Academia Sinica Institute of Astronomy and Astrophysics

Hilo, HI, United States

Academia Sinica Institute of Astronomy and Astrophysics

Hilo, HI, United States
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Bower G.C.,Academia Sinica Institute of Astronomy and Astrophysics | Dexter J.,Max Planck Institute for Extraterrestrial Physics | Markoff S.,University of Amsterdam | Rao R.,Academia Sinica Institute of Astronomy and Astrophysics | Plambeck R.L.,University of California at Berkeley
Astrophysical Journal Letters | Year: 2017

Millimeter-wavelength polarimetry of accreting black hole systems can provide a tomographic probe of the accretion flow on a wide range of linear scales. We searched for linear polarization in two low-luminosity active galactic nuclei (LLAGNs), M81 and M84, using the Combined Array for Millimeter Astronomy and the Submillimeter Array. We find upper limits of ∼1%-2% averaging over the full bandwidth and with a rotation measure (RM) synthesis technique. These low polarization fractions, along with similarly low values for LLAGNs M87 and 3C 84, suggest that LLAGNs have qualitatively different polarization properties than radio-loud sources and Sgr A∗. If the sources are intrinsically polarized and then depolarized by Faraday rotation, then we place lower limits on the RM of a few times 107 rad m-2 for the full bandwidth case and ∼109 rad m-2 for the RM synthesis analysis. These limits are inconsistent with or marginally consistent with expected accretion flow properties. Alternatively, the sources may be depolarized by cold electrons within a few Schwarzschild radii from the black hole, as suggested by numerical models. © 2017. The American Astronomical Society. All rights reserved.


News Article | February 28, 2017
Site: www.eurekalert.org

Figuring out the fate of the Universe is one step closer. The first massive dataset of a "cosmic census" is released using the largest digital camera on the Subaru Telescope. Beautiful images are available for public at large. The first dataset from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) was released to the public on February 27th, 2017. HSC-SSP is a large survey being done using HSC, which is an optical imaging camera mounted at the prime focus of the Subaru Telescope. HSC has 104 scientific CCDs (for a total of 870 million pixels) and a 1.77 square-degree field of view. The National Astronomical Observatory of Japan (NAOJ) has embarked on the HSC-SSP survey in collaboration with the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) in Japan, the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) in Taiwan, and Princeton University in the United States. The project will take 300 nights over 5-6 years. This survey consists of three layers; Wide, Deep, and UltraDeep, using optical and near infrared wavelengths in five broad bands (g, r, i, z, y) and four narrow-band filters. This release includes data from the first 1.7 years (61.5 nights of observations beginning in 2014). The observed areas covered by the Wide, Deep, and UltraDeep layers are 108, 26, and 4 square degrees, respectively. The limiting magnitudes, which refer to the depth (Note) of the observations, are 26.4, 26.6 and 27.3 mag in r-band (about 620 nm wavelength), respectively, allowing observations of some of the most distant galaxies in the universe. In the multi-band images, images are extremely sharp, with star images only 0.6 to 0.8 arcseconds across. 1 arcsecond equals 3600th part of a degree. These high-quality data will allow a unprecedented view into the nature and evolution of galaxies and dark matter. This first public dataset already contains 70 million galaxies and stars. It demonstrates that HSC-SSP is making the most of the performance of the Subaru Telescope and HSC. In 2015, using HSC observations over 2.3 square degrees of sky, nine clumps of dark matter, each weighing as much a galaxy cluster were discovered from their weak lensing signature (Miyazaki et al. 2015, ApJ 807, 22, "Properties of Weak Lensing Clusters Detected on Hyper Suprime-Cam 2.3 Square Degree Field"). The HSC-SSP data release covers about 50 times more sky than was used in this study, showing the potential of these data to reveal the statistical properties of dark matter. The total amount of data taken so far comprises 80 terabytes, which is comparable to the size of about 10 million images by a general digital camera. Since it is difficult to search such a huge dataset with standard tools, NAOJ has developed a dedicated database and interface for ease of access and use of the data. "Since 2014, we have been observing the sky with HSC, which can capture a wide-field image with high resolution," said Dr. Satoshi Miyazaki, the leader of the HSC-SSP. "We believe the data release will lead to many exciting astronomical results, from exploring the nature of dark matter and dark energy, as well as asteroids in our own solar system objects and galaxies in the early universe. SSP team members are now preparing a number of scientific papers based on these data. We plan to publish them in a special issue of the Publications of Astronomical Society of Japan. Moreover, we hope that interested members of the public will also access the data and enjoy the real universe imaged by the Subaru telescope, one of the largest the world." "Depth" of an observation refers to how dim objects can be studied. The light collection power of large aperture mirror (8.2 m for the Subaru Telescope) is the crucial factor, as well as the exposure time. For astronomical objects of the same intrinsic brightness, depth is literally how far one can look.


