sizes, or cosmic variance. We also compare our results with some of the updated semianalytic models of galaxy formation.
    The Astrophysical Journal 12/2008; 610(1):45. · 6.73 Impact Factor
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    ABSTRACT: We study the properties of galaxies at redshift z = 2 in a Λ cold dark matter (ΛCDM) universe, using two different types of hydrodynamic simulation methods—Eulerian total variation diminishing (TVD) and smoothed particle hydrodynamics (SPH)—and a spectrophotometric analysis in the Un, G, R filter set. The simulated galaxies at z = 2 satisfy the color-selection criteria proposed by Adelberger et al. and Steidel et al. when we assume Calzetti extinction with E(B - V) = 0.15. We find that the number density of simulated galaxies brighter than R < 25.5 at z = 2 is about 2 × 10-2 h3 Mpc-3 for E(B - V) = 0.15 in our most representative run, roughly 1 order of magnitude larger than that of Lyman break galaxies at z = 3. The most massive galaxies at z = 2 have stellar masses of 1011 M☉, and their observed-frame G-R colors lie in the range 0.0 < G - R < 1.0. They typically have been continuously forming stars at a rate exceeding 30 M☉ yr-1 over a few gigayears from z = 10 to z = 2, although the TVD simulation indicates a more sporadic star formation history than the SPH simulations. On the order of half of their stellar mass was already assembled by z ~ 4. The bluest galaxies with colors -0.2 < G - R < 0.0 at z = 2 are somewhat less massive, with Mstar < 1011 h-1 M☉, and lack a prominent old stellar population. On the other hand, the reddest massive galaxies at z = 2 with G - R ≥ 1.0 and Mstar > 1010 h-1 M☉ completed the build-up of their stellar mass by z ~ 3. Interestingly, our study indicates that the majority of the most massive galaxies at z = 2 should be detectable at rest-frame ultraviolet wavelengths, contrary to some recent claims made on the basis of near-infrared studies of galaxies at the same epoch, provided the median extinction is less than E(B - V) < 0.3 as indicated by surveys of Lyman break galaxies at z = 3. However, our results also suggest that the fraction of stellar mass contained in galaxies that pass the color-selection criteria used by Steidel et al. (2004) could be as low as 50% of the total stellar mass in the universe at z = 2. Our simulations imply that the missing stellar mass is contained in fainter (R > 25.5) and intrinsically redder galaxies. The bright end of the rest-frame V-band luminosity function of z = 2 galaxies can be characterized by a Schechter function with parameters (Φ*, M, α) = (1.8 × 10-3, - 23.4, - 1.85), while the TVD simulation suggests a flatter faint-end slope of α ~ -1.2. A comparison with z = 3 shows that the rest-frame V-band luminosity function has brightened by about 0.5 mag from z = 3 to z = 2, without a significant change in the shape. Our results do not imply that hierarchical galaxy formation fails to account for the massive galaxies at z 1.
    The Astrophysical Journal 12/2008; 618(1):23. · 6.73 Impact Factor
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    Li-Xin Li, Jeremiah P. Ostriker
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    ABSTRACT: We use the semianalytical approach to analyze gravitational lensing of remote quasars by foreground dark halos in various cold dark matter (CDM) cosmologies in order to determine the sensitivity of the predictions for probabilities of image separations to the input assumptions regarding the properties of halos and cosmological models. The power spectrum of primordial fluctuations is normalized by the cluster abundance constraints. The mass function of dark halos is assumed to be given by the Press-Schechter function. The mass density profile of dark halos is alternatively taken to be the singular isothermal sphere (SIS), the Navarro-Frenk-White (NFW) profile, or the generalized NFW profile. The cosmologies being considered include the Einstein-de Sitter model (SCDM), the open model (OCDM), and the flat Λ-model (LCDM). As expected, we find that the lensing probability is extremely sensitive to the mass density profile of lenses (dark halos) and somewhat less so to the mean mass density in the universe and the amplitude of primordial fluctuations. NFW halos are very much less effective in producing multiple images than SIS halos. For NFW lenses, the SCDM model produces fewer lensing events than the OCDM/LCDM models by 2 orders of magnitude. For SIS lenses, the SCDM model produces more lensing events with small splitting angles and fewer lensing events with large splitting angles than the OCDM/LCDM models, which is due to the fact that for large-mass halos, the Press-Schechter function is very sensitive to the amplitude of primordial fluctuations. In all cases the difference between the OCDM model and the LCDM model is not dramatic. None of these models are consistent with current observations: the SIS models predict too many large splitting lenses, while the NFW models predict too few small splitting lenses. Essentially, the observed high ratio of small splitting to large splitting lenses is not predicted correctly. This indicates that there must be at least two populations of halos in the universe: small-mass halos with a steep inner density slope and large-mass halos with a shallow inner density slope. A combination of SIS and NFW halos can reasonably reproduce the current observations if we choose the mass for the transition from SIS to NFW to be ~1013 M☉, as might plausibly occur because of baryonic cooling and contraction in lower mass systems. Additionally, there is a tendency for CDM models to have too much power on small scales, i.e., too much mass concentration. From our sensitivity studies it appears that the cures proposed for other apparent difficulties of CDM would help here as well, an example being the warm dark matter variant, which is shown to produce fewer large splitting lenses than the corresponding CDM model by 1 order of magnitude.
    The Astrophysical Journal 12/2008; 566(2):652. · 6.73 Impact Factor
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    Laurie D. Shaw, Jochen Weller, Jeremiah P Ostriker, and Paul Bode
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    ABSTRACT: We present a new definition of subhalos in dissipationless dark matter N-body simulations, based on the coherent identification of their dynamically bound constituents. Whereas previous methods of determining the energetically bound components of a subhalo ignored the contribution of all the remaining particles in the halo (those not geometrically or dynamically associated with the subhalo), our method allows for all the forces, both internal and external, exerted on the subhalo. We demonstrate, using the output of a simulation at different time steps, that our new method is more accurate at identifying the bound mass of a subhalo. We then compare our new method to previously adopted means of identifying subhalos by applying each to a sample of 1838 virialized halos extracted from a high-resolution cosmological simulation. We find that the subhalo distributions are similar in each case, and that the increase in the binding energy of a subhalo from including all the particles located within it is almost entirely balanced by the losses due to the external forces; the net increase in the mass fraction of subhalos is roughly 10%, and the extra substructures tend to reside in the inner parts of the system. Finally, we compare the subhalo populations of halos to the subsubhalo populations of subhalos, finding the two distributions to be similar. This is a new and interesting result, suggesting a self-similarity in the hierarchy substructures within cluster mass halos.
    The Astrophysical Journal 12/2008; 659(2):1082. · 6.73 Impact Factor

