A decade ago, Hubble images of the
massive cluster of galaxies Abell 1689,
a powerful gravitational lens, showed
a highly magnified background gal-
axy, designated A1689B11, displaying
spiral structure. Soon afterwards, its
redshift was measured to be z = 2.5,
implying a distance of 11 billion light
years. This made it the most distant
galaxy that appeared to be spiral in na-
ture and indicated that spirals existed
less than 3 billion years after the Big
Bang. Most galaxies at such distances
are irregular in appearance, and even
the more regular ones generally lack
evidence of ordered rotation when
their kinematics are studied through
integral-field spectroscopy. Thus, ki-
nematic confirmation of the spiral nature of
A1689B11 was essential.
Taking advantage of the gravitational magni-
fication by a factor of 7, the team of astrono-
mers from Australia, France, and the United
States (led by Tiantian Yuan of Swinburne
University) used NIFS on Gemini North to
map the internal gas distribution and veloci-
ty structure of A1689B11 (Figure 1). Although
the galaxy is furiously forming stars at a rate
nearly 20 times that of the Milky Way (similar
to other galaxies of these early cosmic times),
the gas kinematics trace out a “tranquil veloc-
ity field” with an ordered rotation of 200 km/s,
very close to the rotation speed of the Milky
Way. They also show a very small dispersion
about this mean value. This makes A1689B11
the most distant kinematically confirmed
spiral, and only the second one at a distance
beyond 10 billion light years. These primitive
spirals mark the formation epoch of galaxies
like our own Milky Way.
The team’s findings appear in a paper pub-
lished in The Astrophysical Journal.
January 2018
A Binary Supermassive Black
Hole System Far Beyond
Andromeda
Figure 1.
Upper left: Hubble
Space Telescope (HST)
image and intensity
map of the lensed spiral
galaxy A1689B11. The
Gemini NIFS field-of-
view is outlined.
Upper right: Intensity
map of redshifted Hα
emission (from an
atomic transition in
hydrogen) as measured
by NIFS.
Lower left: The
NIFS velocity map
for hydrogen gas in
A1689B11, showing
the rotation speed of
200 km/s.
Lower right: NIFS
velocity dispersion
map, showing the
dispersion (velocity
deviations) from the
smooth rotation. The
velocity deviations are
generally less than 10%
of the rotation velocity,
indicative of a very
orderly rotation pattern.
Researchers from the University of Washing-
ton were searching Local Group galaxies for
a “still-theoretical class of exotic stellar bi-
nary” composed of two red supergiant stars
when they stumbled on what may be an
even more exotic type of binary — one com-
posed of a pair of supermassive black holes.
The search, led by Trevor Dorn-Wallenstein,
a doctoral student at the University of Wash-
ington, involved matching possible red su-
pergiants with Chandra X-ray sources and
turned up one object of interest, apparen tly
residing in the outer disk of the spiral galaxy
M31, also known as the Andromeda Galaxy.
This chimera-like object, referred to as
J0045+41, had previously been classified in
one study as an eclipsing stellar binary be-
cause of its optical variability. Other studies
had classified it as a globular star cluster in
M31 because of its brightness and notice-
ably extended appearance. Its X-ray prop-
erties were consistent with being either an
X-ray emitting binary star in M31 or an ac-
tive galactic nucleus (AGN) in the far back-
GeminiFocus
9