Westerhout 3

Westerhout 3

Emission nebula
H II region
Image of Westerhout 3
Observation data: J2000.0 epoch
Right ascension	02h 27m 4.1s [1]
Declination	61° 52′ 22″ [2]
Distance	7,000 [3]   ly    (2,100  pc)
Constellation	Cassiopeia
Designations	W3, Fish Head Nebula
See also: Lists of nebulae

Westerhout 3 (also known as W3) is a giant molecular cloud and a star-forming region in the Perseus arm of the Milky Way Galaxy, first identified by the Dutch Astronmer Gart Westerhout. It is one of the most active sites of massive star formation in the outer parts of our galaxy, located in the constellation Cassiopeia at a distance of approximately 6,000 light-years from Earth. W3, with W4 and W5, forms part of the larger W3/W4/W5 complex, associated with the Heart and Soul Nebula, and corresponds specifically to the bright emission nebula Fish Head Nebula (IC 1795) within the Heart Nebula (Sh 2-190). ^{[4] [5] [6]}

Herschel image of the W3/W4/W5 complex in infrared light

W3/W4/W4 complex in emission lines, as seen by the Northern Sky Narrowband Survey

Star Formation

W3 is a prolific star-forming region, hosting both massive O and B-type stars and lower-mass pre-main-sequence (PMS) stars in embedded clusters. Star formation appears to occur sequentially, triggered by feedback from previous generations of massive stars, including expanding ionization bubbles and stellar winds that compress surrounding gas. Ultracompact H II regions, protostellar outflows, and young stellar objects (YSOs) with circumstellar disks are common, as observed by telescopes like Chandra and Spitzer. The region exemplifies how massive stars accrete material in dense environments despite radiative feedback, with detections of large organic molecules like methanol in vast clouds. ^{[7] [8] [9]}

Subregion

Westerhout 3 Comprises several distinct subregions, each with unique star-forming characteristics, often studied via multi-wavelength data to map embedded clusters, H II regions, and molecular outflows. These include W3 Main, W3(OH), and others such as W3 East and W3 West, illustrating dynamic interactions within the GMC.

• W3 Main: W3 Main is the central subregion, spanning about 7 parsecs and containing a nearly spherical cluster of around 900 X-ray-detected stars, including ultracompact H II regions and high-mass protostars. It features dense cores, filaments, and a southern cavity likely formed by stellar feedback. Intense star formation involves O-type stars and PMS objects, with infrared excesses indicating disks. Herschel observations highlight warmer, heated material in this area. ^{[10] [11] [12] [13] [14]}

Image of W3 Main

• W3(OH): Located east of W3 Main, W3(OH) is a compact H II region known for OH and Methanol maser emissions, signaling early high-mass star formation. It exhibits an optically thick spectrum below 15 GHz, with embedded cores, outflows, and hot gas. Protostellar clusters form here, potentially triggered by cloud collisions involving three overlapping molecular clouds. Additional star-forming sites lie south of W3(OH), contributing to the HDL's diversity. It is one of W3's most luminous compact sources, as per Herschel and JCMT data. ^{[15] [16] [17] [18] [19]}

• Other subregions includes W3 East and W3 West with full widths at half maximum under 0.45 parsecs, showing high densities and protostellar activity akin to the main areas. They exemplify sequential star formation driven by expanding bubbles from prior stellar generations. ^[20]

Observation and Research

W3 has been extensively observed across wavelengths to study its kinematics, gas properties, and stellar populations. Key instruments include the Herschel Space Observatory for far-infrared imaging, the Chandra X-ray Observatory for stellar clusters, and the Spitzer Space Telescope for infrared excesses in YSOs. Research focuses on the interplay between stellar feedback and cloud evolution, making W3 a model for obscured star formation processes. ^{[21] [22]}

