Intermittent behavior of galactic dynamo activities

NASA Technical Reports Server (NTRS)

Ko, C. M.; Parker, E. N.

1989-01-01

Recent observations by Beck and Golla of far-infrared and radio continuum emission from nearby spiral galaxies suggest that the galactic magnetic field strength is connected to the current star formation rate. The role of star formation on the generation of large-scale galactic magnetic field is studied in this paper. Using a simple galactic model, it is shown how the galactic dynamo depends strongly on the turbulent velocity of the interstellar medium. When the star formation efficiency is high, the ISM is churned which in turn amplifies the galactic magnetic field. Between active star formation epochs, the magnetic field is in dormant state and decays at a negligible rate. If density waves trigger star formation, then they also turn on the otherwise dormant dynamo.

NASA puts JWST Back on Track, but ExoMars Collaboration Looks Unlikely; Marsquakes happening yesterday, geologically; UFOs from black holes control shape of galaxies

NASA Astrophysics Data System (ADS)

2012-04-01

NASA's funding plans put the James Webb Space Telescope firmly on track for a launch in 2018, to widespread relief, but the essentially flat funding settlement for 2013 overall means something has to go. Planetary science seems hardest hit, with the especial blow for European planetary scientists of NASA pulling out of ExoMars, the ESA-led mission to look for signs of life on Mars. Images from the High Resolution Imaging Science Experiment have shown boulders displaced by seismic activity on Mars in the past few million years, and possibly much more recently than that. The bigger the supermassive black hole at the centre of a galaxy, the faster the stars in the galactic bulge rotate. Why this should be so has been something of a puzzle, but now a mechanism that is both powerful and common enough to do the job has been identified.

News and Views: NASA puts JWST back on track, but ExoMars collaboration looks unlikely; Marsquakes happening yesterday, geologically; UFOs from black holes control shape of galaxies

NASA Astrophysics Data System (ADS)

2012-04-01

NASA's funding plans put the James Webb Space Telescope firmly on track for a launch in 2018, to widespread relief, but the essentially flat funding settlement for 2013 overall means something has to go. Planetary science seems hardest hit, with the especial blow for European planetary scientists of NASA pulling out of ExoMars, the ESA-led mission to look for signs of life on Mars. Images from the High Resolution Imaging Science Experiment have shown boulders displaced by seismic activity on Mars in the past few million years, and possibly much more recently than that. The bigger the supermassive black hole at the centre of a galaxy, the faster the stars in the galactic bulge rotate. Why this should be so has been something of a puzzle, but now a mechanism that is both powerful and common enough to do the job has been identified.

GSFC Contributions to the NATO X-ray Astronomy Institute, Erice, July 1979. [X-ray spectra of supernova remants, galactic X-ray sources, active galactic nuclei, and clusters of galaxies

NASA Technical Reports Server (NTRS)

Holt, S. S.; Mushotzky, R. F.

1979-01-01

An overview of X-ray astronomical spectroscopy in general is presented and results obtained by HEAO 1 and 2 as well as earlier spacecraft are examined. Particular emphasis is given to the spectra of supernova remnants; galactic binary X-ray sources, cataclysmic variables, bulges, pulsars, and stars; the active nuclei of Seyfert 1 galaxy, BL Lac, and quasars; the diffuse X-ray background; and galactic clusters.

Storage Rings in the Sky: Gamma Ray Bursts and Galactic Gravitational Collapse Stored Energy

NASA Astrophysics Data System (ADS)

Greyber, H. D.

2004-05-01

The recent discovery of almost 100% polarization of the prompt gamma ray emission from GRB021206, (1), confirms my 44 year old ``Strong" Magnetic Field" model (SMF) for galactic dynamics. In SMF, Storage Ring particles were accelerated long ago during the original gravitational collapse of the pregalactic/prequasar plasma cloud that is permeated by an almost uniform primordial magnetic field (2,3) The enormous, intense, slender, relativistic, stable, completely coherent Storage Ring stores a very small fraction of the huge galactic gravitational collapse energy in an almost radiationless state, unless disturbed. The concept of an Astrophysical Storage Ring was introduced by me in l961. At first it was to explain galactic structure, but soon it proved useful to explain active galactic nuclei (AGN) and the dynamics of quasar/AGN jets. AGN and galactic morphology, energetics and dynamics vary as the ratio of magnetic energy to rotational energy in the particular object. Gamma ray bursts (GRB) are due simply to a ``rock". i.e. a white dwarf, ordinary star, neutron sstar, asteroid, planet, etc. falling rapidly through the Storage Ring and being almost instantly vaporized into a hot plasma fireball, causing an electromagnetic shower (2) Then the fireball speeds into the huge organized magnetic field surrounding the current ring, thus generating very highly polarized prompt gamma ray emission (as seen in GRB021206) from the synchrotron radiation process. The timing fits the GRB observations nicely. For instance, a ``rock" racing at 1000 kilometers per second across a 20,000 km. path in the beam would produce a twenty second burst. Other times, a target might track across a short chord for a short burst. Space missions have shown that often typical currents in space plasmas are made up of slender filaments. Thus the puzzling less than one millisecond spikes observed in some GRB are simply describing the structure of that particular ring current at that particular time. 1. W. Coburn and S.E. Boggs, Nature, 423, 415, (2003) 2. H. D. Greyber in a book, After the Dark Ages: When Galaxies Were Young, eds. S.S. Holt and E. P. Smith, AIP Conference Proceedings 470, 388-396. (1998) 3. H. D. Greyber in a Space Telescope Science Institute Report: Poster Papers from their 2001 Spring Symposium, ``The Dark Universe: Matter, Energy and Gravity," ed. Mario Livio, published March 2003, (34-39)

Predictions of cell damage rates for Lifesat missions

NASA Technical Reports Server (NTRS)

Cucinotta, Francis A.; Atwell, William; Hardy, Alva C.; Golightly, Michael J.; Wilson, John W.; Townsend, Lawrence W.; Shinn, Judy; Nealy, John E.; Katz, Robert

1990-01-01

The track model of Katz is used to make predictions of cell damage rates for possible Lifesat experiments. Contributions from trapped protons and electrons and galactic cosmic rays are considered for several orbits. Damage rates for survival and transformation of C3HT10-1/2 cells are predicted for various spacecraft shields.

Simulation of the GCR spectrum in the Mars curiosity rover's RAD detector using MCNP6

NASA Astrophysics Data System (ADS)

Ratliff, Hunter N.; Smith, Michael B. R.; Heilbronn, Lawrence

2017-08-01

The paper presents results from MCNP6 simulations of galactic cosmic ray (GCR) propagation down through the Martian atmosphere to the surface and comparison with RAD measurements made there. This effort is part of a collaborative modeling workshop for space radiation hosted by Southwest Research Institute (SwRI). All modeling teams were tasked with simulating the galactic cosmic ray (GCR) spectrum through the Martian atmosphere and the Radiation Assessment Detector (RAD) on-board the Curiosity rover. The detector had two separate particle acceptance angles, 4π and 30 ° off zenith. All ions with Z = 1 through Z = 28 were tracked in both scenarios while some additional secondary particles were only tracked in the 4π cases. The MCNP6 4π absorbed dose rate was 307.3 ± 1.3 μGy/day while RAD measured 233 μGy/day. Using the ICRP-60 dose equivalent conversion factors built into MCNP6, the simulated 4π dose equivalent rate was found to be 473.1 ± 2.4 μSv/day while RAD reported 710 μSv/day.

Reflections on works by I.S.Shklovsky regarding the nature of radio galaxies

NASA Astrophysics Data System (ADS)

Komberg, B. V.; Zhuravlev, V. I.

The paper is a brief overview of the works by Iosif S. Shklovsky (1916-1985), carried out over almost 30 years (1955-1985), on the nature of activity (primarily in the radio frequency range) in nuclei of some galaxies. Worthy of note is Shklovsky's pioneering work of 1962, in which he made an attempt to consider possible evolutionary tracks of extragalactic radio sources by constructing an analog of the Herzsprung-Russel diagram for stars (radio luminosity at 160 MHz was taken instead of optical luminosity; total radio size at the same frequency, as the other parameter). Later works by other authors are also discussed, where similar diagrams were plotted using a larger observational material. Special attention is paid to the evolution of Shklovsky's views regarding the possible ways of gas getting into radio galaxies' central regions, followed by high-velocity ejections of magnetized plasmons from their nuclei. Shklovsky's assumptions were mainly based on the observational data for the properties of the closest radio galaxy, NGC 4486 (Virgo A, M87), which he believed to be the same reference standard for extragalactic radio astronomy as the Crab Nebula for galactic radio astronomy. Shklovsky's approach to the recurrence of the activity phenomenon in galactic nuclei and the one-sided character of radio ejections from them is discussed. Modern views on these issues are also briefly considered.

Pondermotive acceleration of charged particles along the relativistic jets of an accreting blackhole

NASA Astrophysics Data System (ADS)

Ebisuzaki, T.; Tajima, T.

2014-05-01

Accreting blackholes such as miniquasars and active galactic nuclei can contribute to the highest energy components of intra- (˜1015 eV) galactic and extra-galactic components (˜1020 eV) of cosmic rays. Alfven wave pulses which are excited in the accretion disk around blackholes propagate in relativistic jets. Because of their highly non-linear nature of the waves, charged particles (protons, ions, and electrons) can be accelerated to high energies in relativistic jets in accreting blackhole systems, the central engine of miniquasars and active galactic nuclei.

Induced starburst and nuclear activity: Faith, facts, and theory

NASA Technical Reports Server (NTRS)

Shlosman, Isaac

1990-01-01

The problem of the origin of starburst and nuclear (nonstellar) activity in galaxies is reviewed. A physical understanding of the mechanism(s) that induce both types of activity requires one to address the following issues: (1) what is the source of fuel that powers starbursts and active galactic nuclei; and (2) how is it channeled towards the central regions of host galaxies? As a possible clue, the author examines the role of non-axisymmetric perturbations of galactic disks and analyzes their potential triggers. Global gravitational instabilities in the gas on scales approx. 100 pc appear to be crucial for fueling the active galactic nuclei.

Gravitational-wave localization alone can probe origin of stellar-mass black hole mergers.

PubMed

Bartos, I; Haiman, Z; Marka, Z; Metzger, B D; Stone, N C; Marka, S

2017-10-10

The recent discovery of gravitational waves from stellar-mass binary black hole mergers by the Laser Interferometer Gravitational-wave Observatory opened the door to alternative probes of stellar and galactic evolution, cosmology and fundamental physics. Probing the origin of binary black hole mergers will be difficult due to the expected lack of electromagnetic emission and limited localization accuracy. Associations with rare host galaxy types-such as active galactic nuclei-can nevertheless be identified statistically through spatial correlation. Here we establish the feasibility of statistically proving the connection between binary black hole mergers and active galactic nuclei as hosts, even if only a sub-population of mergers originate from active galactic nuclei. Our results are the demonstration that the limited localization of gravitational waves, previously written off as not useful to distinguish progenitor channels, can in fact contribute key information, broadening the range of astrophysical questions probed by binary black hole observations.Binary black hole mergers have recently been observed through the detection of gravitational wave signatures. The authors demonstrate that their association with active galactic nuclei can be made through a statistical spatial correlation.

Ram-pressure feeding of supermassive black holes.

PubMed

Poggianti, Bianca M; Jaffé, Yara L; Moretti, Alessia; Gullieuszik, Marco; Radovich, Mario; Tonnesen, Stephanie; Fritz, Jacopo; Bettoni, Daniela; Vulcani, Benedetta; Fasano, Giovanni; Bellhouse, Callum; Hau, George; Omizzolo, Alessandro

2017-08-16

When a supermassive black hole at the centre of a galaxy accretes matter, it gives rise to a highly energetic phenomenon: an active galactic nucleus. Numerous physical processes have been proposed to account for the funnelling of gas towards the galactic centre to feed the black hole. There are also several physical processes that can remove gas from a galaxy, one of which is ram-pressure stripping by the hot gas that fills the space between galaxies in galaxy clusters. Here we report that six out of a sample of seven 'jellyfish' galaxies-galaxies with long 'tentacles' of material that extend for dozens of kiloparsecs beyond the galactic disks-host an active nucleus, and two of them also have galactic-scale ionization cones. The high incidence of nuclear activity among heavily stripped jellyfish galaxies may be due to ram pressure causing gas to flow towards the centre and triggering the activity, or to an enhancement of the stripping caused by energy injection from the active nucleus, or both. Our analysis of the galactic position and velocity relative to the cluster strongly supports the first hypothesis, and puts forward ram pressure as another possible mechanism for feeding the central supermassive black hole with gas.

Ram-pressure feeding of supermassive black holes

NASA Astrophysics Data System (ADS)

Poggianti, Bianca M.; Jaffé, Yara L.; Moretti, Alessia; Gullieuszik, Marco; Radovich, Mario; Tonnesen, Stephanie; Fritz, Jacopo; Bettoni, Daniela; Vulcani, Benedetta; Fasano, Giovanni; Bellhouse, Callum; Hau, George; Omizzolo, Alessandro

2017-08-01

When a supermassive black hole at the centre of a galaxy accretes matter, it gives rise to a highly energetic phenomenon: an active galactic nucleus. Numerous physical processes have been proposed to account for the funnelling of gas towards the galactic centre to feed the black hole. There are also several physical processes that can remove gas from a galaxy, one of which is ram-pressure stripping by the hot gas that fills the space between galaxies in galaxy clusters. Here we report that six out of a sample of seven ‘jellyfish’ galaxies—galaxies with long ‘tentacles’ of material that extend for dozens of kiloparsecs beyond the galactic disks—host an active nucleus, and two of them also have galactic-scale ionization cones. The high incidence of nuclear activity among heavily stripped jellyfish galaxies may be due to ram pressure causing gas to flow towards the centre and triggering the activity, or to an enhancement of the stripping caused by energy injection from the active nucleus, or both. Our analysis of the galactic position and velocity relative to the cluster strongly supports the first hypothesis, and puts forward ram pressure as another possible mechanism for feeding the central supermassive black hole with gas.

The Energetic Gamma-Ray Experiment Telescope (EGRET) Science Symposium

NASA Technical Reports Server (NTRS)

Fichtel, Carl E. (Editor); Hunter, Stanley D. (Editor); Sreekumar, Parameswaran (Editor); Stecker, Floyd W. (Editor)

1990-01-01

The principle purpose of this symposium is to provide the EGRET (Energetic Gamma-Ray Experiment Telescope) scientists with an opportunity to study and improve their understanding of high energy gamma ray astronomy. The Symposium began with the galactic diffusion radiation both because of its importance in studying galactic cosmic rays, galactic structure, and dynamic balance, and because an understanding of its characteristics is important in the study of galactic sources. The galactic objects to be reviewed included pulsars, bursts, solar flares, and other galactic sources of several types. The symposium papers then proceeded outward from the Milky Way to normal galaxies, active galaxies, and the extragalactic diffuse radiation.

Track structure in biological models.

PubMed

Curtis, S B

1986-01-01

High-energy heavy ions in the galactic cosmic radiation (HZE particles) may pose a special risk during long term manned space flights outside the sheltering confines of the earth's geomagnetic field. These particles are highly ionizing, and they and their nuclear secondaries can penetrate many centimeters of body tissue. The three dimensional patterns of ionizations they create as they lose energy are referred to as their track structure. Several models of biological action on mammalian cells attempt to treat track structure or related quantities in their formulation. The methods by which they do this are reviewed. The proximity function is introduced in connection with the theory of Dual Radiation Action (DRA). The ion-gamma kill (IGK) model introduces the radial energy-density distribution, which is a smooth function characterizing both the magnitude and extension of a charged particle track. The lethal, potentially lethal (LPL) model introduces lambda, the mean distance between relevant ion clusters or biochemical species along the track. Since very localized energy depositions (within approximately 10 nm) are emphasized, the proximity function as defined in the DRA model is not of utility in characterizing track structure in the LPL formulation.

The heavy particle hazard, what physical data are needed?

NASA Technical Reports Server (NTRS)

Curtis, S. B.; Wilkinson, M. C.

1972-01-01

The physical data required to evaluate the radiation hazard from heavy galactic cosmic rays to astronauts on extended missions are discussed. The spectral characteristics, nuclear interaction parameters, and track structure of particles are emphasized. The data on the lower energy portion of the differential spectrum of the iron group and nuclear fragmentation in tissue and aluminum are tested, and results are shown.

Star formation around active galactic nuclei

NASA Technical Reports Server (NTRS)

Keel, William C.

1987-01-01

Active galactic nuclei (Seyfert nuclei and their relatives) and intense star formation can both deliver substantial amounts of energy to the vicinity of a galactic nucleus. Many luminous nuclei have energetics dominated by one of these mechanisms, but detailed observations show that some have a mixture. Seeing both phenomena at once raises several interesting questions: (1) Is this a general property of some kinds of nuclei? How many AGNs have surround starbursts, and vice versa? (2) As in 1, how many undiscovered AGNs or starbursts are hidden by a more luminous instance of the other? (3) Does one cause the other, and by what means, or do both reflect common influences such as potential well shape or level of gas flow? (4) Can surrounding star formation tell us anything about the central active nuclei, such as lifetimes, kinetic energy output, or mechanical disturbance of the ISM? These are important points in the understanding of activity and star formation in galactic nuclei. Unfortunately, the observational ways of addressing them are as yet not well formulated. Some preliminary studies are reported, aimed at clarifying the issues involved in study of the relationships between stellar and nonstellar excitement in galactic nuclei.

Predicting space climate change

NASA Astrophysics Data System (ADS)

Balcerak, Ernie

2011-10-01

Galactic cosmic rays and solar energetic particles can be hazardous to humans in space, damage spacecraft and satellites, pose threats to aircraft electronics, and expose aircrew and passengers to radiation. A new study shows that these threats are likely to increase in coming years as the Sun approaches the end of the period of high solar activity known as “grand solar maximum,” which has persisted through the past several decades. High solar activity can help protect the Earth by repelling incoming galactic cosmic rays. Understanding the past record can help scientists predict future conditions. Barnard et al. analyzed a 9300-year record of galactic cosmic ray and solar activity based on cosmogenic isotopes in ice cores as well as on neutron monitor data. They used this to predict future variations in galactic cosmic ray flux, near-Earth interplanetary magnetic field, sunspot number, and probability of large solar energetic particle events. The researchers found that the risk of space weather radiation events will likely increase noticeably over the next century compared with recent decades and that lower solar activity will lead to increased galactic cosmic ray levels. (Geophysical Research Letters, doi:10.1029/2011GL048489, 2011)

Reconfinement and loss of stability in jets from active galactic nuclei

NASA Astrophysics Data System (ADS)

Gourgouliatos, Konstantinos N.; Komissarov, Serguei S.

2018-02-01

Jets powered by active galactic nuclei appear impressively stable compared with their terrestrial and laboratory counterparts—they can be traced from their origin to distances exceeding their injection radius by up to a billion times1,2. However, some less energetic jets get disrupted and lose their coherence on the scale of their host galaxy1,3. Quite remarkably, on the same scale, these jets are expected to become confined by the thermal pressure of the intra-galactic gas2. Motivated by these observations, we have started a systematic study of active galactic nuclei jets undergoing reconfinement via computer simulations. Here, we show that in the case of unmagnetized relativistic jets, the reconfinement is accompanied by the development of an instability and transition to a turbulent state. During their initial growth, the perturbations have a highly organized streamwise-oriented structure, indicating that it is not the Kelvin-Helmholtz instability, the instability which has been the main focus of the jet stability studies so far4,5. Instead, it is closely related to the centrifugal instability6. This instability is likely to be behind the division of active galactic nuclei jets into two morphological types in the Fanaroff-Riley classification7.

Acceleration of petaelectronvolt protons in the Galactic Centre

NASA Astrophysics Data System (ADS)

HESS Collaboration; Abramowski, A.; Aharonian, F.; Benkhali, F. Ait; Akhperjanian, A. G.; Angüner, E. O.; Backes, M.; Balzer, A.; Becherini, Y.; Tjus, J. Becker; Berge, D.; Bernhard, S.; Bernlöhr, K.; Birsin, E.; Blackwell, R.; Böttcher, M.; Boisson, C.; Bolmont, J.; Bordas, P.; Bregeon, J.; Brun, F.; Brun, P.; Bryan, M.; Bulik, T.; Carr, J.; Casanova, S.; Chakraborty, N.; Chalme-Calvet, R.; Chaves, R. C. G.; Chen, A.; Chrétien, M.; Colafrancesco, S.; Cologna, G.; Conrad, J.; Couturier, C.; Cui, Y.; Davids, I. D.; Degrange, B.; Deil, C.; Dewilt, P.; Djannati-Ataï, A.; Domainko, W.; Donath, A.; Drury, L. O'C.; Dubus, G.; Dutson, K.; Dyks, J.; Dyrda, M.; Edwards, T.; Egberts, K.; Eger, P.; Ernenwein, J.-P.; Espigat, P.; Farnier, C.; Fegan, S.; Feinstein, F.; Fernandes, M. V.; Fernandez, D.; Fiasson, A.; Fontaine, G.; Förster, A.; Füßling, M.; Gabici, S.; Gajdus, M.; Gallant, Y. A.; Garrigoux, T.; Giavitto, G.; Giebels, B.; Glicenstein, J. F.; Gottschall, D.; Goyal, A.; Grondin, M.-H.; Grudzińska, M.; Hadasch, D.; Häffner, S.; Hahn, J.; Hawkes, J.; Heinzelmann, G.; Henri, G.; Hermann, G.; Hervet, O.; Hillert, A.; Hinton, J. A.; Hofmann, W.; Hofverberg, P.; Hoischen, C.; Holler, M.; Horns, D.; Ivascenko, A.; Jacholkowska, A.; Jamrozy, M.; Janiak, M.; Jankowsky, F.; Jung-Richardt, I.; Kastendieck, M. A.; Katarzyński, K.; Katz, U.; Kerszberg, D.; Khélifi, B.; Kieffer, M.; Klepser, S.; Klochkov, D.; Kluźniak, W.; Kolitzus, D.; Komin, Nu.; Kosack, K.; Krakau, S.; Krayzel, F.; Krüger, P. P.; Laffon, H.; Lamanna, G.; Lau, J.; Lefaucheur, J.; Lefranc, V.; Lemiére, A.; Lemoine-Goumard, M.; Lenain, J.-P.; Lohse, T.; Lopatin, A.; Lu, C.-C.; Lui, R.; Marandon, V.; Marcowith, A.; Mariaud, C.; Marx, R.; Maurin, G.; Maxted, N.; Mayer, M.; Meintjes, P. J.; Menzler, U.; Meyer, M.; Mitchell, A. M. W.; Moderski, R.; Mohamed, M.; Morå, K.; Moulin, E.; Murach, T.; de Naurois, M.; Niemiec, J.; Oakes, L.; Odaka, H.; Öttl, S.; Ohm, S.; Opitz, B.; Ostrowski, M.; Oya, I.; Panter, M.; Parsons, R. D.; Arribas, M. Paz; Pekeur, N. W.; Pelletier, G.; Petrucci, P.-O.; Peyaud, B.; Pita, S.; Poon, H.; Prokoph, H.; Pühlhofer, G.; Punch, M.; Quirrenbach, A.; Raab, S.; Reichardt, I.; Reimer, A.; Reimer, O.; Renaud, M.; de Los Reyes, R.; Rieger, F.; Romoli, C.; Rosier-Lees, S.; Rowell, G.; Rudak, B.; Rulten, C. B.; Sahakian, V.; Salek, D.; Sanchez, D. A.; Santangelo, A.; Sasaki, M.; Schlickeiser, R.; Schüssler, F.; Schulz, A.; Schwanke, U.; Schwemmer, S.; Seyffert, A. S.; Simoni, R.; Sol, H.; Spanier, F.; Spengler, G.; Spies, F.; Stawarz, Ł.; Steenkamp, R.; Stegmann, C.; Stinzing, F.; Stycz, K.; Sushch, I.; Tavernet, J.-P.; Tavernier, T.; Taylor, A. M.; Terrier, R.; Tluczykont, M.; Trichard, C.; Tuffs, R.; Valerius, K.; van der Walt, J.; van Eldik, C.; van Soelen, B.; Vasileiadis, G.; Veh, J.; Venter, C.; Viana, A.; Vincent, P.; Vink, J.; Voisin, F.; Völk, H. J.; Vuillaume, T.; Wagner, S. J.; Wagner, P.; Wagner, R. M.; Weidinger, M.; Weitzel, Q.; White, R.; Wierzcholska, A.; Willmann, P.; Wörnlein, A.; Wouters, D.; Yang, R.; Zabalza, V.; Zaborov, D.; Zacharias, M.; Zdziarski, A. A.; Zech, A.; Zefi, F.; Żywucka, N.

2016-03-01

Galactic cosmic rays reach energies of at least a few petaelectronvolts (of the order of 1015 electronvolts). This implies that our Galaxy contains petaelectronvolt accelerators (‘PeVatrons’), but all proposed models of Galactic cosmic-ray accelerators encounter difficulties at exactly these energies. Dozens of Galactic accelerators capable of accelerating particles to energies of tens of teraelectronvolts (of the order of 1013 electronvolts) were inferred from recent γ-ray observations. However, none of the currently known accelerators—not even the handful of shell-type supernova remnants commonly believed to supply most Galactic cosmic rays—has shown the characteristic tracers of petaelectronvolt particles, namely, power-law spectra of γ-rays extending without a cut-off or a spectral break to tens of teraelectronvolts. Here we report deep γ-ray observations with arcminute angular resolution of the region surrounding the Galactic Centre, which show the expected tracer of the presence of petaelectronvolt protons within the central 10 parsecs of the Galaxy. We propose that the supermassive black hole Sagittarius A* is linked to this PeVatron. Sagittarius A* went through active phases in the past, as demonstrated by X-ray outburstsand an outflow from the Galactic Centre. Although its current rate of particle acceleration is not sufficient to provide a substantial contribution to Galactic cosmic rays, Sagittarius A* could have plausibly been more active over the last 106-107 years, and therefore should be considered as a viable alternative to supernova remnants as a source of petaelectronvolt Galactic cosmic rays.

Galaxy interactions and the stimulation of nuclear activity

NASA Technical Reports Server (NTRS)

Heckman, Timothy M.

1990-01-01

The author discusses the idea that interactions between galaxies can lead to enhanced galactic activity. He discusses whether, apart from the observational evidence, there is a strong theoretical or heuristic motivation for investigating galaxy interactions as stimulators of nuclear activity in galaxies. Galactic interactions as mechanisms for triggering nuclear starbursts are covered.

ECCO: Th/U/Pu/Cm Dating of Galactic Cosmic Ray Nuclei

NASA Technical Reports Server (NTRS)

Westphal, A. J.; Weaver, B. A.; Solarz, M.; Dominquez, G.; Craig, N.; Adams, J. H.; Barbier, L. M.; Christian, E. R.; Mitchell, J. W.; Binns, W. R.;

Infrared Spectroscopy of Star Formation in Galactic and Extragalactic Regions

NASA Technical Reports Server (NTRS)

Smith, Howard A.; Hasan, Hashima (Technical Monitor)

2002-01-01

This report details work done in a project involving spectroscopic studies, including data analysis and modeling, of star-formation regions using an ensemble of archival space-based data including some from the Infrared Space Observatory's Long Wavelength Spectrometer and Short Wavelength Spectrometer, and other spectroscopic databases. We will include four kinds of regions: (1) disks around more evolved objects; (2) young, low or high mass pre-main sequence stars in star-formation regions; (3) star formation in external, bright IR (infrared) galaxies; and (4) the galactic center. During this period, work proceeded fully on track and on time. Details on workshops and conferences attended and research results are presented. A preprint article entitled 'The Far Infrared Lines of OH as Molecular Cloud Diagnostics' is included as an appendix.

A study of ultraviolet absorption lines through the complete Galactic halo by the analysis of HST faint object spectrograph spectra of active Galactic nuclei, 1

NASA Technical Reports Server (NTRS)

Burks, Geoffrey S.; Bartko, Frank; Shull, J. Michael; Stocke, John T.; Sachs, Elise R.; Burbidge, E. Margaret; Cohen, Ross D.; Junkkarinen, Vesa T.; Harms, Richard J.; Massa, Derck

1994-01-01

The ultraviolet (1150 - 2850 A) spectra of a number of active galactic nuclei (AGNs) observed with the Hubble Space Telescope (HST) Faint Object Spectrograph (FOS) have been used to study the properties of the Galactic halo. The objects that served as probes are 3C 273, PKS 0454-220, Pg 1211+143, CSO 251, Ton 951, and PG 1351+640. The equivalent widths of certain interstellar ions have been measured, with special attention paid to the C IV/C II and Si IV/Si II ratios. These ratios have been intercompared, and the highest values are found in the direction of 3C 273, where C IV/C II = 1.2 and Si IV/Si II greater than 1. These high ratios may be due to a nearby supernova remnant, rather than to ionized gas higher up in the Galactic halo. Our data give some support to the notion that QSO metal-line systems may arise from intervening galaxies which contain high supernova rates, galactic fountains, and turbulent mixing layers.

Active Galactic Nucleus

NASA Image and Video Library

2017-09-14

SCI2017_0007: Artist illustration of the thick ring of dust that can obscure the energetic processes that occur near the supermassive black hole of an active galactic nuclei. The SOFIA studies suggest that the dust distribution is about 30 percent smaller than previously thought. Credit: NASA/SOFIA/Lynette Cook

Single track effects, Biostack and risk assessment

NASA Technical Reports Server (NTRS)

Curtis, S. B.; Chatterjee, A. (Principal Investigator)

1994-01-01

The scientific career of Prof. Bucker has spanned a very exciting period in the fledgling science of Space Radiation Biology. The capability for placing biological objects in space was developed, and the methods for properly packaging, retrieving and analyzing them were worked out. Meaningful results on the effects of radiation were obtained for the first time. In fact, many of the successful techniques and methodologies for handling biological samples were developed in Prof. Bucker's laboratories, as attested by the extensive Biostack program. He was the first to suggest and successfully carry out experiments in space directly aimed at measuring effects of single tracks of high-energy heavy galactic cosmic rays by specifically identifying whether or not the object had been hit by a heavy particle track. Because the "hit" frequencies of heavy galactic cosmic rays to cell nuclei in the bodies of space travelers will be low, it is expected that any effects to humans on the cellular level will be dominated by single-track cell traversals. This includes the most important generally recognized late effect of space radiation exposure: radiation-induced cancer. This paper addresses the single-track nature of the space radiation environment, and points out the importance of single "hits" in the evaluation of radiation risk for long-term missions occurring outside the earth's magnetic field. A short review is made of biological objects found to show increased effects when "hit" by a single heavy charged-particle in space. A brief discussion is given of the most provocative results from the bacterial spore Bacillus subtilis: experimental evidence that tracks can affect biological systems at much larger distances from the trajectory than previously suspected, and that the resultant inactivation cross section in space calculated for this system is very large. When taken at face value, the implication of these results, when compared to those from experiments performed at ground-based accelerators with beams at low energies in the same LET range, is that high-energy particles can exert their influence a surprising distance from their trajectory and the inactivation cross sections are some 20 times larger than expected. Clearly, beams from high-energy heavy-ion accelerators should be used to confirm these results. For those end points that can also be caused by low-LET beams such as high-energy protons, it is important to measure their action cross sections as well. The ratio of the cross sections for a high-LET beam to that of a low-LET beam is an interesting experimental ratio and, we suggest, of more intrinsic interest than the RBE (Relative Biological Effectiveness). It is a measure of the "biological" importance of one particle type relative to another particle type. This ratio will be introduced and given the name RPPE (Relative Per Particle Effectiveness). Values of RPPE have appeared in the literature and will be discussed. A rather well-known value of this quantity (13,520) has been suggested for the RPPE of high-energy iron ions to high-energy protons. This value was suggested by Letaw et al. Nature 330, 709-710 (1987)] we will call it the Letaw limit. It will be discussed in terms of the importance of the heavy-ion component vs light-ion component of the galactic cosmic rays. It is also pointed out, however, that there may be unique effects from single tracks of heavy ions that do not occur from light-ion tracks. For such effects, the concepts of both RBE and RPPE lose their meaning.

Early Energetic Particle Irradiation of the HED Parent Body Regolith

NASA Technical Reports Server (NTRS)

Bogard, D. D.; Garrison, D. H.; Rao, M. N.

1996-01-01

Previous studies have shown that many individual grains within the dark phase of the Kapoeta howardite were irradiated with energetic particles while residing on the surface of the early HED regolith. Particle tracks in these grains vary in density by more than an order of magnitude and undoubtedly were formed by energetic heavy (Fe) ions associated with early solar flares. Early Irradiation of HED Regolith: Concentrations of excess Ne alone are not sufficient to decide between competing galactic and solar irradiation models. However, from recent studies of depth samples of oriented lunar rocks, we have shown that the cosmogenic 21-Ne/22-Ne ratio produced in feldspar differs substantially between Galactic Cosmic Radiation (GCR) and solar protons, and that this difference is exactly that predicted from cross-section data. Using Ne literature data and new isotopic data we obtained on acid-etched, separated feldspar from both the light and dark phases of Kapoeta, we derive 21-Ne/22-Ne = 0.80 for the recent GCR irradiation and 21-Ne/22-Ne = 0.68 for the early regolith irradiation. This derived ratio indicates that the early Ne production in the regolith occurred by both galactic and solar protons. If we adopt a likely one-component regolith model in which all grains were exposed to galactic protons but individual grains had variable exposure to solar protons, we estimate that this early GCR irradiation lasted for about 3-6 m.y. More complex two-component regolith models involving separate solar and galactic irradiation would permit this GCR age to be longer. Higher-energy solar protons would permit the GCR to be longer. Higher-energy solar protons would permit the GCR age to be shorter. Further, cosmogenic 126(Xe) in Kapoeta dark is no more than a factor of about 2 higher than that observed in Kapoeta light. Because 126(Xe) can only be formed by galactic protons and not solar protons, these data support a short GCR irradiation for the HED regolith. This would also be the maximum time peRiod for the solar irradiation. Various asteroidal regolith models, based on Monte Carlo modeling of impact rates as a function of size and on irradiation features of meteorites, predict surface exposure times of about 0.1 to 10 m.y., and depend on such factors as gravity, rock mechanical properties, and micrometeoroid flux. Because the depth at which solar Fe tracks are produced (is much less than 1 micrometer) is much less than the depth at which Solar Cosmic Rays (SCR) Ne is produced (about 1 cm), for a reasonably well-stirred HED regolith the "surface exposure time" for SCR 21-Ne production should be significantly longer than that for solar tracks and some other surface irradiation features. Enhanced Solar Proton Irradiation: For bulk samples of Kapoeta dark feldspar and a one-component regolith model, the derived ratio of 21-Ne/22-Ne = 0.68 implies that the early production ratio of SCR 21-Ne to GCR 21-Ne was about 0.5-1.5. This ratio is independent of any assumptions about the fraction of dark grains that are irradiated or of the variability in the degree of solar irradiation among grains. The 21-Ne SCR/GCR ratio indirectly derived from bulk Kapoeta pyroxene is somewhat larger, as is the ratio derived for simple two-component regolith models. Individual feldspar grains that were extensively solar irradiated would require even larger 21-Ne SCR/GCR production ratios. In contrast, the theoretical SCR/GCR production ratio for lunar feldspar with 0 g/CM2 shield ing is is less than or equal to 2, and the lowest ratio observed in near-surface samples of lunar anorthosites is less than or equal to 1. Considering the greater solar distance of Vesta (compared to the Moon), the likelihood that SCR 21-Ne was acquired under some shielding where production rates are lower, and the likelihood that the exposure time to galactic protons exceeded the exposure time to solar protons because of their very different penetration depths, the 21-Ne SCR/GCR production ratio on the HED parent body was probably < 0.1. The relatively large difference between the derived 21-Ne SCR/GCR ratio in Kapoeta dark feldspar and the estimated production ratio strongly indicates that the early solar irradiation involved a flux -20-50x the recent solar flux. This enhanced proton flux was probably associated with an overall greater solar activity in the first approximately 10(exp 7) to 10(exp 8) years of solar history.

PeV Neutrinos Observed by IceCube from Cores of Active Galactic Nuclei

NASA Technical Reports Server (NTRS)

Stecker, Floyd W.

2013-01-01

I show that the high energy neutrino flux predicted to arise from active galactic nuclei cores can explain the PeV neutrinos detected by IceCube without conflicting with the constraints from the observed extragalactic cosmic-ray and gamma-ray backgrounds.

Dual-Frequency VLBI Study of Centaurus A on Sub-Parsec Scales: The Highest-Resolution View of an Extragalactic Jet

NASA Technical Reports Server (NTRS)

Mueller, C.; Kadler, M.; Ojha, R.; Wilms, J.; Boeck, M.; Edwards, P.; Fromm, C. M.; Hase, H.; Horiuchi, S.; Katz, U.;

[Survivability and morphologic anomalies in higher plants wolffia arrhiza following exposure to heavy ions of the galactic space radiation].

PubMed

Nevzgodina, L V; Kaminskaia, E V; Maksimova, E N; Fatsius, R; Sherrer, K; Shtraukh, V

2000-01-01

Experimental data on the effects of spaceflight factors, space radiation in particular, on higher plant Wolffia arrhiza firstly exposed in the "Bioblock" assembly and measurements made by physical track detectors of heavy ions (HI) are presented. Death of individual Wolffia plants and morphologic anomalies were the basic evaluation criteria. The peculiar feature of this biological object consists in the possibility to reveal delayed effects after 1-2 months since space flight as Wolffia has a high rate of vegetative reproduction. German investigators through microscopic examination of track detectors performed identification of individual plants affected by HI. With specially developed software and a coordinate system of supposition of biolayers and track detectors with the accuracy of 1 micron, tracks and even separate sections of individual HI tracks were determined in biological objects. Thereafter each Wolffia plant hit by HI was examined and data were compared with other variants. As a result, correlation between Wolffia death rate and morphologic anomalies were determined at different times post flight and topography of HI tracks was found. It is hypothesized that morphological anomalies in Walffia were caused by direct hits of plant germs by heavy ions or close passage of particles.

Simulation of the GCR spectrum in the Mars curiosity rover's RAD detector using MCNP6.

PubMed

Ratliff, Hunter N; Smith, Michael B R; Heilbronn, Lawrence

2017-08-01

The paper presents results from MCNP6 simulations of galactic cosmic ray (GCR) propagation down through the Martian atmosphere to the surface and comparison with RAD measurements made there. This effort is part of a collaborative modeling workshop for space radiation hosted by Southwest Research Institute (SwRI). All modeling teams were tasked with simulating the galactic cosmic ray (GCR) spectrum through the Martian atmosphere and the Radiation Assessment Detector (RAD) on-board the Curiosity rover. The detector had two separate particle acceptance angles, 4π and 30 ° off zenith. All ions with Z = 1 through Z = 28 were tracked in both scenarios while some additional secondary particles were only tracked in the 4π cases. The MCNP6 4π absorbed dose rate was 307.3 ± 1.3 µGy/day while RAD measured 233 µGy/day. Using the ICRP-60 dose equivalent conversion factors built into MCNP6, the simulated 4π dose equivalent rate was found to be 473.1 ± 2.4 µSv/day while RAD reported 710 µSv/day. Copyright © 2017 The Committee on Space Research (COSPAR). Published by Elsevier Ltd. All rights reserved.

Effects of target fragmentation on evaluation of LET spectra from space radiations: implications for space radiation protection studies

NASA Technical Reports Server (NTRS)

Cucinotta, F. A.; Wilson, J. W.; Shinn, J. L.; Badavi, F. F.; Badhwar, G. D.

1996-01-01

We present calculations of linear energy transfer (LET) spectra in low earth orbit from galactic cosmic rays and trapped protons using the HZETRN/BRYNTRN computer code. The emphasis of our calculations is on the analysis of the effects of secondary nuclei produced through target fragmentation in the spacecraft shield or detectors. Recent improvements in the HZETRN/BRYNTRN radiation transport computer code are described. Calculations show that at large values of LET (> 100 keV/micrometer) the LET spectra seen in free space and low earth orbit (LEO) are dominated by target fragments and not the primary nuclei. Although the evaluation of microdosimetric spectra is not considered here, calculations of LET spectra support that the large lineal energy (y) events are dominated by the target fragments. Finally, we discuss the situation for interplanetary exposures to galactic cosmic rays and show that current radiation transport codes predict that in the region of high LET values the LET spectra at significant shield depths (> 10 g/cm2 of Al) is greatly modified by target fragments. These results suggest that studies of track structure and biological response of space radiation should place emphasis on short tracks of medium charge fragments produced in the human body by high energy protons and neutrons.

IceCube results from point-like source searches using 6 years of through-going muon data

NASA Astrophysics Data System (ADS)

Coenders, Stefan

2016-04-01

The IceCube Neutrino Observatory located at the geographic South Pole was designed to study and discover high energy neutrinos coming from both galactic and extra-galactic astrophysical sources. Track-like events induced by charged-current muon-neutrino interactions close to the IceCube detector give an angular resolution better than 1∘ above TeV energies. We present here the results of searches for point-like astrophysical neutrino sources on the full sky using 6 years of detector livetime, of which three years use the complete IceCube detector. Within 2000 days of detector livetime, IceCube is sensitive to a steady flux substantially below E2∂ϕ/∂E = 10-12 TeV cm-2 s-1 in the northern sky for neutrino energies above 10 TeV.

A Shifting Shield Provides Protection Against Cosmic Rays

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-12-01

The Sun plays an important role in protecting us from cosmic rays, energetic particles that pelt us from outside our solar system. But can we predict when and how it will provide the most protection, and use this to minimize the damage to both pilotedand roboticspace missions?The Challenge of Cosmic RaysSpacecraft outside of Earths atmosphere and magnetic field are at risk of damage from cosmic rays. [ESA]Galactic cosmic rays are high-energy, charged particles that originate from astrophysical processes like supernovae or even distant active galactic nuclei outside of our solar system.One reason to care about the cosmic rays arriving near Earth is because these particles can provide a significant challenge for space missions traveling above Earths protective atmosphere and magnetic field. Since impacts from cosmic rays can damage human DNA, this risk poses a major barrier to plans for interplanetary travel by crewed spacecraft. And roboticmissions arent safe either: cosmic rays can flip bits, wreaking havoc on spacecraft electronics as well.The magnetic field carried by the solar wind provides a protective shield, deflecting galactic cosmic rays from our solar system. [Walt Feimer/NASA GSFCs Conceptual Image Lab]Shielded by the SunConveniently, we do have some broader protection against galactic cosmic rays: a built-in shield provided by the Sun. The interplanetary magnetic field, which is embedded in the solar wind, deflects low-energy cosmic rays from us at the outer reaches of our solar system, decreasing the flux of these cosmic rays that reach us at Earth.This shield, however, isnt stationary; instead, it moves and changes as the strength and direction of the solar wind moves and changes. This results in a much lower cosmic-ray flux at Earth when solar activity is high i.e., at the peak of the 11-year solar cycle than when solar activity is low. This visible change in local cosmic-ray flux with solar activity is known as solar modulation of the cosmic ray flux at Earth.In a new study, a team of scientists led by Nicola Tomassetti (University of Perugia, Italy) has modeled this solar modulation to better understand the process by which the Suns changing activity influences the cosmic ray flux that reaches us at Earth.Modeling a LagTomassetti and collaborators model uses two solar-activity observables as inputs: the number of sunspots and the tilt angle of the heliospheric current sheet. By modeling basic transport processes in the heliosphere, the authors then track the impact that the changing solar properties have on incoming galactic cosmic rays. In particular, the team explores the time lag between when solar activity changes and when we see the responding change in the cosmic-ray flux.Cosmic-ray flux observations are best fit by the authors model when an 8-month lag is included (red bold line). A comparison model with no lag (black dashed line) is included. [Tomassetti et al. 2017]By comparing their model outputs to the large collection of time-dependent observations of cosmic-ray fluxes, Tomassetti and collaborators show that the best fit to data occurs with an 8-month lag between changing solar activity and local cosmic-ray flux modulation.This is an important outcome for studying the processes that affect the cosmic-ray flux that reaches Earth. But theres an additional intriguing consequence of this result: knowledge of the current solar activity could allow us to predict the modulation that will occur for cosmic rays near Earth an entire 8 months from now! If this model is correct, it brings us one step closer to being able to plan safer space missions for the future.CitationNicola Tomassetti et al 2017 ApJL 849 L32. doi:10.3847/2041-8213/aa9373

A summary of recent results from the GRAPES-3 experiment

NASA Astrophysics Data System (ADS)

Gupta, S. K.

2017-06-01

The GRAPES-3 experiment is a combination of a high density extensive air shower (EAS) array of nearly 400 plastic scintillator detectors, and a large 560 m2 area tracking muon telescope with an energy threshold Eμ >1 GeV. GRAPES-3 has been operating continuously in Ooty, India since 2000. By accurately correcting for the effects of atmospheric pressure and temperature, the muon telescope provides a high precision directional survey of the galactic cosmic ray (GCR) intensity. This telescope has been used to observe the acceleration of muons during thunderstorm events. The recent discovery of a transient weakening of the Earth's magnetic shield through the detection of a GCR burst was the highlight of the GRAPES-3 results. We have an ongoing major expansion activity to further enhance the capability of the GRAPES-3 muon telescope by doubling its area.

Galaxy IC 3639 with Obscured Active Galactic Nucleus

NASA Image and Video Library

2017-01-07

IC 3639, a galaxy with an active galactic nucleus, is seen in this image combining data from the Hubble Space Telescope and the European Southern Observatory. This galaxy contains an example of a supermassive black hole hidden by gas and dust. Researchers analyzed NuSTAR data from this object and compared them with previous observations from NASA's Chandra X-Ray Observatory and the Japanese-led Suzaku satellite. The findings from NuSTAR, which is more sensitive to higher energy X-rays than these observatories, confirm the nature of IC 3639 as an active galactic nucleus that is heavily obscured, and intrinsically much brighter than observed. http://photojournal.jpl.nasa.gov/catalog/PIA21087

Gravitational lensing of active galactic nuclei.

PubMed

Hewitt, J N

1995-12-05

Most of the known cases of strong gravitational lensing involve multiple imaging of an active galactic nucleus. The properties of lensed active galactic nuclei make them promising systems for astrophysical applications of gravitational lensing; in particular, they show structure on scales of milliseconds of arc to tens of seconds of arc, they are variable, and they are polarized. More than 20 cases of strong gravitational lenses are now known, and about half of them are radio sources. High-resolution radio imaging is making possible the development of well-constrained lens models. Variability studies at radio and optical wavelengths are beginning to yield results of astrophysical interest, such as an independent measure of the distance scale and limits on source sizes.

Nature of the fossil evidence - Moon and meteorites. [solar activity effects

NASA Technical Reports Server (NTRS)

Walker, R. M.

1980-01-01

The nature of the fossil evidence to be found in extraterrestrial materials concerning the history of solar activity is reviewed. The various types of lunar rocks and meteorites containing evidence of exposure to solar radiations are distinguished, including igneous rocks, breccias, glassy agglutinates, single mineral crystals, carbonaceous meteorites, and the Antarctic meteorites, some of which fell to earth as much as a million years ago. The characteristic effects of energetic particles from space in materials are then examined, including ion implantation and surface radiation damage to a depth of several hundred A by the solar wind, radioactivity, electron trapping and track production induced by solar flares to depths from millimeters to centimeters, and spallation due to galactic cosmic rays at depths from centimeters to meters. Complications in the interpretation of radiation exposure histories represented by dynamic surface processes, the nonsolar origin of some trapped elements, and difficulties in determining the duration and epoch of surface exposure of individual crystals are also noted.

The planetary nebulae populations in five galaxies: abundance patterns and evolution

NASA Astrophysics Data System (ADS)

Stasińska, G.; Richer, M. G.; McCall, M. L.

1998-08-01

We have collected photometric and spectroscopic data on planetary nebulae (PNe) in 5 galaxies: the Milky Way (bulge), M 31 (bulge), M 32, the LMC and the SMC. We have computed the abundances of O, Ne and N and compared them from one galaxy to another. In each Galaxy, the distribution of oxygen abundances has a large dispersion. The average O/H ratio is larger in the M 31 and the Galactic bulge PNe than in those in the Magellanic Clouds. In a given galaxy, it is also larger for PNe with [O III] luminosities greater than 100 L_⊙, which are likely to probe more recent epochs in the galaxy history. We find that the M 31 and the Galactic bulge PNe extend the very tight Ne/H-O/H correlation observed in the Galactic disk and Magellanic Clouds PNe towards higher metallicities. We note that the anticorrelation between N/O and O/H that was known to occur in the Magellanic Clouds and in the disk PNe is also marginally found in the PNe of the Galactic bulge. Furthermore, we find that high N/O ratios are higher for less luminous PNe. In M 32, all PNe have a large N/O ratio, indicating that the stellar nitrogen abundance is enhanced in this galaxy. We have also compared the PN evolution in the different galactic systems by constructing diagrams that are independent of abundances, and have found strikingly different behaviours of the various samples. In order to help in the interpretation of these data, we have constructed a grid of expanding, PN photoionization models in which the central stars evolve according to the evolutionary tracks of Bl{öcker (1995). These models show that the apparent spectroscopic properties of PNe are extremely dependent, not only on the central stars, but also on the masses and expansion velocities of the nebular envelopes. The main conclusion of the confrontation of the observed samples with the model grids is that the PN populations are indeed not the same in the various parent galaxies. Both stars and nebulae are different. In particular, the central stars of the Magellanic Clouds PNe are shown to evolve differently from the hydrogen burning stellar evolutionary models of Bl{öcker (1995). In the Galactic bulge, on the other hand, the behaviour of the observed PNe is roughly compatible with the theoretical stellar evolutionary tracks. The case of M 31 is not quite clear, and additional observations are necessary. It seems that the central star mass distribution is narrower for the M 31 PNe than for the Galactic bulge PNe. We show that spectroscopy of complete samples of PNe down to a factor 100 below the maximum luminosity would help to better characterize the PN central star mass distribution. Tables 1 and 2 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http: //cdsweb.u-strasbg.fr/Abstract.html

First light for GRAVITY: Phase referencing optical interferometry for the Very Large Telescope Interferometer

NASA Astrophysics Data System (ADS)

Gravity Collaboration; Abuter, R.; Accardo, M.; Amorim, A.; Anugu, N.; Ávila, G.; Azouaoui, N.; Benisty, M.; Berger, J. P.; Blind, N.; Bonnet, H.; Bourget, P.; Brandner, W.; Brast, R.; Buron, A.; Burtscher, L.; Cassaing, F.; Chapron, F.; Choquet, É.; Clénet, Y.; Collin, C.; Coudé Du Foresto, V.; de Wit, W.; de Zeeuw, P. T.; Deen, C.; Delplancke-Ströbele, F.; Dembet, R.; Derie, F.; Dexter, J.; Duvert, G.; Ebert, M.; Eckart, A.; Eisenhauer, F.; Esselborn, M.; Fédou, P.; Finger, G.; Garcia, P.; Garcia Dabo, C. E.; Garcia Lopez, R.; Gendron, E.; Genzel, R.; Gillessen, S.; Gonte, F.; Gordo, P.; Grould, M.; Grözinger, U.; Guieu, S.; Haguenauer, P.; Hans, O.; Haubois, X.; Haug, M.; Haussmann, F.; Henning, Th.; Hippler, S.; Horrobin, M.; Huber, A.; Hubert, Z.; Hubin, N.; Hummel, C. A.; Jakob, G.; Janssen, A.; Jochum, L.; Jocou, L.; Kaufer, A.; Kellner, S.; Kendrew, S.; Kern, L.; Kervella, P.; Kiekebusch, M.; Klein, R.; Kok, Y.; Kolb, J.; Kulas, M.; Lacour, S.; Lapeyrère, V.; Lazareff, B.; Le Bouquin, J.-B.; Lèna, P.; Lenzen, R.; Lévêque, S.; Lippa, M.; Magnard, Y.; Mehrgan, L.; Mellein, M.; Mérand, A.; Moreno-Ventas, J.; Moulin, T.; Müller, E.; Müller, F.; Neumann, U.; Oberti, S.; Ott, T.; Pallanca, L.; Panduro, J.; Pasquini, L.; Paumard, T.; Percheron, I.; Perraut, K.; Perrin, G.; Pflüger, A.; Pfuhl, O.; Phan Duc, T.; Plewa, P. M.; Popovic, D.; Rabien, S.; Ramírez, A.; Ramos, J.; Rau, C.; Riquelme, M.; Rohloff, R.-R.; Rousset, G.; Sanchez-Bermudez, J.; Scheithauer, S.; Schöller, M.; Schuhler, N.; Spyromilio, J.; Straubmeier, C.; Sturm, E.; Suarez, M.; Tristram, K. R. W.; Ventura, N.; Vincent, F.; Waisberg, I.; Wank, I.; Weber, J.; Wieprecht, E.; Wiest, M.; Wiezorrek, E.; Wittkowski, M.; Woillez, J.; Wolff, B.; Yazici, S.; Ziegler, D.; Zins, G.

2017-06-01

GRAVITY is a new instrument to coherently combine the light of the European Southern Observatory Very Large Telescope Interferometer to form a telescope with an equivalent 130 m diameter angular resolution and a collecting area of 200 m2. The instrument comprises fiber fed integrated optics beam combination, high resolution spectroscopy, built-in beam analysis and control, near-infrared wavefront sensing, phase-tracking, dual-beam operation, and laser metrology. GRAVITY opens up to optical/infrared interferometry the techniques of phase referenced imaging and narrow angle astrometry, in many aspects following the concepts of radio interferometry. This article gives an overview of GRAVITY and reports on the performance and the first astronomical observations during commissioning in 2015/16. We demonstrate phase-tracking on stars as faint as mK ≈ 10 mag, phase-referenced interferometry of objects fainter than mK ≈ 15 mag with a limiting magnitude of mK ≈ 17 mag, minute long coherent integrations, a visibility accuracy of better than 0.25%, and spectro-differential phase and closure phase accuracy better than 0.5°, corresponding to a differential astrometric precision of better than ten microarcseconds (μas). The dual-beam astrometry, measuring the phase difference of two objects with laser metrology, is still under commissioning. First observations show residuals as low as 50 μas when following objects over several months. We illustrate the instrument performance with the observations of archetypical objects for the different instrument modes. Examples include the Galactic center supermassive black hole and its fast orbiting star S2 for phase referenced dual-beam observations and infrared wavefront sensing, the high mass X-ray binary BP Cru and the active galactic nucleus of PDS 456 for a few μas spectro-differential astrometry, the T Tauri star S CrA for a spectro-differential visibility analysis, ξ Tel and 24 Cap for high accuracy visibility observations, and η Car for interferometric imaging with GRAVITY.

Gravitational lensing of active galactic nuclei.

PubMed Central

Hewitt, J N

1995-01-01

Most of the known cases of strong gravitational lensing involve multiple imaging of an active galactic nucleus. The properties of lensed active galactic nuclei make them promising systems for astrophysical applications of gravitational lensing; in particular, they show structure on scales of milliseconds of arc to tens of seconds of arc, they are variable, and they are polarized. More than 20 cases of strong gravitational lenses are now known, and about half of them are radio sources. High-resolution radio imaging is making possible the development of well-constrained lens models. Variability studies at radio and optical wavelengths are beginning to yield results of astrophysical interest, such as an independent measure of the distance scale and limits on source sizes. PMID:11607613

70 DA White Dwarfs Identified in LAMOST Pilot Survey

NASA Astrophysics Data System (ADS)

Zhao, J. K.; Luo, A. L.; Oswalt, T. D.; Zhao, G.

2013-06-01

We present a spectroscopically identified catalog of 70 DA white dwarfs (WDs) from the LAMOST pilot survey. Thirty-five are found to be new identifications after cross-correlation with the Eisenstein et al. and Villanova catalogs. The effective temperature and gravity of these WDs are estimated by Balmer lines fitting. Most of them are hot WDs. The cooling times and masses of these WDs are estimated by interpolation in theoretical evolution tracks. The peak of the mass distribution is found to be ~0.6 M ⊙, which is consistent with prior work in the literature. The distances of these WDs are estimated using the method of synthetic spectral distances. All of these WDs are found to be in the Galactic disk from our analysis of space motions. Our sample supports the expectation that WDs with high mass are concentrated near the plane of the Galactic disk.

70 DA WHITE DWARFS IDENTIFIED IN LAMOST PILOT SURVEY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, J. K.; Luo, A. L.; Zhao, G.

2013-06-01

We present a spectroscopically identified catalog of 70 DA white dwarfs (WDs) from the LAMOST pilot survey. Thirty-five are found to be new identifications after cross-correlation with the Eisenstein et al. and Villanova catalogs. The effective temperature and gravity of these WDs are estimated by Balmer lines fitting. Most of them are hot WDs. The cooling times and masses of these WDs are estimated by interpolation in theoretical evolution tracks. The peak of the mass distribution is found to be {approx}0.6 M {sub Sun }, which is consistent with prior work in the literature. The distances of these WDs aremore » estimated using the method of synthetic spectral distances. All of these WDs are found to be in the Galactic disk from our analysis of space motions. Our sample supports the expectation that WDs with high mass are concentrated near the plane of the Galactic disk.« less

Massive stars near Eta Carinae - The stellar content of TR 14 and TR 16

NASA Astrophysics Data System (ADS)

Massey, Philip; Johnson, Jennifer

1993-03-01

The stellar content of the region around the star Eta Carinae, including the two Galactic OB clusters Tr 14 and Tr 16, are investigated using CCD photometry and spectroscopy. A physical H-R diagram is constructed which shows that several stars are located above the 85-solar mass track, as well as that the location of Eta Carinae is consistent with the interpretation that it is a very massive star undergoing a normal evolutionary stage. The W-R star which is present in this region is lower in luminosity than expected. The initial mass function derived, which is similar to two other young Galactic clusters studied, has a slope flatter than some regions in the Magellanic Clouds that are also rich in massive stars. The most luminous and massive stars near Eta Carinae are not significantly more than the most luminous and massive stars found in the Magellanic Clouds.

An Electron-positron Jet Model for the Galactic Center

NASA Technical Reports Server (NTRS)

Burns, M. L.

1983-01-01

High energy observations of the galactic center on the subparsec scale seem to be consistent with electron-positron production in the form of relativistic jets. These jets could be produced by an approximately 1,000,000 solar mass black hole dynamo transportating pairs away from the massive core. An electromagnetic cascade shower would develop first from ambient soft protons and then nonlinearly; the shower using itself as a scattering medium. This is suited to producing, cooling and transporting pairs to the observed annihilation region. It is possible the center of our galaxy is a miniature version of more powerful active galactic nuclei that exhibit jet activity.

An electron-positron jet model for the Galactic center

NASA Technical Reports Server (NTRS)

Burns, M. L.

1983-01-01

High energy observations of the galactic center on the subparsec scale seem to be consistent with electron-positron production in the form of relativistic jets. These jets could be produced by an approximately 1,000,000 solar mass black hole dynamo transporting pairs away from the massive core. An electomagnetic cascade shower would develop first from ambient soft protons and then nonlinearly, the shower using itself as a scattering medium. This is suited to producing, cooling and transporting pairs to the observed annihilation region. It is possible the center of our galaxy is a miniature version of more powerful active galactic nuclei that exhibit jet activity.

An electron-positron jet model for the Galactic center

NASA Astrophysics Data System (ADS)

Burns, M. L.

1983-07-01

High energy observations of the galactic center on the subparsec scale seem to be consistent with electron-positron production in the form of relativistic jets. These jets could be produced by an approximately 1,000,000 solar mass black hole dynamo transporting pairs away from the massive core. An electomagnetic cascade shower would develop first from ambient soft protons and then nonlinearly, the shower using itself as a scattering medium. This is suited to producing, cooling and transporting pairs to the observed annihilation region. It is possible the center of our galaxy is a miniature version of more powerful active galactic nuclei that exhibit jet activity.

An electron-positron jet model for the galactic center

NASA Astrophysics Data System (ADS)

Burns, M. L.

1983-03-01

High energy observations of the galactic center on the subparsec scale seem to be consistent with electron-positron production in the form of relativistic jets. These jets could be produced by an approximately 1,000,000 solar mass black hole dynamo transportating pairs away from the massive core. An electromagnetic cascade shower would develop first from ambient soft protons and then nonlinearly; the shower using itself as a scattering medium. This is suited to producing, cooling and transporting pairs to the observed annihilation region. It is possible the center of our galaxy is a miniature version of more powerful active galactic nuclei that exhibit jet activity.

The habitability of the Milky Way during the active phase of its central supermassive black hole.

PubMed

Balbi, Amedeo; Tombesi, Francesco

2017-11-30

During the peak of their accretion phase, supermassive black holes in galactic cores are known to emit very high levels of ionizing radiation, becoming visible over intergalactic distances as quasars or active galactic nuclei (AGN). Here, we quantify the extent to which the activity of the supermassive black hole at the center of the Milky Way, known as Sagittarius A* (Sgr A*), may have affected the habitability of Earth-like planets in our Galaxy. We focus on the amount of atmospheric loss and on the possible biological damage suffered by planets exposed to X-ray and extreme ultraviolet (XUV) radiation produced during the peak of the active phase of Sgr A*. We find that terrestrial planets could lose a total atmospheric mass comparable to that of present day Earth even at large distances (~1 kiloparsec) from the galactic center. Furthermore, we find that the direct biological damage caused by Sgr A* to surface life on planets not properly screened by an atmosphere was probably significant during the AGN phase, possibly hindering the development of complex life within a few kiloparsecs from the galactic center.

Neutrino detection of transient sources with optical follow-up observations

NASA Astrophysics Data System (ADS)

Dornic, D.; Ageron, M.; Al Samarai, I.; Basa, S.; Bertin, V.; Brunner, J.; Busto, J.; Escoffier, S.; Schussler, F.; Vallage, B.; Vecchi, M.

2010-12-01

The ANTARES telescope has the opportunity to detect transient neutrino sources,such as gamma-ray bursts,core-collapse supernovae,flares of active galactic nuclei. To enhance the sensitivity to these sources, a new detection method based on coincident observations of neutrinos and optical signals has been developed. For this purpose the ANTARES Collaboration has implemented a fast on-line muon track reconstruction with a good angular resolution. These characteristics allow to trigger a network of optical telescopes in order to identify the nature of the neutrino sources. An optical follow-up of special events, such as neutrino doublets, coincident in time and direction, or single neutrinos with a very high energy, would not only give access to the nature of their sources but also improve the sensitivity for neutrino detection. The alert system is operational since early 2009, and as of September 2010, 22 alerts have been sent to the TAROT and ROTSE telescopes.

International data transfer for space very long baseline interferometry

NASA Technical Reports Server (NTRS)

Wiercigroch, Alexandria B.

1994-01-01

Space very long baseline interferometry (SVLBI) experiments using a TDRSS satellite have successfully demonstrated the capability of using spacecraft to extend the effective baseline length of VLBI observations beyond the diameter of the Earth, thereby improving the resolution for imaging of active galactic nuclei at centimeter wavelengths. As a result, two spacecraft dedicated to SVLBI, VSOP (Japan) and RadioAstron (Russia), are scheduled to be launched into high Earth orbit in 1996 and 1997. The success of these missions depends on the cooperation of the international community in providing support from ground tracking stations, ground radio telescopes, and correlation facilities. The timely exchange and monitoring of data among the participants requires a well-designed and automated international data transfer system. In this paper, we will discuss the design requirements, data types and flows, and the operational responsibilities associated with the SVLBI data transfer system.

Discovery of very high energy gamma rays associated with an x-ray binary.

PubMed

Aharonian, F; Akhperjanian, A G; Aye, K-M; Bazer-Bachi, A R; Beilicke, M; Benbow, W; Berge, D; Berghaus, P; Bernlöhr, K; Boisson, C; Bolz, O; Borrel, V; Braun, I; Breitling, F; Brown, A M; Bussons Gordo, J; Chadwick, P M; Chounet, L-M; Cornils, R; Costamante, L; Degrange, B; Dickinson, H J; Djannati-Ataï, A; Drury, L O'c; Dubus, G; Emmanoulopoulos, D; Espigat, P; Feinstein, F; Fleury, P; Fontaine, G; Fuchs, Y; Funk, S; Gallant, Y A; Giebels, B; Gillessen, S; Glicenstein, J F; Goret, P; Hadjichristidis, C; Hauser, M; Heinzelmann, G; Henri, G; Hermann, G; Hinton, J A; Hofmann, W; Holleran, M; Horns, D; Jacholkowska, A; de Jager, O C; Khélifi, B; Komin, Nu; Konopelko, A; Latham, I J; Le Gallou, R; Lemière, A; Lemoine-Goumard, M; Leroy, N; Lohse, T; Marcowith, A; Martin, J-M; Martineau-Huynh, O; Masterson, C; McComb, T J L; de Naurois, M; Nolan, S J; Noutsos, A; Orford, K J; Osborne, J L; Ouchrif, M; Panter, M; Pelletier, G; Pita, S; Pühlhofer, G; Punch, M; Raubenheimer, B C; Raue, M; Raux, J; Rayner, S M; Reimer, A; Reimer, O; Ripken, J; Rob, L; Rolland, L; Rowell, G; Sahakian, V; Saugé, L; Schlenker, S; Schlickeiser, R; Schuster, C; Schwanke, U; Siewert, M; Sol, H; Spangler, D; Steenkamp, R; Stegmann, C; Tavernet, J-P; Terrier, R; Théoret, C G; Tluczykont, M; Vasileiadis, G; Venter, C; Vincent, P; Völk, H J; Wagner, S J

2005-07-29

X-ray binaries are composed of a normal star in orbit around a neutron star or stellar-mass black hole. Radio and x-ray observations have led to the presumption that some x-ray binaries called microquasars behave as scaled-down active galactic nuclei. Microquasars have resolved radio emission that is thought to arise from a relativistic outflow akin to active galactic nuclei jets, in which particles can be accelerated to large energies. Very high energy gamma-rays produced by the interactions of these particles have been observed from several active galactic nuclei. Using the High Energy Stereoscopic System, we find evidence for gamma-ray emission of >100 gigaelectron volts from a candidate microquasar, LS 5039, showing that particles are also accelerated to very high energies in these systems.

Mid 19th century minimum of galactic cosmic ray flux inferred from 44Ti in Allegan meteorite

NASA Astrophysics Data System (ADS)

Taricco, C.; Bhandari, N.; Colombetti, P.; Verma, N.

Measurements of 44Ti activity in meteorites show that the galactic cosmic ray (GCR) intensity has been declining in the interplanetary space during the past three centuries and has a component of cyclic variation, with periodicity of about 87 years [Taricco, C., Bhandari, N., Cane, D., et al. Galactic cosmic ray flux decline and periodicities in the interplanetary space during the last 3 centuries revealed by 44Ti in meteorites. J. Geophys. Res. 111, A08102, 2006.]. In order to verify these results, we have measured 44Ti activity in Allegan meteorite which fell in 1899 and in some other meteorites with better precision. The measurements confirm low cosmic ray flux and consequently high solar activity near the middle of 19th century.

X-Ray Processing of ChaMPlane Fields: Methods and Initial Results for Selected Anti-Galactic Center Fields

NASA Astrophysics Data System (ADS)

Hong, JaeSub; van den Berg, Maureen; Schlegel, Eric M.; Grindlay, Jonathan E.; Koenig, Xavier; Laycock, Silas; Zhao, Ping

2005-12-01

We describe the X-ray analysis procedure of the ongoing Chandra Multiwavelength Plane (ChaMPlane) Survey and report the initial results from the analysis of 15 selected anti-Galactic center observations (90deg

Milky Way scattering properties and intrinsic sizes of active galactic nuclei cores probed by very long baseline interferometry surveys of compact extragalactic radio sources

NASA Astrophysics Data System (ADS)

Pushkarev, A. B.; Kovalev, Y. Y.

2015-10-01

We have measured the angular sizes of radio cores of active galactic nuclei (AGNs) and analysed their sky distributions and frequency dependences to study synchrotron opacity in AGN jets and the strength of angular broadening in the interstellar medium. We have used archival very long baseline interferometry (VLBI) data of more than 3000 compact extragalactic radio sources observed at frequencies, ν, from 2 to 43 GHz to measure the observed angular size of VLBI cores. We have found a significant increase in the angular sizes of the extragalactic sources seen through the Galactic plane (|b| ≲ 10°) at 2, 5 and 8 GHz, about one-third of which show significant scattering. These sources are mainly detected in directions to the Galactic bar, the Cygnus region and a region with galactic longitudes 220° ≲ l ≲ 260° (the Fitzgerald window). The strength of interstellar scattering of the AGNs is found to correlate with the Galactic Hα intensity, free-electron density and Galactic rotation measure. The dependence of scattering strengths on source redshift is insignificant, suggesting that the dominant scattering screens are located in our Galaxy. The observed angular size of Sgr A* is found to be the largest among thousands of AGNs observed over the sky; we discuss possible reasons for this strange result. Excluding extragalactic radio sources with significant scattering, we find that the angular size of opaque cores in AGNs scales typically as ν-1, confirming predictions of a conical synchrotron jet model with equipartition.

On the evidence for axionlike particles from active galactic nuclei

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pettinari, Guido Walter; Crittenden, Robert

2010-10-15

Burrage, Davis, and Shaw recently suggested exploiting the correlations between high and low energy luminosities of astrophysical objects to probe possible mixing between photons and axionlike particles (ALP) in magnetic field regions. They also presented evidence for the existence of ALP's by analyzing the optical/UV and x-ray monochromatic luminosities of active galactic nuclei. We extend their work by using the monochromatic luminosities of 320 unobscured active galactic nuclei from the Sloan Digital Sky Survey/Xmm-Newton Quasar Survey which allows the exploration of 18 different combinations of optical/UV and x-ray monochromatic luminosities. However, we do not find compelling evidence for the existencemore » of ALPs. Moreover, it appears that the signal reported by Burrage et al. is more likely due to x-ray absorption rather than to photon-ALP oscillation.« less

THE COVERING FACTOR OF WARM DUST IN WEAK EMISSION-LINE ACTIVE GALACTIC NUCLEI

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Xudong; Liu, Yuan, E-mail: zhangxd@ihep.ac.cn, E-mail: liuyuan@ihep.ac.cn

2016-10-20

Weak emission-line active galactic nuclei (WLAGNs) are radio-quiet active galactic nuclei (AGNs) that have nearly featureless optical spectra. We investigate the ultraviolet to mid-infrared spectral energy distributions of 73 WLAGNs (0.4 < z < 3) and find that most of them are similar to normal AGNs. We also calculate the covering factor of warm dust of these 73 WLAGNs. No significant difference is indicated by a KS test between the covering factor of WLAGNs and normal AGNs in the common range of bolometric luminosity. The implication for several models of WLAGNs is discussed. The super-Eddington accretion is unlikely to bemore » the dominant reason for the featureless spectrum of a WLAGN. The present results are still consistent with the evolution scenario, i.e., WLAGNs are in a special stage of AGNs.« less

Studies of Low Luminosity Active Galactic Nuclei with Monte Carlo and Magnetohydrodynamic Simulations

NASA Astrophysics Data System (ADS)

Hilburn, Guy Louis

Results from several studies are presented which detail explorations of the physical and spectral properties of low luminosity active galactic nuclei. An initial Sagittarius A* general relativistic magnetohydrodynamic simulation and Monte Carlo radiation transport model suggests accretion rate changes as the dominant flaring method. A similar study on M87 introduces new methods to the Monte Carlo model for increased consistency in highly energetic sources. Again, accretion rate variation seems most appropriate to explain spectral transients. To more closely resolve the methods of particle energization in active galactic nuclei accretion disks, a series of localized shearing box simulations explores the effect of numerical resolution on the development of current sheets. A particular focus on numerically describing converged current sheet formation will provide new methods for consideration of turbulence in accretion disks.

Cosmological Origins of Water

NASA Astrophysics Data System (ADS)

Gagliano, Alexander; Taylor, Morgan; Black, William; Smidt, Joseph; Wiggins, Brandon K.

