From ALMA: “ALMA Sees Einstein Ring in Stunning Image of Lensed Galaxy”

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ESO ALMA Array
ALMA

07 April 2015
Valeria Foncea
Education and Public Outreach Officer
Joint ALMA Observatory
Santiago, Chile
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Email: vfoncea@alma.cl

Charles E. Blue
Public Information Officer
National Radio Astronomy Observatory
Charlottesville, Virginia, USA
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Cell: +1 434.242.9559
E-mail: cblue@nrao.edu

Richard Hook
Public Information Officer, ESO
Garching bei München, Germany
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Cell: +49 151 1537 3591
Email: rhook@eso.org

Masaaki Hiramatsu
Education and Public Outreach Officer, NAOJ Chile
Observatory Tokyo, Japan
Tel: +81 422 34 3630
E-mail: hiramatsu.masaaki@nao.ac.jp

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ALMA image of the gravitationally lensed galaxy SDP.81. The bright orange central region of the ring (ALMA’s highest resolution observation ever) reveals the glowing dust in this distant galaxy. The surrounding lower-resolution portions of the ring trace the millimeter wavelength light emitted by carbon monoxide. Credit: ALMA (NRAO/ESO/NAOJ); B. Saxton NRAO/AUI/NSF

Astronomers have discovered that a distant galaxy — seen from Earth with the aid of a gravitational lens — appears like a cosmic ring, thanks to the highest resolution images ever taken with the Atacama Large Millimeter/submillimeter Array (ALMA).

Forged by the chance alignment of two distant galaxies, this striking ring-like structure is a rare and peculiar manifestation of gravitational lensing as predicted by Albert Einstein in his theory of general relativity.

Gravitational lensing occurs when a massive galaxy or cluster of galaxies bends the light emitted from a more distant galaxy, forming a highly magnified, though much distorted image. In this particular case, the galaxy known as SDP.81 and an intervening galaxy line up so perfectly that the light from the more distant one forms a nearly complete circle as seen from Earth.

Discovered by the Herschel Space Observatory, SDP.81 (formally known as HATLAS J090311.6+003906) is an active star-forming galaxy nearly 12 billion light-years away, seen at a time when the Universe was only 15 percent of its current age.

ESA Herschel
ESA/Herschel

It is being lensed by a massive foreground galaxy that is a comparatively nearby 4 billion light-years away.

“Gravitational lensing is used in astronomy to study the very distant, very early Universe because it gives even our best telescopes an impressive boost in power,” said ALMA Deputy Program Scientist Catherine Vlahakis. “With the astounding level of detail in these new ALMA images, astronomers will now be able to reassemble the information contained in the distorted image we see as a ring and produce a reconstruction of the true image of the distant galaxy.”

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ALMA/Hubble composite image of the gravitationally lensed galaxy SDP.81. The bright orange central region of the ring (ALMA’s highest resolution observation ever) reveals the glowing dust in this distant galaxy. The surrounding lower-resolution portions of the ring trace the millimeter wavelength light emitted by carbon monoxide. The diffuse blue element at the center of the ring is from the intervening lensing galaxy, as seen with the Hubble Space Telescope. Credit: ALMA (NRAO/ESO/NAOJ); B. Saxton NRAO/AUI/NSF; NASA/ESA Hubble, T. Hunter (NRAO)

The new SDP.81 images were taken in October 2014 as part of ALMA’s Long Baseline Campaign, an essential program to test and verify the telescope’s highest resolving power, achieved when the antennas are at their greatest separation: up to 15 kilometers apart.

The highest resolution image of SDP.81 was made by observing the relatively bright light emitted by cosmic dust in the distant galaxy. This striking image reveals well-defined arcs in a pattern that hints at a more complete, nearly contiguous ring structure. Other slightly lower-resolution images, made by observing the faint molecular signatures of carbon monoxide and water, help complete the picture and provide important details about this distant galaxy.

Though this intriguing interplay of gravity and light in SDP.81 has been studied previously by other observatories, including radio observations with the Submillimeter Array and the Plateau de Bure Interferometer, and visible light observations with the Hubble Space Telescope, none has captured the remarkable details of the ring structure revealed by ALMA.

Submillimeter Array Hawaii SAO
CfA/Submillimeter Array

IRAM
IRAM/Plateau de Bure Interferometer

NASA Hubble Telescope
NASA/ESA Hubble

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ALMA’s highest resolution image ever reveals the dust glowing inside the distant galaxy SDP.81. The ring structure was created by a gravitational lens that distorted the view of the distant galaxy into a ring-like structure. Credit: ALMA (NRAO/ESO/NAOJ)

“The exquisite amount of information contained in the ALMA images is incredibly important for our understanding of galaxies in the early Universe,” said astronomer Jacqueline Hodge with the National Radio Astronomy Observatory in Charlottesville, Va. “Astronomers use sophisticated computer programs to reconstruct lensed galaxies’ true appearance. This unraveling of the bending of light done by the gravitational lens will allow us to study the actual shape and internal motion of this distant galaxy much more clearly than has been possible until now.”

For these observations, ALMA achieved an astounding maximum resolution of 23 milliarcseconds, which is about the same as seeing the rim of a basketball hoop atop the Eiffel Tower from the observing deck of the Empire State Building.


Animation demonstrating how the gravity from a massive foreground galaxy can bend the light of a more distant galaxy. If the two galaxies line up just right, the result is a highly distorted image of the distant galaxy known as an Einstein ring. The radio image portion of the video is of galaxy SDP.81, which was imaged by ALMA as part of the telescope’s Long Baseline Campaign. Credit: NRAO/AUI/NSF; ALMA (NRAO/ESO/NAOJ); Dana Berry / SkyWorks

SDP.81 is one of five targets selected for study during the ALMA Long Baseline Campaign. The others include the protoplanetary disk HL Tau, the asteroid Juno, the star Mira, and the quasar 3C138.

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HL Tau, This is the sharpest image ever taken by ALMA — sharper than is routinely achieved in visible light with the NASA/ESA Hubble Space Telescope. It shows the protoplanetary disc surrounding the young star HL Tauri. These new ALMA observations reveal substructures within the disc that have never been seen before and even show the possible positions of planets forming in the dark patches within the system.

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Juno seen at four wavelengths with a large crater in the dark (Hooker telescope, 2003)

Mt Wilson 100 inch Hooker Telescope
Mt Wilson 100 inch Hooker Telescope Interior
Mt Wilson Observatory/Hooker telescope

Papers describing these publicly available data and the overall outcome of the ALMA Long Baseline Campaign are to be published in the Astrophysical Journal, Letters.

More information

The paper, ALMA Long Baseline Observations of the Strongly Lensed Submillimeter Galaxy HATLAS J090311.6+003906 at z=3.042, is located here: http://arxiv.org/abs/1503.02652

See the full article here .

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The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA is funded in Europe by the European Organization for Astronomical Research in the Southern Hemisphere (ESO), in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and in East Asia by the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Academia Sinica (AS) in Taiwan.

ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

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