Press Release

Subaru Discovers an Exploding Galaxy at the Edge of the Universe

By SpaceRef Editor
August 13, 2002
Filed under , ,

Observation:
[http://SubaruTelescope.org/Latestnews/200208/S01B-051/LAEJ1044-0130.jpg
(118KB)]

  • Object Name: High Redshift Starburst Galaxy LAE J1044-0130
  • Telescope: Subaru Telescope / Prime Focus
  • Instrument: Suprime-Cam
  • Filter: Narrow-band (816 nanometers)
  • Date: UT 2002 February 15-17
  • Exposure: 600 min
  • Field of View: 1 arcmin x 1 arcmin
  • Orientation: North up, east left
  • Position: RA(J2000.0) = 10h44.5m, Dec(J2000.0) = -1d31m (Sextant)

Explanation:

A collaboration led by astronomers from Tohoku University in Japan
has used Subaru Telescope to discover a galaxy rapidly forming
stars when the Universe was less than a billion years old. Images
and spectra from the Subaru and Keck telescopes reveal that the
galaxy has a high-speed outflow of hydrogen gas believed to be
caused by a massive burst of star formation. The galaxy is more
than 14 billion light years from Earth, and is currently the most
distant galaxy known to harbor such a phenomenon. Studying such
distant galaxies is made possible by combining careful technique
and large telescopes, and is expected to reveal how galaxies are
born and evolve in the early stage of the Universe.


The newly discovered galaxy is so far away that the light which
is now reaching Earth began its journey 14 billion years ago.
Only large telescopes like Subaru can collect enough light to
observe these very faint and distant galaxies to study what the
Universe was like in its infancy. Because the Universe is
expanding, the light emitted from these distant galaxies is
stretched out to longer wavelengths as it travels toward us, a
phenomenon astronomers call redshift. The further an object is
from us, the greater its redshift.

Hoping to find star-forming galaxies at the farthest reaches of
the Universe, the team (including Tohoku University graduate
student Masaru Ajiki and associate professor Yoshiaki Taniguchi,
researchers at the National Astronomical Observatory of Japan
(NAOJ), the University of Tokyo, the University of Hawaii, and
the University of Maryland) installed a special filter (NB816)
into Subaru’s prime focus camera, Suprime-Cam, and observed a
region of sky about the size of the full moon around a distant
quasar named SDSSp J104433.04-012502.2 in the constellation
Sextant. Quasars are believed to be objects powered by black
holes about a billion times the mass of the Sun and, due to
their extreme luminosities, can be readily discovered even at
very large distances. The special filter was designed to
transmit only a very narrow color range of light around 800
nanometers which, for galaxies at the same distance as the
quasar, includes an emission line (called Lyman-alpha) which
is produced when gas is heated by vigorous star formation.

After a 10-hour observation in February 2002, more than 15
galaxies were discovered which could only be seen in the image
taken through the narrow filter. One of these galaxies was
then observed with Subaru’s Faint Object Camera and Spectrograph
(FOCAS) in March 2002, which confirmed that it was a very
distant galaxy. Additional, more detailed, observations with
the Echellette Spectrograph and Imager (ESI) on the Keck II
telescope supported the Subaru results and indicated that
hydrogen gas is flowing from the galaxy at speeds of several
hundred kilometers per second.

Stars more than about 10 times the mass of our Sun end their
lives in vast explosions called supernovae. When many such
stars are being formed in a short space of time, the combined
force of these explosions can cause gas to be ejected out of
the galaxy. Such an outflow, called a “superwind”, can be seen
in the nearby galaxy Messier 82. If the outflow seen in this
young galaxy is also produced by a superwind, it would be the
most distant example of this phenomenon yet discovered and
would mean that large-scale star formation must have begun
within several hundred million years after the start of the
Universe.

By discovering more distant galaxies and studying them in detail,
astronomers expect to learn what galaxies were like when the
Universe was very young, and understand how they are born and
evolve. Says Professor Taniguchi, “For the past 15 years while
Subaru was being planned and built, Keiichi Kodaira [former
Director of NAOJ and now President of the Graduate University
for Advanced Studies] and I have had a dream to look at distant
galaxies, more than 10 billion light years away. At last that
dream has come true.”

These results will be published in the September 1, 2002 issue
of The Astrophysical Journal.

Figure 1:
[http://SubaruTelescope.org/Latestnews/200208/S01B-051/figure1e.jpg]
Thumbnail images and spectral energy distribution of the galaxy,
named LAE J1044-0130 (LAE stands for Lyman-alpha emitter). The
upper row shows images of the galaxy in different filters and
the middle row shows contour maps of the images above them. The
galaxy, at the center of the circle, appears clearly in the
image taken with the special NB816 filter, but is barely
detectable in the other filters. The brighter object to the
upper left of the galaxy is a foreground galaxy only 7 billion
light years away.

The lower panel plots the amount of light detected in each filter
in units of magnitude as a function of wavelength. (Note that
wavelengths of each filter do not align with the image panels
above.) This plot, called the spectral energy distribution, shows
that the galaxy is brightest in the wavelength region of the
special filter, NB816.

Copyright (c) 1999-2002 Subaru Telescope, NAOJ. All rights reserved.

Figure 2:
[http://SubaruTelescope.org/Latestnews/200208/S01B-051/figure2e.jpg]
Spectra of LAE J1044-0130 taken by FOCAS on the Subaru Telescope
on March 11, 2002 UT (upper panel) and March 13, 2002 UT (lower
panel). The spectrum in the upper panel clearly detects the
emission line. In the higher resolution spectrum in the lower
panel, the line shows a slight broadening on its longer
wavelength side (right). This “red wing” suggests the presence
of superwinds in the galaxy.

Copyright (c) 1999-2002 Subaru Telescope, NAOJ. All rights reserved.

Figure 3:
[http://SubaruTelescope.org/Latestnews/200208/S01B-051/figure3e.jpg]
Spectrogram and spectra obtained with Keck II Telescope’s ESI on
March 15, 2002 UT. The spectrogram in the upper panel shows emission
as a function of wavelength and position along a slit placed to
detect light from the galaxy LAE J1044-0130 and the foreground
galaxy. The galaxy LAE J1044-0130 is particularly bright at a
wavelength of 8130 angstroms. The spectrum in the middle panel
clearly shows the line and its red wing.


Comparing the spectrum in the middle panel with the spectrum of
the emission lines in the night sky (OH air glow) in the bottom
panel confirms that the detection is real.


Copyright (c) 1999-2002 Subaru Telescope, NAOJ. All rights reserved.

SpaceRef staff editor.