News Article | February 28, 2017
Site: phys.org

The first dataset from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) was released to the public on February 27th, 2017. HSC-SSP is a large survey being done using HSC, which is an optical imaging camera mounted at the prime focus of the Subaru Telescope. HSC has 104 scientific CCDs (for a total of 870 million pixels) and a 1.77 square-degree field of view. The National Astronomical Observatory of Japan (NAOJ) has embarked on the HSC-SSP survey in collaboration with the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) in Japan, the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) in Taiwan, and Princeton University in the United States. The project will take 300 nights over 5-6 years. This survey consists of three layers; Wide, Deep, and UltraDeep, using optical and near infrared wavelengths in five broad bands (g, r, i, z, y) and four narrow-band filters. This release includes data from the first 1.7 years (61.5 nights of observations beginning in 2014). The observed areas covered by the Wide, Deep, and UltraDeep layers are 108, 26, and 4 square degrees, respectively. The limiting magnitudes, which refer to the depth (Note) of the observations, are 26.4, 26.6 and 27.3 mag in r-band (about 620 nm wavelength), respectively, allowing observations of some of the most distant galaxies in the universe. In the multi-band images, images are extremely sharp, with star images only 0.6 to 0.8 arcseconds across. 1 arcsecond equals 3600th part of a degree. These high-quality data will allow a unprecedented view into the nature and evolution of galaxies and dark matter. This first public dataset already contains 70 million galaxies and stars. It demonstrates that HSC-SSP is making the most of the performance of the Subaru Telescope and HSC. In 2015, using HSC observations over 2.3 square degrees of sky, nine clumps of dark matter, each weighing as much a galaxy cluster were discovered from their weak lensing signature (Miyazaki et al. 2015, ApJ 807, 22, "Properties of Weak Lensing Clusters Detected on Hyper Suprime-Cam 2.3 Square Degree Field"). The HSC-SSP data release covers about 50 times more sky than was used in this study, showing the potential of these data to reveal the statistical properties of dark matter. The total amount of data taken so far comprises 80 terabytes, which is comparable to the size of about 10 million images by a general digital camera. Since it is difficult to search such a huge dataset with standard tools, NAOJ has developed a dedicated database and interface for ease of access and use of the data. "Since 2014, we have been observing the sky with HSC, which can capture a wide-field image with high resolution," said Dr. Satoshi Miyazaki, the leader of the HSC-SSP. "We believe the data release will lead to many exciting astronomical results, from exploring the nature of dark matter and dark energy, as well as asteroids in our own solar system objects and galaxies in the early universe. SSP team members are now preparing a number of scientific papers based on these data. We plan to publish them in a special issue of the Publications of Astronomical Society of Japan. Moreover, we hope that interested members of the public will also access the data and enjoy the real universe imaged by the Subaru telescope, one of the largest the world." Funding for the HSC Project was provided in part by the following grants: Grant-in-Aid for Scientific Research (B) JP15340065; Grant-in-Aid for Scientific Research on Priority Areas JP18072003; and the Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST) entitled, "Uncovering the Origin and Future of the Universe: ultra-wide-field imaging and spectroscopy reveal the nature of dark matter and dark energy." Explore further: Tracing the cosmic web with star-forming galaxies in the distant universe


