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.

Spatially resolved spectra of the 'teacup' active galactic nucleus: tracing the history of a dying quasar

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

Gagne, J. P.; Crenshaw, D. M.; Fischer, T. C.

The Sloan Digital Sky Survey (SDSS) Galaxy Zoo project has revealed a number of spectacular galaxies possessing extended emission-line regions (EELRs), the most famous being Hanny's Voorwerp galaxy. We present another EELR object discovered in the SDSS endeavor: the Teacup active galactic nucleus (AGN). Nicknamed for its EELR, which has a 'handle'-like structure protruding 15 kpc into the northeast quadrant of the galaxy. We analyze the physical conditions of this galaxy with long-slit, ground-based spectroscopy from the Lowell, Lick, and KPNO observatories. With the Lowell 1.8 m Perkin's telescope we took multiple observations at different offset positions, allowing us tomore » recover spatially resolved spectra across the galaxy. Line diagnostics indicate the ionized gas is photoionized primarily by the AGN. Additionally we are able to derive the hydrogen density from the [S II] λ6716/λ6731 ratio. We generated two-component photoionization models for each spatially resolved Lowell spectrum. These models allow us to calculate the AGN bolometric luminosity seen by the gas at different radii from the nuclear center of the Teacup. Our results show a drop in bolometric luminosity by more than two orders of magnitude from the EELR to the nucleus, suggesting that the AGN has decreased in luminosity by this amount in a continuous fashion over 46,000 yr, supporting the case for a dying AGN in this galaxy independent of any IR based evidence. We demonstrate that spatially resolved photoionization modeling could be applied to EELRs to investigate long timescale variability.« less

Active Galactic Nucleus Obscuration from Winds: From Dusty Infrared-Driven to Warm and X-Ray Photoionized

NASA Technical Reports Server (NTRS)

Dorodnitsyn, Anton V.; Kallman, Timothy R.

2012-01-01

We present calculations of active galactic nucleus winds at approx.parsec scales along with the associated obscuration. We take into account the pressure of infrared radiation on dust grains and the interaction of X-rays from a central black hole with hot and cold plasma. Infrared radiation (IR) is incorporated in radiation-hydrodynamic simulations adopting the flux-limited diffusion approximation. We find that in the range of X-ray luminosities L = 0.05-0.6 L(sub Edd), the Compton-thick part of the flow (aka torus) has an opening angle of approximately 72deg - 75deg regardless of the luminosity. At L > or approx. 0.1, the outflowing dusty wind provides the obscuration with IR pressure playing a major role. The global flow consists of two phases: the cold flow at inclinations (theta) > or approx.70deg and a hot, ionized wind of lower density at lower inclinations. The dynamical pressure of the hot wind is important in shaping the denser IR-supported flow. At luminosities < or = 0.1 L(sub Edd) episodes of outflow are followed by extended periods when the wind switches to slow accretion. Key words: acceleration of particles . galaxies: active . hydrodynamics . methods: numerical Online-only material: color figures

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

A luminous hot accretion flow in the low-luminosity active galactic nucleus NGC 7213

NASA Astrophysics Data System (ADS)

Xie, Fu-Guo; Zdziarski, Andrzej A.; Ma, Renyi; Yang, Qi-Xiang

2016-12-01

The active galactic nucleus (AGN) NGC 7213 shows a complex correlation between the monochromatic radio luminosity LR and the 2-10 keV X-ray luminosity LX, I.e. the correlation is unusually weak with p ˜ 0 (in the form L_R∝ L_X^p) when LX is below a critical luminosity, and steep with p > 1 when LX is above that luminosity. Such a hybrid correlation in individual AGNs is unexpected as it deviates from the Fundamental Plane of AGN activity. Interestingly, a similar correlation pattern is observed in the black hole X-ray binary H1743-322, where it has been modelled by switching between different modes of accretion. We propose that the flat LR-LX correlation of NGC 7213 is due to the presence of a luminous hot accretion flow, an accretion model whose radiative efficiency is sensitive to the accretion rate. Given the low luminosity of the source, LX ˜ 10-4 of the Eddington luminosity, the viscosity parameter is determined to be small, α ≈ 0.01. We also modelled the broad-band spectrum from radio to γ-rays, the time lag between the radio and X-ray light curves, and the implied size and the Lorentz factor of the radio jet. We predict that NGC 7213 will enter into a two-phase accretion regime when LX ≳ 1.5 × 1042 erg s- 1. When this happens, we predict a softening of the X-ray spectrum with the increasing flux and a steep radio/X-ray correlation.

Active Galactic Nucleus Host Galaxy Morphologies in COSMOS

NASA Astrophysics Data System (ADS)

Gabor, J. M.; Impey, C. D.; Jahnke, K.; Simmons, B. D.; Trump, J. R.; Koekemoer, A. M.; Brusa, M.; Cappelluti, N.; Schinnerer, E.; Smolčić, V.; Salvato, M.; Rhodes, J. D.; Mobasher, B.; Capak, P.; Massey, R.; Leauthaud, A.; Scoville, N.

2009-01-01

We use Hubble Space Telescope/Advanced Camera for Surveys images and a photometric catalog of the Cosmic Evolution Survey (COSMOS) field to analyze morphologies of the host galaxies of ~400 active galactic nucleus (AGN) candidates at redshifts 0.3 < z < 1.0. We compare the AGN hosts with a sample of nonactive galaxies drawn from the COSMOS field to match the magnitude and redshift distribution of the AGN hosts. We perform two-dimensional surface brightness modeling with GALFIT to yield host galaxy and nuclear point source magnitudes. X-ray-selected AGN host galaxy morphologies span a substantial range that peaks between those of early-type, bulge-dominated and late-type, disk-dominated systems. We also measure the asymmetry and concentration of the host galaxies. Unaccounted for, the nuclear point source can significantly bias results of these measured structural parameters, so we subtract the best-fit point source component to obtain images of the underlying host galaxies. Our concentration measurements reinforce the findings of our two-dimensional morphology fits, placing X-ray AGN hosts between early- and late-type inactive galaxies. AGN host asymmetry distributions are consistent with those of control galaxies. Combined with a lack of excess companion galaxies around AGN, the asymmetry distributions indicate that strong interactions are no more prevalent among AGN than normal galaxies. In light of recent work, these results suggest that the host galaxies of AGN at these X-ray luminosities may be in a transition from disk-dominated to bulge-dominated, but that this transition is not typically triggered by major mergers. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA Inc, under NASA contract NAS 5-26555; also based on data collected at: the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan; the XMM-Newton, an ESA science mission with

Ultrafast Outflows: Galaxy-scale Active Galactic Nucleus Feedback

NASA Astrophysics Data System (ADS)

Wagner, A. Y.; Umemura, M.; Bicknell, G. V.

2013-01-01

We show, using global three-dimensional grid-based hydrodynamical simulations, that ultrafast outflows (UFOs) from active galactic nuclei (AGNs) result in considerable feedback of energy and momentum into the interstellar medium (ISM) of the host galaxy. The AGN wind interacts strongly with the inhomogeneous, two-phase ISM consisting of dense clouds embedded in a tenuous, hot, hydrostatic medium. The outflow floods through the intercloud channels, sweeps up the hot ISM, and ablates and disperses the dense clouds. The momentum of the UFO is primarily transferred to the dense clouds via the ram pressure in the channel flow, and the wind-blown bubble evolves in the energy-driven regime. Any dependence on UFO opening angle disappears after the first interaction with obstructing clouds. On kpc scales, therefore, feedback by UFOs operates similarly to feedback by relativistic AGN jets. Negative feedback is significantly stronger if clouds are distributed spherically rather than in a disk. In the latter case, the turbulent backflow of the wind drives mass inflow toward the central black hole. Considering the common occurrence of UFOs in AGNs, they are likely to be important in the cosmological feedback cycles of galaxy formation.

ULTRAFAST OUTFLOWS: GALAXY-SCALE ACTIVE GALACTIC NUCLEUS FEEDBACK

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

Wagner, A. Y.; Umemura, M.; Bicknell, G. V., E-mail: ayw@ccs.tsukuba.ac.jp

We show, using global three-dimensional grid-based hydrodynamical simulations, that ultrafast outflows (UFOs) from active galactic nuclei (AGNs) result in considerable feedback of energy and momentum into the interstellar medium (ISM) of the host galaxy. The AGN wind interacts strongly with the inhomogeneous, two-phase ISM consisting of dense clouds embedded in a tenuous, hot, hydrostatic medium. The outflow floods through the intercloud channels, sweeps up the hot ISM, and ablates and disperses the dense clouds. The momentum of the UFO is primarily transferred to the dense clouds via the ram pressure in the channel flow, and the wind-blown bubble evolves inmore » the energy-driven regime. Any dependence on UFO opening angle disappears after the first interaction with obstructing clouds. On kpc scales, therefore, feedback by UFOs operates similarly to feedback by relativistic AGN jets. Negative feedback is significantly stronger if clouds are distributed spherically rather than in a disk. In the latter case, the turbulent backflow of the wind drives mass inflow toward the central black hole. Considering the common occurrence of UFOs in AGNs, they are likely to be important in the cosmological feedback cycles of galaxy formation.« less

Active galactic nuclei

PubMed Central

Fabian, Andrew C.

1999-01-01

Active galactic nuclei are the most powerful, long-lived objects in the Universe. Recent data confirm the theoretical idea that the power source is accretion into a massive black hole. The common occurrence of obscuration and outflows probably means that the contribution of active galactic nuclei to the power density of the Universe has been generally underestimated. PMID:10220363

NuSTAR Observations of the Compton-thick Active Galactic Nucleus and Ultraluminous X-Ray Source Candidate in NGC 5643

NASA Astrophysics Data System (ADS)

Annuar, A.; Gandhi, P.; Alexander, D. M.; Lansbury, G. B.; Arévalo, P.; Ballantyne, D. R.; Baloković, M.; Bauer, F. E.; Boggs, S. E.; Brandt, W. N.; Brightman, M.; Christensen, F. E.; Craig, W. W.; Del Moro, A.; Hailey, C. J.; Harrison, F. A.; Hickox, R. C.; Matt, G.; Puccetti, S.; Ricci, C.; Rigby, J. R.; Stern, D.; Walton, D. J.; Zappacosta, L.; Zhang, W.

2015-12-01

We present two Nuclear Spectroscopic Telescope Array (NuSTAR) observations of the local Seyfert 2 active galactic nucleus (AGN) and an ultraluminous X-ray source (ULX) candidate in NGC 5643. Together with archival data from Chandra, XMM-Newton, and Swift-BAT, we perform a high-quality broadband spectral analysis of the AGN over two decades in energy (˜0.5-100 keV). Previous X-ray observations suggested that the AGN is obscured by a Compton-thick (CT) column of obscuring gas along our line of sight. However, the lack of high-quality ≳10 keV observations, together with the presence of a nearby X-ray luminous source, NGC 5643 X-1, have left significant uncertainties in the characterization of the nuclear spectrum. NuSTAR now enables the AGN and NGC 5643 X-1 to be separately resolved above 10 keV for the first time and allows a direct measurement of the absorbing column density toward the nucleus. The new data show that the nucleus is indeed obscured by a CT column of NH ≳ 5 × 1024 cm-2. The range of 2-10 keV absorption-corrected luminosity inferred from the best-fitting models is L2-10,int = (0.8-1.7) × 1042 erg s-1, consistent with that predicted from multiwavelength intrinsic luminosity indicators. In addition, we also study the NuSTAR data for NGC 5643 X-1 and show that it exhibits evidence of a spectral cutoff at energy E ˜ 10 keV, similar to that seen in other ULXs observed by NuSTAR. Along with the evidence for significant X-ray luminosity variations in the 3-8 keV band from 2003 to 2014, our results further strengthen the ULX classification of NGC 5643 X-1.

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.

Multi-phase Nature of a Radiation-driven Fountain with Nuclear Starburst in a Low-mass Active Galactic Nucleus

NASA Astrophysics Data System (ADS)

Wada, Keiichi; Schartmann, Marc; Meijerink, Rowin

2016-09-01

The structures and dynamics of molecular, atomic, and ionized gases are studied around a low-luminosity active galactic nucleus (AGN) with a small (2× {10}6{M}⊙ ) black hole using three-dimensional (3D) radiation-hydrodynamic simulations. We studied, for the first time, the non-equilibrium chemistry for the X-ray-dominated region in the “radiation-driven fountain” with supernova feedback. A double hollow cone structure is naturally formed without postulating a thick “torus” around a central source. The cone is occupied with an inhomogeneous, diffuse ionized gas and surrounded by a geometrically thick (h/r≳ 1) atomic gas. Dense molecular gases are distributed near the equatorial plane, and energy feedback from supernovae enhances their scale height. Molecular hydrogen exists in a hot phase (>1000 K) as well as in a cold (\\lt 100 {{K}}), dense (\\gt {10}3 {{cm}}-3) phase. The velocity dispersion of H2 in the vertical direction is comparable to the rotational velocity, which is consistent with near-infrared observations of nearby Seyfert galaxies. Using 3D radiation transfer calculations for the dust emission, we find polar emission in the mid-infrared band (12 μm), which is associated with bipolar outflows, as suggested in recent interferometric observations of nearby AGNs. If the viewing angle for the nucleus is larger than 75°, the spectral energy distribution is consistent with that of the Circinus galaxy. The multi-phase interstellar medium observed in optical/infrared and X-ray observations is also discussed.

COLLIMATION AND SCATTERING OF THE ACTIVE GALACTIC NUCLEUS EMISSION IN THE SOMBRERO GALAXY

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

Menezes, R. B.; Steiner, J. E.; Ricci, T. V., E-mail: robertobm@astro.iag.usp.br

2013-03-10

We present an analysis of a data cube of the central region of M104, the Sombrero galaxy, obtained with the GMOS-IFU of the Gemini-South telescope, and report the discovery of collimation and scattering of the active galactic nucleus (AGN) emission in the circumnuclear region of this galaxy. Analysis with PCA Tomography and spectral synthesis revealed the existence of collimation and scattering of the AGN featureless continuum and also of a broad component of the H{alpha} emission line. The collimation and scattering of this broad H{alpha} component was also revealed by fitting the [N II] {lambda}{lambda}6548, 6583 and H{alpha} emission linesmore » as a sum of Gaussian functions. The spectral synthesis, together with a V-I image obtained with the Hubble Space Telescope, showed the existence of circumnuclear dust, which may cause the light scattering. We also identify a dusty feature that may be interpreted as a torus/disk structure. The existence of two opposite regions with featureless continuum (P.A. = -18 Degree-Sign {+-} 13 Degree-Sign and P.A. = 162 Degree-Sign {+-} 13 Degree-Sign ) along a direction perpendicular to the torus/disk (P.A. = 72 Degree-Sign {+-} 14 Degree-Sign ) suggests that this structure is approximately edge-on and collimates the AGN emission. The edge-on torus/disk also hides the broad-line region. The proposed scenario is compatible with the unified model and explains why only a weak broad component of the H{alpha} emission line is visible and also why many previous studies detected no broad H{alpha}. The technique used here proved to be an efficient method not only for detecting scattered light, but also for testing the unified model in low-luminosity AGNs.« less

DISSECTING PHOTOMETRIC REDSHIFT FOR ACTIVE GALACTIC NUCLEUS USING XMM- AND CHANDRA-COSMOS SAMPLES

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

Salvato, M.; Hasinger, G.; Ilbert, O.

2011-12-01

In this paper, we release accurate photometric redshifts for 1692 counterparts to Chandra sources in the central square degree of the Cosmic Evolution Survey (COSMOS) field. The availability of a large training set of spectroscopic redshifts that extends to faint magnitudes enabled photometric redshifts comparable to the highest quality results presently available for normal galaxies. We demonstrate that morphologically extended, faint X-ray sources without optical variability are more accurately described by a library of normal galaxies (corrected for emission lines) than by active galactic nucleus (AGN) dominated templates, even if these sources have AGN-like X-ray luminosities. Preselecting the library onmore » the bases of the source properties allowed us to reach an accuracy {sigma}{sub {Delta}z/(1+z{sub s{sub p{sub e{sub c)}}}}}{approx}0.015 with a fraction of outliers of 5.8% for the entire Chandra-COSMOS sample. In addition, we release revised photometric redshifts for the 1735 optical counterparts of the XMM-detected sources over the entire 2 deg{sup 2} of COSMOS. For 248 sources, our updated photometric redshift differs from the previous release by {Delta}z > 0.2. These changes are predominantly due to the inclusion of newly available deep H-band photometry (H{sub AB} = 24 mag). We illustrate once again the importance of a spectroscopic training sample and how an assumption about the nature of a source together, with the number and the depth of the available bands, influences the accuracy of the photometric redshifts determined for AGN. These considerations should be kept in mind when defining the observational strategies of upcoming large surveys targeting AGNs, such as eROSITA at X-ray energies and the Australian Square Kilometre Array Pathfinder Evolutionary Map of the Universe in the radio band.« less

The Jet-driven Outflow in the Radio Galaxy SDSS J1517+3353: Implications for Double-peaked Narrow-line Active Galactic Nucleus

NASA Astrophysics Data System (ADS)

Rosario, D. J.; Shields, G. A.; Taylor, G. B.; Salviander, S.; Smith, K. L.

