Isaac Newton Group

Santa Cruz de la Palma, Spain

Isaac Newton Group

Santa Cruz de la Palma, Spain
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Ellison S.L.,University of Victoria | Prochaska J.X.,University of California at Santa Cruz | Hennawi J.,University of California at Berkeley | Lopez S.,University of Chile | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

We present high-resolution echelle spectra of seven proximate damped Lyman α (PDLA) systems. The relative velocity separation of each PDLA from the background quasar is Δ V < 3000 km s-1. Combining our sample with a further nine PDLAs from the literature we compare the chemical properties of the proximate systems with a control sample of intervening DLAs. The PDLAs are usually excluded from statistical studies of absorption-selected galaxies and this sample constitutes the first systematic study of their chemical and ionization properties. Taken at face value, the sample of 16 PDLAs exhibits a wide range of metallicities, ranging from Z ∼ 1/3 to ∼ 1/1000 Z⊙, including the DLA with the lowest N(Si ii)/N(H i) yet reported in the literature. However, some of these abundances may require ionization corrections. We find several pieces of evidence that indicate enhanced ionization and the presence of a hard ionizing spectrum in PDLAs which lead to properties that contrast with the intervening DLAs, particularly when the N(H i) is low. The abundances of Zn, Si and S in PDLAs with log N(H i) > 21, where ionization corrections are minimized, are systematically higher than the intervening population by a factor of around 3. We also find possible evidence for a higher fraction of N v absorbers amongst the PDLAs, although the statistics are still modest. 6/7 of our echelle sample show high ionization species (Si iv, C iv, O vi or N v) offset by >100 km s-1 from the main low ion absorption. We analyse fine-structure transitions of C ii{black star} and Si ii{black star} to constrain the PDLA distance from the quasi-stellar object (QSO). Lower limits range from tens of kpc to >160 kpc for the most stringent limit. We conclude that (at least some) PDLAs do exhibit different characteristics relative to the intervening population out to 3000 km s-1 (and possibly beyond). None the less, the PDLAs appear distinct from lower column density associated systems, and the inferred QSO-absorber separations mean they are unlikely to be associated with the QSO host. No trends with Δ V are found, although this requires a larger sample with better emission redshifts to confirm. We speculate that the PDLAs preferentially sample more massive galaxies in more highly clustered regions of the high-redshift Universe. © 2010 The Authors. Journal compilation © 2010 RAS.


Dunn J.P.,Virginia Polytechnic Institute and State University | Bautista M.,Virginia Polytechnic Institute and State University | Bautista M.,Western Michigan University | Arav N.,Virginia Polytechnic Institute and State University | And 7 more authors.
Astrophysical Journal | Year: 2010

We present high spectral resolution Very Large Telescope observations of the broad absorption line quasar SDSS J0318 - 0600. This high-quality data set allows us to extract accurate ionic column densities and determine an electron number density of ne = 103.3±0.2cm-3 for the main outflow absorption component. The heavily reddened spectrum of SDSS J0318-0600 requires purely silicate dust with a reddening curve characteristic of predominately large grains, from which we estimate the bolometric luminosity. We carry out photoionization modeling to determine the total column density, ionization parameter, and distance of the gas and find that the photoionization models suggest abundances greater than solar. Due to the uncertainty in the location of the dust extinction, we arrive at two viable distances for the main ouflow component from the central source, 6 and 17kpc, where we consider the 6kpc location as somewhat more physically plausible. Assuming the canonical global covering of 20% for the outflow and a distance of 6kpc, our analysis yields a mass flux of 120 M⊙yr-1 and a kinetic luminosity that is ∼0.1% of the bolometric luminosity of the object. Should the dust be part of the outflow, then these values are ∼4× larger. The large mass flux and kinetic luminosity make this outflow a significant contributor to active galactic nucleus feedback processes. © 2010. The American Astronomical Society. All rights reserved.