2018-01-01

Recent models indicate that the sun's protoplanetary disk provided insufficient pathways for water formation, as evidenced by [D/H]H2O measurements in asteroids and Earth's oceans. It is therefore likely that the early universe contained sites conducive to water chemistry. This research tracks the timeline and abundance rates of water using cosmological simulations in Enzo. A 64 Mpc cube of space is evolved from z = 200 to z = 2. Simulations are then centered on a massive halo, and a 26-species reaction network is applied using operator split to track water formation rates. Density projection plots with metallicity contours predict regions of water formation, which are then compared to simulated abundances at both galactic and extragalactic scales. Observational signatures of formation sites are further discussed, and allow for additional validation of the simulations used.

Proceedings of the Galactic Center Workshop 2002: The Central 300 Parsecs of the Milky Way. Astronomische Nachrichten Supplementary Issue 1/2003

NASA Astrophysics Data System (ADS)

Cotera, Angela; Markoff, Sera; Geballe, T. R.; Falcke, Heino

2004-03-01

Our knowledge of the environment of the nucleus of our galaxy has been greatly enhanced, by more extensive and sensitive observations at radio and infrared wavelengths, the advent of high resolution x-ray imaging and spectroscopy, and considerable theoretical activity to understand the nucleus and its components, and their activity. The Galactic Center Workshop 2002 was organized to review recent research on the galactic center, including the latest state-of-the-art observations and important theoretical developments. The workshop covered phenomena on scales ranging from the central several hundred parsecs to the central parsec and within. Each topic was approached from both multi-wavelength observational and theoretical perspectives.

Theoretical Astrophysics - Volume 3, Galaxies and Cosmology

NASA Astrophysics Data System (ADS)

Padmanabhan, T.

2002-12-01

1. Overview: galaxies and cosmology; 2. Galactic structure and dynamics; 3. Friedmann model of the universe; 4. Thermal history of the universe; 5. Structure formation; 6. Cosmic microwave background radiation; 7. Formation of baryonic structures; 8. Active galactic nuclei; 9. Intergalactic medium and absorption systems; 10. Cosmological observations.

Sagittarius A* as an origin of the Galactic PeV cosmic rays?

NASA Astrophysics Data System (ADS)

Fujita, Yutaka; Murase, Kohta; Kimura, Shigeo S.

2017-04-01

Supernova remnants (SNRs) have commonly been considered as a source of the observed PeV cosmic rays (CRs) or a Galactic PeV particle accelerator ("Pevatron"). In this work, we study Sagittarius A* (Sgr A*), which is the low-luminosity active galactic nucleus of the Milky Way Galaxy, as another possible canditate of the Pevatron, because it sometimes became very active in the past. We assume that a large number of PeV CRs were injected by Sgr A* at the outburst about 107 yr ago when the Fermi bubbles were created. We constrain the diffusion coefficient for the CRs in the Galactic halo on the condition that the CRs have arrived on the Earth by now, while a fairly large fraction of them have escaped from the halo. Based on a diffusion-halo model, we solve a diffusion equation for the CRs and compare the results with the CR spectrum on the Earth. The observed small anisotropy of the arrival directions of CRs may be explained if the diffusion coefficient in the Galactic disk is smaller than that in the halo. Our model predicts that a boron-to-carbon ratio should be energy-independent around the knee, where the CRs from Sgr A* become dominant. It is unlikely that the spectrum of the CRs accelerated at the outburst is represented by a power-law similar to the one for those responsible for the gamma-ray emission from the central molecular zone (CMZ) around the Galactic center.

Neutrino-heated stars and broad-line emission from active galactic nuclei

NASA Technical Reports Server (NTRS)

Macdonald, James; Stanev, Todor; Biermann, Peter L.

1991-01-01

Nonthermal radiation from active galactic nuclei indicates the presence of highly relativistic particles. The interaction of these high-energy particles with matter and photons gives rise to a flux of high-energy neutrinos. In this paper, the influence of the expected high neutrino fluxes on the structure and evolution of single, main-sequence stars is investigated. Sequences of models of neutrino-heated stars in thermal equilibrium are presented for masses 0.25, 0.5, 0.8, and 1.0 solar mass. In addition, a set of evolutionary sequences for mass 0.5 solar mass have been computed for different assumed values for the incident neutrino energy flux. It is found that winds driven by the heating due to high-energy particles and hard electromagnetic radiation of the outer layers of neutrino-bloated stars may satisfy the requirements of the model of Kazanas (1989) for the broad-line emission clouds in active galactic nuclei.

New structures of power density spectra for four Kepler active galactic nuclei

NASA Astrophysics Data System (ADS)

Dobrotka, A.; Antonuccio-Delogu, V.; Bajčičáková, I.

2017-09-01

Many nearby active galactic nuclei display a significant short-term variability. In this work, we reanalyse photometric data of four active galactic nuclei observed by Kepler in order to study the flickering activity, with our main goal to search for multiple components in the power density spectra. We find that all four objects have similar characteristics, with two break frequencies at approximately log( f /Hz) = -5.2 and -4.7. We consider some physical phenomena whose characteristic time-scales are consistent with those observed, in particular mass accretion fluctuations in the inner geometrically thick disc (hot X-ray corona) and unstable relativistic Rayleigh-Taylor modes. The former is supported by detection of the same break frequencies in the Swift X-ray data of ZW229-15. We also discuss rms-flux relations, and we detect a possible typical linear trend at lower flux levels. Our findings support the hypothesis of a multiplicative character of variability, in agreement with the propagating accretion fluctuation model.

Gamma-ray Monitoring of Active Galactic Nuclei with HAWC

NASA Astrophysics Data System (ADS)

Lauer, Robert; HAWC Collaboration

2016-03-01

Active Galactic Nuclei (AGN) are extra-galactic sources that can exhibit extreme flux variability over a wide range of wavelengths. TeV gamma rays have been observed from about 60 AGN and can help to diagnose emission models and to study cosmic features like extra-galactic background light or inter-galactic magnetic fields. The High Altitude Water Cherenkov (HAWC) observatory is a new extensive air shower array that can complement the pointed TeV observations of imaging air Cherenkov telescopes. HAWC is optimized for studying gamma rays with energies between 100 GeV and 100 TeV and has an instantaneous field of view of ~2 sr and a duty cycle >95% that allow us to scan 2/3 of the sky every day. By performing an unbiased monitoring of TeV emissions of AGN over most of the northern and part of the southern sky, HAWC can provide crucial information and trigger follow-up observations in collaborations with pointed TeV instruments. Furthermore, HAWC coverage of AGN is complementary to that provided by the Fermi satellite at lower energies. In this contribution, we will present HAWC flux light curves of TeV gamma rays from various sources, notably the bright AGN Markarian 421 and Markarian 501, and highlight recent results from multi-wavelengths and multi-instrument studies.

Uncorrelated Far Active Galactic Nuclei Flaring with Their Delayed Ultra High Energy Cosmic Rays Events

NASA Astrophysics Data System (ADS)

Fargion, Daniele; Oliva, Pietro; De Sanctis Lucentini, Pier Giorgio

The most distant Active Galactic Nuclei (AGN), within the allowed Greisen-Zatsepin-Kuzmin (GZK) cut-off radius ( ≲ 100 Mpc), have been recently candidate by many authors as the best location for the observed Ultra High Energy Cosmic Rays (UHECR) origination. Indeed, the apparent homogeneity and isotropy of recent UHECR signals seems to require a far cosmic isotropic and homogeneous scenario, involving a proton UHECR courier: our galaxy or nearest local group or super galactic plane (ruled by the Virgo cluster) are too near and apparently too anisotropic to be in agreement with the (Pierre Auger Observatory (PAO) and Telescope Array (TA) almost-homogeneous data sample. However, the few and mild UHECR observed clustering, the so called North and South Hot Spots, are smeared in wide (±18°) solid angles. Their consequent random walk flight from most far GZK UHECR sources, nearly at 100 Mpc, must be delayed — withrespect to a straight AGN photon gamma flaring arrival trajectory — at least by a million years. During this time, the AGN jet blazing signal, its probable axis deflection (such as the helical jet in Mrk 501), its miss alignment or even its almost certain exhaust activity, may lead to a complete misleading correlation between present UHECR events and a much earlier active AGN ejection. UHECR maps may be anyway related to galactic or nearest (Cen A, M82) AGN extragalactic UHECR sources shining in twin Hot Spot. Therefore we defend our (quite different) scenario where UHECR are mostly made by lightest UHECR nuclei originated by nearby AGN sources, or few galactic sources, whose delayed signals are reaching us within few thousand years in the observed smeared sky areas.

Lunar surface cosmic ray experiment S-152, Apollo 16

NASA Technical Reports Server (NTRS)

Fleischer, R. L.; Hart, H. R., Jr.; Carter, M.; Comostock, G. M.; Renshaw, A.; Woods, R. T.

1973-01-01

This investigation was directed at determining the energy spectra and abundances of low energy heavy cosmic rays (0.03 E or = 150 MeV/nucleon). The cosmic rays were detected using plastic and glass particle track detectors. Particles emitted during the 17 April 1972 solar flare dominated the spectra for energies below about 70 MeV/nucleon. Two conclusions emerge from the low energy data: (1) The differential energy spectra for solar particles vary rapidly for energies as low as 0.05 MeV/nucleon for iron-group nuclei. (2) The abundance ratio of heavy elements changes with energy at low energies; heavy elements are enhanced relative to higher elements increasingly as the energy decreases. Galactic particle fluxes recorded within the spacecraft are in agreement with those predicted taking into account solar modulation and spacecraft shielding. The composition of the nuclei at energies above 70 MeV/nucleon imply that these particles originate outside the solar system and hence are galactic cosmic rays.

All flavour point-source search with the ANTARES neutrino telescope

NASA Astrophysics Data System (ADS)

Michael, Tino

2017-09-01

ANTARES is the largest neutrino telescope in the Northern Hemisphere. The detector has established excellent pointing resolution for muon neutrinos (0.4 degrees) and a degree-level resolution also for contained shower events (about 2 degrees). Together with its geographical location, the good angular resolution makes ANTARES an excellent tool to test for the presence of cosmic sources in the Southern Hemisphere and in particular the area around the Galactic Centre, where IceCube reports a number of high-energy events. In this contribution, we present a search for cosmic neutrino sources using ANTARES data taken from early 2007 until the end of 2013. Such sources are identified as a cluster of events in the combined track and shower channels. In addition to the all-flavour full-sky and candidate list searches, we focus on a restricted region around the Galactic Centre. Different spectral indices for the neutrino energy spectrum have been investigated as well as possible extended sources.

Simulation of Galactic Cosmic Rays and Dose-Rate Effects in RITRACKS

NASA Technical Reports Server (NTRS)

Plante, Ianik; Ponomarev, Artem; Slaba, Tony; Blattnig, Steve; Hada, Megumi

2017-01-01

The NASA Space Radiation Laboratory (NSRL) facility has been used successfully for many years to generate ion beams for radiation research experiments by NASA investigators. Recently, modifications were made to the beam lines to allow rapid switching between different types of ions and energies, with the aim to simulate the Galactic Cosmic Rays (GCR) environment. As this will be a focus of space radiation research for upcoming years, the stochastic radiation track structure code RITRACKS (Relativistic Ion Tracks) was modified to simulate beams of various ion types and energies during time intervals specified by the user at the microscopic and nanoscopic scales. For example, particle distributions of a mixed 344.1-MeV protons (18.04 cGy) and 950-MeV/n iron (5.64 cGy) beam behind a 20 g/cm(exp 2) aluminum followed by a 10 g/cm(exp 2) polyethylene shield as calculated by the code GEANT4 were used as an input field in RITRACKS. Similarly, modifications were also made to simulate a realistic radiation environment in a spacecraft exposed to GCR by sampling the ion types and energies from particle spectra pre-calculated by the code HZETRN. The newly implemented features allows RITRACKS to generate time-dependent differential and cumulative 3D dose voxel maps. These new capabilities of RITRACKS will be used to investigate dose-rate effects and synergistic interactions of various types of radiations for many end points at the microscopic and nanoscopic scales such as DNA damage and chromosome aberrations.

Cosmic radiation dose in aircraft--a neutron track etch detector.

PubMed

Vuković, B; Radolić, V; Miklavcić, I; Poje, M; Varga, M; Planinić, J

2007-01-01

Cosmic radiation bombards us at high altitude by ionizing particles. The radiation environment is a complex mixture of charged particles of solar and galactic origin, as well as of secondary particles produced in interaction of the galactic cosmic particles with the nuclei of atmosphere of the Earth. The radiation field at aircraft altitude consists of different types of particles, mainly photons, electrons, positrons and neutrons, with a large energy range. The non-neutron component of cosmic radiation dose aboard ATR 42 and A 320 aircrafts (flight level of 8 and 11 km, respectively) was measured with TLD-100 (LiF:Mg,Ti) detectors and the Mini 6100 semiconductor dosimeter. The estimated occupational effective dose for the aircraft crew (A 320) working 500 h per year was 1.64 mSv. Other experiments, or dose rate measurements with the neutron dosimeter, consisting of LR-115 track detector and boron foil BN-1 or 10B converter, were performed on five intercontinental flights. Comparison of the dose rates of the non-neutron component (low LET) and the neutron one (high LET) of the radiation field at the aircraft flight level showed that the neutron component carried about 50% of the total dose. The dose rate measurements on the flights from the Middle Europe to the South and Middle America, then to Korea and Japan, showed that the flights over or near the equator region carried less dose rate; this was in accordance with the known geomagnetic latitude effect.

Demographics and Case Studies of Galactic Outflows in the Local Universe

NASA Astrophysics Data System (ADS)

Rupke, David

2017-07-01

Galactic outflows driven by both star formation and active black holes are an important driver of galaxy evolution. The local universe is a sensitive laboratory for understanding the scaling relations that characterize these winds and the physics that govern them. I will review what we know from statistical studies about the prevalance and properties of nearby galactic winds and how these properties depend on those of the host galaxy or power source. I will also highlight detailed case studies of key objects that illustrate the multiphase structure of these winds.

Gamma rays from active galactic nuclei

NASA Technical Reports Server (NTRS)

Kazanas, Demosthenes

1990-01-01

The general properties of Active Galactic Nuclei (AGN) and quasars are reviewed with emphasis on their continuum spectral emission. Two general classes of models for the continuum are outlined and critically reviewed in view of the impending GRO (Gamma Ray Observatory) launch and observations. The importance of GRO in distinguishing between these models and in general in furthering the understanding of AGN is discussed. The very broad terms the status of the current understanding of AGN are discussed.

X-ray and gamma-ray emission of Sagittarius A* as a wind-accreting black hole

NASA Technical Reports Server (NTRS)

Mastichiadis, A.; Ozernoy, L. M.

1994-01-01

If, as many believe, Sgr A* is a massive black hole at the Galactic center, one should expect it to be a source of X-ray and gamma-ray activity, behaving basically as a scaled-down active galactic nucleus. An unavoidable source of accretion is the wind from IRS 16, a nearby group of hot, massive stars. Since the density and velocity of the accreting matter are known from observations, the accretion rate is basically a function of the putative black hole mass, M(sub h), only; this value represents a reliable lower limit to a real rate, given the other possible sources of accreting matter. Based on this and on the theories about shock acceleration in active galactic nuclei, we have estimated the expected production of relativistic particles and their hard radiation. These values turn out to be a function of M(sub h) as well. Comparing our results with available X-ray and gamma-ray observations which show Sgr A* to have a relatively low activity level, we conclude tentatively that the putative black hole in the Galactic center cannot have a mass greater than approximately 6 x 10(exp 3) solar mass. This conclusion is consistent with the upper limits to the black hole mass found by different methods earlier, although much more work is needed to make calculations of shock acceleration around black holes more reliable.

Observation of galactic cosmic ray spallation events from the SoHO mission 20-yr operation of LASCO

NASA Astrophysics Data System (ADS)

Koutchmy, S.; Tavabi, E.; Urtado, O.

2018-07-01

A shower of secondary cosmic ray (CR) particles is produced at high altitudes in the Earth's atmosphere, so the primordial galactic cosmic rays (GCRs) are never directly measured outside the Earth magnetosphere and atmosphere. They approach the Earth and other planets in the complex pattern of rigidity's dependence, generally excluded by the magnetosphere. GCRs revealed by images of single nuclear reactions also called spallation events are described here. Such an event was seen on 2015 November 29 using a unique Large Angle and Spectrometric Coronagraphs C3 space coronagraph routine image taken during the Solar and Heliospheric Observatory (SoHO) mission observing uninterruptedly at the Lagrangian L1 point. The spallation signature of a GCR identified well outside the Earth's magnetosphere is obtained for the first time. The resulting image includes different diverging linear `tracks' of varying intensity, leading to a single pixel; this frame identifies the site on the silicon CCD chip of the coronagraph camera. There was no solar flare reported at that time, nor coronal mass ejection and no evidence of optical debris around the spacecraft. More examples of smaller CR events have been discovered through the 20 yr of continuous observations from SoHO. This is the first spallation event from a CR, recorded outside the Earth's magnetosphere. We evaluate the probable energy of these events suggesting a plausible galactic source.

Observation of galactic cosmic ray spallation events from the SoHO mission 20-Year operation of LASCO

NASA Astrophysics Data System (ADS)

Koutchmy, S.; Tavabi, E.; Urtado, O.

2018-05-01

A shower of secondary Cosmic Ray (CR) particles is produced at high altitudes in the Earth's atmosphere, so the primordial Galactic Cosmic Rays (GCRs) are never directly measured outside the Earth magnetosphere and atmosphere. They approach the Earth and other planets in the complex pattern of rigidity's dependence, generally excluded by the magnetosphere. GCRs revealed by images of single nuclear reactions also called spallation events are described here. Such an event was seen on Nov. 29, 2015 using a unique LASCO C3 space coronagraph routine image taken during the Solar and Heliospheric Observatory (SoHO) mission observing uninterruptedly at the Lagrangian L1 point. The spallation signature of a GCR identified well outside the Earth's magnetosphere is obtained for the 1st time. The resulting image includes different diverging linear "tracks" of varying intensity, leading to a single pixel; this frame identifies the site on the silicon CCD chip of the coronagraph camera. There was no solar flare reported at that time, nor Coronal Mass Ejection (CME) and no evidence of optical debris around the spacecraft. More examples of smaller CR events have been discovered through the 20 years of continuous observations from SoHO. This is the first spallation event from a CR, recorded outside the Earth's magnetosphere. We evaluate the probable energy of these events suggesting a plausible galactic source.

Status Of The Swift Burst Alert Telescope Hard X-ray Transient Monitor

NASA Astrophysics Data System (ADS)

Krimm, Hans A.; Barthelmy, S. D.; Baumgartner, W. H.; Cummings, J.; Fenimore, E.; Gehrels, N.; Markwardt, C. B.; Palmer, D.; Sakamoto, T.; Skinner, G. K.; Stamatikos, M.; Tueller, J.

2010-01-01

The Swift Burst Alert Telescope hard X-ray transient monitor has been operating since October 1, 2006. More than 700 sources are tracked on a daily basis and light curves are produced and made available to the public on two time scales: a single Swift pointing (approximately 20 minutes) and the weighted average for each day. Of the monitored sources, approximately 33 are detected daily and another 100 have had one or more outburst during the Swift mission. The monitor is also sensitive to the detection of previously undiscovered sources and we have reported the discovery of four galactic sources and one source in the Large Magellanic Cloud. Follow-up target of opportunity observations with Swift and the Rossi X-Ray Timing Explorer have revealed that three of these new sources are pulsars and two are black hole candidates. In addition, the monitor has led to the announcement of significant outbursts from 24 different galactic and extra-galactic sources, many of which have had follow-up Swift XRT, UVOT and ground based multi-wavelength observations. The transient monitor web pages currently receive an average of 21 visits per day. We will report on the most important results from the transient monitor and also on detection and exposure statistics and outline recent and planned improvements to the monitor. The transient monitor web page is http://swift.gsfc.nasa.gov/docs/swift/results/transients/.

Central stars of planetary nebulae in the Galactic bulge

NASA Astrophysics Data System (ADS)

Hultzsch, P. J. N.; Puls, J.; Méndez, R. H.; Pauldrach, A. W. A.; Kudritzki, R.-P.; Hoffmann, T. L.; McCarthy, J. K.

2007-06-01

Context: Optical high-resolution spectra of five central stars of planetary nebulae (CSPN) in the Galactic bulge have been obtained with Keck/HIRES in order to derive their parameters. Since the distance of the objects is quite well known, such a method has the advantage that stellar luminosities and masses can in principle be determined without relying on theoretical relations between both quantities. Aims: By alternatively combining the results of our spectroscopic investigation with evolutionary tracks, we obtain so-called spectroscopic distances, which can be compared with the known (average) distance of the bulge-CSPN. This offers the possibility to test the validity of model atmospheres and present date post-AGB evolution. Methods: We analyze optical H/He profiles of five Galactic bulge CSPN (plus one comparison object) by means of profile fitting based on state of the art non-LTE modeling tools, to constrain their basic atmospheric parameters (Teff, log g, helium abundance and wind strength). Masses and other stellar radius dependent quantities are obtained from both the known distances and from evolutionary tracks, and the results from both approaches are compared. Results: The major result of the present investigation is that the derived spectroscopic distances depend crucially on the applied reddening law. Assuming either standard reddening or values based on radio-Hβ extinctions, we find a mean distance of 9.0±1.6 kpc and 12.2±2.1 kpc, respectively. An “average extinction law” leads to a distance of 10.7±1.2 kpc, which is still considerably larger than the Galactic center distance of 8 kpc. In all cases, however, we find a remarkable internal agreement of the individual spectroscopic distances of our sample objects, within ±10% to ±15% for the different reddening laws. Conclusions: Due to the uncertain reddening correction, the analysis presented here cannot yet be regarded as a consistency check for our method, and a rigorous test of the CSPN evolution theory becomes only possible if this problem has been solved. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Appendix A is only available in electronic form at http://www.aanda.org

The essential signature of a massive starburst in a distant quasar.

PubMed

Solomon, P; Vanden Bout, P; Carilli, C; Guelin, M

2003-12-11

Observations of carbon monoxide emission in high-redshift (zeta > 2) galaxies indicate the presence of large amounts of molecular gas. Many of these galaxies contain an active galactic nucleus powered by accretion of gas onto a supermassive black hole, and a key question is whether their extremely high infrared luminosities result from the active galactic nucleus, from bursts of massive star formation (associated with the molecular gas), or both. In the Milky Way, high-mass stars form in the dense cores of interstellar molecular clouds, where gas densities are n(H2) > 10(5) cm(-3) (refs 1, 2). Recent surveys show that virtually all galactic sites of high-mass star formation have similarly high densities. The bulk of the cloud material traced by CO observations, however, is at a much lower density. For galaxies in the local Universe, the HCN molecule is an effective tracer of high-density molecular gas. Here we report observations of HCN emission from the infrared-luminous 'Cloverleaf' quasar (at a redshift zeta = 2.5579). The HCN line luminosity indicates the presence of 10 billion solar masses of very dense gas, an essential feature of an immense starburst, which contributes, together with the active galactic nucleus it harbours, to its high infrared luminosity.

Cosmic ray particles with different LET values under various thicknesses of shielding in low altitude orbits: Calculations and Cosmos-2044 measurements

NASA Technical Reports Server (NTRS)

Benton, E. V.; Frank, A. L.; Benton, E. R.; Marenny, A. M.; Nymmik, R. A.; Suslov, A. A.

1995-01-01

Fluxes of cosmic ray particles with different LET values were measured on board the COSMOS-2044 biosatellite under various thicknesses of shielding by stacks of CR-39 and nitrocellulose plastic nuclear track detectors (mounted outside the satellite). The component composition of the particles detected under shieldings of 0.1-2.5 g cm(exp -2) is verified by comparing experimental data with the results of model simulations of the fluxes of galactic cosmic ray particles and of radiation belt protons.

Cosmic ray particles with different LET values under various thicknesses of shielding in low altitude orbits: calculations and Cosmos-2044 measurements

NASA Technical Reports Server (NTRS)

Marenny, A. M.; Nymmik, R. A.; Suslov, A. A.; Benton, E. V.; Frank, A. L.; Benton, E. R.

1992-01-01

Fluxes of cosmic ray particles with different LET values were measured on board the Cosmos-2044 biosatellite under various thicknesses of shielding by stacks of CR-39 and nitrocellulose plastic nuclear track detectors (mounted outside the satellite). The component composition of the particles detected under shieldings of 0.1-2.5 g cm-2 is verified by comparing experimental data with the results of model simulations of the fluxes of galactic cosmic ray particles and of radiation belt protons.

X-ray detections of submillimetre galaxies: active galactic nuclei versus starburst contribution

NASA Astrophysics Data System (ADS)

Johnson, S. P.; Wilson, G. W.; Wang, Q. D.; Williams, C. C.; Scott, K. S.; Yun, M. S.; Pope, A.; Lowenthal, J.; Aretxaga, I.; Hughes, D.; Kim, M. J.; Kim, S.; Tamura, Y.; Kohno, K.; Ezawa, H.; Kawabe, R.; Oshima, T.

2013-05-01

We present a large-scale study of the X-ray properties and near-IR-to-radio spectral energy distributions (SEDs) of submillimetre galaxies (SMGs) detected at 1.1 mm with the AzTEC instrument across a ˜1.2 square degree area of the sky. Combining deep 2-4 Ms Chandra data with Spitzer IRAC/MIPS and Very Large Array data within the Great Observatories Origins Deep Survey North (GOODS-N), GOODS-S and COSMOS fields, we find evidence for active galactic nucleus (AGN) activity in ˜14 per cent of 271 AzTEC SMGs, ˜28 per cent considering only the two GOODS fields. Through X-ray spectral modelling and multiwavelength SED fitting using Monte Carlo Markov chain techniques to Siebenmorgen et al. (AGN) and Efstathiou, Rowan-Robinson & Siebenmorgen (starburst) templates, we find that while star formation dominates the IR emission, with star formation rates (SFRs) ˜100-1000 M⊙ yr-1, the X-ray emission for most sources is almost exclusively from obscured AGNs, with column densities in excess of 1023 cm-2. Only for ˜6 per cent of our sources do we find an X-ray-derived SFR consistent with NIR-to-radio SED derived SFRs. Inclusion of the X-ray luminosities as a prior to the NIR-to-radio SED effectively sets the AGN luminosity and SFR, preventing significant contribution from the AGN template. Our SED modelling further shows that the AGN and starburst templates typically lack the required 1.1 mm emission necessary to match observations, arguing for an extended, cool dust component. The cross-correlation function between the full samples of X-ray sources and SMGs in these fields does not indicate a strong correlation between the two populations at large scales, suggesting that SMGs and AGNs do not necessarily trace the same underlying large-scale structure. Combined with the remaining X-ray-dim SMGs, this suggests that sub-mm-bright sources may evolve along multiple tracks, with X-ray-detected SMGs representing transitionary objects between periods of high star formation and AGN activity, while X-ray-faint SMGs represent a brief starburst phase of more normal galaxies.

Method of incident low-energy gamma-ray direction reconstruction in the GAMMA-400 gamma-ray space telescope

NASA Astrophysics Data System (ADS)

Kheymits, M. D.; Leonov, A. A.; Zverev, V. G.; Galper, A. M.; Arkhangelskaya, I. V.; Arkhangelskiy, A. I.; Suchkov, S. I.; Topchiev, N. P.; Yurkin, Yu T.; Bakaldin, A. V.; Dalkarov, O. D.

2016-02-01

The GAMMA-400 gamma-ray space-based telescope has as its main goals to measure cosmic γ-ray fluxes and the electron-positron cosmic-ray component produced, theoretically, in dark-matter-particles decay or annihilation processes, to search for discrete γ-ray sources and study them in detail, to examine the energy spectra of diffuse γ-rays — both galactic and extragalactic — and to study gamma-ray bursts (GRBs) and γ-rays from the active Sun. Scientific goals of GAMMA-400 telescope require fine angular resolution. The telescope is of a pair-production type. In the converter-tracker, the incident gamma-ray photon converts into electron-positron pair in the tungsten layer and then the tracks are detected by silicon- strip position-sensitive detectors. Multiple scattering processes become a significant obstacle in the incident-gamma direction reconstruction for energies below several gigaelectronvolts. The method of utilising this process to improve the resolution is proposed in the presented work.

A periodicity of approximately 1 hour in X-ray emission from the active galaxy RE J1034+396.

PubMed

Gierliński, Marek; Middleton, Matthew; Ward, Martin; Done, Chris

2008-09-18

Active galactic nuclei and quasars are thought to be scaled-up versions of Galactic black hole binaries, powered by accretion onto supermassive black holes with masses of 10(6)-10(9) M[symbol: see text], as opposed to the approximately 10 M [symbol: see text] in binaries (here M [symbol: see text] is the solar mass). One example of the similarities between these two types of systems is the characteristic rapid X-ray variability seen from the accretion flow. The power spectrum of this variability in black hole binaries consists of a broad noise with multiple quasi-periodic oscillations superimposed on it. Although the broad noise component has been observed in many active galactic nuclei, there have hitherto been no significant detections of quasi-periodic oscillations. Here we report the discovery of an approximately 1-hour X-ray periodicity in a bright active galaxy, RE J1034+396. The signal is highly statistically significant (at the 5.6 sigma level) and very coherent, with quality factor Q > 16. The X-ray modulation arises from the direct vicinity of the black hole.

Elusive active galactic nuclei

NASA Astrophysics Data System (ADS)

Maiolino, R.; Comastri, A.; Gilli, R.; Nagar, N. M.; Bianchi, S.; Böker, T.; Colbert, E.; Krabbe, A.; Marconi, A.; Matt, G.; Salvati, M.

2003-10-01

A fraction of active galactic nuclei do not show the classical Seyfert-type signatures in their optical spectra, i.e. they are optically `elusive'. X-ray observations are an optimal tool to identify this class of objects. We combine new Chandra observations with archival X-ray data in order to obtain a first estimate of the fraction of elusive active galactic nuclei (AGN) in local galaxies and to constrain their nature. Our results suggest that elusive AGN have a local density comparable to or even higher than optically classified Seyfert nuclei. Most elusive AGN are heavily absorbed in the X-rays, with gas column densities exceeding 1024 cm-2, suggesting that their peculiar nature is associated with obscuration. It is likely that in elusive AGN the nuclear UV source is completely embedded and the ionizing photons cannot escape, which prevents the formation of a classical narrow-line region. Elusive AGN may contribute significantly to the 30-keV bump of the X-ray background.

The fueling of active galaxies

NASA Technical Reports Server (NTRS)

Hernquist, Lars

1991-01-01

Collisions of galaxies are often invoked to explain violent phenomena in the universe. The dynamics of interacting galaxies is intrinsically three-dimensional and involves both gas and stellar dynamics. In general, a computational approach is needed to model galactic collisions. Galaxy encounters are studied using a hybrid N-body/hydrodynamics code, capable of integrating systems of stars, gas, and dark matter in a fully self-consistent manner. These experiments demonstrate that gravitational coupling between gas and stars in galactic interactions can drive most of the gas throughout a galaxy into the nucleus of a merger remnant. The high densities in these gas concentrations are likely to result in strong bursts of star formation. Hence, this process may explain the nuclear starbursts in some systems of interacting galaxies. Further collapse of these gas concentrations can trigger even more intense activity if some gas is eventually accreted by a supermassive black hole. Such an evolutionary sequence may account for some quasars and active galactic nuclei.

The Super-TIGER Instrument to Probe Galactic Cosmic Ray Origins

NASA Technical Reports Server (NTRS)

Mitchell, John W.; Binns, W. R.; Bose, R, G.; Braun, D. L.; Christian, E. R.; Daniels, W. M; DeNolfo, G. A.; Dowkontt, P. F.; Hahne, D. J.; Hams, T.;

New look on the origin of cosmic rays

NASA Astrophysics Data System (ADS)

Istomin, Ya. N.

2017-06-01

From the analysis of the flux of high energy particles, E > 3 · 1018 eV, it is shown that the distribution of the power density of extragalactic rays over energy is of the power law, q̅(E) ∝ E-2.7, with the same index of 2.7 that has the distribution of Galactic cosmic rays before the so called `knee', E < 3 · 1015 eV. However, the average power of extragalactic sources, which is of ɛ ≃ 1043 erg s-1, exceeds by at least two orders the power emitted by the Galaxy in cosmic rays, assuming that the density of galaxies is estimated as Ng ≃ 1 Mpc-3. Considering that such power can be provided by relativistic jets from active galactic nuclei with the power ɛ ≃ 1045 - 1046 erg s-1, we estimate the density of extragalactic sources of cosmic rays as Ng ≃ 10-2 - 10-3 Mpc-3. Assuming the same nature of Galactic and extragalactic rays, we conclude that the Galactic rays were produced by a relativistic jet emitted from the Galactic center during the period of its activity in the past. The remnants of a bipolar jet are now observed in the form of bubbles of relativistic gas above and below the Galactic plane. The break, observed in the spectrum of Galactic rays (`knee'), is explained by fast escape of energetic particles, E > 3 · 1015 eV, from the Galaxy because of the dependence of the coefficient of diffusion of cosmic rays on energy, D∝E0.7. The obtained index of the density distribution of particles over energy, N(E)∝E-2.7-0.7/2=E-3.05, for E > 3 · 1015 eV agrees well with the observed one, N(E)∝E-3.1. The estimated time of the termination of the jet in the Galaxy is 4.2 · 104 years ago.

A High Resolution View of Galactic Centers: Arp 220 and M31

NASA Astrophysics Data System (ADS)

Lockhart, Kelly E.

The centers of galaxy are small in size and yet incredibly complex. They play host to supermassive black holes and nuclear star clusters (NSCs) and are subject to large gas inows, nuclear starbursts, and active galactic nuclear (AGN) activity. They can also be the launching site for large-scale galactic outows. However, though these systems are quite important to galactic evolution, observations are quite difficult due to their small size. Using high spatial resolution narrowband imaging with HST/WFC3 of Arp 220, a latestage galaxy merger, I discover an ionized gas bubble feature ( r = 600 pc) just off the nucleus. The bubble is aligned with both the western nucleus and with the large-scale galactic outflow. Using energetics arguments, I link the bubble with a young, obscured AGN or with an intense nuclear starburst. Given its alignment along the large-scale outflow axis, I argue that the bubble presents evidence for a link between the galactic center and the large-scale outflow. I also present new observations of the NSC in M31, the closest large spiral galaxy to our own. Using the OSIRIS near-infrared integral field spectrograph (IFS) on Keck, I map the kinematics of the old stellar population in the eccentric disk of the NSC. I compare the observations to models to derive a precession speed of the disk of 0+/-5 km s-1 pc-1 , and hence confirm that winds from the old stellar population may be the source of gas needed to form the young stellar population in the NSC. Studies of galactic centers are dependent on high spatial resolution observations. In particular, IFSs are ideal instruments for these studies as they provide two-dimensional spectroscopy of the field of view, enabling 2D kinematic studies. I report on work to characterize and improve the data reduction pipeline of the OSIRIS IFS, and discuss implications for future generations of IFS instrumentation.

Dynamics of the CMZ - Giant Magnetic Loops Connection in the Galactic Center

NASA Astrophysics Data System (ADS)

Langer, William

2012-10-01

Understanding the mass transfer and dynamics among the Galactic Center, the disk, and the halo of the Milky Way is fundamental to the study of the evolution of galaxies and star formation. Several giant molecular loops (GML), detected in CO maps of the Galactic Center, are likely the result of the magnetic Parker instability. We have new evidence of a possible dynamical connection between these loops and the Central Molecular Zone (CMZ) from a sparse [CII] sampling from our Herschel Open Time Key Project GOT C+. The CMZ-GML region is dynamically active and is likely to have a significant ionized component. However, we have no information on the distribution and dynamics of the ionized gas. The fine-structure lines of [NII] are key probes of the warm ionized medium (WIM) and along with the [CII] can isolate the different ionization components. We have a Herschel OT2 Priority 1 program to map the GML and the CMZ-GML connection in [CII] in more detail. However, we did not propose needed [NII] observations due to an incomplete analysis of our limited GOT C+ data at the time. Here we propose to observe with the SOFIA/GREAT instrument, [NII] in the CMZ-GML interface region using the L1b band, and serendipitously CO (16-15) using band L2. With this data, combined with our Herschel HIFI [CII], Mopra 12CO (1-0) and 13CO (1-0), and HI, we will characterize these important ISM components and their motions in these Galactic Center features. These observations of the nearest such regions of galactic center activity, also have bearing on the dynamics of other galactic nuclei.

The 136 MHZ/400 MHz earth station antenna-noise temperature prediction program for RAE-B

NASA Technical Reports Server (NTRS)

Taylor, R. E.; Fee, J. J.; Chin, M.

1972-01-01

A simulation study was undertaken to determine the 136 MHz and 400 MHz noise temperature of the ground network antennas which will track the RAE-B satellite during data transmission periods. Since the noise temperature of the antenna effectively sets the signal-to-noise ratio of the received signal, a knowledge of SNR will be helpful in locating the optimum time windows for data transmission during low noise periods. Antenna noise temperatures will be predicted for selected earth-based ground stations which will support RAE-B. Telemetry data acquisition will be at 400 MHz; tracking support at 136 MHz will be provided by the Goddard Range and Range Rate (RARR) stations. The antenna-noise temperature predictions will include the effects of galactic-brightness temperature, the sun, and the brightest radio stars. Predictions will cover the ten-month period from March 1, 1973 to December 31, 1973.

The radiation history of material returned by the Soviet automatic stations Luna 16 and Luna 20, according to track studies

NASA Technical Reports Server (NTRS)

Kashkarov, L. L.; Genayeva, L. I.; Lavrukhina, A. K.

1977-01-01

Fission tracks formed by the vH (very heavy) nuclei group of solar and galactic cosmic rays have been studied in silicate minerals of the lunar regolith returned by the Luna 16 and Luna 20 unmanned spacecraft. It is shown that the material in the Luna 16 core sample, from a typical mare region of the lunar surface, has undergone stronger irradiation by cosmic rays than material returned a highland region by Luna 20. A low-irradiation component (about 10 percent of the total number of crystals) has been found in the Luna 20 core sample materials, which can possibly be attributed to material added to the main bulk of the regolith in the formation of the crater Apollonius C. From the track density distribution of crystals, as a function of depth in the regolith core sample, it follows that the process of formation of the upper layer of the regolith, both for the lunar mare and for the highland region, includes sequential layering of finely crushed crystalline matter and subsequent mixing of it by micrometeorite bombardment. A portion of the crystals with a very high track density may be a component added to the lunar surface from outer space.

Measurement result of the neutron monitor onboard the Space Environment Data Acquisition Equipment - Attached Payload (SEDA-AP)

NASA Astrophysics Data System (ADS)

Koga, K.; Muraki, Y.; Shibata, S.; Yamamoto, T.; Matsumoto, H.; Okudaira, O.; Kawano, H.; Yumoto, K.

2013-12-01

To support future space activities, it is crucial to acquire space environmental data related to the space-radiation degradation of space parts and materials, and spacecraft anomalies. Such data are useful for spacecraft design and manned space activity. SEDA-AP was mounted on 'Kibo' of the ISS (International Space Station) to measure the space environment at a 400-kilometer altitude. Neutrons are very harmful radiation, with electrical neutrality that makes them strongly permeable. SEDA-AP measures the energy of neutrons from thermal to 100 MeV in real time using a Bonner Ball Detector (BBND) and a Scintillation Fiber Detector (FIB). BBND detects neutrons using He-3 counters, which have high sensitivity to thermal neutrons. Neutron energy is derived using the relative response function of polyethylene moderators of 6 different thicknesses. FIB measures the tracks of recoil protons caused by neutrons within a cubic arrayed sensor of 512 scintillation fibers. The charged particles are excluded using an anti-scintillator which surrounds the cube sensor, and the neutron energy is obtained from the track length of a recoil proton. There are three sources of neutrons in space; 1. Albedo Neutrons Produced by reactions of galactic cosmic rays or radiation belt particles with the atmosphere 2. Local Neutrons Produced by the reactions of galactic cosmic rays or radiation belt particles with spacecraft 3. Solar Neutrons Produced by accelerated particles in solar flares An accurate energy spectrum of the solar neutrons includes important information on high-energy particle generation mechanism in a solar flare, because neutrons are unaffected by interplanetary magnetic fields. These data will become useful to forecast solar energetic particles in future. Some candidate events involving solar neutrons were found as a result of analyzing data of the solar flare of M>2 since September 2009. Moreover, it is important to measure albedo neutrons, since protons generated by neutron decays are thought to originate from the radiation belt. This theory is called CRAND (Cosmic Ray Albedo Neutron Decay). Our observation result is consistent with the CRAND theory prediction in the case of low-energy parts. Moreover, the flux and angular distribution of local neutrons were estimated using the nuclear simulation code 'PHITS' to evaluate the influence of local neutrons on the structure of SEDA-AP and 'Kibo'. The results of our analyses on solar and albedo neutrons are reported in this paper.

Gamma ray cosmology: The extra galactic gamma spectrum and methods to detect the underlying source

NASA Technical Reports Server (NTRS)

Cline, David B.

1990-01-01

The possible sources of extragalactic gamma rays and methods to distinguish the different sources are discussed. The sources considered are early universe decays and annihilation of Particles, active galactic nuclei (AGN) sources, and baryon-antibaryon annihilation in a baryon symmetric cosmology. The energy spectrum and possible angular fluctuations due to these sources are described.

DUST IN ACTIVE GALACTIC NUCLEI: ANOMALOUS SILICATE TO OPTICAL EXTINCTION RATIOS?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lyu, Jianwei; Hao, Lei; Li, Aigen, E-mail: haol@shao.ac.cn

Dust plays a central role in the unification theory of active galactic nuclei (AGNs). However, little is known about the nature (e.g., size, composition) of the dust that forms a torus around the AGN. In this Letter, we report a systematic exploration of the optical extinction (A{sub V} ) and the silicate absorption optical depth (Δτ{sub 9.7}) of 110 type 2 AGNs. We derive A{sub V} from the Balmer decrement based on the Sloan Digital Sky Survey data, and Δτ{sub 9.7} from the Spitzer/InfraRed Spectrograph data. We find that with a mean ratio of (A{sub V} /Δτ{sub 9.7}) ≲ 5.5, themore » optical-to-silicate extinction ratios of these AGNs are substantially lower than that of the Galactic diffuse interstellar medium (ISM) for which A{sub V} /Δτ{sub 9.7} ≈ 18.5. We argue that the anomalously low A{sub V} /Δτ{sub 9.7} ratio could be due to the predominance of larger grains in the AGN torus compared to that in the Galactic diffuse ISM.« less

X-ray astronomy from Uhuru to HEAO-1

NASA Technical Reports Server (NTRS)

Clark, G. W.

1981-01-01

The nature of galactic and extragalactic X-ray sources is investigated using observations made with nine satellites and several rockets. The question of X-ray pulsars being neutron stars or white dwarfs is considered, as is the nature of Population II and low-luminosity X-ray stars, the diffuse X-ray emission from clusters of galaxies, the unidentified high-galactic-latitude (UHGL) sources, and the unresolved soft X-ray background. The types of sources examined include binary pulsars, Population II X-ray stars (both nonbursters and bursters) inside and outside globular clusters, coronal X-ray emitters, and active galactic nuclei. It is concluded that: (1) X-ray pulsars are strongly magnetized neutron stars formed in the evolution of massive close binaries; (2) all Population II X-ray stars are weakly magnetized or nonmagnetic neutron stars accreting from low-mass companions in close binary systems; (3) the diffuse emission from clusters is thermal bremsstrahlung of hot matter processed in stars and swept out by ram pressure exerted by the intergalactic gas; (4) most or all of the UHGL sources are active galactic nuclei; and (5) the soft X-ray background is emission from a hot component of the interstellar medium.

Mid-Infrared Properties of the Swift Burst Alert Telescope Active Galactic Nuclei Sample of the Local Universe. 1. Emission-Line Diagnostics

DTIC Science & Technology

2010-06-20

reserved. Printed in the U.S.A. MID-INFRARED PROPERTIES OF THE SWIFT BURST ALERT TELESCOPE ACTIVE GALACTIC NUCLEI SAMPLE OF THE LOCAL UNIVERSE . I. EMISSION... the AGNs. We also compare the mid-infrared emission lines in the BAT AGNs with those from published studies of ULIRGs, Palomar- Green quasars, star...supermassive black holes (e.g., Rees 1984; Peterson et al. 2004). One way to approach the study of AGNs is to concentrate on those in the local universe

The fuelling of active galactic nuclei

NASA Technical Reports Server (NTRS)

Shlosman, Isaac; Begelman, Mitchell C.; Frank, Julian

1990-01-01

Accretion mechanisms for powering the central engines of active galactic nuclei (AGN) and possible sources of fuel are reviewed. It is a argued that the interstellar matter in the main body of the host galaxy is channeled toward the center, and the problem of angular momentum transport is addressed. Thin accretion disks are not a viable means of delivering fuel to luminous AGN on scales much larger than a parsec because of the long inflow time and effects of self-gravity. There are also serious obstacles to maintaining and regulating geometrically thick, hot accretion flows. The role of nonaxisymmetric perturbations of the gravitational potential on galactic scales and their triggers is emphasized. A unified model is outlined for fueling AGN, in which the inflow on large scales is driven by gravitational torques, and on small scales forms a mildly self-gravitating disk of clouds with inflow driven by magnetic torques or cloud-cloud collisions.

Galaxy NGC 1448 with Active Galactic Nucleus

NASA Image and Video Library

2017-01-07

NGC 1448, a galaxy with an active galactic nucleus, is seen in this image combining data from the Carnegie-Irvine Galaxy Survey in the optical range and NuSTAR in the X-ray range. This galaxy contains an example of a supermassive black hole hidden by gas and dust. X-ray emissions from NGC 1448, as seen by NuSTAR and Chandra, suggests for the first time that, like IC 3639 in PIA21087, there must be a thick layer of gas and dust hiding the active black hole in this galaxy from our line of sight. http://photojournal.jpl.nasa.gov/catalog/PIA21086

Monitoring the Galactic - Search for Hard X-Ray Transients

NASA Astrophysics Data System (ADS)

Marshall, Francis

Hard X-ray transients with fluxs from ~1 to ~30 mCrab are a common feature of the galactic plane with apparent concentrations in specific regions of the plane. Concentrations in the Scutum and Carina fields probably indicate an enhancement of Be X-ray binaries along the tangent direction of two spiral arms. The frequency of outbursts suggest that at any one time 1 or 2 transients are active in the Scutum field alone. We propose weekly scans of the galactic plane to understand this population of sources. The scans will also monitor about 50 already known sources with better spectral information than available with the ASM.

Galactic Winds

NASA Astrophysics Data System (ADS)

Veilleux, Sylvain

Galactic winds have become arguably one of the hottest topics in extragalactic astronomy. This enthusiasm for galactic winds is due in part to the detection of winds in many, if not most, high-redshift galaxies. Galactic winds have also been invoked by theorists to (1) suppress the number of visible dwarf galaxies and avoid the "cooling catastrophe" at high redshift that results in the overproduction of massive luminous galaxies, (2) remove material with low specific angular momentum early on and help enlarge gas disks in CDM + baryons simulations, (3) reduce the dark mass concentrations in galaxies, (4) explain the mass-metallicity relation of galaxies from selective loss of metal-enriched gas from smaller galaxies, (5) enrich and "preheat" the ICM, (6) enrich the IGM without disturbing the Lyαforest significantly, and (7) inhibit cooling flows in galaxy clusters with active cD galaxies. The present paper highlights a few key aspects of galactic winds taken from a recent ARAA review by Veilleux, Cecil, &Bland-Hawthorn (2005; herafter VCBH). Readers interested in a more detailed discussion of this topic are encouraged to refer to the original ARAA article.

A complete X-ray sample of the high latitude sky from HEAO-1 A-2: log N lo S and luminosity functions

NASA Technical Reports Server (NTRS)

Piccinotti, G.; Mushotzky, R. F.; Boldt, E. A.; Holt, S. S.; Marshall, F. E.; Serlemitsos, P. J.; Shafer, R. A.

1981-01-01

An experiment was performed in which a complete X-ray survey of the 8.2 steradians of the sky at galactic latitudes where the absolute value of b is 20 deg down to a limiting sensitivity of 3.1 x ten to the minus 11th power ergs/sq cm sec in the 2-10 keV band. Of the 85 detected sources 17 were identified with galactic objects, 61 were identified with extragalactic objects, and 7 remain unidentified. The log N - log S relation for the non-galactic objects is well fit by the Euclidean relationship. The X-ray spectra of these objects were used to construct log N - log S in physical units. The complete sample of identified sources was used to construct X-ray luminosity functions, using the absolute maximum likelihood method, for clusters galaxies and active galactic nuclei.

A Green Bank Telescope 21cm survey of HI clouds in the Milky Way's nuclear wind

NASA Astrophysics Data System (ADS)

Denbo, Sara; Endsley, Ryan; Lockman, Felix J.; Ford, Alyson

2015-01-01

Feedback processes such as large-scale galactic winds are thought to be responsible for distributing enriched gas throughout a galaxy and even into the IGM. Such winds have been found in many galaxies with active star formation near their center, and the Fermi bubbles provide evidence for such a nuclear wind in our own Milky Way. A recent 21 cm HI survey by the Australia Telescope Compact Array discovered a population of compact, isolated clouds surrounding the Galactic Center that may be entrained in the Fermi bubble wind. We present data from a survey of 21cm HI over an extended region around the Galactic Center using the Green Bank Telescope. These observations provide more strict constraints on neutral clouds in the Fermi bubble wind, and a more robust description of the parameters of HI clouds (i.e., mass, column density, and lifetime) near the Galactic Center.

Dose equivalent on the Moon contributed from cosmic rays and their secondary particles

NASA Astrophysics Data System (ADS)

Hayatsu, K.; Hareyama, Makoto; Hasebe, N.; Kobayashi, S.; Yamashita, N.

Estimation of radiation dose on and under the lunar surface is quite important for human activity on the Moon and in the future lunar bases. Radiation environment on the Moon is much different from that on the Earth. Galactic cosmic rays and solar energetic particles directly penetrate the lunar surface because of no atmosphere and no magnetic field around the Moon. Then, those generate many secondary particles such as gamma rays, neutrons and other charged particles by interaction with soils under the lunar surface. Therefore, the estimation of radiation dose from them on the surface and the underground of the Moon are essential for safety human activities. In this study the ambient dose equivalent in the ICRU sphere at the surface and various depths of the Moon is estimated based on the latest galactic cosmic ray spectrum and its generating secondary particles calculated by the Geant4 code. On the surface the most dominant contribution for the dose are not protons and heliums, but heavy components of galactic cosmic rays such as iron, while in the ground, secondary neutrons are the most dominant. In particular, the dose from neutrons becomes maximal at 50 - 100 g/cm2 of lunar soil depth, because fast neutrons with about 1.0 MeV are mostly produced at this depth and give a large dose. On the surface, the dose originated from GCR is quite sensitive for solar cycle activity, while that from secondary neutrons is not so sensitive. Inversely, under the surface, the dose from neutron is much sensitive for solar activity related to the flux of galactic cosmic rays. This difference should be considered to shield cosmic radiation for human activity on the Moon.

X-ray astronomical spectroscopy

NASA Technical Reports Server (NTRS)

Holt, S. S.

1980-01-01

The current status of the X-ray spectroscopy of celestial X-ray sources, ranging from nearby stars to distant quasars, is reviewed. Particular emphasis is placed on the role of such spectroscopy as a useful and unique tool in the elucidation of the physical parameters of the sources. The spectroscopic analysis of degenerate and nondegenerate stellar systems, galactic clusters and active galactic nuclei, and supernova remnants is discussed.

Criteria for retrograde rotation of accreting black holes

NASA Astrophysics Data System (ADS)

Mikhailov, A. G.; Piotrovich, M. Yu; Gnedin, Yu N.; Natsvlishvili, T. M.; Buliga, S. D.

2018-06-01

Rotating supermassive black holes produce jets and their origin is connected to the magnetic field that is generated by accreting matter flow. There is a point of view that electromagnetic fields around rotating black holes are brought to the hole by accretion. In this situation the prograde accreting discs produce weaker large-scale black hole threading magnetic fields, implying weaker jets than in retrograde regimes. The basic goal of this paper is to find the best candidates for retrograde accreting systems in observed active galactic nuclei. We show that active galactic nuclei with low Eddington ratio are really the best candidates for retrograde systems. This conclusion is obtained for kinetically dominated Fanaroff-Riley class II radio galaxies, flat-spectrum radio-loud narrow-line Seyfert I galaxies and a number of nearby galaxies. Our conclusion is that the best candidates for retrograde systems are the noticeable population of active galactic nuclei in the Universe. This result corresponds to the conclusion that in the merging process the interaction of merging black holes with a retrograde circumbinary disc is considerably more effective for shrinking the binary system.

The Pierre Auger Observatory scaler mode for the study of solar activity modulation of galactic cosmic rays

NASA Astrophysics Data System (ADS)

Pierre Auger Collaboration; Abreu, P.; Aglietta, M.; Ahn, E. J.; Allard, D.; Allekotte, I.; Allen, J.; Alvarez Castillo, J.; Alvarez-Muñiz, J.; Ambrosio, M.; Aminaei, A.; Anchordoqui, L.; Andringa, S.; Antičić, T.; Anzalone, A.; Aramo, C.; Arganda, E.; Arisaka, K.; Arqueros, F.; Asorey, H.; Assis, P.; Aublin, J.; Ave, M.; Avenier, M.; Avila, G.; Bäcker, T.; Badagnani, D.; Balzer, M.; Barber, K. B.; Barbosa, A. F.; Bardenet, R.; Barroso, S. L. C.; Baughman, B.; Beatty, J. J.; Becker, B. R.; Becker, K. H.; Bellétoile, A.; Bellido, J. A.; BenZvi, S.; Berat, C.; Bergmann, T.; Bertou, X.; Biermann, P. L.; Billoir, P.; Blanco, F.; Blanco, M.; Bleve, C.; Blümer, H.; Boháčová, M.; Boncioli, D.; Bonifazi, C.; Bonino, R.; Borodai, N.; Brack, J.; Brogueira, P.; Brown, W. C.; Bruijn, R.; Buchholz, P.; Bueno, A.; Burton, R. E.; Busca, N. G.; Caballero-Mora, K. S.; Caramete, L.; Caruso, R.; Castellina, A.; Catalano, O.; Cataldi, G.; Cazon, L.; Cester, R.; Chauvin, J.; Chiavassa, A.; Chinellato, J. A.; Chou, A.; Chudoba, J.; Clay, R. W.; Colombo, E.; Coluccia, M. R.; Conceição, R.; Contreras, F.; Cook, H.; Cooper, M. J.; Coppens, J.; Cordier, A.; Cotti, U.; Coutu, S.; Covault, C. E.; Creusot, A.; Criss, A.; Cronin, J.; Curutiu, A.; Dagoret-Campagne, S.; Dallier, R.; Dasso, S.; Daumiller, K.; Dawson, B. R.; de Almeida, R. M.; De Domenico, M.; De Donato, C.; de Jong, S. J.; De La Vega, G.; de Mello Junior, W. J. M.; de Mello Neto, J. R. T.; De Mitri, I.; de Souza, V.; de Vries, K. D.; Decerprit, G.; del Peral, L.; Deligny, O.; Della Selva, A.; Dembinski, H.; Denkiewicz, A.; Di Giulio, C.; Diaz, J. C.; Díaz Castro, M. L.; Diep, P. N.; Dobrigkeit, C.; D'Olivo, J. C.; Dong, P. N.; Dorofeev, A.; dos Anjos, J. C.; Dova, M. T.; D'Urso, D.; Dutan, I.; Ebr, J.; Engel, R.; Erdmann, M.; Escobar, C. O.; Etchegoyen, A.; Facal San Luis, P.; Falcke, H.; Farrar, G.; Fauth, A. C.; Fazzini, N.; Ferguson, A. P.; Ferrero, A.; Fick, B.; Filevich, A.; Filipčič, A.; Fleck, I.; Fliescher, S.; Fracchiolla, C. E.; Fraenkel, E. D.; Fröhlich, U.; Fuchs, B.; Fulgione, W.; Gamarra, R. F.; Gambetta, S.; García, B.; García Gámez, D.; Garcia-Pinto, D.; Garrido, X.; Gascon, A.; Gelmini, G.; Gemmeke, H.; Gesterling, K.; Ghia, P. L.; Giaccari, U.; Giller, M.; Glass, H.; Gold, M. S.; Golup, G.; Gomez Albarracin, F.; Gómez Berisso, M.; Gonçalves, P.; Gonzalez, D.; Gonzalez, J. G.; Gookin, B.; Góra, D.; Gorgi, A.; Gouffon, P.; Gozzini, S. R.; Grashorn, E.; Grebe, S.; Grigat, M.; Grillo, A. F.; Guardincerri, Y.; Guarino, F.; Guedes, G. P.; Hague, J. D.; Hansen, P.; Harari, D.; Harmsma, S.; Harton, J. L.; Haungs, A.; Hebbeker, T.; Heck, D.; Herve, A. E.; Hojvat, C.; Holmes, V. C.; Homola, P.; Hórandel, J. R.; Horneffer, A.; Hrabovský, M.; Huege, T.; Insolia, A.; Ionita, F.; Italiano, A.; Jiraskova, S.; Kadija, K.; Kaducak, M.; Kampert, K. H.; Karhan, P.; Karova, T.; Kasper, P.; Kégl, B.; Keilhauer, B.; Keivani, A.; Kelley, J. L.; Kemp, E.; Kieckhafer, R. M.; Klages, H. O.; Kleifges, M.; Kleinfeller, J.; Knapp, J.; Koang, D.-H.; Kotera, K.; Krohm, N.; Krömer, O.; Kruppke-Hansen, D.; Kuehn, F.; Kuempel, D.; Kulbartz, J. K.; Kunka, N.; La Rosa, G.; Lachaud, C.; Lautridou, P.; Leão, M. S. A. B.; Lebrun, D.; Lebrun, P.; Leigui de Oliveira, M. A.; Lemiere, A.; Letessier-Selvon, A.; Lhenry-Yvon, I.; Link, K.; López, R.; Lopez Agüera, A.; Louedec, K.; Lozano Bahilo, J.; Lucero, A.; Ludwig, M.; Lyberis, H.; Maccarone, M. C.; Macolino, C.; Maldera, S.; Mandat, D.; Mantsch, P.; Mariazzi, A. G.; Marin, V.; Maris, I. C.; Marquez Falcon, H. R.; Marsella, G.; Martello, D.; Martin, L.; Martínez Bravo, O.; Mathes, H. J.; Matthews, J.; Matthews, J. A. J.; Matthiae, G.; Maurizio, D.; Mazur, P. O.; Medina-Tanco, G.; Melissas, M.; Melo, D.; Menichetti, E.; Menshikov, A.; Meurer, C.; Mičanović, S.; Micheletti, M. I.; Miller, W.; Miramonti, L.; Mollerach, S.; Monasor, M.; Monnier Ragaigne, D.; Montanet, F.; Morales, B.; Morello, C.; Moreno, E.; Moreno, J. C.; Morris, C.; Mostafá, M.; Mueller, S.; Muller, M. A.; Müller, G.; Münchmeyer, M.; Mussa, R.; Navarra, G.; Navarro, J. L.; Navas, S.; Necesal, P.; Nellen, L.; Nhung, P. T.; Nierstenhoefer, N.; Nitz, D.; Nosek, D.; Nožka, L.; Nyklicek, M.; Oehlschläger, J.; Olinto, A.; Oliva, P.; Olmos-Gilbaja, V. M.; Ortiz, M.; Pacheco, N.; Pakk Selmi-Dei, D.; Palatka, M.; Pallotta, J.; Palmieri, N.; Parente, G.; Parizot, E.; Parra, A.; Parrisius, J.; Parsons, R. D.; Pastor, S.; Paul, T.; Pavlidou c, V.; Payet, K.; Pech, M.; Pękala, J.; Pelayo, R.; Pepe, I. M.; Perrone, L.; Pesce, R.; Petermann, E.; Petrera, S.; Petrinca, P.; Petrolini, A.; Petrov, Y.; Petrovic, J.; Pfendner, C.; Phan, N.; Piegaia, R.; Pierog, T.; Pieroni, P.; Pimenta, M.; Pirronello, V.; Platino, M.; Ponce, V. H.; Pontz, M.; Privitera, P.; Prouza, M.; Quel, E. J.; Rautenberg, J.; Ravel, O.; Ravignani, D.; Revenu, B.; Ridky, J.; Riggi, S.; Risse, M.; Ristori, P.; Rivera, H.; Rivière, C.; Rizi, V.; Robledo, C.; Rodriguez, G.; Rodriguez Martino, J.; Rodriguez Rojo, J.; Rodriguez-Cabo, I.; Rodríguez-Frías, M. D.; Ros, G.; Rosado, J.; Rossler, T.; Roth, M.; Rouillé-d'Orfeuil, B.; Roulet, E.; Rovero, A. C.; Salamida, F.; Salazar, H.; Salina, G.; Sánchez, F.; Santander, M.; Santo, C. E.; Santos, E.; Santos, E. M.; Sarazin, F.; Sarkar, S.; Sato, R.; Scharf, N.; Scherini, V.; Schieler, H.; Schiffer, P.; Schmidt, A.; Schmidt, F.; Schmidt, T.; Scholten, O.; Schoorlemmer, H.; Schovancova, J.; Schovánek, P.; Schroeder, F.; Schulte, S.; Schüssler, F.; Schuster, D.; Sciutto, S. J.; Scuderi, M.; Segreto, A.; Semikoz, D.; Settimo, M.; Shadkam, A.; Shellard, R. C.; Sidelnik, I.; Sigl, G.; Śmiałkowski, A.; Šmída, R.; Snow, G. R.; Sommers, P.; Sorokin, J.; Spinka, H.; Squartini, R.; Stapleton, J.; Stasielak, J.; Stephan, M.; Strazzeri, E.; Stutz, A.; Suarez, F.; Suomijärvi, T.; Supanitsky, A. D.; Šuša, T.; Sutherland, M. S.; Swain, J.; Szadkowski, Z.; Tamashiro, A.; Tapia, A.; Tarutina, T.; Taşcǎu, O.; Tcaciuc, R.; Tcherniakhovski, D.; Tegolo, D.; Thao, N. T.; Thomas, D.; Tiffenberg, J.; Timmermans, C.; Tiwari, D. K.; Tkaczyk, W.; Todero Peixoto, C. J.; Tomé, B.; Tonachini, A.; Travnicek, P.; Tridapalli, D. B.; Tristram, G.; Trovato, E.; Tueros, M.; Ulrich, R.; Unger, M.; Urban, M.; Valdés Galicia, J. F.; Valiño, I.; Valore, L.; van den Berg, A. M.; Vargas Cárdenas, B.; Vázquez, J. R.; Vázquez, R. A.; Veberič, D.; Venters, T.; Verzi, V.; Videla, M.; Villaseñor, L.; Wahlberg, H.; Wahrlich, P.; Wainberg, O.; Warner, D.; Watson, A. A.; Weber, M.; Weidenhaupt, K.; Weindl, A.; Westerhoff, S.; Whelan, B. J.; Wieczorek, G.; Wiencke, L.; Wilczyńska, B.; Wilczyński, H.; Will, M.; Williams, C.; Winchen, T.; Winders, L.; Winnick, M. G.; Wommer, M.; Wundheiler, B.; Yamamoto a, T.; Younk, P.; Yuan, G.; Yushkov, A.; Zamorano, B.; Zas, E.; Zavrtanik, D.; Zavrtanik, M.; Zaw, I.; Zepeda, A.; Ziolkowski, M.

2011-01-01

Since data-taking began in January 2004, the Pierre Auger Observatory has been recording the count rates of low energy secondary cosmic ray particles for the self-calibration of the ground detectors of its surface detector array. After correcting for atmospheric effects, modulations of galactic cosmic rays due to solar activity and transient events are observed. Temporal variations related with the activity of the heliosphere can be determined with high accuracy due to the high total count rates. In this study, the available data are presented together with an analysis focused on the observation of Forbush decreases, where a strong correlation with neutron monitor data is found.

Determining the Absolute Magnitudes of Galactic-Bulge Red Clump Giants in the Z and Y Filters of the Vista Sky Surveys and the IRAC Filters of the Spitzer Sky Surveys

NASA Astrophysics Data System (ADS)

Karasev, D. I.; Lutovinov, A. A.

2018-04-01

The properties of red clump giants in the central regions of the Galactic bulge are investigated in the photometric Z and Y bands of the infrared VVV (VISTA/ESO) survey and the [3.6], [4.5], [5.8], and [8.0] μm bands of the GLIMPSE (Spitzer/IRAC) Galactic plane survey. The absolute magnitudes for objects of this class have been determined in these bands for the first time: M Z = -0.20 ± 0.04, M Y = -0.470 ± 0.045, M [3.6] = -1.70 ± 0.03, M [4.5] = -1.60 ± 0.03, M [5.8] = -1.67 ± 0.03, and M [8.0] = -1.70 ± 0.03. A comparison of the measured magnitudes with the predictions of theoretical models for the spectra of the objects under study has demonstrated good mutual agreement and has allowed some important constraints to be obtained for the properties of bulge red clump giants. In particular, a comparison with evolutionary tracks has shown that we are dealing predominantly with the high-metallicity subgroup of bulge red clump giants. Their metallicity is slightly higher than has been thought previously, [ M/H] ≃ 0.40 ( Z ≃ 0.038) with an error of [ M/H] ≃ 0.1 dex, while the effective temperature is 4250± 150 K. Stars with an age of 9-10 Gyr are shown to dominate among the red clump giants, although some number of younger objects with an age of 8 Gyr can also be present. In addition, the distances to several Galactic bulge regions have been measured, as D = 8200-8500 pc, and the extinction law in these directions is shown to differ noticeably from the standard one.

The Fermi Large Area Telescope Thrid Gamma-ray Source Catalog

NASA Astrophysics Data System (ADS)

Stephens, Thomas E.; Ballet, Jean; Burnett, Toby; Cavazzuti, Elisabetta; Digel, Seth William; Fermi LAT Collaboration

2015-01-01

We present an overview of the third Fermi Large Area Telescope source catalog (3FGL) of sources in the 100 MeV - 300 GeV range. Based on the first four years of science data from the Fermi Gamma-ray Space Telescope mission, it is the deepest yet in this energy range. Relative to the 2FGL catalog (Nolan et al. 2012, ApJS 199, 31), the 3FGL catalog incorporates twice as much data as well as a number of analysis improvements, including improved calibrations at the event reconstruction level, an updated model for Galactic diffuse gamma-ray emission, a refined procedure for source detection, and improved methods for associating LAT sources with potential counterparts at other wavelengths. The 3FGL catalog includes 3033 sources, with source location regions, spectral properties, and monthly light curves for each. For approximately one-third of the sources we have not found counterparts at other wavelengths. More than 1100 of the identified or associated sources are active galaxies of the blazar class; several other classes of non-blazar active galaxies are also represented in the 3FGL. Pulsars represent the largest Galactic source class. From source counts of Galactic sources we estimate the contribution of unresolved sources to the Galactic diffuse emission.

Fermi Large Area Telescope third source catalog

DOE PAGES

Acero, F.; Ackermann, M.; Ajello, M.; ...

2015-06-12

Here, we present the third Fermi Large Area Telescope (LAT) source catalog (3FGL) of sources in the 100 MeV–300 GeV range. Based on the first 4 yr of science data from the Fermi Gamma-ray Space Telescope mission, it is the deepest yet in this energy range. Relative to the Second Fermi LAT catalog, the 3FGL catalog incorporates twice as much data, as well as a number of analysis improvements, including improved calibrations at the event reconstruction level, an updated model for Galactic diffuse γ-ray emission, a refined procedure for source detection, and improved methods for associating LAT sources with potential counterparts at other wavelengths. The 3FGL catalog includes 3033 sources abovemore » $$4\\sigma $$ significance, with source location regions, spectral properties, and monthly light curves for each. Of these, 78 are flagged as potentially being due to imperfections in the model for Galactic diffuse emission. Twenty-five sources are modeled explicitly as spatially extended, and overall 238 sources are considered as identified based on angular extent or correlated variability (periodic or otherwise) observed at other wavelengths. For 1010 sources we have not found plausible counterparts at other wavelengths. More than 1100 of the identified or associated sources are active galaxies of the blazar class; several other classes of non-blazar active galaxies are also represented in the 3FGL. Pulsars represent the largest Galactic source class. As a result, from source counts of Galactic sources we estimate that the contribution of unresolved sources to the Galactic diffuse emission is ~3% at 1 GeV.« less

The Galactic Club or Galactic Cliques? Exploring the limits of interstellar hegemony and the Zoo Hypothesis

NASA Astrophysics Data System (ADS)

Forgan, Duncan H.

2017-10-01

The Zoo solution to Fermi's Paradox proposes that extraterrestrial intelligences (ETIs) have agreed to not contact the Earth. The strength of this solution depends on the ability for ETIs to come to agreement, and establish/police treaties as part of a so-called `Galactic Club'. These activities are principally limited by the causal connectivity of a civilization to its neighbours at its inception, i.e. whether it comes to prominence being aware of other ETIs and any treaties or agreements in place. If even one civilization is not causally connected to the other members of a treaty, then they are free to operate beyond it and contact the Earth if wished, which makes the Zoo solution `soft'. We should therefore consider how likely this scenario is, as this will give us a sense of the Zoo solution's softness, or general validity. We implement a simple toy model of ETIs arising in a Galactic Habitable Zone, and calculate the properties of the groups of culturally connected civilizations established therein. We show that for most choices of civilization parameters, the number of culturally connected groups is >1, meaning that the Galaxy is composed of multiple Galactic Cliques rather than a single Galactic Club. We find in our models for a single Galactic Club to establish interstellar hegemony, the number of civilizations must be relatively large, the mean civilization lifetime must be several millions of years, and the inter-arrival time between civilizations must be a few million years or less.

The physics of galactic winds driven by active galactic nuclei

NASA Astrophysics Data System (ADS)

Faucher-Giguère, Claude-André; Quataert, Eliot

2012-09-01

Active galactic nuclei (AGN) drive fast winds in the interstellar medium of their host galaxies. It is commonly assumed that the high ambient densities and intense radiation fields in galactic nuclei imply short cooling times, thus making the outflows momentum conserving. We show that cooling of high-velocity shocked winds in AGN is in fact inefficient in a wide range of circumstances, including conditions relevant to ultraluminous infrared galaxies (ULIRGs), resulting in energy-conserving outflows. We further show that fast energy-conserving outflows can tolerate a large amount of mixing with cooler gas before radiative losses become important. For winds with initial velocity vin ≳ 10 000 km s-1, as observed in ultraviolet and X-ray absorption, the shocked wind develops a two-temperature structure. While most of the thermal pressure support is provided by the protons, the cooling processes operate directly only on the electrons. This significantly slows down inverse Compton cooling, while free-free cooling is negligible. Slower winds with vin ˜ 1000 km s-1, such as may be driven by radiation pressure on dust, can also experience energy-conserving phases but under more restrictive conditions. During the energy-conserving phase, the momentum flux of an outflow is boosted by a factor ˜vin/2vs by work done by the hot post-shock gas, where vs is the velocity of the swept-up material. Energy-conserving outflows driven by fast AGN winds (vin ˜ 0.1c) may therefore explain the momentum fluxes Ṗ≫LAGN/c of galaxy-scale outflows recently measured in luminous quasars and ULIRGs. Shocked wind bubbles expanding normal to galactic discs may also explain the large-scale bipolar structures observed in some systems, including around the Galactic Centre, and can produce significant radio, X-ray and γ-ray emission. The analytic solutions presented here will inform implementations of AGN feedback in numerical simulations, which typically do not include all the important physics.

Effects of Target Fragmentation on Evaluation of LET Spectra From Space Radiation in Low-Earth Orbit (LEO) Environment: Impact on SEU Predictions

NASA Technical Reports Server (NTRS)

Shinn, J. L.; Cucinotta, F. A.; Badhwar, G. D.; ONeill, P. M.; Badavi, F. F.

