Anomalous Microwave Emission: Theory, Modeling, and Observations

Anomalous Microwave Emission (AME) was first identified in the late 1990s, through sensitive high frequency radio CMB observations. The usual emission mechanisms (e.g., blackbody, synchrotron, and free-free) did not appear to be able to account for the excess emission in the frequency range 10– 60GHz. Since then, a large body of observational evidence has emerged showing that AME appears to be emitted both in the diffuse interstellar medium at large, and from specific clouds within our galaxy. Detections from star-forming regions in an external galaxy have also been made. Nevertheless, detailed measurements have been difficult due to the frequency range (difficult to observe from the ground) and confusion with other emission mechanisms that emit in this frequent range. The most promising candidate for the AME is electric dipole radiation from small spinning dust grains (spinning dust emission). This was first predicted in the late 50s, with major developments in the theory over the last 15 years. The theory predicts a peaked spectrum which emits at frequencies from about 10GHz to over 100GHz, but with a wide range of peak frequencies and emissivities, which depend on the local environment and dust grain size distribution. There is still significant debate about the true nature of the AME, and both observations and theory are still relatively unexplored. An exciting possibility is to use detailed radio observations of spinning dust to study the interstellar medium, in a complementary way to the optical, UV, and infrared domains. This special issue is dedicated to the study of AME

The thin layer of Warm Ionized Gas: towards a 3-D reconstruction of the spatial distribution of HII regions

HII regions are known to contribute to the so-called thin layer of the diffuse Warm Ionized Gas. In order to constrain this contribution, we reconstruct the 3-D distribution of the sources. A detailed spatial analysis of the largest up-to-date sample of HII regions is presented.Comment: 4 pages, 3 figures, Proceedings of the September 2002 JENAM meeting: "From Observations to Self-Consistent Modeling of the Interstellar Medium", Porto, Portuga

The Life Cycle of Dust

Dust offers a unique probe of the interstellar medium (ISM) across multiple size, density, and temperature scales. Dust is detected in outflows of evolved stars, star-forming molecular clouds, planet-forming disks, and even in galaxies at the dawn of the Universe. These grains also have a profound effect on various astrophysical phenomena from thermal balance and extinction in galaxies to the building blocks for planets, and changes in dust grain properties will affect all of these phenomena. A full understanding of dust in all of its forms and stages requires a multi-disciplinary investigation of the dust life cycle. Such an investigation can be achieved with a statistical study of dust properties across stellar evolution, star and planet formation, and redshift. Current and future instrumentation will enable this investigation through fast and sensitive observations in dust continuum, polarization, and spectroscopy from near-infrared to millimeter wavelengths

An all-sky Support Vector Machine selection of WISE YSO Candidates

We explored the AllWISE catalogue of the Wide-field Infrared Survey Explorer mission and identified Young Stellar Object candidates. Reliable 2MASS and WISE photometric data combined with Planck dust opacity values were used to build our dataset and to find the best classification scheme. A sophisticated statistical method, the Support Vector Machine (SVM) is used to analyse the multi-dimensional data space and to remove source types identified as contaminants (extragalactic sources, main sequence stars, evolved stars and sources related to the interstellar medium). Objects listed in the SIMBAD database are used to identify the already known sources and to train our method. A new all-sky selection of 133,980 Class I/II YSO candidates is presented. The estimated contamination was found to be well below 1% based on comparison with our SIMBAD training set. We also compare our results to that of existing methods and catalogues. The SVM selection process successfully identified >90% of the Class I/II YSOs based on comparison with photometric and spectroscopic YSO catalogues. Our conclusion is that by using the SVM, our classification is able to identify more known YSOs of the training sample than other methods based on colour-colour and magnitude-colour selection. The distribution of the YSO candidates well correlates with that of the Planck Galactic Cold Clumps in the Taurus--Auriga--Perseus--California region.Comment: 27 pages, 15 figures, 15 table

