Subaru Reveals "Frameworks" of Galaxies at 11 Billion Years Ago(Forwarded)

National Astronomical Observatory of Japan
Tokyo, Japan

December 18, 2007

Subaru Reveals "Frameworks" of Galaxies at 11 Billion Years Ago

A team of Japanese astronomers from the National Astronomical Observatory
of Japan, Tokyo University, and Kyoto University in Japan obtained
infrared and high-resolution images of galaxies from 11 billion years ago
using the adaptive optics (AO) system and the infrared camera and
spectrograph (IRCS) on the Subaru Telescope. Thanks to the removal of
atmospheric blur by the AO system, high spatial resolution imaging was
achieved in the near-infrared and the profiles of the distant galaxies
were revealed (Fig. 1). The images of the distant galaxies show almost all
of the galaxies have a light profile similar to the disk galaxies in the
local universe.

In the local universe around our Milky Way galaxy, there are primarily two
types of galaxies: elliptical and disk. Elliptical galaxies have stars
that cluster in shapes ranging from nearly spherical to highly elongated,
and disk galaxies have stars that make a spiral structure on a flattened
disk shape (sometimes called "spiral galaxies", see Note 1). When, why,
and how these galaxies in the local universe establish their current
shapes are some of the biggest mysteries in astronomy. In order to answer
these questions, it is important to observe galaxies as far away as
possible, going back in time tracing their cosmic history examining their
shapes and forms to determine their evolutionary profile.

Thus far, research with the Hubble Space Telescope (HST) has lead studies
into the profiles of distant galaxies. HST observations have revealed that
galaxies seen in the local universe are similar to the galaxies observed 8
billion years ago, and the elliptical and disk type galaxies prevail in
both eras. The important next step in this study of distant galaxies is to
examine shapes of galaxies even further away at an earlier time in the
universe. Subaru found a galaxy at 12.9 billion years ago, which is the
farthest object found so far, using the wide field imaging camera.
However, the difficulty with looking ever deeper into space is that more
distant galaxies have smaller apparent size and smaller actual size,
making their profiles difficult to distinguish. In response to these
hurdles, astronomers used the sophisticated instruments and
state-of-the-art technology of the Subaru Telescope to explore into
galactic realms billions of light years away.

In 2004, a team of Japanese astronomers from the National Astronomical
Observatory of Japan, Tokyo University, and Kyoto University in Japan used
the adaptive optics (AO) system and the infrared camera and spectrograph
(IRCS) instrument on the Subaru Telescope to obtain infrared and
high-resolution images of galaxies further than previously observed. Over
a 12-month period, astronomers looked at 44 very faint objects within 13
fields of view. Their research was based on knowledge that galaxies
consist of stars with various masses, sizes, and ages, and stars whose
masses are similar to the Sun dominate the total masses of stars inside
galaxies. The shapes of galaxies observed in the visible spectrum reflect
their distribution of stars, and, therefore, astronomers think the shapes
represent the "framework" of the galaxies (see Note 2). Consequently,
studying the profiles of the galaxies in near-infrared light was necessary
in order to reveal this "framework" due to the "red shift" effect of the
expanding universe (see Note 3).

This galactic study obtained high spatial resolution near-infrared images
of galaxies from 11 billion years ago. As a result, the profiles and
"frameworks" of these very distant galaxies were revealed for the first
time (Fig. 1). The results show the light distributions of the very
distant galaxies have similar light profiles to the flatter disk galaxies
in the local universe. Only one galaxy shows the light profile barely
similar to the concentrated elliptical galaxies (Fig. 2). Considering the
two types of galaxies seen in the local universe already exist in the
universe 8 billion years ago, the initial findings showed that
concentrated elliptical galaxies formed from the collision and merging of
extended disk galaxies between 11 billion and 8 billion years ago. The
profiles of the galaxies further away infer that the evolution of the
galaxies is drastic between 11 and 8 billion years ago than the present
and 8 billion years ago (Fig. 3).