News Article | January 20, 2016
Site: phys.org

Figure 1: Color composite image of the spiral galaxy NGC 3521 taken by upgraded MOIRCS and processed by Ichi Tanaka. The field of view is 4 arcminutes x 7 arcminutes. The integration time was 5.3 minutes, 4 minutes and 7.1 minutes for J, H, and Ks band, respectively on the night of December 26, 2015. Unfortunately the seeing was very bad at that night at 1.3 arcseconds. Much better seeing in the usual, good condition should prove much sharper imaging capability of MOIRCS on the Subaru Telescope. Credit: NAOJ MOIRCS, the Multi-Object Infrared Camera and Spectrograph for the Subaru Telescope, has undergone a significant upgrade during 2015. Members of the project team were delighted to achieve first light (the term for the first time an instrument sees starlight), on the night after Christmas of 2015. The upgraded MOIRCS with new detectors, a new temperature control system, and new instrument control system software, demonstrated its good performance on the night of December 26, 2015, with an infrared image of the spiral galaxy NGC 3521 (Figure 1). The distance is 26 million light years, toward the constellation Leo. MOIRCS's FOV is large enough as for the near infrared instrument, to have this galaxy in 7 arcminute in the angular size in one view. MOIRCS was first mounted on the Subaru Telescope in September 2004. At that time, it had the widest field of view and the only multi-object spectroscopy (MOS) capability among near infrared instruments on 8-10 meter telescopes in the world. Over the first decade of its life, there were many unique discoveries made by this instrument. During the intervening time, however, other instruments with similar capabilities came on line and competition became more intense, so a team of scientists, engineers, and technicians at Subaru Telescope got together and planned an upgrade. By installing a new detector and upgrading the instrument's hardware and software infrastructure, the staff at Subaru Telescope hoped to rejuvenate this hard working instrument. What is New with the Upgraded MOIRCS? 1. A New, State of the Art, Infrared Detector MOIRCS now has two new detector arrays (Teledyne Hawaii 2 RG, see Figure 2) and new array control electronics (ASIC and SAM from Teledyne). The new detectors and electronics provide a significant reduction in electronic noise in the data. The new detectors have 14 and 15 electrons respectively of read noise in a CDS frame, an improvement of about a factor of 2. The lower noise improves the sensitivity of the instrument to faint sources and will be especially important when the spectrograph mode of the instrument in recommissioned in the spring of 2016. The instrument control system (ICS) software is the first amongst the Subaru Telescope's second generation instruments that was made entirely by the staff at the Subaru Telescope rather than outsourcing the software work. The original instrument builders, a group at Tohoku University, provided the first generation control system, but that was incompatible with the new detector control electronics. By using the in-house expertise, the project team was able to design a new control system which is simpler during night time use and which automates and scripts many daytime maintenance tasks (Figure 3). MOIRCS was originally designed and built using technologies of early 2000s. The hardware of the communication system, temperature controllers, computers, etc. has changed a lot during the intervening years. The team took this opportunity to replace many of these supporting hardware components with newer, more reliable, devices and to redesign some sub-systems to improve usability and reliability (Figure 4). During the night after Christmas (morning of December 27) in 2015, the upgraded MOIRCS instrument received light from the universe for the first time (Figure 1). The test observations were performed successfully despite this being the first time the new software interfaced with the telescope control system which has been upgraded since the original MOIRCS saw first light in 2004. The detector showed performance as expected. Noise level is less than half what it was before. The throughput improved over all of the near infrared by 12 % to 40 % and the time lost to overhead is significantly reduced. "It was not easy to carry out these daunting tasks of the major upgrade with the limited resource available on-site," says the project manager Josh Walawender. The original instrument builders provided helpful information. Experts from the Institute of Astronomy, the University of Tokyo, and the Academia Sinica Institute of Astronomy and Astrophysics provided valuable resources. "Yet there has been a tremendous pressure on the shoulders of the project team members to minimize the down-time of this instrument. The project team is confident that, after this performance verification, the users of this instrument will be delighted to be able to use it," continued Josh. One unexpected challenge that arose during the upgrade was the presence of a significant flux of alpha particle hits on the detector which appear a very bright spots in the image. This was due to a mildly radioactive coating which was present on a lens very near the detector. The first generation detector had a protective layer which blocked these particles, but the new detector had that layer removed for increased sensitivity. The instrument team will be installing thin blocking windows between the offending lens and the detector before the next engineering run of the instrument. The MOS system is yet to be fully commissioned with the new instrument control software. That will be a goal the Spring 2016 engineering runs along with more detailed noise measurements and characterization of the instrument performance.


