摘要:

Scientific recognition of the existence, evolution, and significance of structure within the cosmos developed slowly. We follow the story here from the earliest times to the first systematic redshift surveys and the “Rubin‐Ford effect,” emphasizing the period beginning with William Herschel and ending about lunch time on Wednesday. The scientific issues cannot be put in any one linear order, because, for instance, some people were studying clusters of galaxies and measuring the mass of M31 while others still denied the existence of external galaxies. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1581767

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Observational constraints on spacetime from supernovae Ia, CMB, lensing, Lyman &agr; Forest and galaxy clustering are reviewed, focusing on how the underlying physics (dark matter, dark energy, gravity) can be tested rather than assumed. This is possible because we are simply measuring spacetime, and to 1st order, all observations probe just three cosmological functions, not a dozen dubious cosmological parameters: the cosmic expansion historyH(z), the primordial power spectrumP* (k) and the fluctuation growthg(z, k). Measuring these functions will clarify the nature of dark energy (from how its density depends on time), the nature of dark matter (from its power spectrum growth) and the nature of early universe (from the primordial power spectrum). © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1581768

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

This paper is a brief introduction to the “cyclic model of the universe,” a radical alternative to standard big bang/inflationary theory in which space and time exist indefinitely, inflation is avoided, and the universe undergoes periodic epochs of expansion and conclusion. This introduction explains the novel way in which density perturbations are generated which seed large scale structure formation and produce spatial variations in the cosmic microwave background temperature. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1581769

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The tremendous experimental progress in cosmic microwave background (CMB) temperature and polarization anisotropy studies over the last few years has helped establish a standard paradigm for cosmology at intermediate epochs and has simultaneously raised questions regarding the physical processes at the two opposite ends of time. We review the acoustic phenomenology that forms the cornerstone of the standard cosmological model and discuss internal consistency relations which lend credence to its interpretation. We touch on future milestones in the study of CMB anisotropy and their implications for inflationary and dark energy models. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1581770

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Acoustic oscillations in the early universe, jumpstarted by superhorizon fluctuations left behind by inflation, give rise to a series of coherent peaks in the spatial power spectrum of the cosmic microwave background (CMB). An inevitable consequence of this scenario is that the CMB photons are left with small polarization anisotropies. Polarization patterns may be separated by parity into E‐modes and B‐modes; acoustic oscillations give rise only to E‐modes. A recent detection of the E‐modes agrees well with predictions. Many experiments are poised to make further measurements of E‐modes, and to begin searching for B‐modes, which should arise at subdegree scales because of weak lensing deflections of the original E‐modes en route to the observer. At larger angular scales, gravitational waves from inflation could produce B‐modes. Experimental prospects are outlined. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1581771

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The hard X‐ray background (XRB) provides a tracer of matter out to a redshift ofz≃ 4. If the universe is open or has a significant cosmological constant, then the cosmic microwave background (CMB) and XRB should be correlated due to the integrated Sachs‐Wolfe (ISW) effect. A comparison of the COBE CMB map with HEAO1 A2 2–10 keV map of the XRB shows no such correlation. If the X‐ray bias factor is on the order of 2–3 as implied by the clustering of the XRB, the implied 95&percent; CL upper limit on a cosmological constant is &OHgr;&Lgr;≲ 0.60. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1581772

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We review recent theoretical results on the formation of the first stars and quasars in the universe, and emphasize related open questions. In particular, we list important differences between the star formation process at high redshifts and in the present‐day universe. We address the importance of heavy elements in bringing about the transition from an early star formation mode dominated by massive stars, to the familiar mode dominated by low mass stars, at later times. We show how gamma‐ray bursts can be utilized to probe the first epoch of star formation. Finally, we discuss how the first supermassive black holes could have formed through the direct collapse of primordial gas clouds. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1581773

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

In the standard Cold Dark Matter (CDM) theory of structure formation, virialized minihalos (withTvir⩽ 10,000K) form in abundance at high redshift (z> 6), during the cosmic “dark ages.” The hydrogen in these minihalos, the first nonlinear baryonic structures to form in the universe, is mostly neutral and sufficiently hot and dense to emit strongly at the 21‐cm line. We calculate the emission from individual minihalos and the radiation background contributed by their combined effect. Minihalos create a “21‐cm forest” of emission lines. We predict that the angular fluctuations in this 21‐cm background should be detectable with the planned LOFAR and SKA radio arrays, thus providing a direct probe of structure formation during the “dark ages.” Such a detection will serve to confirm the basic CDM paradigm while constraining the background cosmology parameters, the shape of the power‐spectrum of primordial density fluctuations, the onset and duration of the reionization epoch, and the conditions which led to the first stars and quasars. We present results here for the currently‐favored, flat &Lgr;CDM model, for different tilts of the primordial power spectrum. These minihalos will also cause a “21‐cm forest” of absorption lines, as well, in the spectrum of radio continuum sources at high redshift, if the latter came into existence before the end of reionization. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1581774

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We present the first gas dynamical simulations of the photoevaporation of cosmological minihalos overtaken by the ionization fronts which swept through the IGM during reionization in a &Lgr;CDM universe, including the effects of radiative transfer. We demonstrate the phenomenon of I‐front trapping inside minihalos, in which the weak, R‐type fronts which traveled supersonically across the IGM decelerated when they encountered the dense, neutral gas inside minihalos, becoming D‐type I‐fronts, preceded by shock waves. For a minihalo with virial temperatureTvir⩽ 104K, the I‐front gradually burned its way through the minihalo which trapped it, removing all of its baryonic gas by causing a supersonic, evaporative wind to blow backwards into the IGM, away from the exposed layers of minihalo gas just behind the advancing I‐front. Such hitherto neglected feedback effects were widespread during reionization. N‐body simulations and analytical estimates of halo formation suggest that sub‐kpc minihalos such as these, withTvir⩽ 104K, were so common as to dominate the absorption of ionizing photons. This means that previous estimates of the number of ionizing photons per H atom required to complete reionization which neglected this effect may be too low. Regardless of their effect on the progress of reionization, however, the minihalos were so abundant that random lines of sight thru the high‐zuniverse should encounter many of them, which suggests that it may be possible to observe the processes described here in the absorption spectra of distant sources. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1581775

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

How massive were the first stars? This question is of fundamental importance for galaxy formation and cosmic reionization. Here we consider how protostellar feedback can limit the mass of a forming star. For this we must understand the rate at which primordial protostars accrete, how they and their feedback output evolve, and how this feedback interacts with the infalling matter. We describe the accretion rate with an “isentropic accretion” model:m˙*is initially very large (0.03M⊙yr−1whenm*= 1M⊙) and declines asm*−3/7. Protostellar evolution is treated with a model that tracks the total energy of the star. A key difference compared to previous studies is allowance for rotation of the infalling envelope. This leads to photospheric conditions at the star and dramatic differences in the feedback. Two feedback mechanisms are considered: HII region breakout and radiation pressure from Lyman‐&agr; and FUV photons. Radiation pressure appears to be the dominant mechanism for suppressing infall, becoming dynamically important around 20M⊙. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1581776

出版商:AIP    

年代:1903

数据来源: AIP