Examining Galaxy Form from the Top of the World Origin of galactic morphology probed using the Paschen alpha emission line

August 23, 2012

38 galaxies observed in hydrogen Paschen alpha emission line at the University of Tokyo Atacama Observatory. ©TAO Project
The red color represents the Paschen alpha emission.

Forming galaxies, usually called starburst galaxies, are known to emit strong infrared rays associated star formation, but detail is hidden by thick dust clouds produced at the same time.

The TAO project team of the Institute of Astronomy, the University of Tokyo, focused on the hydrogen Paschen alpha emission line, using which it is possible to peer through the dust clouds. The problem is that the Paschen alpha emission is easily absorbed by water vapor in the Earth’s atmosphere, and it was thought to be impossible to observe from a ground-based observatory.

The team installed a 1.0m telescope at the University of Tokyo Atacama Observatory at the summit of Mt. Chajnantor (5640m altitude) in northern Chile, the highest astronomical observatory on the Earth, and has been carrying out an imaging survey of nearby starburst galaxies in the Paschen alpha emission line. 38 starburst galaxies have been observed in the Paschen alpha so far, the largest sample of starburst galaxies ever observed. From these observations, the galaxies are clearly separated into two groups according to the morphology of their star-forming regions. In one, star forming regions are concentrated in the center of the galaxy as in elliptical galaxies, and in the other the region is extended as in spiral galaxies. This result suggests that the two types of galaxies currently observed, spiral and elliptical, differ from the stage of their formation. This is an important result and a significant contribution to solving one of the major questions in the formation and evolution of galaxies: the origin of galaxy morphology.

Press release (Japanese)


Ken Tateuchi, Kentaro Motohara, Masahiro Konishi, Hidenori Takahashi,Natsuko Kato, Yuka K. Uchimoto, Koji Toshikawa, Ryou Ohsawa, Yutaro Kitagawa, Yuzuru Yoshii, Mamoru Doi, Kotaro Kohno, Kimiaki Kawara, Masuo Tanaka, Takashi Miyata, Toshihiko Tanabe, Takeo Minezaki, Shigeyuki Sako, Tomoki Morokuma, Yoichi Tamura, Tsutomu Aoki, Takeo Soyano, Kenfichi Tarusawa, Shintaro Koshida, Takafumi Kamizuka, Tomohiko Nakamura, Kentaro Asano, Mizuho Uchiyama, Kazushi Okada, Yoshifusa Ita,
“miniTAO/ANIR Paα Survey of Local LIRGs”,
Publication of the Korean Astronomical Society, accepted


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Institute of Astronomy

TAO Project Group (Japanese)

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