scholarly journals Modelling and simulation of large-scale polarized dust emission over the southern Galactic cap using the GASS Hi data

2017 ◽  
Vol 601 ◽  
pp. A71 ◽  
Author(s):  
T. Ghosh ◽  
F. Boulanger ◽  
P. G. Martin ◽  
A. Bracco ◽  
F. Vansyngel ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Column Density ◽  
Large Scale ◽  
Dust Emission ◽  
Neutral Medium ◽  
Limiting Factor ◽  
Galactic Latitude ◽  
Galactic Magnetic Field ◽  
Emission Data ◽  
Field Orientation

The Planck survey has quantified polarized Galactic foregrounds and established that they are a main limiting factor in the quest for the cosmic microwave background B-mode signal induced by primordial gravitational waves during cosmic inflation. Accurate separation of the Galactic foregrounds therefore binds this quest to our understanding of the magnetized interstellar medium. The two most relevant empirical results from analysis of Planck data are line of sight depolarization arising from fluctuations of the Galactic magnetic field orientation and alignment of filamentary dust structures with the magnetic field at high Galactic latitude. Furthermore, Planck and H I emission data in combination indicate that most of the filamentary dust structures are in the cold neutral medium. The goal of this paper is to test whether these salient observational results, taken together, can account fully for the statistical properties of the dust polarization over a selected low column density region comprising 34% of the southern Galactic cap (b ≤ −30°). To do this, we construct a dust model that incorporates H I column density maps as tracers of the dust intensity structures and a phenomenological description of the Galactic magnetic field. By adjusting the parameters of the dust model, we were able to reproduce the Planck dust observations at 353GHz in the selected region. Realistic simulations of the polarized dust emission enabled by such a dust model are useful for testing the accuracy of component separation methods, studying non-Gaussianity, and constraining the amount of decorrelation with frequency.

scholarly journals Dust spectrum and polarisation at 850 μm in the massive IRDC G035.39-00.33

2018 ◽  
Vol 620 ◽  
pp. A26 ◽  
Author(s):  
Mika Juvela ◽  
Vincent Guillet ◽  
Tie Liu ◽  
Isabelle Ristorcelli ◽  
Veli-Matti Pelkonen ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Column Density ◽  
Dust Emission ◽  
Spatial Filtering ◽  
Black Body ◽  
Field Orientation ◽  
Grain Alignment ◽  
Star Forming ◽  
Average Value ◽  
The Difference

Context. The sub-millimetre polarisation of dust emission from star-forming clouds carries information on grain properties and on the effects that magnetic fields have on cloud evolution. Aims. Using observations of a dense filamentary cloud G035.39-00.33, we aim to characterise the dust emission properties and the variations of the polarisation fraction. Methods. JCMT SCUBA-2/POL-2 observations at 850 μm were combined with Planck 850 μm(353 GHz) data to map polarisation fraction at small and large scales. With previous total intensity SCUBA-2 observations (450 and 850 μm) and Herschel data, the column densities were determined via modified black-body fits and via radiative transfer modelling. Models were constructed to examine how the observed polarisation angles and fractions depend on potential magnetic field geometries and grain alignment processes. Results. POL-2 data show clear changes in the magnetic field orientation. These are not in contradiction with the uniform orientation and almost constant polarisation fraction seen by Planck, because of the difference in the beam sizes and the POL-2 data being affected by spatial filtering. The filament has a peak column density of N(H2) ~ 7 × 1022 cm−2, a minimum dust temperature of T ~ 12 K, and a mass of ~4300 M⊙ for the area N(H2) > 5 × 1021 cm−2. The estimated average value of the dust opacity spectral index is β ~ 1.9. The ratio of sub-millimetre and J-band optical depths is τ (250 μm)∕τ (J) ~ 2.5 × 10−3, more than four times the typical values for diffuse medium. The polarisation fraction decreases as a function of column density to p ~ 1% in the central filament. Because of noise, the observed decrease of p(N) is significant only at N(H2) > 2 × 1022 cm−2. The observations suggest that the grain alignment is not constant. Although the data can be explained with a complete loss of alignment at densities above ~104 cm−3 or using the predictions of radiative torques alignment, the uncertainty of the field geometry and the spatial filtering of the SCUBA-2 data prevent strong conclusions. Conclusions. The G035.39-00.33 filament shows strong signs of dust evolution and the low polarisation fraction is suggestive of a loss of polarised emission from its densest parts.

