We present a new model of interstellar dust in which large grains are a single composite material, “astrodust,” and nanoparticle-sized grains come in distinct varieties including polycyclic aromatic hydrocarbons (PAHs). We argue that a single-composition model for grains larger than ∼0.02
We present the first mid-IR detection of the linear polarization toward the star CygOB2-12, a luminous blue hypergiant that, with
- Award ID(s):
- 1908625
- NSF-PAR ID:
- 10381334
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal Letters
- Volume:
- 940
- Issue:
- 1
- ISSN:
- 2041-8205
- Format(s):
- Medium: X Size: Article No. L26
- Size(s):
- ["Article No. L26"]
- Sponsoring Org:
- National Science Foundation
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Abstract μ m most naturally explains the lack of frequency dependence in the far-infrared (FIR) polarization fraction and the characteristic ratio of optical to FIR polarization. We derive a size distribution and alignment function for 1.4:1 oblate astrodust grains that, with PAHs, reproduce the mean wavelength dependence and polarization of Galactic extinction and emission from the diffuse interstellar medium while respecting constraints on solid-phase abundances. All model data and Python-based interfaces are made publicly available. -
Abstract Using new large-area maps of the cold neutral medium (CNM) fraction,
f CNM, we investigate the relationship between the CNM, the abundance of polycyclic aromatic hydrocarbons (PAHs), and the anomalous microwave emission (AME). We first present ourf CNMmap based on full-sky HI4PI data, using a convolutional neural network to convert the spectroscopic Hi data tof CNM. We demonstrate thatf CNMis strongly correlated with the fraction of dust in PAHs as estimated from mid- and far-infrared dust emission. In contrast, we find no correlation betweenf CNMand the amount of AME per dust emission and no to weakly negative correlation betweenf CNMand the AME peak frequency. These results suggest PAHs preferentially reside in cold, relatively dense gas, perhaps owing to enhanced destruction in more diffuse media. The lack of positive correlation betweenf CNMand AME peak frequency is in tension with expectations from theoretical models positing different spectral energy distributions of AME in the cold versus warm neutral medium. We suggest that different PAH abundances and emission physics in different interstellar environments may explain the weaker-than-expected correlation between 12μ m PAH emission and AME even if PAHs are the AME carriers. -
Abstract Dust-induced polarization in the interstellar medium (ISM) is due to asymmetric grains aligned with an external reference direction, usually the magnetic field. For both the leading alignment theories, the alignment of the grain’s angular momentum with one of its principal axes and the coupling with the magnetic field requires the grain to be paramagnetic. Of the two main components of interstellar dust, silicates are paramagnetic, while carbon dust is diamagnetic. Hence, carbon grains are not expected to align in the ISM. To probe the physics of carbon grain alignment, we have acquired Stratospheric Observatory for Infrared Astronomy/Higch-resolution Airborne Wideband Camera-plus far-infrared photometry and polarimetry of the carbon-rich circumstellar envelope (CSE) of the asymptotic giant branch star IRC+10° 216. The dust in such CSEs are fully carbonaceous and thus provide unique laboratories for probing carbon grain alignment. We find a centrosymmetric, radial, polarization pattern, where the polarization fraction is well correlated with the dust temperature. Together with estimates of a low fractional polarization from optical polarization of background stars, we interpret these results to be due to a second-order, direct radiative external alignment of grains without internal alignment. Our results indicate that (pure) carbon dust does not contribute significantly to the observed ISM polarization, consistent with the nondetection of polarization in the 3.4
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Abstract With ΣSFR∼ 4200
M ⊙yr−1kpc−2, SPT 0346–52 (z = 5.7) is the most intensely star-forming galaxy discovered by the South Pole Telescope. In this paper, we expand on previous spatially resolved studies, using ALMA observations of dust continuum, [Nii ] 205μ m, [Cii ] 158μ m, [Oi ] 146μ m, and undetected [Nii ] 122μ m and [Oi ] 63μ m emission to study the multiphase interstellar medium (ISM) in SPT 0346–52. We use pixelated, visibility-based lens modeling to reconstruct the source-plane emission. We also model the source-plane emission using the photoionization codecloudy and find a supersolar metallicity system. We calculateT dust= 48.3 K andλ peak= 80μ m and see line deficits in all five lines. The ionized gas is less dense than comparable galaxies, withn e < 32 cm−3, while ∼20% of the [Cii ] 158μ m emission originates from the ionized phase of the ISM. We also calculate the masses of several phases of the ISM. We find that molecular gas dominates the mass of the ISM in SPT 0346–52, with the molecular gas mass ∼4× higher than the neutral atomic gas mass and ∼100× higher than the ionized gas mass. -
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