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Issued by: Inge Heyer, Public Information Officer Images, notes, and contact details appear below. 8 December 2009 Towards an Exquisite Look at Black HolesUKIRT imaging and Keck interferometry combine to understand the accreting material around supermassive black holes in galactic nucleiAn international research team led by Makoto Kishimoto from the Max Planck Institute for Radio Astronomy in Bonn has combined infrared imaging from the United Kingdom Infrared Telescope (UKIRT) and some of the first ever infrared long-baseline interferometric measurements from the Keck Observatory to observe nearby Active Galactic Nuclei (AGN). The measurements show a ring-like emission from sublimating dust grains, and its radius yields insights into the shape and geometry of the accreting material around the black hole in these galactic centres. In May 2009, Makoto Kishimoto and his team successfully observed four such AGN with the Keck Interferometer, and they followed the observations up with infrared imaging from the UK Infrared Telescope (UKIRT). Both observatories are on Mauna Kea in Hawaii. The target sources included NGC 4151, a relatively nearby galaxy only 50 million light years away, and a distant quasar at redshift 0.108 (corresponding to a distance of more than a billion light years). "The Keck measurements give us a uniquely high-resolution look at the innermost regions of the active nucleus, and the UKIRT images are very powerful in disentangling the contributions of the host galaxy and the accretion disk in the interferometry data", says Makoto Kishimoto, the paper's leading author. Astronomers have been trying to see directly how the supermassive black hole is eating up the surrounding gas and how the strong jet is being launched around the black hole. However, to spatially resolve such a distant object at infrared wavelengths, a telescope having a diameter of 100 m would be required. Instead of building such a huge telescope, a more practical way is to combine the beams from two or more telescopes that are far apart in order to detect an interference pattern of the two beams and infer what the black hole vicinity looks like. "The technique we are using is very new and very demanding in terms of observing conditions and data analysis", says Robert Antonucci from the University of California at Santa Barbara, co-author of the paper. In the future, there will be many telescopes, or a telescope array extended over several kilometers. Such arrays have already been used at radio, but not yet at infrared or optical wavelengths. Optical/infrared interferometry is still in an early stage - currently using two or three telescopes. A prototype array is formed by the two Keck telescopes of 10 m diameter each, the so-called Keck interferometer (KI). UKIRT's wide field camera (WFCAM) was designed primarily as a survey instrument, capable of observing an area of sky the size of the full moon in the space of a few minutes. However it is very well suited to observations of galaxies, and has sufficient resolution to allow astronomers to separate the bright nucleus of the galaxy from the disk of billions of stars in which it is embedded. Importantly, it also has filters spanning a wide range of wavelengths, from just below twice the wavelength of visible light to more than four times that wavelength. Kishimoto and team have used this to their advantage. Professor Gary Davis, Director of UKIRT, says "This is a slightly unusual use of UKIRT's WFCAM, in that it capitalises on some of the lesser-known strengths of the instrument. The wide field of view allows us to observe entire galaxies up close, but it also gives the sharp images required to look at more distant objects. It is wonderful to see two observatories on Mauna Kea joining forces in this way: by combining UKIRT imaging with Keck interferometry we can get a full and detailed view of these esoteric objects." Until recently, only one AGN had been successfully observed with the KI. This galaxy, NGC 4151, is one of the brightest of these sources in the optical and infrared wavelengths. The new, more sensitive observations of four galaxies have led to a much clearer picture of what is being resolved - a ring-like emission of dust grains, co-existing in the accreting gas, which are hot enough to be sublimating. Using different, independent measurements of the radius of this dust sublimation region (which come from the analysis of the variabilities of the optical and infrared light), the team thinks that they have also possibly started to probe how the accreting material is distributed radially from the black hole - i.e. how compact or how extended the material distribution is. "While we have got the highest spatial resolution in the IR, this is still a relatively outer region of the central black hole system", says Makoto Kishimoto. "We hope to achieve an even higher resolution using telescopes that are much further apart in order to get even closer to the centre, and we also hope to observe many other supermassive black hole systems. When we do that, we will once again be calling on infrared imaging to help us disentangle the results." Images
UKIRT infrared images of the four target galaxies. They show "near-infrared color" where the images at different IR wavelengths are assigned to represent red/green/blue colors. WFCAM on UKIRT allows very quick imaging of the entire galaxy, while the Keck interferometer resolves a part of the very inner structure of the bright nucleus. The inferred ring-like structure obtained for NGC4151 at the top-left (scale for 10,000 light-years is shown as an arrow) is depicted in the top-right panel (the ring radius is 0.13 light-years, corresponding to an extremely small ~0.5 milli-arcsecond angular size on the sky). The distance to each galaxy is indicated in million light-years, together with the redshift (z) of each galaxy. Image: M. Kishimoto, galaxy images with United Kingdom Infrared Telescope (UKIRT).