scholarly journals The supernova-regulated ISM

2018 ◽  
Vol 614 ◽  
pp. A101 ◽  
Author(s):  
M. S. Väisälä ◽  
F. A. Gent ◽  
M. Juvela ◽  
M. J. Käpylä
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Dust Emission ◽  
Mean Field ◽  
Small Scale ◽  
Polarization Angle ◽  
Magnetic Fluctuations ◽  
Field Orientation ◽  
Mhd Simulations ◽  
Large Scale Magnetic Field

Context.Efforts to compare polarization measurements with synthetic observations from magnetohydrodynamics (MHD) models have previously concentrated on the scale of molecular clouds.Aims.We extend the model comparisons to kiloparsec scales, taking into account hot shocked gas generated by supernovae and a non-uniform dynamo-generated magnetic field at both large and small scales down to 4 pc spatial resolution.Methods.We used radiative transfer calculations to model dust emission and polarization on top of MHD simulations. We computed synthetic maps of column densityNH, polarization fractionp, and polarization angle dispersionS, and studied their dependencies on important properties of MHD simulations. These include the large-scale magnetic field and its orientation, the small-scale magnetic field, and supernova-driven shocks.Results.Similar filament-like structures ofSas seen in thePlanckall-sky maps are visible in our synthetic results, although the smallest scale structures are absent from our maps. Supernova-driven shock fronts andSdo not show significant correlation. Instead,Scan clearly be attributed to the distribution of the small-scale magnetic field. We also find that the large-scale magnetic field influences the polarization properties, such that, for a given strength of magnetic fluctuation, a strong plane of the sky mean field weakens the observedS, while strengtheningp. The anticorrelation ofpandS, and decreasingpas a function ofNHare consistent across all synthetic observations. The magnetic fluctuations follow an exponential distribution, rather than Gaussian characteristic of flows with intermittent repetitive shocks.Conclusions.The observed polarization properties and column densities are sensitive to the line-of-sight distance over which the emission is integrated. Studying synthetic maps as the function of maximum integration length will further help with the interpretation of observations. The effects of the large-scale magnetic field orientation on the polarization properties are difficult to be quantified from observations solely, but MHD models might turn out to be useful for separating the effect of the large-scale mean field.

scholarly journals Is there a left-handed magnetic field in the solar neighborhood?

2019 ◽  
Vol 621 ◽  
pp. A97 ◽  
Author(s):  
A. Bracco ◽  
S. Candelaresi ◽  
F. Del Sordo ◽  
A. Brandenburg
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Power Spectra ◽  
Field Structure ◽  
Solar Neighborhood ◽  
Galactic Magnetic Field ◽  
Polarization Data ◽  
Left Handed ◽  
Cross Correlations