1995-01-01

Recent improvements in the radiation transport code HZETRN/BRYNTRN and galactic cosmic ray environmental model have provided an opportunity to investigate the effects of target fragmentation on estimates of single event upset (SEU) rates for spacecraft memory devices. Since target fragments are mostly of very low energy, an SEU prediction model has been derived in terms of particle energy rather than linear energy transfer (LET) to account for nonlinear relationship between range and energy. Predictions are made for SEU rates observed on two Shuttle flights, each at low and high inclination orbit. Corrections due to track structure effects are made for both high energy ions with track structure larger than device sensitive volume and for low energy ions with dense track where charge recombination is important. Results indicate contributions from target fragments are relatively important at large shield depths (or any thick structure material) and at low inclination orbit. Consequently, a more consistent set of predictions for upset rates observed in these two flights is reached when compared to an earlier analysis with CREME model. It is also observed that the errors produced by assuming linear relationship in range and energy in the earlier analysis have fortuitously canceled out the errors for not considering target fragmentation and track structure effects.

DOUBLE-PEAKED NARROW-LINE ACTIVE GALACTIC NUCLEI. II. THE CASE OF EQUAL PEAKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, K. L.; Shields, G. A.; Salviander, S.

Active galactic nuclei (AGNs) with double-peaked narrow lines (DPAGNs) may be caused by kiloparsec-scale binary AGNs, bipolar outflows, or rotating gaseous disks. We examine the class of DPAGNs in which the two narrow-line components have closely similar intensity as being especially likely to involve disks or jets. Two spectroscopic indicators support this likelihood. For DPAGNs from Smith et al., the 'equal-peaked' objects (EPAGNs) have [Ne V]/[O III]ratios lower than for a control sample of non-double-peaked AGNs. This is unexpected for a pair of normal AGNs in a galactic merger, but may be consistent with [O III] emission from a rotatingmore » ring with relatively little gas at small radii. Also, [O III]/H{beta} ratios of the redshifted and blueshifted systems in the EPAGN are more similar to each other than in a control sample, suggestive of a single ionizing source and inconsistent with the binary interpretation.« less

What can Fermi LAT observation of the Galactic Centre tell us about its active past?

NASA Astrophysics Data System (ADS)

Zaharijas, Gabrijela; Petrović, Jovana; Serpico, Pasquale

The Fermi-LAT gamma-ray data in the inner Galaxy region show several prominent features possibly related to the past activity of the Milky Way's super massive black hole. At a large, 50 deg scale, the Fermi LAT revealed symmetric hour glass structures with hard energy spectra extending up to 100 GeV (and dubbed `the Fermi bubbles'). More recently and closer to the Galactic centre, at the 10 deg scale, several groups have claimed evidence for excess gamma-ray emission that appears symmetric around the Galactic center and has an energy spectrum peaking at few GeVs. We explore here the possibility that this emission originates in inverse Compton emission from high-energy electrons produced in a short duration, burst-like event injecting 1052 - 1053 erg, roughly 106 yrs ago. Several lines of evidence suggest that a series of `burst like' events happened in the vicinity of our black hole in the past and gamma-ray observations may offer a new view of that scenario.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ginsburg, A.; Bally, J.; Battersby, C.

We search the {lambda} = 1.1 mm Bolocam Galactic Plane Survey for clumps containing sufficient mass to form {approx}10{sup 4} M{sub Sun} star clusters. Eighteen candidate massive proto-clusters are identified in the first Galactic quadrant outside of the central kiloparsec. This sample is complete to clumps with mass M{sub clump} > 10{sup 4} M{sub Sun} and radius r {approx}< 2.5 pc. The overall Galactic massive cluster formation rate is CFR(M{sub cluster} > 10{sup 4}) {approx}<5 Myr{sup -1}, which is in agreement with the rates inferred from Galactic open clusters and M31 massive clusters. We find that all massive proto-clusters inmore » the first quadrant are actively forming massive stars and place an upper limit of {tau}{sub starless} < 0.5 Myr on the lifetime of the starless phase of massive cluster formation. If massive clusters go through a starless phase with all of their mass in a single clump, the lifetime of this phase is very short.« less

The large-scale effect of environment on galactic conformity

NASA Astrophysics Data System (ADS)

Sun, Shuangpeng; Guo, Qi; Wang, Lan; Lacey, Cedric G.; Wang, Jie; Gao, Liang; Pan, Jun

2018-07-01

We use a volume-limited galaxy sample from the Sloan Digital Sky Survey Data Release 7 to explore the dependence of galactic conformity on the large-scale environment, measured on ˜4 Mpc scales. We find that the star formation activity of neighbour galaxies depends more strongly on the environment than on the activity of their primary galaxies. In underdense regions most neighbour galaxies tend to be active, while in overdense regions neighbour galaxies are mostly passive, regardless of the activity of their primary galaxies. At a given stellar mass, passive primary galaxies reside in higher density regions than active primary galaxies, leading to the apparently strong conformity signal. The dependence of the activity of neighbour galaxies on environment can be explained by the corresponding dependence of the fraction of satellite galaxies. Similar results are found for galaxies in a semi-analytical model, suggesting that no new physics is required to explain the observed large-scale conformity.

The ancient sun: Fossil record in the earth, moon and meteorites; Proceedings of the Conference, Boulder, CO, October 16-19, 1979

NASA Technical Reports Server (NTRS)

Pepin, R. O. (Editor); Eddy, J. A.; Merrill, R. B.

1980-01-01

Papers are presented concerning theories of solar variability and their consequences for luminosity, particle emission and magnetic field changes within the past 4.5 billion years, and on the records of such solar behavior in lunar, meteoritic and terrestrial materials. Specific topics include the neutrino luminosity of the sun, the relation of sunspots to the terrestrial climate of the past 100 years, solar modulation of galactic cosmic rays, the historical record of solar activity, C-14 variations in terrestrial and marine reservoirs, and solar particle fluxes as indicated by track, thermoluminescence and solar wind measurements in lunar rocks. Attention is also given to the spin-down of the solar interior through circulation currents and fluid instabilities, grain surface exposure models in planetary regoliths, rare gases in the solar wind, nitrogen isotopic variations in the lunar regolith, the influence of solar UV radiation on climate, and the pre-main sequence evolution of the sun and evidence of the primordial solar wind in the electromagnetic induction heating of the asteroids and moon.

High resolution Cerenkov and range detectors for balloon-borne cosmic-ray experiment

NASA Technical Reports Server (NTRS)

Ahlen, S. P.; Cartwright, B. G.; Tarle, G.

1975-01-01

A combination of an active Cerenkov detector and passive range detectors is proposed for the high resolution measurement of isotopic composition in the neighborhood of iron in the galactic cosmic rays. A large area (4,300 sq cm) Cerenkov counter and passive range detectors were tested. Tests with heavy ions (2.1 GeV/amu C-12, 289 MeV/amu Ar-40, and 594 MeV/amu Ne-20) revealed the spatial uniformity of response of the Cerenkov counter to be better than 1% peak-to-peak. Light collection efficiency is independent of projectile energy and incidence angle to within at least 0.5%. Passive Lexan track recorders to measure range in the presence of the nuclear interaction background which results from stopping particles through 0.9 interaction lengths of matter were also tested. It was found that nuclear interactions produce an effective range straggling distribution only approximately 75% wider than that expected from range straggling alone. The combination of these tested techniques makes possible high mass resolution in the neighborhood of iron.

Speckle imaging of active galactic nuclei: NGC 1068 and NGC 4151

NASA Astrophysics Data System (ADS)

Ebstein, Steven Michael

High resolution images of NGC 1068 and NGC 4151 in the 5007 A line and the nearby continuum produced from data taken with the PAPA photon counting imaging detector using the technique of speckle imaging are presented. The images show an unresolved core of 5007 A emission in the middle of an extended emission region. The extended emission tends to lie alongside the subarcsecond radio structure. In NGC 4151, the extended emission comes from a nearly linear structure extending on both sides of the unresolved core. In NGC 1068, the extended emission is concentrated in lobes lying to the unresolved core but the emission is concentrated in lobes lying to either side of the major axis. The continuum of NGC 4151 is spatially unresolved. The continuum of NGC 1068 is extended approx. 1 in to the SW of the center of the 5007 A emission. Certain aspects of the PAPA detector are discussed, including the variable threshold discriminators that track the image intensifier pulse height and the camera artifacts. The data processing is described in detail.

Search for neutrinos from transient sources with the ANTARES telescope and optical follow-up observations

NASA Astrophysics Data System (ADS)

Ageron, Michel; Al Samarai, Imen; Akerlof, Carl; Basa, Stéphane; Bertin, Vincent; Boer, Michel; Brunner, Juergen; Busto, Jose; Dornic, Damien; Klotz, Alain; Schussler, Fabian; Vallage, Bertrand; Vecchi, Manuela; Zheng, Weikang

2012-11-01

The ANTARES telescope is well suited to detect neutrinos produced in astrophysical transient sources as it can observe a full hemisphere of the sky at all the times with a duty cycle close to unity and an angular resolution better than 0.5°. Potential sources include gamma-ray bursts (GRBs), core collapse supernovae (SNe), and flaring active galactic nuclei (AGNs). To enhance the sensitivity of ANTARES to such sources, a new detection method based on coincident observations of neutrinos and optical signals has been developed. A fast online muon track reconstruction is used to trigger a network of small automatic optical telescopes. Such alerts are generated one or two times per month for special events such as two or more neutrinos coincident in time and direction or single neutrinos of very high energy. Since February 2009, ANTARES has sent 37 alert triggers to the TAROT and ROTSE telescope networks, 27 of them have been followed. First results on the optical images analysis to search for GRBs are presented.

Scoping estimates of the LDEF satellite induced radioactivity

NASA Technical Reports Server (NTRS)

Armstrong, Tony W.; Colborn, B. L.

1990-01-01

The Long Duration Exposure Facility (LDEF) satellite was recovered after almost six years in space. It was well-instrumented with ionizing radiation dosimeters, including thermoluminescent dosimeters, plastic nuclear track detectors, and a variety of metal foil samples for measuring nuclear activation products. The extensive LDEF radiation measurements provide the type of radiation environments and effects data needed to evaluate and help resolve uncertainties in present radiation models and calculational methods. A calculational program was established to aid in LDEF data interpretation and to utilize LDEF data for assessing the accuracy of current models. A summary of the calculational approach is presented. The purpose of the reported calculations is to obtain a general indication of: (1) the importance of different space radiation sources (trapped, galactic, and albedo protons, and albedo neutrons); (2) the importance of secondary particles; and (3) the spatial dependence of the radiation environments and effects expected within the spacecraft. The calculational method uses the High Energy Transport Code (HETC) to estimate the importance of different sources and secondary particles in terms of fluence, absorbed dose in tissue and silicon, and induced radioactivity as a function of depth in aluminum.

The Pierre Auger Observatory scaler mode for the study of solar activity modulation of galactic cosmic rays

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abreu, P.; /Lisbon, LIFEP /Lisbon, IST; Aglietta, M.

2011-01-01

Since data-taking began in January 2004, the Pierre Auger Observatory has been recording the count rates of low energy secondary cosmic ray particles for the self-calibration of the ground detectors of its surface detector array. After correcting for atmospheric effects, modulations of galactic cosmic rays due to solar activity and transient events are observed. Temporal variations related with the activity of the heliosphere can be determined with high accuracy due to the high total count rates. In this study, the available data are presented together with an analysis focused on the observation of Forbush decreases, where a strong correlation withmore » neutron monitor data is found.« less

OSSE observations of the ultraluminous infrared galaxies ARP 220 and MRK 273

NASA Technical Reports Server (NTRS)

Dermer, C. D.; Shier, L. M.; Sturner, S. J.; McNaron-Brown, K.; Bland-Hawthorn, J.

1997-01-01

The results of oriented scintillation spectrometer experiment (OSSE) observations of the ultraluminous infrared galaxies Arp 220 and Mrk 273 are reported. The pointings of Arp 220 and Mrk 273 concentrated on their upper limits. The gamma ray luminosities from these sources were found to be between one and two orders of magnitude smaller than the infrared luminosities. Multiwavelength luminosity spectra are produced from the radio to the gamma ray regime, and are compared with the typical multiwavelength spectra of active galactic nuclei. The lack of measured gamma ray emission provides no evidence for the existence of buried active galactic nuclei in these ultraluminous infrared galaxies, but is consistent with an origin of the infrared luminosity from starburst activity.

A new approach for measuring power spectra and reconstructing time series in active galactic nuclei

NASA Astrophysics Data System (ADS)

Li, Yan-Rong; Wang, Jian-Min

2018-05-01

We provide a new approach to measure power spectra and reconstruct time series in active galactic nuclei (AGNs) based on the fact that the Fourier transform of AGN stochastic variations is a series of complex Gaussian random variables. The approach parametrizes a stochastic series in frequency domain and transforms it back to time domain to fit the observed data. The parameters and their uncertainties are derived in a Bayesian framework, which also allows us to compare the relative merits of different power spectral density models. The well-developed fast Fourier transform algorithm together with parallel computation enables an acceptable time complexity for the approach.

Active galactic nucleus feedback in clusters of galaxies

PubMed Central

Blanton, Elizabeth L.; Clarke, T. E.; Sarazin, Craig L.; Randall, Scott W.; McNamara, Brian R.

2010-01-01

Observations made during the last ten years with the Chandra X-ray Observatory have shed much light on the cooling gas in the centers of clusters of galaxies and the role of active galactic nucleus (AGN) heating. Cooling of the hot intracluster medium in cluster centers can feed the supermassive black holes found in the nuclei of the dominant cluster galaxies leading to AGN outbursts which can reheat the gas, suppressing cooling and large amounts of star formation. AGN heating can come in the form of shocks, buoyantly rising bubbles that have been inflated by radio lobes, and the dissipation of sound waves. PMID:20351250

The Penrose photoproduction scenario for NGC 4151: A black hole gamma-ray emission mechanism for active galactic nuclei and Seyfert galaxies. [Compton scattering and pair production

NASA Technical Reports Server (NTRS)

Leiter, D.

1979-01-01

A consistent theoretical interpretation is given for the suggestion that a steepening of the spectrum between X-ray and gamma ray energies may be a general, gamma-ray characteristic of Seyfert galaxies, if the diffuse gamma ray spectrum is considered to be a superposition of unresolved contributions, from one or more classes of extragalactic objects. In the case of NGC 4151, the dominant process is shown to be Penrose Compton scattering in the ergosphere of a Kerr black hole, assumed to exist in the Seyfert's active galactic nucleus.

On the origin of power-law X-ray spectra of active galactic nuclei

NASA Technical Reports Server (NTRS)

Schlosman, I.; Shaham, J.; Shaviv, G.

1984-01-01

In the present analytical model for a power law X-ray continuum production in active galactic nuclei, the dissipation of turbulent energy flux above the accretion disk forms an optically thin transition layer with an inverted temperature gradient. The emitted thermal radiation has a power law spectrum in the 0.1-100 keV range, with a photon energy spectral index gamma of about 0.4-1.0. Thermal X-ray contribution from the layer is 5-10 percent of the total disk luminosity. The gamma value of 0.75 is suggested as a 'natural' power law index for Seyfert galaxies and QSOs.

An Axisymmetric, Hydrodynamical Model for the Torus Wind in Active Galactic Nuclei

NASA Technical Reports Server (NTRS)

Dorodnitsyn, A.; Kallman, T.; Proga, D.

2008-01-01

We report on time-dependent axisymmetric simulations of an X-ray-excited flow from a parsec-scale, rotating, cold torus around an active galactic nucleus. Our simulations account for radiative heating and cooling and radiation pressure force. The simulations follow the development of a broad biconical outflow induced mainly by X-ray heating. We compute synthetic spectra predicted by our simulations. The wind characteristics and the spectra support the hypothesis that a rotationally supported torus can serve as the source of a wind which is responsible for the warm absorber gas observed in the X-ray spectra of many Seyfert galaxies.

Echo Mapping of Active Galactic Nuclei

NASA Technical Reports Server (NTRS)

Peterson, B. M.; Horne, K.

2004-01-01

Echo mapping makes use of the intrinsic variability of the continuum source in active galactic nuclei to map out the distribution and kinematics of line-emitting gas from its light travel time-delayed response to continuum changes. Echo mapping experiments have yielded sizes for the broad line-emitting region in about three dozen AGNs. The dynamics of the line-emitting gas seem to be dominated by the gravity of the central black hole, enabling measurement of the black-hole masses in AGNs. We discuss requirements for future echo-mapping experiments that will yield the high quality velocity-delay maps of the broad-line region that are needed to determine its physical nature.

Exploring Black Hole Accretion in Active Galactic Nuclei with Simbol-X

NASA Astrophysics Data System (ADS)

Goosmann, R. W.; Dovčiak, M.; Mouchet, M.; Czerny, B.; Karas, V.; Gonçalves, A.

2009-05-01

A major goal of the Simbol-X mission is to improve our knowledge about black hole accretion. By opening up the X-ray window above 10 keV with unprecedented sensitivity and resolution we obtain new constraints on the X-ray spectral and variability properties of active galactic nuclei. To interpret the future data, detailed X-ray modeling of the dynamics and radiation processes in the black hole vicinity is required. Relativistic effects must be taken into account, which then allow to constrain the fundamental black hole parameters and the emission pattern of the accretion disk from the spectra that will be obtained with Simbol-X.

Kepler Observations of Rapid Optical Variability in Active Galactic Nuclei

NASA Technical Reports Server (NTRS)

Mushotzky, R. F.; Edelson, R.; Baumgartner, W. H.; Gandhi, P.

2012-01-01

Over three quarters in 2010 - 2011, Kepler monitored optical emission from four active galactic nuclei (AGN) with approx 30 min sampling, > 90% duty cycle and approx < 0.1% repeatability. These data determined the AGN optical fluctuation power spectral density functions (PSDs) over a wide range in temporal frequency. Fits to these PSDs yielded power law slopes of -2.6 to -3.3, much steeper than typically seen in the X-rays. We find evidence that individual AGN exhibit intrinsically different PSD slopes. The steep PSD fits are a challenge to recent AGN variability models but seem consistent with first order MRI theoretical calculations of accretion disk fluctuations.

Radio-Loud Narrow-Line Seyfert 1 as a New Class of Gamma-Ray Active Galactic Nuclei

DOE PAGES

Abdo, A. A.; Ackermann, M.; Ajello, M.; ...

2009-12-04

In this work, we report the discovery with Fermi/LAT of γ-ray emission from three radio-loud narrow-line Seyfert 1 galaxies: PKS 1502+036 (z = 0.409), 1H 0323+342 (z = 0.061), and PKS 2004 – 447 (z = 0.24). In addition to PMN J0948+0022 (z = 0.585), the first source of this type to be detected in γ rays, they may form an emerging new class of γ-ray active galactic nuclei (AGNs). Lastly, these findings can have strong implications on our knowledge about relativistic jets and the unified model of the AGN.

Reflection features in the Galactic Center and past activity of Sagittarius A*

NASA Astrophysics Data System (ADS)

Clavel, Maïca; Terrier, Regis; Goldwurm, Andrea; Morris, Mark; Jin, Chichuan; Ponti, Gabriele; Chuard, Dimitri

2016-07-01

X-ray observations carried out over the past two decades have captured an increasing number of reflection features within the molecular clouds located in the inner regions of our Galaxy. The intensity of these structures along with the correlated variations which are detected over the entire central molecular zone are strong evidence that this diffuse emission is created by the past activity of the supermassive black hole at the Galactic center, Sagittarius A*. In particular, within the last centuries, Sgr A* is likely to have experienced several short outbursts during which the black hole was at least a million times brighter than today. However, the precise description of the corresponding past catastrophic events is difficult to assess, mainly because the properties of the reflection features that they create while propagating away from Sgr A* depend on the line-of-sight distance, the geometry, and the size of the reflecting clouds, all of which are poorly known. I will review the different attempts to reconstruct Sgr A*'s past activity from the constraints obtained through the observation of the reflection features in the Galactic center, including the current Chandra monitoring.

Interstellar scintillation as the origin of the rapid radio variability of the quasar J1819+3845.

PubMed

Dennett-Thorpe, J; de Bruyn, A G

2002-01-03

The liberation of gravitational energy as matter falls onto a supermassive black hole at the centre of a galaxy is believed to explain the high luminosity of quasars. The variability of this emission from quasars and other types of active galactic nuclei can provide information on the size of the emitting regions and the physical process of fuelling the black hole. Some active galactic nuclei are variable at optical (and shorter) wavelengths, and display radio outbursts over years and decades. These active galactic nuclei often also show faster intraday variability at radio wavelengths. The origin of this rapid variability has been extensively debated, but a correlation between optical and radio variations in some sources suggests that both are intrinsic. This would, however, require radiation brightness temperatures that seem physically implausible, leading to the suggestion that the rapid variations are caused by scattering of the emission by the interstellar medium inside our Galaxy. Here we show that the rapid variations in the extreme case of quasar J1819+3845 (ref. 10) indeed arise from interstellar scintillation. The transverse velocity of the scattering material reveals the presence of plasma with a surprisingly high velocity close to the Solar System.

A connection between star formation activity and cosmic rays in the starburst galaxy M82.

PubMed

2009-12-10

Although Galactic cosmic rays (protons and nuclei) are widely believed to be mainly accelerated by the winds and supernovae of massive stars, definitive evidence of this origin remains elusive nearly a century after their discovery. The active regions of starburst galaxies have exceptionally high rates of star formation, and their large size-more than 50 times the diameter of similar Galactic regions-uniquely enables reliable calorimetric measurements of their potentially high cosmic-ray density. The cosmic rays produced in the formation, life and death of massive stars in these regions are expected to produce diffuse gamma-ray emission through interactions with interstellar gas and radiation. M82, the prototype small starburst galaxy, is predicted to be the brightest starburst galaxy in terms of gamma-ray emission. Here we report the detection of >700-GeV gamma-rays from M82. From these data we determine a cosmic-ray density of 250 eV cm(-3) in the starburst core, which is about 500 times the average Galactic density. This links cosmic-ray acceleration to star formation activity, and suggests that supernovae and massive-star winds are the dominant accelerators.

A Search for New Galactic Magnetars in Archival Chandra and XMM-Newton Observations

NASA Astrophysics Data System (ADS)

Muno, M. P.; Gaensler, B. M.; Nechita, A.; Miller, J. M.; Slane, P. O.

2008-06-01

We present constraints on the number of Galactic magnetars, which we have established by searching for sources with periodic variability in 506 archival Chandra observations and 441 archival XMM-Newton observations of the Galactic plane (| b| < 5°). Our search revealed four sources with periodic variability on timescales of 200-5000 s, all of which are probably accreting white dwarfs. We identify 7 of 12 known Galactic magnetars, but find no new examples with periods between 5 and 20 s. We convert this nondetection into limits on the total number of Galactic magnetars by computing the fraction of the young Galactic stellar population that our survey covered. We find that easily detectable magnetars, modeled after persistent anomalous X-ray pulsars (e.g., with LX = 1035 ergs s-1 [0.5-10.0 keV] and Arms = 12% ), could have been identified in ≈5% of the Galactic spiral arms by mass. If we assume that three previously known examples randomly fall within our survey, then there are 59+ 92-32 in the Galaxy. Barely detectable magnetars (LX = 3 × 1033 ergs s-1 and Arms = 15% ) could have been identified throughout ≈0.4% of the spiral arms. The lack of new examples implies that <540 exist in the Galaxy (90% confidence). Similar constraints are found by considering the detectability of transient magnetars in outburst. For assumed lifetimes of 104 yr, the birth rate of magnetars is between 0.003 and 0.06 yr-1. Therefore, the birth rate of magnetars is at least 10% of that for normal radio pulsars, and could exceed that value, unless transient magnetars are active for gtrsim105 yr.

GOT C+: A Herschel Space Observatory Key Program to Study the Diffuse ISM

NASA Astrophysics Data System (ADS)

Langer, William; Goldsmith, P. F.; Li, D.; Velusamy, T.; Yorke, H. W.

2009-01-01

Galactic Observations of the Terahertz C+ Line (GOT C+) is a Herschel Space Observatory (HSO) Key Program to study the diffuse interstellar medium by sampling the C+ fine structure line emission at 1.9 THz (158 microns) in the Galactic disk. Star formation activity is regulated by pressures in the interstellar medium, which in turn depend on heating and cooling rates, modulated by the gravitational potential, and shock and turbulent pressures. To understand these processes we need information about properties of the diffuse atomic and diffuse molecular gas clouds. The 158-micron CII line is an important tracer of diffuse regions, and C+ is a major ISM coolant, the Galaxy's strongest emission line virtually unobscured by dust, with a total luminosity about a 1000 times that of CO J=1-0. The GOT C+ program will obtain high spectral resolution CII spectra using the Heterodyne Instrument for the Far Infrared (HIFI) receiver. It will employ deep integrations, wide velocity coverage (350 km/s) with 0.22 km/s resolution, and systematic sparse sampling of the Galactic disk together with observations of selected targets, of over 900 lines of sight. It will be a resource to determine the properties of the atomic gas, in the (a) overall Galactic disk, (b) central 300pc of the Galactic center, (c) Galactic warp, (d) high latitude HI clouds, and (e) Photon Dominated Regions (PDRs). These spectra will provide the astronomical community with a rich statistical database of diffuse cloud properties, especially those of the atomic gas, sampled throughout the Galaxy for understanding the role of barometric pressure and turbulence in cloud evolution in the Galactic ISM and, by extension, other galaxies. The GOT C+ project will provide a template for future even larger-scale Galactic C+ surveys. This research was conducted at the Jet Propulsion Laboratory and is supported by a NASA grant.

New detections of embedded clusters in the Galactic halo

NASA Astrophysics Data System (ADS)

Camargo, D.; Bica, E.; Bonatto, C.

2016-09-01

Context. Until recently it was thought that high Galactic latitude clouds were a non-star-forming ensemble. However, in a previous study we reported the discovery of two embedded clusters (ECs) far away from the Galactic plane (~ 5 kpc). In our recent star cluster catalogue we provided additional high and intermediate latitude cluster candidates. Aims: This work aims to clarify whether our previous detection of star clusters far away from the disc represents just an episodic event or whether star cluster formation is currently a systematic phenomenon in the Galactic halo. We analyse the nature of four clusters found in our recent catalogue and report the discovery of three new ECs each with an unusually high latitude and distance from the Galactic disc midplane. Methods: The analysis is based on 2MASS and WISE colour-magnitude diagrams (CMDs), and stellar radial density profiles (RDPs). The CMDs are built by applying a field-star decontamination procedure, which uncovers the cluster's intrinsic CMD morphology. Results: All of these clusters are younger than 5 Myr. The high-latitude ECs C 932, C 934, and C 939 appear to be related to a cloud complex about 5 kpc below the Galactic disc, under the Local arm. The other clusters are above the disc, C 1074 and C 1100 with a vertical distance of ~3 kpc, C 1099 with ~ 2 kpc, and C 1101 with ~1.8 kpc. Conclusions: According to the derived parameters ECs located below and above the disc occur, which gives evidence of widespread star cluster formation throughout the Galactic halo. This study therefore represents a paradigm shift, by demonstrating that a sterile halo must now be understood as a host for ongoing star formation. The origin and fate of these ECs remain open. There are two possibilities for their origin, Galactic fountains or infall. The discovery of ECs far from the disc suggests that the Galactic halo is more actively forming stars than previously thought. Furthermore, since most ECs do not survive the infant mortality, stars may be raining from the halo into the disc, and/or the halo may be harbouring generations of stars formed in clusters like those detected in our survey.

Yellow evolved stars in open clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sowell, J.R.

1987-05-01

This paper describes a program in which Galactic cluster post-AGB candidates were first identified and then analyzed for cluster membership via radial velocities, monitored for possible photometric variations, examined for evidence of mass loss, and classified as completely as possible in terms of their basic stellar parameters. The intrinsically brightest supergiants are found in the youngest clusters. With increasing cluster age, the absolute luminosities attained by the supergiants decline. It appears that the evolutionary tracks of luminosity class II stars are more similar to those of class I than of class III. Only two superluminous giant star candidates are foundmore » in open clusters. 154 references.« less

Optimized shielding for space radiation protection

NASA Technical Reports Server (NTRS)

Wilson, J. W.; Cucinotta, F. A.; Kim, M. H.; Schimmerling, W.

2001-01-01

Future deep space mission and International Space Station exposures will be dominated by the high-charge and -energy (HZE) ions of the Galactic Cosmic Rays (GCR). A few mammalian systems have been extensively tested over a broad range of ion types and energies. For example, C3H10T1/2 cells, V79 cells, and Harderian gland tumors have been described by various track-structure dependent response models. The attenuation of GCR induced biological effects depends strongly on the biological endpoint, response model used, and material composition. Optimization of space shielding is then driven by the nature of the response model and the transmission characteristics of the given material.

Optimized Shielding for Space Radiation Protection

NASA Technical Reports Server (NTRS)

Wilson, J. W.; Cucinotta, F. A.; Kim, M.-H. Y.; Schimmerling, W.

2000-01-01

Abstract. Future deep space mission and International Space Station exposures will be dominated by the high-charge and -energy (HZE) ions of the Galactic Cosmic Rays (GCR). A few mammalian systems have been extensively tested over a broad range of ion types and energies. For example, C3H10T1/2 cells, V79 cells, and Harderian gland tumors have been described by various track-structure dependent response models. The attenuation of GCR induced biological effects depends strongly on the biological endpoint, response model used, and material composition. Optimization of space shielding is then driven by the nature of the response model and the transmission characteristics of the given material.

Readout technologies for directional WIMP Dark Matter detection

NASA Astrophysics Data System (ADS)

Battat, J. B. R.; Irastorza, I. G.; Aleksandrov, A.; Asada, T.; Baracchini, E.; Billard, J.; Bosson, G.; Bourrion, O.; Bouvier, J.; Buonaura, A.; Burdge, K.; Cebrián, S.; Colas, P.; Consiglio, L.; Dafni, T.; D'Ambrosio, N.; Deaconu, C.; De Lellis, G.; Descombes, T.; Di Crescenzo, A.; Di Marco, N.; Druitt, G.; Eggleston, R.; Ferrer-Ribas, E.; Fusayasu, T.; Galán, J.; Galati, G.; García, J. A.; Garza, J. G.; Gentile, V.; Garcia-Sciveres, M.; Giomataris, Y.; Guerrero, N.; Guillaudin, O.; Guler, A. M.; Harton, J.; Hashimoto, T.; Hedges, M. T.; Iguaz, F. J.; Ikeda, T.; Jaegle, I.; Kadyk, J. A.; Katsuragawa, T.; Komura, S.; Kubo, H.; Kuge, K.; Lamblin, J.; Lauria, A.; Lee, E. R.; Lewis, P.; Leyton, M.; Loomba, D.; Lopez, J. P.; Luzón, G.; Mayet, F.; Mirallas, H.; Miuchi, K.; Mizumoto, T.; Mizumura, Y.; Monacelli, P.; Monroe, J.; Montesi, M. C.; Naka, T.; Nakamura, K.; Nishimura, H.; Ochi, A.; Papevangelou, T.; Parker, J. D.; Phan, N. S.; Pupilli, F.; Richer, J. P.; Riffard, Q.; Rosa, G.; Santos, D.; Sawano, T.; Sekiya, H.; Seong, I. S.; Snowden-Ifft, D. P.; Spooner, N. J. C.; Sugiyama, A.; Taishaku, R.; Takada, A.; Takeda, A.; Tanaka, M.; Tanimori, T.; Thorpe, T. N.; Tioukov, V.; Tomita, H.; Umemoto, A.; Vahsen, S. E.; Yamaguchi, Y.; Yoshimoto, M.; Zayas, E.

2016-11-01

The measurement of the direction of WIMP-induced nuclear recoils is a compelling but technologically challenging strategy to provide an unambiguous signature of the detection of Galactic dark matter. Most directional detectors aim to reconstruct the dark-matter-induced nuclear recoil tracks, either in gas or solid targets. The main challenge with directional detection is the need for high spatial resolution over large volumes, which puts strong requirements on the readout technologies. In this paper we review the various detector readout technologies used by directional detectors. In particular, we summarize the challenges, advantages and drawbacks of each approach, and discuss future prospects for these technologies.

High mass star formation in the galaxy

NASA Technical Reports Server (NTRS)

Scoville, N. Z.; Good, J. C.

1987-01-01

The Galactic distributions of HI, H2, and HII regions are reviewed in order to elucidate the high mass star formation occurring in galactic spiral arms and in active galactic nuclei. Comparison of the large scale distributions of H2 gas and radio HII regions reveals that the rate of formation of OB stars depends on (n sub H2) sup 1.9 where (n sub H2) is the local mean density of H2 averaged over 300 pc scale lengths. In addition the efficiency of high mass star formation is a decreasing function of cloud mass in the range 200,000 to 3,000,000 solar mass. These results suggest that high mass star formation in the galactic disk is initiated by cloud-cloud collisions which are more frequent in the spiral arms due to orbit crowding. Cloud-cloud collisions may also be responsible for high rates of OB star formation in interacting galaxies and galactic nuclei. Based on analysis of the Infrared Astronomy Satellite (IRAS) and CO data for selected GMCs in the Galaxy, the ratio L sub IR/M sub H2 can be as high as 30 solar luminosity/solar mass for GMCs associated with HII regions. The L sub IR/M sub H2 ratios and dust temperature obtained in many of the high luminosity IRAS galaxies are similar to those encountered in galactic GMCs with OB star formation. High mass star formation is therefore a viable explanation for the high infrared luminosity of these galaxies.

HST/COS OBSERVATIONS OF GALACTIC HIGH-VELOCITY CLOUDS: FOUR ACTIVE GALACTIC NUCLEUS SIGHT LINES THROUGH COMPLEX C

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shull, J. Michael; Stevans, Matthew; Danforth, Charles

2011-10-01

We report ultraviolet spectra of Galactic high-velocity clouds (HVCs) in Complex C, taken by the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST), together with new 21 cm spectra from the Green Bank Telescope. The wide spectral coverage and higher signal-to-noise ratio, compared to previous HST spectra, provide better velocity definition of the HVC absorption, additional ionization species (including high ions), and improved abundances in this halo gas. Complex C has a metallicity of 10%-30% solar and a wide range of ions, suggesting dynamical and thermal interactions with hot gas in the Galactic halo. Spectra in the COSmore » medium-resolution G130M (1133-1468 A) and G160M (1383-1796 A) gratings detect ultraviolet absorption lines from eight elements in low-ionization states (O I, N I, C II, S II, Si II, Al II, Fe II, P II) and three elements in intermediate- and high-ionization states (Si III, Si IV, C IV, N V). Our four active galactic nucleus sight lines toward Mrk 817, Mrk 290, Mrk 876, and PG 1259+593 have high-velocity H I and O VI column densities, log N{sub Hi}= 19.39-20.05 and log N{sub Ovi}= 13.58-14.10, with substantial amounts of kinematically associated photoionized gas. The high-ion abundance ratios are consistent with cooling interfaces between photoionized and collisionally ionized gas: N(C IV)/N(O VI) {approx} 0.3-0.5, N(Si IV)/N(O VI) {approx} 0.05-0.11, N(N V)/N(O VI) {approx} 0.07-0.13, and N(Si IV)/N(Si III) {approx}0.2.« less

High-Energy Radiation from a Model of Quasars, Active Galactic Nuclei, and the Galactic Center with Magnetic Monopoles

NASA Astrophysics Data System (ADS)

Peng, Qiu-he; Chou, Chih-kang

2001-04-01

The fact that magnetic monopoles may catalyze nucleon decay (the Rubakov-Callan [RC] effect) as predicated by the grand unified theory of particle physics is invoked as the energy source of quasars and active galactic nuclei. Recent study of this model revealed that the radius of the supermassive object (SMO) located at the Galactic center is much larger than its Schwarzschild radius. We propose that this SMOs could be the source of high-energy gamma-ray radiation, although the emitted radiation may be mainly concentrated in the infrared. The surface temperature of the SMO at the Galactic center is taken as 121 K, inferred from the observed maximum of the flux spectrum of Sgr A* at the near infrared (1×1013 Hz); the radius of the SMO is about 8.1×1015 cm or 1.1×104RS (RS is the Schwarzschild radius). The mass of the SMO is derived from the observed total luminosity of Sgr A* (1×1037 ergs s-1) as 2.5×106 Msolar. Strong gamma-ray radiation with energy higher than 0.5 MeV may be emitted from the SMO. The flux of positrons emitted from the SMO is estimated to be 6.5×1042e+ s-1. The content parameter of magnetic monopoles ξ≡[(Nm/NB)/1.9×10- 25](<σβ>/10-27) also may be deduced from observations to be 230. Taking the cross section of the RC effect as 1×10-27 cm2, the strength of the radial magnetic field at the surface of the SMO is estimated to be 20-100 G. Our model also can predict the production of extreme ultra-high-energy cosmic rays.

Chandra Deep X-ray Observation of a Typical Galactic Plane Region and Near-Infrared Identification

NASA Technical Reports Server (NTRS)

Ebisawa, K.; Tsujimoto, M.; Paizis, A.; Hamaguichi, K.; Bamba, A.; Cutri, R.; Kaneda, H.; Maeda, Y.; Sato, G.; Senda, A.

2004-01-01

Using the Chandra Advanced CCD Imaging Spectrometer Imaging array (ACIS-I), we have carried out a deep hard X-ray observation of the Galactic plane region at (l,b) approx. (28.5 deg,0.0 deg), where no discrete X-ray source has been reported previously. We have detected 274 new point X-ray sources (4 sigma confidence) as well as strong Galactic diffuse emission within two partidly overlapping ACIS-I fields (approx. 250 sq arcmin in total). The point source sensitivity was approx. 3 x 10(exp -15)ergs/s/sq cm in the hard X-ray band (2-10 keV and approx. 2 x 10(exp -16) ergs/s/sq cm in the soft band (0.5-2 keV). Sum of all the detected point source fluxes account for only approx. 10 % of the total X-ray fluxes in the field of view. In order to explain the total X-ray fluxes by a superposition of fainter point sources, an extremely rapid increase of the source population is required below our sensitivity limit, which is hardly reconciled with any source distribution in the Galactic plane. Therefore, we conclude that X-ray emission from the Galactic plane has truly diffuse origin. Only 26 point sources were detected both in the soft and hard bands, indicating that there are two distinct classes of the X-ray sources distinguished by the spectral hardness ratio. Surface number density of the hard sources is only slightly higher than observed at the high Galactic latitude regions, strongly suggesting that majority of the hard X-ray sources are active galaxies seen through the Galactic plane. Following the Chandra observation, we have performed a near-infrared (NIR) survey with SOFI at ESO/NTT to identify these new X-ray sources. Since the Galactic plane is opaque in NIR, we did not see the background extragalactic sources in NIR. In fact, only 22 % of the hard sources had NIR counterparts which are most likely to be Galactic origin. Composite X-ray energy spectrum of those hard X-ray sources having NIR counterparts exhibits a narrow approx. 6.7 keV iron emission line, which is a signature of Galactic quiescent cataclysmic variables (CVs).

Cutting-Edge Science from Arecibo Observatory: Introduction

NASA Astrophysics Data System (ADS)

Schmelz, Joan T.

2017-01-01

The Arecibo Observatory is home to the largest radio telescope in the world operating above 2 GHz, where molecule emission pertaining to the origins of life proliferate. It also houses the most powerful radar system on the planet, providing crucial information for the assessment of impact hazards of near-Earth asteroids (NEA). It was built to study the ionosphere with a radar system that can also monitor the effects of Space Weather and climate change. Arecibo has a proven track record for doing excellent science, even after 50 years of operations. This talk will include brief summaries of several Arecibo astronomy topics including the (1) latest attempts to resolve the Pleiades distance controversy, which include VLBI and Gaia; (2) galactic and extragalactic molecules; and (3) Arecibo 3D orbit determinations of potentially hazardous asteroids, and the crucial observation required to select Bennu as the target for the recently launched NASA OSIRIS-REx mission. This introduction will set the stage for the invited talks in this session, which include such topics as Fast Radio Bursts, galactic and extragalactic HI results, the pulsar emission problem, and NANOGrav. This work is supported by NSF and NASA.

Active galactic nucleus outflows in galaxy discs

NASA Astrophysics Data System (ADS)

Hartwig, Tilman; Volonteri, Marta; Dashyan, Gohar

2018-05-01

Galactic outflows, driven by active galactic nuclei (AGNs), play a crucial role in galaxy formation and in the self-regulated growth of supermassive black holes (BHs). AGN feedback couples to and affects gas, rather than stars, and in many, if not most, gas-rich galaxies cold gas is rotationally supported and settles in a disc. We present a 2D analytical model for AGN-driven outflows in a gaseous disc and demonstrate the main improvements, compared to existing 1D solutions. We find significant differences for the outflow dynamics and wind efficiency. The outflow is energy-driven due to inefficient cooling up to a certain AGN luminosity (˜1043 erg s-1 in our fiducial model), above which the outflow remains momentum-driven in the disc up to galactic scales. We reproduce results of 3D simulations that gas is preferentially ejected perpendicular to the disc and find that the fraction of ejected interstellar medium is lower than in 1D models. The recovery time of gas in the disc, defined as the free-fall time from the radius to which the AGN pushes the ISM at most, is remarkably short, of the order 1 Myr. This indicates that AGN-driven winds cannot suppress BH growth for long. Without the inclusion of supernova feedback, we find a scaling of the BH mass with the halo velocity dispersion of MBH ∝ σ4.8.

The Effects of the Local Environment on Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Manzer, L. H.; De Robertis, M. M.

2014-06-01

There continues to be significant controversy regarding the mechanism(s) responsible for the initiation and maintenance of activity in galactic nuclei. In this paper we will investigate possible environmental triggers of nuclear activity through a statistical analysis of a large sample of galaxy groups. The focus of this paper is to identify active galactic nuclei (AGNs) and other emission-line galaxies in these groups and to compare their frequency with a sample of over 260,000 isolated galaxies from the same catalog. The galaxy groups are taken from the catalog of Yang et al., in which over 20,000 virialized groups of galaxies (2 <= N <= 20) with redshifts between 0.01 and 0.20 are from the Sloan Digital Sky Survey. We first investigate the completeness of our data set and find, though biases are a concern particularly at higher redshift, that our data provide a fair representation of the local universe. After correcting emission-line equivalent widths for extinction and underlying Balmer stellar absorption, we classify galaxies in the sample using traditional emission-line ratios, while incorporating measurement uncertainties. We find a significantly higher fraction of AGNs in groups compared with the isolated sample. Likewise, a significantly higher fraction of absorption-line galaxies are found in groups, while a higher fraction of star-forming galaxies prefer isolated environments. Within grouped environments, AGNs and star-forming galaxies are found more frequently in small- to medium-richness groups, while absorption-line galaxies prefer groups with larger richnesses. Groups containing only emission-line galaxies have smaller virial radii, velocity dispersions, and masses compared with those containing only absorption-line galaxies. Furthermore, the AGN fraction increases with decreasing distance to the group centroid, independent of galaxy morphology. Using properties obtained from Galaxy Zoo, there is an increased fraction of AGNs within merging systems, unlike star-forming galaxies. These results provide some indication that the local environment does play a role in initiating activity in galactic nuclei, but it is by no means simple or straightforward.

Observation of Galactic Sources of Very High Energy γ-RAYS with the Magic Telescope

NASA Astrophysics Data System (ADS)

Bartko, H.

The MAGIC telescope with its 17m diameter mirror is today the largest operating single-dish Imaging Air Cherenkov Telescope (IACT). It is located on the Canary Island La Palma, at an altitude of 2200 m above sea level, as part of the Roque de los Muchachos European Northern Observatory. The MAGIC telescope detects celestial very high energy γ-radiation in the energy band between about 50 GeV and 10 TeV. Since the autumn of 2004 MAGIC has been taking data routinely, observing various objects, like supernova remnants (SNRs), γ-ray binaries, Pulsars, Active Galactic Nuclei (AGN) and Gamma-ray Bursts (GRB). We briefly describe the observational strategy, the procedure implemented for the data analysis, and discuss the results of observations of Galactic Sources.

VizieR Online Data Catalog: Stellar activity and kinematics of FGK stars (Murgas+, 2013)

NASA Astrophysics Data System (ADS)

Murgas, F.; Jenkins, J. S.; Rojo, P.; Jones, H. R. A.; Pinfield, D. J.

2013-02-01

We present a compilation of stellar activity catalogs combined with galactic velocity information of 2529 F, G, and K stars. The stellar activity catalogs use in this work are: Jenkins et al. 2011 (Cat. J/A+A/531/A8); Gray et al. 2003 (Cat. J/AJ/126/2048), 2006 (Cat. J/AJ/132/161); Henry et al 1996 (Cat. J/A+A/111/439); Wright et al. 2004 (Cat. J/ApJS/152/261); Duncan et al. (1991ApJS...76..383D, Cat. III/159). The galactic velocities are taken from the Jenkins et al. 2011 (Cat. J/A+A/531/A8) and the Geneva-Copenhaguen Survey (GCS) Nordstrom et al. (2004A&A...418..989N, Cat. V/117). (1 data file).

The Fermi LAT Very Important Project (VIP) List of Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Thompson, David J.; Fermi Large Area Telescope Collaboration

2018-01-01

Using nine years of Fermi Gamma-ray Space Telescope Large Area Telescope (LAT) observations, we have identified 30 projects for Active Galactic Nuclei (AGN) that appear to provide strong prospects for significant scientific advances. This Very Important Project (VIP) AGN list includes AGNs that have good multiwavelength coverage, are regularly detected by the Fermi LAT, and offer scientifically interesting timing or spectral properties. Each project has one or more LAT scientists identified who are actively monitoring the source. They will be regularly updating the LAT results for these VIP AGNs, working together with multiwavelength observers and theorists to maximize the scientific return during the coming years of the Fermi mission. See https://confluence.slac.stanford.edu/display/GLAMCOG/VIP+List+of+AGNs+for+Continued+Study

Universal energy spectrum from point sources

NASA Technical Reports Server (NTRS)

Tomozawa, Yukio

1992-01-01

The suggestion is made that the energy spectrum from point sources such as galactic black hole candidates (GBHC) and active galactic nuclei (AGN) is universal on the average, irrespective of the species of the emitted particles, photons, nucleons, or others. The similarity between the observed energy spectra of cosmic rays, gamma-rays, and X-rays is discussed. In other words, the existing data for gamma-rays and X-rays seem to support the prediction. The expected data from the Gamma Ray Observatory are to provide a further test.

Chandra Catches "Piranha" Black Holes

NASA Astrophysics Data System (ADS)

2007-07-01

Supermassive black holes have been discovered to grow more rapidly in young galaxy clusters, according to new results from NASA's Chandra X-ray Observatory. These "fast-track" supermassive black holes can have a big influence on the galaxies and clusters that they live in. Using Chandra, scientists surveyed a sample of clusters and counted the fraction of galaxies with rapidly growing supermassive black holes, known as active galactic nuclei (or AGN). The data show, for the first time, that younger, more distant galaxy clusters contained far more AGN than older, nearby ones. Galaxy clusters are some of the largest structures in the Universe, consisting of many individual galaxies, a few of which contain AGN. Earlier in the history of the universe, these galaxies contained a lot more gas for star formation and black hole growth than galaxies in clusters do today. This fuel allows the young cluster black holes to grow much more rapidly than their counterparts in nearby clusters. Illustration of Active Galactic Nucleus Illustration of Active Galactic Nucleus "The black holes in these early clusters are like piranha in a very well-fed aquarium," said Jason Eastman of Ohio State University (OSU) and first author of this study. "It's not that they beat out each other for food, rather there was so much that all of the piranha were able to really thrive and grow quickly." The team used Chandra to determine the fraction of AGN in four different galaxy clusters at large distances, when the Universe was about 58% of its current age. Then they compared this value to the fraction found in more nearby clusters, those about 82% of the Universe's current age. The result was the more distant clusters contained about 20 times more AGN than the less distant sample. AGN outside clusters are also more common when the Universe is younger, but only by factors of two or three over the same age span. "It's been predicted that there would be fast-track black holes in clusters, but we never had good evidence until now," said co-author Paul Martini, also of OSU. "This can help solve a couple of mysteries about galaxy clusters." One mystery is why there are so many blue, star-forming galaxies in young, distant clusters and fewer in nearby, older clusters. AGN are believed to expel or destroy cool gas in their host galaxy through powerful eruptions from the black hole. This may stifle star formation and the blue, massive stars will then gradually die off, leaving behind only the old, redder stars. This process takes about a billion years or more to take place, so a dearth of star-forming galaxies is only noticeable for older clusters. The process that sets the temperature of the hot gas in clusters when they form is also an open question. These new results suggest that even more AGN may have been present when most clusters were forming about ten billion years ago. Early heating of a cluster by large numbers of AGN can have a significant, long-lasting effect on the structure of a cluster by "puffing up" the gas. "In a few nearby clusters we've seen evidence for huge eruptions generated by supermassive black holes. But this is sedate compared to what might be going on in younger clusters," said Eastman. These results appeared in the July 20th issue of The Astrophysical Journal Letters. NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the agency's Science Mission Directorate. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass. Additional information and images are available at: Additional information and images are available at: http://chandra.harvard.edu and http://chandra.nasa.gov

Star-disc interaction in galactic nuclei: formation of a central stellar disc

NASA Astrophysics Data System (ADS)

Panamarev, Taras; Shukirgaliyev, Bekdaulet; Meiron, Yohai; Berczik, Peter; Just, Andreas; Spurzem, Rainer; Omarov, Chingis; Vilkoviskij, Emmanuil

2018-05-01

We perform high-resolution direct N-body simulations to study the effect of an accretion disc on stellar dynamics in an active galactic nucleus (AGN). We show that the interaction of the nuclear stellar cluster (NSC) with the gaseous accretion disc (AD) leads to formation of a stellar disc in the central part of the NSC. The accretion of stars from the stellar disc on to the super-massive black hole is balanced by the capture of stars from the NSC into the stellar disc, yielding a stationary density profile. We derive the migration time through the AD to be 3 per cent of the half-mass relaxation time of the NSC. The mass and size of the stellar disc are 0.7 per cent of the mass and 5 per cent of the influence radius of the super-massive black hole. An AD lifetime shorter than the migration time would result in a less massive nuclear stellar disc. The detection of such a stellar disc could point to past activity of the hosting galactic nucleus.

Exposure to galactic cosmic radiation and solar energetic particles.

PubMed

O'Sullivan, D

2007-01-01

Several investigations of the radiation field at aircraft altitudes have been undertaken during solar cycle 23 which occurred in the period 1993-2003. The radiation field is produced by the passage of galactic cosmic rays and their nuclear reaction products as well as solar energetic particles through the Earth's atmosphere. Galactic cosmic rays reach a maximum intensity when the sun is least active and are at minimum intensity during solar maximum period. During solar maximum an increased number of coronal mass ejections and solar flares produce high energy solar particles which can also penetrate down to aircraft altitudes. It is found that the very complicated field resulting from these processes varies with altitude, latitude and stage of solar cycle. By employing several active and passive detectors, the whole range of radiation types and energies were encompassed. In-flight data was obtained with the co-operation of many airlines and NASA. The EURADOS Aircraft Crew in-flight data base was used for comparison with the predictions of various computer codes. A brief outline of some recent studies of exposure to radiation in Earth orbit will conclude this contribution.

Formation and spatial distribution of hypervelocity stars in AGN outflows

NASA Astrophysics Data System (ADS)

Wang, Xiawei; Loeb, Abraham

2018-05-01

We study star formation within outflows driven by active galactic nuclei (AGN) as a new source of hypervelocity stars (HVSs). Recent observations revealed active star formation inside a galactic outflow at a rate of ∼ 15M⊙yr-1 . We verify that the shells swept up by an AGN outflow are capable of cooling and fragmentation into cold clumps embedded in a hot tenuous gas via thermal instabilities. We show that cold clumps of ∼ 103 M⊙ are formed within ∼ 105 yrs. As a result, stars are produced along outflow's path, endowed with the outflow speed at their formation site. These HVSs travel through the galactic halo and eventually escape into the intergalactic medium. The expected instantaneous rate of star formation inside the outflow is ∼ 4 - 5 orders of magnitude greater than the average rate associated with previously proposed mechanisms for producing HVSs, such as the Hills mechanism and three-body interaction between a star and a black hole binary. We predict the spatial distribution of HVSs formed in AGN outflows for future observational probe.

SPECTRAL ENERGY DISTRIBUTIONS OF TYPE 1 ACTIVE GALACTIC NUCLEI IN THE COSMOS SURVEY. I. THE XMM-COSMOS SAMPLE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elvis, M.; Hao, H.; Civano, F.

2012-11-01

The 'Cosmic Evolution Survey' (COSMOS) enables the study of the spectral energy distributions (SEDs) of active galactic nuclei (AGNs) because of the deep coverage and rich sampling of frequencies from X-ray to radio. Here we present an SED catalog of 413 X-ray (XMM-Newton)-selected type 1 (emission line FWHM > 2000 km s{sup -1}) AGNs with Magellan, SDSS, or VLT spectrum. The SEDs are corrected for Galactic extinction, broad emission line contributions, constrained variability, and host galaxy contribution. We present the mean SED and the dispersion SEDs after the above corrections in the rest-frame 1.4 GHz to 40 keV, and showmore » examples of the variety of SEDs encountered. In the near-infrared to optical (rest frame {approx}8 {mu}m-4000 A), the photometry is complete for the whole sample and the mean SED is derived from detections only. Reddening and host galaxy contamination could account for a large fraction of the observed SED variety. The SEDs are all available online.« less

X-ray light curves of active galactic nuclei are phase incoherent

NASA Technical Reports Server (NTRS)

Krolik, Julian; Done, Chris; Madejski, Grzegorz

1993-01-01

We compute the Fourier phase spectra for the light curves of five low-luminosity active galactic nuclei observed by EXOSAT. There is no statistically significant phase coherence in any of them. This statement is equivalent, subject to a technical caveat, to a demonstration that their fluctuation statistics are Gaussian. Models in which the X-ray output is controlled wholly by a unitary process undergoing a nonlinear limit cycle are therefore ruled out, while models with either a large number of randomly excited independent oscillation modes or nonlinearly interacting spatially dependent oscillations are favored. We also demonstrate how the degree of phase coherence in light curve fluctuations influences the application of causality bounds on internal length scales.

Evidence for Infrared-faint Radio Sources as z > 1 Radio-loud Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Huynh, Minh T.; Norris, Ray P.; Siana, Brian; Middelberg, Enno

2010-02-01

Infrared-Faint Radio Sources (IFRSs) are a class of radio objects found in the Australia Telescope Large Area Survey which have no observable mid-infrared counterpart in the Spitzer Wide-area Infrared Extragalactic (SWIRE) survey. The extended Chandra Deep Field South now has even deeper Spitzer imaging (3.6-70 μm) from a number of Legacy surveys. We report the detections of two IFRS sources in IRAC images. The non-detection of two other IFRSs allows us to constrain the source type. Detailed modeling of the spectral energy distribution of these objects shows that they are consistent with high-redshift (z >~ 1) active galactic nuclei.

EVIDENCE FOR INFRARED-FAINT RADIO SOURCES AS z > 1 RADIO-LOUD ACTIVE GALACTIC NUCLEI

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huynh, Minh T.; Norris, Ray P.; Siana, Brian

2010-02-10

Infrared-Faint Radio Sources (IFRSs) are a class of radio objects found in the Australia Telescope Large Area Survey which have no observable mid-infrared counterpart in the Spitzer Wide-area Infrared Extragalactic (SWIRE) survey. The extended Chandra Deep Field South now has even deeper Spitzer imaging (3.6-70 {mu}m) from a number of Legacy surveys. We report the detections of two IFRS sources in IRAC images. The non-detection of two other IFRSs allows us to constrain the source type. Detailed modeling of the spectral energy distribution of these objects shows that they are consistent with high-redshift (z {approx}> 1) active galactic nuclei.

An astrophysics data program investigation of a synoptic study of quasar continua

NASA Technical Reports Server (NTRS)

Elvis, Martin

1991-01-01

A summary of the program is presented. The major product of the program, an atlas of quasar energy distributions, is presented in the appendices along with papers written as a result of this research. The topics covered in the papers include: (1) accurate galactic N(sub h) values toward quasars and active galactic nuclei (AGN); (2) weak bump quasars; (3) millimeter measurements of hard x ray selected active galaxies- implications for the nature of the continuous spectrum; (3) persistence and change in the soft x ray spectrum of the quasar PG1211+143; (4) the soft x ray excess in einstein quasar spectra; and (5) EXOSAT x ray spectra of quasars.

Very high energy observations of the Galactic Centre: recent results and perspectives with CTA

NASA Astrophysics Data System (ADS)

Terrier, Regis

2016-07-01

The central 300 pc of our Galaxy are a major laboratory for high energy astrophysics. They harbor the closest supermassive black hole (SMBH) and are the site of a sustained star formation activity. The energy released by the supernovae on the ambient medium must be very strong. Similarly, albeit extremely faint nowadays, the SMBH must have experienced episodes of intense activity in the past which can influence significantly the central regions and beyond, e.g. powering the Fermi bubbles. I review observational results at very high energies from the central region and discuss their implications and the questions they leave open. I discuss the perspectives CTA offers for Galactic Centre astrophysics.

Bursts of star formation in computer simulations of dwarf galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Comins, N.F.

1984-09-01

A three-dimensional Stochastic Self-Propagating Star Formation (SSPSF) model of compact galacies is presented. Two phases of gas, active and inactive, are present, and permanent depletion of gas in the form of long lived, low mass stars and remnants occurs. Similarly, global infall of gas from a galactic halo or through galactic cannibalism is permitted. We base our parameters on the observed properties of the compact blue galaxy I Zw 36. Our results are that bursts of star formation occur much more frequently in these runs than continuous nonbursting star formation, suggesting that the blue compact galaxies are probably undergoing burstsmore » rather than continuous, nonbursting low-level star formation activity.« less

Relativistic particles and gamma-ray in quasars and active galactic nuclei

NASA Technical Reports Server (NTRS)

Protheroe, R. J.; Kazanas, D.

1982-01-01

A model for a class of quasars and active galactic nuclei is described in which a shock around a massive black hole randomizes the infall kinetic energy of spherically accreting matter producing a nonthermal spectrum of high energy protons. These protons may be responsible for the secondary production (via tau + or - decay) of the radio emitting high energy electrons and also of high energy gamma rays (via pi decay and inverse Compton interactions of the electrons). The correlation between radio and gamma ray emission implied by the model is in good agreement with observations of 3C273. Observation of the flux of high energy neutrinos from quasars may provide a test for the model.

Relativistic particles and gamma-rays in quasars and active galactic nuclei

NASA Technical Reports Server (NTRS)

Protheroe, R. J.; Kazanas, D.

1983-01-01

A model for a class of quasars and active galactic nuclei is described in which a shock around a massive black hole randomizes the infall kinetic energy of spherically accreting matter producing a nonthermal spectrum of high energy protons. These protons may be responsible for the secondary production (via tau + or - decay) of the radio emitting high energy electrons and also of high energy gamma rays (via Pi decay and inverse Compton interactions of the electrons). The correlation between radio and gamma ray emission implied by the model is in good agreement with observations of 3C273. Observation of the flux of high energy neutrinos from quasars may provide a test for the model.

Relativistic neutrons in active galactic nuclei

NASA Technical Reports Server (NTRS)

Sikora, Marek; Begelman, Mitchell C.; Rudak, Bronislaw

1989-01-01

The acceleration of protons to relativistic energies in active galactic nuclei leads to the creation of relativistic neutrons which escape from the central engine. The neutrons decay at distances of up to 1-100 pc, depositing their energies and momenta in situ. Energy deposition by decaying neutrons may inhibit spherical accretion and drive a wind, which could be responsible for the velocity fields in emission-line regions and the outflow of broad absorption line systems. Enhanced pressure in the neutron decay region may also help to confine emission line clouds. A fraction of the relativistic proton energy is radiated in gamma-rays with energies which may be as large as about 100,000 GeV.

Measurement of LET distribution and dose equivalent on board the space shuttle STS-65

NASA Technical Reports Server (NTRS)

Hayashi, T.; Doke, T.; Kikuchi, J.; Takeuchi, R.; Hasebe, N.; Ogura, K.; Nagaoka, S.; Kato, M.; Badhwar, G. D.

1996-01-01

Space radiation dosimetry measurements have been made on board the Space Shuttle STS-65 in the Second International Microgravity Laboratory (IML-2). In these measurements, three kinds of detectors were used; one is a newly developed active detector telescope called "Real-time Radiation Monitoring Device (RRMD)" utilizing silicon semi-conductor detectors and others are conventional detectors of thermoluminescence dosimeters (TLDs) and CR-39 plastic track detectors. Using the RRMD detector, the first attempt of real-time monitoring of space radiation has been achieved successfully for a continuous period of 251.3 h, giving the temporal variations of LET distribution, particle count rates, and rates of absorbed dose and dose equivalent. The RRMD results indicate that a clear enhancement of the number of trapped particles is seen at the South Atlantic Anomaly (SAA) without clear enhancement of dose equivalent, while some daily periodic enhancements of dose equivalent due to high LET particles are seen at the lower geomagnetic cutoff regions for galactic cosmic ray particles (GCRs). Therefore, the main contribution to dose equivalent is seen to be due to GCRs in this low altitude mission (300 km). Also, the dose equivalent rates obtained by TLDs and CR-39 ranged from 146.9 to 165.2 microSv/day and the average quality factors from 1.45 to 1.57 depending on the locations and directions of detectors inside the Space-lab at this highly protected orbit for space radiation with a small inclination (28.5 degrees) and a low altitude (300 km). The LET distributions obtained by two different detectors, RRMD and CR-39, are in good agreement in the region of 15-200 keV/mm and difference of these distributions in the regions of LET < 15 keV/mm and LET > 200 keV/mm can be explained by considering characteristics of CR-39 etched track formation especially for the low LET tracks.

Measurement of LET distribution and dose equivalent on board the space shuttle STS-65.

PubMed

Hayashi, T; Doke, T; Kikuchi, J; Takeuchi, R; Hasebe, N; Ogura, K; Nagaoka, S; Kato, M; Badhwar, G D

1996-11-01

Space radiation dosimetry measurements have been made on board the Space Shuttle STS-65 in the Second International Microgravity Laboratory (IML-2). In these measurements, three kinds of detectors were used; one is a newly developed active detector telescope called "Real-time Radiation Monitoring Device (RRMD)" utilizing silicon semi-conductor detectors and others are conventional detectors of thermoluminescence dosimeters (TLDs) and CR-39 plastic track detectors. Using the RRMD detector, the first attempt of real-time monitoring of space radiation has been achieved successfully for a continuous period of 251.3 h, giving the temporal variations of LET distribution, particle count rates, and rates of absorbed dose and dose equivalent. The RRMD results indicate that a clear enhancement of the number of trapped particles is seen at the South Atlantic Anomaly (SAA) without clear enhancement of dose equivalent, while some daily periodic enhancements of dose equivalent due to high LET particles are seen at the lower geomagnetic cutoff regions for galactic cosmic ray particles (GCRs). Therefore, the main contribution to dose equivalent is seen to be due to GCRs in this low altitude mission (300 km). Also, the dose equivalent rates obtained by TLDs and CR-39 ranged from 146.9 to 165.2 microSv/day and the average quality factors from 1.45 to 1.57 depending on the locations and directions of detectors inside the Space-lab at this highly protected orbit for space radiation with a small inclination (28.5 degrees) and a low altitude (300 km). The LET distributions obtained by two different detectors, RRMD and CR-39, are in good agreement in the region of 15-200 keV/mm and difference of these distributions in the regions of LET < 15 keV/mm and LET > 200 keV/mm can be explained by considering characteristics of CR-39 etched track formation especially for the low LET tracks.

Medipix in space on-board the ISS

PubMed Central

Pinsky, Lawrence S.; Idarraga-Munoz, J.; Kroupa, M.; Son, H.M.; Stoffle, N.N.; Semones, E.J.; Bahadori, A.A.; Turecek, D.; Pospíšil, S.; Jakubek, J.; Vykydal, Z.; Kitamura, H.; Uchihori, Y.

2014-01-01

On 16 October 2012, five active radiation detectors (referred to by NASA as Radiation Environment Monitors, or REMs) employing the Timepix version of the technology developed by the CERN-based Medipix2 Collaboration were deployed on-board the International Space Station (ISS) using simple USB interfaces to the existing ISS laptops for power, control and readout [ 1– 3]. These devices successfully demonstrated the capabilities of this technology by providing reliable dose and dose-equivalent information based on a track-by-track analysis. Figure 1 shows a sample comparison of the output from all five devices with respect to the on-board tissue equivalent proportional counter (TEPC) for both absorbed dose (top) and dose-equivalent (bottom) as defined in NCRP 142. The lower graph in each set is the TEPC. Several issues were identified and solutions to adjust for them have been included in the analysis. These include items such as the need to identify nuclear interactions in the silicon sensor layer, and to separate penetrating from stopping tracks. The wide effective range in fluence and particle type of this technology was also verified through the highest rates seen during the South Atlantic Anomaly passes and the heavy ions nominally seen in the Galactic Cosmic Rays. Corrections for detector response saturation effects were also successfully implemented as verified by reference to ground-based accelerator data taken at the Heavy-Ion Medical Accelerator Center (HIMAC) facility at the National Institute for Radiological Sciences in Japan, and at the NASA Space Radiation Laboratory (NSRL) at the Brookhaven National Laboratory in New York. Flight hardware has been produced that will be flown on the first launch of the new Orion spacecraft, and flight hardware development is ongoing to accommodate the next generation of this technology as a baseline for radiation monitoring and dosimetry on future operational manned missions. Fig 1.Five ISS REM units compared with ISS IVTEPC in absorbed dose (a) and dose-equivalent (b).

Observing the Next Galactic Supernova with the NOvA Detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vasel, Justin A.; Sheshukov, Andrey; Habig, Alec

The next galactic core-collapse supernova will deliver a wealth of neutrinos which for the first time we are well-situated to measure. These explosions produce neutrinos with energies between 10 and 100 MeV over a period of tens of seconds. Galactic supernovae are relatively rare events, occurring with a frequency of just a few per century. It is therefore essential that all neutrino detectors capable of detecting these neutrinos are ready to trigger on this signal when it occurs. This poster describes a data-driven trigger which is designed to detect the neutrino signal from a galactic core-collapse supernova with the NOvAmore » detectors. The trigger analyzes 5ms blocks of detector activity and applies background rejection algorithms to detect the signal time structure over the background. This background reduction is an essential part of the process, as the NOvA detectors are designed to detect neutrinos from Fermilab's NuMI beam which have an average energy of 2GeV--well above the average energy of supernova neutrinos.« less

EX56a study of extended X-ray emission around isolated galaxies EX56b identification and spectra of bright X-ray sources at high galactic latitude

NASA Technical Reports Server (NTRS)

Schwartz, Daniel A.

1987-01-01

The EXOSAT observations confirmed the identification and extended nature of PKS 2345-35. It gave a good 2 to 10 keV X-ray spectrum and a detailed spatial profile indicating asymmetry of the structure. In the high galactic latitidue investigation, the BL Lac object identified with the HEAO-1 source 1430+423 was detected, and the first X-ray spectrum was obtained. Several simulataneous observations of H0323+022 were obtained over a broad range of electromagnetic spectrum. Studies of luminous active galactic nuclei have given significant information on the spectrum of the quasar PKS 0558-504. In a study of Southern sky cataclysmic variables, the EXOSAT was used to determine the X-ray spectrum and search for periodicities in two objects. Studies of complete identifications have revealed that X-ray sources in two high galactic latitude fields are stars, and therefore are to be excluded from the Piccinotti extragalactic sample. Only one Piccinotti source remains to be identified.

Implications of Fermi-LAT observations on the origin of IceCube neutrinos

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Bin; Li, Zhuo; Zhao, Xiaohong, E-mail: wang_b@pku.edu.cn, E-mail: zhaoxh@ynao.ac.cn, E-mail: zhuo.li@pku.edu.cn

2014-11-01

The IceCube (IC) collaboration recently reported the detection of TeV-PeV extraterrestrial neutrinos whose origin is yet unknown. By the photon-neutrino connection in pp and pγ interactions, we use the Fermi-LAT observations to constrain the origin of the IC detected neutrinos. We find that Galactic origins, i.e., the diffuse Galactic neutrinos due to cosmic ray (CR) propagation in the Milky Way, and the neutrinos from the Galactic point sources, may not produce the IC neutrino flux, thus these neutrinos should be of extragalactic origin. Moreover, the extragalactic gamma-ray bursts (GRBs) may not account for the IC neutrino flux, the jets ofmore » active galactic nuclei may not produce the IC neutrino spectrum, but the starburst galaxies (SBGs) may be promising sources. As suggested by the consistency between the IC detected neutrino flux and the Waxman-Bahcall bound, GRBs in SBGs may be the sources of both the ultrahigh energy, ∼> 10{sup 19}eV, CRs and the 1–100 PeV CRs that produce the IC detected TeV-PeV neutrinos.« less

Revealing two radio-active galactic nuclei extremely near PSR J0437-4715

NASA Astrophysics Data System (ADS)

Li, Zhixuan; Yang, Jun; An, Tao; Paragi, Zsolt; Deller, Adam; Reynolds, Cormac; Hong, Xiaoyu; Wang, Jiancheng; Ding, Hao; Xia, Bo; Yan, Zhen; Guo, Li

2018-05-01

Newton's gravitational constant G may vary with time at an extremely low level. The time variability of G will affect the orbital motion of a millisecond pulsar in a binary system and cause a tiny difference between the orbital period-dependent measurement of the kinematic distance and the direct measurement of the annual parallax distance. PSR J0437-4715 is the nearest millisecond pulsar and the brightest at radio wavelengths. To explore the feasibility of achieving a parallax distance accuracy of one light-year, comparable to the recent timing result, with the technique of differential astrometry, we searched for compact radio sources quite close to PSR J0437-4715. Using existing data from the Very Large Array and the Australia Telescope Compact Array, we detected two sources with flat spectra, relatively stable flux densities of 0.9 and 1.0 mJy at 8.4 GHz and separations of 13 and 45 arcsec. With a network consisting of the Long Baseline Array and the Kunming 40-m radio telescope, we found that both sources have a point-like structure and a brightness temperature of ≥107 K. According to these radio inputs and the absence of counterparts in other bands, we argue that they are most likely the compact radio cores of extragalactic active galactic nuclei, rather than Galactic radio stars. The finding of these two radio active galactic nuclei will enable us to achieve a sub-pc distance accuracy with in-beam phase-referencing very-long-baseline interferometric observations and provide one of the most stringent constraints on the time variability of G in the near future.

Rapid X-Ray Variability of Active Galaxies. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Tennant, A. F., Jr.

1983-01-01

Active galactic nuclei are luminous sources of X-rays. The thesis that the X-rays are generated within 10 gravitational radii from the central object is tested. A very sensitive search for rapid ( 1 day) X-ray variability from active galaxies was made.

V474 Car: A RARE HALO RS CVn BINARY IN RETROGRADE GALACTIC ORBIT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bubar, Eric J.; Mamajek, Eric E.; Jensen, Eric L. N.