CORESHINE : a tracer of grain growth in dark clouds

Scattering by dust grains in the interstellar medium is a well-known phenomenon in the optical and near-infrared domains. We serendipitously discovered the effect of scattering in the mid-infrared in the dark cloud L183, and nicknamed the effect "coreshine". We investigated over 200 sources from both the Spitzer Archive and a new warm Spitzer mission program to check the frequency of the phenomenon and found over 50% of the cases to be positive, which is possibly only a lower limit. We see differences depending on the Galactic regions we investigate. Taurus is a highly successful target while the Galactic plane is too bright to let coreshine appear in emission. We present coreshine as a large grain tracer and we discuss its absence in the Gum/Vela region, which would indicate that big grains have been recently destroyed by the supernova blast wave. Finally, we discuss the prospect for future coreshine searches from archives, present and future instruments

Centimeter-wave continuum radiation from the rho Ophiuchi molecular cloud

The rho Oph molecular cloud is undergoing intermediate-mass star formation. UV radiation from its hottest young stars heats and dissociates exposed layers, but does not ionize hydrogen. Only faint radiation from the Rayleigh-Jeans tail of ~10-100K dust is expected at wavelengths longwards of 3mm. Yet Cosmic Background Imager (CBI) observations reveal that the rho Oph W photo-dissociation region (PDR) is surprisingly bright at centimetre wavelengths. We searched for interpretations consistent with the WMAP radio spectrum, new ISO-LWS parallel mode images and archival Spitzer data. Dust-related emission mechanisms at 1 cm, as proposed by Draine & Lazarian, are a possibility. But a magnetic enhancement of the grain opacity at 1cm is inconsistent with the morphology of the dust column maps Nd and the lack of detected polarization. Spinning dust, or electric-dipole radiation from spinning very small grains (VSGs), comfortably explains the radio spectrum, although not the conspicuous absence from the CBI data of the infrared circumstellar nebulae around the B-type stars S1 and SR~3. Allowing for VSG depletion can marginally reconcile spinning dust with the data. As an alternative interpretation we consider the continuum from residual charges in rho Oph W, where most of carbon should be photoionised by the close binary HD147889 (B2IV, B3IV). Electron densities of ~100 cm^{-3}, or H-nucleus densities n_H > 1E6 cm^{-3}, are required to interpret rho Oph W as the CII Stromgren sphere of HD147889. However the observed steep and positive low-frequency spectral index would then require optically thick emission from an hitherto unobserved ensemble of dense clumps or sheets with a filling factor ~1E-4 and n_H ~ 1E7 cm^{-3}.Comment: accepted for publication in MNRA

Tracing micron-sized grains in molecular clouds with coreshine

Recently discovered scattered light at 3-5 µm from low-mass cores (so-called "coreshine") reveals the presence of grains around 1 µm. But only a fraction of the cores investigated so far show the effect. We derive a simple limit for detecting scattered light from a low-mass core can be derived. The extinction by the core prohibits detection in bright parts of the Galactic plane, the phase function favors the off-plane detection near the Galactic center and to some extent near the Galactic anti-center. Our 3D radiative transfer calculations for the core L260 show that also the K band is capable of probing coreshine, and that the shape of the Ks band surface brightness profile limits the largest grains to sizes of to 1-1.5 µm. For the core L1506C showing coreshine and strong depletion, but low density and turbulence our grain growth calculations and radiative transfer modeling show detectable coreshine at 3.6 µm only when we increase the core density and the turbulence above what is currently observed. The grains could be part of primitive omnipresent large grain population becoming visible in the densest part of the ISM, could have been grown under the turbulent dense conditions of former cores, or in L1506C itself. In the later case, L1506C must have passed through a period of larger density and/or stronger turbulence. This would be consistent with the surprisingly strong depletion usually attributed to high column densities, and with the large-scale outward motion of the core envelope observed today