Extended Lyman-Alpha Blob Himiko

Ouchi et al, 2009;
Subaru, NAOJ, NASA

Larger and field composite
false-color images.

Located around 12.9 billion light-years
away, this unusually large "blob" is
composed of mostly hydrogen gas, stars,
and possibly at least one supermassive
black hole (more).

Breaking News

On June 24, 2009, astronomers (including James Geach and Dave Alexander) announced that at least five of 29 glowing clouds of gas found in huge Lyman-Alpha blobs (like Himiko -- more below) observed around 12 billion light-years away in the direction of Constellation Aquarius ("SSA22 field") may be heated by galaxies bursting with star formation and powered by supermassive black holes (NASA / CXC press release; Geach et al, 2009; Rachel Courtland, New Scientist, June 24, 2009; and Astronomy Picture of the Day). These black holes blast out bi-polar jets of particles and radiation that may be heating and so should be hampering the extragalactic gas around these galaxies from falling inwards. Found when the universe was only two billion years old (some 15 percent of its present age), each blob is several hundred thousand light-years across.

Melissa Weiss;
Geach et al, 2009;
Matsuda et al, 2007;
Chapman et al, 2004;
NAOJ; STScI; CXC;
JPL/CalTech; NASA

Larger composite
image and illustration
of starburst galaxy
with black hole jets.

One of the brightest
SSA22, Lyman-Alpha
blobs with an active
galactic black hole
(blue) towards
Constellation Aquarius
around 12 billion
years ago (more).

Since their discovery about 10 years ago, Lyman-Alpha blobs were found to be optically bright but the mechanism by which they were set aglow was unknown. In the early cosmos, galaxies are believed to form when hydrogen and helium gas flows inwards under the pull of gravity and cooling from radiation emissions. However, this process should stop when the surrounding gas is sufficiently heated by radiation from stellar formation, powerful supernovae that cause outflows from galaxies, and the powerful of central black holes. Glowing Lyman-Alpha blobs could be a result of the first stage of galaxy formation with gas inflows, or of a second stage when gas becomes too warm to flow towards galaxies. The new x-ray observations indicate that the blobs are being heated by the vigorous growth of supermassive black holes and bursts of star formation, and so imply that the blobs represent a stage when the galaxies and black holes are just starting to switch off their rapid growth when heating processes become sufficiently powerful, in a crucial stage of the evolution of galaxies and black holes known as "feedback."

Extended Lyman-Alpha Blobs

Extended Lyman-Alpha Blobs are huge luminous bodies of gas emitting the Lyman-alpha emission line (the ultraviolet wavelength of light produced by ionized hydrogen gas when their electrons lose a certain level of energy) that has been redshifted into the optical or near-infrared wavelengths. They were first detected some time around 1996 to 2000 as hazy galactic haloes in visible-light telescopes. These huge blobs exhibit a very faint continuum of "almost monochromatic emission" and are relatively weak in radiowaves (Smith and Jarvis, 2007; Steidel et al, 2000; and Francis et al, 1996).

GSFC, NASA

Larger and jumbo animation stills.

In 2004, an enormous filament or string of bright and energetic
galaxies and gas (and non-luminous "dark" matter) some 300
million light-years (ly) long and 50 million ly wide was found
in southern Constellation Grus when the cosmos was 10.8 billion
years old (more).

Subsequent observations have revealed that these blobs are extremely bright in infrared light and may contain dusty but exceptionally energetic galaxies with massive rates or starbirth (2005 Spitzer press release). Some blobs may be precursors to galaxies, where primordial gas accretes towards the center or haloes through gravitational cooling of hydrogen gas that eventually leads to massive bursts of stellar formation. In 2005, on the other hand, evidence that at least two of the largest known blobs are envelopes of hot ionized gas that were expelled from merging or developing galaxies (with either massive starbursts or a radio-loud, active galactic nuclei) within them was obtained in infrared and X-ray studies (Ouchi et al, 2009). Extending as wide as 400,000 light-years across, these blobs have been found mostly at distances when the universe was only 2 to 3 billion years old (mostly at z=2-3), which makes it difficult to determine whether they are precursors to galactic formation or, instead, the product of very active galactic starburst or merger activity. Typically, they are located within cosmological filaments (or "strings") of luminous blobs and galaxies that may extend 200 million light-years or more.

