Dissecting the high-z interstellar medium through intensity mapping cross-correlations

We explore the detection, with upcoming spectroscopic surveys, of three-dimensional power spectra of emission line fluctuations produced in different phases of the Interstellar Medium (ISM) by ionized carbon, ionized nitrogen and neutral oxygen at redshift z>4. The emission line [CII] from ionized carbon at 157.7 micron, and multiple emission lines from carbon monoxide, are the main targets of planned ground-based surveys, and an important foreground for future space-based surveys like the Primordial Inflation Explorer (PIXIE). However, the oxygen [OI] (145.5 micron) line, and the nitrogen [NII] (121.9 micron and 205.2 micron) lines, might be detected in correlation with [CII] with reasonable signal-to-noise ratio (SNR). These lines are important coolants of both the neutral and the ionized medium, and probe multiple phases of the ISM. We compute predictions of the three-dimensional power spectra for two surveys designed to target the [CII] line, showing that they have the required sensitivity to detect cross-power spectra with the [OI] line, and the [NII] lines with sufficient SNR. The importance of cross-correlating multiple lines is twofold. On the one hand, we will have multiple probes of the different phases of the ISM, which is key to understand the interplay between energetic sources, the gas and dust at high redshift. This kind of studies will be useful for a next-generation space observatory such as the NASA Far-IR Surveyor. On the other end, emission lines from external galaxies are an important foreground when measuring spectral distortions of the Cosmic Microwave Background spectrum with future space-based experiments like PIXIE; measuring fluctuations in the intensity mapping regime will help constraining the mean amplitude of these lines, and will allow us to better handle this important foreground.Comment: 13 pages, 2 table, 7 figures, Accepted for publication in Ap

Do baryons trace dark matter in the early universe?

Baryon-density perturbations of large amplitude may exist if they are compensated by dark-matter perturbations so that the total density remains unchanged. Big-bang nucleosynthesis and galaxy clusters allow the amplitudes of these compensated isocurvature perturbations (CIPs) to be as large as $\sim10$. CIPs will modulate the power spectrum of cosmic microwave background (CMB) fluctuations---those due to the usual adiabatic perturbations---as a function of position on the sky. This leads to correlations between different spherical-harmonic coefficients of the temperature/polarization map, and it induces B modes in the CMB polarization. Here, the magnitude of these effects is calculated and techniques to measure them are introduced. While a CIP of this amplitude can be probed on the largest scales with WMAP, forthcoming CMB experiments should improve the sensitivity to CIPs by at least an order of magnitude.Comment: 4 pages, 3 figures, updated with version published in Phys. Rev. Lett. Results unchanged. Added expanded discussion of how to disentangle compensated isocurvature perturbations from weak lensing of the CMB. Expanded discussion of early universe motivation for compensated isocurvature perturbation

The CMB Quadrupole in a Polarized Light

The low quadrupole of the cosmic microwave background (CMB), measured by COBE and confirmed by WMAP, has generated much discussion recently. We point out that the well-known correlation between temperature and polarization anisotropies of the CMB further constrains the low multipole anisotropy data. This correlation originates from the fact that the low-multipole polarization signal is sourced by the CMB quadrupole as seen by free electrons during the relatively recent cosmic history. Consequently, the large-angle temperature anisotropy data make restrictive predictions for the large-angle polarization anisotropy, which depend primarily on the optical depth for electron scattering after cosmological recombination, tau. We show that if current cosmological models for the generation of large angle anisotropy are correct and the COBE/WMAP data are not significantly contaminated by non-CMB signals, then the observed C_te amplitude on the largest scales is discrepant at the 99.8% level with the observed C_tt for the concordance LCDM model with tau=0.10. Using tau=0.17, the preferred WMAP model-independent value, the discrepancy is at the level of 98.5%.Comment: 6 pages, 6 figures, ApJ in pres

Primordial non-Gaussianity from the covariance of galaxy cluster counts

It has recently been proposed that the large-scale bias of dark matter halos depends sensitively on primordial non-Gaussianity of the local form. In this paper we point out that the strong scale dependence of the non-Gaussian halo bias imprints a distinct signature on the covariance of cluster counts. We find that using the full covariance of cluster counts results in improvements on constraints on the non-Gaussian parameter f_(NL) of 3 (1) orders of magnitude relative to cluster counts (counts+clustering variance) constraints alone. We forecast f_(NL) constraints for the upcoming Dark Energy Survey in the presence of uncertainties in the mass-observable relation, halo bias, and photometric redshifts. We find that the Dark Energy Survey can yield constraints on non-Gaussianity of σ(f_(NL))~1–5 even for relatively conservative assumptions regarding systematics. Excess of correlations of cluster counts on scales of hundreds of megaparsecs would represent a smoking-gun signature of primordial non-Gaussianity of the local type