Space Infrared Telescope for Cosmology and Astrophysics (SPICA), the cryogenic infrared space telescope recently pre-selected for a ‘Phase A’ concept study as one of the three remaining candidates for European Space Agency (ESA's) fifth medium class (M5) mission, is foreseen to include a far-infrared polarimetric imager [SPICA-POL, now called B-fields with BOlometers and Polarizers (B-BOP)], which would offer a unique opportunity to resolve major issues in our understanding of the nearby, cold magnetised Universe. This paper presents an overview of the main science drivers for B-BOP, including high dynamic range polarimetric imaging of the cold interstellar medium (ISM) in both our Milky Way and nearby galaxies. Thanks to a cooled telescope, B-BOP will deliver wide-field 100–350 $\mu$m images of linearly polarised dust emission in Stokes Q and U with a resolution, signal-to-noise ratio, and both intensity and spatial dynamic ranges comparable to those achieved by Herschel images of the cold ISM in total intensity (Stokes I). The B-BOP 200 $\mu$m images will also have a factor $\sim $30 higher resolution than Planck polarisation data. This will make B-BOP a unique tool for characterising the statistical properties of the magnetised ISM and probing the role of magnetic fields in the formation and evolution of the interstellar web of dusty molecular filaments giving birth to most stars in our Galaxy. B-BOP will also be a powerful instrument for studying the magnetism of nearby galaxies and testing Galactic dynamo models, constraining the physics of dust grain alignment, informing the problem of the interaction of cosmic rays with molecular clouds, tracing magnetic fields in the inner layers of protoplanetary disks, and monitoring accretion bursts in embedded protostars.

We present new measurements of the power spectra of the cosmic infrared background (CIB) anisotropies using the Planck 2015 full-mission HFI data at 353, 545, and 857 GHz over 20 000 square degrees. Unlike previous Planck measurements of the CIB power spectra, we do not rely on external HI data to remove Galactic dust emission from the Planck maps. Instead, we model the Galactic emission at the level of the power spectra, using templates constructed directly from the Planck data by exploiting the statistical isotropy of all extragalactic emission components. This allows us to work at the full resolution of Planck over large sky areas. We construct a likelihood based on the measured spectra (for multipoles 50 ≤ ℓ ≤ 2500) using analytic covariance matrices that account for masking and the realistic instrumental noise properties. The results of an MCMC exploration of this likelihood are presented, based on simple parameterised models of the CIB power that arises from clustering of infrared galaxies. We explore simultaneously the parameters describing the clustered power, the Poisson power levels, and the amplitudes of the Galactic power spectrum templates across the six frequency (cross-)spectra. The best-fit model provides a good fit to all spectra. As an example, Fig. 1 compares the measured auto spectra at 353, 545, and 857 GHz over 40% of the sky to the power in the best-fit model. We find that the power in the CIB anisotropies from galaxy clustering is roughly equal to the Poisson power at multipoles ℓ =2000 (the clustered power dominates on larger scales), and that our dust-cleaned CIB spectra are in good agreement with previous Planck and Herschel measurements. A key feature of our analysis is that it allows one to make many internal consistency tests. We show that our results are stable to data selection and choice of survey area, demonstrating both our ability to remove Galactic dust power to high accuracy and the statistical isotropy of the CIB signal.

The balloon borne experiment PRONAOS has measured the sub-millimetre emission from the diffuse interstellar medium to a quiescent filament in the Taurus molecular cloud. We model the output emission of this filament using a radiative transfer code and an independent tracer of the total column density (near infrared extinction). We show that inside the filament the transiently heated particles responsible of the 60 μm emission are removed and the dust sub-millimetre emissivity is increased by a significant factor, 3.4+0.3-0.7 (for typically nH > 3 ± 1 × 103 cm-3, AV > 2.1 ± 0.5). This induces a deficit in the IRAS I60 μm/I100 μm flux ratio in comparison with the diffuse interstellar medium and a decrease of the grain equilibrium temperature in excess to that predicted by extinction.

We provide insight into the origin of the far-IR to mm emission from the Galaxy by presenting a decomposition of the emission where we separate the contributions from dust in the atomic gas and dust associated with quiescent molecular gas, as a function of Galacto-centric distance. We find that the sub-mm dust emissivity per hydrogen change by a factor 3 between the diffuse ISM and molecular clouds, first observed on localized clouds in the Solar Neighborhood, applies on large scale to the Molecular Ring. The decomposition leaves an emission excess in the sub-mm with a very cold effective temperature, concentrated in the plane but with a brightness independent of Galactic longitude. This emission might be associated with interstellar matter in the outer Galaxy not traced by H I nor CO emission.

