Browsing by Subject "population-iii stars"
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Item Effects Of Rotation On The Minimum Mass Of Primordial Progenitors Of Pair-Instability Supernovae(2012-03) Chatzopoulos, Emmanouil; Wheeler, J. Craig; Chatzopoulos, Emmanouil; Wheeler, J. CraigThe issue of which stars may reach the conditions of electron/positron pair-formation instability is of importance to understand the final evolution both of the first stars and of contemporary stars. The criterion to enter the pair-instability regime in density and temperature is basically controlled by the mass of the oxygen core. The main-sequence masses that produce a given oxygen core mass are, in turn, dependent on metallicity, mass loss, and convective and rotationally induced mixing. We examine the evolution of massive stars to determine the minimum main-sequence mass that can encounter pair-instability effects, either a pulsational pair-instability supernova (PPISN) or a full-fledged pair-instability supernova (PISN). We concentrate on zero-metallicity stars with no mass-loss subject to the Schwarzschild criterion for convective instability, but also explore solar metallicity and mass loss and the Ledoux criterion. As expected, for sufficiently strong rotationally induced mixing, the minimum main-sequence mass is encountered for conditions that induce effectively homogeneous evolution such that the original mass is converted almost entirely to helium and then to oxygen. For this case, we find that the minimum main-sequence mass is about 40 M-circle dot to encounter PPISN and about 65 M-circle dot to encounter a PISN. The implications of these results for the first stars and for contemporary supernovae are discussed.Item The First Galaxies: Assembly Of Disks And Prospects For Direct Detection(2011-04) Pawlik, Andreas H.; Milosavljevic, Milos; Bromm, Volker; Pawlik, Andreas H.; Milosavljevic, Milos; Bromm, VolkerThe James Webb Space Telescope (JWST) will enable observations of galaxies at redshifts z greater than or similar to 10 and hence allow us to test our current understanding of structure formation at very early times. Previous work has shown that the very first galaxies inside halos with virial temperatures T-vir less than or similar to 10(4) K and masses M-vir less than or similar to 10(8) M circle dot at z greater than or similar to 10 are probably too faint, by at least one order of magnitude, to be detected even in deep exposures with JWST. The light collected with JWST may therefore be dominated by radiation from galaxies inside 10 times more massive halos. We use cosmological zoomed smoothed particle hydrodynamics simulations to investigate the assembly of such galaxies and assess their observability with JWST. We compare two simulations that are identical except for the inclusion of non-equilibrium H/D chemistry and radiative cooling by molecular hydrogen. In both simulations a large fraction of the halo gas settles in two nested, extended gas disks which surround a compact massive gas core. The presence of molecular hydrogen allows the disk gas to reach low temperatures and to develop marked spiral structure but does not qualitatively change its stability against fragmentation. We post-process the simulated galaxies by combining idealized models for star formation with stellar population synthesis models to estimate the luminosities in nebular recombination lines as well as in the ultraviolet continuum. We demonstrate that JWST will be able to constrain the nature of the stellar populations in galaxies such as simulated here based on the detection of the He1640 recombination line. Extrapolation of our results to halos with masses both lower and higher than those simulated shows that JWST may find up to a thousand star-bursting galaxies in future deep exposures of the z greater than or similar to 10 universe.Item The First Galaxies: Assembly With Black Hole Feedback(2012-07) Jeon, Myoungwon; Pawlik, Andreas H.; Greif, Thomas H.; Glover, Simon C. O.; Bromm, Volker; Milosavljevic, Milos; Klessen, Ralf S.; Jeon, Myoungwon; Pawlik, Andreas H.; Bromm, Volker; Milosavljevic, MilosWe study how the first galaxies were assembled under feedback from the accretion onto a central black hole (BH) that is left behind by the first generation of metal-free stars through self-consistent, cosmological simulations. X-ray radiation from the accretion of gas onto BH remnants of Population III (Pop III) stars, or from high-mass X-ray binaries (HMXBs), again