The Far‐Infrared Polarization Spectrum: First Results and Analysis

Hildebrand, R. H.; Dotson, Jessie L.; Dowell, C. D.; Schleuning, D. A.; Vaillancourt, John E.

doi:10.1086/307142

Cited by 118 publications

(170 citation statements)

References 46 publications

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“…Asymmetrical dust grains align with the Galactic magnetic field to produce polarized emission. This polarized submillimetre emission has been measured from groundbased and balloon-borne telescopes (e.g., Hildebrand et al 1999;Benoît et al 2004;Ponthieu et al 2005;Vaillancourt 2007;Matthews et al 2014). The observed polarization relates to the nature, size, and shape of dust grains and the mechanisms of alignment, discussed for example by Draine (2004) and Martin (2007).…”

Section: Introductionmentioning

confidence: 71%

Planckintermediate results

Adam¹,

Ade²,

Aghanim³

et al. 2016

A&A

188

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The polarized thermal emission from diffuse Galactic dust is the main foreground present in measurements of the polarization of the cosmic microwave background (CMB) at frequencies above 100 GHz. In this paper we exploit the uniqueness of the Planck HFI polarization data from 100 to 353 GHz to measure the polarized dust angular power spectra C EE and C BB over the multipole range 40 < < 600 well away from the Galactic plane. These measurements will bring new insights into interstellar dust physics and allow a precise determination of the level of contamination for CMB polarization experiments. Despite the non-Gaussian and anisotropic nature of Galactic dust, we show that general statistical properties of the emission can be characterized accurately over large fractions of the sky using angular power spectra. The polarization power spectra of the dust are well described by power laws in multipole, C ∝ α , with exponents α EE,BB = −2.42 ± 0.02. The amplitudes of the polarization power spectra vary with the average brightness in a way similar to the intensity power spectra. The frequency dependence of the dust polarization spectra is consistent with modified blackbody emission with β d = 1.59 and T d = 19.6 K down to the lowest Planck HFI frequencies. We find a systematic difference between the amplitudes of the Galactic B-and E-modes, C BB /C EE = 0.5. We verify that these general properties are preserved towards high Galactic latitudes with low dust column densities. We show that even in the faintest dust-emitting regions there are no "clean" windows in the sky where primordial CMB B-mode polarization measurements could be made without subtraction of foreground emission. Finally, we investigate the level of dust polarization in the specific field recently targeted by the BICEP2 experiment. Extrapolation of the Planck 353 GHz data to 150 GHz gives a dust power D BB ≡ ( + 1)C BB /(2π) of 1.32 × 10 −2 µK 2 CMB over the multipole range of the primordial recombination bump (40 < < 120); the statistical uncertainty is ±0.29 × 10 −2 µK 2 CMB and there is an additional uncertainty (+0.28, −0.24) × 10 −2 µK 2 CMB from the extrapolation. This level is the same magnitude as reported by BICEP2 over this range, which highlights the need for assessment of the polarized dust signal even in the cleanest windows of the sky.

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Section: Introductionmentioning

confidence: 71%

Planckintermediate results

Adam¹,

Ade²,

Aghanim³

et al. 2016

A&A

188

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“…The preferred direction of the magnetic field in the densest parts, however, is still not entirely certain: Dust polarisation maps usually reveal a strong decrease of the polarisation towards the densest regions, which leads to some uncertainty about the field direction within the filament (e.g. Hildebrand et al 1999;Hull et al 2014). Furthermore, as shown by Soler et al (2013), also the initial magnetisation of the surrounding molecular cloud can have a significant impact on the relative orientation of the magnetic field.…”

Section: Initial Conditionsmentioning

confidence: 99%

The impact of turbulence and magnetic field orientation on star-forming filaments

Seifried

Walch

2015

Mon. Not. R. Astron. Soc.

117

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We present simulations of collapsing filaments studying the impact of turbulence and magnetic field morphologies on their evolution and star formation properties. We vary the mass per unit length of the filaments as well as the orientation of the magnetic field with respect to the major axis. We find that the filaments, which have no or a perpendicular magnetic field, typically reveal a smaller width than the universal width of 0.1 pc proposed by e.g. Arzoumanian et al. (2011). We show that this also holds in the presence of supersonic turbulence and that accretion driven turbulence is too weak to stabilize the filaments along their radial direction. On the other hand, we find that a magnetic field that is parallel to the major axis can stabilize the filament against radial collapse resulting in widths of 0.1 pc. Furthermore, depending on the filament mass and magnetic field configuration, gravitational collapse and fragmentation in filaments occurs either in an edge-on way, uniformly distributed across the entire length, or in a mixed way. In the presence of initially moderate density perturbations, a centralized collapse towards a common gravitational centre occurs. Our simulations can thus reproduce different modes of fragmentation observed recently in star forming filaments. Moreover, we find that turbulent motions influence the distance between individual fragments along the filament, which does not always match the results of a Jeans analysis.

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“…The observed decrease of polarization with increasing intensity has been attributed to changes in the dust grain optical properties or shapes in the cold cores interiors due to graingrowth (Vrba et al 1993;or Hildebrand et al 1999): not only are bigger grains more difficult to align than smaller grains, but also the agglomeration process may make grains more spherical, thus further reducing the alignment efficiency.…”

Section: L1544mentioning

confidence: 99%

Polarized dust emission of magnetized molecular cloud cores

Gonçalves

Galli²,

Walmsley³

2005

A&A

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Abstract. We compute polarization maps for molecular cloud cores modeled as magnetized singular isothermal toroids, under the assumption that the emitting dust grains are aspherical and aligned with the large-scale magnetic field. We show that, depending on the inclination of the toroid with the line-of-sight, the bending of the magnetic field lines resulting from the need to counteract the inward pull of gravity naturally produces a depolarization effect toward the centre of the map. We compute the decrease of polarization degree with increasing intensity for different viewing angles and frequencies, and we show that an outward increasing temperature gradient, as expected in starless cores heated by the external radiation field, enhances the decrease of polarization. We compare our results with recent observations, and we conclude that this geometrical effect, together with other mechanisms of depolarization, may significantly contribute to the decrease of polarization degrees with intensity observed in the majority of molecular cloud cores. Finally, we consider the dependence of the polarization degree on the dust temperature gradient predicted for externally heated clouds, and we briefly comment on the limits of the Chandrasekhar-Fermi formula to estimate the magnetic field strength in molecular cloud cores.

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The Far‐Infrared Polarization Spectrum: First Results and Analysis

Cited by 118 publications

References 46 publications

Planckintermediate results

Planckintermediate results

The impact of turbulence and magnetic field orientation on star-forming filaments

Polarized dust emission of magnetized molecular cloud cores

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