SSC, JPL, Caltech, NASA

Larger visible (left) and
infrared composite image.

In 2005, four blobs in a filament some
11 billion years ago were observed in
infrared light to contain dusty but
energetic galaxies with massive rates
of starbirth. of which at least two
were merging together (more).

Himiko

On April 22, 2009, astronomers announced the discovery of the most ancient Lyman-alpha blob found thus far at a high cosmological redshfit (z=6.95), using a diverse but complementary suite of telescopes (Subaru press release). The extended Lyman-alpha blob has been named "Himiko," in honor of a legendary Queen of ancient Japan. Himiko was found by a group of researchers led by Masami Ouchi at the Carnegie Institution who searched among 207 distant galaxy candidates (Lyman-Alpha Emitters) in Constellation Cetus using the Subaru Telescope at the peak of Mauna Kea in Hawaii from 2005 to 2007 (Ouchi's PDF presentation of Subaru Wide-Deep Field Survey). It is the most distant Lyman-alpha Blob ever found and the fourth most distant object ever detected (after the 2006 discovery of Galaxy IOK-1 at a slightly farther redshift of z=6.964).

Ouchi et al, 2009;
DEIMOS, Keck

Larger image and spectrum.

Himiko is a very large and
ancient object, even among
Lyman-alpha blobs or early
galaxies (more).

Himiko was found at a distance of 12.9 billion light-years. This was an age when the universe was only around 800 million years old (6 percent of its present age of 13.7 billion years), which was towards the end of a transition point in the evolution of the universe called the Reionization Epoch, that is nearby as as far back as is possible to observe to date. Reionization occurred between about 200 million and one billion years after the Big Bang, when neutral hydrogen began to form quasars, stars, and the first galaxies, and characteristic hydrogen signatures become prominent from the scattering of photons created by ionized gas clouds.

Djorgovski et al, 2006;
Digital Media Center, CalTech

Larger and jumbo illustrationa.

Himiko was found at an early age
when the universe was near the
end of the Epoch of Reionization.

Around half the width of the Milky Way Galaxy (55,000 light-years) or 17,000 parsecs), Himiko may contain around 40 billion Solar-masses. If so, Himiko is 10 times larger than any other galaxy found so early after the Big Bang. Indeed, its large size may pose a challenge to some accepted current cosmological models (i.e., the "Concordance" or Lambda Cold Dark Matter model), which hypothesize that massive cosmological objects tend to grow up slowly over time via mergers and so should not have bulk up to Himiko's size only 800 million years after the Big Bang. (Subaru press release; and Ouchi et al, 2009).

Himiko's exact nature as an early galaxy is not yet clear. Its unusual luminosity may be due to: gas falling into a supermassive black hole at its center; the heat of an intense burst of star formation; the merger of two or more galaxies; or a developing galaxy that is gobbling up a large amount of gas. Using infrared data from the Spitzer Space Telescope and the United Kingdom Infra-Red Telescope, radio data from the NRAO's Very Large Array (VLA), and X-ray imaging from the XMM-Newton satellite, the astronomers were able to estimate the star-formation rate and stellar mass of this galaxy. A clear determinatio of whether Himiko contains an active nucleus powered by a super-massive black hole, however, will require future X-ray observations. Higher-resolution images should also help discern whether Himiko hides a pair (or more) of merging galaxies, possibly with the Hubble Space Telescope's new Wide Field Camera 3, which is scheduled to be installed in May 2009 with a Space Shuttle crew (more available from: Subaru press release; Rachel Courtland, New Scientist, April 22, 2009; Jason Palmer, BBC News, April 22, 2009; and Ouchi et al, 2009).

Other Information

Up-to-date technical summaries on this object may soon become available at: NASA's ADS Abstract Service for the Astrophysics Data System; the SIMBAD Astronomical Database mirrored from CDS, which may require an account to access; and the NSF-funded, arXiv.org Physics e-Print archive's search interface.

In Greek mythology, Cetus is supposed to be the sea monster that would have devoured the "chained maiden," Andromeda, if Perseus had not come to the rescue. For more information and an illustration about the stars and objects in this constellation, go to Christine Kronberg's Cetus. For another illustration, see David Haworth's Cetus.