We report the discovery that the star V474 Car is an extremely active, high velocity halo RS CVn system. The star was originally identified as a possible pre-main-sequence star in Carina, given its enhanced stellar activity, rapid rotation (10.3 days), enhanced Li, and absolute magnitude which places it above the main sequence (MS). However, its extreme radial velocity (264 km s{sup -1}) suggested that this system was unlike any previously known pre-MS system. Our detailed spectroscopic analysis of echelle spectra taken with the CTIO 4 m finds that V474 Car is both a spectroscopic binary with an orbital period similarmore » to the photometric rotation period and metal-poor ([Fe/H] {approx_equal}-0.99). The star's Galactic orbit is extremely eccentric (e {approx_equal} 0.93) with a perigalacticon of only {approx}0.3 kpc of the Galactic center-and the eccentricity and smallness of its perigalacticon are surpassed by only {approx}0.05% of local F/G-type field stars. The observed characteristics are consistent with V474 Car being a high-velocity, metal-poor, tidally locked, chromospherically active binary, i.e., a halo RS CVn binary, and one of only a few such specimens known.« less

EUCLIA—Exploring the UV/Optical Continuum Lag in Active Galactic Nuclei. I. A Model without Light Echoing

NASA Astrophysics Data System (ADS)

Cai, Zhen-Yi; Wang, Jun-Xian; Zhu, Fei-Fan; Sun, Mou-Yuan; Gu, Wei-Min; Cao, Xin-Wu; Yuan, Feng

2018-03-01

The tight interband correlation and the lag–wavelength relation among UV/optical continua of active galactic nuclei have been firmly established. They are usually understood within the widespread reprocessing scenario; however, the implied interband lags are generally too small. Furthermore, it is challenged by new evidence, such as that the X-ray reprocessing yields too much high-frequency UV/optical variation and that it fails to reproduce the observed timescale-dependent color variations among the Swift light curves of NGC 5548. In a different manner, we demonstrate that an upgraded inhomogeneous accretion disk model, whose local independent temperature fluctuations are subject to a speculated common large-scale temperature fluctuation, can intrinsically generate the tight interband correlation and lag across the UV/optical and be in nice agreement with several observational properties of NGC 5548, including the timescale-dependent color variation. The emergent lag is a result of the differential regression capability of local temperature fluctuations when responding to the large-scale fluctuation. An average speed of propagations as large as ≳15% of the speed of light may be required by this common fluctuation. Several potential physical mechanisms for such propagations are discussed. Our interesting phenomenological scenario may shed new light on comprehending the UV/optical continuum variations of active galactic nuclei.

Paired and interacting galaxies: Conference summary

NASA Technical Reports Server (NTRS)

Norman, Colin A.

1990-01-01

The author gives a summary of the conference proceedings. The conference began with the presentation of the basic data sets on pairs, groups, and interacting galaxies with the latter being further discussed with respect to both global properties and properties of the galactic nuclei. Then followed the theory, modelling and interpretation using analytic techniques, simulations and general modelling for spirals and ellipticals, starbursts and active galactic nuclei. Before the conference the author wrote down the three questions concerning pairs, groups and interacting galaxies that he hoped would be answered at the meeting: (1) How do they form, including the role of initial conditions, the importance of subclustering, the evolution of groups to compact groups, and the fate of compact groups; (2) How do they evolve, including issues such as relevant timescales, the role of halos and the problem of overmerging, the triggering and enhancement of star formation and activity in the galactic nuclei, and the relative importance of dwarf versus giant encounters; and (3) Are they important, including the frequency of pairs and interactions, whether merging and interactions are very important aspects of the life of a normal galaxy at formation, during its evolution, in forming bars, shells, rings, bulges, etc., and in the formation and evolution of active galaxies? Where possible he focuses on these three central issues in the summary.

MID-INFRARED SELECTION OF ACTIVE GALACTIC NUCLEI WITH THE WIDE-FIELD INFRARED SURVEY EXPLORER. I. CHARACTERIZING WISE-SELECTED ACTIVE GALACTIC NUCLEI IN COSMOS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stern, Daniel; Assef, Roberto J.; Eisenhardt, Peter

2012-07-01

The Wide-field Infrared Survey Explorer (WISE) is an extremely capable and efficient black hole finder. We present a simple mid-infrared color criterion, W1 - W2 {>=} 0.8 (i.e., [3.4]-[4.6] {>=}0.8, Vega), which identifies 61.9 {+-} 5.4 active galactic nucleus (AGN) candidates per deg{sup 2} to a depth of W2 {approx} 15.0. This implies a much larger census of luminous AGNs than found by typical wide-area surveys, attributable to the fact that mid-infrared selection identifies both unobscured (type 1) and obscured (type 2) AGNs. Optical and soft X-ray surveys alone are highly biased toward only unobscured AGNs, while this simple WISEmore » selection likely identifies even heavily obscured, Compton-thick AGNs. Using deep, public data in the COSMOS field, we explore the properties of WISE-selected AGN candidates. At the mid-infrared depth considered, 160 {mu}Jy at 4.6 {mu}m, this simple criterion identifies 78% of Spitzer mid-infrared AGN candidates according to the criteria of Stern et al. and the reliability is 95%. We explore the demographics, multiwavelength properties and redshift distribution of WISE-selected AGN candidates in the COSMOS field.« less

Time-integrated directional detection of dark matter

NASA Astrophysics Data System (ADS)

O'Hare, Ciaran A. J.; Kavanagh, Bradley J.; Green, Anne M.

2017-10-01

The analysis of signals in directional dark matter (DM) detectors typically assumes that the directions of nuclear recoils can be measured in the Galactic rest frame. However, this is not possible with all directional detection technologies. In nuclear emulsions, for example, the recoil events must be detected and measured after the exposure time of the experiment. Unless the entire detector is mounted and rotated with the sidereal day, the recoils cannot be reoriented in the Galactic rest frame. We examine the effect of this "time integration" on the primary goals of directional detection, namely: (1) confirming that the recoils are anisotropic; (2) measuring the median recoil direction to confirm their Galactic origin; and (3) probing below the neutrino floor. We show that after time integration the DM recoil distribution retains a preferred direction and is distinct from that of Solar neutrino-induced recoils. Many of the advantages of directional detection are therefore preserved and it is not crucial to mount and rotate the detector. Rejecting isotropic backgrounds requires a factor of 2 more signal events compared with an experiment with event time information, whereas a factor of 1.5-3 more events are needed to measure a median direction in agreement with the expectation for DM. We also find that there is still effectively no neutrino floor in a time-integrated directional experiment. However to reach a cross section an order of magnitude below the floor, a factor of ˜8 larger exposure is required than with a conventional directional experiment. We also examine how the sensitivity is affected for detectors with only 2D recoil track readout, and/or no head-tail measurement. As for non-time-integrated experiments, 2D readout is not a major disadvantage, though a lack of head-tail sensitivity is.

First detection of the white dwarf cooling sequence of the galactic bulge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Calamida, A.; Sahu, K. C.; Anderson, J.

2014-08-01

We present Hubble Space Telescope data of the low-reddening Sagittarius window in the Galactic bulge. The Sagittarius Window Eclipsing Extrasolar Planet Search field (∼3'× 3'), together with three more Advanced Camera for Surveys and eight Wide-Field Camera 3 fields, were observed in the F606W and F814W filters, approximately every two weeks for 2 yr, with the principal aim of detecting a hidden population of isolated black holes and neutron stars through astrometric microlensing. Proper motions were measured with an accuracy of ≈0.1 mas yr{sup –1} (≈4 km s{sup –1}) at F606W ≈ 25.5 mag, and better than ≈0.5 mas yr{supmore » –1} (≈20 km s{sup –1}) at F606W ≈ 28 mag, in both axes. Proper-motion measurements allowed us to separate disk and bulge stars and obtain a clean bulge color-magnitude diagram. We then identified for the first time a white dwarf (WD) cooling sequence in the Galactic bulge, together with a dozen candidate extreme horizontal branch stars. The comparison between theory and observations shows that a substantial fraction of the WDs (≈30%) are systematically redder than the cooling tracks for CO-core H-rich and He-rich envelope WDs. This evidence would suggest the presence of a significant number of low-mass WDs and WD-main-sequence binaries in the bulge. This hypothesis is further supported by the finding of two dwarf novae in outburst, two short-period (P ≲ 1 day) ellipsoidal variables, and a few candidate cataclysmic variables in the same field.« less

First results from the IllustrisTNG simulations: a tale of two elements - chemical evolution of magnesium and europium

NASA Astrophysics Data System (ADS)

Naiman, Jill P.; Pillepich, Annalisa; Springel, Volker; Ramirez-Ruiz, Enrico; Torrey, Paul; Vogelsberger, Mark; Pakmor, Rüdiger; Nelson, Dylan; Marinacci, Federico; Hernquist, Lars; Weinberger, Rainer; Genel, Shy

2018-06-01

The distribution of elements in galaxies provides a wealth of information about their production sites and their subsequent mixing into the interstellar medium. Here we investigate the elemental distributions of stars in the IllustrisTNG simulations. We analyse the abundance ratios of magnesium and europium in Milky Way-like galaxies from the TNG100 simulation (stellar masses log (M⋆/M⊙) ˜ 9.7-11.2). Comparison of observed magnesium and europium for individual stars in the Milky Way with the stellar abundances in our more than 850 Milky Way-like galaxies provides stringent constraints on our chemical evolutionary methods. Here, we use the magnesium-to-iron ratio as a proxy for the effects of our SNII (core-collapse supernovae) and SNIa (Type Ia supernovae) metal return prescription and as a comparison to a variety of galactic observations. The europium-to-iron ratio tracks the rare ejecta from neutron star-neutron star mergers, the assumed primary site of europium production in our models, and is a sensitive probe of the effects of metal diffusion within the gas in our simulations. We find that europium abundances in Milky Way-like galaxies show no correlation with assembly history, present-day galactic properties, and average galactic stellar population age. We reproduce the europium-to-iron spread at low metallicities observed in the Milky Way, and find it is sensitive to gas properties during redshifts z ≈ 2-4. We show that while the overall normalization of [Eu/Fe] is susceptible to resolution and post-processing assumptions, the relatively large spread of [Eu/Fe] at low [Fe/H] when compared to that at high [Fe/H] is quite robust.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fujita, Yutaka; Murase, Kohta; Kimura, Shigeo S., E-mail: fujita@vega.ess.sci.osaka-u.ac.jp, E-mail: murase@psu.edu, E-mail: szk323@psu.edu

Supernova remnants (SNRs) have commonly been considered as a source of the observed PeV cosmic rays (CRs) or a Galactic PeV particle accelerator ('Pevatron'). In this work, we study Sagittarius A* (Sgr A*), which is the low-luminosity active galactic nucleus of the Milky Way Galaxy, as another possible canditate of the Pevatron, because it sometimes became very active in the past. We assume that a large number of PeV CRs were injected by Sgr A* at the outburst about 10{sup 7} yr ago when the Fermi bubbles were created. We constrain the diffusion coefficient for the CRs in the Galacticmore » halo on the condition that the CRs have arrived on the Earth by now, while a fairly large fraction of them have escaped from the halo. Based on a diffusion-halo model, we solve a diffusion equation for the CRs and compare the results with the CR spectrum on the Earth. The observed small anisotropy of the arrival directions of CRs may be explained if the diffusion coefficient in the Galactic disk is smaller than that in the halo. Our model predicts that a boron-to-carbon ratio should be energy-independent around the knee, where the CRs from Sgr A* become dominant. It is unlikely that the spectrum of the CRs accelerated at the outburst is represented by a power-law similar to the one for those responsible for the gamma-ray emission from the central molecular zone (CMZ) around the Galactic center.« less

Hitomi observation of radio galaxy NGC 1275: The first X-ray microcalorimeter spectroscopy of Fe-Kα line emission from an active galactic nucleus

NASA Astrophysics Data System (ADS)

Hitomi Collaboration; Aharonian, Felix; Akamatsu, Hiroki; Akimoto, Fumie; Allen, Steven W.; Angelini, Lorella; Audard, Marc; Awaki, Hisamitsu; Axelsson, Magnus; Bamba, Aya; Bautz, Marshall W.; Blandford, Roger; Brenneman, Laura W.; Brown, Gregory V.; Bulbul, Esra; Cackett, Edward M.; Chernyakova, Maria; Chiao, Meng P.; Coppi, Paolo S.; Costantini, Elisa; de Plaa, Jelle; de Vries, Cor P.; den Herder, Jan-Willem; Done, Chris; Dotani, Tadayasu; Ebisawa, Ken; Eckart, Megan E.; Enoto, Teruaki; Ezoe, Yuichiro; Fabian, Andrew C.; Ferrigno, Carlo; Foster, Adam R.; Fujimoto, Ryuichi; Fukazawa, Yasushi; Furuzawa, Akihiro; Galeazzi, Massimiliano; Gallo, Luigi C.; Gandhi, Poshak; Giustini, Margherita; Goldwurm, Andrea; Gu, Liyi; Guainazzi, Matteo; Haba, Yoshito; Hagino, Kouichi; Hamaguchi, Kenji; Harrus, Ilana M.; Hatsukade, Isamu; Hayashi, Katsuhiro; Hayashi, Takayuki; Hayashida, Kiyoshi; Hiraga, Junko S.; Hornschemeier, Ann; Hoshino, Akio; Hughes, John P.; Ichinohe, Yuto; Iizuka, Ryo; Inoue, Hajime; Inoue, Yoshiyuki; Ishida, Manabu; Ishikawa, Kumi; Ishisaki, Yoshitaka; Iwai, Masachika; Kaastra, Jelle; Kallman, Tim; Kamae, Tsuneyoshi; Kataoka, Jun; Katsuda, Satoru; Kawai, Nobuyuki; Kelley, Richard L.; Kilbourne, Caroline A.; Kitaguchi, Takao; Kitamoto, Shunji; Kitayama, Tetsu; Kohmura, Takayoshi; Kokubun, Motohide; Koyama, Katsuji; Koyama, Shu; Kretschmar, Peter; Krimm, Hans A.; Kubota, Aya; Kunieda, Hideyo; Laurent, Philippe; Lee, Shiu-Hang; Leutenegger, Maurice A.; Limousin, Olivier O.; Loewenstein, Michael; Long, Knox S.; Lumb, David; Madejski, Greg; Maeda, Yoshitomo; Maier, Daniel; Makishima, Kazuo; Markevitch, Maxim; Matsumoto, Hironori; Matsushita, Kyoko; McCammon, Dan; McNamara, Brian R.; Mehdipour, Missagh; Miller, Eric D.; Miller, Jon M.; Mineshige, Shin; Mitsuda, Kazuhisa; Mitsuishi, Ikuyuki; Miyazawa, Takuya; Mizuno, Tsunefumi; Mori, Hideyuki; Mori, Koji; Mukai, Koji; Murakami, Hiroshi; Mushotzky, Richard F.; Nakagawa, Takao; Nakajima, Hiroshi; Nakamori, Takeshi; Nakashima, Shinya; Nakazawa, Kazuhiro; Nobukawa, Kumiko K.; Nobukawa, Masayoshi; Noda, Hirofumi; Odaka, Hirokazu; Ohashi, Takaya; Ohno, Masanori; Okajima, Takashi; Ota, Naomi; Ozaki, Masanobu; Paerels, Frits; Paltani, Stéphane; Petre, Robert; Pinto, Ciro; Porter, Frederick S.; Pottschmidt, Katja; Reynolds, Christopher S.; Safi-Harb, Samar; Saito, Shinya; Sakai, Kazuhiro; Sasaki, Toru; Sato, Goro; Sato, Kosuke; Sato, Rie; Sawada, Makoto; Schartel, Norbert; Serlemitsos, Peter J.; Seta, Hiromi; Shidatsu, Megumi; Simionescu, Aurora; Smith, Randall K.; Soong, Yang; Stawarz, Łukasz; Sugawara, Yasuharu; Sugita, Satoshi; Szymkowiak, Andrew; Tajima, Hiroyasu; Takahashi, Hiromitsu; Takahashi, Tadayuki; Takeda, Shin'ichiro; Takei, Yoh; Tamagawa, Toru; Tamura, Takayuki; Tanaka, Takaaki; Tanaka, Yasuo; Tanaka, Yasuyuki T.; Tashiro, Makoto S.; Tawara, Yuzuru; Terada, Yukikatsu; Terashima, Yuichi; Tombesi, Francesco; Tomida, Hiroshi; Tsuboi, Yohko; Tsujimoto, Masahiro; Tsunemi, Hiroshi; Tsuru, Takeshi Go; Uchida, Hiroyuki; Uchiyama, Hideki; Uchiyama, Yasunobu; Ueda, Shutaro; Ueda, Yoshihiro; Uno, Shin'ichiro; Urry, C. Megan; Ursino, Eugenio; Watanabe, Shin; Werner, Norbert; Wilkins, Dan R.; Williams, Brian J.; Yamada, Shinya; Yamaguchi, Hiroya; Yamaoka, Kazutaka; Yamasaki, Noriko Y.; Yamauchi, Makoto; Yamauchi, Shigeo; Yaqoob, Tahir; Yatsu, Yoichi; Yonetoku, Daisuke; Zhuravleva, Irina; Zoghbi, Abderahmen; Kawamuro, Taiki

2018-03-01

The origin of the narrow Fe-Kα fluorescence line at 6.4 keV from active galactic nuclei has long been under debate; some of the possible sites are the outer accretion disk, the broad line region, a molecular torus, or interstellar/intracluster media. In 2016 February-March, we performed the first X-ray microcalorimeter spectroscopy with the Soft X-ray Spectrometer (SXS) on board the Hitomi satellite of the Fanaroff-Riley type I radio galaxy NGC 1275 at the center of the Perseus cluster of galaxies. With the high-energy resolution of ˜5 eV at 6 keV achieved by Hitomi/SXS, we detected the Fe-Kα line with ˜5.4 σ significance. The velocity width is constrained to be 500-1600 km s-1 (FWHM for Gaussian models) at 90% confidence. The SXS also constrains the continuum level from the NGC 1275 nucleus up to ˜20 keV, giving an equivalent width of ˜20 eV for the 6.4 keV line. Because the velocity width is narrower than that of the broad Hα line of ˜2750 km s-1, we can exclude a large contribution to the line flux from the accretion disk and the broad line region. Furthermore, we performed pixel map analyses on the Hitomi/SXS data and image analyses on the Chandra archival data, and revealed that the Fe-Kα line comes from a region within ˜1.6 kpc of the NGC 1275 core, where an active galactic nucleus emission dominates, rather than that from intracluster media. Therefore, we suggest that the source of the Fe-Kα line from NGC 1275 is likely a low-covering-fraction molecular torus or a rotating molecular disk which probably extends from a parsec to hundreds of parsecs scale in the active galactic nucleus system.

Spectral-luminosity evolution of active galactic nuclei (AGN)

NASA Technical Reports Server (NTRS)

Leiter, Darryl; Boldt, Elihu

1992-01-01

The origin of the cosmic X-ray and gamma-ray backgrounds is explained via the mechanism of AGN spectral-luminosity evolution. The spectral evolution of precursor active galaxies into AGN, and Newton-Raphson input and output parameters are discussed.

Internal absorption of gamma-rays in relativistic blobs of active galactic nuclei

NASA Astrophysics Data System (ADS)

Sitarek, Julian; Bednarek, Wlodek

2007-06-01

We investigate the production of gamma-rays in the inverse Compton (IC) scattering process by leptons accelerated inside relativistic blobs in jets of active galactic nuclei. Leptons are injected homogeneously inside the spherical blob and initiate IC e ± pair cascade in the synchrotron radiation (produced by the same population of leptons, SSC model), provided that the optical depth for gamma-rays is larger than unity. It is shown that for likely parameters internal absorption of gamma-rays has to be important. We suggest that new type of blazars might be discovered by the future simultaneous X-ray and γ-ray observations, showing peak emissions in the hard X-rays, and in the GeV γ-rays. Moreover, the considered scenario might be also responsible for the orphan X-ray flares recently reported from BL Lac type active galaxies.

Inelastic Boosted Dark Matter at direct detection experiments

NASA Astrophysics Data System (ADS)

Giudice, Gian F.; Kim, Doojin; Park, Jong-Chul; Shin, Seodong

2018-05-01

We explore a novel class of multi-particle dark sectors, called Inelastic Boosted Dark Matter (iBDM). These models are constructed by combining properties of particles that scatter off matter by making transitions to heavier states (Inelastic Dark Matter) with properties of particles that are produced with a large Lorentz boost in annihilation processes in the galactic halo (Boosted Dark Matter). This combination leads to new signals that can be observed at ordinary direct detection experiments, but require unconventional searches for energetic recoil electrons in coincidence with displaced multi-track events. Related experimental strategies can also be used to probe MeV-range boosted dark matter via their interactions with electrons inside the target material.

The Electron Spectrum above 20 GeV Measured by ATIC

NASA Technical Reports Server (NTRS)

Chang, J.; Schmidt, W. K. H.; Adams, J. H.; Ahn, H. S.; Bashindzhagyan, G.; Batkov, K. E.; Christl, M.; Fazely, A. R.; Ganel, O.; Gunasingha, R. M.

2004-01-01

The Advanced Thin Ionization Calorimeter (ATIC) Balloon Experiment has been flown from McMurdo, Antarctica in 2000-01 (test flight) and 2002-03 (science flight). ATIC is composed of a segmented BGO calorimeter following a carbon target with scintillator tracking layers and a Silicon matrix detector at the entrance. ATIC measures the composition and energy spectra of the nuclei plus electrons. We present the electron spectrum derived from the ATIC flights, from 20 GeV to 3 TeV, and compare it to existing very high energy measurements from emulsion chambers and to the results of galactic propagation calculations. The good energy resolution and high statistics in the ATIC data allow detailed astrophysical interpretation of the results.

Testing for Dark Matter Trapped in the Solar System

NASA Technical Reports Server (NTRS)

Krisher, Timothy P.

1996-01-01

We consider the possibility of dark matter trapped in the solar system in bound solar orbits. If there exist mechanisms for dissipating excess kinetic energy by an amount sufficient for generating bound solar orbits, then trapping of galactic dark matter might have taken place during formation of the solar system, or could be an ongoing process. Possible locations for acumulation of trapped dark matter are orbital resonances with the planets or regions in the outer solar system. It is posible to test for the presence of unseen matter by detecting its gravitational effects. Current results for dynamical limits obtained from analyses of planetary ephemeris data and spacecraft tracking data are presented. Possible future improvements are discussed.

Biological effects of galactic radiation HZE particles in experiments on the orbital station Salyut 7

NASA Astrophysics Data System (ADS)

Miller, A. T.; Nevzgodina, L. V.

Lettuce (Lactuca sativa) seeds were flown on-board the orbital station Salyut 7 for 66-457 days. It was found that a single heavy charged particle (HZE) hitting a seed only slightly affects the subsequent plant growth. However, morphological anomalies of varying type in primordial leaves and roots were observed that show good correlation with the location of the particle track. The most severe damage detected by light and an electron microscopy were ``channels'' in dry and soaked seeds. The appearance of ``channels'' seems to be related to the LET of the incident particle. This finding is of considerable importance for assessment of space flight radiation hazard.

Triggering active galactic nuclei in galaxy clusters

NASA Astrophysics Data System (ADS)

Marshall, Madeline A.; Shabala, Stanislav S.; Krause, Martin G. H.; Pimbblet, Kevin A.; Croton, Darren J.; Owers, Matt S.

2018-03-01

We model the triggering of active galactic nuclei (AGN) in galaxy clusters using the semi-analytic galaxy formation model SAGE. We prescribe triggering methods based on the ram pressure galaxies experience as they move throughout the intracluster medium, which is hypothesized to trigger star formation and AGN activity. The clustercentric radius and velocity distribution of the simulated active galaxies produced by these models are compared with those of AGN and galaxies with intense star formation from a sample of low-redshift relaxed clusters from the Sloan Digital Sky Survey. The ram pressure triggering model that best explains the clustercentric radius and velocity distribution of these observed galaxies has AGN and star formation triggered if 2.5 × 10-14 Pa < Pram < 2.5 × 10-13 Pa and Pram > 2Pinternal; this is consistent with expectations from hydrodynamical simulations of ram-pressure-induced star formation. Our results show that ram pressure is likely to be an important mechanism for triggering star formation and AGN activity in clusters.

Swift/XRT detects a new accretion outburst of the Galactic center neutron star transient GRS 1741-2853

NASA Astrophysics Data System (ADS)

Degenaar, N.; Wijnands, R.; Reynolds, M. T.; Miller, J. M.; Kennea, J. A.

2017-10-01

Daily Swift/XRT monitoring observations of the Galactic center (Degenaar et al. 2015) have picked up renewed activity of the transient neutron star low-mass X-ray binary and thermonuclear X-ray burster GRS 1741-2853, which is located 10 arcmin NW of Sgr A*. During a 1 ks PC-mode observation performed on 2017 October 11 the source is detected at a net count rate of 0.015 counts/s and it has been steadily brightening since, indicating the onset of a new accretion outburst.

General properties of HII regions in galaxies

NASA Technical Reports Server (NTRS)

Smirnov, M. A.; Komberg, B. V.

1979-01-01

The structure, electron density, and dimensions of HII regions in galaxies are discussed. These parameters are correlated to the chemical composition gradient along the galactic radius, the dimensions of the three largest HII regions in the galaxy, and the amount of hydrogen in the galaxy, as well as the mass, dimensions, and total optical luminosity of the galaxy. The relationships of HII regions to star formation and galactic nucleus activity are discussed and the kinematic properties of the SB and Sab galaxies are related to the size of HII regions.

Feedback first: the surprisingly weak effects of magnetic fields, viscosity, conduction and metal diffusion on sub-L* galaxy formation

NASA Astrophysics Data System (ADS)

Su, Kung-Yi; Hopkins, Philip F.; Hayward, Christopher C.; Faucher-Giguère, Claude-André; Kereš, Dušan; Ma, Xiangcheng; Robles, Victor H.

2017-10-01

Using high-resolution simulations with explicit treatment of stellar feedback physics based on the FIRE (Feedback In Realistic Environments) project, we study how galaxy formation and the interstellar medium (ISM) are affected by magnetic fields, anisotropic Spitzer-Braginskii conduction and viscosity, and sub-grid metal diffusion from unresolved turbulence. We consider controlled simulations of isolated (non-cosmological) galaxies but also a limited set of cosmological 'zoom-in' simulations. Although simulations have shown significant effects from these physics with weak or absent stellar feedback, the effects are much weaker than those of stellar feedback when the latter is modelled explicitly. The additional physics have no systematic effect on galactic star formation rates (SFRs). In contrast, removing stellar feedback leads to SFRs being overpredicted by factors of ˜10-100. Without feedback, neither galactic winds nor volume-filling hot-phase gas exist, and discs tend to runaway collapse to ultra-thin scaleheights with unphysically dense clumps congregating at the galactic centre. With stellar feedback, a multi-phase, turbulent medium with galactic fountains and winds is established. At currently achievable resolutions and for the investigated halo mass range 1010-1013 M⊙, the additional physics investigated here (magnetohydrodynamic, conduction, viscosity, metal diffusion) have only weak (˜10 per cent-level) effects on regulating SFR and altering the balance of phases, outflows or the energy in ISM turbulence, consistent with simple equipartition arguments. We conclude that galactic star formation and the ISM are primarily governed by a combination of turbulence, gravitational instabilities and feedback. We add the caveat that active galactic nucleus feedback is not included in the present work.

The Formation of Galactic Bulges

NASA Astrophysics Data System (ADS)

Carollo, C. Marcella; Ferguson, Henry C.; Wyse, Rosemary F. G.

2000-03-01

Part I. Introduction: What are galactic bulges?; Part II. The Epoch of Bulge Formation: Origin of bulges; Deep sub-mm surveys: High-z ULIRGs and the formation of spheroids; Ages and metallicities for stars in the galactic bulge; Integrated stellar populations of bulges: First results; HST-NICMOS observations of galactic bulges: Ages and dust; Inside-out bulge formation and the origin of the Hubble sequence; Part III. The Timescales of Bulge Formation: Constraints on the bulge formation timescale from stellar populations; Bulge building with mergers and winds; Role of winds, starbursts, and activity in bulge formation; Dynamical timescales of bulge formation; Part IV. Physical Processes in Bulge Formation: the role of bars for secular bulge formation; Bars and boxy/peanut-shaped bulges: an observational point of view; Boxy- and peanut-shaped bulges; A new class of bulges; The role of secondary bars in bulge formation; Radial transport of molecular gas to the nuclei of spiral galaxies; Dynamical evolution of bulge shapes; Two-component stellar systems: Phase-space constraints; Central NGC 2146 - a firehose-type bending instability?; Bulge formation: the role of the multi-phase ISM; Global evolution of a self-gravitating multi-phase ISM in the central kpc region of galaxies; Part V. Bulge Phenomenology: Bulge-disk decomposition of spiral galaxies in the near-infrared; The triaxial bulge of NGC 1371; The bulge-disk orthogonal decoupling in galaxies: NGC 4698 and NGC 4672; The kinematics and the origin of the ionized gas in NGC 4036; Optically thin thermal plasma in the galactic bulge; X-ray properties of bulges; The host galaxies of radio-loud AGN; The centers of radio-loud early-type galaxies with HST; Central UV spikes in two galactic spheroids; Conference summary: where do we stand?

The effects of the local environment on active galactic nuclei

DOE Office of Scientific and Technical Information (OSTI.GOV)

Manzer, L. H.; De Robertis, M. M., E-mail: liannemanzer@gmail.com, E-mail: mmdr@yorku.ca

There continues to be significant controversy regarding the mechanism(s) responsible for the initiation and maintenance of activity in galactic nuclei. In this paper we will investigate possible environmental triggers of nuclear activity through a statistical analysis of a large sample of galaxy groups. The focus of this paper is to identify active galactic nuclei (AGNs) and other emission-line galaxies in these groups and to compare their frequency with a sample of over 260,000 isolated galaxies from the same catalog. The galaxy groups are taken from the catalog of Yang et al., in which over 20,000 virialized groups of galaxies (2more » ≤ N ≤ 20) with redshifts between 0.01 and 0.20 are from the Sloan Digital Sky Survey. We first investigate the completeness of our data set and find, though biases are a concern particularly at higher redshift, that our data provide a fair representation of the local universe. After correcting emission-line equivalent widths for extinction and underlying Balmer stellar absorption, we classify galaxies in the sample using traditional emission-line ratios, while incorporating measurement uncertainties. We find a significantly higher fraction of AGNs in groups compared with the isolated sample. Likewise, a significantly higher fraction of absorption-line galaxies are found in groups, while a higher fraction of star-forming galaxies prefer isolated environments. Within grouped environments, AGNs and star-forming galaxies are found more frequently in small- to medium-richness groups, while absorption-line galaxies prefer groups with larger richnesses. Groups containing only emission-line galaxies have smaller virial radii, velocity dispersions, and masses compared with those containing only absorption-line galaxies. Furthermore, the AGN fraction increases with decreasing distance to the group centroid, independent of galaxy morphology. Using properties obtained from Galaxy Zoo, there is an increased fraction of AGNs within merging systems, unlike star-forming galaxies. These results provide some indication that the local environment does play a role in initiating activity in galactic nuclei, but it is by no means simple or straightforward.« less

Cathode signal in a TPC directional detector: implementation and validation measuring the drift velocity

NASA Astrophysics Data System (ADS)

Couturier, C.; Riffard, Q.; Sauzet, N.; Guillaudin, O.; Naraghi, F.; Santos, D.

2017-11-01

Low-pressure gaseous TPCs are well suited detectors to correlate the directions of nuclear recoils to the galactic Dark Matter (DM) halo. Indeed, in addition to providing a measure of the energy deposition due to the elastic scattering of a DM particle on a nucleus in the target gas, they allow for the reconstruction of the track of the recoiling nucleus. In order to exclude the background events originating from radioactive decays on the surfaces of the detector materials within the drift volume, efforts are ongoing to precisely localize the track nuclear recoil in the drift volume along the axis perpendicular to the cathode plane. We report here the implementation of the measure of the signal induced on the cathode by the motion of the primary electrons toward the anode in a MIMAC chamber. As a validation, we performed an independent measurement of the drift velocity of the electrons in the considered gas mixture, correlating in time the cathode signal with the measure of the arrival times of the electrons on the anode.

Wind from the black-hole accretion disk driving a molecular outflow in an active galaxy.

PubMed

Tombesi, F; Meléndez, M; Veilleux, S; Reeves, J N; González-Alfonso, E; Reynolds, C S

2015-03-26

Powerful winds driven by active galactic nuclei are often thought to affect the evolution of both supermassive black holes and their host galaxies, quenching star formation and explaining the close relationship between black holes and galaxies. Recent observations of large-scale molecular outflows in ultraluminous infrared galaxies support this quasar-feedback idea, because they directly trace the gas from which stars form. Theoretical models suggest that these outflows originate as energy-conserving flows driven by fast accretion-disk winds. Proposed connections between large-scale molecular outflows and accretion-disk activity in ultraluminous galaxies were incomplete because no accretion-disk wind had been detected. Conversely, studies of powerful accretion-disk winds have until now focused only on X-ray observations of local Seyfert galaxies and a few higher-redshift quasars. Here we report observations of a powerful accretion-disk wind with a mildly relativistic velocity (a quarter that of light) in the X-ray spectrum of IRAS F11119+3257, a nearby (redshift 0.189) optically classified type 1 ultraluminous infrared galaxy hosting a powerful molecular outflow. The active galactic nucleus is responsible for about 80 per cent of the emission, with a quasar-like luminosity of 1.5 × 10(46) ergs per second. The energetics of these two types of wide-angle outflows is consistent with the energy-conserving mechanism that is the basis of the quasar feedback in active galactic nuclei that lack powerful radio jets (such jets are an alternative way to drive molecular outflows).

Gamma ray monitoring of a AGN and galactic black hole candidates by the Compton Gamma Ray Observatory

NASA Technical Reports Server (NTRS)

Skelton, R. T.; Ling, James C.; Wheaton, William A.; Harmon, Alan; Fishman, G. J.; Meegan, C. A.; Paciesas, William S.; Gruber, Duane E.; Rubin, Brad; Wilson, R. B.

1992-01-01

The Compton Gamma-Ray Observatory's Burst and Transient Source Experiment (BATSE) has a powerful capability to provide nearly uninterrupted monitoring in the 25 keV-10 MeV range of both active galactic nuclei (AGN) and galactic black hole candidates (GBHC) such as Cygnus X-1, using the occultation of cosmic sources by the Earth. Since the Crab is detected by the BATSE Large Area Detectors with roughly 25(sigma) significance in the 15-125 keV range in a single rise or set, a variation by a factor of two of a source having one-tenth the strength of Cygnus X-1 should be detectable within a day. Methods of modeling the background are discussed which will increase the accuracy, sensitivity, and reliability of the results beyond those obtainable from a linear background fit with a single rise or set discontinuity.

Cosmological evolution of supermassive black holes in galactic centers unveiled by hard X-ray observations.

PubMed

Ueda, Yoshihiro

2015-01-01

We review the current understanding of the cosmological evolution of supermassive black holes in galactic centers elucidated by X-ray surveys of active galactic nuclei (AGNs). Hard X-ray observations at energies above 2 keV are the most efficient and complete tools to find "obscured" AGNs, which are dominant populations among all AGNs. Combinations of surveys with various flux limits and survey area have enabled us to determine the space number density and obscuration properties of AGNs as a function of luminosity and redshift. The results have essentially solved the origin of the X-ray background in the energy band below ∼10 keV. The downsizing (or anti-hierarchical) evolution that more luminous AGNs have the space-density peak at higher redshifts has been discovered, challenging theories of galaxy and black hole formation. Finally, we summarize unresolved issues on AGN evolution and prospects for future X-ray missions.

First neutral atomic hydrogen images of quasar host galaxies.

NASA Astrophysics Data System (ADS)

Lim, J.; Ho, P. T. P.

1999-12-01

Violent galactic encounters or mergers are the leading contenders for triggering luminous quasar activity at low redshifts: such interactions can lead to the concentration of gas in the host galactic nucleus, thus fueling the suspected central supermassive black hole. Here the authors image quasar host galaxies in the redshifted 21-cm line emission of neutral atomic hydrogen (H I) gas, which in nearby galaxies has proven to be a particularly sensitive as well as enduring tracer of tidal interactions. The three quasars studied have different optical environments normally seen around low-redshift quasars, ranging from a perhaps mildly interacting system to a relatively undisturbed host with a projected neighbouring galaxy to an isolated and apparently serene host galaxy. By contrast with their optical appearences, all three quasar host galaxies exhibit ongoing or remnant tidal H I disruptions tracing galactic encounters or mergers. These observations provide a better understanding of the likely stage of their interaction.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Walborn, Nolan R.; Sana, Hugues; Sabbi, Elena, E-mail: walborn@stsci.edu, E-mail: hsana@stsci.edu, E-mail: sabbi@stsci.edu

Extremely broad emission wings at Hβ and Hα have been found in VLT-FLAMES Tarantula Survey data for five very luminous BA supergiants in or near 30 Doradus in the Large Magellanic Cloud. The profiles of both lines are extremely asymmetrical, which we have found to be caused by very broad diffuse interstellar bands (DIBs) in the longward wing of Hβ and the shortward wing of Hα. These DIBs are well known to interstellar but not to many stellar specialists, so that the asymmetries may be mistaken for intrinsic features. The broad emission wings are generally ascribed to electron scattering, althoughmore » we note difficulties for that interpretation in some objects. Such profiles are known in some Galactic hyper/supergiants and are also seen in both active and quiescent Luminous Blue Variables (LBVs). No prior or current LBV activity is known in these 30 Dor stars, although a generic relationship to LBVs is not excluded; subject to further observational and theoretical investigation, it is possible that these very luminous supergiants are approaching the LBV stage for the first time. Their locations in the HRD and presumed evolutionary tracks are consistent with that possibility. The available evidence for spectroscopic variations of these objects is reviewed, while recent photometric monitoring does not reveal variability. A search for circumstellar nebulae has been conducted, with an indeterminate result for one of them.« less

The link between IRAS spectra and near-infrared emission features in external galaxies

NASA Technical Reports Server (NTRS)

Desert, F. X.; Dennefeld, M.

1988-01-01

The relationship in external galaxies between the presence of the near-infrared (NIR) emission features attributed to polycyclic aromatic hydrocarbon (PAH) molecules, and the far-infrared (FIR) properties as observed by IRAS, is investigated. It is found that whenever the NIR features are absent in a galaxy, the FIR spectrum displays an enhancement at shorter wavelengths relative to normal galaxies. This enhancement is always associated with a strong activity in the galactic nucleus. Some Seyfert galaxies do not exhibit such an infrared signature and therefore they are probably energetically dominated by star-formation processes. Finally, the importance of hard UV photons and of the hot medium in the narrow line region of active nuclei is emphasized in relation to the survival of the PAH molecules. In this frame, the absence of PAHs in the galactic center could be taken as evidence for the presence of an active nucleus.

Consequences of hot gas in the broad line region of active galactic nuclei

NASA Technical Reports Server (NTRS)

Kallman, T.; Mushotzky, R.

1985-01-01

Models for hot gas in the broad line region of active galactic nuclei are discussed. The results of the two phase equilibrium models for confinement of broad line clouds by Compton heated gas are used to show that high luminosity quasars are expected to show Fe XXVI L alpha line absorption which will be observed with spectrometers such as those planned for the future X-ray spectroscopy experiments. Two phase equilibrium models also predict that the gas in the broad line clouds and the confining medium may be Compton thick. It is shown that the combined effects of Comptonization and photoabsorption can suppress both the broad emission lines and X-rays in the Einstein and HEAO-1 energy bands. The observed properties of such Compton thick active galaxies are expected to be similar to those of Seyfert 2 nuclei. The implications for polarization and variability are also discussed.

The role of environment in the observed Fundamental Plane of radio Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Shabala, Stanislav S.

2018-05-01

The optical Fundamental Plane of black hole activity relates radio continuum luminosity of Active Galactic Nuclei to [O III] luminosity and black hole mass. We examine the environments of low redshift (z < 0.2) radio-selected AGN, quantified through galaxy clustering, and find that halo mass provides similar mass scalings to black hole mass in the Fundamental Plane relations. AGN properties are strongly environment-dependent: massive haloes are more likely to host radiatively inefficient (low-excitation) radio AGN, as well as a higher fraction of radio luminous, extended sources. These AGN populations have different radio - optical luminosity scaling relations, and the observed mass scalings in the parent AGN sample are built up by combining populations preferentially residing in different environments. Accounting for environment-driven selection effects, the optical Fundamental Plane of supermassive black holes is likely to be mass-independent, as predicted by models.

OUTFLOW AND METALLICITY IN THE BROAD-LINE REGION OF LOW-REDSHIFT ACTIVE GALACTIC NUCLEI

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shin, Jaejin; Woo, Jong-Hak; Nagao, Tohru

2017-01-20

Outflows in active galactic nuclei (AGNs) are crucial to understand in investigating the co-evolution of supermassive black holes (SMBHs) and their host galaxies since outflows may play an important role as an AGN feedback mechanism. Based on archival UV spectra obtained with the Hubble Space Telescope and IUE , we investigate outflows in the broad-line region (BLR) in low-redshift AGNs ( z < 0.4) through detailed analysis of the velocity profile of the C iv emission line. We find a dependence of the outflow strength on the Eddington ratio and the BLR metallicity in our low-redshift AGN sample, which ismore » consistent with earlier results obtained for high-redshift quasars. These results suggest that BLR outflows, gas accretion onto SMBHs, and past star formation activity in host galaxies are physically related in low-redshift AGNs as in powerful high-redshift quasars.« less

Hunting for Active Galactic Nuclei in JWST/MIRI Imaging

NASA Astrophysics Data System (ADS)

Lin, Kenneth W.; Pope, Alexandra; Kirkpatrick, Allison

2018-01-01

The mid-infrared is uniquely sensitive to both star formation and active galactic nuclei (AGN) activity in galaxies. While spectra in this range can unambiguously identify these two processes, imaging data from the Spitzer Space Telescope found that the mid-infrared colors are also able to separate AGN from star forming galaxies. With the launch of the James Webb Space Telescope, our access to mid-infrared will be renewed; specifically, MIRI will provide imaging in 9 bands from 5.6-25.5 microns. While predictions show that color diagnostics will be useful with JWST/MIRI, this does not exploit the full dataset of MIRI imaging. In this poster, we discuss a Principal Component Analysis to identify the JWST filters that are most sensitive to the AGN contribution and demonstrate how to use it to identify large samples of AGN from planned MIRI imaging surveys.

The line-emitting gas in active galaxies - A probe of the nuclear engine

NASA Technical Reports Server (NTRS)

Veilleux, Sylvain

1993-01-01

This paper reviews some of the basic questions regarding the structure of the engine powering active galactic nuclei (AGN), the nature of the interaction between the AGN and the host galaxy, and the origin and evolution of AGN. The study of the dynamics and physical characteristics of the line-emitting gas in these objects has proven fruitful in addressing many of these issues. Recent advances in optical and infrared detector technology combined with the development of superior ground-based instruments have produced efficient new tools for the study of the line-emitting gas on nuclear and Galactic scales. Programs which take advantage of two of these new techniques, Fabry-Perot imaging spectroscopy and infrared spectroscopy, are described in this paper. The origin of nuclear activity in galaxies is also addressed in a third project which aims at determining the nature of luminous infrared galaxies.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kewley, Lisa J.; Dopita, Michael A.; Sutherland, Ralph

We use the chemical evolution predictions of cosmological hydrodynamic simulations with our latest theoretical stellar population synthesis, photoionization, and shock models to predict the strong line evolution of ensembles of galaxies from z = 3 to the present day. In this paper, we focus on the brightest optical emission-line ratios, [N II]/H{alpha} and [O III]/H{beta}. We use the optical diagnostic Baldwin-Phillips-Terlevich (BPT) diagram as a tool for investigating the spectral properties of ensembles of active galaxies. We use four redshift windows chosen to exploit new near-infrared multi-object spectrographs. We predict how the BPT diagram will appear in these four redshiftmore » windows given different sets of assumptions. We show that the position of star-forming galaxies on the BPT diagram traces the interstellar medium conditions and radiation field in galaxies at a given redshift. Galaxies containing active galactic nucleus (AGN) form a mixing sequence with purely star-forming galaxies. This mixing sequence may change dramatically with cosmic time, due to the metallicity sensitivity of the optical emission-lines. Furthermore, the position of the mixing sequence may probe metallicity gradients in galaxies as a function of redshift, depending on the size of the AGN narrow-line region. We apply our latest slow shock models for gas shocked by galactic-scale winds. We show that at high redshift, galactic wind shocks are clearly separated from AGN in line ratio space. Instead, shocks from galactic winds mimic high metallicity starburst galaxies. We discuss our models in the context of future large near-infrared spectroscopic surveys.« less

MOLECULAR CLOUDS AND CLUMPS IN THE BOSTON UNIVERSITY-FIVE COLLEGE RADIO ASTRONOMY OBSERVATORY GALACTIC RING SURVEY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rathborne, J. M.; Johnson, A. M.; Jackson, J. M.

2009-05-15

The Boston University-Five College Radio Astronomy Observatory (BU-FCRAO) Galactic Ring Survey (GRS) of {sup 13}CO J = 1 {yields} 0 emission covers Galactic longitudes 18{sup 0} < l < 55.{sup 0}7 and Galactic latitudes |b| {<=} 1{sup 0}. Using the SEQUOIA array on the FCRAO 14 m telescope, the GRS fully sampled the {sup 13}CO Galactic emission (46'' angular resolution on a 22'' grid) and achieved a spectral resolution of 0.21 km s{sup -1}. Because the GRS uses {sup 13}CO, an optically thin tracer, rather than {sup 12}CO, an optically thick tracer, the GRS allows a much better determination ofmore » column density and also a cleaner separation of velocity components along a line of sight. With this homogeneous, fully sampled survey of {sup 13}CO emission, we have identified 829 molecular clouds and 6124 clumps throughout the inner Galaxy using the CLUMPFIND algorithm. Here we present details of the catalog and a preliminary analysis of the properties of the molecular clouds and their clumps. Moreover, we compare clouds inside and outside of the 5 kpc ring and find that clouds within the ring typically have warmer temperatures, higher column densities, larger areas, and more clumps compared with clouds located outside the ring. This is expected if these clouds are actively forming stars. This catalog provides a useful tool for the study of molecular clouds and their embedded young stellar objects.« less

On the Right Track.

ERIC Educational Resources Information Center

Bieber, Ed

1983-01-01

Suggests thinking of "tracks" as clues and using them as the focus of outdoor activities in the urban environment. Provides 24 examples of possible track activities, including: seeds on the ground (track of a nearby tree), litter (track of a litterbug), and peeling paint (track of weathering forces). (JN)

Search for EeV protons of galactic origin

NASA Astrophysics Data System (ADS)

Abbasi, R. U.; Abe, M.; Abu-Zayyad, T.; Allen, M.; Azuma, R.; Barcikowski, E.; Belz, J. W.; Bergman, D. R.; Blake, S. A.; Cady, R.; Cheon, B. G.; Chiba, J.; Chikawa, M.; Fujii, T.; Fukushima, M.; Goto, T.; Hanlon, W.; Hayashi, Y.; Hayashi, M.; Hayashida, N.; Hibino, K.; Honda, K.; Ikeda, D.; Inoue, N.; Ishii, T.; Ishimori, R.; Ito, H.; Ivanov, D.; Jui, C. C. H.; Kadota, K.; Kakimoto, F.; Kalashev, O.; Kasahara, K.; Kawai, H.; Kawakami, S.; Kawana, S.; Kawata, K.; Kido, E.; Kim, H. B.; Kim, J. H.; Kim, J. H.; Kishigami, S.; Kitamura, S.; Kitamura, Y.; Kuzmin, V.; Kwon, Y. J.; Lan, J.; Lubsandorzhiev, B.; Lundquist, J. P.; Machida, K.; Martens, K.; Matsuda, T.; Matsuyama, T.; Matthews, J. N.; Minamino, M.; Mukai, K.; Myers, I.; Nagasawa, K.; Nagataki, S.; Nakamura, T.; Nonaka, T.; Nozato, A.; Ogio, S.; Ogura, J.; Ohnishi, M.; Ohoka, H.; Oki, K.; Okuda, T.; Ono, M.; Onogi, R.; Oshima, A.; Ozawa, S.; Park, I. H.; Pshirkov, M. S.; Rodriguez, D. C.; Rubtsov, G.; Ryu, D.; Sagawa, H.; Saito, K.; Saito, Y.; Sakaki, N.; Sakurai, N.; Scott, L. M.; Sekino, K.; Shah, P. D.; Shibata, T.; Shibata, F.; Shimodaira, H.; Shin, B. K.; Shin, H. S.; Smith, J. D.; Sokolsky, P.; Stokes, B. T.; Stratton, S. R.; Stroman, T. A.; Suzawa, T.; Takahashi, Y.; Takamura, M.; Takeda, M.; Takeishi, R.; Taketa, A.; Takita, M.; Tameda, Y.; Tanaka, M.; Tanaka, K.; Tanaka, H.; Thomas, S. B.; Thomson, G. B.; Tinyakov, P.; Tirone, A. H.; Tkachev, I.; Tokuno, H.; Tomida, T.; Troitsky, S.; Tsunesada, Y.; Tsutsumi, K.; Uchihori, Y.; Udo, S.; Urban, F.; Wong, T.; Yamane, R.; Yamaoka, H.; Yamazaki, K.; Yang, J.; Yashiro, K.; Yoneda, Y.; Yoshida, S.; Yoshii, H.; Zollinger, R.; Zundel, Z.

2017-01-01

Cosmic rays in the energy range 1018.0-1018.5 eV are thought to have a light, probably protonic, composition. To study their origin one can search for anisotropy in their arrival directions. Extragalactic cosmic rays should be isotropic, but galactic cosmic rays of this type should be seen mostly along the galactic plane, and there should be a shortage of events coming from directions near the galactic anticenter. This is due to the fact that, under the influence of the galactic magnetic field, the transition from ballistic to diffusive behavior is well advanced, and this qualitative picture persists over the whole energy range. Guided by models of the galactic magnetic field that indicate that the enhancement along the galactic plane should have a standard deviation of about 20° in galactic latitude, and the deficit in the galactic anticenter direction should have a standard deviation of about 50° in galactic longitude, we use the data of the Telescope Array surface detector in 1018.0 to 1018.5 eV energy range to search for these effects. The data are isotropic. Neither an enhancement along the galactic plane nor a deficit in the galactic anticenter direction is found. Using these data we place an upper limit on the fraction of EeV cosmic rays of galactic origin at 1.3% at 95% confidence level.

Simulation of major space particles toward selected materials in a near-equatorial low earth orbit

NASA Astrophysics Data System (ADS)

Suparta, Wayan; Zulkeple, Siti Katrina

2017-05-01

A low earth orbit near the equator (LEO-NEqO) is exposed to the highest energies from galactic cosmic rays (GCR) and from trapped protons with a wide range of energies. Moreover, GCR fluxes were seen to be the highest in 2009 to 2010 when communication belonging to the RazakSAT-1 satellite was believed to have been lost. Hence, this study aimed to determine the influence of the space environment toward the operation of LEO-NEqO satellites by investigating the behavior of major space particles toward satellite materials. The space environment was referred to GCR protons and trapped protons. Their fluxes were obtained from the Space Environment Information System (SPENVIS) and their tracks were simulated through three materials using a simulation program called Geometry and Tracking (Geant4). The materials included aluminum (Al), gallium arsenide (GaAs) and silicon (Si). Then the total ionizing dose (TID) and non-ionizing dose (NIEL) were calculated for a three-year period. Simulations showed that GCR traveled at longer tracks and produced more secondary radiation than trapped protons. Al turned out to receive the lowest total dose, while GaAs showed to be susceptible toward GCR than Si. However, trapped protons contributed the most in spacecraft doses where Si received the highest doses. Finally, the comparison between two Geant4 programs revealed the estimated doses differed at <18%.

Statistical analyses of influence of solar and geomagnetic activities on car accident events

NASA Astrophysics Data System (ADS)

Alania, M. V.; Gil, A.; Wieliczuk, R.

2001-01-01

Statistical analyses of the influence of Solar and geomagnetic activity, sector structure of the interplanetary magnetic field and galactic cosmic ray Forbush effects on car accident events in Poland for the period of 1990-1999 have been carried out. Using auto-correlation, cross-correlation, spectral analyses and superposition epochs methods it has been shown that there are separate periods when car accident events have direct correlation with Ap index of the geomagnetic activity, sector structure of the interplanetary magnetic field and Forbush decreases of galactic cosmic rays. Nevertheless, the single-valued direct correlation is not possible to reveal for the whole period of 1990-1999. Periodicity of 7 days and its second harmonic (3.5 days) has been reliably revealed in the car accident events data in Poland for the each year of the period 1990-1999. It is shown that the maximum car accident events take place in Poland on Friday and practically does not depend on the level of solar and geomagnetic activities.

Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Blandford, R. D.; Netzer, H.; Woltjer, L.; Courvoisier, T. J.-L.; Mayor, M.

Starting with this volume, the Lecture Notes of the renowned Advanced Courses of the Swiss Society for Astrophysics and Astronomy will be published annually. In each course, three extensive lectures given by leading experts in their respective fields cover different and essential aspects of the subject. The 20th course, held at Les Diablerets in April 1990, dealt with current research on active galactic nuclei; it represents the most up-to-date views on the subject, presented with particular regard for clarity. The previous courses considered a wide variety of subjects, beginning with "Theory of Stellar Athmospheres" in 1971 and ending with "The Milky Way as a Galaxy" in 1989. The Lecture Notes of these Saas-Fee Courses appeared as publications of the Geneva Observatory, from which they can still be ordered (chemin des Maillettes 51, CH-1290 Sauverny, Switzerland).

Masses, luminosities and dynamics of galactic molecular clouds

NASA Technical Reports Server (NTRS)

Solomon, P. M.; Rivolo, A. R.; Mooney, T. J.; Barrett, J. W.; Sage, L. J.

1987-01-01

Star formation in galaxies takes place in molecular clouds and the Milky Way is the only galaxy in which it is possible to resolve and study the physical properties and star formation activity of individual clouds. The masses, luminosities, dynamics, and distribution of molecular clouds, primarily giant molecular clouds in the Milky Way are described and analyzed. The observational data sets are the Massachusetts-Stony Brook CO Galactic Plane Survey and the IRAS far IR images. The molecular mass and infrared luminosities of glactic clouds are then compared with the molecular mass and infrared luminosities of external galaxies.

The Compton Observatory Science Workshop

NASA Technical Reports Server (NTRS)

Shrader, Chris R. (Editor); Gehrels, Neil (Editor); Dennis, Brian (Editor)

1992-01-01

The Compton Observatory Science Workshop was held in Annapolis, Maryland on September 23-25, 1991. The primary purpose of the workshop was to provide a forum for the exchange of ideas and information among scientists with interests in various areas of high energy astrophysics, with emphasis on the scientific capabilities of the Compton Observatory. Early scientific results, as well as reports on in-flight instrument performance and calibrations are presented. Guest investigator data products, analysis techniques, and associated software were discussed. Scientific topics covered included active galaxies, cosmic gamma ray bursts, solar physics, pulsars, novae, supernovae, galactic binary sources, and diffuse galactic and extragalactic emission.

Indications for a transparent universe at very high energies

NASA Astrophysics Data System (ADS)

Meyer, Manuel; Horns, Dieter

2012-03-01

The transparency of the universe for very high energy (VHE) photons is limited due to pair-production with low energy photons of the extra galactic background light (EBL) in the optical to infrared band. Here, we use 56 energy spectra from VHE emitting active galactic nuclei (AGN) from redshift 0.004 to 0.536 to search for signatures of deviations from the minimum expected opacity. A statistical study of the individual measurements reveals indications for an overcorrection of AGN spectra with current EBL models. Axion like particles are discussed as a possible explanation of the result.

Time variation of galactic cosmic rays

NASA Technical Reports Server (NTRS)

Evenson, Paul

1988-01-01

Time variations in the flux of galactic cosmic rays are the result of changing conditions in the solar wind. Maximum cosmic ray fluxes, which occur when solar activity is at a minimum, are well defined. Reductions from this maximum level are typically systematic and predictable but on occasion are rapid and unexpected. Models relating the flux level at lower energy to that at neutron monitor energy are typically accurate to 20 percent of the total excursion at that energy. Other models, relating flux to observables such as sunspot number, flare frequency, and current sheet tilt are phenomenological but nevertheless can be quite accurate.

A lower bound on the number of cosmic ray events required to measure source catalogue correlations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dolci, Marco; Romero-Wolf, Andrew; Wissel, Stephanie, E-mail: marco.dolci@polito.it, E-mail: Andrew.Romero-Wolf@jpl.nasa.gov, E-mail: swissel@calpoly.edu

2016-10-01

Recent analyses of cosmic ray arrival directions have resulted in evidence for a positive correlation with active galactic nuclei positions that has weak significance against an isotropic source distribution. In this paper, we explore the sample size needed to measure a highly statistically significant correlation to a parent source catalogue. We compare several scenarios for the directional scattering of ultra-high energy cosmic rays given our current knowledge of the galactic and intergalactic magnetic fields. We find significant correlations are possible for a sample of >1000 cosmic ray protons with energies above 60 EeV.

Radiation Physics for Space and High Altitude Air Travel

NASA Technical Reports Server (NTRS)

Cucinotta, F. A.; Wilson, J. W.; Goldhagen, P.; Saganti, P.; Shavers, M. R.; McKay, Gordon A. (Technical Monitor)

2000-01-01

Galactic cosmic rays (GCR) are of extra-solar origin consisting of high-energy hydrogen, helium, and heavy ions. The GCR are modified by physical processes as they traverse through the solar system, spacecraft shielding, atmospheres, and tissues producing copious amounts of secondary radiation including fragmentation products, neutrons, mesons, and muons. We discuss physical models and measurements relevant for estimating biological risks in space and high-altitude air travel. Ambient and internal spacecraft computational models for the International Space Station and a Mars mission are discussed. Risk assessment is traditionally based on linear addition of components. We discuss alternative models that include stochastic treatments of columnar damage by heavy ion tracks and multi-cellular damage following nuclear fragmentation in tissue.

The Electron Spectrum above 20 GeV Measured by ATIC-2

NASA Technical Reports Server (NTRS)

Chang, J.; Schmidt, W. K. H.; Adams, James H.; Ahn, H. S.; Bashindzhagyan, G.; Batkov, K. E.; Christl, M.; Fazely, A. R.; Ganel, O.; Gunasigha, R. M.

2005-01-01

The Advanced Thin Ionization Calorimeter (ATIC) Balloon Experiment has been flown from McMurdo, Antarctica in 2000-01 (test flight) and 2002-03 (science flight). ATIC is composed of a segmented BGO calorimeter following a carbon target with scintillator tracking layers and a Silicon matrix detector at the entrance. ATIC measures the composition and energy spectra of the nuclei plus electrons. We present the electron spectrum derived from the ATIC-2 science flight, from 20 GeV to 1.5 TeV, and compare it to existing very high energy measurements from emulsion chambers and to the results of galactic propagation calculations. The good energy resolution and high statistics in the ATIC data allow detailed astrophysical interpretation of the results.

PREFACE: Astronomy at High Angular Resolution 2011: The central kiloparsec in galactic nuclei

NASA Astrophysics Data System (ADS)

Iserlohe, Christof; Karas, Vladimir; Krips, Melanie; Eckart, Andreas; Britzen, Silke; Fischer, Sebastian

2012-07-01

We are pleased to present the proceedings from the Astronomy at High Angular Resolution 2011: The central kiloparsec in galactic nuclei conference. The conference took place in the Physikzentrum of the Deutsche Physikalische Gesellschaft (DPG), Bad Honnef, Germany, from 28 August to 2 September 2011. It was the second conference of this kind, following the Astronomy at High Angular Resolution conference held in Bad Honnef, three years earlier in 2008. The main objective of the conference was to frame the discussion of the broad range of physical processes that occur in the central 100pc of galactic nuclei. In most cases, this domain is difficult to probe through observations. This is mainly because of the lack of angular resolution, the brightness of the central engine and possible obscurations through dust and gas, which play together in the central regions of host galaxies of galactic nuclei within a broad range of activity. The presence of large amounts of molecular and atomic (both neutral and ionized) gas, dust and central engines with outflows and jets implies that the conditions for star formation in these regions are very special, and probably different from those in the disks of host galaxies. Numerous presentations covering a broad range of topics, both theoretical and experimental, those related to research on Active Galactic Nuclei and on a wide range of observed wavelengths were submitted to the Scientific Organizing Committee. Presentations have been grouped into six sessions: The nuclei of active galaxies The Galactic Center The immediate environment of Super Massive Black Holes The physics of nuclear jets and the interaction of the interstellar medium The central 100pc of the nuclear environment Star formation in that region The editors thank all participants of the AHAR 2011 conference for their enthusiasm and their numerous and vivid contributions to this conference. We would especially like to thank John Hugh Seiradakis from the Aristotle University of Thessaloniki in Greece for giving the dinner talk on the most astounding ancient Antikythera mechanism. We would also like to thank Victor Gomer and the staff of the Physikzentrum of the Deutsche Physikalische Gesellschaft in Bad Honnef where the conference took place. Last but not least we would like to thank all unnamed helpers, without whom the organisation of this conference would not have been possible. Financial support for this conference was granted by the Deutsche Forschungsgemeinschaft (DFG) Sonderforschungsbereich project number SFB 956. We also acknowledge support from the European Community Framework Programme 7, Advanced Radio Astronomy in Europe, grant agreement no. 227290. Christof Iserlohe, Vladimir Karas, Melanie Krips, Andreas Eckart, Silke Britzen and Sebastian Fischer The Editors Conference photograph Conference Group Photo, 1 September 2011 The PDF also contains additional photographs from the conference and the Contents of the Proceedings.

A New Fundamental Plane for Radiatively Efficient Black-hole Sources

NASA Astrophysics Data System (ADS)

Dong, Ai-Jun; Wu, Qingwen; Cao, Xiao-Feng

2014-06-01

In recent years, it has been found that several low/hard states of X-ray binaries (XRBs) follow an "outliers" track in the radio-X-ray correlation (L_R\\propto L_X^{b} and b ~ 1.4), which is much steeper than the former universal track with b ~ 0.6. In this work, we compile a sample of bright radio-quiet active galactic nuclei (AGNs) and find that their hard X-ray photon indices and Eddington ratios are positively correlated, which is similar to that of XRB outliers, where both bright AGNs and XRB outliers have bolometric Eddington ratios >~ 1%L Edd (L Edd is Eddington luminosity). The Eddington-scaled radio-X-ray correlation of these AGNs is also similar to that of XRB outliers, which has the form of L 5 GHz/L Eddvprop(L 2-10 keV/L Edd) c with c ~= 1.59 and 1.53 for AGNs and XRBs, respectively. Both the positively correlated X-ray spectral evolution and the steeper radio-X-ray correlation can be regulated by a radiatively efficient accretion flow (e.g., disk-corona). Based on these similarities, we further present a new fundamental plane for XRB outliers and bright AGNs in black-hole (BH) mass, radio, and X-ray luminosity space: log L_R=1.59^{+0.28}_{-0.22} log L_X- 0.22^{+0.19}_{-0.20}log M_BH-28.97^{+0.45}_{-0.45} with a scatter of σR = 0.51 dex. This fundamental plane is suitable for radiatively efficient BH sources, while the former plane proposed by Merloni et al. and Falcke et al. may be most suitable for radiatively inefficient sources.

Three-dimensional spatiotemporal tracking of fluorine-18 radiolabeled yeast cells via positron emission particle tracking

DOE PAGES

Langford, Seth T.; Wiggins, Cody S.; Santos, Roque; ...

2017-07-06

A method for Positron Emission Particle Tracking (PEPT) based on optical feature point identification techniques is demonstrated for use in low activity tracking experiments. Furthermore, a population of yeast cells of approximately 125,000 members is activated to roughly 55 Bq/cell by 18F uptake. An in vitro particle tracking experiment is performed with nearly 20 of these cells after decay to 32 Bq/cell. These cells are successfully identified and tracked simultaneously in this experiment. Our work extends the applicability of PEPT as a cell tracking method by allowing a number of cells to be tracked together, and demonstrating tracking for verymore » low activity tracers.« less

Three-dimensional spatiotemporal tracking of fluorine-18 radiolabeled yeast cells via positron emission particle tracking

DOE Office of Scientific and Technical Information (OSTI.GOV)

Langford, Seth T.; Wiggins, Cody S.; Santos, Roque

A method for Positron Emission Particle Tracking (PEPT) based on optical feature point identification techniques is demonstrated for use in low activity tracking experiments. Furthermore, a population of yeast cells of approximately 125,000 members is activated to roughly 55 Bq/cell by 18F uptake. An in vitro particle tracking experiment is performed with nearly 20 of these cells after decay to 32 Bq/cell. These cells are successfully identified and tracked simultaneously in this experiment. Our work extends the applicability of PEPT as a cell tracking method by allowing a number of cells to be tracked together, and demonstrating tracking for verymore » low activity tracers.« less

GREEN BANK TELESCOPE OBSERVATIONS OF THE NH{sub 3} (3, 3) AND (6, 6) TRANSITIONS TOWARD SAGITTARIUS A MOLECULAR CLOUDS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Minh, Young Chol; Liu, Hauyu Baobab; Ho, Paul T. P.

2013-08-10

Ammonia (3, 3) and (6, 6) transitions have been observed using the Green Bank Telescope toward the Sgr A region. The gas is mainly concentrated in 50 km s{sup -1} and 20 km s{sup -1} clouds located in a plane inclined to the galactic plane. These 'main' clouds appear to be virialized and influenced by the expansion of the supernova remnant Sgr A East. The observed emission shows very complicated features in the morphology and velocity structure. Gaussian multi-component fittings of the observed spectra revealed that various 'streaming' gas components exist all over the observed region. These components include thosemore » previously known as 'streamers' and 'ridges', but most of these components appear not to be directly connected to the major gas condensations (the 50 km s{sup -1} and 20 km s{sup -1} clouds). They are apparently located out of the galactic plane, and they may have a different origin than the major gas condensations. Some of the streaming components are expected to be sources that feed the circumnuclear disk of our Galactic center directly and episodically. They may also evolve differently than major gas condensations under the influence of the activities of the Galactic center.« less

Large-scale gas dynamical processes affecting the origin and evolution of gaseous galactic halos

NASA Technical Reports Server (NTRS)

Shapiro, Paul R.

1991-01-01

Observations of galactic halo gas are consistent with an interpretation in terms of the galactic fountain model in which supernova heated gas in the galactic disk escapes into the halo, radiatively cools and forms clouds which fall back to the disk. The results of a new study of several large-scale gas dynamical effects which are expected to occur in such a model for the origin and evolution of galactic halo gas will be summarized, including the following: (1) nonequilibrium absorption line and emission spectrum diagnostics for radiatively cooling halo gas in our own galaxy, as well the implications of such absorption line diagnostics for the origin of quasar absorption lines in galactic halo clouds of high redshift galaxies; (2) numerical MHD simulations and analytical analysis of large-scale explosions ad superbubbles in the galactic disk and halo; (3) numerical MHD simulations of halo cloud formation by thermal instability, with and without magnetic field; and (4) the effect of the galactic fountain on the galactic dynamo.

A Search for FRB 121102-like Persistent Radio-luminous Sources—Candidates and Implications for the FRB Rate and Searches

NASA Astrophysics Data System (ADS)

Ofek, Eran O.

2017-09-01

The localization of the repeating fast radio burst (FRB), FRB 121102, suggests that it is associated with a persistent radio-luminous compact source in the FRB host galaxy. Using the FIRST radio catalog, I present a search for luminous persistent sources in nearby galaxies, with radio luminosities > 10 % of the FRB 121102 persistent source luminosity. The galaxy sample contains about 30% of the total galaxy g-band luminosity within < 108 Mpc, in a footprint of 10,600 deg2. After rejecting sources likely due to active galactic nuclei activity or background sources, I am left with 11 candidates that are presumably associated with galactic disks or star-formation regions. At least some of these candidates are likely to be due to chance alignment. In addition, I find 85 sources within 1\\prime\\prime of galactic nuclei. Assuming that the radio persistent sources are not related to galactic nuclei and that they follow the galaxy g-band light, the 11 sources imply a 95% confidence upper limit on the space density of luminous persistent sources of ≲ 5× {10}-5 Mpc-3, and that at any given time only a small fraction of galaxies host a radio-luminous persistent source (≲ {10}-3 {L}* -1). Assuming a persistent source lifetime of 100 years, this implies a birth rate of ≲ 5× {10}-7 yr-1 Mpc-3. Given the FRB volumetric rate, and assuming that all FRBs repeat and are associated with persistent radio sources, this sets a lower limit on the rate of FRB events per persistent source of ≳ 0.8 yr-1. I argue that these 11 candidates are good targets for FRB searches and I estimate the FRB event rate from these candidates.

ORIGIN OF THE GALACTIC DIFFUSE X-RAY EMISSION: IRON K-SHELL LINE DIAGNOSTICS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nobukawa, Masayoshi; Uchiyama, Hideki; Nobukawa, Kumiko K.

This paper reports detailed K-shell line profiles of iron (Fe) and nickel (Ni) of the Galactic Center X-ray Emission (GCXE), Galactic Bulge X-ray Emission (GBXE), Galactic Ridge X-ray Emission (GRXE), magnetic Cataclysmic Variables (mCVs), non-magnetic Cataclysmic Variables (non-mCVs), and coronally Active Binaries (ABs). For the study of the origin of the GCXE, GBXE, and GRXE, the spectral analysis is focused on equivalent widths of the Fe i-K α , Fe xxv-He α , and Fe xxvi-Ly α  lines. The global spectrum of the GBXE is reproduced by a combination of the mCVs, non-mCVs, and ABs spectra. On the other hand,more » the GRXE spectrum shows significant data excesses at the Fe i-K α and Fe xxv-He α  line energies. This means that additional components other than mCVs, non-mCVs, and ABs are required, which have symbiotic phenomena of cold gas and very high-temperature plasma. The GCXE spectrum shows larger excesses than those found in the GRXE spectrum at all the K-shell lines of iron and nickel. Among them the largest ones are the Fe i-K α , Fe xxv-He α , Fe xxvi-Ly α , and Fe xxvi-Ly β  lines. Together with the fact that the scale heights of the Fe i-K α , Fe xxv-He α , and Fe xxvi-Ly α lines are similar to that of the central molecular zone (CMZ), the excess components would be related to high-energy activity in the extreme envelopment of the CMZ.« less

Habitability in the Local Universe

NASA Astrophysics Data System (ADS)

Mason, Paul A.

2017-01-01

Long term habitability on the surface of planets has as a prerequisite a minimum availability of elements to build rocky planets, their atmospheres, and for life sustaining water. They must be within the habitable zone and avoid circumstances that cause them to lose their atmospheres and water. However, many astrophysical sources are hazardous to life on the surfaces of planets. Planets in harsh environments may require strong magnetic fields to protect their biospheres from high energy particles from the host star(s). Planets in harsh environments may additionally require a strong astrosphere to be sufficiently able to deflect galactic cosmic-rays. Supernovae (SNe) play a central role in the habitability of planets in the disks of star forming galaxies. Currently, the SNe rate maintains a relativistic galactic wind shielding planets in the disk from extragalactic cosmic rays. However, if the density of SNe in the disk of the galaxy were significantly higher, as it was 6-8 GYA, the frequency of nearby catastrophic events and often prolonged harsh environment may have strongly constrained life in the early history of the Milky Way. Active galactic nuclei (AGN) may remain quiescent for hundreds of millions of years only to activate for some time due extraordinary accretion episode due to for instance a galactic merger. The starburst galaxy M82 is currently undergoing a merger, probably strongly compromising habitability within that galaxy. The giant elliptical M87 resides in the center of the Virgo supercluster and has probably consumed many such spiral galaxies. We show that super-Eddington accretion onto the supermassive black hole in M87, even for a short while, could compromise the habitability for a large portion of the central supercluster. We discuss environments where these effects may be mitigated.

Determining the nature of faint X-ray sources from the ASCA Galactic center survey

NASA Astrophysics Data System (ADS)

Lutovinov, A. A.; Revnivtsev, M. G.; Karasev, D. I.; Shimansky, V. V.; Burenin, R. A.; Bikmaev, I. F.; Vorob'ev, V. S.; Tsygankov, S. S.; Pavlinsky, M. N.

2015-05-01

We present the results of the the identification of six objects from the ASCA Galactic center and Galactic plane surveys: AX J173548-3207, AX J173628-3141, AX J1739.5-2910, AX J1740.4-2856, AX J1740.5-2937, and AX J1743.9-2846. Chandra, XMM-Newton, and XRT/Swift X-ray data have been used to improve the positions of the optical counterparts to these sources. Thereafter, we have carried out a series of spectroscopic observations of the established optical counterparts at the RTT-150 telescope. Analysis of X-ray and optical spectra as well as photometric measurements in a wide wavelength range based on optical and infrared catalogs has allowed the nature of the program sources to be determined. Two X-ray objects have been detected in the error circle of AX J173628-3141: one is a coronally active G star and the other may be a symbiotic star, a red giant with an accreting white dwarf. Three sources (AX J1739.5-2910, AX J1740.5-2937, AX J1743.9-2846) have turned out to be active G-K stars, presumably RS CVn objects, one (AX J1740.4-2856) is an M dwarf, and another one (AX J173548-3207) most likely a low-mass X-ray binary in its low state. The distances and corresponding luminosities of the sources in the soft X-ray band (0.5-10 keV) have been estimated; analysis of deep INTEGRAL Galactic center observations has not revealed a statistically significant flux at energies >20 keV from any of them.

