On the Collisional Disalignment of Dust Grains in Illuminated and Shaded Regions of IC 63

Soam, Archana; Andersson, B. G.; Acosta–Pulido, J. A.; López, Manuel Fernández; Vaillancourt, John E.; Weaver, Susanna L. Widicus; Piirola, V.; Gordon, Michael S.

doi:10.3847/1538-4357/abcb8e

Cited by 7 publications

(4 citation statements)

References 54 publications

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“…Results obtained from modeling and observations of dust polarization of the diffuse ISM and dense cores tend to favor the scenario where the efficiency of RATs can only be reproduced if grains' magnetic relaxation is sufficiently fast, i.e., for superparamagnetic grains (Hoang & Lazarian 2016;Le Gouellec et al 2020;Reissl et al 2020). We also note that H 2 formation occurring at the grains' surfaces provides additional torque that also increase the grain rotational velocity, eventually bringing the grain to suprathermal rotation (Purcell 1979;Hoang et al 2015), especially toward PDRs (Le Bourlot et al 2012;Andersson et al 2013;Soam et al 2021). These both effects of grains' super-paramagneticity and H 2 formation supplemental torque increase the fraction of grains with high angular momentum, i.e., the fraction of grains at the the so-called high-J attractor point (Lazarian & Hoang 2007;Hoang & Lazarian 2009b.…”

Section: Grain Size Parameter Space For K-ratmentioning

confidence: 65%

The Origin of Dust Polarization in the Orion Bar

Gouellec¹,

Andersson²,

Soam

et al. 2023

ApJ

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The linear polarization of thermal dust emission provides a powerful tool to probe interstellar and circumstellar magnetic fields, because aspherical grains tend to align themselves with magnetic field lines. While the Radiative Alignment Torque (RAT) mechanism provides a theoretical framework for this phenomenon, some aspects of this alignment mechanism still need to be quantitatively tested. One such aspect is the possibility that the reference alignment direction changes from the magnetic field (“B-RAT”) to the radiation field k-vector (“k-RAT”) in areas of strong radiation fields. We investigate this transition toward the Orion Bar PDR, using multiwavelength SOFIA HAWC+ dust polarization observations. The polarization angle maps show that the radiation field direction is on average not the preferred grain alignment axis. We constrain the grain sizes for which the transition from B-RAT to k-RAT occurs in the Orion Bar (grains ≥ 0.1 μm toward the most irradiated locations), and explore the radiatively driven rotational disruption that may take place in the high-radiation environment of the Bar for large grains. While the grains susceptible to rotational disruption should be in suprathermal rotation and aligned with the magnetic field, k-RAT aligned grains would rotate at thermal velocities. We find that the grain size at which the alignment shifts from B-RAT to k-RAT corresponds to grains too large to survive the rotational disruption. Therefore, we expect a large fraction of grains to be aligned at suprathermal rotation with the magnetic field, and to potentially be subject to rotational disruption, depending on their tensile strength.

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Section: Grain Size Parameter Space For K-ratmentioning

confidence: 65%

The Origin of Dust Polarization in the Orion Bar

Gouellec¹,

Andersson²,

Soam

et al. 2023

ApJ

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“…Whereas EXES observations are further capable of resolving temperature of PDRs. Soam et al (2021) showed that the collisional disalignment rate of the dust grains causing the observed polarization follow a bifurcated relation with respect to the gas density. The two observed sequences in derived disalignment rate correspond to lines of sight in front and behind gas clumps, as seen in the HCO + (J=1-0) map of the cloud.…”

Section: Discussionmentioning

confidence: 97%

Spatial variation in temperature and density in the IC 63 PDR from $\rm H_{2}$ Spectroscopy

