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تسجيل مستخدم جديدMetal and molecule cooling in simulations of structure formation
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This submission has been withdrawn by arXiv administrators because it is a duplicate of 0704.2182.
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Cooling is the main process leading to the condensation of gas in the dark matter potential wells and consequently to star and structure formation. In a metal-free environment, the main available coolants are H, He, H$_2$ and HD; once the gas is enri
ched with metals, these also become important in defining the cooling properties of the gas. We discuss the implementation in Gadget-2 of molecular and metal cooling at temperatures lower that $rm10^4 K$, following the time dependent properties of the gas and pollution from stellar evolution. We have checked the validity of our scheme comparing the results of some test runs with previous calculations of cosmic abundance evolution and structure formation, finding excellent agreement. We have also investigated the relevance of molecule and metal cooling in some specific cases, finding that inclusion of HD cooling results in a higher clumping factor of the gas at high redshifts, while metal cooling at low temperatures can have a significant impact on the formation and evolution of cold objects.
We present the results of a numerical study on the effects of metal enrichment and metal cooling on galaxy formation and cosmic star formation (SF) history using cosmological hydrodynamic simulations. We find following differences in the simulation w
ith metal cooling when compared to the run without it: (1) the cosmic star formation rate (SFR) is enhanced by about 50 & 20% at z=1 & 3, respectively; (2) the gas mass fraction in galaxies is lower; (3) the total baryonic mass function (gas + star) at z=3 does not differ significantly, but shows an increase in the number of relatively massive galaxies at z=1; (4) the baryonic mass fraction of intergalactic medium (IGM) is reduced at z<3 due to more efficient cooling and gas accretion onto galaxies. Our results suggest that the metal cooling enhances the galaxy growth by two different mechanisms: (1) increase of SF efficiency in the local interstellar medium (ISM), and (2) increase of IGM accretion onto galaxies. The former process is effective throughout most of the cosmic history, while the latter is effective only at z<3 when the IGM is sufficiently enriched by metals owing to feedback.
We present the analysis of a suite of simulations of a Virgo mass galaxy cluster. Undertaken within the framework of standard cold dark matter cosmology, these simulations were performed at differing resolutions and with increasingly complex physical
processes, with the goal of identifying the effects of each on the evolution of the cluster. We focus on the cluster at the present epoch and examine properties including the radial distributions of density, temperature, entropy and velocity. We also map `observable projected properties such as the surface mass density, X-ray surface brightness and SZ signature. We identify significant differences between the simulations, which highlights the need for caution when comparing numerical simulations to observations of galaxy clusters. While resolution affects the inner density profile in dark matter simulations, the addition of a gaseous component, especially one that cools and forms stars, affects the entire cluster. We conclude that both resolution and included physical processes play an important role in simulating the formation and evolution of galaxy clusters. Therefore, physical inferences drawn from simulations that do not include a gaseous component that can cool and form stars present a poor representation of reality. (Abridged)
Possible detection of signatures of structure formation at the end of the dark age epoch (z~40-20) is examined. We discuss the spectral-spatial fluctuations in the CMBR temperature produced by elastic resonant scattering of CMBR photons on HD molecul
es located in protostructures moving with peculiar velocity. Detailed chemical kinematic evolution of HD molecules in the expanding homogeneous medium is calculated. Then, the HD abundances are linked to protostructures at their maximum expansion, whose properties are estimated by using the top-hat spherical approach and the LambdaCDM cosmology. We find that the optical depths in the HD three lowest pure rotational lines for high-peak protohaloes at their maximum expansion are much higher than those in LiH molecule. The corresponding spectral-spatial fluctuation amplitudes however are probably too weak as to be detected by current and forthcoming millimeter-telescope facilities. We extend our estimates of spectral-spatial fluctuations to gas clouds inside collapsed CDM haloes by using results from a crude model of HD production in these clouds. The fluctuations for the highest-peak CDM haloes at redshifts ~20-30 could be detected in the future. Observations will be important to test model predictions of early structure formation in the universe.
Population III stars are believed to have been more massive than typical stars today and to have formed in relative isolation. The thermodynamic impact of metals is expected to induce a transition leading to clustered, low-mass Population II star for
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