SOFIA Confirms a Spiral Galaxy's Invisible, Opposing Arms

Hubble Space Telescope image of NGC 7479 created from observations at visible and near-infrared wavelengths with 20 cm radio continuum contours in yellow. The boxes highlight the ends of the lower and upper counter-arms; expanded versions of these regions are shown in the left and right panels where the circles depict the aperture of SOFIA’s FIFI-LS instrument. Credit: ESA/Hubble & NASA

Columbia, MD—November 29, 2021. NGC 7479, also known as Caldwell 44, is a barred spiral galaxy, with a bar-shaped center filled with stars (as is characteristic of a majority of spiral galaxies), and S- shaped arms. However, looking at features of NGC 7479 that are hidden from the naked eye reveals another pair of arms bending in an opposite direction to the visible galaxy. The Stratospheric Observatory for Infrared Astronomy (SOFIA) observed ionized carbon emissions to help confirm these counter-arms. The results were published in The Astrophysical Journal.

Radio wavelength emissions from these small, so-called “counter-arms” have been observed before, but with the help of SOFIA – along with observations by ALMA and archival data from a number of other observatories – their presence has now been confirmed by X-ray, ionized carbon, and carbon monoxide emissions as well. SOFIA’s new observations of the counter-arms can help reveal their origin.

Universities Space Research Association's Dario Fadda, the lead author of the paper, noted,“The really important thing in this galaxy are the two little counter-arms that go in the opposite direction of the optical arms that are seen in radio, but nobody had seen them in the X-ray. Seeing them in X-ray is important because it shows there’s energy coming out of the nucleus, something that comes out in jets that originate in the nucleus.”

The fact that these jets originate at the galaxy’s center implies the galaxy harbors an active nucleus – a supermassive black hole.

As the jet approaches the dense molecular clouds along the bar, some of its momentum is absorbed by the clouds, causing the jet to bend in the direction opposite to the rotation of the galaxy. This process is responsible for the orientation of the counter-arms.

By comparing the X-ray emissions of the jet to the ratio of ionized carbon and carbon dioxide emissions from the same area – both of which are considered indicators of star formation – the researchers discovered an anomaly. Certain hotspots within the counter-arms have too much ionized carbon, meaning the X-ray emission cannot entirely be explained by star formation.

“We knew about these counter-arms and tried to observe with SOFIA if ionized carbon is actually produced by star formation, or if there’s some extra component that can come from the energy injected by the active galactic nucleus,” said Fadda.

This calls into question the relationship between ionized carbon and star formation, and can have implications on the study of galaxies that are more distant than NGC 7479.

“This is where SOFIA becomes uniquely useful: Studying these cases of galaxies close to us to have an idea of what to encounter when we go to higher redshift to study galaxies and the farther universe,” Fadda said.NGC 7479

SOFIA’s role in these observations pushes the limits of its capabilities. Primarily suited for studying objects fairly close to our home galaxy, SOFIA’s spatial and spectral resolution were just enough to distinguish ionized carbon in NGC 7479’s region of interest. Specifically, SOFIA’s Far Infrared Field-Imaging Line Spectrometer (FIFI-LS) was used to map the ionized carbon in the area.

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About USRA

Founded in 1969, under the auspices of the National Academy of Sciences at the request of the U.S. Government, the Universities Space Research Association (USRA), is a nonprofit corporation chartered to advance space-related science, technology and engineering. USRA operates scientific institutes and facilities, and conducts other major research and educational programs. USRA engages the university community and employs in-house scientific leadership, innovative research and development, and project management expertise. More information about USRA is available at www.usra.edu

About SOFIA

SOFIA is a joint project of NASA and the German Space Agency at DLR. DLR provides the telescope, scheduled aircraft maintenance, and other support for the mission. NASA’s Ames Research Center in California’s Silicon Valley manages the SOFIA program, science, and mission operations in cooperation with the Universities Space Research Association, headquartered in Columbia, Maryland, and the German SOFIA Institute at the University of Stuttgart. The aircraft is maintained and operated by NASA’s Armstrong Flight Research Center Building 703, in Palmdale, California.