News Article | February 27, 2017
Site: www.eurekalert.org

Stars are ripped apart by supermassive black holes 100 times more often than previously thought Astronomers based at the University of Sheffield have found evidence that stars are ripped apart by supermassive black holes 100 times more often than previously thought. Until now, such stellar cannibalism - known as Tidal Distruption Events, or TDEs - had only been found in surveys which observed many thousands of galaxies, leading astronomers to believe they were exceptionally rare: only one event every 10,000 to 100,000 years per galaxy. However, the pioneering study conducted by leading scientists from the University's Department of Physics and Astronomy, recorded a star being destroyed by a supermassive black hole in a survey of just 15 galaxies - an extremely small sample size by astronomy standards. "Each of these 15 galaxies is undergoing a 'cosmic collision' with a neighbouring galaxy," said Dr James Mullaney, Lecturer in Astronomy and co-author of the study. "Our surprising findings show that the rate of TDEs dramatically increases when galaxies collide. This is likely due to the fact that the collisions lead to large numbers of stars being formed close to the central supermassive black holes in the two galaxies as they merge together." The supermassive black holes that lurk in the hearts of all large galaxies can be elusive. This is because they don't shine in a conventional sense due to their gravity being so strong that nothing can escape, not even light itself. However, the release of energy as stars are ripped apart when they move close to the black holes leads to dramatic flares. The galaxies' nuclei can then appear as bright as all the billions of stars in a typical galaxy combined. In this way, TDEs can be used to locate otherwise dim black holes and study their strong gravity and how they accrete matter. "Our team first observed the 15 colliding galaxies in the sample in 2005, during a previous project," said Rob Spence, University of Sheffield PhD student and co-author of the study. "However, when we observed the sample again in 2015, we noticed that one galaxy - F01004-2237 - appeared strikingly different. This led us to look at data from the Catalina Sky Survey, which monitors the brightness of objects in the sky over time. We found that in 2010, the brightness of F01004-2237 flared dramatically." The particular combination of variability and post-flare spectrum observed in F01004-2237 - which is 1.7 billion light years from Earth - was unlike any known supernova or active galactic nucleus, but characteristic of TDEs. Clive Tadhunter, Professor of Astrophysics and leader of the study, said: "Based on our results for F01004-2237, we expect that TDE events will become common in our own Milky Way galaxy when it eventually merges with the neighbouring Andromeda galaxy in about 5 billion years. "Looking towards the centre of the Milky Way at the time of the merger we'd see a flare approximately every 10 to 100 years. The flares would be visible to the naked eye and appear much brighter than any other star or planet in the night sky." The study, published today (27 February 2017) in the journal Nature Astronomy, was supported by a grant from the UK Science and Technology Facilities Council. The findings were based on observations made with the William Herschel Telescope, which is operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canaria. The study also used data taken with NASA/ESA Hubble Space Telescope, and the Catalina Sky Survey. Scientists at the University of Sheffield's Department of Physics and Astronomy are exploring the fundamental laws of the universe and developing pioneering technologies. They look beyond our planet to tackle global challenges - from climate change to meeting energy demands. For more information about the University's Department of Physics and Astronomy please visit https:/ With almost 27,000 of the brightest students from over 140 countries, learning alongside over 1,200 of the best academics from across the globe, the University of Sheffield is one of the world's leading universities. A member of the UK's prestigious Russell Group of leading research-led institutions, Sheffield offers world-class teaching and research excellence across a wide range of disciplines. Unified by the power of discovery and understanding, staff and students at the university are committed to finding new ways to transform the world we live in. Sheffield is the only university to feature in The Sunday Times 100 Best Not-For-Profit Organisations to Work For 2017 and was voted number one university in the UK for Student Satisfaction by Times Higher Education in 2014. In the last decade it has won four Queen's Anniversary Prizes in recognition of the outstanding contribution to the United Kingdom's intellectual, economic, cultural and social life. Sheffield has six Nobel Prize winners among former staff and students and its alumni go on to hold positions of great responsibility and influence all over the world, making significant contributions in their chosen fields. Global research partners and clients include Boeing, Rolls-Royce, Unilever, AstraZeneca, Glaxo SmithKline, Siemens and Airbus, as well as many UK and overseas government agencies and charitable foundations. For further information, please visit http://www. For further information please contact: Amy Pullan, Media Relations Officer, University of Sheffield, 0114 222 9859, a.l.pullan@sheffield.ac.uk To read other news releases about the University of Sheffield, visit http://www.