2010-06-01

We report on the study of an intriguing active galaxy that was selected as a potential multiple supermassive black hole merger in the early-type host SDSS J151709.20+335324.7 (z = 0.135) from a complete search for double-peaked [O III] lines from the SDSS spectroscopic quasi-stellar object (QSO) database. Ground-based SDSS imaging reveals two blue structures on either side of the photometric center of the host galaxy, separated from each other by about 5.7 kpc. From a combination of SDSS fiber and Keck/HIRES long-slit spectroscopy, it is demonstrated that, in addition to these two features, a third distinct structure surrounds the nucleus of the host galaxy. All three structures exhibit highly ionized line emission with line ratios characteristic of Seyfert II active galactic nuclei. The analysis of spatially resolved emission-line profiles from the HIRES spectrum reveal three distinct kinematic subcomponents, one at rest and the other two moving at -350 km s-1 and 500 km s-1 with respect to the systemic velocity of the host galaxy. A comparison of imaging and spectral data confirm a strong association between the kinematic components and the spatial knots, which implies a highly disturbed and complex active region in this object. A comparative analysis of the broadband positions, colors, kinematics, and spectral properties of the knots in this system lead to two plausible explanations: (1) a multiple active galactic nucleus (AGN) produced due to a massive dry merger, or (2) a very powerful radio jet-driven outflow. Subsequent VLA radio imaging reveals a clear jet aligned with the emission-line gas, confirming the latter explanation. We use the broadband radio measurements to examine the impact of the jet on the interstellar medium of the host galaxy, and find that the energy in the radio lobes can heat a significant fraction of the gas to the virial temperature. Finally, we discuss tests that may help future surveys distinguish between jet-driven kinematics and

Unveiling the nature of the  $$\\gamma$$-ray emitting active galactic nucleus PKS 0521-36

DOE PAGES

D'Ammando, F.; Orienti, M.; Tavecchio, F.; ...

2015-05-19

PKS 0521-36 is an active galactic nucleus (AGN) with uncertain classification. Here, we investigate the properties of this source from radio to γ-rays. The broad emission lines in the optical and ultraviolet bands and steep radio spectrum indicate a possible classification as an intermediate object between broad-line radio galaxies (BLRG) and steep spectrum radio quasars (SSRQ). On pc-scales PKS 0521-36 shows a knotty structure similar to misaligned AGN. The core dominance and the γ-ray properties are similar to those estimated for other SSRQ and BLRG detected in γ-rays, suggesting an intermediate viewing angle with respect to the observer. In thismore » context the flaring activity detected from this source by Fermi-Large Area Telescope between 2010 June and 2012 February is very intriguing. We discuss the γ-ray emission of this source in the framework of the structured jet scenario, comparing the spectral energy distribution (SED) of the flaring state in 2010 June with that of a low state. We present three alternative models corresponding to three different choices of the viewing angles θv = 6°, 15°, and 20°. We obtain a good fit for the first two cases, but the SED obtained with θv = 15° if observed at a small angle does not resemble that of a typical blazar since the synchrotron emission should dominate by a large factor (~100) the inverse Compton component. This suggests that a viewing angle between 6° and 15° is preferred, with the rapid variability observed during γ-ray flares favouring a smaller angle. However, we cannot rule out that PKS 0521-36 is the misaligned counterpart of a synchrotron-dominated blazar.« less

NuSTAR OBSERVATIONS OF THE COMPTON-THICK ACTIVE GALACTIC NUCLEUS AND ULTRALUMINOUS X-RAY SOURCE CANDIDATE IN NGC 5643

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

Annuar, A.; Gandhi, P.; Alexander, D. M.

2015-12-10

We present two Nuclear Spectroscopic Telescope Array (NuSTAR) observations of the local Seyfert 2 active galactic nucleus (AGN) and an ultraluminous X-ray source (ULX) candidate in NGC 5643. Together with archival data from Chandra, XMM-Newton, and Swift-BAT, we perform a high-quality broadband spectral analysis of the AGN over two decades in energy (∼0.5–100 keV). Previous X-ray observations suggested that the AGN is obscured by a Compton-thick (CT) column of obscuring gas along our line of sight. However, the lack of high-quality ≳10 keV observations, together with the presence of a nearby X-ray luminous source, NGC 5643 X–1, have left significantmore » uncertainties in the characterization of the nuclear spectrum. NuSTAR now enables the AGN and NGC 5643 X–1 to be separately resolved above 10 keV for the first time and allows a direct measurement of the absorbing column density toward the nucleus. The new data show that the nucleus is indeed obscured by a CT column of N{sub H} ≳ 5 × 10{sup 24} cm{sup −2}. The range of 2–10 keV absorption-corrected luminosity inferred from the best-fitting models is L{sub 2–10,int} = (0.8–1.7) × 10{sup 42} erg s{sup −1}, consistent with that predicted from multiwavelength intrinsic luminosity indicators. In addition, we also study the NuSTAR data for NGC 5643 X–1 and show that it exhibits evidence of a spectral cutoff at energy E ∼ 10 keV, similar to that seen in other ULXs observed by NuSTAR. Along with the evidence for significant X-ray luminosity variations in the 3–8 keV band from 2003 to 2014, our results further strengthen the ULX classification of NGC 5643 X–1.« less

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

From starburst to quiescence: testing active galactic nucleus feedback in rapidly quenching post-starburst galaxies

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

Yesuf, Hassen M.; Faber, S. M.; Trump, Jonathan R.

Post-starbursts are galaxies in transition from the blue cloud to the red sequence. Although they are rare today, integrated over time they may be an important pathway to the red sequence. This work uses Sloan Digital Sky Survey, the Galaxy Evolution Explorer, and Wide-field Infrared Survey Explorer observations to identify the evolutionary sequence from starbursts to fully quenched post-starbursts (QPSBs) in the narrow mass range log M(M {sub ☉}) = 10.3-10.7, and identifies 'transiting' post-starbursts (TPSBs) which are intermediate between these two populations. In this mass range, ∼0.3% of galaxies are starbursts, ∼0.1% are QPSBs, and ∼0.5% are the transitingmore » types in between. The TPSBs have stellar properties that are predicted for fast-quenching starbursts and morphological characteristics that are already typical of early-type galaxies. The active galactic nucleus (AGN) fraction, as estimated from optical line ratios, of these post-starbursts is about three times higher (≳ 36% ± 8%) than that of normal star forming galaxies of the same mass, but there is a significant delay between the starburst phase and the peak of nuclear optical AGN activity (median age difference of ≳ 200 ± 100 Myr), in agreement with previous studies. The time delay is inferred by comparing the broadband near-NUV-to-optical photometry with stellar population synthesis models. We also find that starbursts and post-starbursts are significantly more dust obscured than normal star forming galaxies in the same mass range. About 20% of the starbursts and 15% of the TPSBs can be classified as 'dust-obscured galaxies' (DOGs), with a near-UV-to-mid-IR flux ratio of ≳ 900, while only 0.8% of normal galaxies are DOGs. The time delay between the starburst phase and AGN activity suggests that AGNs do not play a primary role in the original quenching of starbursts but may be responsible for quenching later low-level star formation by removing gas and dust during the post

Enhancement of Feedback Efficiency by Active Galactic Nucleus Outflows via the Magnetic Tension Force in the Inhomogeneous Interstellar Medium

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

Asahina, Yuta; Ohsuga, Ken; Nomura, Mariko, E-mail: asahina@cfca.jp

By performing three-dimensional magnetohydrodynamics simulations of subrelativistic jets and disk winds propagating into the magnetized inhomogeneous interstellar medium (ISM), we investigate the magnetic effects on the active galactic nucleus feedback. Our simulations reveal that the magnetic tension force promotes the acceleration of the dense gas clouds, since the magnetic field lines, which are initially straight, bend around the gas clouds. In the jet models, the velocity dispersion of the clouds increases with an increase in the initial magnetic fields. The increment of the kinetic energy of the clouds is proportional to the initial magnetic fields, implying that the magnetic tensionmore » force increases the energy conversion efficiency from the jet to the gas clouds. Through simulations of the mildly collimated disk wind and the funnel-shaped disk wind, we confirm that such an enhancement of the energy conversion efficiency via the magnetic fields appears even if the energy is injected via the disk winds. The enhancement of the acceleration of the dense part of the magnetized ISM via the magnetic tension force will occur wherever the magnetized inhomogeneous matter is blown away.« less

Investigating Galaxy Evolution and Active Galactic Nucleus Feedback with the Sunyaev-Zel'dovich Effect

NASA Astrophysics Data System (ADS)

Spacek, Alexander; Scannapieco, Evan; Cohen, Seth H.; Joshi, Bhavin; Mauskopf, Philip; Richardson, Mark L. A.; Devriendt, Julien; Dubois, Yohan; Peirani, Sebastien; Pichon, Christophe

2018-06-01

Galaxy formation is a complex process with aspects that are still very uncertain. A mechanism that has been used in simulations to successfully resolve several of these outstanding issues is active galactic nucleus (AGN) feedback, where a large amount of energy is driven outwards through a galaxy and the surrounding region by a central supermassive black hole. A promising method for directly measuring this energy is by looking at small increases in the energy of the cosmic microwave background (CMB) photons as they pass through hot gas, known as the thermal Sunyaev-Zel'dovich (tSZ) effect. I will present work done to measure the tSZ effect around a large number of 0.5 < z < 1.5 elliptical galaxies using the South Pole Telescope (SPT), Atacama Cosmology Telescope (ACT), and Planck telescope, finding signals at 1-sigma to 3-sigma confindence levels depending on the dataset and redshift range. The results are mixed, including hints at non-gravitational energy possibly due to AGN feedback. Then I will present work done to analyze these results further by comparing them to matching simulated measurements, both including and not including AGN feedback, from the large-scale Horizon-AGN and Horizon-NoAGN cosmological simulations. In these comparisons, the SPT results, which tend to have lower-mass galaxies (<5x10^11 M_Sun), favor the Horizon-AGN results at about a 1-sigma level, while the ACT results, which tend to have higher-mass galaxies (>5x10^11 M_Sun), favor the Horizon-NoAGN results at more than a 6-sigma level. These results indicate that AGN feedback may be milder than often predicted, and they also highlight the promising nature of tSZ effect measurements and the need for further work using better data and more varied simulations.

Functionalized active-nucleus complex sensor

DOEpatents

Pines, Alexander; Wemmer, David E.; Spence, Megan; Rubin, Seth

2003-11-25

A functionalized active-nucleus complex sensor that selectively associates with one or more target species, and a method for assaying and screening for one or a plurality of target species utilizing one or a plurality of functionalized active-nucleus complexes with at least two of the functionalized active-nucleus complexes having an attraction affinity to different corresponding target species. The functionalized active-nucleus complex has an active-nucleus and a targeting carrier. The method involves functionalizing an active-nucleus, for each functionalized active-nucleus complex, by incorporating the active-nucleus into a macromolucular or molecular complex that is capable of binding one of the target species and then bringing the macromolecular or molecular complexes into contact with the target species and detecting the occurrence of or change in a nuclear magnetic resonance signal from each of the active-nuclei in each of the functionalized active-nucleus complexes.

On the Disappearance of a Cold Molecular Torus around the Low-luminosity Active Galactic Nucleus of NGC 1097

NASA Astrophysics Data System (ADS)

Izumi, T.; Kohno, K.; Fathi, K.; Hatziminaoglou, E.; Davies, R. I.; Martín, S.; Matsushita, S.; Schinnerer, E.; Espada, D.; Aalto, S.; Onishi, K.; Turner, J. L.; Imanishi, M.; Nakanishi, K.; Meier, D. S.; Wada, K.; Kawakatu, N.; Nakajima, T.

2017-08-01

We used the Atacama Large Millimeter/Submillimeter Array to map the CO(3-2) and the underlying continuum emissions around the type-1 low-luminosity active galactic nucleus (LLAGN; bolometric luminosity ≲ {10}42 erg s-1) of NGC 1097 at ˜10 pc resolution. These observations revealed a detailed cold gas distribution within a ˜100 pc of this LLAGN. In contrast to the luminous Seyfert galaxy NGC 1068, where a ˜7 pc cold molecular torus was recently revealed, a distinctively dense and compact torus is missing in our CO(3-2) integrated intensity map of NGC 1097. Based on the CO(3-2) flux, the gas mass of the torus of NGC 1097 would be a factor of ≳2-3 less than that found for NGC 1068 by using the same CO-to-H2 conversion factor, which implies less active nuclear star formation and/or inflows in NGC 1097. Our dynamical modeling of the CO(3-2) velocity field implies that the cold molecular gas is concentrated in a thin layer as compared to the hot gas traced by the 2.12 μm H2 emission in and around the torus. Furthermore, we suggest that NGC 1097 hosts a geometrically thinner torus than NGC 1068. Although the physical origin of the torus thickness remains unclear, our observations support a theoretical prediction that geometrically thick tori with high opacity will become deficient as AGNs evolve from luminous Seyferts to LLAGNs.

Examining the High-energy Radiation Mechanisms of Knots and Hotspots in Active Galactic Nucleus Jets

NASA Astrophysics Data System (ADS)

Zhang, Jin; Du, Shen-shi; Guo, Sheng-Chu; Zhang, Hai-Ming; Chen, Liang; Liang, En-Wei; Zhang, Shuang-Nan

2018-05-01

We compile the radio–optical–X-ray spectral energy distributions (SEDs) of 65 knots and 29 hotspots in 41 active galactic nucleus jets to examine their high-energy radiation mechanisms. Their SEDs can be fitted with the single-zone leptonic models, except for the hotspot of Pictor A and six knots of 3C 273. The X-ray emission of 1 hotspot and 22 knots is well explained as synchrotron radiation under the equipartition condition; they usually have lower X-ray and radio luminosities than the others, which may be due to a lower beaming factor. An inverse Compton (IC) process is involved for explaining the X-ray emission of the other SEDs. Without considering the equipartition condition, their X-ray emission can be attributed to the synchrotron-self-Compton process, but the derived jet powers (P jet) are not correlated with L k and most of them are larger than L k, with more than three orders of magnitude, where L k is the jet kinetic power estimated with their radio emission. Under the equipartition condition, the X-ray emission is well interpreted with the IC process for the cosmic microwave background photons (IC/CMB). In this scenario, the derived P jet of knots and hotspots are correlated with and comparable to L k. These results suggest that the IC/CMB model may be a promising interpretation of the X-ray emission. In addition, a tentative knot–hotspot sequence in the synchrotron peak-energy–peak-luminosity plane is observed, similar to the blazar sequence, which may be attributed to the different cooling mechanisms of electrons.

REMOVING COOL CORES AND CENTRAL METALLICITY PEAKS IN GALAXY CLUSTERS WITH POWERFUL ACTIVE GALACTIC NUCLEUS OUTBURSTS

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

Guo Fulai; Mathews, William G., E-mail: fulai@ucolick.or

2010-07-10

Recent X-ray observations of galaxy clusters suggest that cluster populations are bimodally distributed according to central gas entropy and are separated into two distinct classes: cool core (CC) and non-cool core (NCC) clusters. While it is widely accepted that active galactic nucleus (AGN) feedback plays a key role in offsetting radiative losses and maintaining many clusters in the CC state, the origin of NCC clusters is much less clear. At the same time, a handful of extremely powerful AGN outbursts have recently been detected in clusters, with a total energy {approx}10{sup 61}-10{sup 62} erg. Using two-dimensional hydrodynamic simulations, we showmore » that if a large fraction of this energy is deposited near the centers of CC clusters, which is likely common due to dense cores, these AGN outbursts can completely remove CCs, transforming them to NCC clusters. Our model also has interesting implications for cluster abundance profiles, which usually show a central peak in CC systems. Our calculations indicate that during the CC to NCC transformation, AGN outbursts efficiently mix metals in cluster central regions and may even remove central abundance peaks if they are not broad enough. For CC clusters with broad central abundance peaks, AGN outbursts decrease peak abundances, but cannot effectively destroy the peaks. Our model may simultaneously explain the contradictory (possibly bimodal) results of abundance profiles in NCC clusters, some of which are nearly flat, while others have strong central peaks similar to those in CC clusters. A statistical analysis of the sizes of central abundance peaks and their redshift evolution may shed interesting insights on the origin of both types of NCC clusters and the evolution history of thermodynamics and AGN activity in clusters.« less

HOST GALAXY PROPERTIES OF THE SWIFT BAT ULTRA HARD X-RAY SELECTED ACTIVE GALACTIC NUCLEUS

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

Koss, Michael; Mushotzky, Richard; Veilleux, Sylvain

We have assembled the largest sample of ultra hard X-ray selected (14-195 keV) active galactic nucleus (AGN) with host galaxy optical data to date, with 185 nearby (z < 0.05), moderate luminosity AGNs from the Swift BAT sample. The BAT AGN host galaxies have intermediate optical colors (u - r and g - r) that are bluer than a comparison sample of inactive galaxies and optically selected AGNs from the Sloan Digital Sky Survey (SDSS) which are chosen to have the same stellar mass. Based on morphological classifications from the RC3 and the Galaxy Zoo, the bluer colors of BATmore » AGNs are mainly due to a higher fraction of mergers and massive spirals than in the comparison samples. BAT AGNs in massive galaxies (log M{sub *} >10.5) have a 5-10 times higher rate of spiral morphologies than in SDSS AGNs or inactive galaxies. We also see enhanced far-infrared emission in BAT AGN suggestive of higher levels of star formation compared to the comparison samples. BAT AGNs are preferentially found in the most massive host galaxies with high concentration indexes indicative of large bulge-to-disk ratios and large supermassive black holes. The narrow-line (NL) BAT AGNs have similar intrinsic luminosities as the SDSS NL Seyferts based on measurements of [O III] {lambda}5007. There is also a correlation between the stellar mass and X-ray emission. The BAT AGNs in mergers have bluer colors and greater ultra hard X-ray emission compared to the BAT sample as a whole. In agreement with the unified model of AGNs, and the relatively unbiased nature of the BAT sources, the host galaxy colors and morphologies are independent of measures of obscuration such as X-ray column density or Seyfert type. The high fraction of massive spiral galaxies and galaxy mergers in BAT AGNs suggest that host galaxy morphology is related to the activation and fueling of local AGN.« less

A jet-dominated model for a broad-band spectral energy distribution of the nearby low-luminosity active galactic nucleus in M94

NASA Astrophysics Data System (ADS)

van Oers, Pieter; Markoff, Sera; Uttley, Phil; McHardy, Ian; van der Laan, Tessel; Donovan Meyer, Jennifer; Connors, Riley

2017-06-01

We have compiled a new multiwavelength spectral energy distribution (SED) for the closest obscured low-ionization emission-line region active galactic nucleus (AGN), NGC 4736, also known as M94. The SED comprises mainly high-resolution (mostly sub-arcsecond, or, at the distance to M94, ≲23 pc from the nucleus) observations from the literature, archival data, as well as previously unpublished sub-millimetre data from the Plateau de Bure Interferometer (PdBI) and the Combined Array for Research in Millimeter-wave Astronomy, in conjunction with new electronic MultiElement Radio Interferometric Network (e-MERLIN) L-band (1.5 GHz) observations. Thanks to the e-MERLIN resolution and sensitivity, we resolve for the first time a double structure composed of two radio sources separated by ˜1 arcsec, previously observed only at higher frequency. We explore this data set, which further includes non-simultaneous data from the Very Large Array, the Gemini telescope, the Hubble Space Telescope and the Chandra X-ray observatory, in terms of an outflow-dominated model. We compare our results with previous trends found for other AGN using the same model (NGC 4051, M81*, M87 and Sgr A*), as well as hard- and quiescent-state X-ray binaries. We find that the nuclear broad-band spectrum of M94 is consistent with a relativistic outflow of low inclination. The findings in this work add to the growing body of evidence that the physics of weakly accreting black holes scales with mass in a rather straightforward fashion.

