B-fields In STar-forming Region Observations (BISTRO): Dual-Wavelength Constraints on Size-Dependent Grain Alignment in Star-Forming Regions
Year: 2026
Type: preprint
Abstract: We compared 450 and 850 $μ$m POL-2 observations from the James Clerk Maxwell Telescope at $12.6''$ resolution. The median absolute difference in polarization angle between bands is $6.7^\circ$ across 21 regions. For total intensity $I\proptoν^α$ and polarized intensity $PI\proptoν^γ$, 24-27 of 35 regions have $γ<α$, allowing for $3σ$ limits on weak polarized intensities. The median $γ-α$ is $-0.51$, ranging from $-0.57$ to $-0.45$ under these limits. The ratio of polarization fractions is $P_{450}/P_{850}=0.69\pm0.02_{\rm sys}\pm0.03_{\rm stat}$, with no detected dependence on the angle difference. We suggest that the dependence of alignment on grain size offers the simplest explanation of these findings. For optically thin components sharing a polarization angle and opacity law, temperature mixing reproduces the median $-0.51$ only if the warm dust is polarized less efficiently than the cold dust. If the cold dust is at 10 K or warmer and the warm dust at 40 K or cooler, the median requires a ratio of warm to cold effective polarization efficiencies $r\lesssim0.18$. We tested mixtures with opacity index $β=2$ in four fields against Herschel dust temperatures and Green Bank Ammonia Survey kinetic temperatures. We assumed equal gas and dust temperatures, ammonia tracing cold gas, and model ranges of 3-20 K for cold dust and 25-40 K for warm dust carrying at most half the mass. Mixtures matching both temperatures cannot reproduce $γ-α$ within $1σ$ in three fields, including OMC 2 tentatively, even for $r=0$. Allowing warm dust at 10-100 K and up to 95% of the mass permits solutions only for $r\leq0.041$. To explain these three fields by temperature mixing, we need wider model ranges and a very strong contrast in polarization efficiency. The origin of this contrast remains undetermined.
Source: arXiv (Cornell University)
Authors: Furuya, Ray S., Berry, David, Bastien, Pierre, Hasegawa, Tetsuo, Matsumura, Masafumi, Hoang, Thiem, Fanciullo, Lapo, Iwasaki, Kazunari, Coudé, Simon, Onaka, Takashi, Diep, Pham Ngoc, Sadavoy, Sarah, Li, Hua-bai, Kawabata, Koji, Arzoumanian, Doris, Doi, Yasuo, Wang, Jia-Wei, Ching, Tao-Chung, Karoly, Janik, Hwang, Jihye, White, Glenn J., Lyo, A-Ran, Tomisaka, Kohji, Tram, Le Ngoc, Poidevin, Frédérick, Gouellec, Valentin J. M. Le, Shinnaga, Hiroko, Kobayashi, Masato I. N., Liu, Junhao, Tahani, Mehrnoosh, Ngoc, Nguyen Bich, Hatchell, Jennifer, Soam, Archana, Yen, Hsi-Wei, Eswaraiah, Chakali, Könyves, Vera, Wu, Jintai, Lee, Jeong-Eun, Tsukamoto, Yusuke, Sharma, Ekta, Liu, Tie, Gu, Qilao, Nakanishi, Hiroyuki, Inoue, Tsuyoshi, Nakamura, Fumitaka, Friesen, Rachel, Robitaille, Jean-François, Misugi, Yoshiaki, Kashiwagi, Raiga, Friberg, Per, Graves, Sarah, Rawlings, Mark, Parsons, Harriet, Eden, David, Chen, Huei-Ru Vivien, Bijas, Najimudeen, Tamura, Motohide, Bourke, Tyler L., Ohashi, Nagayoshi, Kwon, Woojin, Kim, Jongsoo, Lai, Shih-Ping, Qiu, Keping, Li, Di, Inutsuka, Shu-ichiro, Pattle, Kate, Ward-Thompson, Derek, Collaboration, BISTRO
Institutions: National Astronomical Observatory of Japan, Rutherford Appleton Laboratory, Tokushima University, University College London, The Open University, Universidad de La Laguna, Instituto de Astrofísica de Canarias, Kagoshima University, University of Cologne, University of South Carolina, University of Exeter, Indian Institute of Astrophysics, University of Lancashire, Nanjing University, Seoul National University, Chinese Academy of Sciences, National Astronomical Observatories, Shanghai Astronomical Observatory, Konan University, The Graduate University for Advanced Studies, SOKENDAI, National Radio Astronomy Observatory, Centre National de la Recherche Scientifique, Institut de Planétologie et d'Astrophysique de Grenoble, National Tsing Hua University, Armagh Observatory & Planetarium, University of Manchester, SKA Observatory, University of Bath, East Asian Observatory, Centre for Research in Astrophysics of Québec, Kyushu University
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: National Astronomical Research Institute of Thailand, Academia Sinica, Korea Astronomy and Space Science Institute, University of Tokushima, National Astronomical Observatory of Japan, Russian Science Foundation, Science and Technology Facilities Council, Japan Society for the Promotion of Science, National Institutes of Natural Sciences
OpenAlex ID: W7223227885