Currently the AO observation is limited only for targets close to a local
bright star. For the future, galaxies away from bright stars will be
observed using the recently upgraded AO system with artificial laser guide
star at the Subaru Telescope. It is expected that additional observations
of large numbers of distant galaxies will further reveal their history and
morphology, establishing their shapes and profiles seen in the local
universe around our Milky Way.

The results were presented at the international conference "Panoramic
Views of Galaxy Formation and Evolution" in which astronomers discuss
topics related to the formation and evolution of galaxies based mostly on
the observational results from Subaru Telescope. Additionally, the results
will appear in the March 2008 issue of the Astrophysical Journal
Supplement Series

Akiyama, M., Minowa, Y., Kobayashi, N., Ohta, K., Ando, M., Iwata, I.,
2008, Astrophysical Journal Supplement Series, in press.

NOTES

Note 1: You can see the images of typical elliptical and disk galaxies
from
Elliptical galaxy: http://www.nao.ac.jp/Subaru/hdtv/m87w_s.jpg (130KB)
Disk galaxy: http://www.nao.ac.jp/Subaru/hdtv/m63_s.jpg (121KB)

Elliptical galaxies have shapes ranging from nearly spherical to highly
elongated, and disk galaxies have a flattened disk shape. Disk galaxies
are sometimes called spiral galaxies. They have different light
distributions: elliptical galaxies have concentrated light distributions
which appear smooth and featureless, while disk galaxies have extended
light distributions consisting of a flattened disk with stars forming a
spiral structure.

Note 2: Visible light has a wavelength around 0.6 micron and can be
detected with human eyes. Infrared and ultra violet light cannot be
detected with human eyes. Infrared light have wavelength longer than
1.0micron, and ultra-violet light have wavelength shorter than 0.3 micron.
The shapes of galaxies in visible light reflect the distribution of stars
which dominate the total mass of galaxies. On the other hand, the ultra
violet light of galaxies, which is dominated by heavier stars with shorter
life time than the Sun, reflects only the area where currently stars are
born inside the galaxies.

Note 3: The universe is thought to be expanding uniformly. As a result,
more distant galaxies move away faster. If we observe a galaxy from Earth,
the galaxy moving away faster will be observed in longer wavelength. We
call this effect "redshift". Due to this redshift effect, the visible
light from distant galaxies in the early universe is "shifted" to a longer
wavelength and observed in the infrared. Consequently, ultra-violet light
from a distant galaxy will shift and be observed in the visible
wavelength.

IMAGE CAPTIONS:

[Figure1:
http://subarutelescope.org/Pressrele...18/fig01_e.jpg (3MB)]
Profiles and "frameworks" of galaxies from 11 billion years ago revealed
by AO and IRCS at the Subaru Telescope. The high spatial resolution images
are taken at the near-infrared light with wavelength of 2.0 micron. The
white bar at the bottom right indicates the scale of 1 arcsec, which
corresponds to 25,000 light years scale in the distant universe.

[Figure 2:
http://subarutelescope.org/Pressrele...18/fig02_e.jpg (1.5MB)]
These two figures show Indicator of Light Distributions of Galaxies as the
vertical axis and an Indicator of the Size of the Galaxies as the
horizontal axis. The left figure shows the light distributions of the
galaxies at 11 billion years ago. The figure on the right side shows
simulation of how the galaxies at 5 billion years ago look like if we
"bring" them back to 11 billion years ago, based on the images obtained
with HST.

[Figure 3:
http://subarutelescope.org/Pressrele...18/fig03_e.jpg (3MB)]
This figure summarizes the observed evolution of the shapes of galaxies in
the cosmic history. The disk galaxies observed at 11 billion years ago
evolve into elliptical galaxies until 8 billion years ago through
collision and merging of the galaxies. In the universe 8 billion years
ago, there are elliptical- and disk-type galaxies, and it is thought that
the evolution of the galaxies is much more milder between the present and
8 billion years ago than between 11 billion and 8 billion years ago.