Dissecting the active galactic nucleus in Circinus - I. Peculiar mid-IR morphology explained by a dusty hollow cone

NASA Astrophysics Data System (ADS)

Stalevski, Marko; Asmus, Daniel; Tristram, Konrad R. W.

2017-12-01

Recent high angular resolution observations resolved for the first time the mid-infrared (MIR) structure of nearby active galactic nuclei (AGN). Surprisingly, they revealed that a major fraction of their MIR emission comes from the polar regions. This is at odds with the expectation based on AGN unification, which postulates a dusty torus in the equatorial region. The nearby, archetypical AGN in the Circinus galaxy offers one of the best opportunities to study the MIR emission in greater detail. New, high-quality MIR images obtained with the upgraded VISIR instrument at the Very Large Telescope show that the previously detected bar-like structure extends up to at least 40 pc on both sides of the nucleus along the edges of the ionization cone. Motivated by observations across a wide wavelength range and on different spatial scales, we propose a phenomenological dust emission model for the AGN in the Circinus galaxy consisting of a compact dusty disc and a large-scale dusty cone shell, illuminated by a tilted accretion disc with an anisotropic emission pattern. Undertaking detailed radiative transfer simulations, we demonstrate that such a model is able to explain the peculiar MIR morphology and account for the entire IR spectral energy distribution. Our results call for caution when attributing dust emission of unresolved sources entirely to the torus and warrant further investigation of the MIR emission in the polar regions of the AGN.

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.

Impact of red giant/AGB winds on active galactic nucleus jet propagation

NASA Astrophysics Data System (ADS)

Perucho, M.; Bosch-Ramon, V.; Barkov, M. V.

2017-10-01

Context. Dense stellar winds may mass-load the jets of active galactic nuclei, although it is unclear on what time and spatial scales the mixing takes place. Aims: Our aim is to study the first steps of the interaction between jets and stellar winds, and also the scales on which the stellar wind mixes with the jet and mass-loads it. Methods: We present a detailed 2D simulation - including thermal cooling - of a bubble formed by the wind of a star designed to study the initial stages of jet-star interaction. We also study the first interaction of the wind bubble with the jet using a 3D simulation in which the star enters the jet. Stability analysis is carried out for the shocked wind structure to evaluate the distances over which the jet-dragged wind, which forms a tail, can propagate without mixing with the jet flow. Results.The 2D simulations point to quick wind bubble expansion and fragmentation after about one bubble shock crossing time. Three-dimensional simulations and stability analysis point to local mixing in the case of strong perturbations and relatively low density ratios between the jet and the jet dragged-wind, and to a possibly more stable shocked wind structure at the phase of maximum tail mass flux. Analytical estimates also indicate that very early stages of the star jet-penetration time may be also relevant for mass-loading. The combination of these and previous results from the literature suggests highly unstable interaction structures and efficient wind-jet flow mixing on the scale of the jet interaction height. Conclusions: The winds of stars with strong mass loss can efficiently mix with jets from active galactic nuclei. In addition, the initial wind bubble shocked by the jet leads to a transient, large interaction surface. The interaction between jets and stars can produce strong inhomogeneities within the jet. As mixing is expected to be effective on large scales, even individual asymptotic giant branch stars can significantly contribute to

Markarian 315: A test case for the active galactic nucleus-merger hypothesis?

NASA Technical Reports Server (NTRS)

Mackenty, John W.; Simkin, Susan M.; Griffiths, Richard E.; Ulvestad, James S.; Wilson, Andrew S.

1994-01-01

Using the Hubble Space Telescope (HST) Wide Field/Planetary Camera, (WF/PC) we have detected a diffuse continuum knot in the inner regions of the Seyfert galaxy Markarian 315. This knot may be a remnant nucleus. It is associated with a complex, ringlike structure in both the continuum and ionized gas emission. We have measured the kinematics of the ionized gas in two position angles and find velocities which are consistent with a nonaxisymmetric gravitational disturbance. The galaxy is associated with an extended ionized filament, or tidal tail, and our measurements show that the ionized gas in this feature is redshifted by up to 500 km/s in the line of sight relative to the Seyfert nucleus. This combination of morphological and kinematic features suggests that Mrk 315 has suffered a disruptive, tidal interaction which has significantly influenced regions within 1 kpc of its nucleus.

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.

Unveiling the nucleus of NGC 7172

NASA Astrophysics Data System (ADS)

Smajić, S.; Fischer, S.; Zuther, J.; Eckart, A.

2012-08-01

Aims: We present the results of near-infrared (NIR) H + K European Southern Observatory SINFONI integral field spectroscopy (IFS) of the Seyfert 2 galaxy NGC 7172. We investigate the central 800 pc, concentrating on excitation conditions, morphology, and stellar content. NGC 7172 was selected from a sample of the ten nearest Seyfert 2 galaxies from the Veron-Cetty & Veron catalogue. All objects were chosen as test cases for adaptive optics (AO) assisted observations that allow a detailed study (at high spatial and spectral resolution) of the nuclear and host environments. NGC 7172 has a prominent dustlane crossing the central galaxy region from east to west, which makes it an ideal candidate to investigate the effect of obscuration by strong galactic extinction on (active) galaxies and their classification. Methods: The NIR is less influenced by dust extinction than optical light and is sensitive to the mass-dominating stellar populations. SINFONI integral field spectroscopy combines NIR imaging and spectroscopy and provides us with the opportunity to analyze several emission and absorption lines to investigate the stellar populations and ionization mechanisms over the 4″ × 4″ field of view (FOV). Results: We present emission and absorption line measurements in the central 800 pc of NGC 7172. The detection of [Si vi] and broad Paα and Brγ components are clear signs of an accreting super-massive black hole hiding behind the prominent dustlane at visible wavelengths. Hot temperatures of about 1300 K are indicative of a dusty torus in the nuclear region. Narrow components of Paα and Brγ enable us to make an extinction measurement. Our measures of the molecular hydrogen lines, hydrogen recombination lines, and [Fe ii] indicate that the excitation of these lines is caused by an active galactic nucleus. The central region of the galactic disk is predominantly inhabited by gas, dust, and an old K-M type giant stellar population. The gaseous, molecular, and

Active Galactic Nucleus Feedback in an Isolated Elliptical Galaxy: The Effect of Strong Radiative Feedback in the Kinetic Mode

NASA Astrophysics Data System (ADS)

Gan, Zhaoming; Yuan, Feng; Ostriker, Jeremiah P.; Ciotti, Luca; Novak, Gregory S.

2014-07-01

Based on two-dimensional high-resolution hydrodynamic numerical simulation, we study the mechanical and radiative feedback effects from the central active galactic nucleus (AGN) on the cosmological evolution of an isolated elliptical galaxy. The inner boundary of the simulation domain is carefully chosen so that the fiducial Bondi radius is resolved and the accretion rate of the black hole is determined self-consistently. It is well known that when the accretion rates are high and low, the central AGNs will be in cold and hot accretion modes, which correspond to the radiative and kinetic feedback modes, respectively. The emitted spectrum from the hot accretion flows is harder than that from the cold accretion flows, which could result in a higher Compton temperature accompanied by a more efficient radiative heating, according to previous theoretical works. Such a difference of the Compton temperature between the two feedback modes, the focus of this study, has been neglected in previous works. Significant differences in the kinetic feedback mode are found as a result of the stronger Compton heating. More importantly, if we constrain models to correctly predict black hole growth and AGN duty cycle after cosmological evolution, we find that the favored model parameters are constrained: mechanical feedback efficiency diminishes with decreasing luminosity (the maximum efficiency being ~= 10-3.5), and X-ray Compton temperature increases with decreasing luminosity, although models with fixed mechanical efficiency and Compton temperature can be found that are satisfactory as well. We conclude that radiative feedback in the kinetic mode is much more important than previously thought.

Smallest Black Hole in Galactic Nucleus Detected

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2015-08-01

A team of astronomers have reported the detection of the smallest black hole (BH) ever observed in a galactic nucleus. The BH is hosted in the center of dwarf galaxy RGG 118, and it weighs in at 50,000 solar masses, according to observations made by Vivienne Baldassare of University of Michigan and her collaborators. Small Discoveries: Why is the discovery of a small nuclear BH important? Some open questions that this could help answer are: - Do the very smallest dwarf galaxies have BHs at their centers too? Though we believe that there's a giant BH at the center of every galaxy, we aren't sure how far down the size scale this holds true. - What is the formation mechanism for BHs at the center of galaxies? - What's the behavior of the M-sigma relation at the low-mass end? The M-sigma relation is an observed correlation between the mass of a galaxy's central BH and the velocity dispersion of the stars in the galaxy. This relation is incredibly useful for determining properties of distant BHs and their galaxies empirically, but little data is available to constrain the low-mass end of the relation. M-sigma relation, plotting systems with dynamically-measured black hole masses. RGG 118 is plotted as the pink star. The solid and dashed lines represent various determinations of scaling relations. Credit: Baldassare et al. 2015. Identifying a Black Hole: RGG 118 was identified as a candidate host for an accreting, nuclear BH from the catalog of dwarf galaxies observed in the Sloan Digital Sky Survey. Baldassare and her team followed up with high-resolution spectroscopy from the Clay telescope in Chile and Chandra x-ray observations. Using these observations, the team determined that RGG 118 plays host to a massive BH at its center based on three clues: 1) narrow emission line ratios, which is a signature of accretion onto a massive BH, 2) the presence of broad emission lines, indicating that gas is rotating around a central BH, and 3) the existence of an X-ray point

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

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 effects of baryon physics, black holes and active galactic nucleus feedback on the mass distribution in clusters of galaxies

NASA Astrophysics Data System (ADS)

Martizzi, Davide; Teyssier, Romain; Moore, Ben; Wentz, Tina

2012-06-01

The spatial distribution of matter in clusters of galaxies is mainly determined by the dominant dark matter component; however, physical processes involving baryonic matter are able to modify it significantly. We analyse a set of 500 pc resolution cosmological simulations of a cluster of galaxies with mass comparable to Virgo, performed with the AMR code RAMSES. We compare the mass density profiles of the dark, stellar and gaseous matter components of the cluster that result from different assumptions for the subgrid baryonic physics and galaxy formation processes. First, the prediction of a gravity-only N-body simulation is compared to that of a hydrodynamical simulation with standard galaxy formation recipes, and then all results are compared to a hydrodynamical simulation which includes thermal active galactic nucleus (AGN) feedback from supermassive black holes (SMBHs). We find the usual effects of overcooling and adiabatic contraction in the run with standard galaxy formation physics, but very different results are found when implementing SMBHs and AGN feedback. Star formation is strongly quenched, producing lower stellar densities throughout the cluster, and much less cold gas is available for star formation at low redshifts. At redshift z= 0 we find a flat density core of radius 10 kpc in both the dark and stellar matter density profiles. We speculate on the possible formation mechanisms able to produce such cores and we conclude that they can be produced through the coupling of different processes: (I) dynamical friction from the decay of black hole orbits during galaxy mergers; (II) AGN-driven gas outflows producing fluctuations of the gravitational potential causing the removal of collisionless matter from the central region of the cluster; (III) adiabatic expansion in response to the slow expulsion of gas from the central region of the cluster during the quiescent mode of AGN activity.

The Host Galaxy and Central Engine of the Dwarf Active Galactic Nucleus POX 52

NASA Astrophysics Data System (ADS)

Thornton, Carol E.; Barth, Aaron J.; Ho, Luis C.; Rutledge, Robert E.; Greene, Jenny E.

2008-10-01

We present new multiwavelength observations of the dwarf Seyfert 1 galaxy POX 52 in order to investigate the properties of the host galaxy and the active nucleus and to examine the mass of its black hole, previously estimated to be ~105 M⊙. HST ACS HRC images show that the host galaxy has a dwarf elliptical morphology (MI = - 18.4 mag, Sérsic index n = 4.3) with no detected disk component or spiral structure, confirming previous results from ground-based imaging. X-ray observations from both Chandra and XMM-Newton show strong (factor of 2) variability over timescales as short as 500 s, as well as a dramatic decrease in the absorbing column density over a 9 month period. We attribute this change to a partial covering absorber, with a 94% covering fraction and NH = 58+ 8.4-9.2 × 1021 cm -2, that moved out of the line of sight in between the XMM-Newton and Chandra observations. Combining these data with observations from the VLA, Spitzer, and archival data from 2MASS and GALEX, we examine the SED of the active nucleus. Its shape is broadly similar to typical radio-quiet quasar SEDs, despite the very low bolometric luminosity of Lbol = 1.3 × 1043 ergs s-1. Finally, we compare black hole mass estimators, including methods based on X-ray variability, and optical scaling relations using the broad Hβ line width and AGN continuum luminosity, finding a range of black hole mass from all methods to be MBH = (2.2-4.2) × 105 M⊙, with an Eddington ratio of Lbol/LEdd ≈ 0.2-0.5.

Active galactic nucleus feedback in an isolated elliptical galaxy: The effect of strong radiative feedback in the kinetic mode

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

Gan, Zhaoming; Yuan, Feng; Ostriker, Jeremiah P.

2014-07-10

Based on two-dimensional high-resolution hydrodynamic numerical simulation, we study the mechanical and radiative feedback effects from the central active galactic nucleus (AGN) on the cosmological evolution of an isolated elliptical galaxy. The inner boundary of the simulation domain is carefully chosen so that the fiducial Bondi radius is resolved and the accretion rate of the black hole is determined self-consistently. It is well known that when the accretion rates are high and low, the central AGNs will be in cold and hot accretion modes, which correspond to the radiative and kinetic feedback modes, respectively. The emitted spectrum from the hotmore » accretion flows is harder than that from the cold accretion flows, which could result in a higher Compton temperature accompanied by a more efficient radiative heating, according to previous theoretical works. Such a difference of the Compton temperature between the two feedback modes, the focus of this study, has been neglected in previous works. Significant differences in the kinetic feedback mode are found as a result of the stronger Compton heating. More importantly, if we constrain models to correctly predict black hole growth and AGN duty cycle after cosmological evolution, we find that the favored model parameters are constrained: mechanical feedback efficiency diminishes with decreasing luminosity (the maximum efficiency being ≅ 10{sup –3.5}), and X-ray Compton temperature increases with decreasing luminosity, although models with fixed mechanical efficiency and Compton temperature can be found that are satisfactory as well. We conclude that radiative feedback in the kinetic mode is much more important than previously thought.« less

Discovery of a dual active galactic nucleus with ˜8 kpc separation

NASA Astrophysics Data System (ADS)

Ellison, Sara L.; Secrest, Nathan J.; Mendel, J. Trevor; Satyapal, Shobita; Simard, Luc

2017-09-01

Targeted searches for dual active galactic nuclei (AGNs), with separations 1-10 kpc, have yielded relatively few successes. A recent pilot survey by Satyapal et al. has demonstrated that mid-infrared (mid-IR) pre-selection has the potential to significantly improve the success rate for dual AGN confirmation in late stage galaxy mergers. In this Letter, we combine mid-IR selection with spatially resolved optical AGN diagnostics from the Mapping Nearby Galaxies at Apache Point Observatory survey to identify a candidate dual AGN in the late stage major galaxy merger SDSS J140737.17+442856.2 at z = 0.143. The nature of the dual AGN is confirmed with Chandra X-ray observations that identify two hard X-ray point sources with intrinsic (corrected for absorption) 2-10 keV luminosities of 4 × 1041 and 3.5 × 1043 erg s-1 separated by 8.3 kpc. The neutral hydrogen absorption (˜1022 cm-2) towards the two AGNs is lower than in duals selected solely on their mid-IR colours, indicating that strategies that combine optical and mid-IR diagnostics may complement techniques that identify the highly obscured dual phase, such as at high X-ray energies or mid-IR only.