Soam,

Andersson,

Karoly

et al. 2021

Preprint

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We have measured the gas temperature in the IC 63 photodissociation region (PDR) using the S(1) and S(5) pure rotation lines of molecular hydrogen with SOFIA/EXES. We divide the PDR into three regions for analysis based on the illumination from γ Cas: "sunny", "ridge", and "shady". Constructing rotation diagrams for the different regions, we obtain temperatures of T ex =562 +52 −43 K towards the "ridge" and T ex =495 +28 −25 K in the "shady" side. The H 2 emission was not detected on the "sunny" side of the ridge, likely due to the photo-dissociation of H 2 in this gas. Our temperature values are lower than the value of T ex =685±68 K using the S(1), S(3), and S(5) pure rotation lines, derived by Thi et al. ( 2009) using lower spatial-resolution ISO-SWS data at a different location of the IC 63 PDR. This difference indicates that the PDR is inhomogeneous and illustrates the need for high-resolution mapping of such regions to fully understand their physics. The detection of a temperature gradient correlated with the extinction into the cloud, points to the ability of using H 2 pure rotational line spectroscopy to map the gas temperature on small scales. We used a PDR model to estimate the FUV radiation and corresponding gas densities in IC 63. Our results shows the capability of SOFIA/EXES to resolve and provide detailed information on the temperature in such regions.

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“…We also used HCO + (J = 1-0) position-position-velocity maps observed with CARMA 9 (Soam et al 2021b) , and molecular hydrogen H 2 (1-0)S(1) mapping from CFHT 10 (Andersson et al 2013) in conjunction with low-resolution 12 CO (1-0) data from TRAO 11 as part of a molecular line survey of 16 BRCs by A. Soam et al (2023, in preparation) to help in studying the gas locations at different opacities.…”

Section: Data Acquisition and Reductionmentioning

confidence: 99%

“…These investigations were done to understand the magnetized evolution of these nebulae. Polarization efficiency and collisional disalignment of dust grains in IC 63 are studied by Soam et al (2021d) and Soam et al (2021a), respectively. The gradients in temperature and densities in the PDR region of IC 63 are also studied by Soam et al (2021c) using pure rotational molecular hydrogen observations.…”

Section: Introductionmentioning

confidence: 99%

Physics and Chemistry of Radiation Driven Cloud Evolution. [C ii] Kinematics of IC 59, and IC 63

Dennis¹

2023

ApJ

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We used high-resolution [C ii] 158 μm mapping of two nebulae IC 59 and IC 63 from SOFIA/upGREAT in conjunction with ancillary data of the gas, dust, and polarization to probe the kinematics, structure, and magnetic properties of their photodissociation regions (PDRs). The nebulae are part of the Sh 2-185 H ii region that is illuminated by the B0 IVe star γ Cas. The velocity structure of each PDR changes with distance from γ Cas, which is consistent with driving by the radiation. Based on previous far-ultraviolet (FUV) flux measurements of, and the known distance to, γ Cas, along with the predictions of 3D distances to the clouds, we estimated the FUV radiation field strength (G 0) at the clouds. Assuming negligible extinction between the star and clouds, we find their 3D distances from γ Cas. For IC 63, our results are consistent with earlier estimates of distance from Andersson et al., locating the cloud at ∼2 pc from γ Cas at an angle of 58° to the plane of the sky behind the star. For IC 59, we derive a distance of 4.5 pc at an angle of 70° in front of the star. We do not detect any significant correlation between the orientation of the magnetic field and the velocity gradients of [C ii] gas, which indicates a moderate magnetic field strength. The kinetic energy in IC 63 is estimated to be an order of 10 higher than the magnetic energies. This suggests that kinetic pressure in this nebula is dominant.

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On the Collisional Disalignment of Dust Grains in Illuminated and Shaded Regions of IC 63

Cited by 7 publications

References 54 publications

The Origin of Dust Polarization in the Orion Bar

The Origin of Dust Polarization in the Orion Bar

Spatial variation in temperature and density in the IC 63 PDR from $\rm H_{2}$ Spectroscopy

Physics and Chemistry of Radiation Driven Cloud Evolution. [C ii] Kinematics of IC 59, and IC 63

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