SOFIA Observations of 30 Doradus. I. Far-infrared Dust Polarization and Implications for Grain Alignment and Disruption by Radiative Torques

Abstract Located in the Large Magellanic Cloud and mostly irradiated by the massive star cluster R136, 30 Doradus is an ideal target to test the leading theory of grain alignment and rotational disruption by RAdiative Torques (RATs). Here, we use publicly available polarized thermal dust emission observations of 30 Doradus at 89, 154, and 214 μm using SOFIA/HAWC+. We analyze the variation of the dust polarization degree (p) with the total emission intensity (I), the dust temperature (T d), and the gas column density (N H) constructed from Herschel data. The 30 Doradus complex is divided into two main regions relative to R136, namely North and South. In the North, we find that the polarization degree first decreases and then increases before decreasing again when the dust temperature increases toward the irradiating cluster R136. The first depolarization likely arises from the decrease in grain alignment efficiency toward the dense medium due to the attenuation of the interstellar radiation field and the increase in the gas density. The second trend (the increase of p with T d) is consistent with the RAT alignment theory. The final trend (the decrease of p with T d) is consistent with the RAT alignment theory only when the grain rotational disruption by RATs is taken into account. In the South, we find that the polarization degree is nearly independent of the dust temperature, while the grain alignment efficiency is higher around the peak of the gas column density and decreases toward the radiation source. The latter feature is also consistent with the prediction of rotational disruption by RATs.

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Extended Dust Emission from Nearby Evolved stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318005720 ◽

2018 ◽

Vol 14 (S343) ◽

pp. 181-185

Author(s):

Thavisha E. Dharmawardena ◽

Francisca Kemper ◽

Peter Scicluna ◽

Jan G. A. Wouterloot ◽

Alfonso Trejo ◽

...

Keyword(s):

Bayesian Inference ◽

Column Density ◽

Surface Brightness ◽

Dust Emission ◽

Circumstellar Envelope ◽

Agb Stars ◽

Large Scatter ◽

Evolved Stars ◽

Dust Temperature ◽

Extended Component

AbstractWe derive azimuthally-averaged surface-brightness profiles of 16 AGB stars in the far-IR and sub-mm with the aim of studying the resolved historic mass loss in the extended circumstellar envelope. The PSF-subtracted extended component fluxes were found to be ∼40% of the total source flux. By fitting SEDs at each radial point we derive the dust temperature, column density and spectral index of emissivity via Bayesian inference. The measured dust-to-gas ratios were somewhat consistent with canonical values however with a large scatter.

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Revisiting the dust properties in the molecular clouds of the Large Magellanic Cloud

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935158 ◽

2019 ◽

Vol 627 ◽

pp. A15

Author(s):

D. Paradis ◽

C. Mény ◽

M. Juvela ◽

A. Noriega-Crespo ◽

I. Ristorcelli

Keyword(s):