Bautista M.A.,University of Virginia | Bautista M.A.,Western Michigan University | Dunn J.P.,University of Virginia | Arav N.,University of Virginia | And 3 more authors.
Astrophysical Journal | Year: 2010

Using high-resolution Very Large Telescope spectra, we study the multi-component outflow systems of two quasars exhibiting intrinsic Fe II absorption (QSO 2359-1241 and SDSS J0318-0600). From the extracted ionic column densities and using photoionization modeling, we determine the gas density, total column density, and ionization parameter for several of the components. For each object, the largest column density component is also the densest, and all other components have densities of roughly 1/4 of that of the main component. We demonstrate that all the absorbers lie roughly at the same distance from the source. Further, we calculate the total kinetic luminosities and mass outflow rates of all components and show that these quantities are dominated by the main absorption component. © 2010. The American Astronomical Society. All rights reserved.


Farhang A.,Institute for Research in Fundamental Sciences | Farhang A.,Sharif University of Technology | Khosroshahi H.G.,Institute for Research in Fundamental Sciences | Javadi A.,Institute for Research in Fundamental Sciences | And 10 more authors.
Astrophysical Journal | Year: 2015

We present a new high signal-to-noise ratio spectroscopic survey of the Northern hemisphere to probe the Local Bubble and its surroundings using the λ5780Å and λ5797Å diffuse interstellar bands (DIBs). We observed 432 sightlines to a distance of 200 pc over a duration of three years. In this study, we establish the λ5780 and λ5797 correlations with Na I, Ca II and EB-V, for both inside and outside the Local Bubble. The correlations show that among all neutral and ionized atoms, the correlation between Ca ii and λ5780 is stronger than its correlation with λ5797, suggesting that λ5780 is more associated with regions where Ca+ is more abundant. We study the λ5780 correlation with λ5797, which shows a tight correlation within and outside the Local Bubble. In addition, we investigate the DIB properties in UV irradiated and UV shielded regions. We find that, within and beyond the Local Bubble, λ5797 is located in denser parts of clouds, protected from UV irradiation, while λ5780 is located in the low-density regions of clouds. © 2015. The American Astronomical Society. All rights reserved.


Borguet B.C.J.,Virginia Polytechnic Institute and State University | Edmonds D.,Virginia Polytechnic Institute and State University | Arav N.,Virginia Polytechnic Institute and State University | Benn C.,Isaac Newton Group | Chamberlain C.,Virginia Polytechnic Institute and State University
Astrophysical Journal | Year: 2012

We present spectroscopic analysis of the broad absorption line (BAL) outflow in quasar SDSS J1512+1119. In particular, we focus our attention on a kinematic component in which we identify P V and S IV/S IV* absorption troughs. The shape of the unblended phosphorus doublet troughs and the three S IV/S IV* troughs allow us to obtain reliable column density measurements for these two ions. Photoionization modeling using these column densities and those of He I* constrain the abundance of phosphorus to the range of 0.5-4times the solar value. The total column density, ionization parameter, and metallicity inferred from the P V and S IV column densities lead to large optical depth values for the common transition observed in BAL outflows. We show that the true C IV optical depth is 1000times greater in the core of the absorption profile than the value deduced from its apparent optical depth. © 2012. The American Astronomical Society. All rights reserved.


Borguet B.C.J.,Virginia Polytechnic Institute and State University | Arav N.,Virginia Polytechnic Institute and State University | Edmonds D.,Virginia Polytechnic Institute and State University | Chamberlain C.,Virginia Polytechnic Institute and State University | Benn C.,Isaac Newton Group
Astrophysical Journal | Year: 2013

We present the most energetic BALQSO outflow measured to date, with a kinetic luminosity of at least 1046 erg s-1, which is 5% of the bolometric luminosity of this high Eddington ratio quasar. The associated mass-flow rate is 400 solar masses per year. Such kinetic luminosity and mass-flow rate should provide strong active galactic nucleus feedback effects. The outflow is located at about 300 pc from the quasar and has a velocity of roughly 8000 km s-1. Our distance and energetic measurements are based in large part on the identification and measurement of S IV and S IV* broad absorption lines (BALs). The use of this high-ionization species allows us to generalize the result to the majority of high-ionization BALQSOs that are identified by their C IV absorption. We also report the energetics of two other outflows seen in another object using the same technique. The distances of all three outflows from the central source (100-2000 pc) suggest that we observe BAL troughs much farther away from the central source than the assumed acceleration region of these outflows (0.01-0.1 pc). © 2013. The American Astronomical Society. All rights reserved.