involving Pop III stars, influences the mode of second generation star formation. We track the evolution of the BH accretion rate and the associated X-ray feedback starting with the death of the Pop III progenitor star inside a minihalo and following the subsequent evolution of the BH as the minihalo grows to become an atomically cooling galaxy. We find that X-ray photoionization heating from a stellar-mass BH is able to quench further star formation in the host halo at all times before the halo enters the atomic cooling phase. X-ray radiation from an HMXB, assuming a luminosity close to the Eddington value, exerts an even stronger, and more diverse, feedback on star formation. It photoheats the gas inside the host halo, but also promotes the formation of molecular hydrogen and cooling of gas in the intergalactic medium and in nearby minihalos, leading to a net increase in the number of stars formed at early times. Our simulations further show that the radiative feedback from the first BHs may strongly suppress early BH growth, thus constraining models for the formation of supermassive BHs.Item The First Stars: A Low-Mass Formation Mode(2014-04) Stacy, Athena; Bromm, Volker; Bromm, VolkerWe perform numerical simulations of the growth of a Population III stellar system under photodissociating feedback. We start from cosmological initial conditions at z = 100, self-consistently following the formation of a minihalo at z = 15 and the subsequent collapse of its central gas to high densities. The simulations resolve scales as small as similar to 1 AU, corresponding to gas densities of 1016 cm(-3). Using sink particles to represent the growing protostars, we evolve the stellar system for the next 5000 yr. We find that this emerging stellar group accretes at an unusually low rate compared with minihalos which form at earlier times (z = 20-30), or with lower baryonic angular momentum. The stars in this unusual system will likely reach masses ranging from <1 M-circle dot to similar to 5 M-circle dot by the end of their main-sequence lifetimes, placing them in the mass range for which stars will undergo an asymptotic giant branch (AGB) phase. Based upon the simulation, we predict the rare existence of Population III stars that have survived to the present day and have been enriched by mass overflow from a previous AGB companion.Item The First Supernova Explosions: Energetics, Feedback, And Chemical Enrichment(2007-11) Greif, Thomas H.; Johnson, Jarrett L.; Bromm, Volker; Klessen, Ralf S.; Greif, Thomas H.; Johnson, Jarrett L.; Bromm, VolkerWe perform three-dimensional smoothed particle hydrodynamics simulations in a realistic cosmological setting to investigate the expansion, feedback, and chemical enrichment properties of a 200M(circle dot) pair-instability supernova in the high-redshift universe. We find that the SN remnant propagates for a Hubble time at z similar or equal to 20 to a final mass-weighted mean shock radius of 2.5 kpc (proper), roughly half the size of the H II region, and in this process sweeps up a total gas mass of 2: 5; 10(5) M-circle dot. The morphology of the shock becomes highly anisotropic once it leaves the host halo and encounters filaments and neighboring minihalos, while the bulk of the shock propagates into the voids of the intergalactic medium. The SN entirely disrupts the host halo and terminates further star formation for at least 200 Myr, while in our specific case it exerts positive mechanical feedback on neighboring minihalos by shock-compressing their cores. In contrast, we do not observe secondary star formation in the dense shell via gravitational fragmentation, due to the previous photoheating by the progenitor star. We find that cooling by metal lines is unimportant for the entire evolution of the SN remnant, while the metal-enriched, interior bubble expands adiabatically into the cavities created by the shock, and ultimately into the voids with a maximum extent similar to the final mass-weighted mean shock radius. Finally, we conclude that dark matter halos of at least M-vir greater than or similar to 10(8) M-circle dot must be assembled to recollect all components of the swept-up gas.Item Fragmentation In The First Galaxies(2010-11) Safranek-Shrader, Chalence; Bromm, Volker; Milosavljevic, Milos; Safranek-Shrader, Chalence; Bromm, Volker; Milosavljevic, MilosMotivated by recent simulations of galaxy formation in which protogalaxies acquire their baryonic content through cold accretion, we study the gravitational