Molecular Clouds ◽

Angular Resolution ◽

Dust Emission ◽

Large Magellanic Cloud ◽

Magellanic Cloud ◽

Dense Medium ◽

Ionized Gas ◽

Gas Phases ◽

Dust Component ◽

Dust Evolution

Context. Some Galactic molecular clouds show signs of dust evolution as compared to the diffuse interstellar medium, most of the time through indirect evidence such as color ratios, increased dust emissivity, or scattering (coreshine). These signs are not a feature of all Galactic clouds. Moreover, molecular clouds in the Large Magellanic Cloud (LMC) have been analyzed in a previous study based on Spitzer and IRIS data, at 4′ angular resolution, with the use of one single dust model, and did not show any signs of dust evolution. Aims. In this present analysis we investigate the dust properties associated with the different gas phases (including the ionized phase this time) of the LMC molecular clouds at 1′ angular resolution (four times greater than the previous analysis) and with a larger spectral coverage range thanks to Herschel data. We also ensure the robustness of our results in the framework of various dust models. Methods. We performed a decomposition of the dust emission in the infrared (from 3.6 to 500 μm) associated with the atomic, molecular, and ionized gas phases in the molecular clouds of the LMC. The resulting spectral energy distributions were fitted with four distinct dust models. We then analyzed the model parameters such as the intensity of the radiation field and the relative dust abundances, as well as the slope of the emission spectra at long wavelengths. Results. This work allows dust models to be compared with infrared data in various environments for the first time, which reveals important differences between the models at short wavelengths in terms of data fitting (mainly in the polycyclic aromatic hydrocarbon bands). In addition, this analysis points out distinct results according to the gas phases, such as dust composition directly affecting the dust temperature and the dust emissivity in the submillimeter and different dust emission in the near-infrared (NIR). Conclusions. We observe direct evidence of dust property evolution from the diffuse to the dense medium in a large sample of molecular clouds in the LMC. In addition, the differences in the dust component abundances between the gas phases could indicate different origins of grain formation. We also point out the presence of a NIR-continuum in all gas phases, with an enhancement in the ionized gas. We favor the hypothesis of an additional dust component as the carrier of this continuum.

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Radiative and mechanical feedback into the molecular gas in the Large Magellanic Cloud

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935215 ◽

2019 ◽

Vol 628 ◽

pp. A113 ◽

Cited By ~ 4

Author(s):

M.-Y. Lee ◽

S. C. Madden ◽

F. Le Petit ◽

A. Gusdorf ◽

P. Lesaffre ◽

...

Keyword(s):

Far Infrared ◽

Large Magellanic Cloud ◽

Magellanic Cloud ◽

Continuum Emission ◽

Molecular Gas ◽

Stellar Content ◽

Low Velocity ◽

Line Energy ◽

Star Forming ◽

30 Doradus

With an aim of probing the physical conditions and excitation mechanisms of warm molecular gas in individual star-forming regions, we performed Herschel SPIRE Fourier Transform Spectrometer (FTS) observations of 30 Doradus in the Large Magellanic Cloud. In our FTS observations, important far-infrared (FIR) cooling lines in the interstellar medium, including CO J = 4–3 to J = 13–12, [C I] 370 μm, and [N II] 205 μm, were clearly detected. In combination with ground-based CO J = 1–0 and J = 3–2 data, we then constructed CO spectral line energy distributions (SLEDs) on ~10 pc scales over a ~60 pc × 60 pc area and found that the shape of the observed CO SLEDs considerably changes across 30 Doradus. For example, the peak transition Jp varies from J = 6–5 to J = 10–9, while the slope characterized by the high-to-intermediate J ratio α ranges from ~0.4 to ~1.8. To examine the source(s) of these variations in CO transitions, we analyzed the CO observations, along with [C II] 158 μm, [C I] 370 μm, [O I] 145 μm, H2 0–0 S(3), and FIR luminosity data, using state-of-the-art models of photodissociation regions and shocks. Our detailed modeling showed that the observed CO emission likely originates from highly compressed (thermal pressure P∕kB ~ 107–109 K cm−3) clumps on ~0.7–2 pc scales, which could be produced by either ultraviolet (UV) photons (UV radiation field GUV ~ 103–105 Mathis fields) or low-velocity C-type shocks (pre-shock medium density npre ~ 104–106 cm−3 and shock velocity vs ~ 5–10 km s−1). Considering the stellar content in 30 Doradus, however, we tentatively excluded the stellar origin of CO excitation and concluded that low-velocity shocks driven by kiloparsec-scale processes (e.g., interaction between the Milky Way and the Magellanic Clouds) are likely the dominant source of heating for CO. The shocked CO-bright medium was then found to be warm (temperature T ~ 100–500 K) and surrounded by a UV-regulated low-pressure component (P∕kB ~ a few (104 –105) K cm−3) that is bright in [C II] 158 μm, [C I] 370 μm, [O I] 145 μm, and FIR dust continuum emission.

