bluuebunny/crossref_metadata_2025_split huggingface dataset:
Farmers and nature conservation: What is known about attitudes, context factors and actions affecting conservation?
Authors: Ahnström Johan , Höckert Jenny , Bergeå Hanna L. , Francis Charles A. , Skelton Peter , Hallgren Lars 
Published: December 2008

AbstractFarmers' attitudes towards viability of specific conservation practices or actions strongly impact their decisions on adoption and change. This review of ‘attitude’ information reveals a wide range of perceptions about what conservation means and what the impacts of adoption will mean in economic and environmental terms. Farmers operate in a tight financial situation, and in parts of the world they are highly dependent on government subsidies, and cannot afford to risk losing that support. Use of conservation practices is most effective when these are understood in the context of the individual farm, and decisions are rooted in land and resource stewardship and long-term concerns about health of the farm and the soil. The attitudes of farmers entering agri-environmental schemes decide the quality of the result. A model is developed to show how attitudes of the farmer, the farming context and agri-environmental schemes interact and thus influence how the farming community affects nature and biodiversity. As new agri-environmental schemes are planned, agricultural development specialists need to recognize the complexity of farmer attitudes, the importance of location and individual farmer circumstances, and the multiple factors that influence decisions. We provide these insights and the model to conservation biologists conducting research in farming areas, decision makers who develop future agri-environmental schemes, educators training tomorrow's extension officers and nature conservationists, and researchers dealing with nature conservation issues through a combination of scientific disciplines.
Protostar formation in the early universe
Authors: Yoshida Naoki 
Published: December 2008

AbstractWe study the formation of primordial proto-stars in a ΛCDM universe using ultra high-resolution cosmological simulations. Our approach includes all the relevant atomic and molecular physics to follow the thermal evolution of a prestellar gas cloud to “stellar” densities. We describe the numerical implementation of the physics. We also show the result of a simulation of the formation of primordial stars in a reionized gas.
Population III.1 stars: formation, feedback and evolution of the IMF
Authors: Tan Jonathan C. 
Published: December 2008

AbstractI discuss current theoretical expectations of how primordial, Pop III.1 stars form. Lack of direct observational constraints makes this a challenging task. In particular predicting the mass of these stars requires solving a series of problems, which all affect, perhaps drastically, the final outcome. While there is general agreement on the initial conditions, H2-cooled gas at the center of dark matter minihalos, the subsequent evolution is more uncertain. In particular, I describe the potential effects of dark matter annihilation heating, fragmentation within the minihalo, magnetic field amplification, and protostellar ionizing feedback. After these considerations, one expects that the first stars are massive ≳100M⊙, with dark matter annihilation heating having the potential to raise this scale by large factors. Higher accretion rates in later-forming minihalos may cause the Pop III.1 initial mass function to evolve to higher masses.
Effects of dark matter annihilation on the first stars
Authors: Iocco F. , Bressan A. , Ripamonti E. , Schneider R. , Ferrara A. , Marigo P. 
Published: December 2008

AbstractWe study the evolution of the first stars in the universe (Population III) from the early pre–Main Sequence (MS) until the end of helium burning in the presence of WIMP dark matter annihilation inside the stellar structure. The two different mechanisms that can provide this energy source are the contemporary contraction of baryons and dark matter, and the capture of WIMPs by scattering off the gas with subsequent accumulation inside the star. We find that the first mechanism can generate an equilibrium phase, previously known as a dark star, which is transient and present in the very early stages of pre–MS evolution. The mechanism of scattering and capture acts later, and can support the star virtually forever, depending on environmental characteristics of the dark matter halo and on the specific WIMP model.
The search for Population III stars
Authors: di Serego Alighieri Sperello , Kurk Jaron , Ciardi Benedetta , Cimatti Andrea , Daddi Emanuele , Ferrara Andrea 
Published: December 2008