fragmentation of cold streams flowing into a typical first galaxy. We use a one-zone hydrodynamical model to examine the thermal evolution of the gas flowing into a 10(8) M(circle dot) dark matter halo at redshift z = 10. The goal is to gain an understanding of the expected fragmentation mass scale and thus the characteristic mass of the first population of stars to form by shock fragmentation. Our model accurately describes the chemical and thermal evolution of the gas as we are specifically concerned with how the chemical abundances and initial conditions of the low-density, metal-enriched, cold accretion streams that pass an accretion shock alter the cooling properties and tendency to fragment in the post-shock gas. Cold accretion flows are not shock heated at the virial radius but instead flow along high-baryonic-density filaments of the cosmic web and penetrate deep into the host halo of the protogalaxy. In this physical regime, if molecular cooling is absent because of a strong Lyman-Werner background, we find there to be a sharp drop in the fragmentation mass at a metallicity of Z similar to 10(-4) Z(circle dot). If, however, H(2) and HD molecules are present, they dominate the cooling at T < 10(4) K, and metallicity then has no effect on the fragmentation properties of the cold stream. For a solar abundance pattern of metallicity, O is the most effective metal coolant throughout the evolution, while for a pair instability supernova (PISN) metallicity yield, Si(+) is the most effective coolant. PISN abundance patterns also exhibit a slightly smaller critical metallicity. Dust grains are not included in our chemical model, but we argue that their inclusion would not significantly alter the results. We also find that this physical scenario allows for the formation of stellar clusters and large, 10(4) M(circle dot) bound fragments, possibly the precursors to globular clusters and supermassive black holes. Finally, we conclude that the usual assumption of isobaricity for galactic shocks breaks down in gas of a sufficiently high metallicity, suggesting that metal cooling leads to thermal instabilities.Item GRB Cosmology: Probing The Early Universe(2007-10) Bromm, V.; Loeb, A.; Bromm, V.Current observations are about to open up a direct observational window into the final frontier of cosmology: the crucial first billion years in cosmic history when the first stars and galaxies formed. Even before the launch of the James Webb Space Telescope, it would be possible to utilize Gamma-Ray Bursts (GRBs) as unique probes of cosmic star formation and the state of the intergalactic medium up to redshifts of the first stars. The ongoing Swift mission might be the first observatory to detect individual Population III stars, provided that massive metal-free stars were able to trigger GRBs. Swift will empirically constrain the redshift at which Population III star formation was terminated, thus providing crucial input to models of cosmic reionization and metal enrichment.Item Hydrogen-Poor Circumstellar Shells From Pulsational Pair-Instability Supernovae With Rapidly Rotating Progenitors(2012-12) Chatzopoulos, Emmanouil; Wheeler, J. Craig; Chatzopoulos, Emmanouil; Wheeler, J. CraigIn certain mass ranges, massive stars can undergo a violent pulsation triggered by the electron/positron pair instability that ejects matter, but does not totally disrupt the star. After one or more of these pulsations, such stars are expected to undergo core-collapse to trigger a supernova (SN) explosion. The mass range susceptible to this pulsational phenomena may be as low as 50-70 M-circle dot if the progenitor is of very low metallicity and rotating sufficiently rapidly to undergo nearly homogeneous evolution. The mass, dynamics, and composition of the matter ejected in the pulsation are important aspects for determining the subsequent observational characteristics of the explosion. We examine the dynamics of a sample of stellar models and rotation rates and discuss the implications for the first stars, for LBV-like phenomena, and for superluminous SNe. We find that the shells ejected by pulsational pair-instability events with rapidly rotating progenitors (>30% the critical value) are hydrogen-poor and helium- and oxygen-rich.Item Modeling The Pollution Of Pristine Gas In The Early Universe(2013-10) Pan, Lubin B.; Scannapieco, Evan; Scalo, John; Scalo, JohnWe conduct a comprehensive theoretical and numerical investigation of the pollution of pristine gas in turbulent