Microwave ISM Emission Observed by WMAP

We investigate the nature of the diffuse Galactic emission in the Wilkinson Microwave Anisotropy Probe (WMAP) temperature anisotropy data. Substantial dust-correlated emission is observed at all WMAP frequencies, far exceeding the expected thermal dust emission in the lowest frequency channels (23, 33, 41 GHz). The WMAP team (Bennett et al.) interpret this emission as dust-correlated synchrotron radiation, attributing the correlation to the natural association of relativistic electrons produced by SNae with massive star formation in dusty clouds, and deriving an upper limit of 5% on the contribution of Draine & Lazarian spinning dust at K-band (23 GHz). We pursue an alternative interpretation that much, perhaps most, of the dust-correlated emission at these frequencies is indeed spinning dust, and explore the spectral dependence on environment by considering a few specific objects as well as the full sky average. Models similar to Draine & Lazarian spinning dust provide a good fit to the full-sky data. The full-sky fit also requires a significant component with free-free spectrum uncorrelated with \Halpha, possibly hot (~million K) gas within 30 degrees of the Galactic center.Comment: ApJ in press (accepted 5 Dec 2003), version 2: corrected typos and added references. 23 pages, 5 figures, 2 tables. Free-free haze map is available at http://skymaps.inf

Microwave ISM Emission in the Green Bank Galactic Plane Survey: Evidence for Spinning Dust

We observe significant dust-correlated emission outside of H II regions in the Green Bank Galactic Plane Survey (-4 < b < 4 degrees) at 8.35 and 14.35 GHz. The rising spectral slope rules out synchrotron and free-free emission as majority constituents at 14 GHz, and the amplitude is at least 500 times higher than expected thermal dust emission. When combined with the Rhodes (2.326 GHz), and WMAP (23-94 GHz) data it is possible to fit dust-correlated emission at 2.3-94 GHz with only soft synchrotron, free-free, thermal dust, and an additional dust-correlated component similar to Draine & Lazarian spinning dust. The rising component generally dominates free-free and synchrotron for \nu >~ 14 GHz and is overwhelmed by thermal dust at \nu > 60 GHz. The current data fulfill most of the criteria laid out by Finkbeiner et al. (2002) for detection of spinning dust.Comment: ApJ in press. 26 pages, 11 figures, figures jpeg compressed to save spac

An Absolute Measurement of the Cosmic Microwave Background Radiation Temperature at 10.7 GHz

A balloon-borne experiment has measured the absolute temperature of the cosmic microwave background radiation (CMBR) at 10.7 GHz to be Tcmbr = 2.730 +- .014 K. The error is the quadratic sum of several systematic errors, with statistical error of less than 0.1 mK. The instrument comprises a cooled corrugated horn antenna coupled to a total-power radiometer. A cryogenic mechanical waveguide switch alternately connects the radiometer to the horn and to an internal reference load. The small measured temperature difference (<= 20 mK) between the sky signal and the reference load in conjunction with the use of a cold front end keeps systematic instrumental corrections small. Atmospheric and window emission are minimized by flying the instrument at 24 km altitude. A large outer ground screen and smaller inner screen shield the instrument from stray radiation from the ground and the balloon. In-flight tests constrain the magnitude of ground radiation contamination, and low level interference is monitored through observations in several narrow frequency bands.Comment: 14 pages, 1 figure, submitted to ApJ

Twenty-one centimeter tomography with foregrounds

Twenty-one centimeter tomography is emerging as a powerful tool to explore the end of the cosmic dark ages and the reionization epoch, but it will only be as good as our ability to accurately model and remove astrophysical foreground contamination. Previous treatments of this problem have focused on the angular structure of the signal and foregrounds and what can be achieved with limited spectral resolution (bandwidths in the 1 MHz range). In this paper we introduce and evaluate a ``blind'' method to extract the multifrequency 21cm signal by taking advantage of the smooth frequency structure of the Galactic and extragalactic foregrounds. We find that 21 cm tomography is typically limited by foregrounds on scales $k\ll 1h/$Mpc and limited by noise on scales $k\gg 1h/$Mpc, provided that the experimental bandwidth can be made substantially smaller than 0.1 MHz. Our results show that this approach is quite promising even for scenarios with rather extreme contamination from point sources and diffuse Galactic emission, which bodes well for upcoming experiments such as LOFAR, MWA, PAST, and SKA.Comment: 10 pages, 6 figures. Revised version including various cases with high noise level. Major conclusions unchanged. Accepted for publication in Ap

Galactic emission at 19 GHz

We cross-correlate a 19 GHz full sky Cosmic Microwave Background (CMB) survey with other maps to quantify the foreground contribution. Correlations are detected with the Diffuse Infrared Background Experiment (DIRBE) 240, 140 and 100 micron maps at high latitudes (|b|>30degrees), and marginal correlations are detected with the Haslam 408 MHz and the Reich & Reich 1420 MHz synchrotron maps. The former agree well with extrapolations from higher frequencies probed by the COBE DMR and Saskatoon experiments and are consistent with both free-free and rotating dust grain emission.Comment: 4 pages, with 4 figures included. Accepted for publication in ApJL. Color figure and links at http://www.sns.ias.edu/~angelica/foreground.html#19 or from [email protected]

An upper limit on anomalous dust emission at 31 GHz in the diffuse cloud [LPH96]201.663+1.643

