GeminiFocus January 2018 - Page 11

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