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On the Limitations of the Anomalous Microwave Emission Emissivity

Advances in Astronomy ◽

10.1155/2012/124931 ◽

2012 ◽

Vol 2012 ◽

pp. 1-6 ◽

Cited By ~ 9

Author(s):

Christopher T. Tibbs ◽

Roberta Paladini ◽

Clive Dickinson

Keyword(s):

Column Density ◽

Dust Emission ◽

Microwave Emission ◽

A Value ◽

Dust Temperature

Many studies of anomalous microwave emission (AME) have computed an AME emissivity to compare the strength of the AME detected in different regions. Such a value is usually defined as the ratio between the intensity of the AME at 1 cm and the thermal dust emission at 100 μm. However, as studies of Galactic dust emission have shown, the intensity of the thermal dust emission at 100 μm is strongly dependent on the dust temperature, which has severe implications for the AME emissivity defined in this way. In this work, we illustrate and quantify this effect and find that the AME emissivity decreases by a factor of 11.1 between dust temperatures of 20 and 30 K. We, therefore, conclude that computing the AME emissivity relative to the 100 μm emission does not allow for accurate comparisons between the AME observed in different environments. With this in mind, we investigate the use of other tracers of the dust emission with which to compute the AME emissivity and we ultimately conclude that, despite the difficulty in deriving its value, the column density of the dust would be the most suitable quantity with which to compute the AME emissivity.

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Radio and infrared study of southern H II regions G346.056−0.021 and G346.077−0.056

Astronomy and Astrophysics ◽

10.1051/0004-6361/201730561 ◽

2018 ◽

Vol 612 ◽

pp. A36 ◽

Cited By ~ 2

Author(s):

S. R. Das ◽

A. Tej ◽

S. Vig ◽

T. Liu ◽

S. K. Ghosh ◽

...

Keyword(s):

Column Density ◽

Near Infrared ◽

Local Density ◽

Far Infrared ◽

Radio Continuum ◽

Young Stellar Objects ◽

H Ii Regions ◽

Ionized Gas ◽

Mid Infrared ◽

Dust Temperature

Aim. We present a multiwavelength study of two southern Galactic H II regions G346.056−0.021 and G346.077−0.056 which are located at a distance of 10.9 kpc. The distribution of ionized gas, cold and warm dust, and the stellar population associated with the two H II regions are studied in detail using measurements at near-infrared, mid-infrared, far-infrared, submillimeter and radio wavelengths. Methods. The radio continuum maps at 1280 and 610 MHz were obtained using the Giant Metrewave Radio Telescope to probe the ionized gas. The dust temperature, column density, and dust emissivity maps were generated using modified blackbody fits in the far-infrared wavelength range 160–500 μm. Various near- and mid-infrared color and magnitude criteria were adopted to identify candidate ionizing star(s) and the population of young stellar objects in the associated field. Results. The radio maps reveal the presence of diffuse ionized emission displaying distinct cometary morphologies. The 1280 MHz flux densities translate to zero age main sequence spectral types in the range O7.5V–O7V and O8.5V–O8V for the ionizing stars of G346.056−0.021 and G346.077−0.056, respectively. A few promising candidate ionizing star(s) are identified using near-infrared photometric data. The column density map shows the presence of a large, dense dust clump enveloping G346.077−0.056. The dust temperature map shows peaks towards the two H II regions. The submillimeter image shows the presence of two additional clumps, one being associated with G346.056−0.021. The masses of the clumps are estimated to range between ~1400 and 15250 M⊙. Based on simple analytic calculations and the correlation seen between the ionized gas distribution and the local density structure, the observed cometary morphology in the radio maps is better explained invoking the champagne-flow model.

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The C-Band All-Sky Survey (C-BASS): constraining diffuse Galactic radio emission in the North Celestial Pole region

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz522 ◽

2019 ◽

Vol 485 (2) ◽

pp. 2844-2860 ◽

Cited By ~ 2

Author(s):

C Dickinson ◽

A Barr ◽

H C Chiang ◽

C Copley ◽

R D P Grumitt ◽

...