News Article | March 2, 2017
Site: www.chromatographytechniques.com

The universe has come into sharper focus with the release this week of new images from the one of the largest telescopes in the world. A multinational collaboration led by the National Astronomical Observatory of Japan that includes Princeton University scientists has published a "cosmic census" of a large swath of the night sky containing roughly 100 million stars and galaxies, including some of the most distant objects in the universe. These high-quality images allow an unprecedented view into the nature and evolution of galaxies and dark matter. The images and accompanying data were collected using a digital optical-imaging camera on the Subaru Telescope, located at the Mauna Kea Observatory in Hawaii. The camera, known as Hyper Suprime-Cam, is mounted directly in the optical path, at the "prime focus," of the Subaru Telescope. A single image from the camera captures an amount of sky equal to the area of about nine full moons. The project, known as the Hyper Suprime-Cam Subaru Strategic Program, is led by the National Astronomical Observatory of Japan (NAOJ) in collaboration with the Kavli Institute for the Physics and Mathematics of the Universe in Japan, the Academia Sinica Institute of Astronomy and Astrophysics in Taiwan, and Princeton University. The release includes data from the first one-and-a-half years of the project, consisting of 61.5 nights of observations beginning in 2014. The project will take 300 nights over five to six years. The data will allow researchers to look for previously undiscovered galaxies and to search for dark matter, which is matter that neither emits nor absorbs light but which can be detected via its effects on gravity. A 2015 study using Hyper Suprime-Cam surveyed 2.3 square degrees of sky and found gravitational signatures of nine clumps of dark matter, each weighing as much as a galaxy cluster (Miyazaki et al., 2015). The current data release covers about 50 times more sky than was used in that study, showing the potential of these data to reveal the statistical properties of dark matter. The survey consists of three layers: a Wide survey that will eventually cover an area equal to 7000 full moons, or 1400 square degrees; a Deep survey that will look farther into the universe and encompass 26 square degrees; and an UltraDeep survey that will cover 3.5 square degrees and penetrate deep into space, allowing observations of some of the most distant galaxies in the universe. The surveys use optical and near infrared wavelengths in five broad wavelength bands (green, red, infrared, z, and y) and four narrow-band filters. In the multi-band images, the images are extremely sharp, with star images only 0.6 to 0.8 arcseconds across. (One arcsecond equals 3600th part of a degree.) The ability to capture images from deep in space is made possible by the light-collection power of the Subaru Telescope's mirror, which has an aperture of 8.2 meters, as well as the image exposure time. The depth into space that one can look is measured in terms of the magnitude, or brightness of objects that can be seen from Earth in a given wavelength band. The depths of the three surveys are characterized by magnitudes in the red band of 26.4, 26.6 and 27.3 in the Wide, Deep and Ultradeep data, respectively. As the survey continues, the Deep and Ultradeep surveys will be able to image fainter objects. The Hyper Suprime-Cam contains 104 scientific charge-coupled devices (CCDs) for a total of 870 million pixels. The total amount of data taken so far comprises 80 terabytes, which is comparable to the size of about 10 million images by a typical digital camera, and covers 108 square degrees. Because it is difficult to search such a huge dataset with standard tools, NAOJ has developed a dedicated database and interface for ease of access and use of the data. "Since 2014, we have been observing the sky with HSC, which can capture a wide-field image with high resolution," said Satoshi Miyazaki, the leader of the project and a scientist at NAOJ. "We believe the data release will lead to many exciting astronomical results, from exploring the nature of dark matter and dark energy, as well as asteroids in our own solar system and galaxies in the early universe. The team members are now preparing a number of scientific papers based on these data. We plan to publish them in a special issue of the Publication of Astronomical Society of Japan. Moreover, we hope that interested members of the public will also access the data and enjoy the real universe imaged by the Subaru telescope, one of the largest the world."