References

1. "Simbad - Object view". simbad.cds.unistra.fr. Retrieved 2025-09-25.
2. "Simbad - Object view". simbad.cds.unistra.fr. Retrieved 2025-09-25.
3. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv: 2208.00211 . Bibcode:2023A&A...674A...1G. doi: 10.1051/0004-6361/202243940 . S2CID   244398875. Gaia DR3 record for this source at VizieR.
4. "ESA Science & Technology - Herschel's view of the W3/W4/W5 complex". sci.esa.int. Retrieved 2025-09-25.
5. Elizabeth Howell (2013-03-27). "New Theory of How Giant Stars Grow Unveiled". Space. Retrieved 2025-09-25.
6. "Things Unseen: The Westerhout radio sources | Galaxy Map". galaxymap.org. Retrieved 2025-09-25.
7. Kiminki, Megan M.; Kim, Jinyoung Serena; Bagley, Micaela B.; Sherry, William H.; Rieke, George H. (2015-11-01). "THE O- and B-TYPE STELLAR POPULATION in W3: Beyond the HIGH-DENSITY LAYER". Astrophysical Journal. 813 (1): 42. arXiv: 1509.00081 . Bibcode:2015ApJ...813...42K. doi:10.1088/0004-637X/813/1/42. ISSN   0004-637X.
8. GaryABC, Stuart (2013-03-28). "Massive stars built in stellar nurseries". www.abc.net.au. Retrieved 2025-09-25.
9. "ESA Science & Technology - Herschel's view of the W3/W4/W5 complex". sci.esa.int. Retrieved 2025-09-25.
10. "Chandra :: Photo Album :: W3 Main :: 18 Dec 06". chandra.harvard.edu. Retrieved 2025-09-25.
11. "W3 star-forming region – Herschel Space Observatory". 2013-03-27. Retrieved 2025-09-25.
12. "How to build a really, really big star | University of Toronto". www.utoronto.ca. Retrieved 2025-09-25.
13. Polychroni, Danae; Moore, Toby J. T.; Allsopp, James (2012-02-22), "The gas properties of the W3 giant molecular cloud: A HARP study", Monthly Notices of the Royal Astronomical Society, 422 (4): 2992–3003, arXiv: 1202.5010 , Bibcode:2012MNRAS.422.2992P, doi: 10.1111/j.1365-2966.2012.20803.x
14. Feigelson, Eric D.; Townsley, Leisa K. (2008-01-20). "The Diverse Stellar Populations of the W3 Star-forming Complex". The Astrophysical Journal. 673 (1): 354–362. arXiv: 0710.0090 . Bibcode:2008ApJ...673..354F. doi:10.1086/524031. ISSN   0004-637X.
15. "W3(OH) · NRAO/AUI Archives". www.nrao.edu. Retrieved 2025-09-25.
16. Colley, D. (1980). "1980MNRAS.193..495C Page 495". Monthly Notices of the Royal Astronomical Society. 193: 495. Bibcode:1980MNRAS.193..495C. doi: 10.1093/mnras/193.3.495 .
17. Yamada, Rin I; Sano, Hidetoshi; Tachihara, Kengo; Enokiya, Rei; Nishimura, Atsushi; Fujita, Shinji; Kohno, Mikito; Bieging, John H; Fukui, Yasuo (2024-10-03). "A kinematic analysis of the giant molecular complex W3: Possible evidence for cloud–cloud collisions that triggered OB star clusters in W3 Main and W3(OH)". Publications of the Astronomical Society of Japan. 76 (5): 895–911. doi: 10.1093/pasj/psae056 . ISSN   0004-6264.
18. "Astronomers find alcohol cloud spanning 288 billion miles". phys.org. Retrieved 2025-09-25.
19. "HERSCHELOBSERVATIONS OF THE W3 GMC: CLUES TO THE FORMATION OF CLUSTERS OF HIGH-MASS STARS - McMaster Experts". experts.mcmaster.ca. Archived from the original on 2025-05-21. Retrieved 2025-09-25.
20. "HERSCHELOBSERVATIONS OF THE W3 GMC: CLUES TO THE FORMATION OF CLUSTERS OF HIGH-MASS STARS - McMaster Experts". experts.mcmaster.ca. Archived from the original on 2025-05-21. Retrieved 2025-09-25.
21. "ESA Science & Technology - Herschel's view of the W3/W4/W5 complex". sci.esa.int. Retrieved 2025-09-25.
22. "How to build a really, really big star | University of Toronto". www.utoronto.ca. Retrieved 2025-09-25.