Visibility of Active Galactic Nuclei in the Illustris Simulation

NASA Astrophysics Data System (ADS)

Hutchinson-Smith, Tenley; Kelley, Luke; Moreno, Jorge; Hernquist, Lars; Illustris Collaboration

2018-01-01

Active galactic nuclei (AGN) are the very bright, luminous regions surrounding supermassive black holes (SMBH) located at the centers of galaxies. Supermassive black holes are the source of AGN feedback, which occurs once the SMBH reaches a certain critical mass. Almost all large galaxies contain a SMBH, but SMBH binaries are extremely rare. Finding these binary systems are important because it can be a source of gravitational waves if the two SMBH collide. In order to study supermassive black holes, astronomers will often rely on the AGN’s light in order to locate them, but this can be difficult due to the extinction of light caused by the dust and gas surrounding the AGN. My research project focuses on determining the fraction of light we can observe from galactic centers using the Illustris simulation, one of the most advanced cosmological simulations of the universe which was created using a hydrodynamic code and consists of a moving mesh. Measuring the fraction of light observable from galactic centers will help us know what fraction of the time we can observe dual and binary AGN in different galaxies, which would also imply a binary SMBH system. In order to find how much light is being blocked or scattered by the gas and dust surrounding the AGN, we calculated the density of the gas and dust along the lines of sight. I present results including the density of gas along different lines of sight and how it correlates with the image of the galaxy. Future steps include taking an average of the column densities for all the galaxies in Illustris and studying them as a function of galaxy type (before merger, during merger, and post-merger), which will give us information on how this can also affect the AGN luminosity.

Five Years of the Fermi LAT Flare Advocate

NASA Astrophysics Data System (ADS)

Carpenter, Bryce; Ojha, R.; Gasparrini, D.; Ciprini, S.; Fermi LAT Collaboration; Fermi LAT Flare Advocates

2014-01-01

Since the launch of the Fermi satellite, the Fermi Large Area Telescope (LAT) team has run a program that provides a daily review of the the gamma-ray sky as soon as Fermi LAT data becomes available. The Flare Advocate/Gamma-ray Sky Watcher (FA-GSW) program allows a rapid analysis of the Automatic Science Processing (ASP) products and triggers dedicated followup analyses by several LAT science groups such as those studying Galactic transients, extragalactic sources and new gamma-ray sources. Significant gamma-ray detections also trigger rapid communications to the entire astrophysical community via astronomical telegrams and gamma-ray coordination network notices. The FA-GSW program plays a key role in maximizing the science return from Fermi by increasing the rate of multi-frequency observations of sources in an active gamma-ray state. In the past ~5 years blazar flaring activity of varying strength and duty cycles, gravitationally lensed blazars, flares from Galactic sources (like Nova Delphini and the Crab Nebula), unidentified transients near and off the Galactic plane, and emission from the quiet and flaring Sun, represent the range of detections made. Flare Advocates have published about 250 Astronomical Telegrams and they publish a weekly blog. Timely, extensive multi-frequency campaigns have been organized to follow-up on these phenomena leading to some of Fermi’s most interesting results.

Magnetic activity in the Galactic Centre region - fast downflows along rising magnetic loops

NASA Astrophysics Data System (ADS)

Kakiuchi, Kensuke; Suzuki, Takeru K.; Fukui, Yasuo; Torii, Kazufumi; Enokiya, Rei; Machida, Mami; Matsumoto, Ryoji

2018-06-01

We studied roles of the magnetic field on the gas dynamics in the Galactic bulge by a three-dimensional global magnetohydrodynamical simulation data, particularly focusing on vertical flows that are ubiquitously excited by magnetic activity. In local regions where the magnetic field is stronger, it is frequently seen that fast downflows slide along inclined magnetic field lines that are associated with buoyantly rising magnetic loops. The vertical velocity of these downflows reaches ˜100 km s-1 near the footpoint of the loops by the gravitational acceleration towards the Galactic plane. The two footpoints of rising magnetic loops are generally located at different radial locations and the field lines are deformed by the differential rotation. The angular momentum is transported along the field lines, and the radial force balance breaks down. As a result, a fast downflow is often observed only at the one footpoint located at the inner radial position. The fast downflow compresses the gas to form a dense region near the footpoint, which will be important in star formation afterwards. Furthermore, the horizontal components of the velocity are also fast near the footpoint because the downflow is accelerated along the magnetic sliding slope. As a result, the high-velocity flow creates various characteristic features in a simulated position-velocity diagram, depending on the viewing angle.

Cosmic-ray tracing

NASA Astrophysics Data System (ADS)

Becker Tjus, Julia

2018-04-01

Active galactic nuclei are firm favourites to be revealed as the source of cosmic rays, but solid evidence has proven elusive. A model taking both local and global nuclei propagation into account may help to close the deal.

Number density distribution of near-infrared sources on a sub-degree scale in the Galactic center: Comparison with the Fe XXV Kα line at 6.7 keV

NASA Astrophysics Data System (ADS)

Yasui, Kazuki; Nishiyama, Shogo; Yoshikawa, Tatsuhito; Nagatomo, Schun; Uchiyama, Hideki; Tsuru, Takeshi Go; Koyama, Katsuji; Tamura, Motohide; Kwon, Jungmi; Sugitani, Koji; Schödel, Rainer; Nagata, Tetsuya

2015-12-01

The stellar distribution derived from an H- and KS-band survey of the central region of our Galaxy is compared with the Fe XXV Kα (6.7 keV) line intensity observed with the Suzaku satellite. The survey is for the galactic coordinates |l| ≲ 3.0° and |b | ≲ 1.0° (equivalent to 0.8 kpc × 0.3 kpc for R⊙ = 8 kpc), and the number-density distribution N(KS,0; l, b) of stars is derived by using the extinction-corrected magnitude KS,0 = 10.5. This is deep enough to probe the old red-giant population and in turn to estimate the (l, b) distribution of faint X-ray point sources such as coronally active binaries and cataclysmic variables. In the Galactic plane (b = 0°), N(10.5; l, b) increases in the direction of the Galactic center as |l|-0.30±0.03 in the range of - 0.1° ≥ l ≥ - 0.7°, but this increase is significantly slower than the increase (|l|-0.44±0.02) of the Fe XXV Kα line intensity. If normalized with the ratios in the outer region 1.5° ≤ |l| ≤ 2.8°, where faint X-ray point sources are argued to dominate the diffuse Galactic X-ray ridge emission, the excess of the Fe XXV Kα line intensity over the stellar number density is at least a factor of two at |l| = 0.1°. This indicates that a significant part of the Galactic-center diffuse emission arises from a truly diffuse optically thin thermal plasma, and not from an unresolved collection of faint X-ray point sources related to the old stellar population.

GOT C+: A Herschel Space Observatory Key Program to Study the Diffuse ISM

NASA Astrophysics Data System (ADS)

Langer, William; Velusamy, T.; Goldsmith, P. F.; Li, D.; Pineda, J.; Yorke, H.

2010-01-01

Star formation activity is regulated by pressures in the interstellar medium, which in turn depend on heating and cooling rates, modulated by the gravitational potential, and shock and turbulent pressures. To understand these processes we need information about the diffuse atomic and diffuse molecular gas cloud properties. The ionized carbon CII fine structure line at 1.9 THz is an important tracer of the atomic gas in the diffuse regions and the atomic to molecular cloud transformation. Furthermore, C+ is a major ISM coolant, the Galaxy's strongest emission line, with a total luminosity about a 1000 times that of CO J=1-0. Galactic Observations of the Terahertz C+ Line (GOT C+) is a Herschel Space Observatory Open Time Key Program to study the diffuse interstellar medium by sampling CII line emission throughout the Galactic disk. GOT C+ will obtain high spectral resolution CII using the Heterodyne Instrument for the Far Infrared (HIFI) instrument. It employees deep integrations, wide velocity coverage (350 km s-1) with 0.22 km s-1 resolution, and systematic sparse sampling of the Galactic disk together with observations of selected targets, of over 900 lines of sight. It will be a resource of the atomic gas properties, in the (a) Galactic disk, (b) Galaxy's central 300pc, (c) Galactic warp, (d) high latitude HI clouds, and (e) Photon Dominated Regions (PDRs). Along with HI, CO isotopes, and CI spectra, our C+ data will provide the astronomical community with a rich statistical database of diffuse cloud properties, for understanding the role of barometric pressure and turbulence in cloud evolution in the Galactic ISM and, by extension, other galaxies. The GOT C+ project will provide a template for future even larger-scale CII surveys. This research was conducted at the Jet Propulsion Laboratory, California Institute of Technology and is supported by a NASA grant.

Adherence to Physical Activity from Childhood to Adulthood: A Perspective from Tracking Studies.

ERIC Educational Resources Information Center

Malina, Robert M.

2001-01-01

Considers the tracking of physical activity during childhood, adolescence, and adulthood in the context of adherence. Data generally show moderate tracking of physical activity during childhood and adolescence and more variable but lower tracking levels across longer intervals within adolescence and from adolescence into young adulthood. Various…

Nonthermal electron-positron pairs and cold matter in the central engines of active galactic nuclei

NASA Technical Reports Server (NTRS)

Zdziarski, Andrzej A.

1992-01-01

The nonthermal e(+/-) pair model of the central engine of active galactic nuclei (AGNs) is discussed. The model assumes that nonthermal e(+/-) pairs are accelerated to highly relativistic energies in a compact region close to the central black hole and in the vicinity of some cold matter. The model has a small number of free parameters and explains a large body of AGN observations from EUV to soft gamma-rays. In particular, the model explains the existence of the UV bump, the soft X-rays excess, the canonical hard X-ray power law, the spectral hardening above about 10 keV, and some of the variability patterns in the soft and hard X-rays. In addition, the model explains the spectral steepening above about 50 keV seen in NGC 4151.

Prediction of LDEF exposure to the ionizing radiation environment

NASA Technical Reports Server (NTRS)

Watts, J. W.; Armstrong, T. W.; Colborn, B. L.

1996-01-01

Predictions of the LDEF mission's trapped proton and electron and galactic cosmic ray proton exposures have been made using the currently accepted models with improved resolution near mission end and better modeling of solar cycle effects. An extension of previous calculations, to provide a more definitive description of the LDEF exposure to ionizing radiation, is represented by trapped proton and electron flux as a function of mission time, presented considering altitude and solar activity variation during the mission and the change in galactic cosmic ray proton flux over the mission. Modifications of the AP8MAX and AP8MIN fluence led to a reduction of fluence by 20%. A modified interpolation model developed by Daly and Evans resulted in 30% higher dose and activation levels, which better agreed with measured values than results predicted using the Vette model.

Electron-positron pairs, Compton reflection, and the X-ray spectra of active galactic nuclei

NASA Technical Reports Server (NTRS)

Zdziarski, Andrzej A.; Ghisellini, Gabriele; George, Ian M.; Fabian, A. C.; Svensson, Roland; Done, Chris

1990-01-01

It is shown here that reprocessing of radiation fron nonthermal pair cascades by cold material in the central parts of active galactic nuclei (AGN) gives rise to X-ray and gamma-ray spectra that satisfy current observational constraints. An average 1-30 keV X-ray spectral index alpha(x) of about 0.7 in the compact range 30-300 is obtained for a wide range of Lorentz factors of the injected electrons. The gamma-ray spectra are steep, with alpha(gamma) about two, and satisfy the observational constraints. Radiation from pair cascades exhibits steep power law decreases in soft X-rays similar to those observed in AGN. The overall picture is consistent with AGN having an accretion disk which intercepts and reprocesses a substantial fraction of the nonthermal continuum incident upon it from above and below.

The mineralogy of newly formed dust in active galactic nuclei

NASA Astrophysics Data System (ADS)

Srinivasan, Sundar; Kemper, F.; Zhou, Yeyan; Hao, Lei; Gallagher, Sarah C.; Shangguan, Jinyi; Ho, Luis C.; Xie, Yanxia; Scicluna, Peter; Foucaud, Sebastien; Peng, Rita H. T.

2017-12-01

The tori around active galactic nuclei (AGN) are potential formation sites for large amounts of dust, and they may help resolve the so-called dust budget crisis at high redshift. We investigate the dust composition in 53 of the 87 Palomar Green (PG) quasars showing the 9.7 μm silicate feature in emission. By simultaneously fitting the mid-infrared spectroscopic features and the underlying continuum, we estimate the mass fraction in various amorphous and crystalline dust species. We find that the dust consists predominantly of alumina and amorphous silicates, with a small fraction in crystalline form. The mean crystallinity is 8 ±6%, with more than half of the crystallinities greater than 5%, well above the upper limit determined for the Galaxy. Higher values of crystallinity are found for higher oxide fractions and for more luminous sources.

A long-term space astrophysics research program: An x-ray perspective of the components and structure of galaxies

NASA Technical Reports Server (NTRS)

Fabbiano, G.

1995-01-01

X-ray studies of galaxies by the Smithsonian Astrophysical Observatory (SAO) and MIT are described. Activities at SAO include ROSAT PSPC x-ray data reduction and analysis pipeline; x-ray sources in nearby Sc galaxies; optical, x-ray, and radio study of ongoing galactic merger; a radio, far infrared, optical, and x-ray study of the Sc galaxy NGC247; and a multiparametric analysis of the Einstein sample of early-type galaxies. Activities at MIT included continued analysis of observations with ROSAT and ASCA, and continued development of new approaches to spectral analysis with ASCA and AXAF. Also, a new method for characterizing structure in galactic clusters was developed and applied to ROSAT images of a large sample of clusters. An appendix contains preprints generated by the research.

Active Galactic Videos: A YouTube Channel for Astronomy Education and Outreach

NASA Astrophysics Data System (ADS)

Austin, Carmen; Calahan, Jenny; Resi Baucco, Alexandria; Bullivant, Christopher William; Eckley, Ross; Ekstrom, W. Haydon; Fitzpatrick, M. Ryleigh; Genovese, Taylor Fay; Impey, Chris David; Libby, Kaitlin; McCaw, Galen; Olmedo, Alexander N.; Ritter, Joshua; Wenger, Matthew; Williams, Stephanie

2017-01-01

Active Galactic Videos is an astronomy-focused YouTube channel run by a team at the University of Arizona. The channel has two main purposes: to produce educational content for public audiences, and to learn about astronomy and to open a window into the world of professional astronomy by showcasing the work done at Steward Observatory and in Southern Arizona. Our team consists of faculty, staff, and students from a variety of backgrounds including: astronomy, education, film, music, english, and writing. In addition to providing educational content for public audiences, this project provides opportunities for undergraduate students to learn about astronomy content, educational practice, and science communication while developing the practical skills needed to write, film, score, direct, and edit videos that effectively engage and teach viewers about topics in astronomy. The team has produced various styles of video: presentational, interviews, musical/poetic, and documentaries. In addition to YouTube, the Active Galactic Videos team maintains a social media presence on Facebook, Twitter, and Instagram. These help to widely distribute the content as well as to publicize the main Youtube channel. In addition to providing an overview of our educational work, this poster will present a year's worth of online analytics that we are using to better understand our audience, to examine what videos have been popular and successful and how people are accessing our content. We will present our experience in order to help others learn about improving astronomy education online, and astronomy communication and outreach in general.

A systematic study of the condensation of the corona and the application for Γ 2-10 keV-Lbol/LEdd correlation in luminous active galactic nuclei

NASA Astrophysics Data System (ADS)

Qiao, Erlin; Liu, B. F.

2018-06-01

In this paper, we explained the observed Γ _2-10 keV-L_bol/L_Edd correlation in luminous active galactic nuclei within the framework of the condensation of the corona around a supermassive black hole (Liu et al.; Qiao & Liu). Specifically, we systemically test the effects of black hole mass M, the viscosity parameter α, and the magnetic parameter β (with magnetic pressure p_m=B^2/{8π }=(1-β )p_tot, ptot = pgas + pm) on the structure of the accretion disc and the corona, as well as the corresponding emergent spectra. It is found that the hard X-ray photon index Γ _2-10 keV nearly does not change with changing black hole mass M, or changing magnetic parameter β. Meanwhile, it is found that the geometry of the accretion flow, i.e. the relative configuration of the disc and corona, as well as the emergent spectra can be strongly affected by changing the value of α. By comparing with a sample composed of 29 luminous active galactic nuclei with well constrained X-ray spectra and Eddington ratios, it is found that the observed Γ _2-10 keV-L_bol/L_Edd correlation can be well matched with a relatively bigger value of α, i.e. α ˜ 1, as previously also suggested by Narayan for luminous accreting black holes.

The 3 Ms Chandra campaign on Sgr A*: a census of X-ray flaring activity from the Galactic center

NASA Astrophysics Data System (ADS)

Neilsen, J.; Nowak, M. A.; Gammie, C.; Dexter, J.; Markoff, S.; Haggard, D.; Nayakshin, S.; Wang, Q. D.; Grosso, N.; Porquet, D.; Tomsick, J. A.; Degenaar, N.; Fragile, P. C.; Houck, J. C.; Wijnands, R.; Miller, J. M.; Baganoff, F. K.

2014-05-01

Over the last decade, X-ray observations of Sgr A* have revealed a black hole in a deep sleep, punctuated roughly once per day by brief flares. The extreme X-ray faintness of this supermassive black hole has been a long-standing puzzle in black hole accretion. To study the accretion processes in the Galactic center, Chandra (in concert with numerous ground- and space-based observatories) undertook a 3 Ms campaign on Sgr A* in 2012. With its excellent observing cadence, sensitivity, and spectral resolution, this Chandra X-ray Visionary Project (XVP) provides an unprecedented opportunity to study the behavior of the closest supermassive black hole. We present a progress report from our ongoing study of X-ray flares, including the brightest flare ever seen from Sgr A*. Focusing on the statistics of the flares and the quiescent emission, we discuss the physical implications of X-ray variability in the Galactic center.

The 3 megasecond Chandra campaign on Sgr A*: a census of x-ray flaring activity from the galactic center

NASA Astrophysics Data System (ADS)

Neilsen, Joey

Over the last decade, X-ray observations of Sgr A* have revealed a black hole in a deep sleep, punctuated roughly once per day by brief flares. The extreme X-ray faintness of this supermassive black hole has been a long-standing puzzle in black hole accretion. To study the accretion processes in the Galactic Center, Chandra (in concert with numerous ground- and space-based observatories) undertook a 3 Ms campaign on Sgr A* in 2012. With its excellent observing cadence, sensitivity, and spectral resolution, this Chandra X-ray Visionary Project (XVP) provides an unprecedented opportunity to study the behavior of our closest supermassive black hole. We present a progress report from our ongoing study of X-ray flares, including the brightest flare ever seen from Sgr A*. Focusing on the statistics of the flares, the quiescent emission, and the relationship between the X-ray and the infrared, we discuss the physical implications of X-ray variability in the Galactic Center.

STATISTICS OF GAMMA-RAY POINT SOURCES BELOW THE FERMI DETECTION LIMIT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malyshev, Dmitry; Hogg, David W., E-mail: dm137@nyu.edu

2011-09-10

An analytic relation between the statistics of photons in pixels and the number counts of multi-photon point sources is used to constrain the distribution of gamma-ray point sources below the Fermi detection limit at energies above 1 GeV and at latitudes below and above 30 deg. The derived source-count distribution is consistent with the distribution found by the Fermi Collaboration based on the first Fermi point-source catalog. In particular, we find that the contribution of resolved and unresolved active galactic nuclei (AGNs) to the total gamma-ray flux is below 20%-25%. In the best-fit model, the AGN-like point-source fraction is 17%more » {+-} 2%. Using the fact that the Galactic emission varies across the sky while the extragalactic diffuse emission is isotropic, we put a lower limit of 51% on Galactic diffuse emission and an upper limit of 32% on the contribution from extragalactic weak sources, such as star-forming galaxies. Possible systematic uncertainties are discussed.« less

Scientific Verification of Faraday Rotation Modulators: Detection of Diffuse Polarized Galactic Emission

NASA Technical Reports Server (NTRS)

Moyerman, S.; Bierman, E.; Ade, P. A. R.; Aiken, R.; Barkats, D.; Bischoff, C.; Bock, J. J.; Chiang, H. C.; Dowell, C. D.; Duband, L.;

The near-infrared counterpart of a variable galactic plane radio source

NASA Technical Reports Server (NTRS)

Margon, Bruce; Phillips, Andrew C.; Ciardullo, Robin; Jacoby, George H.

1992-01-01

A near-infrared counterpart to the highly variable, unresolved galactic plane radio source GT 0116 + 622 is identified. This source is of particular interest, as it has been previously suggested to be the counterpart of the gamma-ray source Cas gamma-l. The present NIR and red images detect a faint, spatially extended (3 arcsec FWHM), very red object coincident with the radio position. There is complex spatial structure which may be due in part to an unrelated superposed foreground object. Observations on multiple nights show no evidence for flux variability, despite the high amplitude variability on a time-scale of days reported for the radio source. The data are consistent with an interpretation of GT 0116 + 622 as an unusually variable, obscured active galaxy at a distance of several hundred megaparsecs, although more exotic, and in particular galactic, interpretations cannot yet be ruled out. If the object is extragalactic, the previously suggested identification with the gamma-ray source would seem unlikely.

Discovery of a Nonblazar Gamma-Ray Transient Source Near the Galactic Plane: GRO J1838-04

NASA Technical Reports Server (NTRS)

Tavani, M.; Oliversen, Ronald (Technical Monitor)

2001-01-01

We report the discovery of a remarkable gamma-ray transient source near the Galactic plane, GRO J1838-04. This source was serendipitously discovered by EGRET in 1995 June with a peak intensity of approx. (4 +/- 1) x 10(exp -6) photons/sq cm s (for photon energies larger than 100 MeV) and a 5.9 sigma significance. At that time, GRO J1838-04 was the second brightest gamma-ray source in the sky. A subsequent EGRET pointing in 1995 late September detected the source at a flux smaller than its peak value by a factor of approx. 7. We determine that no radio-loud spectrally flat blazar is within the error box of GRO J1838-04. We discuss the origin of the gamma-ray transient source and show that interpretations in terms of active galactic nuclei or isolated pulsars are highly problematic. GRO J1838-04 provides strong evidence for the existence of a new class of variable gamma-ray sources.

Cosmological evolution of supermassive black holes in galactic centers unveiled by hard X-ray observations

PubMed Central

UEDA, Yoshihiro

2015-01-01

We review the current understanding of the cosmological evolution of supermassive black holes in galactic centers elucidated by X-ray surveys of active galactic nuclei (AGNs). Hard X-ray observations at energies above 2 keV are the most efficient and complete tools to find “obscured” AGNs, which are dominant populations among all AGNs. Combinations of surveys with various flux limits and survey area have enabled us to determine the space number density and obscuration properties of AGNs as a function of luminosity and redshift. The results have essentially solved the origin of the X-ray background in the energy band below ∼10 keV. The downsizing (or anti-hierarchical) evolution that more luminous AGNs have the space-density peak at higher redshifts has been discovered, challenging theories of galaxy and black hole formation. Finally, we summarize unresolved issues on AGN evolution and prospects for future X-ray missions. PMID:25971656

Primary cosmic rays on the lunar surface

NASA Technical Reports Server (NTRS)

Vernov, S. N.; Lavrukhina, A. K.

1977-01-01

Results are reported for determination of the galactic cosmic ray flux during various time intervals in the 1965-1972 period, on the basis of data from the instruments of a spacecraft that made a soft landing on the lunar surface, and from the radioactivity of samples returned by the spacecraft. During minimum solar activity (the second half of 1965 and the beginning of 1966) I sub 0 (E greater than or equal to 30 percent MeV/nucleon) was determined to be 0.43 (plus or minus 10 percent). These values, within the error limits of the determinations, agree with the corresponding values of galactic cosmic ray intensities determined by stratospheric measurements. The mean flux of galactic cosmic rays over the past million years is equal to I (E greater or equal to 100 MeV/nucleon) + 0.28 (plus or minus 20 percent). This value agrees with the mean flux of modulated cosmic rays during the period of the nineteenth solar cycle. The mean flux of solar protons between 1965 and 1972 was 2.46.

The 3 Megasecond Chandra Campaign on Sgr A*: A Census of X-ray Flaring Activity from the Galactic Center

NASA Astrophysics Data System (ADS)

Neilsen, Joseph; Nowak, Michael; Gammie, Charles F.; Dexter, Jason; Markoff, Sera; Haggard, Daryl; Nayakshin, Sergei; Wang, Q. Daniel; Grosso, N.; Porquet, D.; Tomsick, John; Degenaar, Nathalie; Fragile, P. Christopher; Houck, John C.; Wijnands, Rudy; Miller, Jon M.; Baganoff, Frederick K.

2014-08-01

Over the last decade, X-ray observations of Sgr A* have revealed a black hole in a deep sleep, punctuated roughly once per day by brief ares. The extreme X-ray faintness of this supermassive black hole has been a long-standing puzzle in black hole accretion. To study the accretion processes in the Galactic Center, Chandra (in concert with numerous ground- and space-based observatories) undertook a 3 Ms campaign on Sgr A* in 2012. With its excellent observing cadence, sensitivity, and spectral resolution, this Chandra X-ray Visionary Project (XVP) provides an unprecedented opportunity to study the behavior of our closest supermassive black hole. We present a progress report from our ongoing study of X-ray flares, including one of the brightest flares ever seen from Sgr A*. Focusing on the statistics of the flares, the quiescent emission, and the relationship between the X-ray and the infrared, we discuss the physical implications of X-ray variability in the Galactic Center.

The structure and content of the galaxy and galactic gamma rays. [conferences

NASA Technical Reports Server (NTRS)

Fichtel, C. E.; Stecker, F. W.

1976-01-01

Papers are presented dealing with galactic structure drawing on all branches of galactic astronomy with emphasis on the implications of the new gamma ray observations. Topics discussed include: (1) results from the COS-B gamma ray satellite; (2) results from SAS-2 on gamma ray pulsar, Cygnus X-3, and maps of the galactic diffuse flux; (3) recent data from CO surveys of the galaxy; (4) high resolution radio surveys of external galaxies; (5) results on the galactic distribution of pulsars; and (6) theoretical work on galactic gamma ray emission.

Comparison of home and away-from-home physical activity using accelerometers and cellular network-based tracking devices.

PubMed

Ramulu, Pradeep Y; Chan, Emilie S; Loyd, Tara L; Ferrucci, Luigi; Friedman, David S

2012-08-01

Measuring physical at home and away from home is essential for assessing health and well-being, and could help design interventions to increase physical activity. Here, we describe how physical activity at home and away from home can be quantified by combining information from cellular network-based tracking devices and accelerometers. Thirty-five working adults wore a cellular network-based tracking device and an accelerometer for 6 consecutive days and logged their travel away from home. Performance of the tracking device was determined using the travel log for reference. Tracking device and accelerometer data were merged to compare physical activity at home and away from home. The tracking device detected 98.6% of all away-from-home excursions, accurately measured time away from home and demonstrated few prolonged signal drop-out periods. Most physical activity took place away from home on weekdays, but not on weekends. Subjects were more physically active per unit of time while away from home, particularly on weekends. Cellular network-based tracking devices represent an alternative to global positioning systems for tracking location, and provide information easily integrated with accelerometers to determine where physical activity takes place. Promoting greater time spent away from home may increase physical activity.

Initiation-promotion model of tumor prevalence in mice from space radiation exposures

NASA Technical Reports Server (NTRS)

Cucinotta, F. A.; Wilson, J. W.

1995-01-01

Exposures in space consist of low-level background components from galactic cosmic rays (GCR), occasional intense-energetic solar-particle events, periodic passes through geomagnetic-trapped radiation, and exposure from possible onboard nuclear-propulsion engines. Risk models for astronaut exposure from such diverse components and modalities must be developed to assure adequate protection in future NASA missions. The low-level background exposures (GCR), including relativistic heavy ions (HZE), will be the ultimate limiting factor for astronaut career exposure. We consider herein a two-mutation, initiation-promotion, radiation-carcinogenesis model in mice in which the initiation stage is represented by a linear kinetics model of cellular repair/misrepair, including the track-structure model for heavy ion action cross-sections. The model is validated by comparison with the harderian gland tumor experiments of Alpen et al. for various ion beams. We apply the initiation-promotion model to exposures from galactic cosmic rays, using models of the cosmic-ray environment and heavy ion transport, and consider the effects of the age of the mice prior to and after the exposure and of the length of time in space on predictions of relative risk. Our results indicate that biophysical models of age-dependent radiation hazard will provide a better understanding of GCR risk than models that rely strictly on estimates of the initial slopes of these radiations.

Imprints to the terrestrial environment at galactic arm crossings of the solar system

NASA Astrophysics Data System (ADS)

Fahr, H. J.; Fichtner, H.; Scherer, K.; Stawicki, O.

At its itinerary through our milky way galaxy the solar system moves through highly variable interstellar environments. Due to its orbital revolution around the galactic center, the solar system also crosses periodically the spiral arms of our galactic plane and thereby expe riences pronounced enviromental changes. Gas densities, magnetic fields and galactic cosmic ray intensities are substantially higher there compared to interarm conditions. Here we present theoretical calculations describing the SN-averaged galactic cosmic ray spectrum for regions inside and outside of galactic arms which then allow to predict how periodic passages of the solar system through galactic arms should be reflected by enhanced particle irradiations of the earth`s atmosphere and by correlated terrestrial Be-10 production rates.

Observations and analysis activities of the International Ultraviolet Explorer satellite telescope

NASA Technical Reports Server (NTRS)

Shull, J. Michael

1996-01-01

The funds from this grant were used to support observations and analysis with the International Ultraviolet Explorer (IUE) satellite telescope. The main area of scientific research concerned the variability analyses of ultraviolet spectra of Active Galactic Nuclei, primarily quasars, Seyfert galaxies, and BL Lacertae objects. The Colorado group included, at various times, the P.I. (J.M. Shull), Research Associate Dr. Rick Edelson, and graduate students Jon Saken, Elise Sachs, and Steve Penton. A portion of the work was also performed by CU undergraduate student Cheong-ming Fu. A major product of the effort was a database of all IUE spectra of active galactic nuclei. This database is being analyzed to obtain spectral indices, line fluxes, and continuum fluxes for over 500 AGN. As a by-product of this project, we implemented a new, improved technique of spectral extraction of IUE spectra, which has been used in several AGN-WATCH campaigns (on the Seyfert galaxy NGC 4151 and on the BL Lac object PKS 2155-304).

A study of the kinematic dynamo equation with time-dependent coefficients

NASA Technical Reports Server (NTRS)

Ko, Chung-Ming

1990-01-01

During an active star formation epoch the interstellar medium of a galaxy is in a hyperactive state, and the average turbulent velocity is higher than in the long periods between star formation epochs. The galactic magnetic field generated by dynamo action depends strongly on the turbulent velocity, so that generation of magnetic field should vary with star formation activity. This paper is a preliminary study of the kinematic dynamo equation with time-dependent coefficients simulating the time dependence of the star formation activities. Ko and Parker argued in a simple model that the thickness of the dynamo region is the most sensitive dynamo parameter. The present work shows that the effect of inflating the galactic disk suddenly is to transform a stationary magnetic field into a growing field while keeping the profile more or less intact. Plane wave solutions for a dynamo with power-law time-dependent parameters show that the field may decay first and then grow, and vice versa, which is quite different from a constant parameter dynamo.

Multiwavelength Challenges in the Fermi Era

NASA Technical Reports Server (NTRS)

Thompson, D. J.

2010-01-01

The gamma-ray surveys of the sky by AGILE and the Fermi Gamma-ray Space Telescope offer both opportunities and challenges for multiwavelength and multi-messenger studies. Gamma-ray bursts, pulsars, binary sources, flaring Active Galactic Nuclei, and Galactic transient sources are all phenomena that can best be studied with a wide variety of instruments simultaneously or contemporaneously. From the gamma-ray side, a principal challenge is the latency from the time of an astrophysical event to the recognition of this event in the data. Obtaining quick and complete multiwavelength coverage of gamma-ray sources of interest can be difficult both in terms of logistics and in terms of generating scientific interest.

Particle acceleration, transport and turbulence in cosmic and heliospheric physics

NASA Technical Reports Server (NTRS)

Matthaeus, W.

1992-01-01

In this progress report, the long term goals, recent scientific progress, and organizational activities are described. The scientific focus of this annual report is in three areas: first, the physics of particle acceleration and transport, including heliospheric modulation and transport, shock acceleration and galactic propagation and reacceleration of cosmic rays; second, the development of theories of the interaction of turbulence and large scale plasma and magnetic field structures, as in winds and shocks; third, the elucidation of the nature of magnetohydrodynamic turbulence processes and the role such turbulence processes might play in heliospheric, galactic, cosmic ray physics, and other space physics applications.

Linear perturbation theory for tidal streams and the small-scale CDM power spectrum

NASA Astrophysics Data System (ADS)

Bovy, Jo; Erkal, Denis; Sanders, Jason L.

2017-04-01

Tidal streams in the Milky Way are sensitive probes of the population of low-mass dark matter subhaloes predicted in cold dark matter (CDM) simulations. We present a new calculus for computing the effect of subhalo fly-bys on cold streams based on the action-angle representation of streams. The heart of this calculus is a line-of-parallel-angle approach that calculates the perturbed distribution function of a stream segment by undoing the effect of all relevant impacts. This approach allows one to compute the perturbed stream density and track in any coordinate system in minutes for realizations of the subhalo distribution down to 105 M⊙, accounting for the stream's internal dispersion and overlapping impacts. We study the statistical properties of density and track fluctuations with large suites of simulations of the effect of subhalo fly-bys. The one-dimensional density and track power spectra along the stream trace the subhalo mass function, with higher mass subhaloes producing power only on large scales, while lower mass subhaloes cause structure on smaller scales. We also find significant density and track bispectra that are observationally accessible. We further demonstrate that different projections of the track all reflect the same pattern of perturbations, facilitating their observational measurement. We apply this formalism to data for the Pal 5 stream and make a first rigorous determination of 10^{+11}_{-6} dark matter subhaloes with masses between 106.5 and 109 M⊙ within 20 kpc from the Galactic centre [corresponding to 1.4^{+1.6}_{-0.9} times the number predicted by CDM-only simulations or to fsub(r < 20 kpc) ≈ 0.2 per cent] assuming that the Pal 5 stream is 5 Gyr old. Improved data will allow measurements of the subhalo mass function down to 105 M⊙, thus definitively testing whether dark matter is clumpy on the smallest scales relevant for galaxy formation.

Radiation Measured with Different Dosimeters for ISS-Expedition 18-19/ULF2 on Board International Space Station during Solar Minimum

NASA Technical Reports Server (NTRS)

Zhou, Dazhuang; Gaza, R.; Roed, Y.; Semones, E.; Lee, K.; Steenburgh, R.; Johnson, S.; Flanders, J.; Zapp, N.

2010-01-01

Radiation field of particles in low Earth orbit (LEO) is mainly composed of galactic cosmic rays (GCR), solar energetic particles and particles in SAA (South Atlantic Anomaly). GCR are modulated by solar activity, at the period of solar minimum activity, GCR intensity is at maximum and the main contributor for space radiation is GCR. At present for space radiation measurements conducted by JSC (Johnson Space Center) SRAG (Space Radiation Analysis Group), the preferred active dosimeter sensitive to all LET (Linear Energy Transfer) is the tissue equivalent proportional counter (TEPC); the preferred passive dosimeters are thermoluminescence dosimeters (TLDs) and optically stimulated luminescence dosimeters (OSLDs) sensitive to low LET as well as CR-39 plastic nuclear track detectors (PNTDs) sensitive to high LET. For the method using passive dosimeters, radiation quantities for all LET can be obtained by combining radiation results measured with TLDs/OSLDs and CR-39 PNTDs. TEPC, TLDs/OSLDs and CR-39 detectors were used to measure the radiation field for the ISS (International Space Station) - Expedition 18-19/ULF2 space mission which was conducted from 15 November 2008 to 31 July 2009 - near the period of the recent solar minimum activity. LET spectra (differential and integral fluence, absorbed dose and dose equivalent) and radiation quantities were measured for positions TEPC, TESS (Temporary Sleeping Station, inside the polyethylene lined sleep station), SM-P 327 and 442 (Service Module - Panel 327 and 442). This paper presents radiation LET spectra measured with TEPC and CR-39 PNTDs and radiation dose measured with TLDs/OSLDs as well as the radiation quantities combined from results measured with passive dosimeters.

NASA Radiation Track Image GUI for Assessing Space Radiation Biological Effects

NASA Technical Reports Server (NTRS)

Ponomarev, Artem L.; Cucinotta, Francis A.

2006-01-01

The high-charge high-energy (HZE) ion components of the galactic cosmic rays when compared to terrestrial forms of radiations present unique challenges to biological systems. In this paper we present a deoxyribonucleic acid (DNA) breakage model to visualize and analyze the impact of chromatin domains and DNA loops on clustering of DNA damage from X rays, protons, and HZE ions. Our model of DNA breakage is based on a stochastic process of DNA double-strand break (DSB) formulation that includes the amorphous model of the radiation track and a polymer model of DNA packed in the cell nucleus. Our model is a Monte-Carlo simulation based on a randomly located DSB cluster formulation that accomodates both high- and low-linear energy transfer radiations. We demonstrate that HZE ions have a strong impact on DSB clustering, both along the chromosome length and in the nucleus volume. The effects of chromosomal domains and DNA loops on the DSB fragment-size distribution and the spatial distribution of DSB in the nucleus were studied. We compare our model predictions with the spatial distribution of DSB obtained from experiments. The implications of our model predictions for radiation protection are discussed.

Subaru Telescope, Hawaii

NASA Astrophysics Data System (ADS)

Murdin, P.

2000-11-01

The Subaru Telescope, Hawaii is an 8.2 m aperture optical infrared telescope being operated by the NATIONAL ASTRONOMICAL OBSERVATORY, JAPAN (NAOJ) atop Mauna Kea, Hawaii. It is one of the new-generation telescopes with an actively controlled large monolithic mirror, and has been producing testing-phase observational results on solar system, star formation, active galactic nuclei and quasars, grou...

X-rays From Quasars and Active Galaxies

NASA Technical Reports Server (NTRS)

Lightman, Alan P.

1981-01-01

Features of quasars and active galactic nuclei are discussed and include: the nature of the power source, the radiation processes, and the mechanism for the formation and collimation of long-lived jets of matter observed to emanate from the center of these of these objects. The phenomena that produce X-rays are highlighted.

TANAMI: Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry. II. Additional sources

NASA Astrophysics Data System (ADS)

Müller, C.; Kadler, M.; Ojha, R.; Schulz, R.; Trüstedt, J.; Edwards, P. G.; Ros, E.; Carpenter, B.; Angioni, R.; Blanchard, J.; Böck, M.; Burd, P. R.; Dörr, M.; Dutka, M. S.; Eberl, T.; Gulyaev, S.; Hase, H.; Horiuchi, S.; Katz, U.; Krauß, F.; Lovell, J. E. J.; Natusch, T.; Nesci, R.; Phillips, C.; Plötz, C.; Pursimo, T.; Quick, J. F. H.; Stevens, J.; Thompson, D. J.; Tingay, S. J.; Tzioumis, A. K.; Weston, S.; Wilms, J.; Zensus, J. A.

2018-02-01

Context. TANAMI is a multiwavelength program monitoring active galactic nuclei (AGN) south of - 30° declination including high-resolution very long baseline interferometry (VLBI) imaging, radio, optical/UV, X-ray, and γ-ray studies. We have previously published first-epoch8.4 GHz VLBI images of the parsec-scale structure of the initial sample. In this paper, we present images of 39 additional sources. The full sample comprises most of the radio- and γ-ray brightest AGN in the southern quarter of the sky, overlapping with the region from which high-energy (> 100 TeV) neutrino events have been found. Aims: We characterize the parsec-scale radio properties of the jets and compare them with the quasi-simultaneous Fermi/LAT γ-ray data. Furthermore, we study the jet properties of sources which are in positional coincidence with high-energy neutrino events compared to the full sample. We test the positional agreement of high-energy neutrino events with various AGN samples. Methods: TANAMI VLBI observations at 8.4 GHz are made with southern hemisphere radio telescopes located in Australia, Antarctica, Chile, New Zealand, and South Africa. Results: Our observations yield the first images of many jets below - 30° declination at milliarcsecond resolution. We find that γ-ray loud TANAMI sources tend to be more compact on parsec-scales and have higher core brightness temperatures than γ-ray faint jets, indicating higher Doppler factors. No significant structural difference is found between sources in positional coincidence with high-energy neutrino events and other TANAMI jets. The 22 γ-ray brightest AGN in the TANAMI sky show only a weak positional agreement with high-energy neutrinos demonstrating that the > 100 TeV IceCube signal is not simply dominated by a small number of the γ-ray brightest blazars. Instead, a larger number of sources have to contribute to the signal with each individual source having only a small Poisson probability for producing an event in multi-year integrations of current neutrino detectors. The cleaned VLBI images displayed in Figs. 1, 2 and A.1 (FITS files) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/610/A1

HIREGS observations of the Galactic center and Galactic plane: Separation of the diffuse Galactic hard X-ray continuum from the point source spectra

NASA Technical Reports Server (NTRS)

Boggs, S. E.; Lin, R. P.; Coburn, W.; Feffer, P.; Pelling, R. M.; Schroeder, P.; Slassi-Sennou, S.

1997-01-01

The balloon-borne high resolution gamma ray and X-ray germanium spectrometer (HIREGS) was used to observe the Galactic center and two positions along the Galactic plane from Antarctica in January 1995. For its flight, the collimators were configured to measure the Galactic diffuse hard X-ray continuum between 20 and 200 keV by directly measuring the point source contributions to the wide field of view flux for subtraction. The hard X-ray spectra of GX 1+4 and GRO J1655-40 were measured with the diffuse continuum subtracted off. The analysis technique for source separation is discussed and the preliminary separated spectra for these point sources and the Galactic diffuse emission are presented.

X-Ray Reprocessing in Active Galactic Nuclei

NASA Technical Reports Server (NTRS)

Begelman, Mitchell C.

2004-01-01

This is the final report for research entitled "X-ray reprocessing in active galactic nuclei," into X-ray absorption and emission in various classes of active galaxy via X-ray spectral signatures. The fundamental goal of the research was to use these signatures as probes of the central engine structure and circumnuclear environment of active galactic nuclei. The most important accomplishment supported by this grant involved the detailed analysis and interpretation of the XMM data for the bright Seyfert 1 galaxy MCG-6-30-15. This work was performed by Drs. Christopher Reynolds and Mitchell Begelman in collaboration with Dr. Jorn Wilms (University of Tubingen, Germany; PI of the XMM observation) and other European scientists. With XMM we obtained medium resolution X-ray spectra of unprecedented quality for this Seyfert galaxy. Modeling the X-ray spectrum within the framework of accretion disk reflection models produced the first evidence for energy extraction from the spin of a black hole. Specifically, we found that the extreme gravitational redshifts required to explain the X-ray spectrum suggests that the bulk of the energy dissipation is concentrated very close to the black hole, in contrast with the expectations of any pure accretion disk model. In a second paper we addressed the low- energy spectral complexity and used RXTE specta to pin down the high-energy spectral index, thus firming up our initial interpretation. Additionally, we carried out detailed spectral and variability analyses of a number of Seyfert and radio galaxies (e.g., NGC 5548 and 3C 111) and developed general techniques that will be useful in performing X-ray reverberation mapping of accretion disks in AGN, once adequate data becomes available. A list of papers supported by this research is included.

Galactic bulge preferred over dark matter for the Galactic centre gamma-ray excess

NASA Astrophysics Data System (ADS)

Macias, Oscar; Gordon, Chris; Crocker, Roland M.; Coleman, Brendan; Paterson, Dylan; Horiuchi, Shunsaku; Pohl, Martin

2018-05-01

An anomalous gamma-ray excess emission has been found in the Fermi Large Area Telescope data1 covering the centre of the Galaxy2,3. Several theories have been proposed for this `Galactic centre excess'. They include self-annihilation of dark-matter particles4, an unresolved population of millisecond pulsars5, an unresolved population of young pulsars6, or a series of burst events7. Here, we report on an analysis that exploits hydrodynamical modelling to register the position of interstellar gas associated with diffuse Galactic gamma-ray emission. We find evidence that the Galactic centre excess gamma rays are statistically better described by the stellar over-density in the Galactic bulge and the nuclear stellar bulge, rather than a spherical excess. Given its non-spherical nature, we argue that the Galactic centre excess is not a dark-matter phenomenon but rather associated with the stellar population of the Galactic bulge and the nuclear bulge.

The Evolution of the Globular Cluster System in a Triaxial Galaxy: Can a Galactic Nucleus Form by Globular Cluster Capture?

NASA Astrophysics Data System (ADS)

Capuzzo-Dolcetta, Roberto

1993-10-01

Among the possible phenomena inducing evolution of the globular cluster system in an elliptical galaxy, dynamical friction due to field stars and tidal disruption caused by a central nucleus is of crucial importance. The aim of this paper is the study of the evolution of the globular cluster system in a triaxial galaxy in the presence of these phenomena. In particular, the possibility is examined that some galactic nuclei have been formed by frictionally decayed globular clusters moving in a triaxial potential. We find that the initial rapid growth of the nucleus, due mainly to massive clusters on box orbits falling in a short time scale into the galactic center, is later slowed by tidal disruption induced by the nucleus itself on less massive clusters in the way described by Ostriker, Binney, and Saha. The efficiency of dynamical friction is such to carry to the center of the galaxy enough globular cluster mass available to form a compact nucleus, but the actual modes and results of cluster-cluster encounters in the central potential well are complicated phenomena which remains to be investigated. The mass of the resulting nucleus is determined by the mutual feedback of the described processes, together with the initial spatial, velocity, and mass distributions of the globular cluster family. The effect on the system mass function is studied, showing the development of a low- and high-mass turnover even with an initially flat mass function. Moreover, in this paper is discussed the possibility that the globular cluster fall to the galactic center has been a cause of primordial violent galactic activity. An application of the model to M31 is presented.

Does controlling for biological maturity improve physical activity tracking?

PubMed

Erlandson, Marta C; Sherar, Lauren B; Mosewich, Amber D; Kowalski, Kent C; Bailey, Donald A; Baxter-Jones, Adam D G

2011-05-01

Tracking of physical activity through childhood and adolescence tends to be low. Variation in the timing of biological maturation within youth of the same chronological age (CA) might affect participation in physical activity and may partially explain the low tracking. To examine the stability of physical activity over time from childhood to late adolescence when aligned on CA and biological age (BA). A total of 91 males and 96 females aged 8-15 yr from the Saskatchewan Pediatric Bone Mineral Accrual Study (PBMAS) were assessed annually for 8 yr. BA was calculated as years from age at peak height velocity. Physical activity was assessed using the Physical Activity Questionnaire for Children/Adolescents. Tracking was analyzed using intraclass correlations for both CA and BA (2-yr groupings). To be included in the analysis, an individual required a measure at both time points within an interval; however, not all individuals were present at all tracking intervals. Physical activity tracking by CA 2-yr intervals were, in general, moderate in males (r=0.42-0.59) and females (r=0.43-0.44). However, the 9- to 11-yr CA interval was low and nonsignificant (r=0.23-0.30). Likewise, tracking of physical activity by BA 2-yr intervals was moderate to high in males (r=0.44-0.60) and females (r=0.39-0.62). Accounting for differences in the timing of biological maturity had little effect on tracking physical activity. However, point estimates for tracking are higher in early adolescence in males and to a greater extent in females when aligned by BA versus CA. This suggests that maturity may be more important in physical activity participation in females than males. © 2011 by the American College of Sports Medicine

Theory of active galactic nuclei

NASA Technical Reports Server (NTRS)

Shields, G. A.

1986-01-01

The involvement of accretion disks around supermassive black holes in the theory of active galactic nuclei (AGN) is discussed. The physics of thin and thick accretion disks is discussed and the partition between thermal and nonthermal energy production in supermassive disks is seen as uncertain. The thermal limit cycle may operate in supermassive disks (Shields, 1985), with accumulation of gas in the disk for periods of 10 to the 4th to 10 to the 7th years, punctuated by briefer outbursts during which the mass is rapidly transferred to smaller radii. An extended X-ray source in AGN is consistent with observations (Tennant and Mushotsky, 1983), and a large wind mass loss rate exceeding the central accretion rate means that only a fraction of the mass entering the disk will reach the central object; the rest being lost to the wind. Controversy in the relationship between the broad lines and the disk is also discussed.

On the X-Ray Low- and High-Velocity Outflows in Active Galactic Nuclei

NASA Technical Reports Server (NTRS)

Ramirez, J. M.; Tombesi, F.

2012-01-01

An exploration of the relationship between bolometric luminosity and outflow velocity for two classes of X-ray outflows in a large sample of active galactic nuclei has been performed. We find that line radiation pressure could be one physical mechanism that might accelerate the gas we observe in warm absorber, v approx. 100-1000 km/s, and on comparable but less stringent grounds the ultrafast outflows, v approx. 0.03-0.3c. If comparable with the escape velocity of the system, the first is naturally located at distances of the dusty torus, '" I pc, and the second at subparsec scales, approx.0.01 pc, in accordance with large set of observational evidence existing in the literature. The presentation of this relationship might give us key clues for our understanding of the different physical mechanisms acting in the centre of galaxies, the feedback process and its impact on the evolution of the host galaxy.

A Relation between the Mid-Infrared [Ne v] 14.3 Micrometers and [Ne III] 15.6 Micrometer Lines in Active Galactic Nuclei

NASA Technical Reports Server (NTRS)

Gorjian, V.; Cleary, K.; Werner, M. W.; Lawrence, C. R.

2007-01-01

We present a strong correlation between the [Ne v] 14.3 mm and [Ne III] 15.6 mm emission lines arising from the narrow-line regions (NLRs) of active galactic nuclei (AGNs), spanning 4 orders of magnitude in luminosity. The data are compiled primarily from Spitzer Space Telescope observations of nearby Seyfert galaxies (median z p 0.01) and 3C radio sources (median z p 0.52). This correlation is consistent with earlier studies in the optical/UV bands showing that line ratios arising in the NLRs are remarkably constant across AGNs. We also show that the correlation allows only a very narrow range in ionization parameter for simple photoionization models. The observed correlation will place tight constraints on alternative models, which predict constant line ratios over a broader range in ionization parameter.

Black hole feeding and feedback: the physics inside the `sub-grid'

NASA Astrophysics Data System (ADS)

Negri, A.; Volonteri, M.

2017-05-01

Black holes (BHs) are believed to be a key ingredient of galaxy formation. However, the galaxy-BH interplay is challenging to study due to the large dynamical range and complex physics involved. As a consequence, hydrodynamical cosmological simulations normally adopt sub-grid models to track the unresolved physical processes, in particular BH accretion; usually the spatial scale where the BH dominates the hydrodynamical processes (the Bondi radius) is unresolved, and an approximate Bondi-Hoyle accretion rate is used to estimate the growth of the BH. By comparing hydrodynamical simulations at different resolutions (300, 30, 3 pc) using a Bondi-Hoyle approximation to sub-parsec runs with non-parametrized accretion, our aim is to probe how well an approximated Bondi accretion is able to capture the BH accretion physics and the subsequent feedback on the galaxy. We analyse an isolated galaxy simulation that includes cooling, star formation, Type Ia and Type II supernovae, BH accretion and active galactic nuclei feedback (radiation pressure, Compton heating/cooling) where mass, momentum and energy are deposited in the interstellar medium through conical winds. We find that on average the approximated Bondi formalism can lead to both over- and underestimations of the BH growth, depending on resolution and on how the variables entering into the Bondi-Hoyle formalism are calculated.

A NEW ELECTRON-DENSITY MODEL FOR ESTIMATION OF PULSAR AND FRB DISTANCES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yao, J. M.; Wang, N.; Manchester, R. N.

2017-01-20

We present a new model for the distribution of free electrons in the Galaxy, the Magellanic Clouds, and the intergalactic medium (IGM) that can be used to estimate distances to real or simulated pulsars and fast radio bursts (FRBs) based on their dispersion measure (DM). The Galactic model has an extended thick disk representing the so-called warm interstellar medium, a thin disk representing the Galactic molecular ring, spiral arms based on a recent fit to Galactic H ii regions, a Galactic Center disk, and seven local features including the Gum Nebula, Galactic Loop I, and the Local Bubble. An offsetmore » of the Sun from the Galactic plane and a warp of the outer Galactic disk are included in the model. Parameters of the Galactic model are determined by fitting to 189 pulsars with independently determined distances and DMs. Simple models are used for the Magellanic Clouds and the IGM. Galactic model distances are within the uncertainty range for 86 of the 189 independently determined distances and within 20% of the nearest limit for a further 38 pulsars. We estimate that 95% of predicted Galactic pulsar distances will have a relative error of less than a factor of 0.9. The predictions of YMW16 are compared to those of the TC93 and NE2001 models showing that YMW16 performs significantly better on all measures. Timescales for pulse broadening due to interstellar scattering are estimated for (real or simulated) Galactic and Magellanic Cloud pulsars and FRBs.« less

Resonance Trapping in the Galactic Disc and Halo and its Relation with Moving Groups

NASA Astrophysics Data System (ADS)

Pichardo, Barbara; Moreno, Edmundo; william, schuster B.

2015-08-01

With the use of a detailed Milky Way nonaxisymmetric potential, observationally and dynamically constrained, the eects of the bar and the spiral arms in the Galaxy are studied in the disc and in the stellar halo. Especially the trapping of stars in the disk and Galactic halo by resonances on the Galactic plane created by the Galactic bar has been analysed in detail. To this purpose, a new method is presented to delineate the trapping regions using empirical diagrams of some orbital properties obtained in the Galactic potential. In these diagrams we plot in the inertial Galactic frame a characteristic orbital energy versus a characteristic orbital angular momentum, or versus the orbital Jacobi constant in the reference frame of the bar, when this is the only nonaxisymmetric component in the Galactic potential. With these diagrams some trapping regions are obtained in the disc and halo using a sample of disc stars and halo stars in the solar neighborhood. We compute several families of periodic orbits on the Galactic plane, some associated with this resonant trapping. In particular, we nd that the trapping eect of these resonances on the Galactic plane can extend some kpc from this plane, trapping stars in the Galactic halo. The purpose of our analysis is to investigate if the trapping regions contain some known moving groups in our Galaxy. We have applied our method to the Kapteyn group, a moving group in the halo, and we have found that this group appears not to be associated with a particular resonance on the Galactic plane.

Discovering Activities to Recognize and Track in a Smart Environment.

PubMed

Rashidi, Parisa; Cook, Diane J; Holder, Lawrence B; Schmitter-Edgecombe, Maureen

2011-01-01

The machine learning and pervasive sensing technologies found in smart homes offer unprecedented opportunities for providing health monitoring and assistance to individuals experiencing difficulties living independently at home. In order to monitor the functional health of smart home residents, we need to design technologies that recognize and track activities that people normally perform as part of their daily routines. Although approaches do exist for recognizing activities, the approaches are applied to activities that have been pre-selected and for which labeled training data is available. In contrast, we introduce an automated approach to activity tracking that identifies frequent activities that naturally occur in an individual's routine. With this capability we can then track the occurrence of regular activities to monitor functional health and to detect changes in an individual's patterns and lifestyle. In this paper we describe our activity mining and tracking approach and validate our algorithms on data collected in physical smart environments.

Multiwaveband Polarimetric Observations of 15 Active Galactic Nuclei at High Frequencies: Correlated Polarization Behavior

NASA Astrophysics Data System (ADS)

Jorstad, Svetlana G.; Marscher, Alan P.; Stevens, Jason A.; Smith, Paul S.; Forster, James R.; Gear, Walter K.; Cawthorne, Timothy V.; Lister, Matthew L.; Stirling, Alastair M.; Gómez, José L.; Greaves, Jane S.; Robson, E. Ian

2007-08-01

We report on multifrequency linear polarization monitoring of 15 active galactic nuclei containing highly relativistic jets with apparent speeds from ~4c to >40c. The measurements were obtained at optical, 1 mm, and 3 mm wavelengths, and at 7 mm with the Very Long Baseline Array. The data show a wide range in degree of linear polarization among the sources, from <1% to >30%, and interday polarization variability in individual sources. The polarization properties suggest separation of the sample into three groups with low, intermediate, and high variability of polarization in the core at 7 mm (LVP, IVP, and HVP, respectively). The groups are partially associated with the common classification of active galactic nuclei as radio galaxies and quasars with low optical polarization (LVP), BL Lacertae objects (IVP), and highly optically polarized quasars (HVP). Our study investigates correlations between total flux, fractional polarization, and polarization position angle at the different wavelengths. We interpret the polarization properties of the sources in the sample through models in which weak shocks compress turbulent plasma in the jet. The differences in the orientation of sources with respect to the observer, jet kinematics, and abundance of thermal matter external to the jet near the core can account for the diversity in the polarization properties. The results provide strong evidence that the optical polarized emission originates in shocks, most likely situated between the 3 and 7 mm VLBI cores. They also support the idea that the 1 mm core lies at the edge of the transition zone between electromagnetically dominated and turbulent hydrodynamic sections of the jet.

On the Scatter in the Radius-Luminosity Relationship for Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Kilerci Eser, E.; Vestergaard, M.; Peterson, B. M.; Denney, K. D.; Bentz, M. C.

2015-03-01

We investigate and quantify the observed scatter in the empirical relationship between the broad line region size R and the luminosity of the active galactic nucleus, in order to better understand its origin. This study is motivated by the indispensable role of this relationship in the mass estimation of cosmologically distant black holes, but may also be relevant to the recently proposed application of this relationship for measuring cosmic distances. We study six nearby reverberation-mapped active galactic nuclei (AGNs) for which simultaneous UV and optical monitoring data exist. We also examine the long-term optical luminosity variations of the Seyfert 1 galaxy NGC 5548 and employ Monte Carlo simulations to study the effects of the intrinsic variability of individual objects on the scatter in the global relationship for a sample of ~40 AGNs. We find the scatter in this relationship has a correctable dependence on color. For individual AGNs, the size of the Hβ emitting region has a steeper dependence on the nuclear optical luminosity than on the UV luminosity, which can introduce a scatter of ~0.08 dex into the global relationship, due the nonlinear relationship between the variations in the ionizing continuum and those in the optical continuum. Also, our analysis highlights the importance of understanding and minimizing the scatter in the relationship traced by the intrinsic variability of individual AGNs since it propagates directly into the global relationship. We find that using the UV luminosity as a substitute for the ionizing luminosity can reduce a sizable fraction of the current observed scatter of ~0.13 dex.

Gamma ray constraints on the Galactic supernova rate

NASA Technical Reports Server (NTRS)

Hartmann, D.; The, L.-S.; Clayton, Donald D.; Leising, M.; Mathews, G.; Woosley, S. E.

1991-01-01

We perform Monte Carlo simulations of the expected gamma ray signatures of Galactic supernovae of all types to estimate the significance of the lack of a gamma ray signal due to supernovae occurring during the last millenium. Using recent estimates of the nuclear yields, we determine mean Galactic supernova rates consistent with the historic supernova record and the gamma ray limits. Another objective of these calculations of Galactic supernova histories is their application to surveys of diffuse Galactic gamma ray line emission.

Gamma ray constraints on the galactic supernova rate

NASA Technical Reports Server (NTRS)

Hartmann, D.; The, L.-S.; Clayton, D. D.; Leising, M.; Mathews, G.; Woosley, S. E.

1992-01-01

Monte Carlo simulations of the expected gamma-ray signatures of galactic supernovae of all types are performed in order to estimate the significance of the lack of a gamma-ray signal due to supernovae occurring during the last millenium. Using recent estimates of nuclear yields, we determine galactic supernova rates consistent with the historic supernova record and the gamma-ray limits. Another objective of these calculations of galactic supernova histories is their application to surveys of diffuse galactic gamma-ray line emission.

Cortical Circuit for Binding Object Identity and Location During Multiple-Object Tracking

PubMed Central

Nummenmaa, Lauri; Oksama, Lauri; Glerean, Erico; Hyönä, Jukka

2017-01-01

Abstract Sustained multifocal attention for moving targets requires binding object identities with their locations. The brain mechanisms of identity-location binding during attentive tracking have remained unresolved. In 2 functional magnetic resonance imaging experiments, we measured participants’ hemodynamic activity during attentive tracking of multiple objects with equivalent (multiple-object tracking) versus distinct (multiple identity tracking, MIT) identities. Task load was manipulated parametrically. Both tasks activated large frontoparietal circuits. MIT led to significantly increased activity in frontoparietal and temporal systems subserving object recognition and working memory. These effects were replicated when eye movements were prohibited. MIT was associated with significantly increased functional connectivity between lateral temporal and frontal and parietal regions. We propose that coordinated activity of this network subserves identity-location binding during attentive tracking. PMID:27913430

Masses of Black Holes in Active Galactic Nuclei

NASA Technical Reports Server (NTRS)

Peterson, Bradley M.

2003-01-01

We present a progress report on a project whose goal is to improve both the precision and accuracy of reverberation-based black-hole masses. Reverberation masses appear to be accurate to a factor of about three, and the black-hole mass/bulge velocity dispersion (M-sigma) relationship appears to be the same in active and quiescent galaxies.

DISCOVERY OF CANDIDATE H{sub 2}O DISK MASERS IN ACTIVE GALACTIC NUCLEI AND ESTIMATIONS OF CENTRIPETAL ACCELERATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Greenhill, Lincoln J.; Moran, James M.; Tilak, Avanti

2009-12-10

Based on spectroscopic signatures, about one-third of known H{sub 2}O maser sources in active galactic nuclei (AGNs) are believed to arise in highly inclined accretion disks around central engines. These 'disk maser candidates' are of interest primarily because angular structure and rotation curves can be resolved with interferometers, enabling dynamical study. We identify five new disk maser candidates in studies with the Green Bank Telescope, bringing the total number published to 30. We discovered two (NGC 1320, NGC 17) in a survey of 40 inclined active galaxies (v {sub sys} < 20, 000 km s{sup -1}). The remaining three diskmore » maser candidates were identified in monitoring of known sources: NGC 449, NGC 2979, and NGC 3735. We also confirm a previously marginal case in UGC 4203. For the disk maser candidates reported here, inferred rotation speeds are 130-500 km s{sup -1}. Monitoring of three more rapidly rotating candidate disks (CG 211, NGC 6264, VV 340A) has enabled measurement of likely orbital centripetal acceleration, and estimation of central masses ((2-7) x10{sup 7} M {sub sun}) and mean disk radii (0.2-0.4 pc). Accelerations may ultimately permit estimation of distances when combined with interferometer data. This is notable because the three AGNs are relatively distant (10,000 km s{sup -1}

High Fidelity Measurement of Free Space Solar Particle Event and Galactic Cosmic Ray Environments at Intermediate Energies

NASA Astrophysics Data System (ADS)

Leitgab, M.

2018-02-01

A charged particle measurement experiment mounted externally to the Deep Space Gateway is proposed, contributing to improving astronaut radiation exposure management during Solar Particle Events and Extra Vehicular Activities.

Reality and myths of AGN feedback

NASA Astrophysics Data System (ADS)

Husemann, Bernd; Harrison, Chris M.

2018-03-01

Feedback from active galactic nuclei (AGNs) remains controversial despite its wide acceptance as necessary to regulate massive galaxy growth. Consequently, we held a workshop in October 2017, at Leiden's Lorentz Center, to distinguish between the reality and myths of feedback.

Galactic Winds and the Role Played by Massive Stars

NASA Astrophysics Data System (ADS)

Heckman, Timothy M.; Thompson, Todd A.

Galactic winds from star-forming galaxies play at key role in the evolution of galaxies and the intergalactic medium. They transport metals out of galaxies, chemically enriching the intergalactic medium and modifying the chemical evolution of galaxies. They affect the surrounding interstellar and circumgalactic media, thereby influencing the growth of galaxies though gas accretion and star formation. In this contribution we first summarize the physical mechanisms by which the momentum and energy output from a population of massive stars and associated supernovae can drive galactic winds. We use the prototypical example of M 82 to illustrate the multiphase nature of galactic winds. We then describe how the basic properties of galactic winds are derived from the data, and summarize how the properties of galactic winds vary systematically with the properties of the galaxies that launch them. We conclude with a brief discussion of the broad implications of galactic winds.

The galactic contribution to IceCube's astrophysical neutrino flux

DOE Office of Scientific and Technical Information (OSTI.GOV)

Denton, Peter B.; Marfatia, Danny; Weiler, Thomas J., E-mail: peterbd1@gmail.com, E-mail: dmarf8@hawaii.edu, E-mail: tom.weiler@vanderbilt.edu

2017-08-01

High energy neutrinos have been detected by IceCube, but their origin remains a mystery. Determining the sources of this flux is a crucial first step towards multi-messenger studies. In this work we systematically compare two classes of sources with the data: galactic and extragalactic. We assume that the neutrino sources are distributed according to a class of Galactic models. We build a likelihood function on an event by event basis including energy, event topology, absorption, and direction information. We present the probability that each high energy event with deposited energy E {sub dep}>60 TeV in the HESE sample is Galactic,more » extragalactic, or background. For Galactic models considered the Galactic fraction of the astrophysical flux has a best fit value of 1.3% and is <9.5% at 90% CL. A zero Galactic flux is allowed at <1σ.« less

Population Synthesis Studies of the White Dwarfs of the Galactic Disk and Halo

NASA Astrophysics Data System (ADS)

Cojocaru, Elena-Ruxandra

2016-09-01

White dwarfs are fossil stars that can encode valuable information about the formation, evolution and other properties of the different Galactic stellar populations. They are the direct descendants of main-sequence stars with masses ranging from ∼0.8 M⊙ to ∼10 M⊙, which means that over 95% of the stars in our Galaxy will eventually become white dwarfs. This fact, correlated with the excellent quality of modern white dwarf cooling models, clearly marks their potential as cosmic clocks for estimating the ages of Galactic stellar populations, as well as place white dwarfs as privileged objects in understanding several actual astrophysical problems. Stellar population synthesis methods (Tinsley, 1968) use theoretical evolutionary sequences to reproduce luminosities, temperatures and other parameters building up to a synthetic population that can be readily compared to an observed sample of stars. Such techniques are perfect for the study of the different white dwarf populations in our Galaxy and their strength has only grown in recent years, fueled both by improved evolutionary sequences and detailed cooling tracks and also by the ever growing samples of white dwarfs identified through modern survey missions. In particular, the work presented in this thesis uses an updated population synthesis code based on previous versions of the code from our group (García-Berro et al., 1999; Torres et al., 2002; García-Berro et al., 2004; Torres et al., 2005; Camacho et al., 2014). Our synthetic population code, based on Monte Carlo statistical techniques, has been extensively used in the study of the disk (García-Berro et al., 1! 999; Torres et al., 2001; Torres & García-Berro, 2016) and halo (Torres et al., 2002; García-Berro et al., 2004) single white-dwarf population, white dwarf plus main sequence stars (Camacho et al., 2014), as well as open clusters such as NGC 6791 (García-Berro et al., 2010; García-Berro et al., 2011) or globular clusters, as 47 Tuc (García-Berro et al., 2014). In this thesis we investigate different properties of single and binary white dwarf populations in the Galactic disk and halo. We first study the effect of progenitor metallicity on the thin disk white dwarf luminosity function. Stellar metallicity is an important parameter in computing both main-sequence evolutionary sequences and white dwarf cooling tracks. At the same, studies of the metallicity distribution function for the Galactic disk have shown that both high and low-metallicity stars can be found throughout the entire mass range, although a clear dependence between age and metallicity has yet to be proven and more recent findings actually show little correlation. With this in mind, we test two different age-metallicity relations, one assuming a Gaussian distribution of metallicity around the Solar value, the other one a decreasing relation between age and metallicity. We take into account the influence of metallicity on both main sequence lifetimes and white dwarf s! tellar parameters. Finally, we compute the theoretical white dwarf luminosity function applying the observational selection criteria of two different surveys, the Sloan Digital Sky Survey (SDSS) and the Supercosmos Sky Survey (SSS). Next, we compute the white dwarf luminosity, mass and cumulative age functions derived from a sample of DA white dwarfs obtained from the LAMOST Spectroscopic Survey of the Galactic anti-center (LSS-GAC). We also derive the local space density and the formation rate for DA white dwarf. Given that both the observed mass distribution obtained from this sample and that derived from the local sample of white dwarfs present an apparent excess of massive white dwarfs, we investigate the possibility of accounting for this excess by reproducing the white dwarf population of the thin disk under different sets of initial assumptions, accounting also for selection criteria and observational biases. Another issue that we investigate is the robustness of the halo white dwarf luminosity function employing different models for the initial mass function, density profile and stellar formation history. We also analyze if the white dwarf luminosity function can be used as a means to discriminate the role played by residual hydrogen burning in the atmospheres of low-mass white dwarfs. This process is known to become a significant source of energy for white dwarfs descending from very low metallicity progenitors, such as those that characterize the Galactic halo population. Lastly, we simulate the white dwarf-main sequence (WD+MS) binary population of the Galactic disk and compare it to the parameter distributions from the largest and most recent WD+MS catalog derived from the SDSS (Rebassa-Mansergas et al., 2016b). We not only reproduce the selection criteria, but we also account for spectroscopic completeness, observational errors and other biases that affect the sample. We use the observed population as a benchmark for constraining several important physical quantities specific to binary evolution, such as the initial mass ratio distribution and also the common envelope parametrization. This thesis is based on three published papers, Cojocaru et al. (2014), Rebassa-Mansergas et al. (2015) and Cojocaru et al. (2015) and another work in preparation.

Galactic plane gamma-radiation

NASA Technical Reports Server (NTRS)

Hartman, R. C.; Kniffen, D. A.; Thompson, D. J.; Fichtel, C. E.; Ogelman, H. B.; Tumer, T.; Ozel, M. E.

1979-01-01

Analysis of the SAS 2 data together with the COS B results shows that the distribution of galactic gamma-radiation has several similarities to that of other large-scale tracers of galactic structure. The radiation is primarily confined to a thin disc which exhibits offsets from b = 0 degrees similar to warping at radio frequencies. The principal distinction of the gamma-radiation is a stronger contrast in intensity between the region from 310 to 45 degrees in longitude and the regions away from the center that can be attributed to a variation in cosmic-ray density as a function of position in Galaxy. The diffuse galactic gamma-ray energy spectrum shows no significant variation in direction, and the spectrum seen along the plane is the same as that for the galactic component of the gamma-radiation at high altitudes. The uniformity of the galactic gamma-ray spectrum, the smooth decrease in intensity as a function of altitude, and the absence of any galactic gamma-ray sources at high altitudes indicate a diffuse origin for bulk of the galactic gamma-radiation rather than a collection of localized sources.

Spacecraft Materials in the Space Flight Environment: International Space Station - May 2002 to May 2007

NASA Technical Reports Server (NTRS)

Golden, John; Lorenz, Mary J.; Alred, John; Koontz, Steven L.; Pedley, Michael

2008-01-01

The performance of ISS spacecraft materials and systems on prolonged exposure to the low-Earth orbit (LEO) space flight is reported in this paper. In-flight data, flight crew observations, and the results of ground-based test and analysis directly supporting programmatic and operational decision-making are presented. The space flight environments definitions (both natural and induced) used for ISS design, material selection, and verification testing are shown, in most cases, to be more severe than the actual flight environment accounting for the outstanding performance of ISS as a long mission duration spacecraft. No significant ISS material or system failures have been attributed to spacecraft-environments interactions. Nonetheless, ISS materials and systems performance data is contributing to our understanding of spacecraft material interactions in the spaceflight environment so as to reduce cost and risk for future spaceflight projects and programs. Orbital inclination (51.6o) and altitude (nominally near 360 km) determine the set of natural environment factors affecting the functional life of materials and systems on ISS. ISS operates in an electrically conducting environment (the F2 region of Earth s ionosphere) with well-defined fluxes of atomic oxygen, other charged and neutral ionospheric plasma species, solar UV, VUV, and x-ray radiation as well as galactic cosmic rays, trapped radiation, and solar cosmic rays (1-4). The LEO micrometeoroid and orbital debris environment is an especially important determinant of spacecraft design and operations (5, 6). The magnitude of several environmental factors varies dramatically with latitude and longitude as ISS orbits the Earth (1-4). The high latitude orbital environment also exposes ISS to higher fluences of trapped energetic electrons, auroral electrons, solar cosmic rays, and galactic cosmic rays (1-4) than would be the case in lower inclination orbits, largely as a result of the overall shape and magnitude of the geomagnetic field (1-4). As a result, ISS exposure to many environmental factors can vary dramatically along a particular orbital ground track, and from one ground track to the next, during any 24-hour period.