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.

Active galactic nuclei and galaxy interactions

NASA Astrophysics Data System (ADS)

Alonso, M. Sol; Lambas, Diego G.; Tissera, Patricia; Coldwell, Georgina

2007-03-01

We perform a statistical analysis of active galactic nucleus (AGN) host characteristics and nuclear activity for AGNs in pairs and without companions. Our study concerns a sample of AGNs derived from the Sloan Digital Sky Survey Data Release 4 data by Kauffmann et al. and pair galaxies obtained from the same data set by Alonso et al. An eye-ball classification of images of 1607 close pairs (rp < 25 kpc h-1,ΔV < 350 km s-1) according to the evidence of interaction through distorted morphologies and tidal features provides us with a more confident assessment of galaxy interactions from this sample. We notice that, at a given luminosity or stellar mass content, the fraction of AGNs is larger for pair galaxies exhibiting evidence for strong interaction and tidal features which also show signs of strong star formation activity. Nevertheless, this process accounts only for a ~10per cent increase of the fraction of AGNs. As in previous works, we find AGN hosts to be redder and with a larger concentration morphological index than non-AGN galaxies. This effect does not depend on whether AGN hosts are in pairs or in isolation. The OIII luminosity of AGNs with strong interaction features is found to be significantly larger than that of other AGNs, either in pairs or in isolation. Estimations of the accretion rate, L[OIII]/MBH, show that AGNs in merging pairs are actively feeding their black holes, regardless of their stellar masses. We also find that the luminosity of the companion galaxy seems to be a key parameter in the determination of the black hole activity. At a given host luminosity, both the OIII luminosity and the L[ OIII]/MBH are significantly larger in AGNs with a bright companion (Mr < -20) than otherwise.

OBSERVATIONAL LIMITS ON TYPE 1 ACTIVE GALACTIC NUCLEUS ACCRETION RATE IN COSMOS

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

Trump, Jonathan R.; Impey, Chris D.; Gabor, Jared

2009-07-20

We present black hole masses and accretion rates for 182 Type 1 active galactic nuclei (AGNs) in COSMOS. We estimate masses using the scaling relations for the broad H {beta}, Mg II, and C IV emission lines in the redshift ranges 0.16 < z < 0.88, 1 < z < 2.4, and 2.7 < z < 4.9. We estimate the accretion rate using an Eddington ratio L{sub I}/L{sub Edd} estimated from optical and X-ray data. We find that very few Type 1 AGNs accrete below L{sub I} /L{sub Edd} {approx} 0.01, despite simulations of synthetic spectra which show that themore » survey is sensitive to such Type 1 AGNs. At lower accretion rates the broad-line region may become obscured, diluted, or nonexistent. We find evidence that Type 1 AGNs at higher accretion rates have higher optical luminosities, as more of their emission comes from the cool (optical) accretion disk with respect to shorter wavelengths. We measure a larger range in accretion rate than previous works, suggesting that COSMOS is more efficient at finding low accretion rate Type 1 AGNs. However, the measured range in accretion rate is still comparable to the intrinsic scatter from the scaling relations, suggesting that Type 1 AGNs accrete at a narrow range of Eddington ratio, with L{sub I} /L{sub Edd} {approx} 0.1.« less

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.

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

COLA. III. Radio Detection of Active Galactic Nucleus in Compact Moderate Luminosity Infrared Galaxies

NASA Astrophysics Data System (ADS)

Parra, R.; Conway, J. E.; Aalto, S.; Appleton, P. N.; Norris, R. P.; Pihlström, Y. M.; Kewley, L. J.

2010-09-01

We present results from 4.8 GHz Very Large Array (VLA) and global very long baseline interferometry (VLBI) observations of the northern half of the moderate FIR luminosity (median L IR = 1011.01 L sun) COLA sample of star-forming galaxies. VLBI sources are detected in a high fraction (20/90) of the galaxies observed. The radio luminosities of these cores (~1021 W Hz-1) are too large to be explained by radio supernovae or supernova remnants and we argue that they are instead powered by active galactic nuclei (AGNs). These sub-parsec scale radio cores are preferentially detected toward galaxies whose VLA maps show bright 100-500 parsec scale nuclear radio components. Since these latter structures tightly follow the FIR to radio-continuum correlation for star formation, we conclude that the AGN-powered VLBI sources are associated with compact nuclear starburst environments. The implications for possible starburst-AGN connections are discussed. The detected VLBI sources have a relatively narrow range of radio luminosity consistent with models in which intense compact Eddington-limited starbursts regulate the gas supply onto a central supermassive black hole. The high incidence of AGN radio cores in compact starbursts suggests little or no delay between the starburst phase and the onset of AGN activity.

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.

Star trapping and metallicity enrichment in quasars and active galactic nuclei

NASA Technical Reports Server (NTRS)

Artymowicz, Pawel; Lin, D. N. C.; Wampler, E. J.

1993-01-01

Recent observational evidence suggests that the metallicity in quasars within a wide range of redshifts, in particular in gas flowing out of the nuclear regions, may be approximately redshift-independent and comparable with or larger than solar. It is plausible that the nuclear metallicity can be internally generated and maintained at approximately time-stationary values in quasars. We identify and estimate efficiency of a mechanism for rapid metallicity enrichment of quasar nuclear gas (in general, in active galactic nuclei) based on star-gas interactions and equivalent to an unusual mode of massive star formation. The mechanism involves capture of low-mass stars from the host galaxy's nucleus by the assemblages of clouds or by accretion disks orbiting the central massive objects (e.g., black holes). Trapping of stars within gaseous disks/clouds occurs through resonant density and bending wave excitation, as well as by hydrodynamical drag. The time scale for trapping stars with total mass equal to that of disk fragment/cloud is of order Hubble time and is remarkably model-independent. Our results show that the described mechanism can produce features suggested by observations, for example, the (super) solar gas metallicity in the nucleus. Thus the observed metallicities in high-redshift quasars do not necessarily imply that global star formation and efficient chemical changes have occurred in their host galaxies at very early cosmological epochs.

COLA. III. RADIO DETECTION OF ACTIVE GALACTIC NUCLEUS IN COMPACT MODERATE LUMINOSITY INFRARED GALAXIES

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

Parra, R.; Conway, J. E.; Aalto, S.

2010-09-01

We present results from 4.8 GHz Very Large Array (VLA) and global very long baseline interferometry (VLBI) observations of the northern half of the moderate FIR luminosity (median L{sub IR} = 10{sup 11.01} L{sub sun}) COLA sample of star-forming galaxies. VLBI sources are detected in a high fraction (20/90) of the galaxies observed. The radio luminosities of these cores ({approx}10{sup 21} W Hz{sup -1}) are too large to be explained by radio supernovae or supernova remnants and we argue that they are instead powered by active galactic nuclei (AGNs). These sub-parsec scale radio cores are preferentially detected toward galaxies whosemore » VLA maps show bright 100-500 parsec scale nuclear radio components. Since these latter structures tightly follow the FIR to radio-continuum correlation for star formation, we conclude that the AGN-powered VLBI sources are associated with compact nuclear starburst environments. The implications for possible starburst-AGN connections are discussed. The detected VLBI sources have a relatively narrow range of radio luminosity consistent with models in which intense compact Eddington-limited starbursts regulate the gas supply onto a central supermassive black hole. The high incidence of AGN radio cores in compact starbursts suggests little or no delay between the starburst phase and the onset of AGN activity.« less

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.

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.

Dual Active Galactic Nuclei in Nearby Galaxies

NASA Astrophysics Data System (ADS)

Das, Mousumi; Rubinur, Khatun; Karb, Preeti; Varghese, Ashlin; Novakkuni, Navyasree; James, Atul

2018-04-01

Galaxy mergers play a crucial role in the formation of massive galaxies and the buildup of their bulges. An important aspect of the merging process is the in-spiral of the supermassive black-holes (SMBHs) to the centre of the merger remnant and the eventual formation of a SMBH binary. If both the SMBHs are accreting they will form a dual or binary active galactic nucleus (DAGN). The final merger remnant is usually very bright and shows enhanced star formation. In this paper we summarise the current sample of DAGN from previous studies and describe methods that can be used to identify strong DAGN candidates from optical and spectroscopic surveys. These methods depend on the Doppler separation of the double peaked AGN emission lines, the nuclear velocity dispersion of the galaxies and their optical/UV colours. We describe two high resolution, radio observations of DAGN candidates that have been selected based on their double peaked optical emission lines (DPAGN). We also examine whether DAGN host galaxies have higher star formation rates (SFRs) compared to merging galaxies that do not appear to have DAGN. We find that the SFR is not higher for DAGN host galaxies. This suggests that the SFRs in DAGN host galaxies is due to the merging process itself and not related to the presence of two AGN in the system.

Active galactic nucleus X-ray variability in the XMM-COSMOS survey

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

Lanzuisi, G.; Ponti, G.; Salvato, M.

2014-02-01

We used the observations carried out by XMM in the COSMOS field over 3.5 yr to study the long term variability of a large sample of active galactic nuclei (AGNs) (638 sources) in a wide range of redshifts (0.1 < z < 3.5) and X-ray luminosities (10{sup 41} < L {sub 0.5-10} <10{sup 45.5}). Both a simple statistical method to assess the significance of variability and the Normalized Excess Variance (σ{sub rms}{sup 2}) parameter were used to obtain a quantitative measurement of the variability. Variability is found to be prevalent in most AGNs, whenever we have good statistics to measuremore » it, and no significant differences between type 1 and type 2 AGNs were found. A flat (slope –0.23 ± 0.03) anti-correlation between σ{sub rms}{sup 2} and X-ray luminosity is found when all significantly variable sources are considered together. When divided into three redshift bins, the anti-correlation becomes stronger and evolving with z, with higher redshift AGNs being more variable. We prove, however, that this effect is due to the pre-selection of variable sources: when considering all of the sources with an available σ{sub rms}{sup 2} measurement, the evolution in redshift disappears. For the first time, we were also able to study long term X-ray variability as a function of M {sub BH} and Eddington ratio for a large sample of AGNs spanning a wide range of redshifts. An anti-correlation between σ{sub rms}{sup 2} and M {sub BH} is found, with the same slope of anti-correlation between σ{sub rms}{sup 2} and X-ray luminosity, suggesting that the latter may be a by-product of the former. No clear correlation is found between σ{sub rms}{sup 2} and the Eddington ratio in our sample. Finally, no correlation is found between the X-ray σ{sub rms}{sup 2} and optical variability.« less

Short-Term Variability and Power Spectral Density Analysis of the Radio-Loud Active Galactic Nucleus 3C 390.3

NASA Astrophysics Data System (ADS)

Gliozzi, Mario; Papadakis, Iossif E.; Eracleous, Michael; Sambruna, Rita M.; Ballantyne, David R.; Braito, Valentina; Reeves, James N.

2009-09-01

We investigate the short-term variability properties and the power spectral density (PSD) of the broad-line radio galaxy (BLRG) 3C 390.3 using observations made by XMM-Newton, RXTE, and Suzaku on several occasions between 2004 October and 2006 December. The main aim of this work is to derive model-independent constraints on the origin of the X-ray emission and on the nature of the central engine in 3C 390.3. On timescales of the order of few hours, probed by uninterrupted XMM-Newton light curves, the flux of 3C 390.3 is consistent with being constant in all energy bands. On longer timescales, probed by the 2-day RXTE and Suzaku observations, the flux variability becomes significant. The latter observation confirms that the spectral variability behavior of 3C 390.3 is consistent with the spectral evolution observed in (radio-quiet) Seyfert galaxies: the spectrum softens as the source brightens. The correlated variability between soft and hard X-rays, observed during the Suzaku exposure and between the two XMM-Newton pointings, taken 1 week apart, argues against scenarios characterized by the presence of two distinct variable components in the 0.5-10 keV X-ray band. A detailed PSD analysis carried out over five decades in frequency suggests the presence of a break at T br = 43+34 -25 days at a 92% confidence level. This is the second tentative detection of a PSD break in a radio-loud, non-jet dominated active galactic nucleus (AGN), after the BLRG 3C 120, and appears to be in general agreement with the relation between T br, M BH, and L bol, followed by Seyfert galaxies. Our results indicate that the X-ray variability properties of 3C 390.3 are broadly consistent with those of radio-quiet AGN, suggesting that the X-ray emission mechanism in 3C 390.3 is similar to that of nearby Seyfert galaxies without any significant contribution from a jet component.

The Weak Fe Fluorescence Line and Long-Term X-Ray Evolution of the Compton-Thick Active Galactic Nucleus in NGC7674

NASA Technical Reports Server (NTRS)

Ghandi, P.; Annuar, A.; Lansbury, G. B.; Stern, D.; Alexander, D. M.; Bauer, F. E.; Bianchi, S.; Boggs, S. E.; Boorman, P. G.; Brandt, W. N.;

The weak Fe fluorescence line and long-term X-ray evolution of the Compton-thick active galactic nucleus in NGC 7674

NASA Astrophysics Data System (ADS)

Gandhi, P.; Annuar, A.; Lansbury, G. B.; Stern, D.; Alexander, D. M.; Bauer, F. E.; Bianchi, S.; Boggs, S. E.; Boorman, P. G.; Brandt, W. N.; Brightman, M.; Christensen, F. E.; Comastri, A.; Craig, W. W.; Del Moro, A.; Elvis, M.; Guainazzi, M.; Hailey, C. J.; Harrison, F. A.; Koss, M.; Lamperti, I.; Malaguti, G.; Masini, A.; Matt, G.; Puccetti, S.; Ricci, C.; Rivers, E.; Walton, D. J.; Zhang, W. W.

2017-06-01

We present NuSTAR X-ray observations of the active galactic nucleus (AGN) in NGC 7674. The source shows a flat X-ray spectrum, suggesting that it is obscured by Compton-thick gas columns. Based upon long-term flux dimming, previous work suggested the alternate possibility that the source is a recently switched-off AGN with the observed X-rays being the lagged echo from the torus. Our high-quality data show the source to be reflection-dominated in hard X-rays, but with a relatively weak neutral Fe Kα emission line (equivalent width [EW] of ≈ 0.4 keV) and a strong Fe xxvi ionized line (EW ≈ 0.2 keV). We construct an updated long-term X-ray light curve of NGC 7674 and find that the observed 2-10 keV flux has remained constant for the past ≈ 20 yr, following a high-flux state probed by Ginga. Light travel time arguments constrain the minimum radius of the reflector to be ˜ 3.2 pc under the switched-off AGN scenario, ≈ 30 times larger than the expected dust sublimation radius, rendering this possibility unlikely. A patchy Compton-thick AGN (CTAGN) solution is plausible, requiring a minimum line-of-sight column density (NH) of 3 × 1024 cm-2 at present, and yields an intrinsic 2-10 keV luminosity of (3-5) × 1043 erg s-1. Realistic uncertainties span the range of ≈ (1-13) × 1043 erg s-1. The source has one of the weakest fluorescence lines amongst bona fide CTAGN, and is potentially a local analogue of bolometrically luminous systems showing complex neutral and ionized Fe emission. It exemplifies the difficulty of identification and proper characterization of distant CTAGN based on the strength of the neutral Fe Kα line.

Glucokinase activity in the arcuate nucleus regulates glucose intake

PubMed Central

Hussain, Syed; Richardson, Errol; Ma, Yue; Holton, Christopher; De Backer, Ivan; Buckley, Niki; Dhillo, Waljit; Bewick, Gavin; Zhang, Shuai; Carling, David; Bloom, Steve; Gardiner, James

2014-01-01

The brain relies on a constant supply of glucose, its primary fuel, for optimal function. A taste-independent mechanism within the CNS that promotes glucose delivery to the brain has been postulated to maintain glucose homeostasis; however, evidence for such a mechanism is lacking. Here, we determined that glucokinase activity within the hypothalamic arcuate nucleus is involved in regulation of dietary glucose intake. In fasted rats, glucokinase activity was specifically increased in the arcuate nucleus but not other regions of the hypothalamus. Moreover, pharmacologic and genetic activation of glucokinase in the arcuate nucleus of rodent models increased glucose ingestion, while decreased arcuate nucleus glucokinase activity reduced glucose intake. Pharmacologic targeting of potential downstream glucokinase effectors revealed that ATP-sensitive potassium channel and P/Q calcium channel activity are required for glucokinase-mediated glucose intake. Additionally, altered glucokinase activity affected release of the orexigenic neurotransmitter neuropeptide Y in response to glucose. Together, our results suggest that glucokinase activity in the arcuate nucleus specifically regulates glucose intake and that appetite for glucose is an important driver of overall food intake. Arcuate nucleus glucokinase activation may represent a CNS mechanism that underlies the oft-described phenomena of the “sweet tooth” and carbohydrate craving. PMID:25485685

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

Deconvolving the Nucleus of Centaurus A Using Chandra PSF Library

NASA Technical Reports Server (NTRS)

Karovska, Margarita

2000-01-01

Centaurus A (NGC 5128) is a giant early-type galaxy containing the nearest (at 3.5 Mpc) radio-bright Active Galactic Nucleus (AGN). Cen A was observed with the High Resolution Camera (HRC) on the Chandra X-ray Observatory on several occasions since the launch in July 1999. The high-angular resolution (less than 0.5 arcsecond) Chandra/HRC images reveal X ray multi-scale structures in this object with unprecedented detail and clarity, including the bright nucleus believed to be associated with a supermassive black hole. We explored the spatial extent of the Cen A nucleus using deconvolution techniques on the full resolution Chandra images. Model point spread functions (PSFs) were derived from the standard Chandra raytrace PSF library as well as unresolved point sources observed with Chandra. The deconvolved images show that the Cen A nucleus is resolved and asymmetric. We discuss several possible causes of this extended emission and of the asymmetries.

