Cross-Correlation Studies with CMB Polarization Maps

The free-electron population during the reionized epoch rescatters CMB temperature quadrupole and generates a now well-known polarization signal at large angular scales. While this contribution has been detected in the temperature-polarization cross power spectrum measured with WMAP data, due to the large cosmic variance associated with anisotropy measurements at tens of degree angular scales only limited information related to reionization, such as the optical depth to electron scattering, can be extracted. The inhomogeneities in the free-electron population lead to an additional secondary polarization anisotropy contribution at arcminute scales. While the fluctuation amplitude, relative to dominant primordial fluctuations, is small, we suggest that a cross-correlation between arcminute scale CMB polarization data and a tracer field of the high redshift universe, such as through fluctuations captured by the 21 cm neutral Hydrogen background or those in the infrared background related to first proto-galaxies, may allow one to study additional details related to reionization. For this purpose, we discuss an optimized higher order correlation measurement, in the form of a three-point function, including information from large angular scale CMB temperature anisotropies in addition to arcminute scale polarization signal related to inhomogeneous reionization. We suggest that the proposed bispectrum can be measured with a substantial signal-to-noise ratio and does not require all-sky maps of CMB polarization or that of the tracer field. A measurement such as the one proposed may allow one to establish the epoch when CMB polarization related to reionization is generated and to address if the universe was reionized once or twice.Comment: 13 pages, 7 figures; Version in press with Phys. Rev.

Gravitational Stability of Circumnuclear Disks in Elliptical Galaxies

A significant fraction of nearby elliptical galaxies are known to have high density gas disks in their circumnuclear (CN) region (0.1 to a few kpc). Yet, ellipticals, especially luminous ones, show little signs of recent star formation (SF). To investigate the possible cause of the dearth of SF in these systems, we study the gravitational stability of CN gas disks embedded within the potentials of both the stellar bulge and the central massive black hole (BH) in ellipticals. We find that CN disks in higher mass galaxies are generally more stable than those in lower mass galaxies, because higher mass galaxies tend to have more massive BHs and more centrally concentrated stellar density profiles. We also consider the case in which the central stellar density profile has a core, which is often observed for ellipticals whose total stellar mass is higher than about 10^11 Msun. Such a cored stellar density profile leads to more unstable CN disks than the power-law density profile characteristic of less massive galaxies. However, the more massive BHs in high-mass galaxies act to stabilize the CN disk. Our results demonstrate that the gravitational potentials of both the central BH and the stellar component should be taken into account when studying the properties of CN disks, as their stability is sensitive to both the BH mass and the stellar density profile. Our results could explain the observed trend that less luminous ellipticals have a greater tendency to exhibit ongoing SF than giant ellipticals.Comment: 8 pages, 5 figures, accepted for publication in Ap

Hydrogen-like nitrogen radio line from hot interstellar and warm-hot intergalactic gas

Hyperfine structure lines of highly-charged ions may open a new window in observations of hot rarefied astrophysical plasmas. In this paper we discuss spectral lines of isotopes and ions abundant at temperatures 10^5-10^7 K, characteristic for warm-hot intergalactic medium, hot interstellar medium, starburst galaxies, their superwinds and young supernova remnants. Observations of these lines will allow to study bulk and turbulent motions of the observed target and will broaden the information about the gas ionization state, chemical and isotopic composition. The most prospective is the line of the major nitrogen isotope having wavelength 5.65 mm (Sunyaev and Churazov 1084). Wavelength of this line is well-suited for observation of objects at z=0.15-0.6 when it is redshifted to 6.5-9 mm spectral band widely-used in ground-based radio observations, and, for example, for z>=1.3, when the line can be observed in 1.3 cm band and at lower frequencies. Modern and future radio telescopes and interferometers are able to observe the absorption by 14-N VII in the warm-hot intergalactic medium at redshifts above z=0.15 in spectra of brightest mm-band sources. Sub-millimeter emission lines of several most abundant isotopes having hyperfine splitting might also be detected in spectra of young supernova remnants.Comment: 12 pages, 5 figures, accepted by Astronomy Letters; v3: details added; error fixe

Cosmological Limits on the Neutrino Mass from the Lya Forest

The Lya forest in quasar spectra probes scales where massive neutrinos can strongly suppress the growth of mass fluctuations. Using hydrodynamic simulations with massive neutrinos, we successfully test techniques developed to measure the mass power spectrum from the forest. A recent observational measurement in conjunction with a conservative implementation of other cosmological constraints places upper limits on the neutrino mass: m_nu < 5.5 eV for all values of Omega_m, and m_nu < 2.4 (Omega_m/0.17 -1) eV, if 0.2 < Omega_m <0.5 as currently observationally favored (both 95 % C.L.).Comment: 4 pages, 2 ps figures, REVTex, submitted to Phys. Rev. Let

Recovering the Inflationary Potential

A procedure is developed for the recovery of the inflationary potential over the interval that affects astrophysical scales (\approx 1\Mpc - 10^4\Mpc). The amplitudes of the scalar and tensor metric perturbations and their power-spectrum indices, which can in principle be inferred from large-angle CBR anisotropy experiments and other cosmological data, determine the value of the inflationary potential and its first two derivatives. From these, the inflationary potential can be reconstructed in a Taylor series and the consistency of the inflationary hypothesis tested. A number of examples are presented, and the effect of observational uncertainties is discussed.Comment: 13 pages LaTeX, 6 Figs. available on request, FNAL-Pub-93/182-

A Texture Bestiary

Textures are topologically nontrivial field configurations which can exist in a field theory in which a global symmetry group $G$ is broken to a subgroup $H$, if the third homotopy group \p3 of $G/H$ is nontrivial. We compute this group for a variety of choices of $G$ and $H$, revealing what symmetry breaking patterns can lead to texture. We also comment on the construction of texture configurations in the different models.Comment: 34 pages, plain Tex. (Minor corrections to an old paper.