AbstractPopulation III stars, the first generation of stars formed from primordial Big Bang material with a top–heavy IMF, should contribute substantially to the Universe reionization and they are crucial for understanding the early metal enrichment of galaxies. Therefore it is very important that these objects, foreseen by theories, are detected by observations. However PopIII stars, searched through the HeII 1640Å line signature, have remained elusive. We report about the search for the HeII line in a galaxy at z = 6.5, which is a very promising candidate. Unfortunately we are not yet able to show the results of this search. However we call attention to the possible detection of PopIII stars in a lensed HII dwarf galaxy at z = 3.4, which appeared in the literature some years ago, but has been overlooked.
Insights into the Origin of the Galaxy Mass-Metallicity Relation
Authors: Lee Henry , Bell Eric F. , Somerville Rachel S. 
Published: December 2008

AbstractWe examine mass–metallicity relations for nearby (D < 2 Mpc) gas-rich and gas-poor dwarf galaxies. We derived stellar and baryonic masses using photometric data and used average stellar iron abundances as the metallicity indicator. With the inclusion of available data for massive galaxies, we find a continuous mass–metallicity relation for galaxies spanning nine orders of magnitude in mass, and that the mass–metallicity relations are the same for both gas-rich and gas-poor dwarf galaxies. We derive stellar effective yields from the stellar abundances, finding that gas-poor dwarf galaxies form a single sequence with mass, whereas gas-rich dwarf galaxies have higher yields at comparable mass. Simple chemical evolution models show that a mass-dependent star-formation efficiency can simultaneously account for the correlations between metallicity, gas fraction, and stellar effective yield with mass. In agreement with recent and independent results, we conclude that a key driver of the mass-metallicity relation is the variation of star-formation efficiency with galaxy mass, modulated by galaxy mass-dependent outflows and/or stellar IMF variations, and coupled with environmental gas-removal processes.
Three Modes of Metal-Enriched Star Formation at High Redshift
Authors: Smith Britton D. , Turk Matthew J. , Sigurdsson Steinn , O'Shea Brian W. , Norman Michael L. 
Published: December 2008

AbstractIt is generally accepted that the very first stars in the universe were significantly more massive and formed much more in isolation than stars observed today. This suggests that there was a transition in star formation modes that was most likely related to the metallicity of the star-forming environment. We study how the addition of heavy elements alters the dynamics of collapsing gas by performing a series of numerical simulations of primordial star formation with various levels of pre-enrichment, using the adaptive mesh refinement, hydrodynamic + N-body code, Enzo. At high redshifts, the process of star formation is heavily influenced by the cosmic microwave background (CMB), which creates a temperature floor for the gas. Our results show that cloud-collapse can follow three distinct paths, depending on the metallicity. For very low metallicities (log10(Z/Z⊙) < −3.5), star formation proceeds in the primordial mode, producing only massive, singular objects. For high metallicities (log10(Z/Z⊙) > −3), efficient cooling from the metals cools the gas to the CMB temperature when the core density is still very low. When the gas temperature reaches the CMB temperature, the core becomes very thermally stable, and further fragmentation is heavily suppressed. In our simulations with log10(Z/Z⊙) > −3, only a single object forms with a mass-scale of a few hundred M⊙. We refer to this as the CMB-regulated star formation mode. For metallicities between these two limits (−3.5 < log10(Z/Z⊙) < −3), the gas cools efficiently, but never reaches the CMB temperature. In this mode, termed the metallicity-regulated star formation mode, the minimum gas temperature is reached at much higher densities, allowing the core to fragment and form multiple objects with mass-scales of only a few M⊙. Our results imply that the stellar initial mass function was top-heavy at very high redshift due to stars forming in the CMB-regulated mode. As the CMB temperature lowers with time, the metallicity-regulated star formation mode (producing multiple low-mass stars) operates at higher metallicities and eventually becomes the sole mode of star formation.
About the Chemical Evolution of dSphs (and the peculiar Globular Cluster ω Cen)
Authors: Marcolini Andrea , D'Ercole Annibale 
Published: December 2008