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

Implosive accretion and outbursts of active galactic nuclei

NASA Technical Reports Server (NTRS)

Lovelace, R. V. E.; Romanova, M. M.; Newman, W. I.

1994-01-01

A model and simulation code have been developed for time-dependent axisymmetric disk accretion onto a compact object including for the first time the influence of an ordered magnetic field. The accretion rate and radiative luminosity of the disk are naturally coupled to the rate of outflow of energy and angular momentum in magnetically driven (+/- z) winds. The magnetic field of the wind is treated in a phenomenological way suggested by self-consistent wind solutions. The radial accretion speed u(r, t) of the disk matter is shown to be the sum of the usual viscous contribution and a magnetic contribution proportional to r(exp 3/2)(B(sub p exp 2))/sigma, where B(sub p)(r,t) is the poloidal field threading the disk and sigma(r,t) is the disk's surface mass density. An enhancement or variation in B(sub p) at a large radial distance leads to the formation of a soliton-like structure in the disk density, temperature, and B-field which propagates implosively inward. The implosion gives a burst in the power output in winds or jets and a simultaneous burst in the disk radiation. The model is pertinent to the formation of discrete fast-moving components in jets observed by very long baseline interferometry. These components appear to originate at times of optical outbursts of the active galactic nucleus.

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

Coded-aperture imaging of the Galactic center region at gamma-ray energies

NASA Technical Reports Server (NTRS)

Cook, Walter R.; Grunsfeld, John M.; Heindl, William A.; Palmer, David M.; Prince, Thomas A.

1991-01-01

The first coded-aperture images of the Galactic center region at energies above 30 keV have revealed two strong gamma-ray sources. One source has been identified with the X-ray source IE 1740.7 - 2942, located 0.8 deg away from the nucleus. If this source is at the distance of the Galactic center, it is one of the most luminous objects in the galaxy at energies from 35 to 200 keV. The second source is consistent in location with the X-ray source GX 354 + 0 (MXB 1728-34). In addition, gamma-ray flux from the location of GX 1 + 4 was marginally detected at a level consistent with other post-1980 measurements. No significant hard X-ray or gamma-ray flux was detected from the direction of the Galactic nucleus or from the direction of the recently discovered gamma-ray source GRS 1758-258.

Gas cloud G2 can illuminate the black hole population near the galactic center.

PubMed

Bartos, Imre; Haiman, Zoltán; Kocsis, Bence; Márka, Szabolcs

2013-05-31

Galactic nuclei are expected to be densely populated with stellar- and intermediate-mass black holes. Exploring this population will have important consequences for the observation prospects of gravitational waves as well as understanding galactic evolution. The gas cloud G2 currently approaching Sgr A* provides an unprecedented opportunity to probe the black hole and neutron star population of the Galactic nucleus. We examine the possibility of a G2-cloud-black-hole encounter and its detectability with current x-ray satellites, such as Chandra and NuSTAR. We find that multiple encounters are likely to occur close to the pericenter, which may be detectable upon favorable circumstances. This opportunity provides an additional important science case for leading x-ray observatories to closely follow G2 on its way to the nucleus.

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.

Constraining the Active Galactic Nucleus Contribution in a Multiwavelength Study of Seyfert Galaxies

NASA Technical Reports Server (NTRS)

Melendez, M.; Kraemer, S.B.; Schmitt, H.R.; Crenshaw, D.M.; Deo, R.P.; Mushotzky, R.F.; Bruhweiler, F.C.

2008-01-01

We have studied the relationship between the high- and low-ionization [O IV] (lambda)25.89 microns, [Ne III] (lambda)15.56 microns, and [Ne II] (lambda)12.81 microns emission lines with the aim of constraining the active galactic nuclei (AGNs) and star formation contributions for a sample of 103 Seyfert galaxies.We use the [O IV] and [Ne II] emission as tracers for the AGN power and star formation to investigate the ionization state of the emission-line gas.We find that Seyfert 2 galaxies have, on average, lower [O IV]/[Ne II] ratios than Seyfert 1 galaxies. This result suggests two possible scenarios: (1) Seyfert 2 galaxies have intrinsically weaker AGNs, or (2) Seyfert 2 galaxies have relatively higher star formation rates than Seyfert 1 galaxies. We estimate the fraction of [Ne II] directly associated with the AGNs and find that Seyfert 2 galaxies have a larger contribution from star formation, by a factor of approx.1.5 on average, than what is found in Seyfert 1 galaxies. Using the stellar component of [Ne II] as a tracer of the current star formation, we found similar star formation rates in Seyfert 1 and Seyfert 2 galaxies.We examined the mid- and far-infrared continua and found that [Ne II] is well correlated with the continuum luminosity at 60 microns and that both [Ne III] and [O IV] are better correlated with the 25 micron luminosities than with the continuum at longer wavelengths, suggesting that the mid-infrared continuum luminosity is dominated by the AGN, while the far-infrared luminosity is dominated by star formation. Overall, these results test the unified model of AGNs and suggest that the differences between Seyfert galaxies cannot be solely due to viewing angle dependence.

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.

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.

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).

Optogenetic Activation of the Sublaterodorsal (SLD) Nucleus Induces Rapid Muscle Inhibition

DTIC Science & Technology

2015-09-01

ARL-CR-0783 ● SEP 2015 US Army Research Laboratory Optogenetic Activation of the Sublaterodorsal (SLD) Nucleus Induces Rapid...ARL-CR-0783 ● SEP 2015 US Army Research Laboratory Optogenetic Activation of the Sublaterodorsal (SLD) Nucleus Induces Rapid Muscle...Optogenetic Activation of the Sublaterodorsal (SLD) Nucleus Induces Rapid Muscle Inhibition 5a. CONTRACT NUMBER 1120-1120-99 5b. GRANT NUMBER 5c

On the Physical Environment in the Galactic Nuclei. Ph.D. Thesis - Maryland Univ.

NASA Technical Reports Server (NTRS)

Beall, J. H.

1979-01-01

Galactic nuclei and quasars emit radiation over the entire electromagnetic spectrum. This suggests that concurrent observations over a wide frequency range may provide useful information in determining appropriate models for the physical environment in which the radiation is produced. In conjunction with observations by the high energy spectrometer on OSO-8, four sources have been studied in this manner; the nucleus of the elliptical galaxy, Centaurus A (NGG 5128); the quasar, 30273; the Seyfert galaxy, NGC 4151 and the nucleus of the Milky Way (GCX). Concurrent observations are used to construct the composite spectra (from radio to X-ray) for Cen A and NGC 4151 while the composite spectra of 30273 and GCX are derived from the OSO-8 data and from other observers. A skymap technique used to analyze observations of the galactic center region yielded data consistent with a significant, hard X-ray source at the radio and infrared position of the nucleus of the Milky Way. A theoretical analysis of the temporal variability of the Cen A data is undertaken and its implications discussed. Similarities between the composite spectra of the observed sources suggest that radio-bright and radio-quiet quasars may represent the emission from galactic nuclei with elliptical and Seyfert-like morphologies, respectively.

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.

Unveiling the past of the Galactic nucleus with X-ray echoes

NASA Astrophysics Data System (ADS)

Chuard, D.; Terrier, R.; Goldwurm, A.; Clavel, M.; Soldi, S.; Morris, M. R.; Ponti, G.; Walls, M.; Chernyakova, M.

2017-12-01

Giant molecular clouds populating the central molecular zone have a high enough column density to reflect X-rays coming from strong compact sources in their neighbourhood, including possible powerful outbursts from the Galactic supermassive black hole SgrA. From observations of the molecular complex Sgr C made with the X-ray observatories XMM and Chandra between 2000 and 2014, we confirm this reflection scenario, even though the region hosts several objects (including two PWN candidates) that may be responsible for intense cosmic-ray production. By comparing data to Monte Carlo simulated reflection spectra, we are able to put the best constraints to date on the line-of-sight positions of the main bright clumps of the molecular complex. Ultimately, extending this approach by the inclusion of other molecular complexes allows us to partially reconstruct the past lightcurve of the Galactic supermassive black hole.

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.

Photoevaporation of Dusty Clouds near Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Pier, Edward A.; Voit, G. Mark

1995-09-01

We investigate the hydrodynamic and line-emitting properties of dusty clouds exposed to an active galactic nucleus (AGN) continuum. Such clouds may be found on the inner edges of the tori commonly implicated in AGN unification schemes. An X-ray-heated wind will be driven off the surface of such a cloud, eventually destroying it. Dust grains are carried along with the flow and are destroyed by sputtering as the wind heats. In smaller clouds, sputtering regulates the outflow by reducing the radiation force opposing the flow. Cloud evaporation may be fast enough to determine the location of the inner edge of the torus. However, since the evaporation time is much longer than the orbital time, clouds on eccentric orbits can penetrate well inside the inner edge of the torus. Therefore, the ionization structure of the cloud is determined only by the incipient continuum shape. The inner faces of exposed clouds are pressurized primarily by the incident radiation. Radiation pressure on dust grains regulates how gas pressure increases with optical depth. Ionization levels decrease inward, and the bulk of the cloud is molecular and neutral. The effects of dust extinction and high density suppress the hydrogen recombination lines and the forbidden lines from C, N, and 0 ions below observed levels despite the high covering factor expected for the torus. However, the inner edge of the torus is a natural place for producing the iron coronal lines often seen in the spectra of AGNs (i.e., [Fe VII] λ6087, [Fe X] λ6375, [Fe XI] λ7892, and [Fe XIV] λ5303).

The Mid-Infrared Spectrum of the Galactic Center: A Starburst Nucleus

NASA Technical Reports Server (NTRS)

Simpson, J. P.; Witteborn, F. C.; Cohen, M.; Price, S. D.

1998-01-01

Using the Michelson interferometer on the Midcourse Space Experiment (MSX), we have taken spectra of many positions in the central 25 min of the Galactic Center (GC) with a 6 min x 9 min FOV. The spectral coverage was 380 to 1700/ cm (6 to 26 microns) and the resolution was approx. 21/cm. The spectra exhibit strong UIR/PAH features at 6.2, 7.7, 8.6 and 11.3 microns, in addition to the ionic lines of (Ne II), at 12.8 microns, (S III) 18.7 microns, and (Ar II) 6.98 microns. There are deep silicate absorption features at 10 and 18 microns and a cold continuum increasing at the longest wavelengths. Additional weak features are present in the spectra. We discuss the variation in the extinction at 10 microns as a function of location in the GC. Compared to the MSX spectrum of the Orion nebula, smoothed to the same resolution and multiplied by the estimated GC extinction, the GC spectra have similar PAH features, but the Orion Nebula also has strong lines of (He III) 15.6 microns, (S IV) 10.5 microns, and (Ar III) 8.99 microns and its 25 microns continuum is stronger (colder). Thus, the GC exhibits the mid-IR spectrum of a low excitation H II region and a nearby molecular cloud with a surface photodissociation region (PDR). This is in excellent agreement with the canonical model of a starburst nucleus in which the hot stars and molecular clouds are randomly distributed. The outer surfaces of the clouds are photodissociated and ionized by the photons from the stars located outside the clouds. The PAH molecules are transiently heated by the stellar photons. Since the exciting stars are located well outside the clouds, the radiation field is dilute compared to a newly-formed blister H II region like Orion; this dilute radiation field causes the relatively low excitation of the ionic lines.

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.

AN EMBEDDED ACTIVE NUCLEUS IN THE OH MEGAMASER GALAXY IRAS16399–0937

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

Sales, Dinalva A.; Robinson, A.; Axon, D. J.

2015-01-20

We present a multiwavelength study of the OH megamaser galaxy IRAS16399–0937, based on new Hubble Space Telescope (HST)/Advanced Camera for Surveys F814W and Hα+[N II] images and archive data from HST, Two Micron All Sky Survey, Spitzer, Herschel and the Very Large Array. This system has a double nucleus, whose northern (IRAS16399N) and southern (IRAS16399S) components have a projected separation of ∼6'' (3.4 kpc) and have previously been identified based on optical spectra as a low ionization nuclear emission line region (LINER) and starburst nucleus, respectively. The nuclei are embedded in a tidally distorted common envelope, in which star formation is mostlymore » heavily obscured. The infrared spectrum is dominated by strong polycyclic aromatic hydrocarbon, but deep silicate and molecular absorption features are also present, and are strongest in the IRAS16399N nucleus. The 0.435-500 μm spectral energy distribution was fitted with a model including stellar, interstellar medium and active galactic nucleus (AGN) torus components using our new Markov Chain Monte Carlo code, CLUMPYDREAM. The results indicate that the IRAS16399N contains an AGN (L {sub bol} ∼ 10{sup 44} erg s{sup –1}) deeply embedded in a quasi-spherical distribution of optically thick clumps with a covering fraction ≈1. We suggest that these clumps are the source of the OHM emission in IRAS16399–0937. The high torus covering fraction precludes AGN photoionization as the origin of the LINER spectrum, however, the spectrum is consistent with shocks (v ∼ 100-200 km s{sup –1}). We infer that the ∼10{sup 8} M {sub ☉} black hole in IRAS16399N is accreting at a small fraction (∼1%) of its Eddington rate. The low accretion rate and modest nuclear star formation rates suggest that while the gas-rich major merger forming the IRAS16399–0937 system has triggered widespread star formation, the massive gas inflows expected from merger simulations have not yet fully developed.« less

"Signal" search for intelligence in the galactic nucleus with the array of the Lowlands.

PubMed

Shostak, G S; Tarter, J

1985-01-01

In August, 1981, the Westerbork Synthesis Radio Telescope was used for 4 h to search for narrowband pulsing radio beacons in the direction of the Galactic Center. By using both the spatial discrimination and temporal stability available to an interferometric measurement, weak intermittent signals can be detected even in the face of the strong, naturally caused radiation from this region. A radio beacon within our bandwidth, centered on the 21 cm neutral hydrogen line, would be recognizable if it had a repetition period between 40 sec and 1/2 h. The rms sensitivity to point sources was approximately 50 mJy/cycle, and the detection limit was 500 mJy/cycle. The limit degrades for pulse widths < 0.02s. No repetitive signals were found. For a swept, narrow-band radio beacon constrained to the Galactic Disk (beamwidth = 0.02 rad), our detection limit corresponds to a transmitter power of 10(11) MW at the Galactic Center.

The inner jet of an active galactic nucleus as revealed by a radio-to-gamma-ray outburst.

PubMed

Marscher, Alan P; Jorstad, Svetlana G; D'Arcangelo, Francesca D; Smith, Paul S; Williams, G Grant; Larionov, Valeri M; Oh, Haruki; Olmstead, Alice R; Aller, Margo F; Aller, Hugh D; McHardy, Ian M; Lähteenmäki, Anne; Tornikoski, Merja; Valtaoja, Esko; Hagen-Thorn, Vladimir A; Kopatskaya, Eugenia N; Gear, Walter K; Tosti, Gino; Kurtanidze, Omar; Nikolashvili, Maria; Sigua, Lorand; Miller, H Richard; Ryle, Wesley T

2008-04-24

Blazars are the most extreme active galactic nuclei. They possess oppositely directed plasma jets emanating at near light speeds from accreting supermassive black holes. According to theoretical models, such jets are propelled by magnetic fields twisted by differential rotation of the black hole's accretion disk or inertial-frame-dragging ergosphere. The flow velocity increases outward along the jet in an acceleration and collimation zone containing a coiled magnetic field. Detailed observations of outbursts of electromagnetic radiation, for which blazars are famous, can potentially probe the zone. It has hitherto not been possible to either specify the location of the outbursts or verify the general picture of jet formation. Here we report sequences of high-resolution radio images and optical polarization measurements of the blazar BL Lacertae. The data reveal a bright feature in the jet that causes a double flare of radiation from optical frequencies to TeV gamma-ray energies, as well as a delayed outburst at radio wavelengths. We conclude that the event starts in a region with a helical magnetic field that we identify with the acceleration and collimation zone predicted by the theories. The feature brightens again when it crosses a standing shock wave corresponding to the bright 'core' seen on the images.

Particle Acceleration in Active Galactic Nuclei

NASA Technical Reports Server (NTRS)

Miller, James A.