News Article | March 1, 2017
Site: www.eurekalert.org

The universe has come into sharper focus with the release this week of new images from the one of the largest telescopes in the world. A multinational collaboration led by the National Astronomical Observatory of Japan that includes Princeton University scientists has published a "cosmic census" of a large swath of the night sky containing roughly 100 million stars and galaxies, including some of the most distant objects in the universe. These high-quality images allow an unprecedented view into the nature and evolution of galaxies and dark matter. The images and accompanying data were collected using a digital optical-imaging camera on the Subaru Telescope, located at the Mauna Kea Observatory in Hawaii. The camera, known as Hyper Suprime-Cam, is mounted directly in the optical path, at the "prime focus," of the Subaru Telescope. A single image from the camera captures an amount of sky equal to the area of about nine full moons. The project, known as the Hyper Suprime-Cam Subaru Strategic Program, is led by the National Astronomical Observatory of Japan (NAOJ) in collaboration with the Kavli Institute for the Physics and Mathematics of the Universe in Japan, the Academia Sinica Institute of Astronomy and Astrophysics in Taiwan, and Princeton University. The release includes data from the first one-and-a-half years of the project, consisting of 61.5 nights of observations beginning in 2014. The project will take 300 nights over five to six years. The data will allow researchers to look for previously undiscovered galaxies and to search for dark matter, which is matter that neither emits nor absorbs light but which can be detected via its effects on gravity. A 2015 study using Hyper Suprime-Cam sur-veyed 2.3 square degrees of sky and found gravitational signatures of nine clumps of dark matter, each weighing as much as a galaxy cluster (Miyazaki et al., 2015). The current data release covers about 50 times more sky than was used in that study, showing the potential of these data to reveal the statistical properties of dark matter. The survey consists of three layers: a Wide survey that will eventually cover an area equal to 7000 full moons, or 1400 square degrees; a Deep survey that will look farther into the universe and encompass 26 square degrees; and an UltraDeep survey that will cover 3.5 square degrees and penetrate deep into space, allowing observations of some of the most distant galaxies in the universe. The surveys use optical and near infrared wavelengths in five broad wavelength bands (green, red, infrared, z, and y) and four narrow-band filters. In the multi-band images, the images are extremely sharp, with star images only 0.6 to 0.8 arcseconds across. (One arcsecond equals 3600th part of a degree.) The ability to capture images from deep in space is made possible by the light-collection power of the Subaru Telescope's mirror, which has an aperture of 8.2 meters, as well as the image exposure time. The depth into space that one can look is measured in terms of the magnitude, or brightness of objects that can be seen from Earth in a given wavelength band. The depths of the three surveys are characterized by magnitudes in the red band of 26.4, 26.6 and 27.3 in the Wide, Deep and Ultradeep data, respectively. As the survey continues, the Deep and Ultradeep surveys will be able to image fainter objects. The Hyper Suprime-Cam contains 104 scientific charge-coupled devices (CCDs) for a total of 870 million pixels. The total amount of data taken so far comprises 80 terabytes, which is comparable to the size of about 10 million images by a typical digital camera, and covers 108 square degrees. Because it is difficult to search such a huge dataset with standard tools, NAOJ has developed a dedicated database and interface for ease of access and use of the data. "Since 2014, we have been observing the sky with HSC, which can capture a wide-field image with high resolution," said Satoshi Miyazaki, the leader of the project and a scientist at NAOJ. "We believe the data release will lead to many exciting astronomical results, from exploring the nature of dark matter and dark energy, as well as asteroids in our own solar system and galaxies in the early universe. The team members are now preparing a number of scientific papers based on these data. We plan to publish them in a special issue of the Publication of Astronomical Society of Japan. Moreover, we hope that interested members of the public will also access the data and enjoy the real universe imaged by the Subaru telescope, one of the largest the world." At Princeton, the project is co-led by Michael Strauss and Robert Lupton of the De-partment of Astrophysical Sciences. "The HSC data are really beautiful," Strauss said. "Princeton scientists are using these data to explore the nature of merging galaxies, to search for the most distant quasars in the universe, to map the outer reaches of the Milky Way Galaxy, and for many other projects. We are delighted to make these won-derful images available to the world-wide astronomical community." Funding for the HSC Project was provided in part by the following grants: Grant-in-Aid for Scientific Research (B) JP15340065; Grant-in-Aid for Scientific Research on Priority Areas JP18072003; and the Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST) entitled, "Uncovering the origin and future of the Universe-ultra-wide-field imaging and spectroscopy reveal the nature of dark matter and dark energy." Funding was also provided by Princeton University.


