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The interstellar medium contains filamentary structure over a wide range of scales. Understanding the role of this structure, both as a conduit of gas across the scales and a diagnostic tool of local physics, is a major focus of star formation studies. We review recent progress in studying filamentary structure in the ISM, interpreting its properties in terms of physical processes, and exploring formation and evolution scenarios. We include structures from galactic-scale filaments to tenth-of-a-parsec scale filaments, comprising both molecular and atomic structures, from both observational and theoretical perspectives. In addition to the literature overview, we assemble a large amount of catalogue data from different surveys and provide the most comprehensive census of filamentary structures to date. Our census consists of 22 803 filamentary structures, facilitating a holistic perspective and new insights. We use our census to conduct a meta-analysis, leading to a description of filament properties over four orders of magnitudes in length and eight in mass. Our analysis emphasises the hierarchical and dynamical nature of filamentary structures. Filaments do not live in isolation, nor they generally resemble static structures close to equilibrium. We propose that accretion during filament formation and evolution sets some of the key scaling properties of filaments. This highlights the role of accretion during filament formation and evolution and also in setting the initial conditions for star formation. Overall, the study of filamentary structures during the past decade has been observationally driven. While great progress has been made on measuring the basic properties of filaments, our understanding of their formation and evolution is clearly lacking. In this context, we identify a number of directions and questions we consider most pressing for the field., 36 pages, 10 figures. To appear in Protostars and Planets VII, Editors: Shu-ichiro Inutsuka, Yuri Aikawa, Takayuki Muto, Kengo Tomida, and Motohide Tamura

Fits files used for the machine learning algorithm used in the article. These data are mostly derived from observations with the IRAM-30m telescope in the context of the ORION-B project, cf., https://www.iram.fr/~pety/ORION-B/ The original version of this archive is available at https://www.iram.fr/~pety/ORION-B/data/orionb-2020-gratier.tar.xz All the maps are gridded in a custom set of coordinates, with the origin set on the PDR of the Horsehead Nebula (RA-Dec coordinates provided in the header), and with an axis position angle rotated by 14 degrees with respect to the North-South orientation. The FITS file headers are WCS compliant, and our custom set of coordinates should be understood by any standard FITS reader. fits subdirectory contains the integrated line intensities maps (files ending in -area-cropped.fits) and the peak temperatures (files ending in -tpeak-cropped.fits) of the Orion B molecular cloud in 18 molecular tracers, used as features for the machine learning algorithms used in the paper. Maps of two physical parameters NH2 and Tdust derived from Hershel data and used as predictor are also included, you should refer to Lombardi et al. (2014A&A...566A..45L) for the details of the Herschel data reduction. The molecular line is encoded in the string at the begining of the filenames, see Table 1 for the corresponding frequencies. (3 data files).

16th Specialist Meeting on on Microwave Radiometry and Remote Sensing of the Environment, 16-20 November 2020

Using a method based on Faraday rotation measurements, Tahani et al. 2018 find the line-of-sight component of magnetic fields in Orion-A and show that their direction changes from the eastern side of this filamentary structure to its western side. Three possible magnetic field morphologies that can explain this reversal across the Orion-A region are toroidal, helical, and bow-shaped morphologies. In this paper we construct simple models to represent these three morphologies and compare them with the available observational data to find the most probable morphology(ies). To compare the observations with the models, we use probability values and a Monte-Carlo analysis to determine the most likely magnetic field morphology among these three morphologies. We find that the bow morphology has the highest probability values and that our Monte-Carlo analysis suggests that the bow morphology is more likely. We suggest that the bow morphology is the most likely and the most natural of the three morphologies that could explain a magnetic field reversal across the Orion-A filamentary structure (i.e., bow, helical and toroidal morphologies)., 11 pages, 15 Figures