1997-01-01

The high efficiency of energy generation inferred from radio observations of quasars and X-ray observations of Seyfert active galactic nuclei (AGNs) is apparently achieved only by the gravitational conversion of the rest mass energy of accreting matter onto supermassive black holes. Evidence for the acceleration of particles to high energies by a central engine is also inferred from observations of apparent superluminal motion in flat spectrum, core-dominated radio sources. This phenomenon is widely attributed to the ejection of relativistic bulk plasma from the nuclei of active galaxies, and accounts for the existence of large scale radio jets and lobes at large distances from the central regions of radio galaxies. Reports of radio jets and superluminal motion from galactic black hole candidate X-ray sources indicate that similar processes are operating in these sources. Observations of luminous, rapidly variable high-energy radiation from active galactic nuclei (AGNs) with the Compton Gamma Ray Observatory show directly that particles are accelerated to high energies in a compact environment. The mechanisms which transform the gravitational potential energy of the infalling matter into nonthermal particle energy in galactic black hole candidates and AGNs are not conclusively identified, although several have been proposed. These include direct acceleration by static electric fields (resulting from, for example, magnetic reconnection), shock acceleration, and energy extraction from the rotational energy of Kerr black holes. The dominant acceleration mechanism(s) operating in the black hole environment can only be determined, of course, by a comparison of model predictions with observations. The purpose of the work proposed for this grant was to investigate stochastic particle acceleration through resonant interactions with plasma waves that populate the magnetosphere surrounding an accreting black hole. Stochastic acceleration has been successfully applied to the

Science of active galactic nuclei with the GTC and CanariCam

NASA Astrophysics Data System (ADS)

Levenson, Nancy A.; Packham, Christopher C.; Alonso-Herrero, Almudena; Aretxaga, Itziar; Colina, Luis; Díaz-Santos, Tanio; Elitzur, Moshe; Mason, Rachel E.; Perlman, Eric S.; Radomski, James T.; Roche, Patrick F.; Rodríguez Espinosa, José Miguel; Young, Stuart; Telesco, Charles M.

2008-07-01

CanariCam is the facility mid-infrared (MIR) instrument for the Gran Telescopio Canarias (GTC), a 10.4m telescope at the Observatorio del Roque de los Muchachos on La Palma. One of the science drivers for CanariCam is the study of active galactic nuclei (AGN). We will exploit the instrument's high sensitivity in imaging, spectroscopy, and polarimetry modes to answer fundamental questions of AGN and their host galaxies. Dust in the nucleus of an active galaxy reprocesses the intrinsic radiation of the central engine to emerge in the MIR. Current work demonstrates that the hot dust immediately associated with the AGN, which blocks direct views of the AGN from some lines of sight, is confined to small (parsec) scales. Thus, high spatial resolution is essential to probe the "torus" of unified AGN models separate from the host galaxy. CanariCam provides a 0.08" pixel scale for Nyquist sampling the diffraction-limited point spread function at 8μm, and narrow (0.2") spectroscopy slits (with R=120-1300). New observations with the GTC/CanariCam will provide key constraints on the physical conditions in the clumpy torus, and we will sensitively determine AGN obscuration as a function of nuclear activity. We will therefore address the fueling process and its relationship to the torus, the interaction with the host galaxy, and dust chemistry. These data will be essential preparation for the next generation of telescopes that will observe the distant universe directly to explore galaxy and black hole formation and evolution, and the GTC/CanariCam system uniquely provides multiple modes to probe AGN.

ANALYSIS OF OPTICAL Fe II EMISSION IN A SAMPLE OF ACTIVE GALACTIC NUCLEUS SPECTRA

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

Kovacevic, Jelena; Popovic, Luka C.; Dimitrijevic, Milan S., E-mail: jkovacevic@aob.bg.ac.r

We present a study of optical Fe II emission in 302 active galactic nuclei (AGNs) selected from the Sloan Digital Sky Survey. We group the strongest Fe II multiplets into three groups according to the lower term of the transition (b{sup 4} F, a{sup 6} S, and a{sup 4} G terms). These approximately correspond to the blue, central, and red parts, respectively, of the 'iron shelf' around H{beta}. We calculate an Fe II template that takes into account transitions into these three terms and an additional group of lines, based on a reconstruction of the spectrum of I Zw 1.more » This Fe II template gives a more precise fit of the Fe II lines in broad-line AGNs than other templates. We extract Fe II, H{alpha}, H{beta}, [O III], and [N II] emission parameters and investigate correlations between them. We find that Fe II lines probably originate in an intermediate line region. We note that the blue, red, and central parts of the iron shelf have different relative intensities in different objects. Their ratios depend on continuum luminosity, FWHM H{beta}, the velocity shift of Fe II, and the H{alpha}/H{beta} flux ratio. We examine the dependence of the well-known anti-correlation between the equivalent widths of Fe II and [O III] on continuum luminosity. We find that there is a Baldwin effect for [O III] but an inverse Baldwin effect for the Fe II emission. The [O III]/Fe II ratio thus decreases with L {sub {lambda}5100}. Since the ratio is a major component of the Boroson and Green Eigenvector 1 (EV1), this implies a connection between the Baldwin effect and EV1 and could be connected with AGN evolution. We find that spectra are different for H{beta} FWHMs greater and less than {approx}3000 km s{sup -1}, and that there are different correlation coefficients between the parameters.« less

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 OPTX Project. V. Identifying Distant Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Trouille, L.; Barger, A. J.; Tremonti, C.

2011-11-01

The Baldwin, Phillips, and Terlevich emission-line ratio diagnostic ([O III]/Hβ versus [N II]/Hα, hereafter BPT diagram) efficiently separates galaxies whose signal is dominated by star formation (BPT-SF) from those dominated by active galactic nucleus (AGN) activity (BPT-AGN). Yet this BPT diagram is limited to z < 0.5, the redshift at which [N II]λ6584 leaves the optical spectral window. Using the Sloan Digital Sky Survey (SDSS), we construct a new diagnostic, or TBT diagram, that is based on rest-frame g - z color, [Ne III]λ3869, and [O II]λλ3726 + 3729 and can be used for galaxies out to z < 1.4. The TBT diagram identifies 98.7% of the SDSS BPT-AGN as TBT-AGN and 97% of the SDSS BPT-SF as TBT-SF. Furthermore, it identifies 97% of the OPTX Chandra X-ray-selected AGNs as TBT-AGN. This is in contrast to the BPT diagram, which misidentifies 20% of X-ray-selected AGNs as BPT-SF. We use the Great Observatories Origins Deep Survey North and Lockman Hole galaxy samples, with their accompanying deep Chandra imaging, to perform X-ray and infrared stacking analyses to further validate our TBT-AGN and TBT-SF selections; that is, we verify the dominance of AGN activity in the former and star formation activity in the latter. Finally, we address the inclusion of the majority of the BPT-comp (sources lying between the BPT-SF and BPT-AGN regimes) in our TBT-AGN regime. We find that the stacked BPT-comp source is X-ray hard (langΓeffrang = 1.0+0.4 -0.4) and has a high X-ray luminosity to total infrared luminosity ratio. This suggests that, on average, the X-ray signal in BPT-comp is dominated by obscured or low accretion rate AGN activity rather than by star formation, supporting their inclusion in the TBT-AGN regime. Some of 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

A Long Decay of X-Ray Flux and Spectral Evolution in the Supersoft Active Galactic Nucleus GSN 069

NASA Astrophysics Data System (ADS)

Shu, X. W.; Wang, S. S.; Dou, L. M.; Jiang, N.; Wang, J. X.; Wang, T. G.

2018-04-01

GSN 069 is an optically identified very low-mass active galactic nuclei (AGN) that shows supersoft X-ray emission. The source is known to exhibit a huge X-ray outburst, with flux increased by more than a factor of ∼240 compared to the quiescence state. We report its long-term evolution in the X-ray flux and spectral variations over a timescale of ∼decade, using both new and archival X-ray observations from the XMM-Newton and Swift. The new Swift observations detected the source in its lowest level of X-ray activity since the outburst, a factor of ∼4 lower in the 0.2–2 keV flux than that obtained with the XMM-Newton observations nearly eight years ago. Combining with the historical X-ray measurements, we find that the X-ray flux is decreasing slowly. There seemed to be spectral softening associated with the drop of X-ray flux. In addition, we find evidence for the presence of a weak, variable, hard X-ray component, in addition to the dominant thermal blackbody emission reported before. The long decay of X-ray flux and spectral evolution, as well as the supersoft X-ray spectra, suggest that the source could be a tidal disruption event (TDE), though a highly variable AGN cannot be fully ruled out. Further continued X-ray monitoring would be required to test the TDE interpretation, by better determining the flux evolution in the decay phase.

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.

Gas inflows towards the nucleus of NGC 1358

NASA Astrophysics Data System (ADS)

Schnorr-Müller, Allan; Storchi-Bergmann, Thaisa; Nagar, Neil M.; Robinson, Andrew; Lena, Davide

2017-11-01

We use optical spectra from the inner 1.8 × 2.5 kpc2 of the Seyfert 2 galaxy NGC 1358, obtained with the GMOS integral field spectrograph on the Gemini South telescope at a spatial resolution of ≈ 165 pc, to assess the feeding and feedback processes in this nearby active galaxy. Five gaseous kinematical components are observed in the emission line profiles. One of the components is present in the entire field-of-view and we interpret it as due to gas rotating in the disc of the galaxy. Three of the remaining components we interpret as associated with active galactic nucleus (AGN) feedback: a compact unresolved outflow in the inner 1 arcsec and two gas clouds observed at opposite sides of the nucleus, which we propose have been ejected in a previous AGN burst. The disc component velocity field is strongly disturbed by a large-scale bar. The subtraction of a velocity model combining both rotation and bar flows reveals three kinematic nuclear spiral arms: two in inflow and one in outflow. We estimate the mass inflow rate in the inner 180 pc obtaining \\dot{M}_{in} ≈ 1.5 × 10-2 M⊙ yr-1, about 160 times larger than the accretion rate necessary to power this AGN.

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.

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.

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.

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.

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.

Unusual Metals in Galactic Center Stars

NASA Astrophysics Data System (ADS)

Hensley, Kerry

2018-03-01

Far from the galactic suburbs where the Sun resides, a cluster of stars in the nucleus of the Milky Way orbits a supermassive black hole. Can chemical abundance measurements help us understand the formation history of the galactic center nuclear star cluster?Studying Stellar PopulationsMetallicity distributions for stars in the inner two degrees of the Milky Way (blue) and the central parsec (orange). [Do et al. 2018]While many galaxies host nuclear star clusters, most are too distant for us to study in detail; only in the Milky Way can we resolve individual stars within one parsec of a supermassive black hole. The nucleus of our galaxy is an exotic and dangerous place, and its not yet clear how these stars came to be where they are were they siphoned off from other parts of the galaxy, or did they form in place, in an environment rocked by tidal forces?Studying the chemical abundances of stars provides a way to separate distinct stellar populations and discern when and where these stars formed. Previous studies using medium-resolution spectroscopy have revealed that many stars within the central parsec of our galaxy have very high metallicities possibly higher than any other region of the Milky Way. Can high-resolution spectroscopy tell us more about this unusual population of stars?Spectral Lines on DisplayTuan Do (University of California, Los Angeles, Galactic Center Group) and collaborators performed high-resolution spectroscopic observations of two late-type giant starslocated half a parsec from the Milky Ways supermassive black hole.Comparison of the observed spectra of the two galactic center stars (black) with synthetic spectra with low (blue) and high (orange) [Sc/Fe] values. Click to enlarge. [Do et al. 2018]In order to constrain the metallicities of these stars, Do and collaborators compared the observed spectra to a grid of synthetic spectra and used a spectral synthesis technique to determine the abundances of individual elements. They found that

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.

Active Galactic Nucleus Feedback with the Square Kilometre Array and Implications for Cluster Physics and Cosmology

NASA Astrophysics Data System (ADS)

Iqbal, Asif; Kale, Ruta; Majumdar, Subhabrata; Nath, Biman B.; Pandge, Mahadev; Sharma, Prateek; Malik, Manzoor A.; Raychaudhury, Somak

2017-12-01

Active Galactic Nuclei (AGN) feedback is regarded as an important non-gravitational process in galaxy clusters, providing useful constraints on large-scale structure formation. It modifies the structure and energetics of the intra-cluster medium (ICM) and hence its understanding is crucially needed in order to use clusters as high precision cosmological probes. In this context, particularly keeping in mind the upcoming high quality radio data expected from radio surveys like Square Kilometre Array (SKA) with its higher sensitivity, high spatial and spectral resolutions, we review our current understanding of AGN feedback, its cosmological implications and the impact that SKA can have in revolutionizing our understanding of AGN feedback in large-scale structures. Recent developments regarding the AGN outbursts and its possible contribution to excess entropy in the hot atmospheres of groups and clusters, its correlation with the feedback energy in ICM, quenching of cooling flows and the possible connection between cool core clusters and radio mini-halos, are discussed. We describe current major issues regarding modeling of AGN feedback and its impact on the surrounding medium. With regard to the future of AGN feedback studies, we examine the possible breakthroughs that can be expected from SKA observations. In the context of cluster cosmology, for example, we point out the importance of SKA observations for cluster mass calibration by noting that most of z>1 clusters discovered by eROSITA X-ray mission can be expected to be followed up through a 1000 hour SKA1-mid programme. Moreover, approximately 1000 radio mini halos and ˜ 2500 radio halos at z<0.6 can be potentially detected by SKA1 and SKA2 and used as tracers of galaxy clusters and determination of cluster selection function.

Deep Chandra observations of HCG 16. I. Active nuclei, star formation, and galactic winds

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

O'Sullivan, E.; Zezas, A.; Vrtilek, J. M.

2014-10-01

We present new, deep Chandra X-ray and Giant Metrewave Radio Telescope 610 MHz observations of the spiral-galaxy-rich compact group HCG 16, which we use to examine nuclear activity, star formation, and high-luminosity X-ray binary populations in the major galaxies. We confirm the presence of obscured active nuclei in NGC 833 and NGC 835, and identify a previously unrecognized nuclear source in NGC 838. All three nuclei are variable on timescales of months to years, and for NGC 833 and NGC 835 this is most likely caused by changes in accretion rate. The deep Chandra observations allow us to detect formore » the first time an Fe Kα emission line in the spectrum of the Seyfert 2 nucleus of NGC 835. We find that NGC 838 and NGC 839 are both starburst-dominated systems, with only weak nuclear activity, in agreement with previous optical studies. We estimate the star formation rates in the two galaxies from their X-ray and radio emission, and compare these results with estimates from the infrared and ultraviolet bands to confirm that star formation in both galaxies is probably declining after galaxy-wide starbursts were triggered ∼400-500 Myr ago. We examine the physical properties of their galactic superwinds, and find that both have temperatures of ∼0.8 keV. We also examine the X-ray and radio properties of NGC 848, the fifth largest galaxy in the group, and show that it is dominated by emission from its starburst.« less

Deep Chandra Observations of HCG 16. I. Active Nuclei, Star Formation, and Galactic Winds

NASA Astrophysics Data System (ADS)

O'Sullivan, E.; Zezas, A.; Vrtilek, J. M.; Giacintucci, S.; Trevisan, M.; David, L. P.; Ponman, T. J.; Mamon, G. A.; Raychaudhury, S.

2014-10-01

We present new, deep Chandra X-ray and Giant Metrewave Radio Telescope 610 MHz observations of the spiral-galaxy-rich compact group HCG 16, which we use to examine nuclear activity, star formation, and high-luminosity X-ray binary populations in the major galaxies. We confirm the presence of obscured active nuclei in NGC 833 and NGC 835, and identify a previously unrecognized nuclear source in NGC 838. All three nuclei are variable on timescales of months to years, and for NGC 833 and NGC 835 this is most likely caused by changes in accretion rate. The deep Chandra observations allow us to detect for the first time an Fe Kα emission line in the spectrum of the Seyfert 2 nucleus of NGC 835. We find that NGC 838 and NGC 839 are both starburst-dominated systems, with only weak nuclear activity, in agreement with previous optical studies. We estimate the star formation rates in the two galaxies from their X-ray and radio emission, and compare these results with estimates from the infrared and ultraviolet bands to confirm that star formation in both galaxies is probably declining after galaxy-wide starbursts were triggered ~400-500 Myr ago. We examine the physical properties of their galactic superwinds, and find that both have temperatures of ~0.8 keV. We also examine the X-ray and radio properties of NGC 848, the fifth largest galaxy in the group, and show that it is dominated by emission from its starburst.

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

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

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.

Characterizing the population of active galactic nuclei in dwarf galaxies

NASA Astrophysics Data System (ADS)

Baldassare, Vivienne F.; Reines, Amy E.; Gallo, Elena; Greene, Jenny E.

2017-01-01

Clues to super-massive black hole (BH) formation and growth reside in the population and properties of BHs in local dwarf galaxies. The masses of BHs in these systems are our best observational constraint on the masses of the first BH "seeds" at high redshift. Moreover, present-day dwarf galaxies are unlikely to have undergone major mergers, making them a relatively pristine testbed for studying triggers of BH accretion. However, in order to find BHs in dwarf galaxies outside the Local Group, it is necessary to search for signatures of accretion, i.e., active galactic nuclei (AGN). Until recently, only a handful of dwarf galaxies were known to contain AGN. However, large surveys such as the SDSS have led to the production of samples of over a hundred dwarf galaxies with AGN signatures (see e.g., Reines et al. 2013). My dissertation work has involved in-depth, multi-wavelength follow-up of nearby (z<0.055) dwarf galaxies with optical spectroscopic AGN signatures in SDSS.I analyzed high resolution spectra of dwarf galaxies with narrow-line AGN, which led to the discovery of a 50,000 MSun BH in the nucleus of RGG 118 - the smallest BH yet reported in a galaxy nucleus (Baldassare et al. 2015). I also used multi-epoch optical spectroscopy to study the nature of broad H-alpha emission in dwarf galaxies. A characteristic signature of dense gas orbiting around a BH, broad emission can also be produced by transient stellar processes. I showed that broad H-alpha in star-forming dwarf galaxies fades over a baseline of 5-10 years, and is likely produced by e.g., a Type II SN as opposed to an AGN. However, broad emission in dwarf galaxies with AGN/composite narrow lines is persistent and consistent across observations, suggesting an AGN origin (Baldassare et al. 2016). Finally, I analyzed X-ray and UV observations of dwarf galaxies with broad and narrow-line AGN signatures. All targets had nuclear X-ray detections at levels significantly higher than expected from X-ray binaries

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.