flows, designed to provide useful new tools for modeling the evolution of the first generation of stars. The properties of such Population III (Pop III) stars are thought to be very different than those of later stellar generations, because cooling is dramatically different in gas with a metallicity below a critical value Z(c), which lies between similar to 10(-6) and similar to 10(-3) Z(circle dot). The critical value is much smaller than the typical overall average metallicity, < Z >, and therefore the mixing efficiency of the pristine gas in the interstellar medium plays a crucial role in determining the transition from Pop III to normal star formation. The small critical value, Z(c), corresponds to the far left tail of the probability distribution function (PDF) of the metal abundance. Based on closure models for the PDF formulation of turbulent mixing, we derive evolution equations for the fraction of gas, P, lying below Z(c), in statistically homogeneous compressible turbulence. Our simulation data show that the evolution of the pristine fraction P can be well approximated by a generalized "self-convolution" model, which predicts that (P) over dot = -(n/tau(con))P(1 - P-1/n), where n is a measure of the locality of the mixing or PDF convolution events and the convolution timescale tau(con) is determined by the rate at which turbulence stretches the pollutants. Carrying out a suite of numerical simulations with turbulent Mach numbers ranging from M = 0.9 to 6.2, we are able to provide accurate fits to n and tau(con) as a function of M, Z(c)/< Z >, and the length scale, L-p, at which pollutants are added to the flow. For pristine fractions above P = 0.9, mixing occurs only in the regions surrounding blobs of pollutants, such that n = 1. For smaller values of P, n is larger as the mixing process becomes more global. We show how these results can be used to construct one-zone models for the evolution of Pop III stars in a single high-redshift galaxy, as well as subgrid models for tracking the evolution of the first stars in large cosmological numerical simulations.Item A Panchromatic View Of The Restless SN 2009ip Reveals The Explosive Ejection Of A Massive Star Envelope(2014-01) Margutti, R.; Milisavljevic, Dan; Soderberg, Alicia M.; Chornock, Ryan; Zauderer, B. A.; Murase, K.; Guidorzi, C.; Sanders, N. E.; Kuin, P.; Fransson, C.; Levesque, E. M.; Chandra, P.; Berger, E.; Bianco, F. B.; Brown, Peter J.; Challis, Peter; Chatzopoulos, Emmanouil; Cheung, C. C.; Choi, C.; Chomiuk, L.; Chugai, N.; Contreras, C.; Drout, M. R.; Fesen, R.; Foley, Ryan J.; Fong, W.; Friedman, A. S.; Gall, C.; Gehrels, N.; Hjorth, J.; Hsiao, E.; Kirshner, R.; Im, M.; Leloudas, G.; Lunnan, R.; Marion, G. H.; Martin, J.; Morrell, N.; Neugent, K. F.; Omodei, N.; Phillips, Mark M.; Rest, A.; Silverman, Jeffrey M.; Strader, J.; Stritzinger, Maximillian D.; Szalai, T.; Utterback, N. B.; Vinko, Jozsef; Wheeler, J. Craig; Arnett, D.; Campana, S.; Chevalier, R.; Ginsburg, Adam; Kamble, A.; Roming, Peter W. A.; Pritchard, T.; Stringfellow, G.; Chatzopoulos, Emmanouil; Silverman, Jeffrey M.; Vinko, Jozsef; Wheeler, J. CraigThe double explosion of SN 2009ip in 2012 raises questions about our understanding of the late stages of massive star evolution. Here we present a comprehensive study of SN 2009ip during its remarkable rebrightenings. High-cadence photometric and spectroscopic observations from the GeV to the radio band obtained from a variety of ground-based and space facilities (including the Very Large Array, Swift, Fermi, Hubble Space Telescope, and XMM) constrain SN 2009ip to be a low energy (E similar to 1050 erg for an ejecta mass similar to 0.5 M-circle dot) and asymmetric explosion in a complex medium shaped by multiple eruptions of the restless progenitor star. Most of the energy is radiated as a result of the shock breaking out through a dense shell of material located at similar to 5 x 10(14) cm with M similar to 0.1 M-circle dot, ejected by the precursor outburst similar to 40 days before the major explosion. We interpret the NIR excess of emission as signature of material located further out, the origin of which has to be connected with documented mass-loss episodes in the previous years. Our modeling predicts bright neutrino emission associated with the shock break-out if the cosmic-ray energy is comparable to the radiated energy. We connect this phenomenology with the explosive ejection of the outer layers of the massive progenitor star, which later interacted with