Keyword(s):

Dust Emission ◽

High Sensitivity ◽

Far Infrared ◽

Microwave Emission ◽

Correlation Technique ◽

The North ◽

Sky Survey ◽

Celestial Pole ◽

Source Confusion ◽

5 Ghz

ABSTRACT The C-Band All-Sky Survey (C-BASS) is a high sensitivity all-sky radio survey at an angular resolution of 45 arcmin and a frequency of 4.7 GHz. We present a total intensity map of the North Celestial Pole (NCP) region of sky, above declination >+80°, which is limited by source confusion at a level of ≈0.6 mK rms. We apply the template-fitting (cross-correlation) technique to WMAP and Planck data, using the C-BASS map as the synchrotron template, to investigate the contribution of diffuse foreground emission at frequencies ∼20–40 GHz. We quantify the anomalous microwave emission (AME) that is correlated with far-infrared dust emission. The AME amplitude does not change significantly (${\lt }10\, {{\ \rm per\ cent}}$) when using the higher frequency C-BASS 4.7 GHz template instead of the traditional Haslam 408 MHz map as a tracer of synchrotron radiation. We measure template coefficients of 9.93 ± 0.35 and $9.52\pm 0.34\,$ K per unit τ353 when using the Haslam and C-BASS synchrotron templates, respectively. The AME contributes $55\pm 2\, \mu$K rms at 22.8 GHz and accounts for ${\approx } 60{{\ \rm per\ cent}}$ of the total foreground emission. Our results show that a harder (flatter spectrum) component of synchrotron emission is not dominant at frequencies ≳5 GHz; the best-fitting synchrotron temperature spectral index is β = −2.91 ± 0.04 from 4.7 to 22.8 GHz and β = −2.85 ± 0.14 from 22.8 to 44.1 GHz. Free–free emission is weak, contributing ${\approx } 7\, \mu$K rms (${\approx } 7{{\ \rm per\ cent}}$) at 22.8 GHz. The best explanation for the AME is still electric dipole emission from small spinning dust grains.

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

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833245 ◽

2018 ◽

Vol 620 ◽

pp. A26 ◽

Cited By ~ 15

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.

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ALMA resolves molecular clouds in metal-poor Magellanic Bridge A

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937232 ◽

2020 ◽

Vol 641 ◽

pp. A97 ◽

Cited By ~ 1

Author(s):

M. T. Valdivia-Mena ◽

M. Rubio ◽

A. D. Bolatto ◽

H. P. Saldaño ◽

C. Verdugo

Keyword(s):

Star Formation ◽

Molecular Clouds ◽

Dust Emission ◽

Line Emission ◽

Far Infrared ◽

Continuum Emission ◽

Molecular Gas ◽

The North ◽

Mass Conversion ◽

North And South

Context. The Magellanic Bridge is a tidal feature located between the Magellanic Clouds, containing young stars formed in situ. Its proximity allows high-resolution studies of molecular gas, dust, and star formation in a tidal low-metallicity environment. Aims. Our goal is to characterize gas and dust emission in Magellanic Bridge A, the source with the highest 870 μm excess of emission found in single-dish surveys. Methods. Using the ALMA telescope including the Morita Array, we mapped a 3′ field of view centered on the Magellanic Bridge A molecular cloud, in 1.3 mm continuum emission and 12CO(2−1) line emission at subparsec resolution. This region was also mapped in continuum at 870 μm and in 12CO(2−1) line emission at ~6 pc resolution with the APEX telescope. To study its dust properties, we also use archival Herschel and Spitzer data. We combine the ALMA and APEX 12CO(2−1) line cubes to study the molecular gas emission. Results. Magellanic Bridge A breaks up into two distinct molecular clouds in dust and 12CO(2−1) emission, which we call North and South. Dust emission in the North source, according to our best parameters from fitting the far-infrared fluxes, is ≈3 K colder than in the South source in correspondence to its less developed star formation. Both dust sources present large submillimeter excesses in LABOCA data: according to our best fits the excess over the modified blackbody (MBB) fit to the Spitzer/Herschel continuum is E(870 μm) ~ 7 and E(870 μm) ~ 3 for the North and South sources, respectively. Nonetheless, we do not detect the corresponding 1.3 mm continuum with ALMA. Our limits are compatible with the extrapolation of the MBB fits, and therefore we cannot independently confirm the excess at this longer wavelength. The 12CO(2−1) emission is concentrated in two parsec-sized clouds with virial masses of around 400 and 700 M⊙. Their bulk volume densities are n(H2) ~ 0.7−2.6 × 103 cm−3, higher than typical bulk densities of Galactic molecular clouds. The 12CO luminosity to H2 mass conversion factor αCO is 6.5 and 15.3 M⊙ (K km s−1 pc2)−1 for the North and South clouds, calculated using their respective virial masses and 12CO(2−1) luminosities. Gas mass estimates from our MBB fits to dust emission yields masses M ~ 1.3 × 103 M⊙ and 2.9 × 103 M⊙ for North and South, respectively, a factor of ~4 higher than the virial masses we infer from 12CO.