We present (1) new fully sampled maps of CO and {}13{CO} J = 2-1 emission and CO J = 3-2 emission toward the molecular clouds Cep B and C, associated with the Cep OB3 association; (2) a map of extinction, A V , derived from IR colors of background stars; and (3) the distribution of young stellar objects (YSOs) over the same field as the molecular maps. An LTE analysis of the CO and {}13{CO} maps yields the distribution of molecular column densities and temperatures. Substantial variations are evident across the clouds; smaller subregions show correlations between molecular properties and dust extinction, consistent with a picture of outer photodissociation regions with a layer of CO-dark molecular gas, a CO self-shielded interior, and an inner cold dense region where CO is largely depleted onto grains. Comparing the distribution of YSOs with molecular gas surface density shows a power-law relation very similar in slope to that for the giant molecular cloud associated with the H II region Sh2-235 from a previous paper in this series that employed the same methodology. We note the presence of several compact, isolated CO emission sources in the J = 3-2 maps. The gas temperature and {}13{CO} velocity dispersion yield a map of the sonic Mach number, which varies across the cloud but always exceeds unity, confirming the pervasiveness of supersonic turbulence over length scales ≳0.1 pc (the map resolution). We also compute a J = 2-1 CO X-factor that varies with position but is, on average, within 20% of the Galactic average derived from CO J = 1-0 observations.

Context: The past decade has witnessed a large number of Galactic plane surveys at angular resolutions below 20". However, no comparable high-resolution survey exists at long radio wavelengths around 21cm in line and continuum emission. Methods: Employing the Very Large Array (VLA) in the C-array configuration and a large program, we observe the HI 21cm line, four OH lines, nineteen Halpha radio recombination lines as well as the continuum emission from 1 to 2GHz in full polarization over a large part of the first Galactic quadrant. Results: Covering Galactic longitudes from 14.5 to 67.4deg and latitudes between +-1.25deg, we image all of these lines and the continuum at ~20" resolution. These data allow us to study the various components of the interstellar medium (ISM): from the atomic phase, traced by the HI line, to the molecular phase, observed by the OH transitions, to the ionized medium, revealed by the cm continuum and the Halpha radio recombination lines. Furthermore, the polarized continuum emission enables magnetic field studies. In this overview paper, we discuss the survey outline and present the first data release as well as early results from the different datasets. We now release the first half of the survey; the second half will follow later after the ongoing data processing has been completed. The data in fits format (continuum images and line data cubes) can be accessed through the project web-page http://www.mpia.de/thor. Conclusions: The HI/OH/Recombination line survey of the Milky Way (THOR) opens a new window to the different parts of the ISM. It enables detailed studies of molecular cloud formation, conversion of atomic to molecular gas, and feedback from HII regions as well as the magnetic field in the Milky Way. It is highly complementary to other surveys of our Galaxy, and comparing different datasets allows us to address many open questions., Comment: Accepted for Astronomy & Astrophysics, 23 pages, 17 figures, a high-resolution version can be found at http://www.mpia.de/thor

Throughout the Milky Way, molecular clouds typically appear filamentary, and mounting evidence indicates that this morphology plays an important role in star formation. What is not known is to what extent the dense filaments most closely associated with star formation are connected to the surrounding diffuse clouds up to arbitrarily large scales. How are these cradles of star formation linked to the Milky Way's spiral structure? Using archival Galactic plane survey data, we have used multiple datasets in search of large-scale, velocity-coherent filaments in the Galactic plane. In this paper, we present our methods employed to identify coherent filamentary structures first in extinction and confirmed using Galactic Ring Survey data. We present a sample of seven Giant Molecular Filaments (GMFs) that have lengths of order $\sim$100 pc, total masses of 10$^4$ - 10$^5$ M$_{\odot}$, and exhibit velocity coherence over their full length. The GMFs we study appear to be inter-arm clouds and may be the Milky Way analogues to spurs observed in nearby spiral galaxies. We find that between 2 and 12% of the total mass (above $\sim$10$^{20}$ cm$^{-2}$) is "dense" (above 10$^{22}$ cm$^{-2}$), where filaments near spiral arms in the Galactic midplane tend to have higher dense gas mass fractions than those further from the arms., Comment: 22 pages, 16 figures. Accepted to A&A