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.

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

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.

The active galactic nucleus population in X-ray-selected galaxy groups at 0.5 < Z < 1.1

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

Oh, Semyeong; Woo, Jong-Hak; Matsuoka, Kenta

2014-07-20

We use Chandra data to study the incidence and properties of active galactic nuclei (AGNs) in 16 intermediate redshift (0.5 < z < 1.1) X-ray-selected galaxy groups in the Chandra Deep Field-South. We measure an AGN fraction of f(L{sub X,H}>10{sup 42};M{sub R}<−20)=8.0{sub −2.3}{sup +3.0}% at z-bar ∼0.74, approximately a factor of two higher than the AGN fraction found for rich clusters at comparable redshift. This extends the trend found at low redshift for groups to have higher AGN fractions than clusters. Our estimate of the AGN fraction is also more than a factor of three higher than that of lowmore » redshift X-ray-selected groups. Using optical spectra from various surveys, we also constrain the properties of emission-line selected AGNs in these groups. In contrast to the large population of X-ray AGNs (N(L{sub X,{sub H}} > 10{sup 41} erg s{sup –1}) = 25), we find only four emission-line AGNs, three of which are also X-ray bright. Furthermore, most of the X-ray AGNs in our groups are optically dull (i.e., lack strong emission-lines), similar to those found in low redshift X-ray groups and clusters of galaxies. This contrasts with the AGN population found in low redshift optically selected groups which are dominated by emission-line AGNs. The differences between the optically and X-ray-selected AGNs populations in groups are consistent with a scenario where most AGNs in the densest environments are currently in a low accretion state.« less

Silicate Dust in Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Xie, Yanxia; Li, Aigen; Hao, Lei

2017-01-01

The unification theory of active galactic nuclei (AGNs) hypothesizes that all AGNs are surrounded by an anisotropic dust torus and are essentially the same objects but viewed from different angles. However, little is known about the dust that plays a central role in the unification theory. There are suggestions that the AGN dust extinction law appreciably differs from that of the Galaxy. Also, the silicate emission features observed in type 1 AGNs appear anomalous (I.e., their peak wavelengths and widths differ considerably from that of the Galaxy). In this work, we explore the dust properties of 147 AGNs of various types at redshifts z≲ 0.5, with special attention paid to 93 AGNs that exhibit the 9.7 and 18 μm silicate emission features. We model their silicate emission spectra obtained with the Infrared Spectrograph aboard the Spitzer Space Telescope. We find that 60/93 of the observed spectra can be well explained with “astronomical silicate,” while the remaining sources favor amorphous olivine or pyroxene. Most notably, all sources require the dust to be micron-sized (with a typical size of ˜1.5 ± 0.1 μm), much larger than submicron-sized Galactic interstellar grains, implying a flat or “gray” extinction law for AGNs. We also find that, while the 9.7 μm emission feature arises predominantly from warm silicate dust of temperature T ˜ 270 K, the ˜5-8 μm continuum emission is mostly from carbon dust of T ˜ 640 K. Finally, the correlations between the dust properties (e.g., mass, temperature) and the AGN properties (e.g., luminosity, black hole mass) have also been investigated.

Regular theta-firing neurons in the nucleus incertus during sustained hippocampal activation.

PubMed

Martínez-Bellver, Sergio; Cervera-Ferri, Ana; Martínez-Ricós, Joana; Ruiz-Torner, Amparo; Luque-Garcia, Aina; Luque-Martinez, Aina; Blasco-Serra, Arantxa; Guerrero-Martínez, Juan; Bataller-Mompeán, Manuel; Teruel-Martí, Vicent

2015-04-01

This paper describes the existence of theta-coupled neuronal activity in the nucleus incertus (NI). Theta rhythm is relevant for cognitive processes such as spatial navigation and memory processing, and can be recorded in a number of structures related to the hippocampal activation including the NI. Strong evidence supports the role of this tegmental nucleus in neural circuits integrating behavioural activation with the hippocampal theta rhythm. Theta oscillations have been recorded in the local field potential of the NI, highly coupled to the hippocampal waves, although no rhythmical activity has been reported in neurons of this nucleus. The present work analyses the neuronal activity in the NI in conditions leading to sustained hippocampal theta in the urethane-anaesthetised rat, in order to test whether such activation elicits a differential firing pattern. Wavelet analysis has been used to better define the neuronal activity already described in the nucleus, i.e., non-rhythmical neurons firing at theta frequency (type I neurons) and fast-firing rhythmical neurons (type II). However, the most remarkable finding was that sustained stimulation activated regular-theta neurons (type III), which were almost silent in baseline conditions and have not previously been reported. Thus, we describe the electrophysiological properties of type III neurons, focusing on their coupling to the hippocampal theta. Their spike rate, regularity and phase locking to the oscillations increased at the beginning of the stimulation, suggesting a role in the activation or reset of the oscillation. Further research is needed to address the specific contribution of these neurons to the entire circuit. © 2015 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.

Active galactic nucleus and quasar science with aperture masking interferometry on the James Webb Space Telescope

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

Ford, K. E. Saavik; McKernan, Barry; Sivaramakrishnan, Anand

Due to feedback from accretion onto supermassive black holes (SMBHs), active galactic nuclei (AGNs) are believed to play a key role in ΛCDM cosmology and galaxy formation. However, AGNs extreme luminosities and the small angular size of their accretion flows create a challenging imaging problem. We show that the James Webb Space Telescope's Near Infrared Imager and Slitless Spectrograph (JWST-NIRISS) Aperture Masking Interferometry (AMI) mode will enable true imaging (i.e., without any requirement of prior assumptions on source geometry) at ∼65 mas angular resolution at the centers of AGNs. This is advantageous for studying complex extended accretion flows around SMBHsmore » and in other areas of angular-resolution-limited astrophysics. By simulating data sequences incorporating expected sources of noise, we demonstrate that JWST-NIRISS AMI mode can map extended structure at a pixel-to-pixel contrast of ∼10{sup –2} around an L = 7.5 point source, using short exposure times (minutes). Such images will test models of AGN feedback, fueling, and structure (complementary with ALMA observations), and are not currently supported by any ground-based IR interferometer or telescope. Binary point source contrast with NIRISS is ∼10{sup –4} (for observing binary nuclei in merging galaxies), significantly better than current ground-based optical or IR interferometry. JWST-NIRISS's seven-hole non-redundant mask has a throughput of 15%, and utilizes NIRISS's F277W (2.77 μm), F380M (3.8 μm), F430M (4.3 μm), and F480M (4.8 μm) filters. NIRISS's square pixels are 65 mas per side, with a field of view ∼2' × 2'. We also extrapolate our results to AGN science enabled by non-redundant masking on future 2.4 m and 16 m space telescopes working at long-UV to near-IR wavelengths.« 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.

Social interaction reward decreases p38 activation in the nucleus accumbens shell of rats

PubMed Central

Salti, Ahmad; Kummer, Kai K.; Sadangi, Chinmaya; Dechant, Georg; Saria, Alois; El Rawas, Rana

2016-01-01

We have previously shown that animals acquired robust conditioned place preference (CPP) to either social interaction alone or cocaine alone. Recently it has been reported that drugs of abuse abnormally activated p38, a member of mitogen-activated protein kinase family, in the nucleus accumbens. In this study, we aimed to investigate the expression of the activated form of p38 (pp38) in the nucleus accumbens shell and core of rats expressing either cocaine CPP or social interaction CPP 1 h, 2 h and 24 h after the CPP test. We hypothesized that cocaine CPP will increase pp38 in the nucleus accumbens shell/core as compared to social interaction CPP. Surprisingly, we found that 24 h after social interaction CPP, pp38 neuronal levels were decreased in the nucleus accumbens shell to the level of naïve rats. Control saline rats that received saline in both compartments of the CPP apparatus and cocaine CPP rats showed similar enhanced p38 activation as compared to naïve and social interaction CPP rats. We also found that the percentage of neurons expressing dopaminergic receptor D2R and pp38 was also decreased in the shell of the nucleus accumbens of social interaction CPP rats as compared to controls. Given the emerging role of p38 in stress/anxiety behaviors, these results suggest that (1) social interaction reward has anti-stress effects; (2) cocaine conditioning per se does not affect p38 activation and that (3) marginal stress is sufficient to induce p38 activation in the shell of the nucleus accumbens. PMID:26300300

The Growth of Stellar Mass Black Hole Binaries Trapped in the Accretion Disks of Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Yi, Shu-Xu; Cheng, K. S.; Taam, Ronald E.

2018-06-01

Among the four black hole (BH) binary merger events detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO), six progenitor BHs have masses greater than 20 M ⊙. The existence of such massive BHs suggests that extreme metal-poor stars are the progenitors. An alternative possibility, that a pair of stellar mass BHs each with mass ∼7 M ⊙ increases to >20 M ⊙ via accretion from a disk surrounding a supermassive BH (SMBH) in an active galactic nucleus (AGN), is considered. The growth of mass of the binary and the transfer of orbital angular momentum to the disk accelerates the merger. Based on the recent numerical work of Tang et al., it is found that, in the disk of a low-mass AGN with mass ∼106 M ⊙ and Eddington ratio >0.01, the mass of an individual BH in the binary can grow to >20 M ⊙ before coalescence, provided that accretion takes place at a rate more than 10 times the Eddington value. This mechanism predicts a new class of gravitational wave (GW) sources involving the merger of two extreme Kerr black holes associated with AGNs and a possible electromagnetic wave counterpart.

Forced precession of the cometary nucleus with randomly placed active regions

NASA Technical Reports Server (NTRS)

Szutowicz, Slawomira

1992-01-01

The cometary nucleus is assumed to be triaxial or axisymmetric spheroid rotating about its axis of maximum moment of inertia and is forced to precess due to jets of ejected material. Randomly placed regions of exposed ice on the surface of the nucleus are assumed to produce gas and dust. The solution of the heat conduction equation for each active region is used to find the gas sublimation rate and the jet acceleration. Precession of the comet nucleus is followed numerically using a phase-averaged system of equations. The gas production curves and the variation of the spin axis during the orbital motion of the comet are presented.

The Dual Role of Starbursts and Active Galactic Nuclei in Driving Extreme Molecular Outflows

NASA Astrophysics Data System (ADS)

Gowardhan, Avani; Spoon, Henrik; Riechers, Dominik A.; González-Alfonso, Eduardo; Farrah, Duncan; Fischer, Jacqueline; Darling, Jeremy; Fergulio, Chiara; Afonso, Jose; Bizzocchi, Luca

2018-05-01

We report molecular gas observations of IRAS 20100‑4156 and IRAS 03158+4227, two local ultraluminous infrared galaxies (ULIRGs) hosting some of the fastest and most massive molecular outflows known. Using Atacama Large Millimeter Array and Plateau de Bure Interferometer observations, we spatially resolve the CO (1‑0) emission from the outflowing molecular gas in both and find maximum outflow velocities of v max ∼ 1600 and ∼1700 km s‑1 for IRAS 20100‑4156 and IRAS 03158+4227, respectively. We find total gas mass outflow rates of {\\dot{M}}OF}∼ 670 and ∼350 M ⊙ yr‑1, respectively, corresponding to molecular gas depletion timescales {τ }OF}dep}∼ 11 and ∼16 Myr. This is nearly 3 times shorter than the depletion timescales implied by star formation, {τ }SFR}dep}∼ 33 and ∼46 Myr, respectively. To determine the outflow driving mechanism, we compare the starburst luminosity (L *) and active galactic nucleus (AGN) luminosity (L AGN) to the outflowing energy and momentum fluxes, using mid-infrared spectral decomposition to discern L AGN. Comparison to other molecular outflows in ULIRGs reveals that outflow properties correlate similarly with L * and L IR as with L AGN, indicating that AGN luminosity alone may not be a good tracer of feedback strength and that a combination of AGN and starburst activity may be driving the most powerful molecular outflows. We also detect the OH 1.667 GHz maser line from both sources and demonstrate its utility in detecting molecular outflows.

RESOLVING THE ACTIVE GALACTIC NUCLEUS AND HOST EMISSION IN THE MID-INFRARED USING A MODEL-INDEPENDENT SPECTRAL DECOMPOSITION

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

Hernán-Caballero, Antonio; Alonso-Herrero, Almudena; Hatziminaoglou, Evanthia

2015-04-20

We present results on the spectral decomposition of 118 Spitzer Infrared Spectrograph (IRS) spectra from local active galactic nuclei (AGNs) using a large set of Spitzer/IRS spectra as templates. The templates are themselves IRS spectra from extreme cases where a single physical component (stellar, interstellar, or AGN) completely dominates the integrated mid-infrared emission. We show that a linear combination of one template for each physical component reproduces the observed IRS spectra of AGN hosts with unprecedented fidelity for a template fitting method with no need to model extinction separately. We use full probability distribution functions to estimate expectation values andmore » uncertainties for observables, and find that the decomposition results are robust against degeneracies. Furthermore, we compare the AGN spectra derived from the spectral decomposition with sub-arcsecond resolution nuclear photometry and spectroscopy from ground-based observations. We find that the AGN component derived from the decomposition closely matches the nuclear spectrum with a 1σ dispersion of 0.12 dex in luminosity and typical uncertainties of ∼0.19 in the spectral index and ∼0.1 in the silicate strength. We conclude that the emission from the host galaxy can be reliably removed from the IRS spectra of AGNs. This allows for unbiased studies of the AGN emission in intermediate- and high-redshift galaxies—currently inaccesible to ground-based observations—with archival Spitzer/IRS data and in the future with the Mid-InfraRed Instrument of the James Webb Space Telescope. The decomposition code and templates are available at http://denebola.org/ahc/deblendIRS.« less

Mass distribution in galaxy clusters: the role of Active Galactic Nuclei feedback

NASA Astrophysics Data System (ADS)

Teyssier, Romain; Moore, Ben; Martizzi, Davide; Dubois, Yohan; Mayer, Lucio

2011-06-01

We use 1-kpc resolution cosmological Adaptive Mesh Refinement (AMR) simulations of a Virgo-like galaxy cluster to investigate the effect of feedback from supermassive black holes on the mass distribution of dark matter, gas and stars. We compared three different models: (i) a standard galaxy formation model featuring gas cooling, star formation and supernovae feedback, (ii) a 'quenching' model for which star formation is artificially suppressed in massive haloes and finally (iii) the recently proposed active galactic nucleus (AGN) feedback model of Booth and Schaye. Without AGN feedback (even in the quenching case), our simulated cluster suffers from a strong overcooling problem, with a stellar mass fraction significantly above observed values in M87. The baryon distribution is highly concentrated, resulting in a strong adiabatic contraction (AC) of dark matter. With AGN feedback, on the contrary, the stellar mass in the brightest cluster galaxy (BCG) lies below observational estimates and the overcooling problem disappears. The stellar mass of the BCG is seen to increase with increasing mass resolution, suggesting that our stellar masses converge to the correct value from below. The gas and total mass distributions are in better agreement with observations. We also find a slight deficit (˜10 per cent) of baryons at the virial radius, due to the combined effect of AGN-driven convective motions in the inner parts and shock waves in the outer regions, pushing gas to Mpc scales and beyond. This baryon deficit results in a slight adiabatic expansion of the dark matter distribution that can be explained quantitatively by AC theory.

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.

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

Social interaction reward decreases p38 activation in the nucleus accumbens shell of rats.

PubMed

Salti, Ahmad; Kummer, Kai K; Sadangi, Chinmaya; Dechant, Georg; Saria, Alois; El Rawas, Rana

2015-12-01

We have previously shown that animals acquired robust conditioned place preference (CPP) to either social interaction alone or cocaine alone. Recently it has been reported that drugs of abuse abnormally activated p38, a member of mitogen-activated protein kinase family, in the nucleus accumbens. In this study, we aimed to investigate the expression of the activated form of p38 (pp38) in the nucleus accumbens shell and core of rats expressing either cocaine CPP or social interaction CPP 1 h, 2 h and 24 h after the CPP test. We hypothesized that cocaine CPP will increase pp38 in the nucleus accumbens shell/core as compared to social interaction CPP. Surprisingly, we found that 24 h after social interaction CPP, pp38 neuronal levels were decreased in the nucleus accumbens shell to the level of naïve rats. Control saline rats that received saline in both compartments of the CPP apparatus and cocaine CPP rats showed similar enhanced p38 activation as compared to naïve and social interaction CPP rats. We also found that the percentage of neurons expressing dopaminergic receptor D2R and pp38 was also decreased in the shell of the nucleus accumbens of social interaction CPP rats as compared to controls. Given the emerging role of p38 in stress/anxiety behaviors, these results suggest that (1) social interaction reward has anti-stress effects; (2) cocaine conditioning per se does not affect p38 activation and that (3) marginal stress is sufficient to induce p38 activation in the shell of the nucleus accumbens. Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.

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

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.