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A statistical analysis of dust polarization properties in ALMA observations of Class 0 protostellar cores

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038404 ◽

2020 ◽

Vol 644 ◽

pp. A11

Author(s):

V. J. M. Le Gouellec ◽

A. J. Maury ◽

V. Guillet ◽

C. L. H. Hull ◽

J. M. Girart ◽

...

Keyword(s):

Statistical Analysis ◽

Column Density ◽

Spatial Scales ◽

Dust Emission ◽

Mean Value ◽

Local Conditions ◽

Grain Alignment ◽

Star Forming ◽

Alignment Mechanism ◽

Dust Grain

Context. Recent observational progress has challenged the dust grain-alignment theories used to explain the polarized dust emission routinely observed in star-forming cores. Aims. In an effort to improve our understanding of the dust grain alignment mechanism(s), we have gathered a dozen ALMA maps of (sub)millimeter-wavelength polarized dust emission from Class 0 protostars and carried out a comprehensive statistical analysis of dust polarization quantities. Methods. We analyze the statistical properties of the polarization fraction Pfrac and the dispersion of polarization position angles S. More specifically, we investigate the relationship between S and Pfrac as well as the evolution of the product S × Pfrac as a function of the column density of the gas in the protostellar envelopes. We compare the observed trends with those found in polarization observations of dust in the interstellar medium and in synthetic observations of non-ideal magneto-hydrodynamic (MHD) simulations of protostellar cores. Results. We find a significant S ∝ Pfrac−0.79 correlation in the polarized dust emission from protostellar envelopes seen with ALMA; the power-law index significantly differs from the one observed by Planck in star-forming clouds. The product S × Pfrac, which is sensitive to the dust grain alignment efficiency, is approximately constant across three orders of magnitude in envelope column density (from NH2 = 1022 cm−2 to NH2 = 1025 cm−2), with a mean value of 0.36−0.17+0.10. This suggests that the grain alignment mechanism producing the bulk of the polarized dust emission in star-forming cores may not systematically depend on the local conditions such as the local gas density. However, in the lowest-luminosity sources in our sample, we find a hint of less efficient dust grain alignment with increasing column density. Our observations and their comparison with synthetic observations of MHD models suggest that the total intensity versus the polarized dust are distributed at different intrinsic spatial scales, which can affect the statistics from the ALMA observations, for example, by producing artificially high Pfrac. Finally, synthetic observations of MHD models implementing radiative alignment torques (RATs) show that the statistical estimator S × Pfrac is sensitive to the strength of the radiation field in the core. Moreover, we find that the simulations with a uniform perfect alignment (PA) of dust grains yield, on average, much higher S × Pfrac values than those implementing RATs; the ALMA values lie among those predicted by PA, and they are significantly higher than the ones obtained with RATs, especially at large column densities. Conclusions. Ultimately, our results suggest that dust alignment mechanism(s) are efficient at producing dust polarized emission in the various local conditions typical of Class 0 protostars. The grain alignment efficiency found in these objects seems to be higher than the efficiency produced by the standard RAT alignment of paramagnetic grains. Further studies will be needed to understand how more efficient grain alignment via, for example, different irradiation conditions, dust grain characteristics, or additional grain alignment mechanisms can reproduce the observations.

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