AbstractWe present three dimensional hydrodynamical simulations aimed at studying the dynamical and chemical evolution of the interstellar medium (ISM) in isolated dwarf spheroidal galaxies (dSphs). This evolution is driven by the explosion of Type II and Type Ia supernovae, whose different contribution on both the dynamics and chemical enrichment is taken into account. Radiative losses are effective in radiating away the huge amount of energy released by SNe explosions, and the dSph is able to retain most of the gas allowing a long period (≥ 2 − 3 Gyr) of star formation, as usually observed in this kind of galaxies. We are able to reproduce the stellar metallicity distribution function (MDF) as well as the peculiar chemical properties of strongly O-depleted stars observed in several dSphs. The model also naturally predicts two different stellar populations, with an anti-correlation between [Fe/H] and velocity dispersion, similarly to what observed in the Sculptor and Fornax dSphs. These results derive from the inhomogeneous pollution of the SNe Ia, a distinctive characteristic of our model. We also applied the model to the peculiar globular cluster (GC) ω Cen in the hypothesis that it is the remnant of a formerly larger stellar system, possibly a dSph.
Modeling the ISM Properties of Metal-Poor Galaxies and Gamma-Ray Burst Hosts
Authors: Levesque Emily M. , Kewley Lisa J. , Larson Kirsten , Snijders Leonie 
Published: December 2008

AbstractRecent research has suggested that long-duration gamma-ray bursts (LGRBs) occur preferentially in low-metallicity environments, but the exact nature of this correlation is currently a matter of intense debate. We use the newest generation of the Starburst99/Mappings code to generate an extensive suite of cutting-edge stellar population synthesis models, covering a wide range of physical parameters specifically tailored for modeling the ISM environments of metal-poor galaxies and LGRB host galaxies. With our models, we generate optical emission line diagnostics, which will allow us to examine the ISM properties and stellar populations of a variety of galaxy populations in unprecedented detail. While accurately modeling low-metallicity galaxies still poses a challenge to these models, future improvements to these grids will have profound consequences for our understanding of metal-poor galaxies, their ISM environments, and the nature of their role as the hosts of LGRBs.
Supernova Nucleosynthesis in the early universe
Authors: Tominaga Nozomu , Umeda Hideyuki , Maeda Keiichi , Nomoto Ken'ichi , Iwamoto Nobuyuki 
Published: December 2008

AbstractThe first metal enrichment in the universe was made by supernova (SN) explosions of population (Pop) III stars. The history of chemical evolution is recorded in abundance patterns of extremely metal-poor (EMP) stars. We investigate the properties of nucleosynthesis in Pop III SNe by comparing their yields with the abundance patterns of the EMP stars. We focus on (1) jet-induced SNe with various properties of the jets, especially energy deposition rates [Ėdep = (0.3 − 1500) × 1051 ergs s−1], and (2) SNe of stars with various main-sequence masses (Mms = 13 − 50M⊙) and explosion energies [E = (1 − 40) × 1051ergs]. The varieties of Pop III SNe can explain the observations of the EMP stars: (1) higher [C/Fe] for lower [Fe/H] and (2) trends of abundance ratios [X/Fe] against [Fe/H].
Interstellar Chemistry: Radiation, Dust and Metals
Authors: Spaans Marco 
Published: December 2008

AbstractAn overview is given of the chemical processes that occur in primordial systems under the influence of radiation, metal abundances and dust surface reactions. It is found that radiative feedback effects differ for UV and X-ray photons at any metallicity, with molecules surviving quite well under irradiation by X-rays. Starburst and AGN will therefore enjoy quite different cooling abilities for their dense molecular gas. The presence of a cool molecular phase is strongly dependent on metallicity. Strong irradiation by cosmic rays (>200× the Milky Way value) forces a large fraction of the CO gas into neutral carbon. Dust is important for H2 and HD formation, already at metallicities of 10−4 − 10−3 solar, for electron abundances below 10−3.
Dust Evolution from Nearby Galaxies: Bridging the Gap Between Local Universe and Primordial Systems
Authors: Galliano Frédéric 
Published: December 2008

