摘要:

It is now well known that a primordial chemistry, involving light elements produced during the nucleosynthesis period, might develop during the hydrogen post-recombination era. In particular, molecular ions and primordial molecules such asH2,HDandLiHwill be produced. We summarize this primordial chemistry after the recombination epoch, and then present a simple gravitational collapse model of a cloud. The potentiality of fragmentation of this collapsing protoclouds through the thermal instability is also discussed. We suggest that this study could also be extended to theCOmolecule, because the carbon reservoir moleculeCOhas already been observed in high redshifts objects. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59317

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

It becomes possible now to detect cold molecules at high redshift in the millimeter domain. Since the first discovery in 1992 by Brown and van den Bout of CO lines atz=2.28in a gravitationally lensed starburst galaxy, nearly ten objects are now known to possess large quantities of molecular gas beyondz=1and up toz∼5,through millimeter and sub-millimeter emission lines. Even more objects have been detected in their continuum dust emission, and a few galaxies through millimeter absorption lines in front of quasars atz⩽1.The continuum dust emission is the most easily detected: for a starburst dust atTd∼60&hthinsp;K,the emission peaks around 60 &mgr;m, and falls as&lgr;−4at longer wavelengths. In the mm domain, the emission is then stronger for the more redshifted objects. For the CO lines, the situation is less favorable, and the reported detections are helped by gravitational amplification. The increase of the CMB temperatureTbgwith redshift helps the rotational line excitation (especially at highz), but not its detection. Absorption in front of quasars is a more sensitive probe of cold gas at high redshift, able to detect individual clouds of a few solar masses (instead of1010&hthinsp;M⊙for emission). Taking advantage of the small size of the QSO, very high spatial resolution (of the order of milli-arcsec) can be achieved, and high spectral (30 m/s) resolution, due to the heterodyne technique. The sampled column-densities range betweenN(H2)=1020et1024&hthinsp;cm−2.The high sensitivity allows to detect a multitude of molecular lines in a single object (HCO+,HNC, HCN,N2H+,C18O,CS,H2CO,CN, CCH,H2Setc&ellip;.), and compare the chemistry with the local one, atz=0.From the diffuse components, one can measure the cosmic black body temperature as a function of redshift. The high column densities component allow to observe important molecules not observable from the ground, likeO2,H2Oand LiH for example. All these preliminary studies carry a great hope for what will be observed with future millimeter instruments, and some perspectives are given. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59347

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Measurements of light elements in the Solar system can provide important constraints upon their abundances in the protosolar nebula. In the case of helium, different results have been obtained in the four giant planets. These divergences can be accounted for if an evolutionary mechanism, involving helium differentiation in Jupiter and Saturn, is taken into account; if this scenario is correct, the He/H ratio in Uranus and Neptune might be representative of its protosolar value. In the case of deuterium, various determinations derived from planetary and cometary atmospheres show the existence of two deuterium reservoirs: the protosolar nebula, and the interstellar ices(H2O,CH4&ellip;)from which planetesimals accreted. Recent results by Galileo and ISO show that Jupiter and Saturn are the only objects where D/H can be expected to be close to protosolar, while in all other outer solar-system objects (including Uranus and Neptune), deuterium exhibits a significant enrichment due to the contribution of ices incorporated in their nuclei. The3Heabundance in Jupiter, recently measured by Galileo, is believed to be representative of its protosolar value. Finally, lithium has been observed for the first time in a comet, at the time of the collision of comet Shoemaker-Levy 9 in Jupiter in July 1994; however, no information can be derived about its abundance, because the excitation mechanism of the emission line is not understood presently. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59319

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We present the basics of microlensing and give an overview of the results obtained so far. We also describe a scenario in which dark clusters of MACHOs (Massive Astrophysical Compact Halo Objects) and cold molecular clouds (mainly ofH2) naturally form in the halo at galactocentric distances larger than 10-20 Kpc. Moreover, we discuss various experimental tests of this picture in particular a &ggr;-ray emission from the clouds due to the scattering of high- energy cosmic-ray protons. Our estimate for the &ggr;-ray flux turns out to be in remarkably good agreement with the recent discovery by Dixon &etal; [1] of a possible &ggr;-ray emission from the halo using EGRET data. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59348

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The search of distortions (deviations from a Planck distribution) in the spectrum of the Cosmic Microwave Background allows to probe the conditions existing in our Universe up toZ≃106.We analyze the status of the observations (so far no distortion has been detected) and discuss the possibility and the astrophysical interest of searching distortions at long wavelengths, in the Rayleigh Jeans portion of the Cosmic Microwave Background spectrum. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59320

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Detection of Cosmic Microwave Background (CMB) polarization gives a confirmation of the mechanisms undergoing the matter condensation at the epoch of decoupling. Furthermore CMB polarization at large angular scales is a direct probe of a possible reionization occurred after the recombination. Expected degree of polarization is a small part (less than 10&percent;) of the anisotropy at a fixed angular scale. This extremely faint signal requires dedicated experiments in order to be detected. In this contribution we describe our experimental approach and the solution we adopted and discuss the ultimate sensitivity reachable with our instrument. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59321

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The uncertainty on the temperature of the Cosmic Microwave Background (CMB) measured below 1 GHz is larger than 30&percent;. To improve our knowledge it is necessary to perform measurements at different wavelengths and directions, to disentangle the various components of the antenna temperature (CMB, Galaxy, unresolved sources, atmosphere, ground). In this contribution we briefly describe the apparatus of TRIS EXPERIMENT, the observation strategy, calibration techniques and results of extensive tests. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59322

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We propose a new inflationary toy model that produces two episodes of phase transitions. With the first one, super-horizon-sized bubbles are nucleated, which are seen from inside as open universes, thereby reconciling inflation with the recent observations of a low&OHgr;0.With the second transition, a distribution of sub-horizon voids, of sizes typically around 10–100 Mpc/hare generated inside the open universes. These primordial voids can be the seeds of the present large scale voids that are detected in redshift surveys, and provide a non-Gaussian signal on the microwave background. The model realizes this sequence along the same slow-rolling path, by modulating the energy difference between the vacuum states. In this model, that we call extended Bubbly CDM, openness and bubblyness, rather than flatness and homogeneity, are the main products of inflation. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59323

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The Sky Polarization Observatory (SPOrt) is presented as a project aimed to measure the diffuse sky polarized emission, from the International Space Station, in the frequency range 20–90 GHz with 7° ofHPBW. The SPOrt experimental configuration is described with emphasis on the aspects that make SPOrt the first European scientific payload operating at microwave wavelengths. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59324

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We present the cosmological and astrophysical objectives of the SPOrt mission, which is scheduled for flying on the International Space Station (ISS) in the year 2002 with the purpose of measuring the diffuse sky polarized radiation in the microwave region. We discuss the problem of disentangling the cosmic background polarized signal from the Galactic foregrounds. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59345

出版商:AIP    

年代:1999

数据来源: AIP