Bower G.C.,Academia Sinica Institute of Astronomy and Astrophysics | Markoff S.,University of Amsterdam | Dexter J.,Max Planck Institute for Extraterrestrial Physics | Gurwell M.A.,Harvard - Smithsonian Center for Astrophysics | And 11 more authors.
Astrophysical Journal | Year: 2015

We report new observations with the Very Large Array, Atacama Large Millimeter Array, and Submillimeter Array at frequencies from 1.0 to 355 GHz of the Galactic Center black hole, Sagittarius A∗. These observations were conducted between 2012 October and 2014 November. While we see variability over the whole spectrum with an amplitude as large as a factor of 2 at millimeter wavelengths, we find no evidence for a change in the mean flux density or spectrum of Sgr A∗ that can be attributed to interaction with the G2 source. The absence of a bow shock at low frequencies is consistent with a cross-sectional area for G2 that is less than 2 × 1029 cm2. This result fits with several model predictions including a magnetically arrested cloud, a pressure-confined stellar wind, and a stellar photosphere of a binary merger. There is no evidence for enhanced accretion onto the black hole driving greater jet and/or accretion flow emission. Finally, we measure the millimeter wavelength spectral index of Sgr A∗ to be flat; combined with previous measurements, this suggests that there is no spectral break between 230 and 690 GHz. The emission region is thus likely in a transition between optically thick and thin at these frequencies and requires a mix of lepton distributions with varying temperatures consistent with stratification. © 2015. The American Astronomical Society. All rights reserved.


Girart J.M.,Institute Of Ciencies Of Lespai | Patel N.,Harvard - Smithsonian Center for Astrophysics | Vlemmings W.H.T.,Chalmers University of Technology | Rao R.,Academia Sinica Institute of Astronomy and Astrophysics
Astrophysical Journal Letters | Year: 2012

We present spectro-polarimetric observations of several molecular lines obtained with the Submillimeter Array toward the carbon-rich asymptotic giant branch star IRC+10216. We have detected and mapped the linear polarization of the CO 3-2, SiS 19-18, and CS 7-6 lines. The polarization arises at a distance of ≃ 450 AU from the star and is blueshifted with respect to the Stokes I. The SiS 19-18 polarization pattern appears to be consistent with a locally radial magnetic field configuration. However, the CO 3-2 and CS 7-6 line polarization suggests an overall complex magnetic field morphology within the envelope. This work demonstrates the feasibility of using spectro-polarimetric observations to carry out tomographic imaging of the magnetic field in circumstellar envelopes. © 2012. The American Astronomical Society. All rights reserved..