Context. The analysis of the full-sky Planck polarization data at 850 μm revealed unexpected properties of the E- and B-mode power spectra of dust emission in the interstellar medium (ISM). The positive cross-correlations over a wide range of angular scales between the total dust intensity, T, and both E and (most of all) B modes has raised new questions about the physical mechanisms that affect dust polarization, such as the Galactic magnetic field structure. This is key both to better understanding ISM dynamics and to accurately describing Galactic foregrounds to the polarization of the cosmic microwave background (CMB). In particular, in the quest to find primordial B modes of the CMB, the observed positive cross-correlation between T and B for interstellar dust requires further investigation towards parity-violating processes in the ISM. Aims. In this theoretical paper we investigate the possibility that the observed cross-correlations in the dust polarization power spectra, and specifically the one between T and B, can be related to a parity-odd quantity in the ISM such as the magnetic helicity. Methods. We produce synthetic dust polarization data, derived from 3D analytical toy models of density structures and helical magnetic fields, to compare with the E and B modes of observations. We present several models. The first is an ideal fully helical isotropic case, such as the Arnold-Beltrami-Childress field. Second, following the nowadays favored interpretation of the T–E signal in terms of the observed alignment between the magnetic field morphology and the filamentary density structure of the diffuse ISM, we design models for helical magnetic fields wrapped around cylindrical interstellar filaments. Lastly, focusing on the observed T–B correlation, we propose a new line of interpretation of the Planck observations advocating the presence of a large-scale helical component of the Galactic magnetic field in the solar neighborhood. Results. Our analysis shows that: I) the sign of magnetic helicity does not affect E and B modes for isotropic magnetic-field configurations; II) helical magnetic fields threading interstellar filaments cannot reproduce the Planck results; and III) a weak helical left-handed magnetic field structure in the solar neighborhood may explain the T–B correlation seen in the Planck data. Such a magnetic-field configuration would also account for the observed large-scale T–E correlation. Conclusions. This work suggests a new perspective for the interpretation of the dust polarization power spectra that supports the imprint of a large-scale structure of the Galactic magnetic field in the solar neighborhood.

scholarly journals MAGMO: polarimetry of 1720-MHz OH masers towards southern star-forming regions

2020 ◽  
Vol 493 (1) ◽  
pp. 199-233 ◽  
Author(s):  
C S Ogbodo ◽  
J A Green ◽  
J R Dawson ◽  
S L Breen ◽  
S A Mao ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Ground State ◽  
Supernova Remnants ◽  
Galactic Centre ◽  
Galactic Magnetic Field ◽  
Field Orientation ◽  
Star Forming ◽  
Star Forming Regions ◽  
Methanol Masers

ABSTRACT From targeted observations of ground-state hydroxyl (OH) masers towards 702 Methanol Multibeam survey 6.7-GHz methanol masers, in the Galactic longitude range from 186° through the Galactic Centre to 20°, made as part of the ‘MAGMO’ (Mapping the Galactic Magnetic field through OH masers) project, we present the physical and polarization properties of the 1720-MHz OH maser transition, including the identification of Zeeman pairs. We present 10 new and 23 previously catalogued 1720-MHz OH maser sources detected towards star-forming regions (SFRs). In addition, we also detected 16 1720-MHz OH masers associated with supernova remnants and two sites of diffuse OH emission. Towards the 33 star formation masers, we identify 44 Zeeman pairs, implying magnetic field strengths ranging from −11.4 to +13.2 mG, and a median magnetic field strength of |BLOS| ∼ 6 mG. With limited statistics, we present the in situ magnetic field orientation of the masers and the Galactic magnetic field distribution revealed by the 1720-MHz transition. We also examine the association statistics of 1720-MHz OH SFR masers with other ground-state OH masers, excited-state OH masers, class I and class II methanol masers, and water masers, and compare maser positions with mid-infrared images of the parent SFRs. Of the 33 1720-MHz star formation masers, 10 are offset from their central exciting sources, and appear to be associated with outflow activity.

scholarly journals An Imprint of the Galactic Magnetic Field in the Diffuse Unpolarized Dust Emission

2019 ◽  
Vol 887 (2) ◽  
pp. 159 ◽  
Author(s):  
Brandon S. Hensley ◽  
Cheng Zhang ◽  
James J. Bock
Keyword(s):  
Magnetic Field ◽  
Dust Emission ◽  
Galactic Magnetic Field

Recent and Future Measurements of Pulsar Rotation Measures and the Structure of the Large-Scale Galactic Magnetic Field

2011 ◽  
Author(s):  
Aristeidis Noutsos ◽  
Marta Burgay ◽  
Nicolò D’Amico ◽  
Paolo Esposito ◽  
Alberto Pellizzoni ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Galactic Magnetic Field

scholarly journals A study of the regular structure of the galactic magnetic field using WMAP5 polarization data at 22 GHz