material deposited in the surroundings by previous eruptions. Future observations will reveal if the massive luminous progenitor star survived. Irrespective of whether the explosion was terminal, SN 2009ip brought to light the existence of new channels for sustained episodic mass loss, the physical origin of which has yet to be identified.Item Pregalactic metal enrichment: the chemical signatures of the first stars(2013-05) Karlsson, Torgny; Bromm, Volker; Bland-Hawthorn, Joss; Bromm, VolkerThe emergence of the first sources of light at redshifts of z similar to 10-30 signaled the transition from the simple initial state of the Universe to one of increasing complexity. Recent progress in our understanding of the formation of the first stars and galaxies, starting with cosmological initial conditions, primordial gas cooling, and subsequent collapse and fragmentation are reviewed. The important open question of how the pristine gas was enriched with heavy chemical elements in the wake of the first supernovae is emphasized. The review concludes by discussing how the chemical abundance patterns conceivably allow us to probe the properties of the first stars, and allow us to test models of early metal enrichment.Item Probing Pre-Galactic Metal Enrichment With High-Redshift Gamma-Ray Bursts(2012-11) Wang, F. Y.; Bromm, Volker; Greif, Thomas H.; Stacy, Athena; Dai, Z. G.; Loeb, Abraham; Cheng, K. S.; Wang, F. Y.; Bromm, VolkerWe explore high-redshift gamma-ray bursts (GRBs) as promising tools to probe pre-galactic metal enrichment. We utilize the bright afterglow of a Population III (Pop III) GRB exploding in a primordial dwarf galaxy as a luminous background source, and calculate the strength of metal absorption lines that are imprinted by the first heavy elements in the intergalactic medium (IGM). To derive the GRB absorption line diagnostics, we use an existing highly resolved simulation of the formation of a first galaxy which is characterized by the onset of atomic hydrogen cooling in a halo with virial temperature greater than or similar to 10(4) K. We explore the unusual circumburst environment inside the systems that hosted Pop III stars, modeling the density evolution with the self-similar solution for a champagne flow. For minihalos close to the cooling threshold, the circumburst density is roughly proportional to (1 + z) with values of about a few cm(-3). In more massive halos, corresponding to the first galaxies, the density may be larger, n greater than or similar to 100 cm(-3). The resulting afterglow fluxes are weakly dependent on redshift at a fixed observed time, and may be detectable with the James Webb Space Telescope and Very Large Array in the near-IR and radio wavebands, respectively, out to redshift z greater than or similar to 20. We predict that the maximum of the afterglow emission shifts from near-IR to millimeter bands with peak fluxes from mJy to Jy at different observed times. The metal absorption line signature is expected to be detectable in the near future. GRBs are ideal tools for probing the metal enrichment in the early IGM, due to their high luminosities and featureless power-law spectra. The metals in the first galaxies produced by the first supernova (SN) explosions are likely to reside in low-ionization stages (C II, OI, Si II and Fe II). We show that, if the afterglow can be observed sufficiently early, analysis of the metal lines may distinguish whether the first heavy elements were produced in a pair-instability supernova or a core-collapse (Type II) SN, thus constraining the initial mass function of the first stars.Item Reconstructing Emission From Pre-Reionization Sources With Cosmic Infrared Background Fluctuation Measurements By The JWST(2015-05) Kashlinsky, A.; Mather, J. C.; Helgason, K.; Arendt, R. G.; Bromm, Volker; Moseley, S. H.; Bromm, VolkerWe present new methodology to use cosmic infrared background (CIB) fluctuations to probe sources at 10 less than or similar to z less than or similar to 30 from a James Webb Space Telescope (JWST)/NIRCam configuration that will isolate known galaxies to 28 AB mag at 0.5-5 mu m. At present significant mutually consistent source-subtracted CIB fluctuations have been identified in the Spitzer and AKARI data at similar to 2-5 mu m, but we demonstrate internal inconsistencies at shorter wavelengths in the recent CIBER data. We evaluate CIB contributions from remaining galaxies and show that the bulk of the high-z sources will be in the confusion noise of the NIRCam