AbstractThis paper presents the results of a study aimed at understanding the evolution of the dust properties, as a function of both the environmental conditions and the metal enrichment of the system. I first review the peculiar dust properties of dwarf galaxies, and discuss attempts to understand their origin. Then, I discuss the evolution of the PAH and dust abundances, constrained by the UV-to-radio SED of nearby galaxies, comparing the properties of low-metallicity environments and more evolved systems. I discuss the long term evolution of dust in galaxies, comparing the grain production by various stellar progenitors to their destruction by SN blast waves and in H ii regions. Finally, I will show how these models explain the paucity of PAHs in low-metallicity environments.
Evolution of newly formed dust in Population III supernova remnants and its impact on the elemental composition of Population II.5 stars
Authors: Nozawa Takaya , Kozasa Takashi , Habe Asao , Dwek Eli , Umeda Hideyuki , Tominaga Nozomu , Maeda Keiichi , Nomoto Ken'ichi 
Published: December 2008

AbstractWe investigate the evolution of dust formed in Population III supernovae (SNe) by considering its transport and processing by sputtering within the SN remnants (SNRs). We find that the fate of dust grains within SNRs heavily depends on their initial radii aini. For Type II SNRs expanding into the ambient medium with density of nH,0 = 1 cm−3, grains of aini < 0.05 μm are detained in the shocked hot gas and are completely destroyed, while grains of aini > 0.2 μm are injected into the surrounding medium without being significantly destroyed. Grains with aini = 0.05–0.2 μm are finally trapped in the dense shell behind the forward shock. We show that the grains piled up in the dense shell enrich the gas up to 10−6–10−4Z⊙, high enough to form low-mass stars with 0.1–1 M⊙. In addition, [Fe/H] in the dense shell ranges from −6 to −4.5, which is in good agreement with the ultra-metal-poor stars with [Fe/H] < −4. We suggest that newly formed dust in a Population III SN can have great impact on the stellar mass and elemental composition of Population II.5 stars formed in the shell of the SNR.
The Resolved Properties of Extragalactic Giant Molecular Clouds
Authors: Bolatto Alberto D. , Leroy Adam K. , Rosolowsky Erik , Walter Fabian , Blitz Leo 
Published: December 2008

AbstractGiant molecular clouds (GMCs) are the major reservoirs of molecular gas in galaxies, and the starting point for star formation. As such, their properties play a key role in setting the initial conditions for the formation of stars. We present a comprehensive combined inteferometric/single-dish study of the resolved GMC properties in a number of extragalactic systems, including both normal and dwarf galaxies. We find that the extragalactic GMC properties measured across a wide range of environments, characterized by the Larson relations, are to first order remarkably compatible with those in the Milky Way. Using these data to investigate trends due to galaxy metallicity, we find that: 1) these measurements are not in accord with simple expectations from photoionization-regulated star formation theory; 2) there is no trend in the virial CO-to-H2conversion factor on the spatial scales studied; and 3) there are measurable departures from the Galactic Larson relations in the Small Magellanic Cloud — the object with the lowest metallicity in the sample — where GMCs have velocity dispersions that are too small for their sizes. We will discuss the stability of these clouds in the light of our recent far-infrared analysis of this galaxy, and will contrast the results of the virial and far-infrared studies on the issue of the CO-to-H2conversion factor and what they tell us about the structure of molecular clouds in primitive galaxies.
Is there any pristine gas in nearby starburst galaxies?
Authors: Lebouteiller Vianney , Kunth Daniel 
Published: December 2008

AbstractWe derive the chemical composition of the neutral gas in the blue compact dwarf (BCD) Pox 36 observed with FUSE. Metals (N, O, Ar, and Fe) are underabundant as compared to the ionized gas associated with H ii regions by a factor ~7. The neutral gas, although it is not pristine, is thus probably less chemically evolved than the ionized gas. This could be due to different dispersal and mixing timescales. Results are compared to those of other BCDs observed with FUSE. The metallicity of the neutral gas in BCDs seems to reach a lower threshold of ~1/50 Z⊙ for extremely-metal poor galaxies.
Revision of Star-Formation Measures
Authors: Leitherer Claus 
Published: December 2008

