The formation of molecular clouds, which serve as stellar nurseries in galaxies, is poorly understood. A class of cloud formation models suggests that a large-scale galactic magnetic field is irrelevant at the scale of individual clouds, because the turbulence and rotation of a cloud may randomize the orientation of its magnetic field1,2. Alternatively, galactic fields could be strong enough to impose their direction upon individual clouds3,4, thereby regulating cloud accumulation and fragmentation5, and affecting the rate and efficiency of star formation6. Our location in the disk of the Galaxy makes an assessment of the situation difficult. Here we report observations of the magnetic field orientation of six giant molecular cloud complexes in the nearby, almost face-on, galaxy M33. The fields are aligned with the spiral arms, suggesting that the large-scale field in M33 anchors the clouds.
This is a preview of subscription content, access via your institution
Open Access articles citing this article.
The Astronomy and Astrophysics Review Open Access 29 December 2015
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Get time limited or full article access on ReadCube.
All prices are NET prices.
Dobbs, C. GMC formation by agglomeration and self gravity. Mon. Not. R. Astron. Soc. 391, 844–858 (2008)
Hartmann, L., Ballesteros-Paredes, J. & Bergin, E. Rapid formation of molecular clouds and stars in the solar neighborhood. Astrophys. J. 562, 852–868 (2001)
Passot, T., Vazquez-Semadeni, E. & Pouquet, A. A turbulent model for the interstellar medium. II. Magnetic fields and rotation. Astrophys. J. 455, 536–555 (1995)
Shetty, R. & Ostriker, E. Global modeling of spur formation in spiral galaxies. Astrophys. J. 647, 997–1017 (2006)
Li, H.-b. et al. Evidence for dynamically important magnetic fields in molecular clouds. Mon. Not. R. Astron. Soc. 411, 2067–2075 (2011)
Price, D. & Bate, M. The effect of magnetic fields on star cluster formation. Mon. Not. R. Astron. Soc. 385, 1820–1834 (2008)
Kim, M., Kim, E., Lee, M., Sarajedini, A. & Geisler, D. Determination of the distance to M33 based on the tip of the red giant branch and the red clump. Astron. J. 123, 244–254 (2002)
Ho, P., Moran, J. M. & Lo, K. Y. The submillimeter array. Astrophys. J. 616, L1–L6 (2004)
Rosolowsky, E., Engargiola, G., Plambeck, R. & Blitz, L. Giant molecular clouds in M33. II. High-resolution observations. Astrophys. J. 599, 258–274 (2003)
Goldreich, P. & Kylafis, N. On mapping the magnetic field direction in molecular clouds by polarization measurements. Astrophys. J. 243, L75–L78 (1981)
Li, H.-b., Dowell, C., Goodman, A., Hildebrand, R. & Novak, G. Anchoring magnetic field in turbulent molecular clouds. Astrophys. J. 704, 891–897 (2009)
Greaves, J., Holland, W., Friberg, P., Dent, W. & Polarized, C. O. Emission from molecular clouds. Astrophys. J. 512, L139–L142 (1999)
Falceta-Gonçalves, D., Lazarian, A. & Kowal, G. Studies of regular and random magnetic fields in the ISM: statistics of polarization vectors and the Chandrasekhar-Fermi technique. Astrophys. J. 679, 537–551 (2008)
Frick, P., Beck, R., Berkhuijsen, E. & Patrickeyev, I. Scaling and correlation analysis of galactic images. Mon. Not. R. Astron. Soc. 327, 1145–1157 (2001)
Shukurov, A. in Dynamic Interstellar Medium: Recent Numerical Simulations. Plasma Turbulence and Energetic Particles in Astrophysics (eds Ostrowski, M. & Schlickeiser, R. ) 66–73 (Obserwatorium Astronomiczne, Uniwersytet Jagielloński, 1999)
Field, G., Goldsmith, D. & Habing, H. Cosmic-ray heating of the interstellar gas. Astrophys. J. 155, L149–L154 (1969)
Kim, C.-G., Kim, W.-T. & Ostriker, E. Galactic spiral shocks with thermal instability. Astrophys. J. 681, 1148–1162 (2008)
Chandrasekhar, S. & Fermi, E. Magnetic fields in spiral arms. Astrophys. J. 118, 113–115 (1953)
Crutcher, R. In The Magnetized Plasma in Galaxy Evolution (eds Chyży, K. Otmianowska-Mazur, K., Soida, M. & Dettmar, R.-J. ). 103–110 (2005)
Wilson, C., Walker, C. & Thornley, M. The density and temperature of molecular clouds in M33. Astrophys. J. 483, 210–219 (1997)
Tabatabaei, F., Krause, M., Fletcher, A. & Beck, R. High-resolution radio continuum survey of M 33. III. Magnetic fields. Astron. Astrophys. 490, 1005–1017 (2008)
Han, J. & Zhang, J. The Galactic distribution of magnetic fields in molecular clouds and HII regions. Astron. Astrophys. 464, 609–614 (2007)
Heyer, M., Gong, H., Ostriker, E. & Brunt, C. Magnetically aligned velocity anisotropy in the Taurus molecular cloud. Astrophys. J. 680, 420–427 (2008)
Mouschovias, T., Kunz, M. & Christie, D. Formation of interstellar clouds: Parker instability with phase transitions. Mon. Not. R. Astron. Soc. 397, 14–23 (2009)
Li, H.-b. et al. Results of SPARO 2003: mapping magnetic fields in giant molecular clouds. Astrophys. J. 648, 340–354 (2006)
Kwak, K., Shelton, R. & Raley, E. The evolution of gas clouds falling in the magnetized Galactic halo: high-velocity clouds (HVCs) originated in the Galactic fountain. Astrophys. J. 699, 1775–1788 (2009)
Sandage, A. & Humphreys, R. On the warped optical plane of M33. Astrophys. J. 236, L1–L5 (1980)
Men'shchikov, A. et al. Filamentary structures and compact objects in the Aquila and Polaris clouds observed by Herschel. Astron. Astrophys. 518, L103–L107 (2010)
Kramer, C. et al. PACS and SPIRE photometer maps of M 33: first results of the HERschel M 33 Extended Survey (HERM33ES). Astron. Astrophys. 518, L67–L71 (2010)
Rogstad, D., Wright, M. & Lockhart, I. Aperture synthesis of neutral hydrogen in the galaxy M33. Astrophys. J. 204, 703–716 (1976)
We thank E. Rosolowsky, R. Shetty, T. K. Sridharan, M. Houde, S. Paine, H.-H. Wang, A. Karim, S. Ragan, K. Smith, P. Boley and T. Wu for comments. We appreciate the help of D. Marrone, G. Petitpas and R. Rao with the observations. We are grateful for the Herschel maps of M33 offered by C. Kramer. This research is supported by the Max-Planck-Institut für Astronomie and Harvard-Smithsonian Center for Astrophysics. The Submillimeter Array is a joint project between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics and is funded by the Smithsonian Institution and the Academia Sinica.
The authors declare no competing financial interests.
About this article
Cite this article
Li, Hb., Henning, T. The alignment of molecular cloud magnetic fields with the spiral arms in M33. Nature 479, 499–501 (2011). https://doi.org/10.1038/nature10551
This article is cited by
Nature Astronomy (2021)
Nature Astronomy (2018)
The Astronomy and Astrophysics Review (2016)
Space Science Reviews (2014)
Astrophysics and Space Science (2014)