The European Space Agency's Soil Moisture and Ocean Salinity (SMOS) satellite was launched in November 2009 and delivers now brightness temperature and soil moisture products over terrestrial areas on a regular three-day basis. In 2010, several airborne campaigns were conducted to validate the SMOS products with microwave emission radiometers at L-band (1.4 GHz). In this paper, we present results from measurements performed in the Rur and Erft catchments in May and June 2010. The measurement sites were situated in the very west of Germany close to the borders to Belgium and The Netherlands. We developed an approach to validate spatial and temporal SMOS brightness temperature products. An area-wide brightness temperature reference was generated by using an area-wide modeling of top soil moisture and soil temperature with the WaSiM-ETH model and radiative transfer calculation based on the L-band Microwave Emission of the Biosphere model. Measurements of the airborne L-band sensors EMIRAD and HUT-2D on-board a Skyvan aircraft as well as ground-based mobile measurements performed with the truck mounted JÜLBARA L-band radiometer were analyzed for calibration of the simulated brightness temperature reference. Radiative transfer parameters were estimated by a data assimilation approach. By this versatile reference data set, it is possible to validate the spaceborne brightness temperature and soil moisture data obtained from SMOS. However, comparisons with SMOS observations for the campaign period indicate severe differences between simulated and observed SMOS data. Copyright © 1980-2012 IEEE.

After the six-month long In-Orbit Commissioning Phase (IOCP) the SMOS satellite started to work in its fully operational mode. During the IOCP, the payload MIRAS was completely characterized, both in short- and long-term, and the optimum calibration rate for in-flight operation was established. The results show that the amplitude of the visibility is very stable, thus allowing a very low calibration rate, and that the phase has a systematic and periodic variation, easily tracked with short but frequent internal calibration sequences. Absolute calibration for antenna temperature is carried out by external maneuvers to account for drift in the reference Noise Injection Radiometer. Brightness temperature images of good quality are obtained by inverting the calibrated visibility. The images show features compatible with ocean salinity over ocean and soil moisture over land.

We investigate the relationship between the C18O column density and the visual extinction in Chamaeleon I and in a part of the Chamaeleon III molecular cloud. The C18O column densities, N(C18O), are calculated from J=1-0 rotational line data observed with the SEST telescope. The visual extinctions, Av, are derived using JHK photometry from the 2MASS survey and the NICER color excess technique. In contrast with the previous results of Hayakawa et al. (2001), we find that the average N(C18O) / Av ratios are similar in Cha I and Cha III, and lie close to values derived for other clouds, i.e. N(C18O) ~ 2 x 10^14 cm^-2 (Av - 2). We find, however, clear deviations from this average relationship towards individual clumps. Larger than average N(C18O) / Av ratios can be found in clumps associated with the active star forming region in the northern part of Ch a I. On the other hand, some regions in the relatively quiescent southern part of Cha I show smaller than average N(C18O) / Av ratios and also very shallow proportionality between N(C18O) and Av. The shallow proportionality suggests that C18O is heavily depleted in these regions. As the degree of depletion is proportional to the gas density, these regions probably contain very dense, cold cores, which do not stand out in CO mappings. A comparison with the dust temperature map derived from the ISO data shows that the most prominent of the potentially depleted cores indeed coincides with a dust temperature minimum. It seems therefore feasible to use N(C18O) and Av data together for identifying old, dense cores in large scale mappings., 15 pages, 8 figures. Accepted for publication in A&A. Replaced with a version with corrected illustrations

The global navigation satellite system (GNSS) Transpolar Earth Reflectometry exploriNg system (G-TERN) was proposed in response to ESA's Earth Explorer 9 revised call by a team of 33 multi-disciplinary scientists. The primary objective of the mission is to quantify at high spatio-temporal resolution crucial characteristics, processes and interactions between sea ice, and other Earth system components in order to advance the understanding and prediction of climate change and its impacts on the environment and society. The objective is articulated through three key questions. 1) In a rapidly changing Arctic regime and under the resilient Antarctic sea ice trend, how will highly dynamic forcings and couplings between the various components of the ocean, atmosphere, and cryosphere modify or influence the processes governing the characteristics of the sea ice cover (ice production, growth, deformation, and melt)? 2) What are the impacts of extreme events and feedback mechanisms on sea ice evolution? 3) What are the effects of the cryosphere behaviors, either rapidly changing or resiliently stable, on the global oceanic and atmospheric circulation and mid-latitude extreme events? To contribute answering these questions, G-TERN will measure key parameters of the sea ice, the oceans, and the atmosphere with frequent and dense coverage over polar areas, becoming a "dynamic mapper'' of the ice conditions, the ice production, and the loss in multiple time and space scales, and surrounding environment. Over polar areas, the G-TERN will measure sea ice surface elevation (