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Contact:

Suraiya Farukhi, Ph.D.
Director, External Communications
sfarukhi@usra.edu
443-812-6945

Source: University Space Research Association (USRA)/Newsroom

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Subaru Telescope's Prime Focus Camera Suprime-Cam Takes Its Final Data

Figure 1: Barred spiral galaxy NGC 7479 was Suprime-Cam's final target from Subaru Telescope. This color image is a composite of g', r', i', and NA656 band images. (Credit: NAOJ, Data processed by Dr. Ichi Tanaka)

Suprime-Cam, the wide-field imager mounted at the primary focus of the Subaru Telescope, had its final night of observation on May 29, 2017. The instrument's wide-field imaging capability – 200 times larger than that of Hubble Space Telescope – coupled with sensitive CCD detectors, Subaru's large mirror, and superb weather conditions on Maunakea, gave Suprime-Cam unique imaging power. Some scientists consider it to be the driving force of modern observational astronomy. Since its first observation in 1999, Suprime-Cam made countless discoveries, and has repeatedly broken a world record for the most distant galaxy ever observed.

Three groups of scientists came together for Suprime-Cam's final night of observation, and spotted asteroids, galaxies, and supermassive black holes. Before sunrise, the observers held a ceremony and celebrated the camera's contributions to astronomy.

At the remote observing room in the headquarters of the National Astronomical Observatory of Japan (NAOJ) in Mitaka, Tokyo, astronomers and engineers gathered to share the experience. One of them was Professor Sadanori Okamura from Hosei University, a key figure in the development of Suprime-Cam. Professor Okamura shared stories of the trials, tribulations, and triumphs, that contributed to the camera's successful journey. 

Suprime-Cam's final target was NGC 7479, a barred spiral galaxy about 100 million light-years away in the direction of the constellation Pegasus. Professor Okamura first observed this galaxy in 1970s at the Okayama Astrophysical Observatory in Japan for a morphological study. He built the basis for galaxy imaging observations in Japan, and his work was internationally recognized. He also advanced extragalactic astronomy by using wide-field imaging observations, and his research activities directly led to Suprime-Cam's development.

NGC 7479 had never been observed by the Subaru Telescope. The resulting image shows clear and detailed structures of a star-forming region that was not visible in 1970s photographic plates. This high-quality imaging data was the "Final Light" that Suprime-Cam captured, and it will create opportunities for even more study.

Figure 2: Observation team pointing the telescope to Suprime-Cam's final target: NGC 7479.

Credit: NAOJ

The Subaru Telescope was specially built to mount Suprime-Cam at its prime focus at the top of the telescope. That placement allows a wide field of view, an arrangement unique to the Subaru Telescope. The technological advancements and expertise that emerged from Suprime-Cam have been inherited by its successor, the Hyper Suprime-Cam (HSC).

With a field of view seven times larger than Suprime-Cam, HSC has been in operation for open use since March 2014. "HSC has already brought revolutionary results in various astronomical fields," said Professor Okamura, "and it is the world's most powerful wide field imaging camera. After Suprime-Cam, I expect HSC will pioneer new advances in observational astronomy."

Figure 3: Many people gathered at the remote observing room in Mitaka, Tokyo (left) and at the summit observing room on Maunakea (right) to watch the final observations made by Suprime-Cam on Subaru Telescope.

Source: Subaru Telescope

Spiral Spins Both Ways

NGC 7479

Credit:ESA/Hubble & NASA

In this NASA/ESA Hubble Space Telescope image of NGC 7479 — created from observations at visible and near-infrared wavelengths — the tightly wound arms of the spiral galaxy create an inverted ‘S’, as they spin in an anticlockwise direction. However, at radio wavelengths, this galaxy, sometimes nicknamed the Propeller Galaxy, spins the other way, with a jet of radiation that bends in the opposite direction to the stars and dust in the arms of the galaxy.

Astronomers think that the radio jet in NGC 7479 was put into its bizarre backwards spin following a merger with another galaxy.

Star formation is reignited by galactic collisions, and indeed NGC 7479 is undergoing starburst activity, with many bright, young stars visible in the spiral arms and disc. The three brightest stars in this image, however, are foreground stars — caught on camera because they lie between the galaxy and Hubble.

This striking galaxy is easily visible in moderate telescopes as an elongated fuzzy patch of light. The spiral arms can be seen with more difficulty in larger telescopes under dark conditions.

This picture was created from images taken with the Wide Field Channel of Hubble’s Advanced Camera for Surveys. Images through a yellow filter (F555W, coloured blue) were combined with images taken in the near-infrared (F814W, coloured red). The total exposure times were 520 s per filter and the field of view is 2.7 arcminutes across.