Highlights of GeV Gamma-Ray Astronomy

NASA Technical Reports Server (NTRS)

Thompson, David J.

2010-01-01

Because high-energy gamma rays are primarily produced by high-energy particle interactions, the gamma-ray survey of the sky by the Fermi Gamma-ray Space Telescope offers a view of sites of cosmic ray production and interactions. Gamma-ray bursts, pulsars, pulsar wind nebulae, binary sources, and Active Galactic Nuclei are all phenomena that reveal particle acceleration through their gamma-ray emission. Diffuse Galactic gamma radiation, Solar System gamma-ray sources, and energetic radiation from supernova remnants are likely tracers of high-energy particle interactions with matter and photon fields. This paper will present a broad overview of the constantly changing sky seen with the Large Area Telescope (LAT) on the Fermi spacecraft.

Wide Field X-Ray Telescope Mission Concept Study Results

NASA Technical Reports Server (NTRS)

Hopkins, R. C.; Thomas, H. D.; Fabisinski, L. L.; Baysinger, M.; Hornsby, L. S.; Maples, C. D.; Purlee, T. E.; Capizzo, P. D.; Percy, T. K.

2014-01-01

The Wide Field X-Ray Telescope (WFXT) is an astrophysics mission concept for detecting and studying extra-galactic x-ray sources, including active galactic nuclei and clusters of galaxies, in an effort to further understand cosmic evolution and structure. This Technical Memorandum details the results of a mission concept study completed by the Advanced Concepts Office at NASA Marshall Space Flight Center in 2012. The design team analyzed the mission and instrument requirements, and designed a spacecraft that enables the WFXT mission while using high heritage components. Design work included selecting components and sizing subsystems for power, avionics, guidance, navigation and control, propulsion, structures, command and data handling, communications, and thermal control.

Galactic gamma-ray sources, SNOBs, and giant H2 regions

NASA Technical Reports Server (NTRS)

Montmerle, T.

1985-01-01

Progress towards understanding the nature of the COS-B galactic gamma-ray sources was made by two recent developments. The developments are: (1) the existence of extensive wide-latitude CO surveys, from the Northern Hemisphere, and from the Southern Hemisphere which give more precise information on molecular cloud population of the Perseus, Sagittarius, and Carina spiral arms; (2) the study of the time variability of gamma-ray sources in gamma-rays but also at other wavelengths, leading to the discovery of four new variable sources in addition to the already known Crab and Vela pulsars. Three classes of gamma-ray sources are found; invariable sources, active sources, and passive sources.

Local Stellar Kinematics from RAVE data - V. Kinematic Investigation of the Galaxy with Red Clump Stars

NASA Astrophysics Data System (ADS)

Karaali, S.; Bilir, S.; Ak, S.; Gökçe, E. Yaz; Önal, Ö.; Ak, T.

2014-02-01

We investigated the space velocity components of 6 610 red clump (RC) stars in terms of vertical distance, Galactocentric radial distance and Galactic longitude. Stellar velocity vectors are corrected for differential rotation of the Galaxy which is taken into account using photometric distances of RC stars. The space velocity components estimated for the sample stars above and below the Galactic plane are compatible only for the space velocity component in the direction to the Galactic rotation of the thin disc stars. The space velocity component in the direction to the Galactic rotation (V lsr) shows a smooth variation relative to the mean Galactocentric radial distance (Rm ), while it attains its maximum at the Galactic plane. The space velocity components in the direction to the Galactic centre (U lsr) and in the vertical direction (W lsr) show almost flat distributions relative to Rm , with small changes in their trends at Rm ~ 7.5 kpc. U lsr values estimated for the RC stars in quadrant 180° < l ⩽ 270° are larger than the ones in quadrants 0° < l ⩽ 90° and 270° < l ⩽ 360°. The smooth distribution of the space velocity dispersions reveals that the thin and thick discs are kinematically continuous components of the Galaxy. Based on the W lsr space velocity components estimated in the quadrants 0° < l ⩽ 90° and 270° < l ⩽ 360°, in the inward direction relative to the Sun, we showed that RC stars above the Galactic plane move towards the North Galactic Pole, whereas those below the Galactic plane move in the opposite direction. In the case of quadrant 180° < l ⩽ 270°, their behaviour is different, i.e. the RC stars above and below the Galactic plane move towards the Galactic plane. We stated that the Galactic long bar is the probable origin of many, but not all, of the detected features.

Chandra X-Ray Observations of the Two Brightest Unidentified High Galactic Latitude Fermi-LAT Gamma-Ray Sources

NASA Technical Reports Server (NTRS)

Cheung, C. C.; Donato, D.; Gehrels, N.; Sokolovsky, K. V.; Giroletti, M.

2012-01-01

We present Chandra ACIS-I X-ray observations of 0FGL J1311.9-3419 and 0FGL J1653.4-0200, the two brightest high Galactic latitude (absolute value (beta) >10 deg) gamma-ray sources from the three-month Fermi Large Area Telescope (LAT) bright source list that are still unidentified. Both were also detected previously by EGRET, and despite dedicated multi-wavelength follow-up, they are still not associated with established classes of gamma-ray emitters like pulsars or radio-loud active galactic nuclei. X-ray sources found in the ACIS-I fields of view are cataloged, and their basic properties are determined. These are discussed as candidate counterparts to 0FGL J1311.9-3419 and 0FGL J1653.4-0200, with particular emphasis on the brightest of the 9 and 13 Chandra sources detected within the respective Fermi-LAT 95% confidence regions. Further follow-up studies, including optical photometric and spectroscopic observations, are necessary to identify these X-ray candidate counterparts in order to ultimately reveal the nature of these enigmatic gamma-ray objects.

First Extended Catalogue of Galactic bubble infrared fluxes from WISE and Herschel surveys

NASA Astrophysics Data System (ADS)

Bufano, F.; Leto, P.; Carey, D.; Umana, G.; Buemi, C.; Ingallinera, A.; Bulpitt, A.; Cavallaro, F.; Riggi, S.; Trigilio, C.; Molinari, S.

2018-01-01

In this paper, we present the first extended catalogue of far-infrared fluxes of Galactic bubbles. Fluxes were estimated for 1814 bubbles, defined here as the 'golden sample', and were selected from the Milky Way Project First Data Release (Simpson et al.) The golden sample was comprised of bubbles identified within the Wide-field Infrared Survey Explorer (WISE) dataset (using 12- and 22-μm images) and Herschel data (using 70-, 160-, 250-, 350- and 500-μm wavelength images). Flux estimation was achieved initially via classical aperture photometry and then by an alternative image analysis algorithm that used active contours. The accuracy of the two methods was tested by comparing the estimated fluxes for a sample of bubbles, made up of 126 H II regions and 43 planetary nebulae, which were identified by Anderson et al. The results of this paper demonstrate that a good agreement between the two was found. This is by far the largest and most homogeneous catalogue of infrared fluxes measured for Galactic bubbles and it is a step towards the fully automated analysis of astronomical datasets.

The Optical Gravitational Lensing Experiment. BVI Maps of Dense Stellar Regions. III. The Galactic Bulge

NASA Astrophysics Data System (ADS)

Udalski, A.; Szymanski, M.; Kubiak, M.; Pietrzynski, G.; Soszynski, I.; Wozniak, P.; Zebrun, K.; Szewczyk, O.; Wyrzykowski, L.

2002-09-01

We present the VI photometric maps of the Galactic bulge. They contain VI photometry and astrometry of about 30 million stars from 49 fields of 0.225 square degree each in the Galactic center region. The data were collected during the second phase of the OGLE microlensing project. We discuss the accuracy of data and present color-magnitude diagrams of selected fields observed by OGLE in the Galactic bulge. The VI maps of the Galactic bulge are accessible electronically for the astronomical community from the OGLE Internet archive.

Anisotropy and corotation of galactic cosmic rays.

PubMed

Amenomori, M; Ayabe, S; Bi, X J; Chen, D; Cui, S W; Danzengluobu; Ding, L K; Ding, X H; Feng, C F; Feng, Zhaoyang; Feng, Z Y; Gao, X Y; Geng, Q X; Guo, H W; He, H H; He, M; Hibino, K; Hotta, N; Hu, Haibing; Hu, H B; Huang, J; Huang, Q; Jia, H Y; Kajino, F; Kasahara, K; Katayose, Y; Kato, C; Kawata, K; Labaciren; Le, G M; Li, A F; Li, J Y; Lou, Y-Q; Lu, H; Lu, S L; Meng, X R; Mizutani, K; Mu, J; Munakata, K; Nagai, A; Nanjo, H; Nishizawa, M; Ohnishi, M; Ohta, I; Onuma, H; Ouchi, T; Ozawa, S; Ren, J R; Saito, T; Saito, T Y; Sakata, M; Sako, T K; Sasaki, T; Shibata, M; Shiomi, A; Shirai, T; Sugimoto, H; Takita, M; Tan, Y H; Tateyama, N; Torii, S; Tsuchiya, H; Udo, S; Wang, B; Wang, H; Wang, X; Wang, Y G; Wu, H R; Xue, L; Yamamoto, Y; Yan, C T; Yang, X C; Yasue, S; Ye, Z H; Yu, G C; Yuan, A F; Yuda, T; Zhang, H M; Zhang, J L; Zhang, N J; Zhang, X Y; Zhang, Y; Zhang, Yi; Zhaxisangzhu; Zhou, X X

2006-10-20

The intensity of Galactic cosmic rays is nearly isotropic because of the influence of magnetic fields in the Milky Way. Here, we present two-dimensional high-precision anisotropy measurement for energies from a few to several hundred teraelectronvolts (TeV), using the large data sample of the Tibet Air Shower Arrays. Besides revealing finer details of the known anisotropies, a new component of Galactic cosmic ray anisotropy in sidereal time is uncovered around the Cygnus region direction. For cosmic-ray energies up to a few hundred TeV, all components of anisotropies fade away, showing a corotation of Galactic cosmic rays with the local Galactic magnetic environment. These results have broad implications for a comprehensive understanding of cosmic rays, supernovae, magnetic fields, and heliospheric and Galactic dynamic environments.

Radio Wavelength Studies of the Galactic Center Source N3, Spectroscopic Instrumentation For Robotic Telescope Systems, and Developing Active Learning Activities for Astronomy Laboratory Courses

NASA Astrophysics Data System (ADS)

Ludovici, Dominic Alesio

2017-08-01

The mysterious radio source N3 appears to be located within the vicinity of the Radio Arc region of the Galactic Center. To investigate the nature of this source, we have conducted radio observations with the VLA and the VLBA. Continuum observations between 2 and 50 GHz reveal that N3 is an extremely compact and bright source with a non-thermal spectrum. Molecular line observations with the VLA reveal a compact molecular cloud adjacent to N3 in projection. The properties of this cloud are consistent with other galactic center clouds. We are able to rule out several hypotheses for the nature of N3, though a micro-blazar origin cannot be ruled out. Robotic Telescope systems are now seeing widespread deployment as both teaching and research instruments. While these systems have traditionally been able to produce high quality images, these systems have lacked the capability to conduct spectroscopic observations. To enable spectroscopic observations on the Iowa Robotic Observatory, we have developed a low cost (˜ 500), low resolution (R ˜ 300) spectrometer which mounts inside a modified filter wheel and a moderate cost (˜ 5000), medium resolution (R ˜ 8000) fiber-fed spectrometer. Software has been developed to operate both instruments robotically and calibration pipelines are being developed to automate calibration of the data. The University of Iowa offers several introductory astronomy laboratory courses taken by many hundreds of students each semester. To improve student learning in these laboratory courses, we have worked to integrate active learning into laboratory activities. We present the pedagogical approaches used to develop and update the laboratory activities and present an inventory of the current laboratory exercises. Using the inventory, we make observations of the strengths and weaknesses of the current exercises and provide suggestions for future refinement of the astronomy laboratory curriculum.

Physical properties of high-mass star-forming clumps in different evolutionary stages from the Bolocam Galactic Plane Survey

NASA Astrophysics Data System (ADS)

Svoboda, Brian; Shirley, Yancy; Rosolowsky, Erik; Dunham, Miranda; Ellsworth-Bowers, Timothy; Ginsburg, Adam

2013-07-01

High mass stars play a key role in the physical and chemical evolution of the interstellar medium, yet the evolutionary sequence for high mass star forming regions is poorly understood. Recent Galactic plane surveys are providing the first systematic view of high-mass star-forming regions in all evolutionary phases across the Milky Way. We present observations of the 22.23 GHz H2O maser transition J(Ka,Kc) = 6(1,6)→5(2,3) transition toward 1398 clumps identified in the Bolocam Galactic Plane Survey using the 100m Green Bank Telescope (GBT). We detect 392 H2O masers, 279 (71%) newly discovered. We show that H2O masers can identify the presence of protostars which were not previously identified by Spitzer/MSX Galactic plane IR surveys: 25% of IR-dark clumps have an H2O maser. We compare the physical properties of the clumps in the Bolocam Galactic Plane Survey (BGPS) with observations of diagnostics of star formation activity: 8 and 24 um YSO candidates, H2O and CH3OH masers, shocked H2, EGOs, and UCHII regions. We identify a sub-sample of 400 clumps with no star formation indicators representing the largest and most robust sample of pre-protocluster candidates from an unbiased survey to date. The different evolutionary stages show strong separations in HCO+ linewidth and integrated intensity, surface mass density, and kinetic temperature. Monte Carlo techniques are applied to distance probability distribution functions (DPDFs) in order to marginalize over the kinematic distance ambiguity and calculate the distribution of derived quantities for clumps in different evolutionary stages. Surface area and dust mass show weak separations above > 2 pc^2 and > 3x10^3 solar masses. An observed breakdown occurs in the size-linewidth relationship with no differentiation by evolutionary stage. Future work includes adding evolutionary indicators (MIPSGAL, HiGal, MMB) and expanding DPDF priors (HI self-absorption, Galactic structure) for more well-resolved KDAs.

Discovering Activities to Recognize and Track in a Smart Environment

PubMed Central

Rashidi, Parisa; Cook, Diane J.; Holder, Lawrence B.; Schmitter-Edgecombe, Maureen

2011-01-01

The machine learning and pervasive sensing technologies found in smart homes offer unprecedented opportunities for providing health monitoring and assistance to individuals experiencing difficulties living independently at home. In order to monitor the functional health of smart home residents, we need to design technologies that recognize and track activities that people normally perform as part of their daily routines. Although approaches do exist for recognizing activities, the approaches are applied to activities that have been pre-selected and for which labeled training data is available. In contrast, we introduce an automated approach to activity tracking that identifies frequent activities that naturally occur in an individual’s routine. With this capability we can then track the occurrence of regular activities to monitor functional health and to detect changes in an individual’s patterns and lifestyle. In this paper we describe our activity mining and tracking approach and validate our algorithms on data collected in physical smart environments. PMID:21617742

When Supermassive Black Holes Wander

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2018-05-01

Are supermassive black holes found only at the centers of galaxies? Definitely not, according to a new study in fact, galaxies like the Milky Way may harbor several such monsters wandering through their midst.Collecting Black Holes Through MergersIts generally believed that galaxies are built up hierarchically, growing in size through repeated mergers over time. Each galaxy in a major merger likely hosts a supermassive black hole a black hole of millions to billions of times the mass of the Sun at its center. When a pair of galaxies merges, their supermassive black holes will often sink to the center of the merger via a process known as dynamical friction. There the supermassive black holes themselves will eventually merge in a burst of gravitational waves.Spatial distribution and velocities of wandering supermassive black holes in three of the authors simulated galaxies, shown in edge-on (left) and face-on (right) views of the galaxy disks. Click for a closer look. [Tremmel et al. 2018]But if a galaxy the size of the Milky Way was built through a history of many major galactic mergers, are we sure that all its accumulated supermassive black holes eventually merged at the galactic center? A new study suggests that some of these giants might have escaped such a fate and they now wander unseen on wide orbits through their galaxies.Black Holes in an Evolving UniverseLed by Michael Tremmel (Yale Center for Astronomy Astrophysics), a team of scientists has used data from a large-scale cosmological simulation, Romulus25, to explore the possibility of wandering supermassive black holes. The Romulus simulations are uniquely suited to track the formation and subsequent orbital motion of supermassive black holes as galactic halos are built up through mergers over the history of the universe.From these simulations, Tremmel and collaborators find an end total of 316 supermassive black holes residing within the bounds of 26 Milky-Way-mass halos. Of these, roughly a third are wanderers within 10 kpc of the halo center (roughly the size of the Milky Ways disk).These wandering supermassive black holes were kicked onto wide orbits during the merger of their host galaxy with the main halo; Tremmel and collaborators find that their orbits are often tilted, lying outside of the galactic disk. Because these black holes travel through relatively deserted regions, they accumulate little mass and are rarely perturbed in their journeys, wandering for billions of years.Finding MonstersCumulative fraction of simulated Milky-Way-mass halos as a function of the number of supermassive black holes they host. All of the halos host at least one SMBH within 10 kpc from halo center, but the majority host more than that. [Tremmel et al. 2018]Tremmel and collaborators simulations suggest that, regardless of its merger history, a Milky-Way-mass halo will end up with an average of 5 supermassive black holes within 10 kpc of the galaxy center, and an average of 12 within its larger virial radius! This means there could be a number of supermassive black holes just like the enormous Sgr A* at our galaxys core wandering the Milky Way unseen.So how can we find these invisible monsters? We already have some observational evidence in the form of offset and dual active galactic nuclei of non-central supermassive black holes in distant galaxies. As for nearby, our best bet is to look for tidal disruption events, the burps of emission that occur when an otherwise invisible black hole encounters a star or a cloud of gas.CitationMichael Tremmel et al 2018 ApJL 857 L22. doi:10.3847/2041-8213/aabc0a

Active controllers and the time duration to learn a task

NASA Technical Reports Server (NTRS)

Repperger, D. W.; Goodyear, C.

1986-01-01

An active controller was used to help train naive subjects involved in a compensatory tracking task. The controller is called active in this context because it moves the subject's hand in a direction to improve tracking. It is of interest here to question whether the active controller helps the subject to learn a task more rapidly than the passive controller. Six subjects, inexperienced to compensatory tracking, were run to asymptote root mean square error tracking levels with an active controller or a passive controller. The time required to learn the task was defined several different ways. The results of the different measures of learning were examined across pools of subjects and across controllers using statistical tests. The comparison between the active controller and the passive controller as to their ability to accelerate the learning process as well as reduce levels of asymptotic tracking error is reported here.

Cloud-cloud collision in the Galactic center 50 km s-1 molecular cloud

NASA Astrophysics Data System (ADS)

Tsuboi, Masato; Miyazaki, Atsushi; Uehara, Kenta

2015-12-01

We performed a search of star-forming sites influenced by external factors, such as SNRs, H II regions, and cloud-cloud collisions (CCCs), to understand the star-forming activity in the Galactic center region using the NRO Galactic Center Survey in SiO v = 0, J = 2-1, H13CO+J = 1-0, and CS J = 1-0 emission lines obtained with the Nobeyama 45 m telescope. We found a half-shell-like feature (HSF) with a high integrated line intensity ratio of ∫TB(SiO v = 0, J = 2-1)dv/∫TB(H13CO+J = 1-0)dv ˜ 6-8 in the 50 km s-1 molecular cloud; the HSF is a most conspicuous molecular cloud in the region and harbors an active star-forming site where several compact H II regions can be seen. The high ratio in the HSF indicates that the cloud contains huge shocked molecular gas. The HSF can be also seen as a half-shell feature in the position-velocity diagram. A hypothesis explaining the chemical and kinetic properties of the HSF is that the feature originates from a CCC. We analyzed the CS J = 1-0 emission line data obtained with the Nobeyama Millimeter Array to reveal the relation between the HSF and the molecular cloud cores in the cloud. We made a cumulative core mass function (CMF) of the molecular cloud cores within the HSF. The CMF in the CCC region is not truncated at least up to ˜2500 M⊙, although the CMF of the non-CCC region reaches the upper limit of ˜1500 M⊙. Most massive molecular cores with Mgas > 750 M⊙ are located only around the ridge of the HSF and adjoin the compact H II region. These may be a sign of massive star formation induced by CCCs in the Galactic center region.

A simulation of high energy cosmic ray propagation 2

NASA Technical Reports Server (NTRS)

Honda, M.; Kamata, K.; Kifune, T.; Matsubara, Y.; Mori, M.; Nishijima, K.

1985-01-01

The cosmic ray propagation in the Galactic arm is simulated. The Galactic magnetic fields are known to go along with so called Galactic arms as a main structure with turbulences of the scale about 30pc. The distribution of cosmic ray in Galactic arm is studied. The escape time and the possible anisotropies caused by the arm structure are discussed.

Recent Progress in Active Antenna Designs for the Long Wavelength Array (LWA)

NASA Astrophysics Data System (ADS)

Hicks, B. C.; Stewart, K. P.; Paravastu, N.; Bradley, R. F.; Parashare, C. R.; Erickson, W. C.; Gross, C.; Polisensky, E.; Crane, P. C.; Ray, P. S.; Kassim, N. E.; Weiler, K. W.

2005-12-01

We present new designs for active antenna systems optimized for HF/VHF radio astronomy, ionospheric science, space weather, and other radio science applications. Active antenna designs have been developed and tested which satisfy the need for high linearity and stability while achieving Galactic background dominated noise levels. The presence of very strong terrestrial radio-frequency interference (RFI), and world-wide propagation at these frequencies require that the preamplifiers have very high dynamic range. Distortion products must be below the Galactic background level for RFI mitigation techniques to be successful. Individual antennas should have broad response patterns to cover most of the sky without pointing mechanisms, but with decreased sensitivity at low elevations. Ideal designs would also be immune to environmental effects such as temperature variations and precipitation. For projects such as the LWA, where thousands of receptors will be needed, they must also be robust, inexpensive, and easy to manufacture and install. We discuss high-performance designs that are optimized for cost-sensitive applications such as the LWA. Basic research in astronomy is supported by the Office of Naval Research.

The evolution of active galactic nuclei in clusters of galaxies from the Dark Energy Survey

DOE PAGES

Bufanda, E.; Hollowood, D.; Jeltema, T. E.; ...

2016-12-13

The correlation between active galactic nuclei (AGN) and environment provides important clues to AGN fueling and the relationship of black hole growth to galaxy evolution. Here, we analyze the fraction of galaxies in clusters hosting AGN as a function of redshift and cluster richness for X-ray detected AGN associated with clusters of galaxies in Dark Energy Survey (DES) Science Verification data. The present sample includes 33 AGN with L_X > 10 43 ergs s -1 in non-central, host galaxies with luminosity greater than 0.5 L* from a total sample of 432 clusters in the redshift range of 0.10.7. Our resultmore » is in good agreement with previous work and parallels the increase in star formation in cluster galaxies over the same redshift range. But, the AGN fraction in clusters is observed to have no significant correlation with cluster mass. Future analyses with DES Year 1 through Year 3 data will be able to clarify whether AGN activity is correlated to cluster mass and will tightly constrain the relationship between cluster AGN populations and redshift.« less

Galactic Cosmic Ray Intensity in the Upcoming Minimum of the Solar Activity Cycle

NASA Astrophysics Data System (ADS)

Krainev, M. B.; Bazilevskaya, G. A.; Kalinin, M. S.; Svirzhevskaya, A. K.; Svirzhevskii, N. S.

2018-03-01

During the prolonged and deep minimum of solar activity between cycles 23 and 24, an unusual behavior of the heliospheric characteristics and increased intensity of galactic cosmic rays (GCRs) near the Earth's orbit were observed. The maximum of the current solar cycle 24 is lower than the previous one, and the decline in solar and, therefore, heliospheric activity is expected to continue in the next cycle. In these conditions, it is important for an understanding of the process of GCR modulation in the heliosphere, as well as for applied purposes (evaluation of the radiation safety of planned space flights, etc.), to estimate quantitatively the possible GCR characteristics near the Earth in the upcoming solar minimum ( 2019-2020). Our estimation is based on the prediction of the heliospheric characteristics that are important for cosmic ray modulation, as well as on numeric calculations of GCR intensity. Additionally, we consider the distribution of the intensity and other GCR characteristics in the heliosphere and discuss the intercycle variations in the GCR characteristics that are integral for the whole heliosphere (total energy, mean energy, and charge).

ON THE HOST GALAXY OF GRB 150101B AND THE ASSOCIATED ACTIVE GALACTIC NUCLEUS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, Chen; Fang, Taotao; Wang, Junfeng

We present a multi-wavelength analysis of the host galaxy of short-duration gamma-ray burst (GRB) 150101B. Follow-up optical and X-ray observations suggested that the host galaxy, 2MASX J12320498-1056010, likely harbors low-luminosity active galactic nuclei (AGNs). Our modeling of the spectral energy distribution has confirmed the nature of the AGN, making it the first reported GRB host that contains an AGN. We have also found the host galaxy is a massive elliptical galaxy with stellar population of ∼5.7 Gyr, one of the oldest among the short-duration GRB hosts. Our analysis suggests that the host galaxy can be classified as an X-ray bright,more » optically normal galaxy, and the central AGN is likely dominated by a radiatively inefficient accretion flow. Our work explores an interesting connection that may exist between GRB and AGN activities of the host galaxy, which can help in understanding the host environment of the GRB events and the roles of AGN feedback.« less

1.75 h {sup -1} kpc SEPARATION DUAL ACTIVE GALACTIC NUCLEI AT z = 0.36 IN THE COSMOS FIELD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Comerford, Julia M.; Davis, Marc; Griffith, Roger L.

2009-09-01

We present strong evidence for dual active galactic nuclei (AGNs) in the z = 0.36 galaxy COSMOS J100043.15+020637.2. COSMOS Hubble Space Telescope (HST) imaging of the galaxy shows a tidal tail, indicating that the galaxy recently underwent a merger, as well as two bright point sources near the galaxy's center. The luminosities of these sources (derived from the HST image) and their emission line flux ratios (derived from Keck/DEIMOS slit spectroscopy) suggest that both are AGNs and not star-forming regions or supernovae. Observations from zCOSMOS, the Sloan Digital Sky Survey, XMM-Newton, Spitzer, and the Very Large Array fortify the evidencemore » for AGN activity. With HST imaging we measure a projected spatial offset between the two AGNs of 1.75 {+-} 0.03 h {sup -1} kpc, and with DEIMOS we measure a 150 {+-} 40 km s{sup -1} line-of-sight velocity offset between the two AGNs. Combined, these observations provide substantial evidence that COSMOS J100043.15+020637.2 is a merger-remnant galaxy with dual AGNs.« less

Astronomers Go Behind The Milky Way To Solve X-Ray Mystery

NASA Astrophysics Data System (ADS)

2001-08-01

Through layers of gas and dust that stretch for more than 30,000 light years, astronomers using NASA's Chandra X-ray Observatory have taken a long, hard look at the plane of the Milky Way galaxy and found that its X-ray glow comes from hot and diffuse gas. The findings, published in the August 10 issue of Science, help to settle a long-standing mystery about the source of the X-ray emission from the galactic plane. Scientists have debated whether the Milky Way plane's X-ray emission was diffuse light or from individual stars. Armed with Chandra, an international team led Dr. Ken Ebisawa of NASA's Goddard Space Flight Center, Greenbelt, MD zoomed in on a tiny region of the galactic plane in the constellation Scutum. "The point sources we saw in the galactic plane were actually active galaxies with bright cores millions of light years behind our galaxy," said Ebisawa. "The number of these sources is consistent with the expected number of extragalactic sources in the background sky. We saw few additional point sources within our Galaxy." The observation marks the deepest X-ray look at the so-called "zone of avoidance" -- a region of space behind which no optical observation has ever been taken because thick dust and gas in the spiral arms of the Milky Way galaxy block out visible radiation. Infrared, radio, and X-rays, however, can penetrate this dust and gas. Detection of diffuse X rays emanating from the Galactic plane, what we call the "Milky Way" in visible light, indicates the presence of plasma gas with temperatures of tens of millions of degrees Celsius. Smoothed X-ray Image of the Galactic Plane Smoothed X-ray Image of the Galactic Plane Gas this hot would escape the gravitational confines of the Milky Way galaxy under normal circumstances. The fact that it still lingers within the Galactic plane is the next mystery to solve. One possibility, suggested by Ebisawa is that hot plasma may be confined to the Milky Way by magnetic fields. The Chandra observation, conducted in February 2000, lasted 28 hours. The team observed what was known to be a "blank" region of the galactic plane where the Japanese X-ray satellite ASCA had previously observed but found no individual X-ray sources. The team also discovered 36 bright distant galaxies lurking in the background of this section of the galactic plane, while the foreground was devoid of stars or other individual objects emitting X-rays. Chandra, and now the European XMM-Newton satellite, are at long last beginning to collect light from behind our galaxy. X-radiation from the 36 newly discovered galaxies passes through the Milky Way on its journey towards Earth. This light, therefore, carries the imprint of all that it passes through and will allow astronomers to measure the distribution and physical condition of matter in our Galaxy. Participating in the Chandra observation and Science article are Yoshitomo Maeda of Pennsylvania State University; Hidehiro Kaneda of the Institute of Space and Astronautical Science in Japan; and Shigeo Yamauchi of Iwate University in Japan. Chandra observed the galactic plane with its Advanced CCD Imaging Spectrometer (ACIS) instrument, which was developed for NASA by Pennsylvania State University, University Park, and Massachusetts Institute of Technology, Cambridge. NASA's Marshall Space Flight Center in Huntsville, AL, manages the Chandra program, and TRW, Inc., Redondo Beach, CA, is the prime contractor for the spacecraft. The Smithsonian's Chandra X-ray Center controls science and flight operations from Cambridge, MA.

Monocular Stereo Measurement Using High-Speed Catadioptric Tracking

PubMed Central

Hu, Shaopeng; Matsumoto, Yuji; Takaki, Takeshi; Ishii, Idaku

2017-01-01

This paper presents a novel concept of real-time catadioptric stereo tracking using a single ultrafast mirror-drive pan-tilt active vision system that can simultaneously switch between hundreds of different views in a second. By accelerating video-shooting, computation, and actuation at the millisecond-granularity level for time-division multithreaded processing in ultrafast gaze control, the active vision system can function virtually as two or more tracking cameras with different views. It enables a single active vision system to act as virtual left and right pan-tilt cameras that can simultaneously shoot a pair of stereo images for the same object to be observed at arbitrary viewpoints by switching the direction of the mirrors of the active vision system frame by frame. We developed a monocular galvano-mirror-based stereo tracking system that can switch between 500 different views in a second, and it functions as a catadioptric active stereo with left and right pan-tilt tracking cameras that can virtually capture 8-bit color 512×512 images each operating at 250 fps to mechanically track a fast-moving object with a sufficient parallax for accurate 3D measurement. Several tracking experiments for moving objects in 3D space are described to demonstrate the performance of our monocular stereo tracking system. PMID:28792483

Penrose pair production as a power source of quasars and active galactic nuclei. [black hole mechanisms

NASA Technical Reports Server (NTRS)

Kafatos, M.; Leiter, D.

1979-01-01

Penrose pair production in massive canonical Kerr black holes (those with a/M equal to 0.998) is proposed as a way to explain the nature of the vast fluctuating energy production associated with active galactic nuclei and quasars. It is assumed that a Kerr black hole with a mass of the order of 100 million solar masses lies at the center of an active nucleus and that an accretion disk is formed. Penrose pair production in the inner ergosphere of such a massive canonical Kerr black hole is analyzed. The results indicate that: (1) particle pairs are ejected within a 40 deg angle relative to the equator; (2) the particle energy is of the order of 1 GeV per pair; (3) the pressure of the electron-positron relativistic gas is proportional to the electron-positron number density; (4) pair production may occur in bursts; and (5) the overall lifetime of an active nucleus would depend on the time required to exhaust the disk of its matter content. A test of the theory is suggested which involves observation of the 0.5-MeV pair-annihilation gamma rays that would be generated by annihilating particle pairs.

A Census of Broad-line Active Galactic Nuclei in Nearby Galaxies: Coeval Star Formation and Rapid Black Hole Growth

NASA Astrophysics Data System (ADS)

Trump, Jonathan R.; Hsu, Alexander D.; Fang, Jerome J.; Faber, S. M.; Koo, David C.; Kocevski, Dale D.

2013-02-01

We present the first quantified, statistical map of broad-line active galactic nucleus (AGN) frequency with host galaxy color and stellar mass in nearby (0.01 < z < 0.11) galaxies. Aperture photometry and z-band concentration measurements from the Sloan Digital Sky Survey are used to disentangle AGN and galaxy emission, resulting in estimates of uncontaminated galaxy rest-frame color, luminosity, and stellar mass. Broad-line AGNs are distributed throughout the blue cloud and green valley at a given stellar mass, and are much rarer in quiescent (red sequence) galaxies. This is in contrast to the published host galaxy properties of weaker narrow-line AGNs, indicating that broad-line AGNs occur during a different phase in galaxy evolution. More luminous broad-line AGNs have bluer host galaxies, even at fixed mass, suggesting that the same processes that fuel nuclear activity also efficiently form stars. The data favor processes that simultaneously fuel both star formation activity and rapid supermassive black hole accretion. If AGNs cause feedback on their host galaxies in the nearby universe, the evidence of galaxy-wide quenching must be delayed until after the broad-line AGN phase.

A water-vapour giga-maser in the active galaxy TXFS2226-184.

PubMed

Koekemoer, A M; Henkel, C; Greenhill, L J; Dey, A; van Breugel, W; Codella, C; Antonucci, R

1995-12-14

Active galactic nuclei are thought to be powered by gas falling into a massive black hole; the different types of active galaxy may arise because we view them through a thick torus of molecular gas at varying angles of inclination. One way to determine whether the black hole is surrounded by a torus, which would obscure the accretion disk around the black hole along certain lines of sight, is to search for water masers, as these exist only in regions with plentiful molecular gas. Since the first detection of an extra-galactic water maser in 1979, they have come to be associated primarily with active galaxies, and have even been used to probe the mass of the central engine. Here we report the detection of a water giga-maser in the radio galaxy TXFS2226-184. The strength of the emission supports a recently proposed theory of maser pumping that allows for even more powerful masers, which might be detectable at cosmological distances. Water masers may accordingly provide a way to determine distances to galaxies outside the usual distance ladder, providing an independent calibration of the Hubble constant.

Metal enrichment in the Fermi bubbles as a probe of their origin

NASA Astrophysics Data System (ADS)

Inoue, Yoshiyuki; Nakashima, Shinya; Tahara, Masaya; Kataoka, Jun; Totani, Tomonori; Fujita, Yutaka; Sofue, Yoshiaki

2015-06-01

The Fermi bubbles are gigantic gamma-ray structures in our Galaxy. The physical origin of the bubbles is still under debate. The leading scenarios can be divided into two categories. One is nuclear star-forming activity similar to extragalactic starburst galaxies and the other is past active galactic nucleus (AGN)-like activity of the Galactic center supermassive black hole. In this letter, we propose that metal abundance measurements will provide an important clue to probe their origin. Based on a simple spherically symmetric bubble model, we find that the generated metallicity and abundance patterns of the bubbles' gas strongly depend on assumed star formation or AGN activities. Star formation scenarios predict higher metallicities and abundance ratios of [O/Fe] and [Ne/Fe] than AGN scenarios do because of supernovae ejecta. Furthermore, the resultant abundance depends on the gamma-ray emission process because different mass injection histories are required for the different gamma-ray emission processes due to the acceleration and cooling time scales of non-thermal particles. Future X-ray missions such as ASTRO-H and Athena will give a clue to probe the origin of the bubbles through abundance measurements with their high energy resolution instruments.

Long time scale hard X-ray variability in Seyfert 1 galaxies

NASA Astrophysics Data System (ADS)

Markowitz, Alex Gary

This dissertation examines the relationship between long-term X-ray variability characteristics, black hole mass, and luminosity of Seyfert 1 Active Galactic Nuclei. High dynamic range power spectral density functions (PSDs) have been constructed for six Seyfert 1 galaxies. These PSDs show "breaks" or characteristic time scales, typically on the order of a few days. There is resemblance to PSDs of lower-mass Galactic X-ray binaries (XRBs), with the ratios of putative black hole masses and variability time scales approximately the same (106--7) between the two classes of objects. The data are consistent with a linear correlation between Seyfert PSD break time scale and black hole mass estimate; the relation extrapolates reasonably well over 6--7 orders of magnitude to XRBs. All of this strengthens the case for a physical similarity between Seyfert galaxies and XRBs. The first six years of RXTE monitoring of Seyfert 1s have been systematically analyzed to probe hard X-ray variability on multiple time scales in a total of 19 Seyfert is in an expansion of the survey of Markowitz & Edelson (2001). Correlations between variability amplitude, luminosity, and black hole mass are explored, the data support the model of PSD movement with black hole mass suggested by the PSD survey. All of the continuum variability results are consistent with relatively more massive black holes hosting larger X-ray emission regions, resulting in 'slower' observed variability. Nearly all sources in the sample exhibit stronger variability towards softer energies, consistent with softening as they brighten. Direct time-resolved spectral fitting has been performed on continuous RXTE monitoring of seven Seyfert is to study long-term spectral variability and Fe Kalpha variability characteristics. The Fe Kalpha line displays a wide range of behavior but varies less strongly than the broadband continuum. Overall, however, there is no strong evidence for correlated variability between the line and continuum, severely challenging models in which the line tracks continuum variations modified only by a light-travel time delay. This experiment yields further support for spectral softening as continuum flux increases.

Active eye-tracking for an adaptive optics scanning laser ophthalmoscope

PubMed Central

Sheehy, Christy K.; Tiruveedhula, Pavan; Sabesan, Ramkumar; Roorda, Austin

2015-01-01

We demonstrate a system that combines a tracking scanning laser ophthalmoscope (TSLO) and an adaptive optics scanning laser ophthalmoscope (AOSLO) system resulting in both optical (hardware) and digital (software) eye-tracking capabilities. The hybrid system employs the TSLO for active eye-tracking at a rate up to 960 Hz for real-time stabilization of the AOSLO system. AOSLO videos with active eye-tracking signals showed, at most, an amplitude of motion of 0.20 arcminutes for horizontal motion and 0.14 arcminutes for vertical motion. Subsequent real-time digital stabilization limited residual motion to an average of only 0.06 arcminutes (a 95% reduction). By correcting for high amplitude, low frequency drifts of the eye, the active TSLO eye-tracking system enabled the AOSLO system to capture high-resolution retinal images over a larger range of motion than previously possible with just the AOSLO imaging system alone. PMID:26203370

The interstellar medium and star formation of galactic disks. I. Interstellar medium and giant molecular cloud properties with diffuse far-ultraviolet and cosmic-ray backgrounds

NASA Astrophysics Data System (ADS)

Li, Qi; Tan, Jonathan C.; Christie, Duncan; Bisbas, Thomas G.; Wu, Benjamin

2018-05-01

We present a series of adaptive mesh refinement hydrodynamic simulations of flat rotation curve galactic gas disks, with a detailed treatment of the interstellar medium (ISM) physics of the atomic to molecular phase transition under the influence of diffuse far-ultraviolet (FUV) radiation fields and cosmic-ray backgrounds. We explore the effects of different FUV intensities, including a model with a radial gradient designed to mimic the Milky Way. The effects of cosmic rays, including radial gradients in their heating and ionization rates, are also explored. The final simulations in this series achieve 4 pc resolution across the ˜20 kpc global disk diameter, with heating and cooling followed down to temperatures of ˜10 K. The disks are evolved for 300 Myr, which is enough time for the ISM to achieve a quasi-statistical equilibrium. In particular, the mass fraction of molecular gas is stabilized by ˜200 Myr. Additional global ISM properties are analyzed. Giant molecular clouds (GMCs) are also identified and the statistical properties of their populations are examined. GMCs are tracked as the disks evolve. GMC collisions, which may be a means of triggering star cluster formation, are counted and their rates are compared with analytic models. Relatively frequent GMC collision rates are seen in these simulations, and their implications for understanding GMC properties, including the driving of internal turbulence, are discussed.

Monash Chemical Yields Project (Monχey) Element production in low- and intermediate-mass stars

NASA Astrophysics Data System (ADS)

Doherty, Carolyn; Lattanzio, John; Angelou, George; Campbell, Simon W.; Church, Ross; Constantino, Thomas; Cristallo, Sergio; Gil-Pons, Pilar; Karakas, Amanda; Lugaro, Maria; Stancliffe, Richard

The Monχey project will provide a large and homogeneous set of stellar yields for the low- and intermediate- mass stars and has applications particularly to galactic chemical evolution modelling. We describe our detailed grid of stellar evolutionary models and corresponding nucleosynthetic yields for stars of initial mass 0.8 M⊙ up to the limit for core collapse supernova (CC-SN) ~ 10 M⊙. Our study covers a broad range of metallicities, ranging from the first, primordial stars (Z = 0) to those of super-solar metallicity (Z = 0.04). The models are evolved from the zero-age main-sequence until the end of the asymptotic giant branch (AGB) and the nucleosynthesis calculations include all elements from H to Bi. A major innovation of our work is the first complete grid of heavy element nucleosynthetic predictions for primordial AGB stars as well as the inclusion of extra-mixing processes (in this case thermohaline) during the red giant branch. We provide a broad overview of our results with implications for galactic chemical evolution as well as highlight interesting results such as heavy element production in dredge-out events of super-AGB stars. We briefly introduce our forthcoming web-based database which provides the evolutionary tracks, structural properties, internal/surface nucleosynthetic compositions and stellar yields. Our web interface includes user- driven plotting capabilities with output available in a range of formats. Our nucleosynthetic results will be available for further use in post processing calculations for dust production yields.

The zero age main sequence of WIMP burners

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fairbairn, Malcolm; Scott, Pat; Edsjoe, Joakim

2008-02-15

We modify a stellar structure code to estimate the effect upon the main sequence of the accretion of weakly-interacting dark matter onto stars and its subsequent annihilation. The effect upon the stars depends upon whether the energy generation rate from dark matter annihilation is large enough to shut off the nuclear burning in the star. Main sequence weakly-interacting massive particles (WIMP) burners look much like proto-stars moving on the Hayashi track, although they are in principle completely stable. We make some brief comments about where such stars could be found, how they might be observed and more detailed simulations whichmore » are currently in progress. Finally we comment on whether or not it is possible to link the paradoxically hot, young stars found at the galactic center with WIMP burners.« less

Cosmic-ray record in solar system matter

NASA Technical Reports Server (NTRS)

Reedy, R. C.; Arnold, J. R.; Lal, D.

1983-01-01

The interaction of galactic cosmic rays (GCR) and solar cosmic rays (SCR) with bodies in the solar system is discussed, and what the record of that interaction reveals about the history of the solar system is considered. The influence of the energy, charge, and mass of the particles on the interaction is addressed, showing long-term average fluxes of solar protons, predicted production rates for heavy-nuclei tracks and various radionuclides as a function of depth in lunar rock, and integral fluxes of protons emitted by solar flares. The variation of the earth's magnetic field, the gardening of the lunar surface, and the source of meteorites and cosmic dust are studied using the cosmic ray record. The time variation of GCR, SCR, and VH and VVH nuclei is discussed for both the short and the long term.

Evolutionary synthesis of simple stellar populations. Colours and indices

NASA Astrophysics Data System (ADS)

Kurth, O. M.; Fritze-v. Alvensleben, U.; Fricke, K. J.

1999-07-01

We construct evolutionary synthesis models for simple stellar populations using the evolutionary tracks from the Padova group (1993, 1994), theoretical colour calibrations from \\cite[Lejeune et al. (1997, 1998)]{lejeune} and fit functions for stellar atmospheric indices from \\cite[Worthey et al. (1994)]{worthey}. A Monte-Carlo technique allows us to obtain a smooth time evolution of both broad band colours in UBVRIK and a series of stellar absorption features for Single Burst Stellar Populations (SSPs). We present colours and indices for SSPs with ages from 1 \\ 10(9) yrs to 1.6 \\ 10(10) yrs and metallicities [M/H]=-2.3, -1.7, -0.7, -0.4, 0.0 and 0.4. Model colours and indices at an age of about a Hubble time are in good agreement with observed colours and indices of the Galactic and M 31 GCs.

The Mass Function of Young Star Clusters in the "Antennae" Galaxies.

PubMed

Zhang; Fall

1999-12-20

We determine the mass function of young star clusters in the merging galaxies known as the "Antennae" (NGC 4038/9) from deep images taken with the Wide Field Planetary Camera 2 on the refurbished Hubble Space Telescope. This is accomplished by means of reddening-free parameters and a comparison with stellar population synthesis tracks to estimate the intrinsic luminosity and age, and hence the mass, of each cluster. We find that the mass function of the young star clusters (with ages less, similar160 Myr) is well represented by a power law of the form psi&parl0;M&parr0;~M-2 over the range 104 less, similarM less, similar106 M middle dot in circle. This result may have important implications for our understanding of the origin of globular clusters during the early phases of galactic evolution.

A census of radio-selected AGNs on the COSMOS field and of their FIR properties

NASA Astrophysics Data System (ADS)

Magliocchetti, M.; Popesso, P.; Brusa, M.; Salvato, M.

2018-01-01

We use the new catalogue by Laigle et al. to provide a full census of VLA-COSMOS radio sources. We identify 90 per cent of such sources and sub-divide them into active galactic nuclei (AGNs) and star-forming galaxies on the basis of their radio luminosity. The AGN sample is complete with respect to radio selection at all z ≲ 3.5. Out of 704 AGNs, 272 have a counterpart in the Herschel maps. By exploiting the better statistics of the new sample, we confirm the results of Magliocchetti et al.: the probability for a radio-selected AGN to be detected at far-infrared (FIR) wavelengths is both a function of radio luminosity and redshift, whereby powerful sources are more likely FIR emitters at earlier epochs. Such an emission is due to star-forming processes within the host galaxy. FIR emitters and non-FIR emitters only differentiate in the z ≲ 1 universe. At higher redshifts, they are indistinguishable from each other, as there is no difference between FIR-emitting AGNs and star-forming galaxies. Lastly, we focus on radio AGNs which show AGN emission at other wavelengths. We find that mid-infrared (MIR) emission is mainly associated with ongoing star formation and with sources which are smaller, younger and more radio luminous than the average parent population. X-ray emitters instead preferentially appear in more massive and older galaxies. We can therefore envisage an evolutionary track whereby the first phase of a radio-active AGN and of its host galaxy is associated with MIR emission, while at later stages the source becomes only active at radio wavelengths and possibly also in the X-ray.

VizieR Online Data Catalog: OGLE II. VI photometry of Galactic Bulge (Udalski+, 2002)

NASA Astrophysics Data System (ADS)

Udalski, A.; Szymanski, M.; Kubiak, M.; Pietrzynski, G.; Soszynski, I.; Wozniak, P.; Zebrun, K.; Szewczyk, O.; Wyrzykowski, L.

2003-09-01

We present the VI photometric maps of the Galactic bulge. They contain VI photometry and astrometry of about 30 million stars from 49 fields of 0.225 square degree each in the Galactic center region. The data were collected during the second phase of the OGLE microlensing project. We discuss the accuracy of data and present color-magnitude diagrams of selected fields observed by OGLE in the Galactic bulge. The VI maps of the Galactic bulge are accessible electronically for the astronomical community from the OGLE Internet archive (2 data files).

Two chemically similar stellar overdensities on opposite sides of the plane of the Galactic disk.

PubMed

Bergemann, Maria; Sesar, Branimir; Cohen, Judith G; Serenelli, Aldo M; Sheffield, Allyson; Li, Ting S; Casagrande, Luca; Johnston, Kathryn V; Laporte, Chervin F P; Price-Whelan, Adrian M; Schönrich, Ralph; Gould, Andrew

2018-03-15

Our Galaxy is thought to have an active evolutionary history, dominated over the past ten billion years or so by star formation, the accretion of cold gas and, in particular, the merging of clumps of baryonic and dark matter. The stellar halo-the faint, roughly spherical component of the Galaxy-reveals rich 'fossil' evidence of these interactions, in the form of stellar streams, substructures and chemically distinct stellar components. The effects of interactions with dwarf galaxies on the content and morphology of the Galactic disk are still being explored. Recent studies have identified kinematically distinct stellar substructures and moving groups of stars in our Galaxy, which may have extragalactic origins. There is also mounting evidence that stellar overdensities (regions with greater-than-average stellar density) at the interface between the outer disk and the halo could have been caused by the interaction of a dwarf galaxy with the disk. Here we report a spectroscopic analysis of 14 stars from two stellar overdensities, each lying about five kiloparsecs above or below the Galactic plane-locations suggestive of an association with the stellar halo. We find that the chemical compositions of these two groups of stars are almost identical, both within and between these overdensities, and closely match the abundance patterns of stars in the Galactic disk. We conclude that these stars came from the disk, and that the overdensities that they are part of were created by tidal interactions of the disk with passing or merging dwarf galaxies.

Two chemically similar stellar overdensities on opposite sides of the plane of the Galactic disk

NASA Astrophysics Data System (ADS)

Bergemann, Maria; Sesar, Branimir; Cohen, Judith G.; Serenelli, Aldo M.; Sheffield, Allyson; Li, Ting S.; Casagrande, Luca; Johnston, Kathryn V.; Laporte, Chervin F. P.; Price-Whelan, Adrian M.; Schönrich, Ralph; Gould, Andrew

2018-03-01

Our Galaxy is thought to have an active evolutionary history, dominated over the past ten billion years or so by star formation, the accretion of cold gas and, in particular, the merging of clumps of baryonic and dark matter. The stellar halo—the faint, roughly spherical component of the Galaxy—reveals rich ‘fossil’ evidence of these interactions, in the form of stellar streams, substructures and chemically distinct stellar components. The effects of interactions with dwarf galaxies on the content and morphology of the Galactic disk are still being explored. Recent studies have identified kinematically distinct stellar substructures and moving groups of stars in our Galaxy, which may have extragalactic origins. There is also mounting evidence that stellar overdensities (regions with greater-than-average stellar density) at the interface between the outer disk and the halo could have been caused by the interaction of a dwarf galaxy with the disk. Here we report a spectroscopic analysis of 14 stars from two stellar overdensities, each lying about five kiloparsecs above or below the Galactic plane—locations suggestive of an association with the stellar halo. We find that the chemical compositions of these two groups of stars are almost identical, both within and between these overdensities, and closely match the abundance patterns of stars in the Galactic disk. We conclude that these stars came from the disk, and that the overdensities that they are part of were created by tidal interactions of the disk with passing or merging dwarf galaxies.

The influence of nonstationarity of the solar activity and general solar field on modulation of cosmic rays

NASA Technical Reports Server (NTRS)

Zusmanovich, A. G.; Kryakunova, O. N.; Churunova, L. F.; Shvartsman, Y. E.

1985-01-01

A numerical model of the propagation of galactic cosmic rays in interplanetary space was constructed for the case when the modulation depth determined by the level of solar activity changed in time. Also the contribution of particle drift in the regular field was calculated, and the agreement with experimental data concerning the ratio of protons and electrons in two solar activity minima is shown.

A Census of Large-scale (≥10 PC), Velocity-coherent, Dense Filaments in the Northern Galactic Plane: Automated Identification Using Minimum Spanning Tree

NASA Astrophysics Data System (ADS)

Wang, Ke; Testi, Leonardo; Burkert, Andreas; Walmsley, C. Malcolm; Beuther, Henrik; Henning, Thomas

2016-09-01

Large-scale gaseous filaments with lengths up to the order of 100 pc are on the upper end of the filamentary hierarchy of the Galactic interstellar medium (ISM). Their association with respect to the Galactic structure and their role in Galactic star formation are of great interest from both an observational and theoretical point of view. Previous “by-eye” searches, combined together, have started to uncover the Galactic distribution of large filaments, yet inherent bias and small sample size limit conclusive statistical results from being drawn. Here, we present (1) a new, automated method for identifying large-scale velocity-coherent dense filaments, and (2) the first statistics and the Galactic distribution of these filaments. We use a customized minimum spanning tree algorithm to identify filaments by connecting voxels in the position-position-velocity space, using the Bolocam Galactic Plane Survey spectroscopic catalog. In the range of 7\\buildrel{\\circ}\\over{.} 5≤slant l≤slant 194^\\circ , we have identified 54 large-scale filaments and derived mass (˜ {10}3{--}{10}5 {M}⊙ ), length (10-276 pc), linear mass density (54-8625 {M}⊙ pc-1), aspect ratio, linearity, velocity gradient, temperature, fragmentation, Galactic location, and orientation angle. The filaments concentrate along major spiral arms. They are widely distributed across the Galactic disk, with 50% located within ±20 pc from the Galactic mid-plane and 27% run in the center of spiral arms. An order of 1% of the molecular ISM is confined in large filaments. Massive star formation is more favorable in large filaments compared to elsewhere. This is the first comprehensive catalog of large filaments that can be useful for a quantitative comparison with spiral structures and numerical simulations.

ON THE SCATTER IN THE RADIUS-LUMINOSITY RELATIONSHIP FOR ACTIVE GALACTIC NUCLEI

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kilerci Eser, E.; Vestergaard, M.; Peterson, B. M.

2015-03-01

We investigate and quantify the observed scatter in the empirical relationship between the broad line region size R and the luminosity of the active galactic nucleus, in order to better understand its origin. This study is motivated by the indispensable role of this relationship in the mass estimation of cosmologically distant black holes, but may also be relevant to the recently proposed application of this relationship for measuring cosmic distances. We study six nearby reverberation-mapped active galactic nuclei (AGNs) for which simultaneous UV and optical monitoring data exist. We also examine the long-term optical luminosity variations of the Seyfert 1more » galaxy NGC 5548 and employ Monte Carlo simulations to study the effects of the intrinsic variability of individual objects on the scatter in the global relationship for a sample of ∼40 AGNs. We find the scatter in this relationship has a correctable dependence on color. For individual AGNs, the size of the Hβ emitting region has a steeper dependence on the nuclear optical luminosity than on the UV luminosity, which can introduce a scatter of ∼0.08 dex into the global relationship, due the nonlinear relationship between the variations in the ionizing continuum and those in the optical continuum. Also, our analysis highlights the importance of understanding and minimizing the scatter in the relationship traced by the intrinsic variability of individual AGNs since it propagates directly into the global relationship. We find that using the UV luminosity as a substitute for the ionizing luminosity can reduce a sizable fraction of the current observed scatter of ∼0.13 dex.« less

The COS-AGN survey: Revealing the nature of circum-galactic gas around hosts of active galactic nuclei

NASA Astrophysics Data System (ADS)

Berg, Trystyn A. M.; Ellison, Sara L.; Tumlinson, Jason; Oppenheimer, Benjamin D.; Horton, Ryan; Bordoloi, Rongmon; Schaye, Joop

2018-04-01

Active galactic nuclei (AGN) are thought to play a critical role in shaping galaxies, but their effect on the circumgalactic medium (CGM) is not well studied. We present results from the COS-AGN survey: 19 quasar sightlines that probe the CGM of 20 optically-selected AGN host galaxies with impact parameters 80 <ρimp<300 kpc. Absorption lines from a variety of species are measured and compared to a stellar mass and impact parameter matched sample of sightlines through non-AGN galaxies. Amongst the observed species in the COS-AGN sample (Lyα, Cii , Siii , Siiii , Civ , Siiv , Nv ), only Lyα shows a high covering fraction (94^{+6}_{-23}% for rest-frame equivalent widths EW≥124 mÅ) whilst many of the metal ions are not detected in individual sightlines. A sightline-by-sightline comparison between COS-AGN and the control sample yields no significant difference in EW distribution. However, stacked spectra of the COS-AGN and control samples show significant (>3σ) enhancements in the EW of both Siiii And Lyα at impact parameters >164 kpc by a factor of +0.45 ± 0.05 dex and >+0.75 dex respectively. The lack of detections of both high-ionization species near the AGN and strong kinematic offsets between the absorption systemic galaxy redshifts indicates that neither the AGN's ionization nor its outflows are the origin of these differences. Instead, we suggest the observed differences could result from either AGN hosts residing in haloes with intrinsically distinct gas properties, or that their CGM has been affected by a previous event, such as a starburst, which may also have fuelled the nuclear activity.

A Chandra Observation of the Ultraluminous Infrared Galaxy IRAS 19254-7245 (THE SUPERANTENNAE): X-Ray Emission From the Compton-Thick Active Galactic Nucleus and the Diffuse Starburst

NASA Technical Reports Server (NTRS)

Jia, Jianjun; Ptak, Andrew Francis; Heckman, Timothy M.; Braito, Valantina; Reeves, James

2012-01-01

We present a Chandra observation of IRAS 19254-7245, a nearby ultraluminous infrared galaxy also known as the Superantennae. The high spatial resolution of Chandra allows us to disentangle for the first time the diffuse starburst (SB) emission from the embedded Compton-thick active galactic nucleus (AGN) in the southern nucleus. No AGN activity is detected in the northern nucleus. The 2-10 keV spectrum of the AGN emission is fitted by a flat power law (G = 1.3) and an He-like Fe Ka line with equivalent width 1.5 keV, consistent with previous observations. The Fe Ka line profile could be resolved as a blend of a neutral 6.4 keV line and an ionized 6.7 keV (He-like) or 6.9 keV (H-like) line. Variability of the neutral line is detected compared with the previous XMM-Newton and Suzaku observations, demonstrating the compact size of the iron line emission. The spectrum of the galaxy-scale extended emission excluding the AGN and other bright point sources is fitted with a thermal component with a best-fit kT of 0.8 keV. The 2-10 keV luminosity of the extended emission is about one order of magnitude lower than that of the AGN. The basic physical and structural properties of the extended emission are fully consistent with a galactic wind being driven by the SB. A candidate ultraluminous X-ray source is detected 8 south of the southern nucleus. The 0.3-10 keV luminosity of this off-nuclear point source is 6 × 1040 erg s-1 if the emission is isotropic and the source is associated with the Superantennae.

The e-ASTROGAM gamma-ray space mission

NASA Astrophysics Data System (ADS)

Tatischeff, V.; Tavani, M.; von Ballmoos, P.; Hanlon, L.; Oberlack, U.; Aboudan, A.; Argan, A.; Bernard, D.; Brogna, A.; Bulgarelli, A.; Bykov, A.; Campana, R.; Caraveo, P.; Cardillo, M.; Coppi, P.; De Angelis, A.; Diehl, R.; Donnarumma, I.; Fioretti, V.; Giuliani, A.; Grenier, I.; Grove, J. E.; Hamadache, C.; Hartmann, D.; Hernanz, M.; Isern, J.; Kanbach, G.; Kiener, J.; Knödlseder, J.; Labanti, C.; Laurent, P.; Limousin, O.; Longo, F.; Marisaldi, M.; McBreen, S.; McEnery, J. E.; Mereghetti, S.; Mirabel, F.; Morselli, A.; Nakazawa, K.; Peyré, J.; Piano, G.; Pittori, C.; Sabatini, S.; Stawarz, L.; Thompson, D. J.; Ulyanov, A.; Walter, R.; Wu, X.; Zdziarski, A.; Zoglauer, A.

2016-07-01

e-ASTROGAM is a gamma-ray space mission to be proposed as the M5 Medium-size mission of the European Space Agency. It is dedicated to the observation of the Universe with unprecedented sensitivity in the energy range 0.2 { 100 MeV, extending up to GeV energies, together with a groundbreaking polarization capability. It is designed to substantially improve the COMPTEL and Fermi sensitivities in the MeV-GeV energy range and to open new windows of opportunity for astrophysical and fundamental physics space research. e-ASTROGAM will operate as an open astronomical observatory, with a core science focused on (1) the activity from extreme particle accelerators, including gamma-ray bursts and active galactic nuclei and the link of jet astrophysics to the new astronomy of gravitational waves, neutrinos, ultra-high energy cosmic rays, (2) the high-energy mysteries of the Galactic center and inner Galaxy, including the activity of the supermassive black hole, the Fermi Bubbles, the origin of the Galactic positrons, and the search for dark matter signatures in a new energy window; (3) nucleosynthesis and chemical evolution, including the life cycle of elements produced by supernovae in the Milky Way and the Local Group of galaxies. e-ASTROGAM will be ideal for the study of high-energy sources in general, including pulsars and pulsar wind nebulae, accreting neutron stars and black holes, novae, supernova remnants, and magnetars. And it will also provide important contributions to solar and terrestrial physics. The e-ASTROGAM telescope is optimized for the simultaneous detection of Compton and pair-producing gamma-ray events over a large spectral band. It is based on a very high technology readiness level for all subsystems and includes many innovative features for the detectors and associated electronics.

Active Galactic Videos: A YouTube Channel for Astronomy Education and Outreach

NASA Astrophysics Data System (ADS)

Calahan, Jenny; Gibbs, Aidan; Hardegree-Ullman, Melody; Hardegree-Ullman, Michael; Impey, Chris David; Kevis, Charlotte; Lewter, Austin; Mauldin, Emmalee; McKee, Carolyn; Olmedo, Alejandro; Pereira, Victoria; Thomas, Melissa; Wenger, Matthew

2018-01-01

Active Galactic Videos is an astronomy-focused YouTube channel run by a team at the University of Arizona. The channel both produces astronomy-focused educational content for public audiences and opens a window into the world of professional astronomy by showcasing the work done at Steward Observatory and in Southern Arizona. The channel is mainly run by undergraduate students from a variety of backgrounds including: astronomy, education, film, music, english, and writing. In addition to providing educational content for public audiences, this project provides opportunities for undergraduate students to learn about astronomy content, general astronomy pedagogy, as well as science communication. This is done through developing the practical skills needed to take on the challenge of creating effective and engaging videos. Students write, film, score, direct, and edit each video while conscious of how each piece can affect the teaching/storytelling of the concept at hand. The team has produced various styles of video: presentational, interviews, musical/poetic, tours, and documentaries. In addition to YouTube, the Active Galactic Videos team maintains a social media presence on Facebook, Twitter, and Instagram. These help to widely distribute the content as well as to publicize the main Youtube channel. In addition to providing an overview of our educational work, we present 51 videos, or two year's, worth of online analytics that we are using to better understand our audience, to examine what videos have been popular and successful, and how people are accessing our content. We will present our experience in order to help others learn about improving astronomy education online, as well as astronomy communication and outreach in general.We acknowledge the Howard Hughes Medical Institute for grant support of this and related education initiatives

SDSS-IV MaNGA: Galaxy Pair Fraction and Correlated Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Fu, Hai; Steffen, Joshua L.; Gross, Arran C.; Dai, Y. Sophia; Isbell, Jacob W.; Lin, Lihwai; Wake, David; Xue, Rui; Bizyaev, Dmitry; Pan, Kaike

2018-04-01

We have identified 105 galaxy pairs at z ∼ 0.04 with the MaNGA integral-field spectroscopic data. The pairs have projected separations between 1 and 30 kpc, and are selected to have radial velocity offsets less than 600 km s‑1 and stellar mass ratio between 0.1 and 1. The pair fraction increases with both the physical size of the integral-field unit and the stellar mass, consistent with theoretical expectations. We provide the best-fit analytical function of the pair fraction and find that ∼3% of M* galaxies are in close pairs. For both isolated galaxies and paired galaxies, active galactic nuclei (AGNs) are selected using emission-line ratios and Hα equivalent widths measured inside apertures at a fixed physical size. We find AGNs in ∼24% of the paired galaxies and binary AGNs in ∼13% of the pairs. To account for the selection biases in both the pair sample and the MaNGA sample, we compare the AGN comoving volume densities with those expected from the mass- and redshift-dependent AGN fractions. We find a strong (∼5×) excess of binary AGNs over random pairing and a mild (∼20%) deficit of single AGNs. The binary AGN excess increases from ∼2× to ∼6× as the projected separation decreases from 10–30 to 1–10 kpc. Our results indicate that the pairing of galaxies preserves the AGN duty cycle in individual galaxies but increases the population of binary AGNs through correlated activities. We suggest tidally induced galactic-scale shocks and AGN cross-ionization as two plausible channels to produce low-luminosity narrow-line-selected binary AGNs.

The e-astrogam Gamma-Ray Space Mission

NASA Technical Reports Server (NTRS)

Tatischeff, V.; Tavani, M.; Von Ballmoos, P.; Hanlon, L.; Oberlack, U.; Aboudan, A.; Argan, A.; Bernard, D.; Brogna, A.; Bulgarelli, A.;

Object tracking with stereo vision

NASA Technical Reports Server (NTRS)

Huber, Eric

1994-01-01

A real-time active stereo vision system incorporating gaze control and task directed vision is described. Emphasis is placed on object tracking and object size and shape determination. Techniques include motion-centroid tracking, depth tracking, and contour tracking.

Black-hole model of galactic nuclei

DOE Office of Scientific and Technical Information (OSTI.GOV)

Norman, C.A.; ter Haar, D.

1973-04-01

It is shown that the observed large infrared emission from some galactic nuclei finds a natural explanation, if one takes plasma turbulence into account in Lynden-Bell and Rees' blackhole model of galactic nuclei. (auth)

Star Formation in Galaxies

NASA Technical Reports Server (NTRS)

1987-01-01

Topics addressed include: star formation; galactic infrared emission; molecular clouds; OB star luminosity; dust grains; IRAS observations; galactic disks; stellar formation in Magellanic clouds; irregular galaxies; spiral galaxies; starbursts; morphology of galactic centers; and far-infrared observations.

Chandra/HETG Observations of NGC1275

NASA Astrophysics Data System (ADS)

Reynolds, Christopher

2017-09-01

NGC1275 is the active galactic nucleus (AGN) at the heart of the Perseus cluster of galaxies responsible for the mechanical heating of the intracluster medium (ICM) cool core. We propose a deep (500ks) HETG observation of NGC1275, allowing the first high-S/N, high resolution spectrum of this AGN free from contamination by the bright ICM. We will seek the signatures of powerful winds, answering the central question of whether galactic-scale quasar-mode feedback is occuring simultaneously with cluster-scale radio-mode feedback. We also probe circumnuclear gas (i.e. the fuel supply) through the 6.4keV line previously seen by XMM and Hitomi. These issues are crucial unknowns in our models for the evolution of the most massive galaxies and cluster cores.

Testing the AGN paradigm for our home Galaxy

NASA Technical Reports Server (NTRS)

Ozernoy, Leonid

1992-01-01

Although there are some flaws in each of the methods to constrain the black hole mass, which are described in the above paper, all of them unambiguously indicate that the mass of a putative black hole at the Galactic center is much smaller than a widely quoted value, about 10 exp 6 M(solar). Possibly, the mass of the black hole, if any, does not exceed 100 M(solar) or so. Further work is needed in order to distinguish between such a modest-mass black hole and its potential rival such as a very massive star of about the same mass. Anyway, the Galactic nucleus seems to be a tracer of a past star burst rather than a remnant of a Seyfert galaxy activity.

Activity Tracking for Pilot Error Detection from Flight Data

NASA Technical Reports Server (NTRS)

Callantine, Todd J.; Ashford, Rose (Technical Monitor)

2002-01-01

This report presents an application of activity tracking for pilot error detection from flight data, and describes issues surrounding such an application. It first describes the Crew Activity Tracking System (CATS), in-flight data collected from the NASA Langley Boeing 757 Airborne Research Integrated Experiment System aircraft, and a model of B757 flight crew activities. It then presents an example of CATS detecting actual in-flight crew errors.

Biological Effects of Particles with Very High Energy Deposition on Mammalian Cells Utilizing the Brookhaven Tandem Van de Graaff Accelerator

NASA Technical Reports Server (NTRS)

Saha, Janapriya; Cucinotta, Francis A.; Wang, Minli

2013-01-01

High LET radiation from GCR (Galactic Cosmic Rays) consisting mainly of high charge and energy (HZE) nuclei and secondary protons and neutrons, and secondaries from protons in SPE (Solar Particle Event) pose a major health risk to astronauts due to induction of DNA damage and oxidative stress. Experiments with high energy particles mimicking the space environment for estimation of radiation risk are being performed at NASA Space Radiation Laboratory at BNL. Experiments with low energy particles comparing to high energy particles of similar LET are of interest for investigation of the role of track structure on biological effects. For this purpose, we report results utilizing the Tandem Van de Graaff accelerator at BNL. The primary objective of our studies is to elucidate the influence of high vs low energy deposition on track structure, delta ray contribution and resulting biological responses. These low energy ions are of special relevance as these energies may occur following absorption through the spacecraft and shielding materials in human tissues and nuclear fragments produced in tissues by high energy protons and neutrons. This study will help to verify the efficiency of these low energy particles and better understand how various cell types respond to them.

The first catalog of active galactic nuclei detected by the FERMI large area telescope

DOE PAGES

Abdo, A. A.; Ackermann, M.; Ajello, M.; ...

2010-04-29

Here, we present the first catalog of active galactic nuclei (AGNs) detected by the Large Area Telescope (LAT), corresponding to 11 months of data collected in scientific operation mode. The First LAT AGN Catalog (1LAC) includes 671 γ-ray sources located at high Galactic latitudes (|b|>10°) that are detected with a test statistic greater than 25 and associated statistically with AGNs. Some LAT sources are associated with multiple AGNs, and consequently, the catalog includes 709 AGNs, comprising 300 BL Lacertae objects, 296 flat-spectrum radio quasars, 41 AGNs of other types, and 72 AGNs of unknown type. We also classify the blazarsmore » based on their spectral energy distributions as archival radio, optical, and X-ray data permit. In addition to the formal 1LAC sample, we provide AGN associations for 51 low-latitude LAT sources and AGN "affiliations" (unquantified counterpart candidates) for 104 high-latitude LAT sources without AGN associations. The overlap of the 1LAC with existing γ-ray AGN catalogs (LBAS, EGRET, AGILE, Swift, INTEGRAL, TeVCat) is briefly discussed. Various properties—such as γ-ray fluxes and photon power-law spectral indices, redshifts, γ-ray luminosities, variability, and archival radio luminosities—and their correlations are presented and discussed for the different blazar classes. Lastly, we compare the 1LAC results with predictions regarding the γ-ray AGN populations, and we comment on the power of the sample to address the question of the blazar sequence.« less

Molecular Abundances in the Disk of AN Active Galactic Nucleus

NASA Astrophysics Data System (ADS)

Harada, N.; Thompson, T. A.; Herbst, E.

2011-06-01

There are galactic nuclei that emit high luminosities L˜1044-46 erg S-1 including luminosity produced by X-rays from high mass accretion onto the central black holes. These nuclei are called active galactic nuclei (AGNs), and they are accompanied by molecular disks. Observations show high abundances of CN and HCN in the disks; the molecules are proposed to be probes of X-ray dominated regions (XDRs) created by the X-rays from AGNs. We have constructed a spatially-dependent chemical-abundance model of the molecular disk in NGC 1068, a typical AGN-dominated galaxy. Recently, new observations of CN and HCN have been made at much higher spatial resolution, and there are also detections of polyatomic molecules such as HC3N, c-C3H2, and C2H. We discuss how these observations and our simulations can help us to better understand the physical conditions, the disk structure, and conditions for star formation within molecular disks, which are still uncertain. We also include a comparison with other types of galaxies such as (ultra-) luminous infrared galaxies. Usero et al.Astronomy and Astrophysics. 419 (897), 2004. Initial results were presented at the International Symposium on Molecular Spectroscopy 2010, RF05 Garcia-Burillo et al. Astronomy and Astrophysics. 519 (2), 2010. Garcia-Burillo et al. Journal of Physics Conference Series, 131 (12031), 2008. Costagliola et al. ArXiv e-print arXiv:1101.2122, 2011. Nakajima et al. Astrophysical Journal Letters 728 (L38), 2008.

