Monje R.R.,California Institute of Technology |
Phillips T.G.,California Institute of Technology |
Peng R.,Caltech Submillimeter Observatory |
Lis D.C.,California Institute of Technology |
And 2 more authors.
Astrophysical Journal Letters
We report the first detection of hydrogen fluoride (HF) toward a high-redshift quasar. Using the Caltech Submillimeter Observatory, we detect the HF J = 1-0 transition in absorption toward the Cloverleaf, a broad absorption line quasi-stellar object at z = 2.56. The detection is statistically significant at the ∼6σ level. We estimate a lower limit of 4 × 1014cm-2 for the HF column density and using a previous estimate of the hydrogen column density, we obtain a lower limit of 1.7 × 10-9 for the HF abundance. This value suggests that, assuming a Galactic N(HF)/N H ratio, HF accounts for at least ∼10% of the fluorine in the gas phase along the line of sight to the Cloverleaf quasar. This observation corroborates the prediction that HF should be a good probe of the molecular gas at high redshift. Measurements of the HF abundance as a function of redshift are urgently needed to better constrain the fluorine nucleosynthesis mechanism(s). © 2011. The American Astronomical Society. All rights reserved.. Source
Tanaka T.,Osaka Prefecture University |
Nakamura F.,Japan National Astronomical Observatory |
Awazu Y.,Osaka Prefecture University |
Shimajiri Y.,Nobeyama Radio Observatory |
And 5 more authors.
We present the results of N2H+ (J = 1-0) observations toward Serpens South, the nearest cluster-forming, infrared dark cloud. The physical quantities are derived by fitting the hyperfine structure of N2H+. The Herschel and 1.1 mm continuum maps show that a parsec-scale filament fragments into three clumps with radii of 0.1-0.2 pc and masses of 40-230 M . We find that the clumps contain smaller-scale (0.04 pc) structures, i.e., dense cores. We identify 70 cores by applying CLUMPFIND to the N2H+ data cube. In the central cluster-forming clump, the excitation temperature and line-width tend to be large, presumably due to protostellar outflow feedback and stellar radiation. However, for all the clumps, the virial ratios are evaluated to be 0.1-0.3, indicating that the internal motions play only a minor role in the clump support. The clumps exhibit no free fall but exhibit low-velocity infall, and thus the clumps should be supported by additional forces. The most promising force is the globally ordered magnetic field observed toward this region. We propose that the Serpens South filament was close to magnetically critical and ambipolar diffusion triggered the cluster formation. We find that the northern clump, which shows no active star formation, has a mass and radius comparable to the central cluster-forming clump and is therefore a likely candidate of a pre-protocluster clump. The initial condition for cluster formation is likely to be a magnetically supported clump of cold, quiescent gas. This appears to contradict the accretion-driven turbulence scenario, for which the turbulence in the clumps is maintained by the accretion flow. © 2013. The American Astronomical Society. All rights reserved.. Source
Fish V.L.,Massachusetts Institute of Technology |
Doeleman S.S.,Massachusetts Institute of Technology |
Beaudoin C.,Massachusetts Institute of Technology |
Blundell R.,Harvard - Smithsonian Center for Astrophysics |
And 28 more authors.