2008 ◽  
Vol 4 (S259) ◽  
pp. 573-576 ◽  
Author(s):  
Beatriz Ruiz-Granados ◽  
J. A. Rubiño-Martín ◽  
E. Battaner
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Regular Structure ◽  
Distribution Functions ◽  
Likelihood Method ◽  
Galactic Magnetic Field ◽  
Polarization Data ◽  
3 Dimensional ◽  
Large Scale Magnetic Field ◽  
Parameter Values

AbstractWe study the spatial structure of the 3-dimensional large-scale pattern of the Galactic Magnetic Field using the polarization maps obtained by the WMAP satellite at 22 GHz. By using five different models of the large-scale magnetic field of the Milky Way and a model for the cosmic rays distribution, we predict the expected polarized synchrotron emission. Those maps are compared to the observed 22 GHz polarization data using a Maximum Likelihood method. For each model, we obtain the parameter values which better reproduce the data and obtain their marginal probability distribution functions. We find that the model that best reproduces the observed polarization maps is an “axisymmetric” model.

scholarly journals Formation of the Musca filament: evidence for asymmetries in the accretion flow due to a cloud–cloud collision

2020 ◽  
Vol 644 ◽  
pp. A27
Author(s):  
L. Bonne ◽  
S. Bontemps ◽  
N. Schneider ◽  
S. D. Clarke ◽  
D. Arzoumanian ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Radiative Transfer ◽  
Velocity Gradient ◽  
Large Scale ◽  
Transverse Velocity ◽  
Local Magnetic Field ◽  
Filament Formation ◽  
Field Orientation ◽  
Physical Conditions ◽  
The Magnetic Field

Context. Dense molecular filaments are ubiquituous in the interstellar medium, yet their internal physical conditions and the role of gravity, turbulence, the magnetic field, radiation, and the ambient cloud during their evolution remain debated. Aims. We study the kinematics and physical conditions in the Musca filament, the ambient cloud, and the Chamaeleon-Musca complex to constrain the physics of filament formation. Methods. We produced CO(2–1) isotopologue maps with the APEX telescope that cut through the Musca filament. We further study a NANTEN2 12CO(1–0) map of the full Musca cloud, H I emission of the Chamaeleon-Musca complex, a Planck polarisation map, line radiative transfer models, Gaia data, and synthetic observations from filament formation simulations. Results. The Musca cloud, with a size of ~3–6 pc, contains multiple velocity components. Radiative transfer modelling of the CO emission indicates that the Musca filament consists of a cold (~10 K), dense (nH2 ∼ 104 cm−3) crest, which is best described with a cylindrical geometry. Connected to the crest, a separate gas component at T ~ 15 K and nH2 ∼ 103 cm−3 is found, the so-called strands. The velocity-coherent filament crest has an organised transverse velocity gradient that is linked to the kinematics of the nearby ambient cloud. This velocity gradient has an angle ≥30° with respect to the local magnetic field orientation derived from Planck, and the magnitude of the velocity gradient is similar to the transonic linewidth of the filament crest. Studying the large scale kinematics, we find coherence of the asymmetric kinematics from the 50 pc H I cloud down to the Musca filament. We also report a strong [C18O]/[13CO] abundance drop by an order of magnitude from the filament crest to the strands over a distance <0.2 pc in a weak ambient far-ultraviolet (FUV) field. Conclusions. The dense Musca filament crest is a long-lived (several crossing times), dynamic structure that can form stars in the near future because of continuous mass accretion replenishing the filament. This mass accretion on the filament appears to be triggered by a H I cloud–cloud collision, which bends the magnetic field around dense filaments. This bending of the magnetic field is then responsible for the observed asymmetric accretion scenario of the Musca filament, which is, for instance, seen as a V-shape in the position–velocity (PV) diagram.

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