[LPH96]201.663+1.643, a diffuse H{\sc ii} region, has been reported to be a candidate for emission from rapidly spinning dust grains. Here we present Cosmic Background Imager (CBI) observations at 26-36 GHz that show no evidence for significant anomalous emission. The spectral index within the CBI band, and between CBI and Effelsberg data at 1.4/2.7 GHz, is consistent with optically thin free-free emission. The best-fitting temperature spectral index from 2.7 to 31 GHz, $\beta=-2.06 \pm 0.03$, is close to the theoretical value, $\beta=-2.12$ for $T_{e}=9100$ K. We place an upper limit of 24% ~ (2\sigma) for excess emission at 31 GHz as seen in a 6\arcmin FWHM beam. Current spinning dust models are not a good fit to the spectrum of LPH96. No polarized emission is detected in the CBI data with an upper limit of 2% on the polarization fraction.Comment: 5 pages, 3 figures, submitted to ApJ

Effects of Foreground Contamination on the Cosmic Microwave Background Anisotropy Measured by MAP

We study the effects of diffuse Galactic, far-infrared extragalactic source, and radio point source emission on the cosmic microwave background (CMB) anisotropy data anticipated from the MAP experiment. We focus on the correlation function and genus statistics measured from mock MAP foreground-contaminated CMB anisotropy maps generated in a spatially-flat cosmological constant dominated cosmological model. Analyses of the simulated MAP data at 90 GHz (0.3 deg FWHM resolution smoothed) show that foreground effects on the correlation function are small compared with cosmic variance. However, the Galactic emission, even just from the region with |b| > 20 deg, significantly affects the topology of CMB anisotropy, causing a negative genus shift non-Gaussianity signal. Given the expected level of cosmic variance, this effect can be effectively reduced by subtracting existing Galactic foreground emission models from the observed data. IRAS and DIRBE far-infrared extragalactic sources have little effect on the CMB anisotropy. Radio point sources raise the amplitude of the correlation function considerably on scales below 0.5 deg. Removal of bright radio sources above a 5 \sigma detection limit effectively eliminates this effect. Radio sources also result in a positive genus curve asymmetry (significant at 2 \sigma) on 0.5 deg scales. Accurate radio point source data is essential for an unambiguous detection of CMB anisotropy non-Gaussianity on these scales. Non-Gaussianity of cosmological origin can be detected from the foreground-subtracted CMB anisotropy map at the 2 \sigma level if the measured genus shift parameter |\Delta\nu| >= 0.02 (0.04) or if the measured genus asymmetry parameter |\Delta g| >= 0.03 (0.08) on a 0.3 (1.0) deg FWHM scale.Comment: 26 pages, 7 figures, Accepted for Publication in Astrophysical Journal (Some sentences and figures modified

Global 21cm signal experiments: a designer's guide

[Abridged] The spatially averaged global spectrum of the redshifted 21cm line has generated much experimental interest, for it is potentially a direct probe of the Epoch of Reionization and the Dark Ages. Since the cosmological signal here has a purely spectral signature, most proposed experiments have little angular sensitivity. This is worrisome because with only spectra, the global 21cm signal can be difficult to distinguish from foregrounds such as Galactic synchrotron radiation, as both are spectrally smooth and the latter is orders of magnitude brighter. We establish a mathematical framework for global signal data analysis in a way that removes foregrounds optimally, complementing spectra with angular information. We explore various experimental design trade-offs, and find that 1) with spectral-only methods, it is impossible to mitigate errors that arise from uncertainties in foreground modeling; 2) foreground contamination can be significantly reduced for experiments with fine angular resolution; 3) most of the statistical significance in a positive detection during the Dark Ages comes from a characteristic high-redshift trough in the 21cm brightness temperature; and 4) Measurement errors decrease more rapidly with integration time for instruments with fine angular resolution. We show that if observations and algorithms are optimized based on these findings, an instrument with a 5 degree beam can achieve highly significant detections (greater than 5-sigma) of even extended (high Delta-z) reionization scenarios after integrating for 500 hrs. This is in contrast to instruments without angular resolution, which cannot detect gradual reionization. Abrupt ionization histories can be detected at the level of 10-100's of sigma. The expected errors are also low during the Dark Ages, with a 25-sigma detection of the expected cosmological signal after only 100 hrs of integration.Comment: 34 pages, 30 figures. Replaced (v2) to match accepted PRD version (minor pedagogical additions to text; methods, results, and conclusions unchanged). Fixed two typos (v3); text, results, conclusions etc. completely unchange

Evidence for Inverted Spectrum 20 GHz Emission in the Galactic Plane

A comparison of a 19 GHz full-sky map with the WMAP satellite K band (23 GHz) map indicates that the bulk of the 20 GHz emission within 7 degrees of the Galactic plane has an inverted (rising) spectrum with an average spectral index alpha = 0.21 +/- 0.05. While such a spectrum is inconsistent with steep spectrum synchrotron (alpha ~ -0.7) and flat spectrum free-free (alpha ~ -0.1) emission, it is consistent with various models of electric dipole emission from thermally excited spinning dust grains as well as models of magnetic dipole emission from ferromagnetic dust grains. Several regions in the plane, e.g., near the Cygnus arm, have spectra with even larger alpha. While low signal to noise of the 19 GHz data precludes a detailed map of spectral index, especially off the Galactic plane, it appears that the bulk of the emission in the plane is correlated with the morphology of dust. Regions with higher 23 GHz flux tend to have harder spectra. Off the plane, at Galactic latitudes between 7 and 20 degree the spectrum steepens to alpha = -0.16 +/- 0.15.Comment: 11 page, 3 figure