beam, requiring CIB studies. The accurate measurement of the angular spectrum of the fluctuations and probing the dependence of its clustering component on the remaining shot noise power would discriminate between the various currently proposed models for their origin and probe the flux distribution of its sources. We show that the contribution to CIB fluctuations from remaining galaxies is large at visible wavelengths for the current instruments precluding probing the putative Lyman-break of the CIB fluctuations. We demonstrate that with the proposed JWST configuration such measurements will enable probing the Lyman-break. We develop a Lyman-break tomography method to use the NIRCam wavelength coverage to identify or constrain, via the adjacent two-band subtraction, the history of emissions over 10 less than or similar to z less than or similar to 30 as the universe comes out of the "Dark Ages." We apply the proposed tomography to the current Spitzer/IRAC measurements at 3.6 and 4.5 mu m, to find that it already leads to interestingly low upper limit on emissions at z greater than or similar to 30.Item The Source Density And Observability Of Pair-Instability Supernovae From The First Stars(2012-08) Hummel, Jacob A.; Pawlik, Andreas H.; Milosavljevic, Milos; Bromm, Volker; Hummel, Jacob A.; Pawlik, Andreas H.; Milosavljevic, Milos; Bromm, VolkerTheoretical models predict that some of the first stars ended their lives as extremely energetic pair-instability supernovae (PISNe). With energies approaching 10(53) erg, these supernovae are expected to be within the detection limits of the upcoming James Webb Space Telescope (JWST), allowing observational constraints to be placed on the properties of the first stars. We estimate the source density of PISNe using a semi-analytic halo mass function based approach, accounting for the effects of feedback from star formation on the PISN rate using cosmological simulations. We estimate an upper limit of similar to 0.2 PISNe per JWST field of view at any given time. Feedback can reduce this rate significantly, e. g., lowering it to as little as one PISN per 4000 JWST fields of view for the most pessimistic explosion models. We also find that the main obstacle to observing PISNe from the first stars is their scarcity, not their faintness; exposures longer than a few times 10(4) s will do little to increase the number of PISNe found. Given this, we suggest a mosaic style search strategy for detecting PISNe from the first stars. Even rather high-redshift PISNe are unlikely to be missed by moderate exposures, and a large number of pointings will be required to ensure a detection.Item Uncovering The Chemical Signature Of The First Stars In The Universe(2008-05) Karlsson, Torgny; Johnson, Jarrett L.; Bromm, Volker; Johnson, Jarrett L.; Bromm, VolkerThe chemical abundance patterns observed in metal-poor Galactic halo stars contain the signature of the first supernovae, and thus allow us to probe the first stars that formed in the universe. We construct a theoretical model for the early chemical enrichment history of the Milky Way, aiming in particular at the contribution from pair-instability supernovae (PISNe). These are a natural consequence of current theoretical models for primordial star formation at the highest masses. However, no metal-poor star displaying the distinct PISN signature has yet been observed. We here argue that this apparent absence of any PISN signature is due to an observational selection effect. Whereas most surveys traditionally focus on the most metal-poor stars, we predict that early PISN enrichment tends to "overshoot,'' reaching enrichment levels of [Ca/H] similar or equal to -2.5 that would be missed by current searches. We utilize existing observational data to place constraints on the primordial initial mass function (IMF). The number fraction of PISNe in the primordial stellar population is estimated to be < 0.07, or <= 40% by mass, assuming that metal-free stars have masses in excess of 10 M-circle dot. We further predict, based on theoretical estimates for the relative number of PISNe, that the expected fraction of second-generation stars below [Ca/H] = -2 with a dominant (i. e., > 90%) contribution from PISNe is merely similar to 10(-4) to 5 x 10(-4). The corresponding fraction of stars formed from gas exclusively enriched by PISNe is a factor of similar to 4 smaller. With the advent of next-generation telescopes and new, deeper surveys, we should be able to test these predictions.