Vlemmings W.H.T.,Chalmers University of Technology | Ramstedt S.,University of Bonn | Rao R.,Academia Sinica Institute of Astronomy and Astrophysics | Maercker M.,University of Bonn | Maercker M.,European Southern Observatory
Astronomy and Astrophysics | Year: 2012

Molecular line polarization is a unique source of information about the magnetic fields and anisotropies in the circumstellar envelopes of evolved stars. Here we present the first detection of thermal CO(J = 2 → 1) and SiO(J = 5 → 4, ν = 0) polarization, in the envelope of the asymptotic giant branch star IK Tau. The observed polarization direction does not match predictions for circumstellar envelope polarization induced only by an anisotropic radiation field. Assuming that the polarization is purely due to the Goldreich-Kylafis effect, the linear polarization direction is defined by the magnetic field as even the small Zeeman splitting of CO and SiO dominates the molecular collisional and spontaneous emission rates. The polarization was mapped using the Submillimeter Array (SMA) and is predominantly north-south. There is close agreement between the CO and SiO observations, even though the CO polarization arises in the circumstellar envelope at ∼800 AU and the SiO polarization at ≈250 AU. If the polarization indeed traces the magnetic field, we can thus conclude that it maintains a large-scale structure throughout the circumstellar envelope. We propose that the magnetic field, oriented either east-west or north-south is responsible for the east-west elongation of the CO distribution and asymmetries in the dust envelope. In the future, the Atacama Large Millimeter/submillimeter Array will be able to map the magnetic field using CO polarization for a large number of evolved stars. © 2012 ESO.


Muoz D.J.,Harvard - Smithsonian Center for Astrophysics | Marrone D.P.,University of Chicago | Marrone D.P.,University of Arizona | Moran J.M.,Harvard - Smithsonian Center for Astrophysics | Rao R.,Academia Sinica Institute of Astronomy and Astrophysics
Astrophysical Journal | Year: 2012

We report the first detections of circularly polarized emission at submillimeter wavelengths from the compact radio source and supermassive black hole candidate SgrA* at a level of 1.2% 0.3% at 1.3 mm wavelength (230GHz) and 1.6% 0.3% at 860 μm (345GHz) with the same handedness, left circular polarization (LCP), as observed at all lower frequencies (1.4-15GHz). The observations, taken with the Submillimeter Array in multiple epochs, also show simultaneous linear polarization (LP) at both wavelengths of about 6%. These properties differ sharply from those at wavelengths longer than 1 cm (frequencies below 30GHz), where weak circular polarization (CP) (0.5%) dominates over LP, which is not detected at similar fractional limits. We describe an extensive set of tests to ensure the accuracy of our measurements. We find no CP in any other source, including the bright quasar 1924-292, which traces the same path on the sky as SgrA* and therefore should be subject to identical systematic errors originating in the instrument frame. Since a relativistic synchrotron plasma is expected to produce little CP, the observed CP is probably generated close to the event horizon by the Faraday conversion process. We use a simple approximation to show that the phase shift associated with Faraday conversion can be nearly independent of frequency, a sufficient condition to make the handedness of CP independent of frequency. Because the size of the τ = 1 surface changes by more than an order of magnitude between 1.4 and 345GHz, the magnetic field must be coherent over such scales to consistently produce LCP. To improve our understanding of the environment of SgrA* critical future measurements includes determining whether the Faraday rotation deviates from a λ2 dependence in wavelength and whether the circular and linear components of the flux density are correlated. © 2012. The American Astronomical Society. All rights reserved.

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