The Wide Field Camera (long black tube) on the United Kingdom Infrared Telescope on Mauna Kea, Hawaii. Credit: UKIRT/JAC.
The United Kingdom Infrared Telescope on Mauna Kea, Hawaii. Credit: UKIRT/JAC.
The Keck interferometer on Mauna Kea, Hawaii. The interferometer consists of two 10m telescopes in separate domes, about 85 m apart. Credit: Keck Observatory.
Notes for EditorsLight YearOne light year is about 10 million million kilometres or 6 million million miles. Infrared LightInfrared wavelengths are longer wavelengths than light waves. They are typically measured in microns, also called micrometres. One micron is one millionth of a metre, one 10000th of a centimetre, or one 25000th of an inch. Visible light has wavelengths around half a micron, while the observations reported here were at wavelengths of about 2 microns. SublimationTo sublimate a substance means to transform it directly from the solid to the gaseous state without going through the liquid stage. Active Galactic Nucleus (AGN)An active galactic nucleus is a compact region at the centre of a galaxy which has a much higher than normal energy output over some or all of the electromagnetic spectrum. A galaxy with an AGN is called an active galaxy. The radiation from AGNs is believed to be a result of accretion of mass by a supermassive black hole at the centre of that galaxy. QuasarA quasar (quasi-stellar object) is a very bright point-like source of light emanating from the centres of massive elliptical galaxies. The quasar's power is provided by the black hole at the galactic core. The light received from the quasar has contributions from both the black hole jets and the accretion disk. If the jet should be pointed at us, the quasar will appear even brighter. Every quasar has a black hole at its core. A galaxy and its black hole have to have sufficient mass, and sufficient "food matter" for the black hole, in order to generate enough power to host a quasar. Quasars were more common in the early universe, as this energy production ends when the supermassive black hole has consumed all of the matter near it. UKIRTThe world's largest telescope dedicated solely to infrared astronomy, the 3.8-metre (12.5-foot) UK Infrared Telescope (UKIRT) is sited near the summit of Mauna Kea, Hawaii, at an altitude of 4194 metres (13760 feet) above sea level. It is operated by the Joint Astronomy Centre in Hilo, Hawaii, on behalf of the UK Science and Technology Facilities Council. UKIRT's technical innovation and privileged position on the high, dry Mauna Kea site have placed it at the forefront of infrared astronomy since its opening in 1979. UKIRT is currently engaged in a world-leading infrared sky survey as well as the type of innovative individual programmes described in this press release. More about the UK Infrared Telescope: http://outreach.jach.hawaii.edu/articles/aboutukirt/ W. M. Keck ObservatoryKeck Observatory operates twin 10-meter optical/infrared telescopes located on the summit of Mauna Kea. Made possible by grants totaling more than $138 million from the W. M. Keck Foundation, Keck I telescope began science observations in 1993, Keck II began in 1996. The vision of the Keck Observatory is a world in which all humankind is inspired and united by the pursuit of knowledge of the infinite variety and richness of the Universe. More about Keck Observatory: https://www.keckobservatory.org/ Science and Technology Facilities CouncilThe Science and Technology Facilities Council is an independent, non-departmental public body of the Office of Science and Innovation which itself is part of the Department of Innovation, Universities and Skills. It was formed as a new Research Council on 1 April 2007 through a merger of the Council for the Central Laboratory of the Research Councils (CCLRC) and the Particle Physics and Astronomy Research Council (PPARC) and the transfer of responsibility for nuclear physics from the Engineering and Physical Sciences Research Council (EPSRC). We are one of seven national research councils in the UK. The Science and Technology Facilities Council is government funded and provides research grants and studentships to scientists in British universities, gives researchers access to world-class facilities and funds the UK membership of international bodies such as the European Organisation for Nuclear Research, CERN, the European Space Agency and the European Southern Observatory. It also contributes money for the UK telescopes overseas on La Palma, Hawaii, Australia and in Chile, the UK Astronomy Technology Centre at the Royal Observatory, Edinburgh and the MERLIN/VLBI National Facility. Media ContactsPlease note that it is best to contact these individuals by email.
Science ContactsPlease note that it is best to contact these individuals by email.
ReferenceThis press release refers to a paper to be published in Astronomy & Astrophysics Web links
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