nonthermal radio emission. From these behaviors, Sakka’s group suggested that,
while the energy scale is comparable with Seyfert galaxies, the form of activity is
rather different (Sakka et al. 1973). Kyoto group continued the observations of
peculiar galaxies such as Haro galaxies and polar-ring galaxies up to the 1980s at
the OAO. The polar-ring galaxy is a type of active galaxy characterized by an outer
ring of stars and gas. The ring is vertical to the galactic plane and rotating around the
center of the galaxy.
7.8.2 Normal Galaxies
7.8.2.1 Andromeda Galaxy (M31)
M31 is the nearest giant spiral galaxy, composed of central spheroidal bulge and
outer disk component.
In Japan, first observations of the central bulge of M31 were made by Matsumoto
Toshio, Murakami Hiroshi and Hamajima Kiyotoshi (Nagoya University and TAO)
in 1977. They observed at 7000–9000 Å and 2.2 μ m, using the 100-cm Agematsu
Infrared Telescope. They measured the position angle (PA) and axial ratio (a/b) of
the spheroid, and found that both PA and a/b exhibited larger values in 2.2 μ m than
in λ7000–9000 Å band. Since infrared light comes from late-type giants, they
suggested that the larger values of these parameters infer the distribution of evolved
giant stars which form a more elongated prolate bar-like structure in the bulge of
M31 (Matsumoto et al. 1977).
For the outer disk component, Sawa Takeyasu and Sofue Yoshiaki calculated the
spatial distribution of neutral hydrogen gas in M31, based on the HI data obtained by
the 100-m radio telescope at the Max Planck Institute for Radio Astronomy. In this
analysis, they applied the density-wave theory to determine the positions of spiral
arms. The result is shown in Fig. 7.41, where several spiral arms are visible, making
a two-armed trailing spiral structure especially at radii greater than 15 kpc from the
center (Sawa et al. 1981). In 1985, Ichikawa Takashi, Nakano Makoto and their
group observed the southern arm of M31 with CO line using the 45-m telescope of
the NRO. They found conspicuous dark clouds and a complex of HII regions located
in the arm, where CO emitting regions are likely avoiding HII regions (Ichikawa
et al. 1985).
Makishima Kazuo, Ohashi Takaya and their group observed a wide field of M31
with GINGA in 2–20 keV range of X ray, and they detected a weak X-ray source at
the center of M31. The observed X-ray spectrum showed the spectra of low-mass
X-ray binaries. From these results they suggested that the low-mass X-ray binaries
dominate in the central part of M31 (Makishima et al. 1989).
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7 Postwar Development of Astrophysics, 1946–2000 (Part II: Astrophysics)
while the energy scale is comparable with Seyfert galaxies, the form of activity is
rather different (Sakka et al. 1973). Kyoto group continued the observations of
peculiar galaxies such as Haro galaxies and polar-ring galaxies up to the 1980s at
the OAO. The polar-ring galaxy is a type of active galaxy characterized by an outer
ring of stars and gas. The ring is vertical to the galactic plane and rotating around the
center of the galaxy.
7.8.2 Normal Galaxies
7.8.2.1 Andromeda Galaxy (M31)
M31 is the nearest giant spiral galaxy, composed of central spheroidal bulge and
outer disk component.
In Japan, first observations of the central bulge of M31 were made by Matsumoto
Toshio, Murakami Hiroshi and Hamajima Kiyotoshi (Nagoya University and TAO)
in 1977. They observed at 7000–9000 Å and 2.2 μ m, using the 100-cm Agematsu
Infrared Telescope. They measured the position angle (PA) and axial ratio (a/b) of
the spheroid, and found that both PA and a/b exhibited larger values in 2.2 μ m than
in λ7000–9000 Å band. Since infrared light comes from late-type giants, they
suggested that the larger values of these parameters infer the distribution of evolved
giant stars which form a more elongated prolate bar-like structure in the bulge of
M31 (Matsumoto et al. 1977).
For the outer disk component, Sawa Takeyasu and Sofue Yoshiaki calculated the
spatial distribution of neutral hydrogen gas in M31, based on the HI data obtained by
the 100-m radio telescope at the Max Planck Institute for Radio Astronomy. In this
analysis, they applied the density-wave theory to determine the positions of spiral
arms. The result is shown in Fig. 7.41, where several spiral arms are visible, making
a two-armed trailing spiral structure especially at radii greater than 15 kpc from the
center (Sawa et al. 1981). In 1985, Ichikawa Takashi, Nakano Makoto and their
group observed the southern arm of M31 with CO line using the 45-m telescope of
the NRO. They found conspicuous dark clouds and a complex of HII regions located
in the arm, where CO emitting regions are likely avoiding HII regions (Ichikawa
et al. 1985).
Makishima Kazuo, Ohashi Takaya and their group observed a wide field of M31
with GINGA in 2–20 keV range of X ray, and they detected a weak X-ray source at
the center of M31. The observed X-ray spectrum showed the spectra of low-mass
X-ray binaries. From these results they suggested that the low-mass X-ray binaries
dominate in the central part of M31 (Makishima et al. 1989).
226
7 Postwar Development of Astrophysics, 1946–2000 (Part II: Astrophysics)