Spectroscopic classification of X-ray sources in the Galactic Bulge Survey

NASA Astrophysics Data System (ADS)

Wevers, T.; Torres, M. A. P.; Jonker, P. G.; Nelemans, G.; Heinke, C.; Mata Sánchez, D.; Johnson, C. B.; Gazer, R.; Steeghs, D. T. H.; Maccarone, T. J.; Hynes, R. I.; Casares, J.; Udalski, A.; Wetuski, J.; Britt, C. T.; Kostrzewa-Rutkowska, Z.; Wyrzykowski, Ł.

2017-10-01

We present the classification of 26 optical counterparts to X-ray sources discovered in the Galactic Bulge Survey. We use (time-resolved) photometric and spectroscopic observations to classify the X-ray sources based on their multiwavelength properties. We find a variety of source classes, spanning different phases of stellar/binary evolution. We classify CX21 as a quiescent cataclysmic variable (CV) below the period gap, and CX118 as a high accretion rate (nova-like) CV. CXB12 displays excess UV emission, and could contain a compact object with a giant star companion, making it a candidate symbiotic binary or quiescent low-mass X-ray binary (although other scenarios cannot be ruled out). CXB34 is a magnetic CV (polar) that shows photometric evidence for a change in accretion state. The magnetic classification is based on the detection of X-ray pulsations with a period of 81 ± 2 min. CXB42 is identified as a young stellar object, namely a weak-lined T Tauri star exhibiting (to date unexplained) UX Ori-like photometric variability. The optical spectrum of CXB43 contains two (resolved) unidentified double-peaked emission lines. No known scenario, such as an active galactic nucleus or symbiotic binary, can easily explain its characteristics. We additionally classify 20 objects as likely active stars based on optical spectroscopy, their X-ray to optical flux ratios and photometric variability. In four cases we identify the sources as binary stars.

Office of Tracking and Data Acquisition. [deep space network and spacecraft tracking

NASA Technical Reports Server (NTRS)

1975-01-01

The Office of Tracking and Data Acquisition (OTDA) and its two worldwide tracking network facilities, the Spaceflight Tracking and Data Network and the Deep Space Network, are described. Other topics discussed include the NASA communications network, the tracking and data relay satellite system, other OTDA tracking activities, and OTDA milestones.

Global dynamics and diffusion in triaxial galactic models

NASA Astrophysics Data System (ADS)

Papaphilippou, Y.

We apply the Frequency Map Analysis method to the 3--dimensional logarithmic galactic potential in order to clarify the dynamical behaviour of triaxial power--law galactic models. All the fine dynamical details are displayed in the complete frequency map, a direct representation of the system's Arnol'd web. The influence of resonant lines and the extent of the chaotic zones are directly associated with the physical space of the system. Some new results related with the diffusion of galactic orbits are also discussed. This approach reveals many unknown dynamical features of triaxial galactic potentials and provides strong indications that chaos should be an innate characteristic of triaxial configurations.

The Planck Catalogue of Galactic Cold Clumps : PGCC

NASA Astrophysics Data System (ADS)

Montier, L.

The Planck satellite has provided an unprecedented view of the submm sky, allowing us to search for the dust emission of Galactic cold sources. Combining Planck-HFI all-sky maps in the high frequency channels with the IRAS map at 100um, we built the Planck catalogue of Galactic Cold Clumps (PGCC, Planck 2015 results. XXVIII), counting 13188 sources distributed over the whole sky, and following mainly the Galactic structures at low and intermediate latitudes. This is the first all-sky catalogue of Galactic cold sources obtained with a single instrument at this resolution and sensitivity, which opens a new window on star-formation processes in our Galaxy.

Hustle and Bustle at Center of Milky Way

NASA Image and Video Library

2013-05-07

This artist concept illustrates the frenzied activity at the core of our Milky Way galaxy. The galactic center hosts a supermassive black hole in the region known as Sagittarius A*, or Sgr A*, with a mass of about four million times that of our sun.

The Challenge of Space Futures: Starcomber's Galactic Voyage to Xeranthemom.

ERIC Educational Resources Information Center

Shimonauff, Jacqueline

1998-01-01

Describes a curriculum enrichment activity for gifted middle school students. Students design a long-range space travel vehicle and plan for colonizing a discovered planet. Students contact people in science and industry and produce a handbook for space travel and colonization. (DB)

Proto-jet configurations in RADs orbiting a Kerr SMBH: symmetries and limiting surfaces

NASA Astrophysics Data System (ADS)

Pugliese, D.; Stuchlík, Z.

2018-05-01

Ringed accretion disks (RADs) are agglomerations of perfect-fluid tori orbiting around a single central attractor that could arise during complex matter inflows in active galactic nuclei. We focus our analysis to axi-symmetric accretion tori orbiting in the equatorial plane of a supermassive Kerr black hole; equilibrium configurations, possible instabilities, and evolutionary sequences of RADs were discussed in our previous works. In the present work we discuss special instabilities related to open equipotential surfaces governing the material funnels emerging at various regions of the RADs, being located between two or more individual toroidal configurations of the agglomerate. These open structures could be associated to proto-jets. Boundary limiting surfaces are highlighted, connecting the emergency of the jet-like instabilities with the black hole dimensionless spin. These instabilities are observationally significant for active galactic nuclei, being related to outflows of matter in jets emerging from more than one torus of RADs orbiting around supermassive black holes.

NEW CLASS OF VERY HIGH ENERGY {gamma}-RAY EMITTERS: RADIO-DARK MINI SHELLS SURROUNDING ACTIVE GALACTIC NUCLEUS JETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kino, Motoki; Ito, Hirotaka; Kawakatu, Nozomu

We explore non-thermal emission from a shocked interstellar medium, which is identified as an expanding shell, driven by a relativistic jet in active galactic nuclei (AGNs). In this work, we particularly focus on parsec-scale size mini shells surrounding mini radio lobes. From the radio to X-ray band, the mini radio lobe emission dominates the faint emission from the mini shell. On the other hand, we find that inverse-Compton (IC) emission from the shell can overwhelm the associated lobe emission at the very high energy (VHE; E > 100 GeV) {gamma}-ray range, because energy densities of synchrotron photons from the lobemore » and/or soft photons from the AGN nucleus are large and IC scattering works effectively. The predicted IC emission from nearby mini shells can be detected with the Cherenkov Telescope Array and they are potentially a new class of VHE {gamma}-ray emitters.« less

Thermal wind from hot accretion flows at large radii

NASA Astrophysics Data System (ADS)

Bu, De-Fu; Yang, Xiao-Hong

2018-06-01

We study slowly rotating accretion flow at parsec and subparsec scales irradiated by low-luminosity active galactic nuclei. We take into account the Compton heating, photoionization heating by the central X-rays. The bremsstrahlung cooling, recombination, and line cooling are also included. We find that due to the Compton heating, wind can be thermally driven. The power of wind is in the range (10-6-10-3) LEdd, with LEdd being the Eddington luminosity. The mass flux of wind is in the range (0.01-1) \\dot{M}_Edd (\\dot{M}_Edd= L_Edd/0.1c^2 is the Eddington accretion rate, c is speed of light). We define the wind generation efficiency as ɛ = P_W/\\dot{M}_BHc^2, with PW being wind power, \\dot{M}_BH being the mass accretion rate on to the black hole. ɛ lies in the range 10-4-1.18. Wind production efficiency decreases with increasing mass accretion rate. The possible role of the thermally driven wind in the active galactic feedback is briefly discussed.

Cooling Timescale of Dust Tori in Dying Active Galactic Nuclei

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ichikawa, Kohei; Tazaki, Ryo, E-mail: k.ichikawa@astro.columbia.edu

We estimate the dust torus cooling timescale once the active galactic nucleus (AGN) is quenched. In a clumpy torus system, once the incoming photons are suppressed, the cooling timescale of one clump from T {sub dust} = 1000 K to several 10 K is less than 10 years, indicating that the dust torus cooling time is mainly governed by the light crossing time of the torus from the central engine. After considering the light crossing time of the torus, the AGN torus emission at 12 μ m becomes over two orders of magnitude fainter within 100 years after the quenching.more » We also propose that those “dying” AGNs could be found using the AGN indicators with a different physical scale R such as 12 μ m band luminosity tracing AGN torus ( R ∼ 10 pc) and the optical [O iii] λ 5007 emission line tracing narrow line regions ( R = 10{sup 2–4} pc).« less

All-Sky Earth Occultation Observations with the Fermi Gamma Ray Burst Monitor

NASA Technical Reports Server (NTRS)

Wilson-Hodge, C. A.; Beklen, E.; Bhat, P. N.; Briggs, M.; Camero-Arranz, A.; Case, G.; Chaplin, V.; Cherry, M.; Connaughton, V.; Finger, M.;

Accretion-induced variability links young stellar objects, white dwarfs, and black holes.

PubMed

Scaringi, Simone; Maccarone, Thomas J; Körding, Elmar; Knigge, Christian; Vaughan, Simon; Marsh, Thomas R; Aranzana, Ester; Dhillon, Vikram S; Barros, Susana C C

2015-10-01

The central engines of disc-accreting stellar-mass black holes appear to be scaled down versions of the supermassive black holes that power active galactic nuclei. However, if the physics of accretion is universal, it should also be possible to extend this scaling to other types of accreting systems, irrespective of accretor mass, size, or type. We examine new observations, obtained with Kepler/K2 and ULTRACAM, regarding accreting white dwarfs and young stellar objects. Every object in the sample displays the same linear correlation between the brightness of the source and its amplitude of variability (rms-flux relation) and obeys the same quantitative scaling relation as stellar-mass black holes and active galactic nuclei. We also show that the most important parameter in this scaling relation is the physical size of the accreting object. This establishes the universality of accretion physics from proto-stars still in the star-forming process to the supermassive black holes at the centers of galaxies.

Submillimeter evidence for the coeval growth of massive black holes and galaxy bulges.

PubMed

Page, M J; Stevens, J A; Mittaz, J P; Carrera, F J

2001-12-21

The correlation, found in nearby galaxies, between black hole mass and stellar bulge mass implies that the formation of these two components must be related. Here we report submillimeter photometry of eight x-ray-absorbed active galactic nuclei that have luminosities and redshifts characteristic of the sources that produce the bulk of the accretion luminosity in the universe. The four sources with the highest redshifts are detected at 850 micrometers, with flux densities between 5.9 and 10.1 millijanskies, and hence are ultraluminous infrared galaxies. If the emission is from dust heated by starbursts, then the majority of stars in spheroids were formed at the same time as their central black holes built up most of their mass by accretion. This would account for the observed demography of massive black holes in the local universe. The skewed rate of submillimeter detection with redshift is consistent with a high redshift epoch of star formation in radio-quiet active galactic nuclei, similar to that seen in radio galaxies.

Accretion-induced variability links young stellar objects, white dwarfs, and black holes

PubMed Central

Scaringi, Simone; Maccarone, Thomas J.; Körding, Elmar; Knigge, Christian; Vaughan, Simon; Marsh, Thomas R.; Aranzana, Ester; Dhillon, Vikram S.; Barros, Susana C. C.

2015-01-01

The central engines of disc-accreting stellar-mass black holes appear to be scaled down versions of the supermassive black holes that power active galactic nuclei. However, if the physics of accretion is universal, it should also be possible to extend this scaling to other types of accreting systems, irrespective of accretor mass, size, or type. We examine new observations, obtained with Kepler/K2 and ULTRACAM, regarding accreting white dwarfs and young stellar objects. Every object in the sample displays the same linear correlation between the brightness of the source and its amplitude of variability (rms-flux relation) and obeys the same quantitative scaling relation as stellar-mass black holes and active galactic nuclei. We also show that the most important parameter in this scaling relation is the physical size of the accreting object. This establishes the universality of accretion physics from proto-stars still in the star-forming process to the supermassive black holes at the centers of galaxies. PMID:26601307

Probing the Physics of Active Galactic Nuclei

NASA Technical Reports Server (NTRS)

Peterson, Bradley M.

2004-01-01

As a result of a number of large multiwavelength monitoring campaigns that have taken place since the late 1980s, there are now several very large data sets on bright variable active galactic nuclei (AGNs) that are well-sampled in time and can be used to probe the physics of the AGN continuum source and the broad-line emitting region. Most of these data sets have been underutilized, as the emphasis thus far has been primarily on reverberation-mapping issues alone. Broader attempts at analysis have been made on some of the earlier IUE data sets (e.g., data from the 1989 campaign on NGC5 548) , but much of this analysis needs to be revisited now that improved versions of the data are now available from final archive processing. We propose to use the multiwavelength monitoring data that have been accumulated to undertake more thorough investigations of the AGN continuum and broad emission lines, including a more detailed study of line-profile variability, making use of constraints imposed by the reverberation results.

Dielectronic Recombination In Active Galactic Nuclei

NASA Technical Reports Server (NTRS)

Lukic, D. V.; Schnell, M.; Savin, D. W.; Altun, Z.; Badnell, N.; Brandau, C.; Schmidt, E. W.; Mueller, A.; Schippers, S.; Sprenger, F.;

PeV neutrinos from intergalactic interactions of cosmic rays emitted by active galactic nuclei.

PubMed

Kalashev, Oleg E; Kusenko, Alexander; Essey, Warren

2013-07-26

The observed very high energy spectra of distant blazars are well described by secondary gamma rays produced in line-of-sight interactions of cosmic rays with background photons. In the absence of the cosmic-ray contribution, one would not expect to observe very hard spectra from distant sources, but the cosmic ray interactions generate very high energy gamma rays relatively close to the observer, and they are not attenuated significantly. The same interactions of cosmic rays are expected to produce a flux of neutrinos with energies peaked around 1 PeV. We show that the diffuse isotropic neutrino background from many distant sources can be consistent with the neutrino events recently detected by the IceCube experiment. We also find that the flux from any individual nearby source is insufficient to account for these events. The narrow spectrum around 1 PeV implies that some active galactic nuclei can accelerate protons to EeV energies.

IRAS and the Boston University Arecibo Galactic H I Survey: A catalog of cloud properties

NASA Technical Reports Server (NTRS)

Bania, Thomas M.

1992-01-01

The Infrared Astronomy Satellite (IRAS) Galactic Plane Surface Brightness Images were used to identify infrared emission associated with cool, diffuse H I clouds detected by the Boston University-Arecibo Galactic H I Survey. These clouds are associated with galactic star clusters, H II regions, and molecular clouds. Using emission-absorption experiments toward galactic H II regions, we determined the H I properties of cool H I clouds seen in absorption against the thermal continuum, including their kinematic distances. Correlations were then made between IRAS sources and these H II regions, thus some of the spatial confusion associated with the IRAS fields near the galactic plane was resolved since the distances to these sources was known. Because we can also correlate the BU-Arecibo clouds with existing CO surveys, these results will allow us to determine the intrinsic properties of the gas (neutral and ionized atomic as well as molecular) and dust for interstellar clouds in the inner galaxy. For the IRAS-identified H II region sample, we have established the far infrared (FIR) luminosities and galactic distribution of these sources.

On the relation of optical obscuration and X-ray absorption in Seyfert galaxies

NASA Astrophysics Data System (ADS)

Burtscher, L.; Davies, R. I.; Graciá-Carpio, J.; Koss, M. J.; Lin, M.-Y.; Lutz, D.; Nandra, P.; Netzer, H.; Orban de Xivry, G.; Ricci, C.; Rosario, D. J.; Veilleux, S.; Contursi, A.; Genzel, R.; Schnorr-Müller, A.; Sternberg, A.; Sturm, E.; Tacconi, L. J.

2016-02-01

The optical classification of a Seyfert galaxy and whether it is considered X-ray absorbed are often used interchangeably. There are many borderline cases, however, and also numerous examples where the optical and X-ray classifications appear to be in disagreement. In this article we revisit the relation between optical obscuration and X-ray absorption in active galactic nuclei (AGNs). We make use of our "dust colour" method to derive the optical obscuration AV, and consistently estimated X-ray absorbing columns using 0.3-150 keV spectral energy distributions. We also take into account the variable nature of the neutral gas column NH and derive the Seyfert subclasses of all our objects in a consistent way. We show in a sample of 25 local, hard-X-ray detected Seyfert galaxies (log LX/ (erg / s) ≈ 41.5-43.5) that there can actually be a good agreement between optical and X-ray classification. If Seyfert types 1.8 and 1.9 are considered unobscured, the threshold between X-ray unabsorbed and absorbed should be chosen at a column NH = 1022.3 cm-2 to be consistent with the optical classification. We find that NH is related to AV and that the NH/AV ratio is approximately Galactic or higher in all sources, as indicated previously. However, in several objects we also see that deviations from the Galactic ratio are only due to a variable X-ray column, showing that (1) deviations from the Galactic NH/AV can be simply explained by dust-free neutral gas within the broad-line region in some sources; that (2) the dust properties in AGNs can be similar to Galactic dust and that (3) the dust colour method is a robust way to estimate the optical extinction towards the sublimation radius in all but the most obscured AGNs.

Quality Initiatives in the Commercial Development of Reusable Launch Vehicles

DTIC Science & Technology

2015-03-01

National Reconnaissance Office OTV Orbital Test Vehicle RLV Reusable Launch Vehicles SpaceX Space Exploration Technology SRB Solid Rocket...activities within industry and private development efforts such as SpaceX , Blue Origin, and Scaled Composites and their partnership with Virgin Galactic...second section addresses specific activities within industry and private development efforts such as SpaceX , Blue Origin, and Scaled Composites and

Galactic Haze seen by Planck and Galactic Bubbles seen by Fermi

NASA Image and Video Library

2012-02-13

This all-sky image shows the distribution of the galactic haze seen by ESA Planck mission at microwave frequencies superimposed over the high-energy sky, as seen by NASA Fermi Gamma-ray Space Telescope.

The Origin of IRS 16: Dynamically Driven In-Spiral of a Dense Star Cluster to the Galactic Center?

NASA Astrophysics Data System (ADS)

Portegies Zwart, Simon F.; McMillan, Stephen L. W.; Gerhard, Ortwin

2003-08-01

We use direct N-body simulations to study the in-spiral and internal evolution of dense star clusters near the Galactic center. These clusters sink toward the center owing to dynamical friction with the stellar background and may go into core collapse before being disrupted by the Galactic tidal field. If a cluster reaches core collapse before disruption, its dense core, which has become rich in massive stars, survives to reach close to the Galactic center. When it eventually dissolves, the cluster deposits a disproportionate number of massive stars in the innermost parsec of the Galactic nucleus. Comparing the spatial distribution and kinematics of the massive stars with observations of IRS 16, a group of young He I stars near the Galactic center, we argue that this association may have formed in this way.

The structure and content of the galaxy and galactic gamma rays

NASA Technical Reports Server (NTRS)

Fichtel, C. E. (Editor); Stecker, F. W. (Editor)

1977-01-01

Gamma radiation investigations by COS-B and SAS-2 satellite are reported. Data from CO surveys of the galaxy and the galactic distribution of pulsars are analyzed. Theories of galactic gamma ray emission are explored.

Survey of the galactic disk from 1 = -150 deg to 1 = 82 deg in the submillimeter range

NASA Technical Reports Server (NTRS)

Caux, Emmanuel; Serra, Guy

1987-01-01

The first almost complete survey of the galactic disk from 1 = -150 deg to 1 = 82 deg in the submillimeter range (effective wavelength = 380 microns), performed with the AGLAE balloon-borne instrument modified to include a submillimeter channel, is reported. The instrumentation and observational procedures are described, as are the signal processing and calibration. The results are presented as a profile of the submillimeter brightness of the galactic disk displayed as a function of the galactic longitude. This profile exhibits diffuse emission all along the disk with bright peaks associated with resolved sources. The averaged galactic spectrum is in agreement with a temperature distribution of the interstellar cold dust.

Open star clusters and Galactic structure

NASA Astrophysics Data System (ADS)

Joshi, Yogesh C.

2018-04-01

In order to understand the Galactic structure, we perform a statistical analysis of the distribution of various cluster parameters based on an almost complete sample of Galactic open clusters yet available. The geometrical and physical characteristics of a large number of open clusters given in the MWSC catalogue are used to study the spatial distribution of clusters in the Galaxy and determine the scale height, solar offset, local mass density and distribution of reddening material in the solar neighbourhood. We also explored the mass-radius and mass-age relations in the Galactic open star clusters. We find that the estimated parameters of the Galactic disk are largely influenced by the choice of cluster sample.

MIRIS observation of near-infrared diffuse Galactic light

NASA Astrophysics Data System (ADS)

Onishi, Yosuke; Sano, Kei; Matsuura, Shuji; Jeong, Woong-Seob; Pyo, Jeonghyun; Kim, Il-Jong; Seo, Hyun Jong; Han, Wonyong; Lee, DaeHee; Moon, Bongkon; Park, Wonkee; Park, Younsik; Kim, MinGyu; Matsumoto, Toshio; Matsuhara, Hideo; Nakagawa, Takao; Tsumura, Kohji; Shirahata, Mai; Arai, Toshiaki; Ienaka, Nobuyuki

2018-06-01

We report near-infrared (IR) observations of high Galactic latitude clouds to investigate diffuse Galactic light (DGL), which is starlight scattered by interstellar dust grains. The observations were performed at 1.1 and 1.6 μm with a wide-field camera instrument, the Multi-purpose Infra-Red Imaging System (MIRIS) onboard the Korean satellite STSAT-3. The DGL brightness is measured by correlating the near-IR images with a far-IR 100 μm map of interstellar dust thermal emission. The wide-field observation of DGL provides the most accurate DGL measurement achieved to-date. We also find a linear correlation between optical and near-IR DGL in the MBM32 field. To study interstellar dust properties in MBM32, we adopt recent dust models with and without μm-sized very large grains and predict the DGL spectra, taking into account the reddening effect of the interstellar radiation field. The result shows that the observed color of the near-IR DGL is closer to the model spectra without very large grains. This may imply that dust growth in the observed MBM32 field is not active owing to the low density of its interstellar medium.

The first Fermi-LAT catalog of sources above 10 GeV

DOE PAGES

Ackermann, M.; Ajello, M.; Allafort, A.; ...

2013-11-14

Here, we present a catalog of γ-ray sources at energies above 10 GeV based on data from the Large Area Telescope (LAT) accumulated during the first 3 yr of the Fermi Gamma-ray Space Telescope mission. The first Fermi-LAT catalog of >10 GeV sources (1FHL) has 514 sources. For each source we present location, spectrum, a measure of variability, and associations with cataloged sources at other wavelengths. We found that 449 (87%) could be associated with known sources, of which 393 (76% of the 1FHL sources) are active galactic nuclei. Of the 27 sources associated with known pulsars, we find 20more » (12) to have significant pulsations in the range >10 GeV (>25 GeV). In this work we also report that, at energies above 10 GeV, unresolved sources account for 27% ± 8% of the isotropic γ-ray background, while the unresolved Galactic population contributes only at the few percent level to the Galactic diffuse background. We also highlight the subset of the 1FHL sources that are best candidates for detection at energies above 50-100 GeV with current and future ground-based γ-ray observatories.« less

Recent Results on SNRs and PWNe from the Fermi Large Area Telescope

NASA Technical Reports Server (NTRS)

Hays, Elizabeth

2010-01-01

Topics include: Fermi LAT Collaboration groups; galactic results from LAT; a GeV, wide-field instrument; the 1FGL catalog, the Fermi LAT 1FGL source catalog, unidentified gamma-ray sources; variability in 1FGL sources; curvature in 1FGL sources; spectral-variability classification; pulsars and their wind nebulae; gamma-ray pulsars and MSPs; GeV PWN search; Crab pulsar and nebula; Vela X nebular of Vela pulsar; MSH 15-52; supernova remnants, resolved GeV sources, galactic transients, LAT unassociated transient detections; gamma rays from a nova; V407 Cyngi - a symbiotic nova; V407 Cygni: a variable star; and March 11 - a nova. Summary slides include pulsars everywhere, blazars, LAT as an electron detector, cosmic ray spectrum, the Large Area Telescope, the Fermi Observatory, LAT sensitivity with time, candidate gamma-ray events, on-orbit energy calibration and rate, a 1 year sky map, LAT automated science processing, reported GeV flares, early activity and spectacular flare, gamma-ray transients near the galactic plane , two early unassociated transients, counter part search - Fermi J0910-5404; counterpart search 3EG J0903-3531, and a new LAT transient - J1057-6027.

The First Fermi-LAT Catalog of Sources Above 10 GeV

NASA Technical Reports Server (NTRS)

Ackermann, M.; Ajello, M.; Allafort, A.; Atwood, W. B.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Moiseev, Alexander A.

2013-01-01

We present a catalog of gamma-ray sources at energies above 10 GeV based on data from the Large Area Telescope (LAT) accumulated during the first 3 yr of the Fermi Gamma-ray Space Telescope mission. The first Fermi-LAT catalog of >10 GeV sources (1FHL) has 514 sources. For each source we present location, spectrum, a measure of variability, and associations with cataloged sources at other wavelengths. We found that 449 (87%) could be associated with known sources, of which 393 (76% of the 1FHL sources) are active galactic nuclei. Of the 27 sources associated with known pulsars, we find 20 (12) to have significant pulsations in the range >10 GeV (>25 GeV). In this work we also report that, at energies above 10 GeV, unresolved sources account for 27% +/- 8% of the isotropic ? -ray background, while the unresolved Galactic population contributes only at the few percent level to the Galactic diffuse background. We also highlight the subset of the 1FHL sources that are best candidates for detection at energies above 50-100 GeV with current and future ground-based ? -ray observatories.

Interpreting radiative efficiency in radio-loud AGNs

NASA Astrophysics Data System (ADS)

Hardcastle, Martin

2018-04-01

Radiative efficiency in radio-loud active galactic nuclei is governed by the accretion rate onto the central black hole rather than directly by the type of accreted matter; while it correlates with real differences in host galaxies and environments, it does not provide unambiguous information about particular objects.

The annihilation of galactic positrons

NASA Technical Reports Server (NTRS)

Bussard, R.; Rematy, R.

1978-01-01

The probabilities of various channels of galactic positron annihilation were evaluated and the spectrum of the resulting radiation was calculated. The narrow width (FWHM less than 3.2 keV) of the 0.511 MeV line observed from the galactic center implies that a large fraction of positrons should annihilate in a medium of temperature less than 100,000 K and ionization fraction greater than 0.05. HII regions at the galactic center could be possible sites of annihilation.

A complete system for head tracking using motion-based particle filter and randomly perturbed active contour

NASA Astrophysics Data System (ADS)

Bouaynaya, N.; Schonfeld, Dan

2005-03-01

Many real world applications in computer and multimedia such as augmented reality and environmental imaging require an elastic accurate contour around a tracked object. In the first part of the paper we introduce a novel tracking algorithm that combines a motion estimation technique with the Bayesian Importance Sampling framework. We use Adaptive Block Matching (ABM) as the motion estimation technique. We construct the proposal density from the estimated motion vector. The resulting algorithm requires a small number of particles for efficient tracking. The tracking is adaptive to different categories of motion even with a poor a priori knowledge of the system dynamics. Particulary off-line learning is not needed. A parametric representation of the object is used for tracking purposes. In the second part of the paper, we refine the tracking output from a parametric sample to an elastic contour around the object. We use a 1D active contour model based on a dynamic programming scheme to refine the output of the tracker. To improve the convergence of the active contour, we perform the optimization over a set of randomly perturbed initial conditions. Our experiments are applied to head tracking. We report promising tracking results in complex environments.

Moodog: Tracking Student Activity in Online Course Management Systems

ERIC Educational Resources Information Center

Zhang, Hangjin; Almeroth, Kevin

2010-01-01

Many universities are currently using Course Management Systems (CMSes) to conduct online learning, for example, by distributing course materials or submitting homework assignments. However, most CMSes do not include comprehensive activity tracking and analysis capabilities. This paper describes a method to track students' online learning…

Projected WIMP Sensitivity of the LUX-ZEPLIN (LZ) Dark Matter Experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akerib, D.S.; et al.

LUX-ZEPLIN (LZ) is a next generation dark matter direct detection experiment that will operate 4850 feet underground at the Sanford Underground Research Facility (SURF) in Lead, South Dakota, USA. Using a two-phase xenon detector with an active mass of 7 tonnes, LZ will search primarily for low-energy interactions with Weakly Interacting Massive Particles (WIMPs), which are hypothesized to make up the dark matter in our galactic halo. In this paper, the projected WIMP sensitivity of LZ is presented based on the latest background estimates and simulations of the detector. For a 1000 live day run using a 5.6 tonne fiducial mass, LZ is projected to exclude at 90% confidence level spin-independent WIMP-nucleon cross sections abovemore » $$1.6 \\times 10^{-48}$$ cm$$^{2}$$ for a 40 $$\\mathrm{GeV}/c^{2}$$ mass WIMP. Additionally, a $$5\\sigma$$ discovery potential is projected reaching cross sections below the existing and projected exclusion limits of similar experiments that are currently operating. For spin-dependent WIMP-neutron(-proton) scattering, a sensitivity of $$2.7 \\times 10^{-43}$$ cm$$^{2}$$ ($$8.1 \\times 10^{-42}$$ cm$$^{2}$$) for a 40 $$\\mathrm{GeV}/c^{2}$$ mass WIMP is expected. With construction well underway, LZ is on track for underground installation at SURF in 2019 and will start collecting data in 2020.« less

Tracking dynamic team activity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tambe, M.

1996-12-31

AI researchers are striving to build complex multi-agent worlds with intended applications ranging from the RoboCup robotic soccer tournaments, to interactive virtual theatre, to large-scale real-world battlefield simulations. Agent tracking - monitoring other agent`s actions and inferring their higher-level goals and intentions - is a central requirement in such worlds. While previous work has mostly focused on tracking individual agents, this paper goes beyond by focusing on agent teams. Team tracking poses the challenge of tracking a team`s joint goals and plans. Dynamic, real-time environments add to the challenge, as ambiguities have to be resolved in real-time. The central hypothesismore » underlying the present work is that an explicit team-oriented perspective enables effective team tracking. This hypothesis is instantiated using the model tracing technology employed in tracking individual agents. Thus, to track team activities, team models are put to service. Team models are a concrete application of the joint intentions framework and enable an agent to track team activities, regardless of the agent`s being a collaborative participant or a non-participant in the team. To facilitate real-time ambiguity resolution with team models: (i) aspects of tracking are cast as constraint satisfaction problems to exploit constraint propagation techniques; and (ii) a cost minimality criterion is applied to constrain tracking search. Empirical results from two separate tasks in real-world, dynamic environments one collaborative and one competitive - are provided.« less

COMPACT GALACTIC PLANETARY NEBULAE: AN HST /WFC3 MORPHOLOGICAL CATALOG, AND A STUDY OF THEIR ROLE IN THE GALAXY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stanghellini, Letizia; Shaw, Richard A.; Villaver, Eva

We present the images of a Hubble Space Telescope ( HST /WFC3) snapshot program of angularly compact Galactic planetary nebulae (PNe), acquired with the aim of studying their size, evolutionary status, and morphology. PNe that are smaller than ∼4″ are underrepresented in most morphological studies, and today they are less well studied than their immediate evolutionary predecessors, the pre-planetary nebulae. The images have been acquired in the light of [O iii] λ 5007, which is commonly used to classify the PN morphology, in the UV continuum with the aim of detecting the central star unambiguously, and in the I -bandmore » to detect a cool stellar companion, if present. The sample of 51 confirmed PNe exhibits nearly the full range of primary morphological classes, with the distribution more heavily weighted toward bipolar PNe, but with the total of aspherical PNe almost identical to that of the general Galactic sample. A large range of microstructures is evident in our sample as well, with many nebulae displaying attached shells, halos, ansae, and internal structure in the form of arcs, rings, and spirals. Various aspherical structures in a few PNe, including detached arcs, suggest an interaction with the ISM. We studied the observed sample of compact Galactic PNe in the context of the general Galactic PN population, and explore whether their physical size, spatial distribution, reddening, radial metallicity gradient, and possible progenitors are peculiar within the population of Galactic PNe. We found that these compact Galactic PNe, which have been selected based on apparent dimensions, constitute a diverse Galactic PN population that is relatively uniformly distributed across the Galactic disk, including the outskirts of our Galaxy. This unique sample will be used in the future to probe the old Galactic disk population.« less

STABILITY OF GAS CLOUDS IN GALACTIC NUCLEI: AN EXTENDED VIRIAL THEOREM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Xian; Cuadra, Jorge; Amaro-Seoane, Pau, E-mail: xchen@astro.puc.cl, E-mail: jcuadra@astro.puc.cl, E-mail: Pau.Amaro-Seoane@aei.mpg.de

2016-03-10

Cold gas entering the central 1–10{sup 2} pc of a galaxy fragments and condenses into clouds. The stability of the clouds determines whether they will be turned into stars or can be delivered to the central supermassive black hole (SMBH) to turn on an active galactic nucleus (AGN). The conventional criteria to assess the stability of these clouds, such as the Jeans criterion and Roche (or tidal) limit, are insufficient here, because they assume the dominance of self-gravity in binding a cloud, and neglect external agents, such as pressure and tidal forces, which are common in galactic nuclei. We formulatemore » a new scheme for judging this stability. We first revisit the conventional Virial theorem, taking into account an external pressure, to identify the correct range of masses that lead to stable clouds. We then extend the theorem to further include an external tidal field, which is equally crucial for the stability in the region of our interest—in dense star clusters, around SMBHs. We apply our extended Virial theorem to find new solutions to controversial problems, namely, the stability of the gas clumps in AGN tori, the circum-nuclear disk in the Galactic Center, and the central molecular zone of the Milky Way. The masses we derive for these structures are orders of magnitude smaller than the commonly used Virial masses (equivalent to the Jeans mass). Moreover, we prove that these clumps are stable, contrary to what one would naively deduce from the Roche (tidal) limit.« less

The combined effect of AGN and supernovae feedback in launching massive molecular outflows in high-redshift galaxies

NASA Astrophysics Data System (ADS)

Biernacki, Pawel; Teyssier, Romain

2018-04-01

We have recently improved our model of active galactic nucleus (AGN) by attaching the supermassive black hole (SMBH) to a massive nuclear star cluster (NSC). Here, we study the effects of this new model in massive, gas-rich galaxies with several simulations of different feedback recipes with the hydrodynamics code RAMSES. These simulations are compared to a reference simulation without any feedback, in which the cooling halo gas is quickly consumed in a burst of star formation. In the presence of strong supernovae (SN) feedback, we observe the formation of a galactic fountain that regulates star formation over a longer period, but without halting it. If only AGN feedback is considered, as soon as the SMBH reaches a critical mass, strong outflows of hot gas are launched and prevent the cooling halo gas from reaching the disc, thus efficiently halting star formation, leading to the so-called `quenching'. If both feedback mechanisms act in tandem, we observe a non-linear coupling, in the sense that the dense gas in the supernovae-powered galactic fountain is propelled by the hot outflow powered by the AGN at much larger radii than without AGN. We argue that these particular outflows are able to unbind dense gas from the galactic halo, thanks to the combined effect of SN and AGN feedback. We speculate that this mechanism occurs at the end of the fast growing phase of SMBH, and is at the origin of the dense molecular outflows observed in many massive high-redshift galaxies.

VizieR Online Data Catalog: Einstein EMSS Survey (Gioia+ 1990, Stocke+ 1991)

NASA Astrophysics Data System (ADS)

Gioia, I. M.; Maccacaro, T.; Schild, R. E.; Wolter, A.

1995-07-01

The Einstein Extended Medium Sensitivity Survey (EMSS) consists of 835 serendipitous X-ray sources detected at or above 4 times the rms level in 1435 IPC fields with their centers located away from the galactic plane. Their limiting sensitivities range from ~5*10-14 to to ~ 3*10-12 erg.cm-2.s-1 in the 0.3-3.5keV band. A total area of 778 square degrees of the high galactic latitude sky (|b|>20) has been covered. The analysis has been performed using data from the Rev 1 processing system at the CfA. The resulting EMSS catalog is a flux-limited and homogeneous sample of astronomical objects that can be used for statistical studies. Here we present the table listing all the sources taken from the publication referenced below and the optical identifications. At present over 96% of the 835 X-ray sources have been successfully identified in the following proportions: active galactic nuclei (QSO's, quasars and Seyfert), 51.1%; BL Lacertae objects, 4.3%; clusters of galaxies, 12.2%; normal galaxies, 2.1%; cooling flow galaxies, 0.6%; Galactic stars 25.8%; and unidentified, 3.9%. Most of the individual optical counterparts are previously unknown objects and so constitute large statistical samples independent of previously selection methods. The contents of the table is described below. The sky coverage computed for a specific assumed source spectrum is also given under "Additional Information" below. For further details please see the published articles: Gioia et al. 1990, Stocke et al. 1991. (1 data file).

The life cycle of starbursting circumnuclear gas discs

NASA Astrophysics Data System (ADS)

Schartmann, M.; Mould, J.; Wada, K.; Burkert, A.; Durré, M.; Behrendt, M.; Davies, R. I.; Burtscher, L.

2018-01-01

High-resolution observations from the submm to the optical wavelength regime resolve the central few 100 pc region of nearby galaxies in great detail. They reveal a large diversity of features: thick gas and stellar discs, nuclear starbursts, inflows and outflows, central activity, jet interaction, etc. Concentrating on the role circumnuclear discs play in the life cycles of galactic nuclei, we employ 3D adaptive mesh refinement hydrodynamical simulations with the RAMSES code to self-consistently trace the evolution from a quasi-stable gas disc, undergoing gravitational (Toomre) instability, the formation of clumps and stars and the disc's subsequent, partial dispersal via stellar feedback. Our approach builds upon the observational finding that many nearby Seyfert galaxies have undergone intense nuclear starbursts in their recent past and in many nearby sources star formation is concentrated in a handful of clumps on a few 100 pc distant from the galactic centre. We show that such observations can be understood as the result of gravitational instabilities in dense circumnuclear discs. By comparing these simulations to available integral field unit observations of a sample of nearby galactic nuclei, we find consistent gas and stellar masses, kinematics, star formation and outflow properties. Important ingredients in the simulations are the self-consistent treatment of star formation and the dynamical evolution of the stellar distribution as well as the modelling of a delay time distribution for the supernova feedback. The knowledge of the resulting simulated density structure and kinematics on pc scale is vital for understanding inflow and feedback processes towards galactic scales.

The Arches Cluster Out to its Tidal Radius: Dynamical Mass Segregation and the Effect of the Extinction Law on the - Lar Mass Function

NASA Astrophysics Data System (ADS)

Habibi, Maryam; Stolte, Andrea; Brandner, Wolfgang; Hussman, Benjamin

2013-07-01

The Galactic Center is the most active site of star formation in the Milky Way Galaxy, where particularly high-mass stars have formed very recently and are still forming today. However, since we are looking at the Galactic Center through the Galactic disk, knowledge of extinction is crucial to study this region. The Arches cluster is a young, massive starburst cluster near the Galactic Center. We observed the Arches cluster out to its tidal radius using Ks-band imaging obtained with NAOS/CONICA at the VLT combined with Subaro/Cisco J-band data to gain a full understanding of the cluster mass distribution. We show that the determination of the mass of the most massive star in the Arches cluster, which had been used in previous studies to establish an upper-mass limit for the star formation process in the Milky Way, strongly depends on the assumed slope of the extinction law. Assuming the two regimes of widely used infrared extinction laws, we show that the difference can reach up to 30% for individually derived stellar masses and ∆AKs˜1 magnitude in acquired Ks-band extinction, while the present mass function slope changes by ˜0.17 dex. The present-day mass function slope derived assuming the Nishiyama et al. (2009) extinction law increases from a flat slope of α-Nishi = 1.50 ± 0.35 in the core (r<0.2 pc) to α-Nishi = 2.21±0.27 in the intermediate annulus (0.2

Constraining dark matter annihilation with the isotropic γ-ray background: Updated limits and future potential

NASA Astrophysics Data System (ADS)

Bringmann, Torsten; Calore, Francesca; Di Mauro, Mattia; Donato, Fiorenza

2014-01-01

The nature of the isotropic γ-ray background (IGRB) measured by the Large Area Telescope (LAT) on the Fermi γ-ray space telescope (Fermi) remains partially unexplained. Non-negligible contributions may originate from extragalactic populations of unresolved sources such as blazars, star-forming galaxies or galactic millisecond pulsars. A recent prediction of the diffuse γ-ray emission from active galactic nuclei (AGN) with a large viewing angle with respect to the line of sight has demonstrated that this faint but numerous population is also expected to contribute significantly to the total IGRB intensity. A more exotic contribution to the IGRB invokes the pair annihilation of dark matter (DM) weakly interacting massive particles (WIMPs) into γ rays. In this work, we evaluate the room left for galactic DM at high latitudes (>10∘) by including photons from both prompt emission and inverse Compton scattering, emphasizing the impact of the newly discovered contribution from misaligned AGN (MAGN) for such an analysis. Summing up all significant galactic and extragalactic components of the IGRB, we find that an improved understanding of the associated astrophysical uncertainties is still mandatory to put stringent bounds on thermally produced DM. On the other hand, we also demonstrate that the IGRB has the potential to be one of the most competitive future ways to test the DM WIMP hypothesis, once the present uncertainties are even slightly reduced. In fact, if MAGN contribute even at 90% of the maximal level consistent with our current understanding, thermally produced WIMPs would be severely constrained as DM candidates for masses up to several TeV.

Implications of the IRAS data for galactic gamma ray astronomy and EGRET

NASA Technical Reports Server (NTRS)

Stecker, Floyd W.

1990-01-01

Using the results of gamma-ray, millimeter wave and far surveys of the galaxy, logically consistent picture of the large scale distribution of galactic gas and cosmic rays was derived, tied to the overall processes of stellar birth and destruction on a galactic scale. Using the results of the IRAS far-infrared survey of te galaxy, the large scale radial distributions of galactic far-infrared emission independently was obtained for both the Northern and Southern Hemisphere sides of the Galaxy. The dominant feature in these distributions was found to be a broad peak coincident with the 5 kpc molecular gas cloud ring. Evidence was found for spiral arm features. Strong correlations are evident between the large scale galactic distributions of far-infrared emission, gamma-ray emission and total CO emission. There is particularly tight correlation between the distribution of warm molecular clouds and far-infrared emission on a galactic scale. The 5 kpc ring was evident in existing galactic gamma-ray data. The extent to which the more detailed spiral arm features are evident in the more resolved EGRET (Energetic Gamma-Ray Experimental Telescope) data will help to determine more precisely the propagation characteristics of cosmic rays.

32 CFR 701.8 - Processing FOIA requests.

Code of Federal Regulations, 2011 CFR

2011-07-01

... queues as they wish, however, at a minimum three processing tracks shall be established, all based on a... simple requests, one track for complex requests, and one track for expedited processing. Determinations as to whether a request is simple or complex shall be made by each DON activity. (2) DON activities...

Simulating pre-galactic metal enrichment for JWST deep-field observations

NASA Astrophysics Data System (ADS)

Jaacks, Jason

2017-08-01

We propose to create a new suite of mesoscale cosmological volume simulations with custom built sub-grid physics in which we independently track the contribution from Population III and Population II star formation to the total metals in the interstellar medium (ISM) of the first galaxies, and in the diffuse IGM at an epoch prior to reionization. These simulations will fill a gap in our simulation knowledge about chemical enrichment in the pre-reionization universe, which is a crucial need given the impending observational push into this epoch with near-future ground and space-based telescopes. This project is the natural extension of our successful Cycle 24 theory proposal (HST-AR-14569.001-A; PI Jaacks) in which we developed a new Pop III star formation sub-grid model which is currently being utilized to study the baseline metal enrichment of pre-reionization systems.

A Daytime Aspect Camera for Balloon Altitudes

NASA Technical Reports Server (NTRS)

Dietz, Kurt L.; Ramsey, Brian D.; Alexander, Cheryl D.; Apple, Jeff A.; Ghosh, Kajal K.; Swift, Wesley R.; Six, N. Frank (Technical Monitor)

2001-01-01

We have designed, built, and flight-tested a new star camera for daytime guiding of pointed balloon-borne experiments at altitudes around 40km. The camera and lens are commercially available, off-the-shelf components, but require a custom-built baffle to reduce stray light, especially near the sunlit limb of the balloon. This new camera, which operates in the 600-1000 nm region of the spectrum, successfully provided daytime aspect information of approximately 10 arcsecond resolution for two distinct star fields near the galactic plane. The detected scattered-light backgrounds show good agreement with the Air Force MODTRAN models, but the daytime stellar magnitude limit was lower than expected due to dispersion of red light by the lens. Replacing the commercial lens with a custom-built lens should allow the system to track stars in any arbitrary area of the sky during the daytime.

Daytime Aspect Camera for Balloon Altitudes

NASA Technical Reports Server (NTRS)

Dietz, Kurt L.; Ramsey, Brian D.; Alexander, Cheryl D.; Apple, Jeff A.; Ghosh, Kajal K.; Swift, Wesley R.

2002-01-01

We have designed, built, and flight-tested a new star camera for daytime guiding of pointed balloon-borne experiments at altitudes around 40 km. The camera and lens are commercially available, off-the-shelf components, but require a custom-built baffle to reduce stray light, especially near the sunlit limb of the balloon. This new camera, which operates in the 600- to 1000-nm region of the spectrum, successfully provides daytime aspect information of approx. 10 arcsec resolution for two distinct star fields near the galactic plane. The detected scattered-light backgrounds show good agreement with the Air Force MODTRAN models used to design the camera, but the daytime stellar magnitude limit was lower than expected due to longitudinal chromatic aberration in the lens. Replacing the commercial lens with a custom-built lens should allow the system to track stars in any arbitrary area of the sky during the daytime.

The 136 MHz/400 MHz earth station antenna-noise temperature prediction program documentation for RAE-B

NASA Technical Reports Server (NTRS)

Chin, M.

1972-01-01

A simulation study to determine the 136 MHz and 400 MHz noise temperature of the ground network antennas which will track the RAE-B satellite during data transmission periods is described. Since the noise temperature of the antenna effectively sets the signal-to-noise ratio (SNR) of the received signal, a knowledge of SNR will be helpful in locating the optimum time windows for data transmission during low-noise periods. Antenna-noise temperatures at 136 MHz and 400 MHz will be predicted for selected earth-based ground stations which will support RAE-B. The antenna-noise temperature predictions will include the effects of galactic-brightness temperature, the sun, and the brightest radio stars. Predictions will cover the ten-month period from March 1, 1973 to December 31, 1973. The RAE-B mission will be expecially susceptible to SNR degradation during the two eclipses of the Sun occurring in this period.

CRPropa 2.0 - A public framework for propagating high energy nuclei, secondary gamma rays and neutrinos

NASA Astrophysics Data System (ADS)

Kampert, Karl-Heinz; Kulbartz, Jörg; Maccione, Luca; Nierstenhoefer, Nils; Schiffer, Peter; Sigl, Günter; van Vliet, Arjen René

2013-02-01

Version 2.0 of CRPropa [CRPropa is published under the 3rd version of the GNU General Public License (GPLv3). It is available, together with a detailed documentation of the code, at https://crpropa.desy.de.] is public software to model the extra-galactic propagation of ultra-high energy nuclei of atomic number Z⩽26 through structured magnetic fields and ambient photon backgrounds taking into account all relevant particle interactions. CRPropa covers the energy range 7×1016

Particle tagging and its implications for stellar population dynamics

NASA Astrophysics Data System (ADS)

Le Bret, Theo; Pontzen, Andrew; Cooper, Andrew P.; Frenk, Carlos; Zolotov, Adi; Brooks, Alyson M.; Governato, Fabio; Parry, Owen H.

2017-07-01

We establish a controlled comparison between the properties of galactic stellar haloes obtained with hydrodynamical simulations and with 'particle tagging'. Tagging is a fast way to obtain stellar population dynamics: instead of tracking gas and star formation, it 'paints' stars directly on to a suitably defined subset of dark matter particles in a collisionless, dark-matter-only simulation. Our study shows that 'live' particle tagging schemes, where stellar masses are painted on to the dark matter particles dynamically throughout the simulation, can generate good fits to the hydrodynamical stellar density profiles of a central Milky Way-like galaxy and its most prominent substructure. Energy diffusion processes are crucial to reshaping the distribution of stars in infalling spheroidal systems and hence the final stellar halo. We conclude that the success of any particular tagging scheme hinges on this diffusion being taken into account, and discuss the role of different subgrid feedback prescriptions in driving this diffusion.

All-Sky Earth Occultation Observations with the Fermi Gamma-Ray Burst Monitor

NASA Technical Reports Server (NTRS)

Wilson-Hodge, C. A.; Beklen, E.; Bhat, P. N.; Briggs, M.; Camero-Arranz, A.; Case, G.; Jenke, P.; Chaplin, V.; Cherry, M.; Connaughton, V.;

The ionizing radiation of Seyfert 2 galactic nuclei

NASA Technical Reports Server (NTRS)

Ho, Luis C.; Shields, Joseph C.; Filippenko, Alexei V.

1993-01-01

We report the discovery of a nonrandom trend in the dispersion of emission-line intensity ratios for Seyfert 2 galaxies. The sense of this pattern suggests the influence of a single physical parameter, the hardness of the ionizing continuum, which controls the heating energy per ionizing photon. We compare the observed line ratios with new photoionization calculations and find that the observed distributions can be reproduced if the ionizing continuum is parametrized by a power law. Our results also suggest an inverse correlation between luminosity and continuum hardness for Seyfert 2 nuclei; if true, this trend extends a similar pattern known in quasars and Seyfert 1 galaxies to active galactic nuclei of lower luminosity. Samples of Seyfert 2 nuclei with improved selection uniformity are desirable for elaboration of these findings.

Solar particle events observed at Mars: dosimetry measurements and model calculations.

PubMed

Cleghorn, Timothy F; Saganti, Premkumar B; Zeitlin, Cary J; Cucinotta, Francis A

2004-01-01

During the period from March 13, 2002 to mid-September, 2002, six solar particle events (SPE) were observed by the MARIE instrument onboard the Odyssey Spacecraft in Martian Orbit. These events were observed also by the GOES 8 satellite in Earth orbit, and thus represent the first time that the same SPE have been observed at these separate locations. The characteristics of these SPE are examined, given that the active regions of the solar disc from which the event originated can usually be identified. The dose rates at Martian orbit are calculated, both for the galactic and solar components of the ionizing particle radiation environment. The dose rates due to galactic cosmic rays (GCR) agree well with the HZETRN model calculations. Published by Elsevier Ltd on behalf of COSPAR.

Solar particle events observed at Mars: dosimetry measurements and model calculations

NASA Technical Reports Server (NTRS)

Cleghorn, Timothy F.; Saganti, Premkumar B.; Zeitlin, Cary J.; Cucinotta, Francis A.

2004-01-01

During the period from March 13, 2002 to mid-September, 2002, six solar particle events (SPE) were observed by the MARIE instrument onboard the Odyssey Spacecraft in Martian Orbit. These events were observed also by the GOES 8 satellite in Earth orbit, and thus represent the first time that the same SPE have been observed at these separate locations. The characteristics of these SPE are examined, given that the active regions of the solar disc from which the event originated can usually be identified. The dose rates at Martian orbit are calculated, both for the galactic and solar components of the ionizing particle radiation environment. The dose rates due to galactic cosmic rays (GCR) agree well with the HZETRN model calculations. Published by Elsevier Ltd on behalf of COSPAR.

Characteristics and Energy Dependence of Recurrent Galactic Cosmic-Ray Flux Depressions and of a Forbush Decrease with LISA Pathfinder

NASA Astrophysics Data System (ADS)

Armano, M.; Audley, H.; Baird, J.; Bassan, M.; Benella, S.; Binetruy, P.; Born, M.; Bortoluzzi, D.; Cavalleri, A.; Cesarini, A.; Cruise, A. M.; Danzmann, K.; de Deus Silva, M.; Diepholz, I.; Dixon, G.; Dolesi, R.; Fabi, M.; Ferraioli, L.; Ferroni, V.; Finetti, N.; Fitzsimons, E. D.; Freschi, M.; Gesa, L.; Gibert, F.; Giardini, D.; Giusteri, R.; Grimani, C.; Grzymisch, J.; Harrison, I.; Heinzel, G.; Hewitson, M.; Hollington, D.; Hoyland, D.; Hueller, M.; Inchauspé, H.; Jennrich, O.; Jetzer, P.; Karnesis, N.; Kaune, B.; Korsakova, N.; Killow, C. J.; Laurenza, M.; Lobo, J. A.; Lloro, I.; Liu, L.; López-Zaragoza, J. P.; Maarschalkerweerd, R.; Mance, D.; Martín, V.; Martin-Polo, L.; Martino, J.; Martin-Porqueras, F.; Mateos, I.; McNamara, P. W.; Mendes, J.; Mendes, L.; Nofrarias, M.; Paczkowski, S.; Perreur-Lloyd, M.; Petiteau, A.; Pivato, P.; Plagnol, E.; Ramos-Castro, J.; Reiche, J.; Robertson, D. I.; Rivas, F.; Russano, G.; Sabbatini, F.; Slutsky, J.; Sopuerta, C. F.; Sumner, T.; Telloni, D.; Texier, D.; Thorpe, J. I.; Vetrugno, D.; Vitale, S.; Wanner, G.; Ward, H.; Wass, P.; Weber, W. J.; Wissel, L.; Wittchen, A.; Zambotti, A.; Zenoni, C.; Zweifel, P.

2018-02-01

Galactic cosmic-ray (GCR) energy spectra observed in the inner heliosphere are modulated by the solar activity, the solar polarity and structures of solar and interplanetary origin. A high counting rate particle detector (PD) aboard LISA Pathfinder, meant for subsystems diagnostics, was devoted to the measurement of GCR and solar energetic particle integral fluxes above 70 MeV n‑1 up to 6500 counts s‑1. PD data were gathered with a sampling time of 15 s. Characteristics and energy dependence of GCR flux recurrent depressions and of a Forbush decrease dated 2016 August 2 are reported here. The capability of interplanetary missions, carrying PDs for instrument performance purposes, in monitoring the passage of interplanetary coronal mass ejections is also discussed.

New constraints on all flavor Galactic diffuse neutrino emission with the ANTARES telescope

NASA Astrophysics Data System (ADS)

Albert, A.; André, M.; Anghinolfi, M.; Anton, G.; Ardid, M.; Aubert, J.-J.; Avgitas, T.; Baret, B.; Barrios-Martí, J.; Basa, S.; Belhorma, B.; Bertin, V.; Biagi, S.; Bormuth, R.; Bourret, S.; Bouwhuis, M. C.; Bruijn, R.; Brunner, J.; Busto, J.; Capone, A.; Caramete, L.; Carr, J.; Celli, S.; Cherkaoui El Moursli, R.; Chiarusi, T.; Circella, M.; Coelho, J. A. B.; Coleiro, A.; Coniglione, R.; Costantini, H.; Coyle, P.; Creusot, A.; Díaz, A. F.; Deschamps, A.; de Bonis, G.; Distefano, C.; di Palma, I.; Domi, A.; Donzaud, C.; Dornic, D.; Drouhin, D.; Eberl, T.; El Bojaddaini, I.; El Khayati, N.; Elsässer, D.; Enzenhöfer, A.; Ettahiri, A.; Fassi, F.; Felis, I.; Fusco, L. A.; Galatà, S.; Gay, P.; Giordano, V.; Glotin, H.; Grégoire, T.; Gracia Ruiz, R.; Graf, K.; Hallmann, S.; van Haren, H.; Heijboer, A. J.; Hello, Y.; Hernández-Rey, J. J.; Hößl, J.; Hofestädt, J.; Hugon, C.; Illuminati, G.; James, C. W.; de Jong, M.; Jongen, M.; Kadler, M.; Kalekin, O.; Katz, U.; Kießling, D.; Kouchner, A.; Kreter, M.; Kreykenbohm, I.; Kulikovskiy, V.; Lachaud, C.; Lahmann, R.; Lefèvre, D.; Leonora, E.; Lotze, M.; Loucatos, S.; Marcelin, M.; Margiotta, A.; Marinelli, A.; Martínez-Mora, J. A.; Mele, R.; Melis, K.; Michael, T.; Migliozzi, P.; Moussa, A.; Navas, S.; Nezri, E.; Organokov, M.; Pǎvǎlaş, G. E.; Pellegrino, C.; Perrina, C.; Piattelli, P.; Popa, V.; Pradier, T.; Quinn, L.; Racca, C.; Riccobene, G.; Sánchez-Losa, A.; Saldaña, M.; Salvadori, I.; Samtleben, D. F. E.; Sanguineti, M.; Sapienza, P.; Schüssler, F.; Sieger, C.; Spurio, M.; Stolarczyk, Th.; Taiuti, M.; Tayalati, Y.; Trovato, A.; Turpin, D.; Tönnis, C.; Vallage, B.; van Elewyck, V.; Versari, F.; Vivolo, D.; Vizzoca, A.; Wilms, J.; Zornoza, J. D.; Zúñiga, J.; Gaggero, D.; Grasso, D.; ANTARES Collaboration

2017-09-01

The flux of very high-energy neutrinos produced in our Galaxy by the interaction of accelerated cosmic rays with the interstellar medium is not yet determined. The characterization of this flux will shed light on Galactic accelerator features, gas distribution morphology and Galactic cosmic ray transport. The central Galactic plane can be the site of an enhanced neutrino production, thus leading to anisotropies in the extraterrestrial neutrino signal as measured by the IceCube Collaboration. The ANTARES neutrino telescope, located in the Mediterranean Sea, offers a favorable view of this part of the sky, thereby allowing for a contribution to the determination of this flux. The expected diffuse Galactic neutrino emission can be obtained, linking a model of generation and propagation of cosmic rays with the morphology of the gas distribution in the Milky Way. In this paper, the so-called "gamma model" introduced recently to explain the high-energy gamma-ray diffuse Galactic emission is assumed as reference. The neutrino flux predicted by the "gamma model" depends on the assumed primary cosmic ray spectrum cutoff. Considering a radially dependent diffusion coefficient, this proposed scenario is able to account for the local cosmic ray measurements, as well as for the Galactic gamma-ray observations. Nine years of ANTARES data are used in this work to search for a possible Galactic contribution according to this scenario. All flavor neutrino interactions are considered. No excess of events is observed, and an upper limit is set on the neutrino flux of 1.1 (1.2) times the prediction of the "gamma model," assuming the primary cosmic ray spectrum cutoff at 5 (50) PeV. This limit excludes the diffuse Galactic neutrino emission as the major cause of the "spectral anomaly" between the two hemispheres measured by IceCube.

BATSE Observations of the Large-Scale Isotropy of Gamma-Ray Bursts

NASA Technical Reports Server (NTRS)

Briggs, Michael S.; Paciesas, William S.; Pendleton, Geoffrey N.; Meegan, Charles A.; Fishman, Gerald J.; Horack, John M.; Brock, Martin N.; Kouveliotou, Chryssa; Hartmann, Dieter H.; Hakkila, Jon

1996-01-01

We use dipole and quadrupole statistics to test the large-scale isotropy of the first 1005 gamma-ray bursts observed by the Burst and Transient Source Experiment (BATSE). In addition to the entire sample of 1005 gamma-ray bursts, many subsets are examined. We use a variety of dipole and quadrupole statistics to search for Galactic and other predicted anisotropies and for anisotropies in a coordinate-system independent manner. We find the gamma-ray burst locations to be consistent with isotropy, e.g., for the total sample the observed Galactic dipole moment (cos theta) differs from the value predicted for isotropy by 0.9 sigma and the observed Galactic quadrupole moment (sin(exp 2) b - 1/3) by 0.3 sigma. We estimate for various models the anisotropies that could have been detected. If one-half of the locations were within 86 deg of the Galactic center, or within 28 deg of the Galactic plane, the ensuing dipole or quadrupole moment would have typically been detected at the 99% confidence level. We compare the observations with the dipole and quadrupole moments of various Galactic models. Several Galactic gamma-ray bursts models have moments within 2 sigma of the observations; most of the Galactic models proposed to date are no longer in acceptable agreement with the data. Although a spherical dark matter halo distribution could be consistent with the data, the required core radius is larger than the core radius of the dark matter halo used to explain the Galaxy's rotation curve. Gamma-ray bursts are much more isotropic than any observed Galactic population, strongly favoring but not requiring an origin at cosmological distances.

Supermassive black-hole growth over cosmic time: active galaxy demography, physics, and ecology from Chandra surveys.

PubMed

Brandt, W N; Alexander, D M

2010-04-20

Extragalactic X-ray surveys over the past decade have dramatically improved understanding of the majority populations of active galactic nuclei (AGNs) over most of the history of the universe. Here we briefly highlight some of the exciting discoveries about AGN demography, physics, and ecology, with a focus on results from Chandra. We also discuss some key unresolved questions and future prospects.

Supermassive black-hole growth over cosmic time: Active galaxy demography, physics, and ecology from Chandra surveys

PubMed Central

Brandt, W. N.; Alexander, D. M.

2010-01-01

Extragalactic X-ray surveys over the past decade have dramatically improved understanding of the majority populations of active galactic nuclei (AGNs) over most of the history of the universe. Here we briefly highlight some of the exciting discoveries about AGN demography, physics, and ecology, with a focus on results from Chandra. We also discuss some key unresolved questions and future prospects. PMID:20404160

Particle Acceleration in Relativistic Outflows

NASA Technical Reports Server (NTRS)

Bykov, Andrei; Gehrels, Neil; Krawczynski, Henric; Lemoine, Martin; Pelletier, Guy; Pohl, Martin

2012-01-01

In this review we confront the current theoretical understanding of particle acceleration at relativistic outflows with recent observational results on various source classes thought to involve such outflows, e.g. gamma-ray bursts, active galactic nuclei, and pulsar wind nebulae. We highlight the possible contributions of these sources to ultra-high-energy cosmic rays.

Extragalactic Gravitational Collapse

NASA Astrophysics Data System (ADS)

Rees, Martin J.

After some introductory "numerology", routes towards black hole formation are briefly reviewed; some properties of black holes relevant to theories for active galactic nuclei are then described. Applications are considered to specific models for energy generation and the production of relativistic beams. The paper concludes with a discussion of extragalactic sources of gravitational waves.

Starburst Galaxies. III. Properties of a Radio-selected Sample

NASA Astrophysics Data System (ADS)

Smith, Denise A.; Herter, Terry; Haynes, Martha P.

1998-02-01

We have analyzed the properties of the 20 most radio-luminous UGC starburst galaxies from Condon, Frayer, & Broderick. Near-infrared images, spectra, and optical rotation curves were presented in Smith et al. In this paper, we use these data and published radio data to assess the stellar populations, dust contents, ionizing conditions, and dynamics of the starbursts. Certain properties of the star formation occurring in these galaxies differ from those observed locally. The infrared excesses (IREs) are lower than and span a narrower range of values than those of Galactic H II regions. The starbursts appear to produce a higher proportion of ionizing photons than most Galactic H II regions. Consequently, the initial mass functions (IMFs) of the starbursts may be more strongly biased toward high-mass star formation. The starbursts may also contain fewer old H II regions than the Milky Way. Furthermore, the starburst IRE is likely to be influenced by the presence of large reservoirs of gas that absorb a larger fraction of the Lyman continuum photons. The OB stellar and far-infrared luminosities imply that the upper mass range of the starburst IMF (M > 10 M⊙) is characterized by a slope of 2.7 +/- 0.2. The starburst IMF thus bears a strong similarity to that observed in Magellanic OB associations. Optical line ratios indicate that a range of excitation conditions are present. We conclude that the near-infrared light from many of the starbursts is dominated by a heavily obscured mixture of emission from evolved red stars and young blue stars with small contributions (~5%) from thermal gas and hot dust, under the assumptions that a Galactic or SMC extinction law can be applied to these systems and that the true reddening curve follows one of the models currently existing in the literature. In some cases, larger amounts of emission from blue stars or hot dust may be required to explain the observed near-infrared colors. The amount of dust emission exceeds that predicted from comparisons with Galactic H II regions. The near-infrared colors of some of the systems may also be influenced by the presence of a low-luminosity active galactic nucleus (AGN). Emission from blue stars and hot dust, if present, dilutes the observed CO index. The activity in the redder, more luminous systems is strongly peaked. The galaxies hosting the starbursts exhibit a wide range of morphological and star-forming properties. While all of the host galaxies are interacting systems, the nuclear separations of the interacting nuclei range from <1 kpc to >1 Mpc. The dynamical behavior ranges from relaxed to strongly perturbed. The off-nuclear regions of the galaxies are sites of active star formation and are characterized by a range of excitation conditions. Spatially extended LINER emission is consistent with shock excitation produced by superwinds or galaxy-galaxy collisions. Violent star formation activity occurs over a larger physical scale in the most active starbursts. Systems containing mergers and widely separated nuclei possess similar colors and luminosities. The burst properties are most likely regulated by the internal structures of the interacting galaxies and not the separations of the interacting galaxies. Observations at the Palomar Observatory were made as part of a continuing collaborative agreement between the California Institute of Technology and Cornell University.

Massive Star Formation Viewed through Extragalactic-Tinted Glasses

NASA Astrophysics Data System (ADS)

Willis, Sarah; Marengo, M.; Smith, H. A.; Allen, L.

2014-01-01

Massive Galactic star forming regions are the local analogs to the luminous star forming regions that dominate the emission from star forming galaxies. Their proximity to us enables the characterization of the full range of stellar masses that form in these more massive environments, improving our understanding of star formation tracers used in extragalactic studies. We have surveyed a sample of massive star forming regions with a range of morphologies and luminosities to probe the star formation activity in a variety of environments. We have used Spitzer IRAC and deep ground based J, H, Ks observations to characterize the Young Stellar Object (YSO) content of 6 massive star forming regions. These YSOs provide insight into the rate and efficiency of star formation within these regions, and enable comparison with nearby, low mass star forming regions as well as extreme cases of Galactic star formation including ‘mini-starburst’ regions. In addition, we have conducted an in-depth analysis of NGC 6334 to investigate how the star formation activity varies within an individual star forming region, using Herschel data in the far-infrared to probe the earliest stages of the ongoing star formation activity.

The rotating wind of the quasar PG 1700+518.

PubMed

Young, S; Axon, D J; Robinson, A; Hough, J H; Smith, J E

2007-11-01

It is now widely accepted that most galaxies undergo an active phase, during which a central super-massive black hole generates vast radiant luminosities through the gravitational accretion of gas. Winds launched from a rotating accretion disk surrounding the black hole are thought to play a critical role, allowing the disk to shed angular momentum that would otherwise inhibit accretion. Such winds are capable of depositing large amounts of mechanical energy in the host galaxy and its environs, profoundly affecting its formation and evolution, and perhaps regulating the formation of large-scale cosmological structures in the early Universe. Although there are good theoretical grounds for believing that outflows from active galactic nuclei originate as disk winds, observational verification has proven elusive. Here we show that structures observed in polarized light across the broad Halpha emission line in the quasar PG 1700+518 originate close to the accretion disk in an electron scattering wind. The wind has large rotational motions (approximately 4,000 km s(-1)), providing direct observational evidence that outflows from active galactic nuclei are launched from the disks. Moreover, the wind rises nearly vertically from the disk, favouring launch mechanisms that impart an initial acceleration perpendicular to the disk plane.

Teacher's Guide for Tracks. Elementary Science Study.

ERIC Educational Resources Information Center

Alexander, David; And Others

This teacher's guide suggests activities that provide opportunities for students in grades 4-6 to study animal tracks. Methods are explained for using sets of 52 Track Cards which show life-size drawings of tracks made by 14 animals; sets of 10 large Mystery Track Cards with life-size drawings of the prints of large mammals; and a Track Picture…

Implications of the IRAS data for galactic gamma-ray astronomy and EGRET

NASA Technical Reports Server (NTRS)

Stecker, F. W.

1990-01-01

Using the results of gamma-ray, millimeter wave and far infrared surveys of the galaxy, one can derive a logically consistent picture of the large scale distribution of galactic gas and cosmic rays, one tied to the overall processes of stellar birth and destruction on a galactic scale. Using the results of the IRAS far-infrared survey of the galaxy, the large scale radial distribution of galactic far-infrared emission were obtained independently for both the Northern and Southern Hemisphere sides of the Galaxy. It was found that the dominant feature in these distributions to be a broad peak coincident with the 5 kpc molecular gas cloud ring. Also found was evidence of spiral arm features. Strong correlations are evident between the large scale galactic distributions of far infrared emission, gamma-ray emission and total CO emission. There is a particularly tight correlation between the distribution of warm molecular clouds and far-infrared emission on a galactic scale.

Galactic gamma-ray observations and galactic structure

NASA Technical Reports Server (NTRS)

Stecker, F. W.

1975-01-01

Recent observations of gamma-rays originating in the galactic disk together with radio observations, support an emerging picture of the overall structure of our galaxy with higher interstellar gas densities and star formation rates in a region which corresponds to that of the inner arms. The emerging picture is one where molecular clouds make up the dominant constituent of the interstellar gas in the inner galaxy and play a key role in accounting for the gamma-rays and phenomena associated with the production of young stars and other population 1 objects. In this picture, cosmic rays are associated with supernovae and are primarily of galactic origin. These newly observed phenomena can be understood as consequences of the density wave theories of spiral structure. Based on these new developments, the suggestion is made that a new galactic population class, Population O, be added to the standard Populations 1 and 2 in order to recognize important differences in dynamics and distribution between diffuse galactic H1 and interstellar molecular clouds.

The relationship between the galactic matter distribution, cosmic ray dynamics, and gamma ray production

NASA Technical Reports Server (NTRS)

Kniffen, D. A.; Fichtel, C. E.; Thompson, D. J.

1976-01-01

Theoretical considerations and analysis of the results of gamma ray astronomy suggest that the galactic cosmic rays are dynamically coupled to the interstellar matter through the magnetic fields, and hence the cosmic ray density should be enhanced where the matter density is greatest on the scale of galactic arms. This concept has been explored in a galactic model using recent 21 cm radio observations of the neutral hydrogen and 2.6 mm observations of carbon monoxide, which is considered to be a tracer of molecular hydrogen. The model assumes: (1) cosmic rays are galactic and not universal; (2) on the scale of galactic arms, the cosmic ray column (surface) density is proportional to the total interstellar gas column density; (3) the cosmic ray scale height is significantly larger than the scale height of the matter; and (4) ours is a spiral galaxy characterized by an arm to interarm density ratio of about 3:1.

The Optical Gravitational Lensing Experiment Catalog of stellar proper motions in the OGLE-II Galactic bulge fields

NASA Astrophysics Data System (ADS)

Sumi, T.; Wu, X.; Udalski, A.; Szymański, M.; Kubiak, M.; Pietrzyński, G.; Soszyński, I.; Woźniak, P.; Zebruń, K.; Szewczyk, O.; Wyrzykowski, L.

2003-12-01

We present proper motion (μ ) catalogue of 5,078,188 stars in 49 Optical Gravitational Lensing Experiment II (OGLE-II) Galactic bulge fields, with the total area close to 11 square degrees. The proper motion measurements are based on 138 - 555 I-band images taken during four observing seasons: 1997-2000. The catalogue stars are in the magnitude range 11 < I < 18 mag. In particular, the catalogue includes Red Clump Giants (RCGs) and Red Giants in the Galactic Bulge, and main sequence stars in the Galactic disc. The proper motions up to μ = 500 mas yr -1 were measured with the mean accuracy of 0.8 ˜ 3.5 mas yr-1, depending on the brightness of a star. This catalogue may be useful for studying the kinematic of stars in the Galactic Bulge and the Galactic disk with Extinction maps in these fields which are construncted by using two-band photometry of RCGs.

ARCADE 2 Observations of Galactic Radio Emission

NASA Technical Reports Server (NTRS)

Kogut, A.; Fixsen, D. J.; Levin, S. M.; Limon, M.; Lubin, P. M.; Mirel, P.; Seiffert, M.; Singal, J.; Villela, T.; Wollack, E.;

Tracking of Physical Activity across the Lifespan.

ERIC Educational Resources Information Center

Malina, Robert M.