Publication Stats

11k Citations
1,371.25 Total Impact Points

Institutions

  • 1994–2014
    • Princeton University
      • • Department of Astrophysical Sciences
      • • Department of Physics
      Princeton, New Jersey, United States
  • 2009
    • Pontifical Catholic University of Chile
      • Departamento de Astronomía y Astrofísica
      CiudadSantiago, Santiago, Chile
    • California Institute of Technology
      • Department of Astronomy
      Pasadena, California, United States
    • University of Bologna
      • Department of Physics and Astronomy DIFA
      Bolonia, Emilia-Romagna, Italy
  • 2008
    • Chinese Academy of Sciences
      • Shanghai Astronomical Observatory
      Peping, Beijing, China
  • 2003–2008
    • University of Cambridge
      • Institute of Astronomy
      Cambridge, ENG, United Kingdom
    • Università degli Studi di Siena
      Siena, Tuscany, Italy
  • 2007
    • Los Alamos National Laboratory
      • Theoretical Division
      Los Alamos, California, United States
  • 1993–2007
    • TRI/Princeton
      Princeton, New Jersey, United States
  • 2002
    • Cancer Research UK Cambridge Institute
      Cambridge, England, United Kingdom
    • Fermi National Accelerator Laboratory (Fermilab)
      Batavia, Illinois, United States
  • 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