Astrophysical Journal Letters
Sagittarius A*, the ∼4 × 106 M ⊙ black hole candidate at the Galactic center, can be studied on Schwarzschild radius scales with (sub)millimeter wavelength very long baseline interferometry (VLBI). We report on 1.3 mm wavelength observations of Sgr A * using a VLBI array consisting of the JCMT on Mauna Kea, the Arizona Radio Observatory's Submillimeter Telescope on Mt. Graham in Arizona, and two telescopes of the CARMA array at Cedar Flat in California. Both Sgr A* and the quasar calibrator 1924-292 were observed over three consecutive nights, and both sources were clearly detected on all baselines. For the first time, we are able to extract 1.3 mm VLBI interferometer phase information on Sgr A* through measurement of closure phase on the triangle of baselines. On the third night of observing, the correlated flux density of Sgr A* on all VLBI baselines increased relative to the first two nights, providing strong evidence for time-variable change on scales of a few Schwarzschild radii. These results suggest that future VLBI observations with greater sensitivity and additional baselines will play a valuable role in determining the structure of emission near the event horizon of Sgr A*. © 2011. The American Astronomical Society. Source
Crawled News Article
The announcement of the closure of a third telescope on Hawaii's Mauna Kea fulfills the request of the state governor. More A British-built observatory located on Hawaii's tallest mountain announced last week that it would be closing, meeting the request of Hawaii's Gov. David Ige to shut down 25 percent of the telescopes on the mountain, in order to facilitate the construction of the Thirty-Meter Telescope (TMT). The UKIRT observatory, located on the dormant volcano Mauna Kea, "had already been identified in the Mauna Kea management plan … as one of the telescopes that will not be recycled after the end of its productive life," Guenther Hasinger, director of the Institute for Astronomy at the University of Hawaii, which runs the telescope, told Space.com by email. "This process has been advanced to fulfill Gov. Ige's request for a visibly improved stewardship of the mountain." [Keck Observatory: Cosmic Photos from Hawaii's Mauna Kea] Located on the island of Hawaii, Mauna Kea's high altitude and dry environment make it one of the best sites in the world for astronomical observation. Since the 1960s, 13 observatories have been built on and around the mountaintop. However, many people in the region also consider Mauna Kea sacred. During the TMT's 2014 groundbreaking ceremony, the telescope attracted significant controversy, and construction was halted earlier this year due to protests, several of which resulted in arrests. In May, Ige announced a plan to enhance the stewardship of the mountain, calling for the removal of at least 25 percent of the telescopes by the time TMT is ready for operations. The Caltech Submillimeter Observatory has since closed down operations, while the University of Hawaii at Hilo has initiated the decommissioning process for its Hoku Kea telescope. UKIRT marks the third instrument to announce its closure, meeting the governor's goal. Formerly known as the United Kingdom Infrared Telescope, UKIRT began operation in 1979. Ownership was transferred to the University of Hawaii in 2014. "Over the past several years, UKIRT has become one of the most productive telescopes on the globe," Hasinger said. The measurement of productivity is based on the number of publications using UKIRT data and those papers' corresponding impact. Hasinger said he attributed UKIRT's productivity to a set of very large, specialized imaging sky surveys performed by the telescope that a significant number of researchers use. The telescope has also discovered some of the most distant objects in the universe, the most notable of which is the most distant known quasar, a supermassive black hole that emitted an incredible amount of light when the universe was less than 1 billion years into its total age of 13.8 billion years. The instrument won't be shut down immediately. Hasinger said that the plan will start some time after the other two telescopes have been decommissioned. "The general decommissioning process for observatories is outlined in the Office of Mauna Kea Management's Comprehensive Management Plan to ensure that the decommissioning is handled properly and in a culturally and environmentally respectful manner," the University of Hawaii said in a statement. UKIRT will continue to operate for several years until it is time to begin the shutdown process, which will involve a site deconstruction and removal plan, and a site-restoration plan. "The whole process needs to be done with utmost care and with public input," Hasinger said. Follow Nola Taylor Redd on Twitter @NolaTRedd or Google+. Follow us at @Spacedotcom, Facebook or Google+. Originally published on Space.com. Copyright 2015 SPACE.com, a Purch company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
Chapman N.L.,The Interdisciplinary Center |
Davidson J.A.,University of Western Australia |
Goldsmith P.F.,Jet Propulsion Laboratory |
Houde M.,University of Western Ontario |
And 12 more authors.
We present 350 μm polarization observations of four low-mass cores containing Class 0 protostars: L483, L1157, L1448-IRS2, and Serp-FIR1. This is the second paper in a larger survey aimed at testing magnetically regulated models for core-collapse. One key prediction of these models is that the mean magnetic field in a core should be aligned with the symmetry axis (minor axis) of the flattened young stellar object inner envelope (aka pseudodisk). Furthermore, the field should exhibit a pinched or hourglass-shaped morphology as gravity drags the field inward toward the central protostar. We combine our results for the four cores with results for three similar cores that were published in the first paper from our survey. An analysis of the 350 μm polarization data for the seven cores yields evidence of a positive correlation between mean field direction and pseudodisk symmetry axis. Our rough estimate for the probability of obtaining by pure chance a correlation as strong as the one we found is about 5%. In addition, we combine together data for multiple cores to create a source-averaged magnetic field map having improved signal-to-noise ratio, and this map shows good agreement between mean field direction and pseudodisk axis (they are within 15°). We also see hints of a magnetic pinch in the source-averaged map. We conclude that core-scale magnetic fields appear to be strong enough to guide gas infall, as predicted by the magnetically regulated models. Finally, we find evidence of a positive correlation between core magnetic field direction and bipolar outflow axis. © 2013. The American Astronomical Society. All rights reserved.. Source