2001-01-01

This report considers evidence for tracking of indicators of physical activity during childhood and adolescence, the transition from adolescence into adulthood, and adulthood. Tracking refers to the tendency of individuals to maintain their rank or position within a group over time. Longitudinal data for at least two points in time are necessary.…

Nuclear Radio Jet from a Low-luminosity Active Galactic Nucleus in NGC 4258

NASA Astrophysics Data System (ADS)

Doi, Akihiro; Kohno, Kotaro; Nakanishi, Kouichiro; Kameno, Seiji; Inoue, Makoto; Hada, Kazuhiro; Sorai, Kazuo

2013-03-01

The nearby low-luminosity active galactic nucleus (LLAGN) NGC 4258 has a weak radio continuum component at the galactic center. We investigate its radio spectral properties on the basis of our new observations using the Nobeyama Millimeter Array at 100 GHz and archival data from the Very Large Array at 1.7-43 GHz and the James Clerk Maxwell telescope at 347 GHz. The NGC 4258 nuclear component exhibits (1) an intra-month variable and complicated spectral feature at 5-22 GHz and (2) a slightly inverted spectrum at 5-100 GHz (α ~ 0.3; F νvpropνα) in time-averaged flux densities, which are also apparent in the closest LLAGN M81. These similarities between NGC 4258 and M81 in radio spectral natures in addition to previously known core shift in their AU-scale jet structures produce evidence that the same mechanism drives their nuclei. We interpret the observed spectral property as the superposition of emission spectra originating at different locations with frequency-dependent opacity along the nuclear jet. Quantitative differences between NGC 4258 and M81 in terms of jet/counter jet ratio, radio loudness, and degree of core shift can be consistently understood by fairly relativistic speeds (Γ >~ 3) of jets and their quite different inclinations. The picture established from the two closest LLAGNs is useful for understanding the physical origin of unresolved and flat/inverted spectrum radio cores that are prevalently found in LLAGNs, including Sgr A*, with starved supermassive black holes in the present-day universe.

The SAMI Galaxy Survey: understanding observations of large-scale outflows at low redshift with EAGLE simulations

NASA Astrophysics Data System (ADS)

Tescari, E.; Cortese, L.; Power, C.; Wyithe, J. S. B.; Ho, I.-T.; Crain, R. A.; Bland-Hawthorn, J.; Croom, S. M.; Kewley, L. J.; Schaye, J.; Bower, R. G.; Theuns, T.; Schaller, M.; Barnes, L.; Brough, S.; Bryant, J. J.; Goodwin, M.; Gunawardhana, M. L. P.; Lawrence, J. S.; Leslie, S. K.; López-Sánchez, Á. R.; Lorente, N. P. F.; Medling, A. M.; Richards, S. N.; Sweet, S. M.; Tonini, C.

2018-01-01

This work presents a study of galactic outflows driven by stellar feedback. We extract main-sequence disc galaxies with stellar mass 109 ≤ M⋆/ M⊙ ≤ 5.7 × 1010 at redshift z = 0 from the highest resolution cosmological simulation of the Evolution and Assembly of GaLaxies and their Environments (EAGLE) set. Synthetic gas rotation velocity and velocity dispersion (σ) maps are created and compared to observations of disc galaxies obtained with the Sydney-AAO (Australian Astronomical Observatory) Multi-object Integral field spectrograph (SAMI), where σ-values greater than 150 km s-1 are most naturally explained by bipolar outflows powered by starburst activity. We find that the extension of the simulated edge-on (pixelated) velocity dispersion probability distribution depends on stellar mass and star formation rate surface density (ΣSFR), with low-M⋆/low-ΣSFR galaxies showing a narrow peak at low σ (∼30 km s-1) and more active, high-M⋆/high-ΣSFR galaxies reaching σ > 150 km s-1. Although supernova-driven galactic winds in the EAGLE simulations may not entrain enough gas with T <105 K compared to observed galaxies, we find that gas temperature is a good proxy for the presence of outflows. There is a direct correlation between the thermal state of the gas and its state of motion as described by the σ-distribution. The following equivalence relations hold in EAGLE: (i) low-σ peak ⇔ disc of the galaxy ⇔ gas with T <105 K; (ii) high-σ tail ⇔ galactic winds ⇔ gas with T ≥105 K.

Self-Motion Impairs Multiple-Object Tracking

ERIC Educational Resources Information Center

Thomas, Laura E.; Seiffert, Adriane E.

2010-01-01

Investigations of multiple-object tracking aim to further our understanding of how people perform common activities such as driving in traffic. However, tracking tasks in the laboratory have overlooked a crucial component of much real-world object tracking: self-motion. We investigated the hypothesis that keeping track of one's own movement…

Monash Chemical Yields Project (Monχey) - Element production in low- and intermediate-mass stars of metallicities Z = 0 to 0.04

NASA Astrophysics Data System (ADS)

Doherty, Carolyn Louise; Lattanzio, John; Angelou, George; Wattana Campbell, Simon; Church, Ross; Constantino, Thomas; Cristallo, Sergio; Gil-Pons, Pilar; Karakas, Amanda; Lugaro, Maria; Stancliffe, Richard James

2015-08-01

The Monχey project provides a large and homogeneous set of stellar yields for the low- and intermediate- mass stars and has applications particularly to galactic chemical evolution modelling.We present a detailed grid of stellar evolutionary models and corresponding nucleosynthetic yields for stars of initial mass 0.8 M⊙ up to the limit for core collapse supernova ≈ 10 M⊙. Our study covers a broad range of metallicities, ranging from the first, primordial stars (Z=0) to those of super-solar metallicity (Z=0.04). The models are evolved from the zero-age main-sequence until the end of the asymptotic giant branch (AGB) and the nucleosynthesis calculations include all elements from H to Bi.A major innovation of our work is the first complete grid of heavy element nucleosynthetic predictions for primordial AGB stars as well as the inclusion of extra-mixing processes (in this case thermohaline) during the red giant branch. We provide a broad overview of our results with implications for galactic chemical evolution as well as highlight interesting results such as heavy element production in dredge-out events of super-AGB stars.We briefly introduce our easy to use web-based database which provides the evolutionary tracks, structural properties, internal/surface nucleosynthetic compositions and stellar yields. Our web interface includes user- driven plotting capabilities with output available in a range of formats. Our nucleosynthetic results are available for further use in post processing calculations for dust production yields.

Proper Motion of the Compact, Nonthermal Radio Source in the Galactic Center, Sagittarius A*

NASA Astrophysics Data System (ADS)

Backer, D. C.; Sramek, R. A.

1999-10-01

Proper motions and radial velocities of luminous infrared stars in the Galactic center have provided strong evidence for a dark mass of 2.5×106 Msolar in the central 0.05 pc of the Galaxy. The leading hypothesis for this mass is a black hole. High angular resolution measurements at radio wavelengths find a compact radio source, Sagittarius (Sgr) A*, that is either the faint glow from a small amount of material accreting onto the hole with low radiative efficiency or a miniature active galactic nucleus (AGN) core-jet system. This paper provides a full report on the first program that has measured the apparent proper motion of Sgr A* with respect to background extragalactic reference frame. Our current result isμl,*=[-6.18+/-0.19] mas yr-1 μb,*=[-0.65+/-0.17] mas yr-1 . The observations were obtained with the NRAO Very Large Array at 4.9 GHz over 16 yr. The proper motion of Sgr A* provides an estimate of its mass based on equipartition of kinetic energy between the hole and the surrounding stars. The measured motion is largest in galactic longitude. This component of the motion is consistent with the secular parallax that results from the rotation of the solar system about the center, which is a global measure of the difference between Oort's constants (A-B), with no additional peculiar motion of Sgr A*. The current uncertainty in Oort's galactic rotation constants limits the use of this component of the proper motion for a mass inference. In latitude, we find a small, and weakly significant, peculiar motion of Sgr A*, -19+/-7 km s-1 after correction for the motion of the solar system with respect to the local standard of rest. We consider sources of peculiar motion of Sgr A* ranging from unstable radio wave propagation through intervening turbulent plasma to the effects of asymmetric masses in the center. These fail to account for a significant peculiar motion. One can appeal to an m=1 dynamical instability that numerical simulations have revealed. However, the measurement of a latitude peculiar proper motion of comparable magnitude and error but with opposite sign in the companion paper by Reid leads us to conclude at the present time that our errors may be underestimated and that the actual peculiar motion might therefore be closer to zero. Improvement of these measurements with further observations and resolving the differences between independent experiments will provide the accuracies of a few km s-1 in both coordinates that will provide both a black hole mass estimate and a definitive determination of Oort's galactic rotation constants on a global Galactic scale.

The role of water tracks in altering biotic and abiotic soil properties and processes in a polar desert in Antarctica

NASA Astrophysics Data System (ADS)

Ball, Becky A.; Levy, Joseph

2015-02-01

Groundwater discharge via water tracks is a largely unexplored passageway routing salts and moisture from high elevations to valley floors in the McMurdo Dry Valleys (MDV) of Antarctica. Given the influence that water tracks have on the distribution of liquid water in seasonally thawed Antarctic soils, it is surprising how little is known about their role in structuring biotic and abiotic processes this cold desert ecosystem. Particularly, it is unclear how soil biota will respond to the activation of new water tracks resulting from enhanced active layer thickening or enhanced regional snowmelt. In the MDV, water tracks are both wetter and more saline than the surrounding soils, constituting a change in soil habitat suitability for soil biology and therefore the ecological processes they carry out. To investigate the net impact that water tracks have on Dry Valley soil biology, and therefore the ecosystem processes for which they are responsible, we analyzed microbial biomass and activity in soils inside and outside of three water tracks and relate this to the physical soil characteristics. Overall, our results suggest that water tracks can significantly influence soil properties, which can further impact biological biovolume and both biotic and abiotic fluxes of CO2. However, the nature of its impact differs with water track, further suggesting that not all water tracks can be regarded the same.

Simulation of TGF-Beta Activation by Low-Dose HZE Radiation in a Cell Culture

NASA Technical Reports Server (NTRS)

Plante, Ianik; Cucinotta, Francis A.

2009-01-01

High charge (Z) and energy (E) (HZE) nuclei comprised in the galactic cosmic rays are main contributors to space radiation risk. They induce many lesions in living matter such as non-specific oxidative damage and the double-strand breaks (DSBs), which are considered key precursors of early and late effects of radiation. There is increasing evidence that cells respond collectively rather than individually to radiation, suggesting the importance of cell signaling1. The transforming growth factor (TGF ) is a signaling peptide that is expressed in nearly all cell type and regulates a large array of cellular processes2. TGF have been shown to mediate cellular response to DNA damage3 and to induce apoptosis in non-irradiated cells cocultured with irradiated cells4. TFG molecules are secreted by cells in an inactive complex known as the latency-associated peptide (LAP). TGF is released from the LAP by a conformational change triggered by proteases, thrombospondin-1, integrins, acidic conditions and .OH radical5. TGF then binds to cells receptors and activates a cascade of events mediated by Smad proteins6, which might interfere with the repair of DNA. Meanwhile, increasingly sophisticated Brownian Dynamics (BD) algorithms have appeared recently in the literature7 and can be applied to study the interaction of molecules with receptors. These BD computer models have contributed to the elucidation of signal transduction, ligand accumulation and autocrine loops in the epidermal growth factor (EGF) and its receptor (EFGR) system8. To investigate the possible roles of TGF in an irradiated cell culture, our Monte-Carlo simulation codes of the radiation track structure9 will be used to calculate the activation of TFG triggered by .OH produced by low doses of HZE ions. The TGF molecules will then be followed by a BD algorithm in a medium representative of a cell culture to estimate the number of activated receptors.

Badhwar-O'Neil 2007 Galactic Cosmic Ray (GCR) Model Using Advanced Composition Explorer (ACE) Measurements for Solar Cycle 23

NASA Technical Reports Server (NTRS)

ONeill, P. M.

2007-01-01

Advanced Composition Explorer (ACE) satellite measurements of the galactic cosmic ray flux and correlation with the Climax Neutron Monitor count over Solar Cycle 23 are used to update the Badhwar O'Neill Galactic Cosmic Ray (GCR) model.

Testing Galactic Cosmic Ray Models

NASA Technical Reports Server (NTRS)

Adams, James H., Jr.

2009-01-01

Models of the Galactic Cosmic Ray Environment are used for designing and planning space missions. The existing models will be reviewed. Spectral representations from these models will be compared with measurements of galactic cosmic ray spectra made on balloon flights and satellite flights over a period of more than 50 years.

Testing Galactic Cosmic Ray Models

NASA Technical Reports Server (NTRS)

Adams, James H., Jr.

2010-01-01

Models of the Galactic Cosmic Ray Environment are used for designing and planning space missions. The exising models will be reviewed. Spectral representations from these models will be compared with measurements of galactic cosmic ray spectra made on balloon flights and satellite flights over a period of more than 50 years.

Science Brought by JASMINE Data

NASA Astrophysics Data System (ADS)

Tsujimoto, T.

The planned astrometric space mission JASMINE will provide the exact positions, distances, and proper motions of the bulge stars. These data will certainly reveal the origin and evolution of the Galactic bulge. In fact, the formation process of the bulge is still veiled. It is generally believed that the Galactic bulge possesses a simple old population. On the other hand, the Galactic bulge has a bar with some kinematic implications for a secular evolution. Here we review some evidences for the recent star formation in the Galactic bulge, that will be verified by JASMINE.

JASMINE: constructor of the dynamical structure of the Galactic bulge

NASA Astrophysics Data System (ADS)

Gouda, N.; Kobayashi, Y.; Yamada, Y.; Yano, T.; Tsujimoto, T.; Suganuma, M.; Niwa, Y.; Yamauchi, M.

2008-07-01

We introduce a Japanese space astrometry project which is called JASMINE. JASMINE (Japan Astrometry Satellite Mission for INfrared Exploration) will measure distances and tangential motions of stars in the Galactic bulge with yet unprecedented precision. JASMINE will operate in z-band whose central wavelength is 0.9 micron. It will measure parallaxes, positions with accuracy of about 10 micro-arcsec and proper motions with accuracy of about 10 micro- arcsec/year for the stars brighter than z=14 mag. The number of stars observed by JASMINE with high accuracy of parallaxes in the Galactic bulge is much larger than that observed in other space astrometry projects operating in optical bands. With the completely new “map of the Galactic bulge” including motions of bulge stars, we expect that many new exciting scientific results will be obtained in studies of the Galactic bulge. One of them is the construction of the dynamical structure of the Galactic bulge. Kinematics and distance data given by JASMINE are the closest approach to a view of the exact dynamical structure of the Galactic bulge. Presently, JASMINE is in a development phase, with a target launch date around 2016. We comment on the outline of JASMINE mission, scientific targets and a preliminary design of JASMINE in this paper.

Interacting Cosmic Rays with Molecular Clouds: A Bremsstrahlung Origin of Diffuse High-energy Emission from the Inner 2°×1° of the Galactic Center

NASA Astrophysics Data System (ADS)

Yusef-Zadeh, F.; Hewitt, J. W.; Wardle, M.; Tatischeff, V.; Roberts, D. A.; Cotton, W.; Uchiyama, H.; Nobukawa, M.; Tsuru, T. G.; Heinke, C.; Royster, M.

2013-01-01

The high-energy activity in the inner few degrees of the Galactic center is traced by diffuse radio, X-ray, and γ-ray emission. The physical relationship between different components of diffuse gas emitting at multiple wavelengths is a focus of this work. We first present radio continuum observations using the Green Bank Telescope and model the nonthermal spectrum in terms of a broken power-law distribution of ~GeV electrons emitting synchrotron radiation. We show that the emission detected by Fermi is primarily due to nonthermal bremsstrahlung produced by the population of synchrotron emitting electrons in the GeV energy range interacting with neutral gas. The extrapolation of the electron population measured from radio data to low and high energies can also explain the origin of Fe I 6.4 keV line and diffuse TeV emission, as observed with Suzaku, XMM-Newton, Chandra, and the H.E.S.S. observatories. The inferred physical quantities from modeling multiwavelength emission in the context of bremsstrahlung emission from the inner ~300 × 120 pc of the Galactic center are constrained to have the cosmic-ray ionization rate ~1-10 × 10-15 s-1, molecular gas heating rate elevating the gas temperature to 75-200 K, fractional ionization of molecular gas 10-6-10-5, large-scale magnetic field 10-20 μG, the density of diffuse and dense molecular gas ~100 and ~103 cm-3 over 300 pc and 50 pc path lengths, and the variability of Fe I Kα 6.4 keV line emission on yearly timescales. Important implications of our study are that GeV electrons emitting in radio can explain the GeV γ-rays detected by Fermi and that the cosmic-ray irradiation model, like the model of the X-ray irradiation triggered by past activity of Sgr A*, can also explain the origin of the variable 6.4 keV emission from Galactic center molecular clouds.

Giant Molecular Clouds with High Abundance of Atomic Carbon and Cyano Radical in the Milky Way's Central Molecular Zone

NASA Astrophysics Data System (ADS)

Tanaka, Kunihiko; Oka, Tomoharu; Nagai, Makoto; Kamegai, Kazuhisa

2015-08-01

The central 400 pc region of the Milky Way Galaxy is the closest galactic central region to us, providing a unique opportunity to detailedly investigate gas dynamics, star formation activity, and chemistry under the extreme environment of galactic centers, where the presence of bar, intense UV/cosmic-ray fluxes, high degree of turbulence may significantly affect those processes. We report the results of molecular line surveys toward the Milky Way's central molecular zone (CMZ) performed with the ASTE 10m telescope, the Mopra 22m telescope, and the Nobeyama 45 m telescope. With the observations of the 500 GHz [CI] fine structure line of atomic carbon (C0), we have found a molecular cloud structure with remarkably bright [CI] emission in the Sgr A comlex in the innermost 20 pc region. The [CI] cloud is more extended than the GMCs in the region, and appears to connect the northern part of the 50 kms-1 (M-0.02-0.07) and the circumnuclear disk (CND), though no corresponding structures are visible in other molecular lines. The [C0]/[CO] abundance ratio is measured to be 0.5-2, which is 2-10 times those measured to the clouds at larger Galactic radii. This high ratio is close to the values measured toward centers of galaxies with starburst and AGN, suggesting that the chemical state of the cloud is similar to that in those active galaxies. We have also found a large scale gradient of the cyano radical (CN) abundance toward the Galactic center in the innermost 100 pc radius, showing near the Sgr A complex. We suggest that the cloud with high C0 and CN abundance is a feature formed as a result of inward transfer of diffuse molecular gas by the bar potential in the inner Galaxy, in which PDR-like chemical composition remains preserved, and that thus the [CI] cloud could be deeply related to formation of the GMCs and star formation in the CMZ. We also discuss other possible mechanisms to enhance C0 and CN abundances, including the enhanced cosmic-ray dissociation ratio.

UNCOVERING THE NUCLEUS CANDIDATE FOR NGC 253

DOE Office of Scientific and Technical Information (OSTI.GOV)

Günthardt, G. I.; Camperi, J. A.; Agüero, M. P.

2015-11-15

NGC 253 is the nearest spiral galaxy with a nuclear starburst that becomes the best candidate for studying the relationship between starburst and active galactic nucleus activity. However, this central region is veiled by large amounts of dust, and it has been so far unclear which is the true dynamical nucleus to the point that there is no strong evidence that the galaxy harbors a supermassive black hole co-evolving with the starburst as was supposed earlier. Near-infrared (NIR) spectroscopy, especially NIR emission line analysis, could be advantageous in shedding light on the true nucleus identity. Using Flamingos-2 at Gemini Southmore » we have taken deep K-band spectra along the major axis of the central structure and through the brightest infrared source. In this work, we present evidence showing that the brightest NIR and mid-infrared source in the central region, already known as radio source TH7 and so far considered just a large stellar supercluster, in fact presents various symptoms of a genuine galactic nucleus. Therefore, it should be considered a valid nucleus candidate. Mentioning some distinctive aspects, it is the most massive compact infrared object in the central region, located at 2.″0 of the symmetry center of the galactic bar, as measured in the K-band emission. Moreover, our data indicate that this object is surrounded by a large circumnuclear stellar disk and it is also located at the rotation center of the large molecular gas disk of NGC 253. Furthermore, a kinematic residual appears in the H{sub 2} rotation curve with a sinusoidal shape consistent with an outflow centered in the candidate nucleus position. The maximum outflow velocity is located about 14 pc from TH7, which is consistent with the radius of a shell detected around the nucleus candidate, observed at 18.3 μm (Qa) and 12.8 μm ([Ne ii]) with T-ReCS. Also, the Brγ emission line profile shows a pronounced blueshift and this emission line also has the highest equivalent width at this position. All this evidence points to TH7 as the best candidate for the galactic nucleus of NGC 253.« less

INTERACTING COSMIC RAYS WITH MOLECULAR CLOUDS: A BREMSSTRAHLUNG ORIGIN OF DIFFUSE HIGH-ENERGY EMISSION FROM THE INNER 2 Degree-Sign Multiplication-Sign 1 Degree-Sign OF THE GALACTIC CENTER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yusef-Zadeh, F.; Roberts, D. A.; Royster, M.

2013-01-01

The high-energy activity in the inner few degrees of the Galactic center is traced by diffuse radio, X-ray, and {gamma}-ray emission. The physical relationship between different components of diffuse gas emitting at multiple wavelengths is a focus of this work. We first present radio continuum observations using the Green Bank Telescope and model the nonthermal spectrum in terms of a broken power-law distribution of {approx}GeV electrons emitting synchrotron radiation. We show that the emission detected by Fermi is primarily due to nonthermal bremsstrahlung produced by the population of synchrotron emitting electrons in the GeV energy range interacting with neutral gas.more » The extrapolation of the electron population measured from radio data to low and high energies can also explain the origin of Fe I 6.4 keV line and diffuse TeV emission, as observed with Suzaku, XMM-Newton, Chandra, and the H.E.S.S. observatories. The inferred physical quantities from modeling multiwavelength emission in the context of bremsstrahlung emission from the inner {approx}300 Multiplication-Sign 120 pc of the Galactic center are constrained to have the cosmic-ray ionization rate {approx}1-10 Multiplication-Sign 10{sup -15} s{sup -1}, molecular gas heating rate elevating the gas temperature to 75-200 K, fractional ionization of molecular gas 10{sup -6}-10{sup -5}, large-scale magnetic field 10-20 {mu}G, the density of diffuse and dense molecular gas {approx}100 and {approx}10{sup 3} cm{sup -3} over 300 pc and 50 pc path lengths, and the variability of Fe I K{alpha} 6.4 keV line emission on yearly timescales. Important implications of our study are that GeV electrons emitting in radio can explain the GeV {gamma}-rays detected by Fermi and that the cosmic-ray irradiation model, like the model of the X-ray irradiation triggered by past activity of Sgr A*, can also explain the origin of the variable 6.4 keV emission from Galactic center molecular clouds.« less

Behavioral characteristics and neurobiological substrates shared by Pavlovian sign-tracking and drug abuse.

PubMed

Tomie, Arthur; Grimes, Kathryn L; Pohorecky, Larissa A

2008-06-01

Drug abuse researchers have noted striking similarities between behaviors elicited by Pavlovian sign-tracking procedures and prominent symptoms of drug abuse. In Pavlovian sign-tracking procedures, repeated paired presentations of a small object (conditioned stimulus, CS) with a reward (unconditioned stimulus, US) elicits a conditioned response (CR) that typically consists of approaching the CS, contacting the CS, and expressing consummatory responses at the CS. Sign-tracking CR performance is poorly controlled and exhibits spontaneous recovery and long-term retention, effects that resemble relapse. Sign-tracking resembles psychomotor activation, a syndrome of behavioral responses evoked by addictive drugs, and the effects of sign-tracking on corticosterone levels and activation of dopamine pathways resemble the neurobiological effects of abused drugs. Finally, the neurobiological profile of individuals susceptible to sign-tracking resembles the pathophysiological profile of vulnerability to drug abuse, and vulnerability to sign-tracking predicts vulnerability to impulsive responding and alcohol self-administration. Implications of sign-tracking for models of drug addiction are considered.

Behavioral Characteristics and Neurobiological Substrates Shared by Pavlovian Sign-Tracking and Drug Abuse

PubMed Central

Tomie, Arthur; Grimes, Kathryn L.; Pohorecky, Larissa A.

2008-01-01

Drug abuse researchers have noted striking similarities between behaviors elicited by Pavlovian sign-tracking procedures and prominent symptoms of drug abuse. In Pavlovian sign-tracking procedures, repeated paired presentations of a small object (conditioned stimulus, CS) with a reward (unconditioned stimulus, US) elicits a conditioned response (CR) that typically consists of approaching the CS, contacting the CS, and expressing consummatory responses at the CS. Sign-tracking CR performance is poorly controlled and exhibits spontaneous recovery and long-term retention, effects that resemble relapse. Sign-tracking resembles psychomotor activation, a syndrome of behavioral responses evoked by addictive drugs, and the effects of sign-tracking on corticosterone levels and activation of dopamine pathways resemble the neurobiological effects of abused drugs. Finally, the neurobiological profile of individuals susceptible to sign-tracking resembles the pathophysiological profile of vulnerability to drug abuse, and vulnerability to sign-tracking predicts vulnerability to impulsive responding and alcohol self-administration. Implications of sign-tracking for models of drug addiction are considered. PMID:18234349

Measurements of LET distribution and dose equivalent onboard the Space Shuttle IML-2 (STS-65) and S/MM#4 (STS-79).

PubMed

Hayashi, T; Doke, T; Kikuchi, J; Sakaguchi, T; Takeuchi, R; Takashima, T; Kobayashi, M; Terasawa, K; Takahashi, K; Watanabe, A; Kyan, A; Hasebe, N; Kashiwagi, T; Ogura, K; Nagaoka, S; Kato, M; Nakano, T; Takahashi, S; Yamanaka, H; Yamaguchi, K; Badhwar, G D

1997-12-01

Space radiation dosimetry measurements have been made onboard the Space Shuttle STS-65 in the Second International Microgravity Laboratory (IML-2: 28.5 degrees x 300 km: 14.68 days) and the STS-79 in the 4th Shuttle MIR mission (S/MM#4: 51.6 degrees x 300-400km: 10.2 days). In these measurements, three kinds of detectors were used; one is a newly developed active detector telescope called "Real-time Radiation Monitoring Device (RRMD-I for IML-2 and RRMD-II with improved triggering system for S/MM#4)" utilizing silicon semi-conductor detectors and the other detectors are conventional passive detectors of thermoluminescence dosimeters (TLDs) and CR-39 plastic track detectors. The main contribution to dose equivalent for particles with LET > 5.0 keV/micrometer (IML-2) and LET > 3.5 keV/micrometer (S/MM#4) is seen to be due to galactic cosmic rays (GCRs) and the contribution of the South Atlantic Anomaly (SAA) is less than 5% (IML-2: 28.5 degrees x 300 km) and 15% (S/MM#4: 51.6 degrees x 400 km) in the above RRMD LET detection conditions. For the whole LET range (> 0.2 kev/micrometer) obtained by TLDs and CR-39 in these two typical orbits (a small inclination x low altitude and a large inclination x high altitude), absorbed dose rates range from 94 to 114 microGy/day, dose equivalent rates from 186 to 207 microSv/day and average quality factors from 1.82 to 2.00 depending on the locations and directions of detectors inside the Spacelab at the highly protected IML-2 orbit (28.5 degrees x 300 km), and also, absorbed dose rates range from 290 to 367 microGy/day, dose equivalent rates from 582 to 651 microSv/day and average quality factors from 1.78 to 2.01 depending on the dosimeter packages around the RRMD-II "Detector Unit" at the S/MM#4 orbit (5l.6 degrees x 400km). In general, it is seen that absorbed doses depend on the orbit altitude (SAA trapped particles contribution dominant) and dose equivalents on the orbit inclination (GCR contribution dominant). The LET distributions obtained by two different types of active and passive detectors, RRMDs and CR-39, are in good agreement for LET of 15 - 200 kev/micrometer and difference of these distributions in the regions of LET < 15 kev/micrometer and LET > 200 kev/micrometer can be explained by considering characteristics of CR-39 etched track formation especially for the low LET tracks and chemical etching conditions.

Measurements of LET distribution and dose equivalent onboard the Space Shuttle IML-2 (STS-65) and S/MM#4 (STS-79)

NASA Technical Reports Server (NTRS)

Hayashi, T.; Doke, T.; Kikuchi, J.; Sakaguchi, T.; Takeuchi, R.; Takashima, T.; Kobayashi, M.; Terasawa, K.; Takahashi, K.; Watanabe, A.;

Cross-Modal Attention Effects in the Vestibular Cortex during Attentive Tracking of Moving Objects.

PubMed

Frank, Sebastian M; Sun, Liwei; Forster, Lisa; Tse, Peter U; Greenlee, Mark W

2016-12-14

The midposterior fundus of the Sylvian fissure in the human brain is central to the cortical processing of vestibular cues. At least two vestibular areas are located at this site: the parietoinsular vestibular cortex (PIVC) and the posterior insular cortex (PIC). It is now well established that activity in sensory systems is subject to cross-modal attention effects. Attending to a stimulus in one sensory modality enhances activity in the corresponding cortical sensory system, but simultaneously suppresses activity in other sensory systems. Here, we wanted to probe whether such cross-modal attention effects also target the vestibular system. To this end, we used a visual multiple-object tracking task. By parametrically varying the number of tracked targets, we could measure the effect of attentional load on the PIVC and the PIC while holding the perceptual load constant. Participants performed the tracking task during functional magnetic resonance imaging. Results show that, compared with passive viewing of object motion, activity during object tracking was suppressed in the PIVC and enhanced in the PIC. Greater attentional load, induced by increasing the number of tracked targets, was associated with a corresponding increase in the suppression of activity in the PIVC. Activity in the anterior part of the PIC decreased with increasing load, whereas load effects were absent in the posterior PIC. Results of a control experiment show that attention-induced suppression in the PIVC is stronger than any suppression evoked by the visual stimulus per se. Overall, our results suggest that attention has a cross-modal modulatory effect on the vestibular cortex during visual object tracking. In this study we investigate cross-modal attention effects in the human vestibular cortex. We applied the visual multiple-object tracking task because it is known to evoke attentional load effects on neural activity in visual motion-processing and attention-processing areas. Here we demonstrate a load-dependent effect of attention on the activation in the vestibular cortex, despite constant visual motion stimulation. We find that activity in the parietoinsular vestibular cortex is more strongly suppressed the greater the attentional load on the visual tracking task. These findings suggest cross-modal attentional modulation in the vestibular cortex. Copyright © 2016 the authors 0270-6474/16/3612720-09$15.00/0.

How Can I Keep Track of Physical Activity and Eating?

MedlinePlus

... Weight Management How Can I Keep Track of Physical Activity and Healthy Eating? Taking care of your heart ... life. Planning a healthy diet and a regular physical activity program is the key to success. Prepare yourself ...

Identification of 1.4 Million Active Galactic Nuclei In the Mid-Infrared Using WISE Data

DTIC Science & Technology

2015-11-01

galaxies – infrared: stars – galaxies : active – quasars: general Supporting material: machine-readable table 1. INTRODUCTION The International Celestial...AGN-dominated galaxies , optical emission is thought to originate from the compact accretion disk surrounding the supermassive black hole (SMBH), while... galaxies , an optical centroid can be shifted relative to the radio position because of contamination from the host galaxy . Depending on the distance to

Foreword

NASA Astrophysics Data System (ADS)

Boulanger, François; Miville-Deschênes, Marc-Antoine

Scientific awareness of the galactic magnetic field arose in the late 40's with Fermi's work on cosmic rays, the discovery of the polarization of dust reddened starlight by Hiltner and Hall, and its interpretation in terms of magnetically aligned dust grains by Spitzer and Tukey and Davis and Greenstein. It was soon clear that the magnetic field and the cosmic ray are tied to the interstellar gas and form together an active dynamical system. Its importance for star formation and interstellar matter energetics was also quickly recognized but more than 50 years after most questions remain quantitatively open due to the paucity of data on the small scale structure of the field. In the last decade, interferometric surveys have revealed striking patterns in the diffuse polarized emission, imposed by Faraday rotation, that give a way to study the field structure in the intervening ionized medium. The advent of high sensitivity measurements of polarized emission at sub-millimeter wavelengths promise to further open our perspective on the Galactic field. The dust observations will soon extend from high resolution observations from star forming regions with ground based telescopes and the ALMA interferometer to the continuous mapping of the diffuse interstellar medium with Planck. A few months after the discovery of optical interstellar polarization, the Galactic magnetic field was an unexpected highlight of the first symposium on Cosmical Gas Dynamics held in Paris in august 1949. The Polarization 2005 meeting held at the University of Orsay was also a premiere. For the first time, two communities with disconnected backgrounds but common interests in polarization observations were given the opportunity to meet and learn from each other's research. The measurement of the polarization of the Cosmic Microwave Background has become a major Physics challenge of the decade(s) to come. The numerous experiments designed to achieve this goal have started providing data with unprecedented sensitivity on the Galactic polarization from sub-millimeter to centimetric wavelengths. Detailed modeling of the Galactic contribution to the observed polarization is a required key to the success of their endeavor. This book gathers invited lectures presented at the meeting. It gives an in depth account of our present knowledge of the Galactic magnetic field from measurements of its structure and intensity to its role in the physics of interstellar matter and star formation. The Galactic part of the book is complemented by three papers that introduce the Cosmic Microwave Background polarization and describe the experiments being built to observe it, with special attention to the Planck ESA mission. Few years after the Paris Cosmical Gas Dynamics symposium, the discovery of polarized synchrotron emission in the Crab was a new highlight in magnetic field research. Quoting a review by van de Hulst: “From that time on, measuring the polarization and thus mapping the magnetic field became a prime desideratum in galactic radio astronomy”. We hope that observations to come will stimulate similar enthusiasm and bring more and more scientists to the field for whom this book will be a useful and lasting reference. The editors would like to thank the IAS staff that took care of the organization with a special mention for Catherine Cougrand.

Featured Image: Globular Cluster Orbits

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-04-01

This figure (click for the full view) shows the meridional galactic orbits of 12 globular clusters that orbit the Milky Way. The recent release of stellar parallax data from Gaia allowed a team of scientists at Dartmouth College to improve measurements of a number of galactic globular clusters very old clusters of stars that can either orbit within the galactic disk and bulge or more distantly in the galactic halo. In a recent publication led by Erin OMalley, the team presents their findings and combines their new measurements for the clusters with proper motions from past studies to calculate the orbits that these globulars take. These calculations show us whether the clusters reside in the galactic disk and bulge (as only NGC 104 does in the sample shown here, since its orbit is confined to 8 kpc radially and 4 kpc vertically of the galactic center), or if they are halo clusters. To learn more about the authors work, you can check out the paper below!CitationErin M. OMalley et al 2017 ApJ 838 162. doi:10.3847/1538-4357/aa6574

Impact of a workplace physical activity tracking program on biometric health outcomes.

PubMed

Yu, Jiani; Abraham, Jean M; Dowd, Bryan; Higuera, Lucas F; Nyman, John A

2017-12-01

Wellness programs are a popular strategy utilized by large U.S. employers. As mobile health applications and wearable tracking devices increase in prevalence, many employers now offer physical activity tracking applications. This longitudinal study evaluates the impact of engagement with a web-based, physical activity tracking program on changes in individuals' biometric outcomes in an employer population. The study population includes active employees and adult dependents continuously enrolled in an eligible health plan and who have completed at least two biometric screenings (n=36,882 person-years with 11,436 unique persons) between 2011 and 2014. Using difference-in-differences (DID) regression, we estimate the effect of participation in the physical activity tracking application on BMI, total cholesterol, and blood pressure. Participation was significantly associated with a reduction of 0.275 in BMI in the post-period, relative to the comparison group, representing a 1% change from baseline BMI. The program did not have a statistically significant impact on cholesterol or blood pressure. Sensitivity checks revealed slightly larger BMI reductions among participants with higher intensity of tracking activity and in the period following the employer's shift to an outcomes-based incentive design. Results are broadly consistent with the existing literature on changes in biometric outcomes from workplace initiatives promoting increased physical activity. Employers should have modest expectations about the potential health benefits of such programs, given current designs and implementation in real-world settings. Copyright © 2017 Elsevier Inc. All rights reserved.

Well-Being Tracking via Smartphone-Measured Activity and Sleep: Cohort Study

PubMed Central

Feygin, Sidney; Dembo, Aluma; Aguilera, Adrian; Recht, Benjamin

2017-01-01

Background Automatically tracking mental well-being could facilitate personalization of treatments for mood disorders such as depression and bipolar disorder. Smartphones present a novel and ubiquitous opportunity to track individuals’ behavior and may be useful for inferring and automatically monitoring mental well-being. Objective The aim of this study was to assess the extent to which activity and sleep tracking with a smartphone can be used for monitoring individuals’ mental well-being. Methods A cohort of 106 individuals was recruited to install an app on their smartphone that would track their well-being with daily surveys and track their behavior with activity inferences from their phone’s accelerometer data. Of the participants recruited, 53 had sufficient data to infer activity and sleep measures. For this subset of individuals, we related measures of activity and sleep to the individuals’ well-being and used these measures to predict their well-being. Results We found that smartphone-measured approximations for daily physical activity were positively correlated with both mood (P=.004) and perceived energy level (P<.001). Sleep duration was positively correlated with mood (P=.02) but not energy. Our measure for sleep disturbance was not found to be significantly related to either mood or energy, which could imply too much noise in the measurement. Models predicting the well-being measures from the activity and sleep measures were found to be significantly better than naive baselines (P<.01), despite modest overall improvements. Conclusions Measures of activity and sleep inferred from smartphone activity were strongly related to and somewhat predictive of participants’ well-being. Whereas the improvement over naive models was modest, it reaffirms the importance of considering physical activity and sleep for predicting mood and for making automatic mood monitoring a reality. PMID:28982643

Characterizing the Optical Variability of Bright Blazars: Variability-Based Selection of Fermi Active Galactic Nuclei

DTIC Science & Technology

2012-11-20

10′. We do not apply cosmological redshift corrections here for blazar selection. Similar to the conclusions drawn from Figure 4, there is clear...effects. For example, the observed blazar characteristic damping timescale τblz,obs (after correcting for cosmological redshift) should be shortened in

The Pearson-Readhead AGN Survey

NASA Astrophysics Data System (ADS)

Lister, M. L.

2009-08-01

The Pearson-Readhead survey of active galactic nuclei (AGN) was the first complete sample to be studied by VLBI, and was the subject of a detailed investigation by the VSOP program. We discuss the scientific findings from this unique survey, and how it has provided robust confirmation of the relativistic beaming model for AGN jets.

Active Multimodal Sensor System for Target Recognition and Tracking

PubMed Central

Zhang, Guirong; Zou, Zhaofan; Liu, Ziyue; Mao, Jiansen

2017-01-01

High accuracy target recognition and tracking systems using a single sensor or a passive multisensor set are susceptible to external interferences and exhibit environmental dependencies. These difficulties stem mainly from limitations to the available imaging frequency bands, and a general lack of coherent diversity of the available target-related data. This paper proposes an active multimodal sensor system for target recognition and tracking, consisting of a visible, an infrared, and a hyperspectral sensor. The system makes full use of its multisensor information collection abilities; furthermore, it can actively control different sensors to collect additional data, according to the needs of the real-time target recognition and tracking processes. This level of integration between hardware collection control and data processing is experimentally shown to effectively improve the accuracy and robustness of the target recognition and tracking system. PMID:28657609

The near-infrared radius-luminosity relationship for active galactic nuclei

NASA Astrophysics Data System (ADS)

Landt, Hermine; Bentz, Misty C.; Peterson, Bradley M.; Elvis, Martin; Ward, Martin J.; Korista, Kirk T.; Karovska, Margarita

2011-05-01

Black hole masses for samples of active galactic nuclei (AGNs) are currently estimated from single-epoch optical spectra. In particular, the size of the broad-line emitting region needed to compute the black hole mass is derived from the optical or ultraviolet continuum luminosity. Here we consider the relationship between the broad-line region size, R, and the near-infrared (near-IR) AGN continuum luminosity, L, as the near-IR continuum suffers less dust extinction than at shorter wavelengths and the prospects for separating the AGN continuum from host-galaxy starlight are better in the near-IR than in the optical. For a relationship of the form R∝Lα, we obtain for a sample of 14 reverberation-mapped AGN a best-fitting slope of α= 0.5 ± 0.1, which is consistent with the slope of the relationship in the optical band and with the value of 0.5 naïvely expected from photoionization theory. Black hole masses can then be estimated from the near-IR virial product, which is calculated using the strong and unblended Paschen broad emission lines (Paα or Paβ).

Oscillatory patterns in the light curves of five long-term monitored type 1 active galactic nuclei

NASA Astrophysics Data System (ADS)

Kovačević, Andjelka B.; Pérez-Hernández, Ernesto; Popović, Luka Č.; Shapovalova, Alla I.; Kollatschny, Wolfram; Ilić, Dragana

2018-04-01

New combined data of five well-known type 1 active galactic nuclei (AGNs) are probed with a novel hybrid method in a search for oscillatory behaviour. Additional analysis of artificial light curves obtained from the coupled oscillatory models gives confirmation for detected periods that could have a physical background. We find periodic variations in the long-term light curves of 3C 390.3, NGC 4151 and NGC 5548, and E1821 + 643, with correlation coefficients larger than 0.6. We show that the oscillatory patterns of two binary black hole candidates, NGC 5548 and E1821 + 643, correspond to qualitatively different dynamical regimes of chaos and stability, respectively. We demonstrate that the absence of oscillatory patterns in Arp 102B could be the result of a weak coupling between oscillatory mechanisms. This is the first good evidence that 3C 390.3 and Arp 102B, categorized as double-peaked Balmer line objects, have qualitative different dynamics. Our analysis shows a novelty in the oscillatory dynamical patterns of the light curves of these type 1 AGNs.

Nonlinear excitations in electron-positron-ion plasmas in accretion disks of active galactic nuclei

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moslem, W. M.; Kourakis, I.; Shukla, P. K.

2007-10-15

The propagation of acoustic nonlinear excitations in an electron-positron-ion (e-p-i) plasma composed of warm electrons and positrons, as well as hot ions, has been investigated by adopting a two-dimensional cylindrical geometry. The electrons and positrons are modeled by hydrodynamic fluid equations, while the ions are assumed to follow a temperature-parametrized Boltzmann distribution (the fixed ion model is recovered in the appropriate limit). This situation applies in the accretion disk near a black hole in active galactic nuclei, where the ion temperature may be as high as 3 to 300 times that of the electrons. Using a reductive perturbation technique, amore » cylindrical Kadomtsev-Petviashvili equation is derived and its exact soliton solutions are presented. Furthermore, real situations in which the strength of the nonlinearity may be weak are considered, so that higher-order nonlinearity plays an important role. Accordingly, an extended cylindrical Kadomtsev-Petviashvili equation is derived, which admits both soliton and double-layer solutions. The characteristics of the nonlinear excitations obtained are investigated in detail.« less

The standard model and some new directions. [for scientific theory of Active Galactic Nuclei

NASA Technical Reports Server (NTRS)

Blandford, R. D.; Rees, M. J.

1992-01-01

A 'standard' model of Active Galactic Nuclei (AGN), based upon a massive black hole surrounded by a thin accretion disk, is defined. It is argued that, although there is good evidence for the presence of black holes and orbiting gas, most of the details of this model are either inadequate or controversial. Magnetic field may be responsible for the confinement of continuum and line-emitting gas, for the dynamical evolution of accretion disks and for the formation of jets. It is further argued that gaseous fuel is supplied in molecular form and that this is responsible for thermal re-radiation, equatorial obscuration and, perhaps, the broad line gas clouds. Stars may also supply gas close to the black hole, especially in low power AGN and they may be observable in discrete orbits as probes of the gravitational field. Recent observations suggest that magnetic field, stars, dusty molecular gas and orientation effects must be essential components of a complete description of AGN. The discovery of quasars with redshifts approaching 5 is an important clue to the mechanism of galaxy formation.

A DISTANT ECHO OF MILKY WAY CENTRAL ACTIVITY CLOSES THE GALAXY’s BARYON CENSUS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nicastro, F.; Senatore, F.; Krongold, Y.

2016-09-01

We report on the presence of large amounts of million-degree gas in the Milky Way’s interstellar and circum-galactic medium. This gas (1) permeates both the Galactic plane and the halo, (2) extends to distances larger than 60–200 kpc from the center, and (3) its mass is sufficient to close the Galaxy’s baryon census. Moreover, we show that a vast, ∼6 kpc radius, spherically symmetric central region of the Milky Way above and below the 0.16 kpc thick plane has either been emptied of hot gas or the density of this gas within the cavity has a peculiar profile, increasing frommore » the center up to a radius of ∼6 kpc, and then decreasing with a typical halo density profile. This, and several other converging pieces of evidence, suggest that the current surface of the cavity, at 6 kpc from the Galaxy’s center, traces the distant echo of a period of strong nuclear activity of our supermassive black hole, occurring about 6 Myr ago.« less

On the formation and confinement of dense clouds in QSOs and active galactic nuclei

NASA Technical Reports Server (NTRS)

Marscher, A. P.; Weaver, R. P.

1979-01-01

A model for the formation and confinement of dense (at least about 1 billion per cu cm) clouds in QSOs and active galactic nuclei is presented wherein thermal instabilities behind radiative shocks cause the collapse of regions where the preshock density is enhanced over that of the surrounding medium. Such shocks (of total energy around 10 to the 51st ergs) are likely to occur if the frequent optical outbursts observed in many of these objects are accompanied by mass ejections of comparable energy. It is found that clouds quite similar to those thought to exist in QSOs etc. can be created in this manner at radii of the order of 10 to the 17th cm. The clouds can be subsequently accelerated to observed bulk velocities by either radiation pressure or a collision with a much stronger (total energy around 10 to the 53 ergs) shock. Alternatively, their high observed velocities could be caused by gravitational infall or rotation. The mass production required at inner radii by the outflow models can be supplied through a mechanism previously discussed by Shields (1977).

Automatized Photometric Monitoring of Active Galactic Nuclei with the 46cm Telescope of the Wise Observatory

NASA Astrophysics Data System (ADS)

Pozo Nuñez, Francisco; Chelouche, Doron; Kaspi, Shai; Niv, Saar

2017-09-01

We present the first results of an ongoing variability monitoring program of active galactic nuclei (AGNs) using the 46 cm telescope of the Wise Observatory in Israel. The telescope has a field of view of 1.25^\\circ × 0.84^\\circ and is specially equipped with five narrowband filters at 4300, 5200, 5700, 6200, and 7000 Å to perform photometric reverberation mapping studies of the central engine of AGNs. The program aims to observe a sample of 27 AGNs (V < 17 mag) selected according to tentative continuum and line time delay measurements obtained in previous works. We describe the autonomous operation of the telescope together with the fully automatic pipeline used to achieve high-performance unassisted observations, data reduction, and light curves extraction using different photometric methods. The science verification data presented here demonstrates the performance of the monitoring program in particular for efficiently photometric reverberation mapping of AGNs with additional capabilities to carry out complementary studies of other transient and variable phenomena such as variable stars studies.

Intrinsic physical conditions and structure of relativistic jets in active galactic nuclei

NASA Astrophysics Data System (ADS)

Nokhrina, E. E.; Beskin, V. S.; Kovalev, Y. Y.; Zheltoukhov, A. A.

2015-03-01

The analysis of the frequency dependence of the observed shift of the cores of relativistic jets in active galactic nuclei (AGNs) allows us to evaluate the number density of the outflowing plasma ne and, hence, the multiplicity parameter λ = ne/nGJ, where nGJ is the Goldreich-Julian number density. We have obtained the median value for λmed = 3 × 1013 and the median value for the Michel magnetization parameter σM, med = 8 from an analysis of 97 sources. Since the magnetization parameter can be interpreted as the maximum possible Lorentz factor Γ of the bulk motion which can be obtained for relativistic magnetohydrodynamic (MHD) flow, this estimate is in agreement with the observed superluminal motion of bright features in AGN jets. Moreover, knowing these key parameters, one can determine the transverse structure of the flow. We show that the poloidal magnetic field and particle number density are much larger in the centre of the jet than near the jet boundary. The MHD model can also explain the typical observed level of jet acceleration. Finally, casual connectivity of strongly collimated jets is discussed.

Accretion disk modeling of AGN continuum using non-LTE stellar atmospheres. [active galactic nuclei (AGN)

NASA Technical Reports Server (NTRS)

Sun, Wei-Hsin; Malkan, Matthew A.

1988-01-01

Active galactic nuclei (AGN) accretion disk spectra were calculated using non-LTE stellar atmosphere models for Kerr and Schwarzschild geometries. It is found that the Lyman limit absorption edge, probably the most conclusive observational evidence for the accretion disk, would be drastically distorted and displaced by the relativistic effects from the large gravitational field of the central black hole and strong Doppler motion of emitting material on the disk surface. These effects are especially pronounced in the Kerr geometry. The strength of the Lyman limit absorption is very sensitive to the surface gravity in the stellar atmosphere models used. For models at the same temperature but different surface gravities, the strength of the Lyman edge exhibits an almost exponential decrease as the surface gravity approach the Eddington limit, which should approximate the thin disk atmosphere. The relativistic effects as well as the vanishing of the Lyman edge at the Eddington gravity may be the reasons that not many Lyman edges in the rest frames of AGNs and quasars are found.

Active galactic nuclei. II - The acceleration of relativistic particles in a cluster of accreting black holes

NASA Technical Reports Server (NTRS)

Pacholczyk, A. G.; Stepinski, T. F.

1988-01-01

An accreting cluster of black holes in an active galactic nucleus is a natural site for a system of shock structures with a hierarchy of sizes, corresponding to the distribution of masses in the cluster. Accreted gas containing some magnetic fields and supersonically falling onto the core forms shocks on the outside of each hole and these shocks are capable of accelerating relativistic particles. The energies reached in a single shock are size rather than acceleration time limited and are proportional to the mass of the hole with a proportionality constant being a function of the position of the hole within a cluster and the model of the cluster and the shock formation. These energies are adequate to explain the observed properties of synchrotron and inverse-Compton radiation from these objects. The resulting energy spectrum of particles in the cluster in 'zeroth' approximation has the form of a doubly broken power law with indices of two and three on both extremes of the energy domain respectively, bridged by an index of about 2.5.

An ultra-relativistic outflow from a neutron star accreting gas from a companion.

PubMed

Fender, Rob; Wu, Kinwah; Johnston, Helen; Tzioumis, Tasso; Jonker, Peter; Spencer, Ralph; Van Der Klis, Michiel

2004-01-15

Collimated relativistic outflows-also known as jets-are amongst the most energetic phenomena in the Universe. They are associated with supermassive black holes in distant active galactic nuclei, accreting stellar-mass black holes and neutron stars in binary systems and are believed to be responsible for gamma-ray bursts. The physics of these jets, however, remains something of a mystery in that their bulk velocities, compositions and energetics remain poorly determined. Here we report the discovery of an ultra-relativistic outflow from a neutron star accreting gas within a binary stellar system. The velocity of the outflow is comparable to the fastest-moving flows observed from active galactic nuclei, and its strength is modulated by the rate of accretion of material onto the neutron star. Shocks are energized further downstream in the flow, which are themselves moving at mildly relativistic bulk velocities and are the sites of the observed synchrotron emission from the jet. We conclude that the generation of highly relativistic outflows does not require properties that are unique to black holes, such as an event horizon.

Does the Iron K and Alpha: Line of Active Galactic Nuclei Arise from the Cerenkov Line-like Radiation?

NASA Technical Reports Server (NTRS)

You, J. H.; Liu, D. B.; Chen, W. P.; Chen, L.; Zhang, S. N.

2003-01-01

When thermal relativistic electrons with isotropic distribution of velocities move in a gas region or impinge upon the surface of a cloud that consists of a dense gas or doped dusts, the Cerenkov effect produces peculiar atomic or ionic emission lines, which is known as the Cerenkov line - like radiation. This newly recognized emission mechanism may find wide applications in high-energy astrophysics. In this paper we tentatively adopt this new line emission mechanism to discuss the origin of the iron Kα feature of active galactic nuclei (AGNs). The motivation of this research is to attempt a solution to a problem encountered by the "disk fluorescence line" model, i.e. , the lack of temporal response of the observed iron Kα line flux to the changes of the X-ray continuum flux. If the Cerenkov line emission is indeed responsible significant ly for the iron Kα feature, the conventional scenario around the central supermassive black holes of AGNs would need to be modified to accomodate more energetic, more violent, and much denser environments than previously thought.

X-ray spectra and time variability of active galactic nuclei

NASA Technical Reports Server (NTRS)

Mushotzky, R. F.

1984-01-01

The X-ray spectra of broad line active galactic nuclei (AGN) of all types (Seyfert I's, NELG's, broadline radio galaxies) are well fit by a power law in the .5 to 100 keV band of man energy slope alpha = .68 + or - .15. There is, as yet, no strong evidence for time variability of this slope in a given object. The constraints that this places on simple models of the central energy source are discussed. BL Lac objects have quite different X-ray spectral properties and show pronounced X-ray spectral variability. On time scales longer than 12 hours most radio quiet AGN do not show strong, delta I/I .5, variability. The probability of variability of these AGN seems to be inversely related to their luminosity. However characteristics timescales for variability have not been measured for many objects. This general lack of variability may imply that most AGN are well below the Eddington limit. Radio bright AGN tend to be more variable than radio quiet AGN on long, tau approx 6 month, timescales.

The Intrinsic Eddington Ratio Distribution of Active Galactic Nuclei in Young Galaxies from SDSS

NASA Astrophysics Data System (ADS)

Jones, Mackenzie L.; Hickox, Ryan C.; Black, Christine; Hainline, Kevin Nicholas; DiPompeo, Michael A.

2016-04-01

An important question in extragalactic astronomy concerns the distribution of black hole accretion rates, i.e. the Eddington ratio distribution, of active galactic nuclei (AGN). Specifically, it is matter of debate whether AGN follow a broad distribution in accretion rates, or if the distribution is more strongly peaked at characteristic Eddington ratios. Using a sample of galaxies from SDSS DR7, we test whether an intrinsic Eddington ratio distribution that takes the form of a broad Schechter function is in fact consistent with previous work that suggests instead that young galaxies in optical surveys have a more strongly peaked lognormal Eddington ratio distribution. Furthermore, we present an improved method for extracting the AGN distribution using BPT diagnostics that allows us to probe over one order of magnitude lower in Eddington ratio, counteracting the effects of dilution by star formation. We conclude that the intrinsic Eddington ratio distribution of optically selected AGN is consistent with a power law with an exponential cutoff, as is observed in the X-rays. This work was supported in part by a NASA Jenkins Fellowship.

SMM detection of diffuse Galactic 511 keV annihilation radiation

NASA Technical Reports Server (NTRS)

Share, G. H.; Kinzer, R. L.; Kurfess, J. D.; Messina, D. C.; Purcell, W. R.

1988-01-01

Observations of the 511 keV annihilation line from the vicinity of the Galactic center from October to February for 1980/1981, 1981/1982, 1982/1983, 1984/1985, and 1985/1986 are presented. The measurements were made with the gamma-ray spectrometer on the SMM. The design of the instrument and some of its properties used in the analysis are described, and the methods used for accumulating, fitting, and analyzing the data are outlined. It is shown how the Galactic 511 keV line was separated from the intense and variable background observed in orbit. The SMM observations are compared with previous measurements of annihilation radiation from the Galactic center region, and the astrophysical implications are discussed. It is argued that most of the measurements made to date suggest the presence of an extended Galactic source of annihilation radiation.

Actively learning to distinguish suspicious from innocuous anomalies in a batch of vehicle tracks

NASA Astrophysics Data System (ADS)

Qiu, Zhicong; Miller, David J.; Stieber, Brian; Fair, Tim

2014-06-01

We investigate the problem of actively learning to distinguish between two sets of anomalous vehicle tracks, innocuous" and suspicious", starting from scratch, without any initial examples of suspicious" and with no prior knowledge of what an operator would deem suspicious. This two-class problem is challenging because it is a priori unknown which track features may characterize the suspicious class. Furthermore, there is inherent imbalance in the sizes of the labeled innocuous" and suspicious" sets, even after some suspicious examples are identified. We present a comprehensive solution wherein a classifier learns to discriminate suspicious from innocuous based on derived p-value track features. Through active learning, our classifier thus learns the types of anomalies on which to base its discrimination. Our solution encompasses: i) judicious choice of kinematic p-value based features conditioned on the road of origin, along with more explicit features that capture unique vehicle behavior (e.g. U-turns); ii) novel semi-supervised learning that exploits information in the unlabeled (test batch) tracks, and iii) evaluation of several classifier models (logistic regression, SVMs). We find that two active labeling streams are necessary in practice in order to have efficient classifier learning while also forwarding (for labeling) the most actionable tracks. Experiments on wide-area motion imagery (WAMI) tracks, extracted via a system developed by Toyon Research Corporation, demonstrate the strong ROC AUC performance of our system, with sparing use of operator-based active labeling.

THE NuSTAR Hard X-Ray Survey of the Norma Arm Region

NASA Technical Reports Server (NTRS)

Fornasini, Francesca M.; Tomsick, John A.; Hong, Jaesub; Gotthelf, Eric V.; Bauer, Franz; Rahoui, Farid; Stern, Daniel K.; Bodaghee, Arash; Chiu, Jeng-Lun; Clavel, Maïca;

Feedback by AGN Jets and Wide-angle Winds on a Galactic Scale

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dugan, Zachary; Silk, Joseph; Gaibler, Volker

To investigate the differences in mechanical feedback from radio-loud and radio-quiet active galactic nuclei on the host galaxy, we perform 3D AMR hydrodynamic simulations of wide-angle, radio-quiet winds with different inclinations on a single, massive, gas-rich disk galaxy at a redshift of 2–3. We compare our results to hydrodynamic simulations of the same galaxy but with a jet. The jet has an inclination of 0° (perpendicular to the galactic plane), and the winds have inclinations of 0°, 45°, and 90°. We analyze the impact on the host’s gas, star formation, and circumgalactic medium. We find that jet feedback is energy-drivenmore » and wind feedback is momentum-driven. In all the simulations, the jet or wind creates a cavity mostly devoid of dense gas in the nuclear region where star formation is then quenched, but we find strong positive feedback in all the simulations at radii greater than 3 kpc. All four simulations have similar SFRs and stellar velocities with large radial and vertical components. However, the wind at an inclination of 90° creates the highest density regions through ram pressure and generates the highest rates of star formation due to its ongoing strong interaction with the dense gas of the galactic plane. With increased wind inclination, we find greater asymmetry in gas distribution and resulting star formation. Our model generates an expanding ring of triggered star formation with typical velocities of the order of 1/3 of the circular velocity, superimposed on the older stellar population. This should result in a potentially detectable blue asymmetry in stellar absorption features at kiloparsec scales.« less

New places and phases of CO-poor/CI-rich molecular gas in the Universe

NASA Astrophysics Data System (ADS)

Papadopoulos, Padelis P.; Bisbas, Thomas G.; Zhang, Zhiyu

2018-04-01

In this work we extend the work on the recently discovered role of Cosmic Rays (CRs) in regulating the average CO/H_2 abundance ratio in molecular clouds (and thus their CO line visibility) in starburst galaxies, and find that it can lead to a CO-poor/CI-rich H_2 gas phase even in environments with Galactic or in only modestly enhanced CR backgrounds expected in ordinary star-forming galaxies. Furthermore, the same CR-driven astro-chemistry raises the possibility of a widespread phase transition of molecular gas towards a CO-poor/CI-rich phase in: a) molecular gas outflows found in star-forming galaxies, b) active galactic nuclei (AGNs), and c) near synchrotron-emitting radio jets and the radio-loud cores of powerful radio galaxies. For main sequence galaxies we find that CRs can render some of their molecular gas mass CO-invisible, compounding the effects of low metallicities. Imaging the two fine structure lines of atomic carbon with resolution high enough to search beyond the CI/CO-bright line regions associated with central starbursts can reveal such a CO-poor/CI-rich molecular gas phase, provided that relative brightness sensitivity levels of Tb(CI 1 - 0)/Tb(CO J = 1 - 0) ˜0.15 are reached. The capability to search for such gas in the Galaxy is now at hand with the new high-frequency survey telescope HEAT deployed in Antarctica and future ones to be deployed in Dome A. ALMA can search for such gas in star-forming spiral disks, galactic molecular gas outflows and the CR-intense galactic and circumgalactic gas-rich environments of radio-loud objects.

Searches for anisotropies in the arrival directions of the highest energy cosmic rays detected by the Pierre Auger Observatory

DOE PAGES

Aab, Alexander

2015-05-01

We analyze the distribution of arrival directions of ultra-high-energy cosmic rays recorded at the Pierre Auger Observatory in 10 years of operation. The data set, about three times larger than that used in earlier studies, includes arrival directions with zenith angles up to 80°, thus covering from -90° to +45° in declination. After updating the fraction of events correlating with the active galactic nuclei (AGNs) in the Véron-Cetty and Véron catalog, we subject the arrival directions of the data with energies in excess of 40 EeV to different tests for anisotropy. We search for localized excess fluxes, self-clustering of event directions at angular scales up to 30°, and different threshold energies between 40 and 80 EeV. We then look for correlations of cosmic rays with celestial structures both in the Galaxy (the Galactic Center and Galactic Plane) and in the local universe (the Super-Galactic Plane). We also examine their correlation with different populations of nearby extragalactic objects: galaxies in the 2MRS catalog, AGNs detected by Swift-BAT, radio galaxies with jets, and the Centaurus A (Cen A) galaxy. None of the tests show statistically significant evidence of anisotropy. As a result, the strongest departures from isotropy (post-trial probabilitymore » $$\\sim 1.4$$%) are obtained for cosmic rays with $$E\\gt 58$$ EeV in rather large windows around Swift AGNs closer than 130 Mpc and brighter than 10 44 erg s -1 (18° radius), and around the direction of Cen A (15° radius).« less

WATCHDOG: A COMPREHENSIVE ALL-SKY DATABASE OF GALACTIC BLACK HOLE X-RAY BINARIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tetarenko, B. E.; Sivakoff, G. R.; Heinke, C. O.

With the advent of more sensitive all-sky instruments, the transient universe is being probed in greater depth than ever before. Taking advantage of available resources, we have established a comprehensive database of black hole (and black hole candidate) X-ray binary (BHXB) activity between 1996 and 2015 as revealed by all-sky instruments, scanning surveys, and select narrow-field X-ray instruments on board the INTErnational Gamma-Ray Astrophysics Laboratory, Monitor of All-Sky X-ray Image, Rossi X-ray Timing Explorer, and Swift telescopes; the Whole-sky Alberta Time-resolved Comprehensive black-Hole Database Of the Galaxy or WATCHDOG. Over the past two decades, we have detected 132 transient outbursts, trackedmore » and classified behavior occurring in 47 transient and 10 persistently accreting BHs, and performed a statistical study on a number of outburst properties across the Galactic population. We find that outbursts undergone by BHXBs that do not reach the thermally dominant accretion state make up a substantial fraction (∼40%) of the Galactic transient BHXB outburst sample over the past ∼20 years. Our findings suggest that this “hard-only” behavior, observed in transient and persistently accreting BHXBs, is neither a rare nor recent phenomenon and may be indicative of an underlying physical process, relatively common among binary BHs, involving the mass-transfer rate onto the BH remaining at a low level rather than increasing as the outburst evolves. We discuss how the larger number of these “hard-only” outbursts and detected outbursts in general have significant implications for both the luminosity function and mass-transfer history of the Galactic BHXB population.« less

Chandra Survey Of Galactic Coronae Around Nearby Edge-on Disk Galaxies

NASA Astrophysics Data System (ADS)

Li, Jiang-Tao; Wang, D.

2012-01-01

The X-ray emitting coronae in nearby galaxies are expected to be produced either by accretion from the IGM or by various galactic feedbacks. It is already well known that the total hot gas luminosity of these galaxies is correlated with the stellar mass for early-type galaxies and with SFR for star forming galaxies. However, such relations always have large scatter, indicating various other processes must be involved in regulating the coronal properties. In this work, we conduct a systematical analysis of the Chandra data of 53 nearby edge-on disk galaxies. The data are reduced in a uniform manner. Various coronal properties, such as the luminosity, temperature, emission measure, electron number density, total mass, thermal energy, radiative cooling timescale, vertical and horizontal extension, elongation, and steepness of the vertical distribution, are characterized for most of the sample galaxies. For some galaxies with high enough counting statistics, we also study the thermal and chemical states of the coronal gas. We then compare these hot gas properties to other galactic properties to further study the role of different processes in producing and/or maintaining the coronae. The soft X-ray luminosity of the coronae generally correlates well with the SF activity for our sample galaxies over more than 3 orders of magnitude in SFR or Lx. In addition, the inclusion of other galactic properties could significantly improve the correlation of the SFR-Lx relation. The SN feedback efficiency is at most 10% for all the sample galaxies. We also find evidence for the effectiveness of old stellar feedback, gravitation, environmental effects, and cold-hot gas interaction in regulating the coronal properties.

Feedback by AGN Jets and Wide-angle Winds on a Galactic Scale

NASA Astrophysics Data System (ADS)

Dugan, Zachary; Gaibler, Volker; Silk, Joseph

2017-07-01

To investigate the differences in mechanical feedback from radio-loud and radio-quiet active galactic nuclei on the host galaxy, we perform 3D AMR hydrodynamic simulations of wide-angle, radio-quiet winds with different inclinations on a single, massive, gas-rich disk galaxy at a redshift of 2-3. We compare our results to hydrodynamic simulations of the same galaxy but with a jet. The jet has an inclination of 0° (perpendicular to the galactic plane), and the winds have inclinations of 0°, 45°, and 90°. We analyze the impact on the host’s gas, star formation, and circumgalactic medium. We find that jet feedback is energy-driven and wind feedback is momentum-driven. In all the simulations, the jet or wind creates a cavity mostly devoid of dense gas in the nuclear region where star formation is then quenched, but we find strong positive feedback in all the simulations at radii greater than 3 kpc. All four simulations have similar SFRs and stellar velocities with large radial and vertical components. However, the wind at an inclination of 90° creates the highest density regions through ram pressure and generates the highest rates of star formation due to its ongoing strong interaction with the dense gas of the galactic plane. With increased wind inclination, we find greater asymmetry in gas distribution and resulting star formation. Our model generates an expanding ring of triggered star formation with typical velocities of the order of 1/3 of the circular velocity, superimposed on the older stellar population. This should result in a potentially detectable blue asymmetry in stellar absorption features at kiloparsec scales.

Tracking of pedometer-determined physical activity: a 10-year follow-up study from adolescence to adulthood in Sweden.

PubMed

Raustorp, Anders; Ekroth, Yvonne

2013-11-01

Tracking refers to the tendency for an individual to maintain their rank within a group over time. To identify levels of pedometer determined physical activity and explore tracking over 10-year follow up period. In October of 2000, 2003, 2005, and 2010, data of physical activity as steps/day was measured with Yamax SW-200 Tokyo, Japan for 4 consecutive schooldays in 40 (19 females) Swedish individuals (mean age 12.7 in 2000). In boys a decrease of mean step/day occurred between baseline and the 3-year (P < .001), the 5-year (P < .001) and the 10-year follow-up (P < .014). A significant moderate tracking occurred in those at baseline classified insufficient active, both over the 3- to 5-year span (rs = 0.56, P = .005) and the 0- to 10-year span (rs = 0.47, P = .05). The significant decrease of physical activity, as steps/day, in males at early adolescent seems to level out during late adolescence and early adulthood. Further, youth classified insufficient active according to published BMI reference standards at the baseline measures showed a significant moderate tracking over the 10-year follow-up period.

Starburst clusters in the Galactic center

NASA Astrophysics Data System (ADS)

Habibi, Maryam

2014-09-01

The central region of the Galaxy is the most active site of star formation in the Milky Way, where massive stars have formed very recently and are still forming today. The rich population of massive stars in the Galactic center provide a unique opportunity to study massive stars in their birth environment and probe their initial mass function, which is the spectrum of stellar masses at their birth. The Arches cluster is the youngest among the three massive clusters in the Galactic center, providing a collection of high-mass stars and a very dense core which makes this cluster an excellent site to address questions about massive star formation, the stellar mass function and the dynamical evolution of massive clusters in the Galactic center. In this thesis, I perform an observational study of the Arches cluster using K_{s}-band imaging obtained with NAOS/CONICA at the VLT combined with Subaru/Cisco J-band data to gain a full understanding of the cluster mass distribution out to its tidal radius for the first time. Since the light from the Galactic center reaches us through the Galactic disc, the extinction correction is crucial when studying this region. I use a Bayesian method to construct a realistic extinction map of the cluster. It is shown in this study that the determination of the mass of the most massive star in the Arches cluster, which had been used in previous studies to establish an upper mass limit for the star formation process in the Milky Way, strongly depends on the assumed slope of the extinction law. Assuming the two regimes of widely used infrared extinction laws, I show that the difference can reach up to 30% for individually derived stellar masses and Δ A_{Ks}˜ 1 magnitude in acquired K_{s}-band extinction, while the present-day mass function slope changes by ˜ 0.17 dex. The present-day mass function slope derived assuming the more recent extinction law, which suggests a steeper wavelength dependence for the infrared extinction law, reveals an overpopulation of massive stars in the core (r<0.2 pc) with a flat slope of α_{Nishi}=-1.50 ±0.35 in comparison to the Salpeter slope of α=-2.3. The slope of the mass function increases to α_{Nishi}=-2.21 ±0.27 in the intermediate annulus (0.2

Parsec-Scale Obscuring Accretion Disk with Large-Scale Magnetic Field in AGNs

NASA Technical Reports Server (NTRS)

Dorodnitsyn, A.; Kallman, T.

2017-01-01

A magnetic field dragged from the galactic disk, along with inflowing gas, can provide vertical support to the geometrically and optically thick pc (parsec) -scale torus in AGNs (Active Galactic Nuclei). Using the Soloviev solution initially developed for Tokamaks, we derive an analytical model for a rotating torus that is supported and confined by a magnetic field. We further perform three-dimensional magneto-hydrodynamic simulations of X-ray irradiated, pc-scale, magnetized tori. We follow the time evolution and compare models that adopt initial conditions derived from our analytic model with simulations in which the initial magnetic flux is entirely contained within the gas torus. Numerical simulations demonstrate that the initial conditions based on the analytic solution produce a longer-lived torus that produces obscuration that is generally consistent with observed constraints.

Variations in atmospheric transparency under the action of galactic cosmic rays as a possible cause of their effect on the formation of cloudiness

NASA Astrophysics Data System (ADS)

Kudryavtsev, I. V.; Jungner, H.

2011-10-01

The possible mechanism by which cosmic rays affect the formation of neutral water droplets and ice crystals in the Earth's atmosphere has been considered. This mechanism is based on changes in atmospheric transparency and vertical temperature distribution. It has been indicated that a change in the optical thickness for visible and IR radiation by several percents, which can take place when cosmic-ray particles penetrate into the atmosphere, results in a change in the temperature vertical distribution, affecting the growth of water droplets, concentration of active condensation nuclei, and the formation of ice particles. This mechanism makes it possible to explain the correlation between the intensity of galactic cosmic rays at low altitudes and the absence of this correlation at middle altitudes.

Galactic archaeology for amateur astronomers: RR Lyrae stars as tracers of the Milky Way formation

NASA Astrophysics Data System (ADS)

Carballo-Bello, Julio A.; Martínez-Delgado, David; Fliri, Jürgen

2011-06-01

Cosmological models predict that large galaxies like the Milky Way formed from the accretion of smaller stellar systems. The most spectacular of these merger events are stellar tidal streams, rivers of stars and dark matter that envelop the discs of spiral galaxies. We present a research project for a collaboration with amateur astronomers in the study of the formation process of our Galaxy. The main objective is the search for RR Lyrae variable stars in the known stellar streams (Sagitarius, Monoceros, Orphan, etc) a project that can be carried out using small telescopes. The catalogue of candidate variable stars were selected from SDSS data based in colour criteria and it will be sent to interested amateur astronomers who wish to participate in scientific research in one of the most active and competitive topics in Galactic astronomy.