The FIRBACK survey is a deep imaging survey carried out with ISOPHOT on board ISO, at 170 μm. The survey covers ≈4 sq deg in three high galactic latitude fields (FIRBACK South Marano, FIRBACK North 1 and FIRBACK/ELAIS North 2). In these fields, fluctuations due to unresolved extra-galactic sources were isolated for the first time [1]. We are using a P(D) (probability distribution of fluctuations) analysis to gain information about the N(≥S) curve of the unresolved sources which make up the background. Many planned surveys (e.g. SIRTF, FIRST, PLANCK...) will pose the same analysis challenges and we hope that the outcome of this study will be useful in that context. As a preparation to the analysis of the FIRBACK maps we analyze simulated sky maps. We create histograms of number of pixels per flux bin. The histograms are binned such that there are enough pixels per bin to allow us to apply Gaussian estimates for the errors. We then calculate the expected number of pixels within the relevant flux ranges and evaluate the χ2 statistic. We will use a maximum likelihood algorithm to find the parameters of N(≥S).

We present an extinction map of the Polaris molecular cirrus cloud derived from star counts and compare it with the Schlegel et al. [13] extinction map derived from the far-infrared dust opacity. We find that, within the Polaris cloud, the Schlegel et al. [13] AV values are, on average, a factor 2 higher than the star count values. We propose that this discrepancy results from a difference in τFIR/AV between the diffuse atomic medium and the Polaris cloud. We use the difference in spectral energy distribution, warm for the diffuse atomic medium, cold for the Polaris cloud, to separate their respective contribution to the line of sight integrated infrared emission and find that the τFIR/AV of cold dust in Polaris is on average 4 times higher than the Schlegel et al. [13] value for dust in atomic cirrus. This change in dust property could be interpreted by a growth of fluffy particles within low opacity molecular cirrus clouds such as Polaris. Our work suggests that variations in dust emissivity must be taken into account to estimate AV from dust emission wherever cold infrared emission is present (i.e. molecular clouds).

This paper presents the scientific objectives and technical aspects of the balloon-borne Experiment for Large Infrared Survey Astronomy (ELISA). The emphasis is put upon the synergies existing between the ELISA project and future space missions, both with respect to scientific and technical aspects. ELISA is a small balloon project for an experiment dedicated to measure the Far-Infrared to Sub-millimeter continuum emission of Galactic dust over a large fraction of the sky, with unprecedented sensitivity and angular resolution. The primary mirror of the telescope, similar to the one used for the Top-Hat mission, will have a diameter of 1 m, ensuring an angular resolution of about 3.5'. Bolometer arrays will be used in four photometric bands centered at 170, 240, 400, and 650 μm and providing a 22' × 45' instantaneous field of view per channel. A liquid He cryostat will host the cold optics, including the secondary mirror of the telescope, as well as the detectors, which will be cooled to 0.3 K using an 3He close-cycle fridge. Mapping of the sky will be accomplished by rotating the gondola over a large azimuth range (up to 60° amplitude). The pointing of the experiment will be maintained to a constant elevation during the azimuth scans through a feed back loop using the signal from a large format, fast stellar sensor, operating day and night. The scientific goal of the experiment is to map the diffuse Sub-millimeter emission along a large fraction of the Milky Way. The astronomical data obtained will be used to derive the emission properties of the dust grains in the Interstellar Medium (ISM), such as their temperature and emissivity. It will also allow to systematically measure the polarization of the dust emission. It should also lead to the detection of a few thousand point sources such as newly formed stars and distant galaxies. In addition to these goals, the ELISA project will serve as a test bed for the detector technology that will be used for the HERSCHEL space mission to be launched in 2007. The ELISA data will be made available to help calibrate the observations of HERSCHEL and PLANCK and to plan the large-scale surveys to be undertaken with HERSCHEL. Owing to these objectives, 3 flights of the ELISA experiment, are foreseen in the period from 2004 to 2006. The ELISA project is carried out by an international collaboration including France (CESR, IAS, CEA, CNES), The Netherlands (SSD/ESTEC), Denmark (DSRI), UK (Cardiff Univ.).

This paper reviews what we know on the Extragalactic Background (EB) and on the nature of its contributing galaxies in the infrared (IR) and sub-millimeter (sub-mm). I first present the EB observationnal constraints, their main cosmological implications, and results from deep IR and sub-mm surveys. Then, using a phenomelogical model of IR galaxy evolution, I show how these data constrain the evolution of IR galaxies, in particular the luminosity density and the luminosity function. And finally, I briefly review the detection of the IR EB fluctuations and their potential implications.

The cosmic far-infrared background is now well measured from 140 μm to 1 mm. Uncertainties remain at 100 μm (and even more at 60 μm). These are dominated by limitations of the zodiacal model. The nature of sources dominating the background near its maximum are beginning to be studied through deep surveys carried out with ISOPHOT. These surveys show very steep number counts and fluctuations of the background due to unresolved sources.