AbstractRotation plays a major role in the evolution of massive stars. A revised grid of stellar evolutionary tracks accounting for rotation has recently been released by the Geneva group and implemented into the Starburst99 evolutionary synthesis code. Massive stars are predicted to be hotter and more luminous than previously thought, and the spectral energy distributions of young populations mirror this trend. The hydrogen ionizing continuum in particular increases by a factor of up to 3 in the presence of rotating massive stars. The effects of rotation generally increase towards shorter wavelengths and with decreasing metallicity. Revised relations between star-formation rates and monochromatic luminosities for the new stellar models are presented.
Truncated star formation in dwarf spheroidal galaxies and photometric scaling relations
Authors: De Rijcke Sven , Valcke Sander , Conselice Christopher J. , Penny Samantha 
Published: December 2008

AbstractWe investigate the global photometric scaling relations traced by early-type galaxies in different environments, ranging from dwarf spheroidals, over dwarf elliptical galaxies, up to giant ellipticals (−8 mag ≳ MV ≳ −24 mag). These results are based in part on our new HST/ACS F555W and F814W imagery of dwarf spheroidal galaxies in the Perseus Cluster. We show that at MV ~ −14 mag, the slopes of the photometric scaling relations involving the Sérsic parameters change significantly. We argue that these changes in slope reflect the different physical processes that dominate the evolution of early-type galaxies in different mass regimes. We present N-body/SPH simulations of the formation and evolution of dwarf spheroidals that reproduce these slope changes and discuss the underlying physics. As such, these scaling relations contain a wealth of information that can be used to test models for the formation of early-type galaxies.
Relics of Primordial Star Formation: The Milky Way and Local Dwarfs
Authors: Beers Timothy C. , Lee Young Sun , Carollo Daniela 
Published: December 2008

AbstractMassive spectroscopic surveys of stars in the thick disk and halo populations of the Galaxy hold the potential to provide strong constraints on the processes involved in (and the timing of) the assembly history of the primary structural components of the Galaxy. In this talk, we explore what has been learned from one of the first such dedicated surveys, SDSS/SEGUE. Over the course of the past three years, SEGUE has obtained spectra for over 200,000 stars, while another hundred thousand stars been added from the calibration star observations of the (primarily extragalactic) SDSS, and other directed programs. A total of well over 10,000 stars with [Fe/H] < −2.0 have been discovered, including several hundred with [Fe/H] < −3.0. Their kinematics have revealed a inner/outer halo structure of the Galaxy.New determinations of the alpha element ratios for tens of thousands of these stars are reported. Correlations of the alpha-element ratios with kinematics and orbital parameters can be used to test models of the likely formation of the thick-disk and halo components. These new data will (eventually) be considered in connection with possible associations with the present dwarf satellite galaxies of the Milky Way.
Galactic archeology with extremely metal-poor stars
Authors: Komiya Yutaka , Suda Takuma , Habe Asao , Fujimoto Masayuki 
Published: December 2008

AbstractExtremely metal-poor (EMP) stars are thought to be formed in the low-mass protogalaxies as building blocks of the Milky Way and can be probes to investigate the early stage of galaxy formation and star formation in the early universe. We study the formation history of EMP stars in the Milky Way halo using a new model of chemical evolution based on the hierarchical theory of the galaxy formation. We construct the merging history of the Milky Way halo based on the extended Press-Schechter formalism, and follow the star formation and chemical evolution along the merger tree. The abundance trends and number of low-mass stars predicted in our model are compared with those of observed EMP stars. Additionally, in order to clarify the origin of hyper metal poor stars, we investigate the change of the surface metal abundances of stars by accretion of interstellar matter. We also investigate the pre-enrichment of intergalactic matter by the first supernovae.
Blue Compact Dwarf Galaxies: Laboratories for probing the Primordial Universe
Authors: Thuan Trinh X. 
Published: December 2008

AbstractBlue Compact Dwarf (BCD) galaxies are the most metal-deficient star-forming galaxies known in the universe, with metallicities ranging from 1/40 to 1/3 that of the Sun. I review how they constitute excellent nearby laboratories for studying big bang nucleosynthesis and star formation and galaxy evolution processes in a nearly primordial environment.