Benn C.,Isaac Newton Group
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

The user support model at the ING telescopes has evolved considerably over the last 20 years, mainly in response to improvements in the reliability and efficiency of the observing systems. Observers at the 4.2-m William Her-schel Telescope (WHT) currently get first-night (afternoon + evening) support from staff support astronomers, and all-night support from telescope operators. As of 2010, the telescope operators also provide engineering support at night. Observers at the 2.5-m Isaac Newton Telescope (INT) get first-night support from student support astronomers, but no night-time operator/engineering support. Feedback from observers indicates a continuing high level of satisfaction with the support they receive. © 2012 SPIE.


Chamberlain C.,Virginia Polytechnic Institute and State University | Arav N.,Virginia Polytechnic Institute and State University | Benn C.,Isaac Newton Group
Monthly Notices of the Royal Astronomical Society | Year: 2015

We measure the location and energetics of a S IV BALQSO outflow. This outflow has a velocity of 10 800 km s-1 and a kinetic luminosity of 1045.7 erg s-1, which is 5.2 per cent of the Eddington luminosity of the quasar. From collisional excitation models of the observed S IV/S IV* absorption troughs, we measure a hydrogen number density of nH = 104.3 cm-3, which allows us to determine that the outflow is located 110 pc from the quasar. Since S IV is formed in the same ionization phase asC IV, our results can be generalized to the ubiquitousC IV broad absorption lines (BALs). Our accumulated distance measurements suggest that observed BAL outflows are located much farther away from the central source than is generally assumed (0.01-0.1 pc). © 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


News Article | February 27, 2017
Site: www.futurity.org

Supermassive black holes rip apart stars 100 times more often than previously thought, report researchers. Until now, such stellar cannibalism—known as Tidal Distruption Events, or TDEs—had only been found in surveys which observed many thousands of galaxies, leading astronomers to believe they were exceptionally rare: only one event every 10,000 to 100,000 years per galaxy. However, new study recorded a star being destroyed by a supermassive black hole in a survey of just 15 galaxies—an extremely small sample size by astronomy standards. “Each of these 15 galaxies is undergoing a ‘cosmic collision’ with a neighboring galaxy,” says James Mullaney, lecturer in astronomy at the University of Sheffield and coauthor of the study in Nature: Astronomy. “Our surprising findings show that the rate of TDEs dramatically increases when galaxies collide. This is likely due to the fact that the collisions lead to large numbers of stars being formed close to the central supermassive black holes in the two galaxies as they merge together.” The supermassive black holes that lurk in the hearts of all large galaxies can be elusive. This is because they don’t shine in a conventional sense due to their gravity being so strong that nothing can escape, not even light itself. However, the release of energy as stars are ripped apart when they move close to the black holes leads to dramatic flares. The galaxies’ nuclei can then appear as bright as all the billions of stars in a typical galaxy combined. In this way, TDEs can be used to locate otherwise dim black holes and study their strong gravity and how they accrete matter. “Our team first observed the 15 colliding galaxies in the sample in 2005, during a previous project,” sys Rob Spence, PhD student and coauthor of the study. “However, when we observed the sample again in 2015, we noticed that one galaxy—F01004-2237—appeared strikingly different. This led us to look at data from the Catalina Sky Survey, which monitors the brightness of objects in the sky over time. We found that in 2010, the brightness of F01004-2237 flared dramatically.” The particular combination of variability and post-flare spectrum observed in F01004-2237—which is 1.7 billion light years from Earth—was unlike any known supernova or active galactic nucleus, but characteristic of TDEs. “Based on our results for F01004-2237, we expect that TDE events will become common in our own Milky Way galaxy when it eventually merges with the neighboring Andromeda galaxy in about 5 billion years,” says Clive Tadhunter, professor of astrophysics and leader of the study. “Looking towards the centre of the Milky Way at the time of the merger we’d see a flare approximately every 10 to 100 years. The flares would be visible to the naked eye and appear much brighter than any other star or planet in the night sky.” The UK Science and Technology Facilities Council supported the work. Observations used in the study come from the William Herschel Telescope on the island of La Palma, which the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canaria operates. The study also used data from the NASA/ESA Hubble Space Telescope and the Catalina Sky Survey.

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