A new topological aspect of the arbitrary dimensional topological defects

We present a new generalized topological current in terms of the order parameter field $\vec \phi$ to describe the arbitrary dimensional topological defects. By virtue of the $$-mapping method, we show that the topological defects are generated from the zero points of the order parameter field $\vec \phi$, and the topological charges of these topological defects are topological quantized in terms of the Hopf indices and Brouwer degrees of $\phi$-mapping under the condition that the Jacobian $$. When $J(\frac \phi v)=0$, it is shown that there exist the crucial case of branch process. Based on the implicit function theorem and the Taylor expansion, we detail the bifurcation of generalized topological current and find different directions of the bifurcation. The arbitrary dimensional topological defects are found splitting or merging at the degenerate point of field function $\vec \phi$ but the total charge of the topological defects is still unchanged.Comment: 24 pages, 10 figures, Revte

The Universe Was Reionized Twice

We show the universe was reionized twice, first at z~15-16 and second at z~6. Such an outcome appears inevitable, when normalizing to two well determined observational measurements, namely, the epoch of the final cosmological reionization at z~6 and the density fluctuations at z~6, which in turn are tight ly constrained by Lyman alpha forest observations at z~3. These two observations most importantly fix the product of star formation efficiency and ionizing photon escape fraction from galaxies at high redshift. To the extent that the relative star formation efficiencies in gaseous minihalos with H2 cooling and large halos with atomic cooling at high redshift are still unknown, the primary source for the first reionization could be Pop III stars either in minihalos or in large halos. We show that gas in minihalos can be cooled efficiently by H2 molecules and star formation can continue to take place largely unimpeded throughout the first reionization period, thanks to two new mechanisms for generating a high X-ray background during the Pop III era, put forth here. Moreover, an important process for producing a large number of H2 molecules in relic HII regions of Pop III galaxies, first pointed out by Ricotti, Gnedin, & Shull, is quantified here. It is shown that the Lyman-Werner background may never build up during the Pop III era. The long cosmological reionization and reheating history is complex. We discuss a wide range of implications and possible tests for this new reionization picture. In particular, Thomson scattering optical depth is increased to 0.10 +- 0.03, compared to 0.027 for the case of only one rapid reionization at z=6. Upcoming Microwave Anisotropy Probe observation of the polarization of the cosmic microwave background should be able to distinguish between these two scenarios.Comment: submitted to ApJ, 69 pages, substantial revision made and conclusions strengthene

Sizes, Shapes, and Correlations of Lyman Alpha Clouds and Their Evolution in the CDM+Λ+\Lambda Universe

This study analyzes the sizes, shapes and correlations of \lya clouds produced by a hydrodynamic simulation of a spatially flat CDM universe with a non-zero cosmological constant ($\Omega_0=0.4$, $\Lambda_0=0.6$, $\sigma_8 =0.79$), over the redshift range $2\le z \le 4$. The \lya clouds range in size from several kiloparsecs to about a hundred kiloparsecs in proper units, and they range in shape from roundish, high column density regions with \nhi\ge 10^{15} cm^{-2} to low column density sheet-like structures with \nhi \le 10^{13} cm^{-2} at z=3. The most common shape found in the simulation resembles that of a flattened cigar. The physical size of a typical cloud grows with time roughly as $(1+z)^{-3/2}$ while its shape hardly evolves (except for the most dense regions $\rho_{cut}>30$). Our result indicates that any simple model with a population of spheres (or other shapes) of a uniform size is oversimplified; if such a model agrees with observational evidence, it is probably only by coincidence. We also illustrate why the use of double quasar sightlines to set lower limits on cloud sizes is useful only when the perpendicular sightline separation is small ($\Delta r \le 50h^{-1}$ kpc). Finally, we conjecture that high column density \lya clouds (\nhi\ge 10^{15} cm^{-2}) may be the progenitors of the lower redshift faint blue galaxies. This seems plausible because their correlation length, number density (extrapolated to lower redshift) and their masses are in fair agreement with those observed.Comment: ApJ, in press, 34 pages, 21 figures, figs (1a,b,c) can be at http://astro.princeton.edu/~cen/LYASSC/lyassc.htm

Quantum Correlation in One-dimensional Extend Quantum Compass Model

We study the correlations in the one-dimensional extended quantum compass model in a transverse magnetic field. By exactly solving the Hamiltonian, we find that the quantum correlation of the ground state of one-dimensional quantum compass model is vanishing. We show that quantum discord can not only locate the quantum critical points, but also discern the orders of phase transitions. Furthermore, entanglement quantified by concurrence is also compared.Comment: 8 pages, 14 figures, to appear in Eur. Phys. J.