The large scale structure of the universe.

Cosmology at low frequencies: The 21 cm transition and the high-redshift Universe

Large-scale CO surveys of the entire Galactic plane and specific nearby clouds have been combined to produce a panorama of the entire Milky Way in molecular clouds at an angular resolution of 1/2 deg. This survey is the only molecular line survey to date with sky coverage and resolution comparable to that of the early 21 cm surveys. The telescopes and the observing techniques used for the individual surveys and the methods of reconciling the survey results are described. The composite survey is presented as a spatial map integrated over velocity and as a longitude-velocity map integrated over latitude; individual clouds and large-scale features of the maps are briefly discussed. The distribution and properties of molecular clouds within 1 kpc of the sun are investigated, and a comparison with other Population I tracers is used to demonstrate that the composite survey probably provides a nearly complete inventory of nearby molecular clouds. 92 references.

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A Composite CO survey of the entire Milky Way

Planck has mapped the microwave sky in temperature over nine frequency bands between 30 and 857 GHz and in polarization over seven frequency bands between 30 and 353 GHz in polarization. In this paper we consider the problem of diffuse astrophysical component separation, and process these maps within a Bayesian framework to derive an internally consistent set of full-sky astrophysical component maps. Component separation dedicated to cosmic microwave background (CMB) reconstruction is described in a companion paper. For the temperature analysis, we combine the Planck observations with the 9-yr Wilkinson Microwave Anisotropy Probe (WMAP) sky maps and the Haslam et al. 408 MHz map, to derive a joint model of CMB, synchrotron, free-free, spinning dust, CO, line emission in the 94 and 100 GHz channels, and thermal dust emission. Full-sky maps are provided for each component, with an angular resolution varying between 7.5 and 1deg. Global parameters (monopoles, dipoles, relative calibration, and bandpass errors) are fitted jointly with the sky model, and best-fit values are tabulated. For polarization, the model includes CMB, synchrotron, and thermal dust emission. These models provide excellent fits to the observed data, with rms temperature residuals smaller than 4μK over 93% of the sky for all Planck frequencies up to 353 GHz, and fractional errors smaller than 1% in the remaining 7% of the sky. The main limitations of the temperature model at the lower frequencies are internal degeneracies among the spinning dust, free-free, and synchrotron components; additional observations from external low-frequency experiments will be essential to break these degeneracies. The main limitations of the temperature model at the higher frequencies are uncertainties in the 545 and 857 GHz calibration and zero-points. For polarization, the main outstanding issues are instrumental systematics in the 100–353 GHz bands on large angular scales in the form of temperature-to-polarization leakage, uncertainties in the analogue-to-digital conversion, and corrections for the very long time constant of the bolometer detectors, all of which are expected to improve in the near future.

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Planck 2015 results - X. Diffuse component separation: Foreground maps

Context. Our position inside the Galaxy requires 3D-modelling to obtain the distribution of the Galactic magnetic field, cosmic- ray (CR) electrons and thermal electrons. Aims. Our intention is to find a Galactic 3D-model which agrees best with available radio observations. Methods. We constrain simulated all-sky maps in total intensity, lin ear polarization, and rotation measure (RM) by observations. For the simulated maps as a function of frequency we integrate in 15 ′ wide cones the emission along the line of sight calculated from Galactic 3D-models. We test a number of large-scale magnetic field configurations and take the properties of the warm inte rstellar medium into account. Results. From a comparison of simulated and observed maps we are able to constrain the regular large-scale Galactic magnetic field in the disk and the halo of the Galaxy. The local regular fi eld is 2� G and the average random field is about 3 � G. The known local excess of synchrotron emission originating either fr om enhanced CR electrons or random magnetic fields is able to e xplain the observed high-latitude synchrotron emission. The thermal electron model (NE2001) in conjunction with a proper fill ing factor accounts for the observed optically thin thermal emission and low frequency absorption by optically thick emission. A coupling factor between thermal electrons and the random magnetic field comp onent is proposed, which in addition to the small filling fact or of thermal electrons increases small-scale RM fluctuations an d thus accounts for the observed depolarization at 1.4 GHz. Conclusions. We conclude that an axisymmetric magnetic disk field configur ation with reversals inside the solar circle fits available observations best. Out of the plane a strong toroidal magnetic field with di fferent signs above and below the plane is needed to account for the observed high-latitude RMs. The large field strength is a consequence of the small thermal electron scale height of 1 kpc, which also limits the CR electron extent up to a height of 1 kpc not to contradict with the observed synchrotron emission out of the plane. Our preferred 3D-model fits the observed Galactic total intensi ty and polarized emission better than other models over a wide frequency range and also agrees with the observed RM from extragalactic sources.

/pdf/radio-observational-constraints-on-galactic-3d-emission-245m3npx21.pdf

Radio observational constraints on Galactic 3D-emission models

Wilkinson Microwave Anisotropy Probe (WMAP) data when combined with ancillary data on free-free, synchrotron and dust allow an improved understanding of the spectrum of emission from each of these components. Here, we examine the sky variation at intermediate latitudes using a cross-correlation technique. In particular, we compare the observed emission in 15 selected sky regions to three 'standard' templates. 

The free-free emission of the diffuse ionized gas is fitted by a well-known spectrum at K and Ka band, but the derived emissivity corresponds to a mean electron temperature of similar to 4000-5000 K. This is inconsistent with estimates from Galactic H II regions although a variation in the derived ratio of H alpha to free-free intensity by a factor of similar to 2 is also found from region to region. The origin of the discrepancy is unclear. 

The anomalous emission associated with dust is clearly detected in most of the 15 fields studied. The anomalous emission correlates well with the Finkbeiner, Davis & Schlegel model 8 predictions (FDS8) at 94 GHz, with an effective spectral index between 20 and 60 GHz, of beta similar to -2.85. Furthermore, the emissivity varies by a factor of similar to 2 from cloud to cloud. A modestly improved fit to the anomalous dust at K band is provided by modulating the template by an estimate of the dust colour temperature, specifically FDS8 x T^n. We find a preferred value n similar to 1.6, although there is a scatter from region to region. Nevertheless, the preferred index drops to zero at higher frequencies where the thermal dust emission dominates. 

The synchrotron emission steepens between GHz frequencies and the WMAP bands. There are indications of spectral index variations across the sky but the current data are not precise enough to accurately quantify this from region to region. 

Our analysis of the WMAP data indicates strongly that the dust-correlated emission at the low WMAP frequencies has a spectrum which is compatible with spinning dust; we find no evidence for a synchrotron component correlated with dust. The importance of these results for the correction of cosmic microwave background data for Galactic foreground emission is discussed.

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A determination of the spectra of Galactic components observed by the Wilkinson Microwave Anisotropy Probe

/pdf/a-study-of-neutral-hydrogen-in-the-solar-neighbourhood-of-3qa5ux6325.pdf

A Study of Neutral Hydrogen in the Solar Neighbourhood of the Milky Way

The peculiar velocity of the Local Group – III. Dipole, quadrupole and infall solutions

/pdf/a-search-for-neutral-hydrogen-in-primordial-protoclusters-at-1qgl99sla2.pdf

R. D. Davies

Papers

A determination of the spectra of Galactic components observed by the Wilkinson Microwave Anisotropy Probe

A Study of Neutral Hydrogen in the Solar Neighbourhood of the Milky Way

The peculiar velocity of the Local Group – III. Dipole, quadrupole and infall solutions

A search for neutral hydrogen in primordial protoclusters at z = 3.33 and 4.92.

A Search for Intergalactic Neutral Hydrogen: II. Data of Cosmological Significance Derived from the Observations