On the Evolution of High-redshift Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Mao, Jirong; Kim, Minsun

2016-09-01

We build a simple physical model to study the high-redshift active galactic nucleus (AGN) evolution within the co-evolution framework of central black holes (BHs) and their host galaxies. The correlation between the circular velocity of a dark halo V c and the velocity dispersion of a galaxy σ is used to link the dark matter halo mass and BH mass. The dark matter halo mass function is converted to the BH mass function for any given redshift. The high-redshift optical AGN luminosity functions (LFs) are constructed. At z˜ 4, the flattening feature is not shown at the faint end of the optical AGN LF. This is consistent with observational results. If the optical AGN LF at z˜ 6 can be reproduced in the case in which central BHs have the Eddington-limited accretion, it is possible for the AGN lifetime to have a small value of 2× {10}5 {{years}}. The X-ray AGN LFs and X-ray AGN number counts are also calculated at 2.0\\lt z\\lt 5.0 and z\\gt 3, respectively, using the same parameters adopted in the calculation for the optical AGN LF at z˜ 4. It is estimated that about 30 AGNs per {{{\\deg }}}2 at z\\gt 6 can be detected with a flux limit of 3× {10}-17 {erg} {{cm}}-2 {{{s}}}-1 in the 0.5-2 keV band. Additionally, the cosmic reionization is also investigated. The ultraviolet photons emitted from the high-redshift AGNs mainly contribute to the cosmic reionization, and the central BHs of the high-redshift AGNs have a mass range of {10}6{--}{10}8{M}⊙ . We also discuss some uncertainties in both the AGN LFs and AGN number counts originating from the {M}{{BH}}{--}σ relation, Eddington ratio, AGN lifetime, and X-ray attenuation in our model.

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.

Properties and Expected Number Counts of Active Galactic Nuclei and Their Hosts in the Far-infrared

NASA Astrophysics Data System (ADS)

Draper, A. R.; Ballantyne, D. R.

2011-03-01

Telescopes like Herschel and the Atacama Large Millimeter/submillimeter Array (ALMA) are creating new opportunities to study sources in the far-infrared (FIR), a wavelength region dominated by cold dust emission. Probing cold dust in active galaxies allows for study of the star formation history of active galactic nucleus (AGN) hosts. The FIR is also an important spectral region for observing AGNs which are heavily enshrouded by dust, such as Compton thick (CT) AGNs. By using information from deep X-ray surveys and cosmic X-ray background synthesis models, we compute Cloudy photoionization simulations which are used to predict the spectral energy distribution (SED) of AGNs in the FIR. Expected differential number counts of AGNs and their host galaxies are calculated in the Herschel bands. The expected contribution of AGNs and their hosts to the cosmic infrared background (CIRB) and the infrared luminosity density are also computed. Multiple star formation scenarios are investigated using a modified blackbody star formation SED. It is found that FIR observations at ~500 μm are an excellent tool in determining the star formation history of AGN hosts. Additionally, the AGN contribution to the CIRB can be used to determine whether star formation in AGN hosts evolves differently than in normal galaxies. The contribution of CT AGNs to the bright end differential number counts and to the bright source infrared luminosity density is a good test of AGN evolution models where quasars are triggered by major mergers.

The 1.4-2.7 micron spectrum of the point source at the galactic center

NASA Technical Reports Server (NTRS)

Treffers, R. R.; Fink, U.; Larson, H. P.; Gautier, T. N., III

1976-01-01

The spectrum of the 2-micron point source at the galactic center is presented over the range from 1.4 to 2.7 microns. The two-level-transition CO band heads are seen near 2.3 microns, confirming that the radiation from this source is due to a cool supergiant star. The heliocentric radial velocity is found to be - 173 (+ or -90) km/s and is consistent with the star being in orbit about a dense galactic nucleus. No evidence is found for Brackett-gamma emission, and no interstellar absorption features are seen. Upper limits for the column densities of interstellar H2, CH4, CO, and NH3 are derived.

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.

The Ionization Fraction in the Obscuring ``Torus'' of an Active Galactic Nucleus

NASA Astrophysics Data System (ADS)

Wilson, A. S.; Roy, A. L.; Ulvestad, J. S.; Colbert, E. J. M.; Weaver, K. A.; Braatz, J. A.; Henkel, C.; Matsuoka, M.; Xue, S.; Iyomoto, N.; Okada, K.

1998-10-01

The LINER galaxy NGC 2639 contains a water vapor megamaser, suggesting the presence of a nuclear accretion disk or torus viewed close to edge-on. This galaxy is thus a good candidate for revealing absorption by the torus of any compact nuclear continuum emission. In this paper, we report VLBA radio maps at three frequencies and an ASCA X-ray spectrum obtained to search for free-free and photoelectric absorptions, respectively. The radio observations reveal a compact (<0.2 pc) nuclear source with a spectrum that turns over sharply near 5 GHz. This turnover may reflect either synchrotron self-absorption or free-free absorption. The galaxy is detected by ASCA with an observed luminosity of 1.4 × 1041 ergs s-1 in the 0.6-10 keV band. The X-ray spectrum shows emission in excess of a power-law model at energies greater than 4 keV; we interpret this excess as compact, nuclear, hard X-ray emission with the lower energies photoelectrically absorbed by an equivalent hydrogen column of ~= 5 × 1023 cm-2. If we assume that the turnover in the radio spectrum is caused by free-free absorption and that both the free-free and photoelectric absorptions are produced by the same gaseous component, the ratio n2edl/nHdl may be determined. If the masing molecular gas is responsible for both absorptions, the required ionization fraction is >~1.3 × 10-5, which is comparable to the theoretical upper limit derived by Neufeld, Maloney, and Conger for X-ray heated molecular gas. The two values may be reconciled if the molecular gas is very dense: nH2>~109 cm-3. The measured ionization fraction is also consistent with the idea that both absorptions occur in a hot (~6000 K), weakly ionized (ionization fraction a few times 10-2) atomic region that may coexist with the warm molecular gas. If this is the case, the absorbing gas is ~1 pc from the nucleus. We rule out the possibility that both absorptions occur in a fully ionized gas near 104 K. If our line of sight passes through more than one

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.

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.

Local vs. volume conductance activity of field potentials in the human subthalamic nucleus

PubMed Central

Marmor, Odeya; Valsky, Dan; Joshua, Mati; Bick, Atira S; Arkadir, David; Tamir, Idit; Bergman, Hagai; Israel, Zvi

2017-01-01

Subthalamic nucleus field potentials have attracted growing research and clinical interest over the last few decades. However, it is unclear whether subthalamic field potentials represent locally generated neuronal subthreshold activity or volume conductance of the organized neuronal activity generated in the cortex. This study aimed at understanding of the physiological origin of subthalamic field potentials and determining the most accurate method for recording them. We compared different methods of recordings in the human subthalamic nucleus: spikes (300–9,000 Hz) and field potentials (3–100 Hz) recorded by monopolar micro- and macroelectrodes, as well as by differential-bipolar macroelectrodes. The recordings were done outside and inside the subthalamic nucleus during electrophysiological navigation for deep brain stimulation procedures (150 electrode trajectories) in 41 Parkinson’s disease patients. We modeled the signal and estimated the contribution of nearby/independent vs. remote/common activity in each recording configuration and area. Monopolar micro- and macroelectrode recordings detect field potentials that are considerably affected by common (probably cortical) activity. However, bipolar macroelectrode recordings inside the subthalamic nucleus can detect locally generated potentials. These results are confirmed by high correspondence between the model predictions and actual correlation of neuronal activity recorded by electrode pairs. Differential bipolar macroelectrode subthalamic field potentials can overcome volume conductance effects and reflect locally generated neuronal activity. Bipolar macroelectrode local field potential recordings might be used as a biological marker of normal and pathological brain functions for future electrophysiological studies and navigation systems as well as for closed-loop deep brain stimulation paradigms. NEW & NOTEWORTHY Our results integrate a new method for human subthalamic recordings with a development of

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.;

Excitatory innervation of caudal hypoglossal nucleus from nucleus reticularis gigantocellularis in the rat.

PubMed

Yang, C C; Chan, J Y; Chan, S H

1995-03-01

We examined the possible innervation of the caudal hypoglossal nucleus by the nucleus reticularis gigantocellularis of the medulla oblongata, based on single-neuron recording and retrograde tracing experiments in Sprague-Dawley rats. Under pentobarbital sodium (50 mg/kg, i.p.) anesthesia, electrical stimulation of the caudal portion of the nucleus reticularis gigantocellularis with repetitive 0.5-ms rectangular pulses increased (46 of 51 neurons) the basal discharge frequency of spontaneously active cells, or evoked spike activity in silent, hypoglossal neurons located at the level of the obex. This excitatory effect was related to the intensity (25-100 microA) and/or frequency (0.5-20 Hz) of the stimulating pulses to the nucleus reticularis gigantocellularis. Perikaryal activation of neurons by microinjection of L-glutamate (0.5 nmol, 25 nl) into the caudal portion of the nucleus reticularis gigantocellularis similarly produced an excitatory action on eight of 14 hypoglossal neurons. Retrogradely labeled neurons were found bilaterally within the confines of the nucleus reticularis gigantocellularis following unilateral microinjection of wheatgerm agglutinin-conjugated horseradish peroxidase or Fast Blue into the corresponding hypoglossal recording sites. Furthermore, the distribution of labeled neurons in the nucleus reticularis gigantocellularis substantially overlapped with the loci of electrical or chemical stimulation. These complementary electrophysiological and neuroanatomical results support the conclusion that an excitatory link exists between the nucleus reticularis gigantocellularis and at least the caudal portion of the hypoglossal nucleus in the rat.

Pedunculopontine Nucleus Gamma Band Activity-Preconscious Awareness, Waking, and REM Sleep

PubMed Central

Urbano, Francisco J.; D’Onofrio, Stasia M.; Luster, Brennon R.; Beck, Paige B.; Hyde, James Robert; Bisagno, Veronica; Garcia-Rill, Edgar

2014-01-01

The pedunculopontine nucleus (PPN) is a major component of the reticular activating system (RAS) that regulates waking and REM sleep, states of high-frequency EEG activity. Recently, we described the presence of high threshold, voltage-dependent N- and P/Q-type calcium channels in RAS nuclei that subserve gamma band oscillations in the mesopontine PPN, intralaminar parafascicular nucleus (Pf), and pontine subcoeruleus nucleus dorsalis (SubCD). Cortical gamma band activity participates in sensory perception, problem solving, and memory. Rather than participating in the temporal binding of sensory events as in the cortex, gamma band activity in the RAS may participate in the processes of preconscious awareness, and provide the essential stream of information for the formulation of many of our actions. That is, the RAS may play an early permissive role in volition. Our latest results suggest that (1) the manifestation of gamma band activity during waking may employ a separate intracellular pathway compared to that during REM sleep, (2) neuronal calcium sensor (NCS-1) protein, which is over expressed in schizophrenia and bipolar disorder, modulates gamma band oscillations in the PPN in a concentration-dependent manner, (3) leptin, which undergoes resistance in obesity resulting in sleep dysregulation, decreases sodium currents in PPN neurons, accounting for its normal attenuation of waking, and (4) following our discovery of electrical coupling in the RAS, we hypothesize that there are cell clusters within the PPN that may act in concert. These results provide novel information on the mechanisms controlling high-frequency activity related to waking and REM sleep by elements of the RAS. PMID:25368599

Pedunculopontine Nucleus Gamma Band Activity-Preconscious Awareness, Waking, and REM Sleep.

PubMed

Urbano, Francisco J; D'Onofrio, Stasia M; Luster, Brennon R; Beck, Paige B; Hyde, James Robert; Bisagno, Veronica; Garcia-Rill, Edgar

2014-01-01

The pedunculopontine nucleus (PPN) is a major component of the reticular activating system (RAS) that regulates waking and REM sleep, states of high-frequency EEG activity. Recently, we described the presence of high threshold, voltage-dependent N- and P/Q-type calcium channels in RAS nuclei that subserve gamma band oscillations in the mesopontine PPN, intralaminar parafascicular nucleus (Pf), and pontine subcoeruleus nucleus dorsalis (SubCD). Cortical gamma band activity participates in sensory perception, problem solving, and memory. Rather than participating in the temporal binding of sensory events as in the cortex, gamma band activity in the RAS may participate in the processes of preconscious awareness, and provide the essential stream of information for the formulation of many of our actions. That is, the RAS may play an early permissive role in volition. Our latest results suggest that (1) the manifestation of gamma band activity during waking may employ a separate intracellular pathway compared to that during REM sleep, (2) neuronal calcium sensor (NCS-1) protein, which is over expressed in schizophrenia and bipolar disorder, modulates gamma band oscillations in the PPN in a concentration-dependent manner, (3) leptin, which undergoes resistance in obesity resulting in sleep dysregulation, decreases sodium currents in PPN neurons, accounting for its normal attenuation of waking, and (4) following our discovery of electrical coupling in the RAS, we hypothesize that there are cell clusters within the PPN that may act in concert. These results provide novel information on the mechanisms controlling high-frequency activity related to waking and REM sleep by elements of the RAS.

AEGIS: Demographics of X-ray and Optically Selected Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Yan, Renbin; Ho, Luis C.; Newman, Jeffrey A.; Coil, Alison L.; Willmer, Christopher N. A.; Laird, Elise S.; Georgakakis, Antonis; Aird, James; Barmby, Pauline; Bundy, Kevin; Cooper, Michael C.; Davis, Marc; Faber, S. M.; Fang, Taotao; Griffith, Roger L.; Koekemoer, Anton M.; Koo, David C.; Nandra, Kirpal; Park, Shinae Q.; Sarajedini, Vicki L.; Weiner, Benjamin J.; Willner, S. P.

2011-02-01

We develop a new diagnostic method to classify galaxies into active galactic nucleus (AGN) hosts, star-forming galaxies, and absorption-dominated galaxies by combining the [O III]/Hβ ratio with rest-frame U - B color. This can be used to robustly select AGNs in galaxy samples at intermediate redshifts (z < 1). We compare the result of this optical AGN selection with X-ray selection using a sample of 3150 galaxies with 0.3 < z < 0.8 and I AB < 22, selected from the DEEP2 Galaxy Redshift Survey and the All-wavelength Extended Groth Strip International Survey. Among the 146 X-ray sources in this sample, 58% are classified optically as emission-line AGNs, the rest as star-forming galaxies or absorption-dominated galaxies. The latter are also known as "X-ray bright, optically normal galaxies" (XBONGs). Analysis of the relationship between optical emission lines and X-ray properties shows that the completeness of optical AGN selection suffers from dependence on the star formation rate and the quality of observed spectra. It also shows that XBONGs do not appear to be a physically distinct population from other X-ray detected, emission-line AGNs. On the other hand, X-ray AGN selection also has strong bias. About 2/3 of all emission-line AGNs at L bol > 1044 erg s-1 in our sample are not detected in our 200 ks Chandra images, most likely due to moderate or heavy absorption by gas near the AGN. The 2-7 keV detection rate of Seyfert 2s at z ~ 0.6 suggests that their column density distribution and Compton-thick fraction are similar to that of local Seyferts. Multiple sample selection techniques are needed to obtain as complete a sample as possible.

DUST-CORRECTED COLORS REVEAL BIMODALITY IN THE HOST-GALAXY COLORS OF ACTIVE GALACTIC NUCLEI AT z {approx} 1

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

Cardamone, Carolin N.; Megan Urry, C.; Brammer, Gabriel

2010-09-20

Using new, highly accurate photometric redshifts from the MUSYC medium-band survey in the Extended Chandra Deep Field-South (ECDF-S), we fit synthetic stellar population models to compare active galactic nucleus (AGN) host galaxies to inactive galaxies at 0.8 {<=} z {<=} 1.2. We find that AGN host galaxies are predominantly massive galaxies on the red sequence and in the green valley of the color-mass diagram. Because both passive and dusty galaxies can appear red in optical colors, we use rest-frame near-infrared colors to separate passively evolving stellar populations from galaxies that are reddened by dust. As with the overall galaxy population,more » {approx}25% of the 'red' AGN host galaxies and {approx}75% of the 'green' AGN host galaxies have colors consistent with young stellar populations reddened by dust. The dust-corrected rest-frame optical colors are the blue colors of star-forming galaxies, which imply that these AGN hosts are not passively aging to the red sequence. At z {approx} 1, AGN activity is roughly evenly split between two modes of black hole growth: the first in passively evolving host galaxies, which may be heating up the galaxy's gas and preventing future episodes of star formation, and the second in dust-reddened young galaxies, which may be ionizing the galaxy's interstellar medium and shutting down star formation.« less

An X-Ray Spectral Model for Clumpy Tori in Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Liu, Yuan; Li, Xiaobo

2014-05-01

We construct an X-ray spectral model for the clumpy torus in an active galactic nucleus (AGN) using Geant4, which includes the physical processes of the photoelectric effect, Compton scattering, Rayleigh scattering, γ conversion, fluorescence line, and Auger process. Since the electrons in the torus are expected to be bounded instead of free, the deviation of the scattering cross section from the Klein-Nishina cross section has also been included, which changes the X-ray spectra by up to 25% below 10 keV. We have investigated the effect of the clumpiness parameters on the reflection spectra and the strength of the fluorescent line Fe Kα. The volume filling factor of the clouds in the clumpy torus only slightly influences the reflection spectra, however, the total column density and the number of clouds along the line of sight significantly change the shapes and amplitudes of the reflection spectra. The effect of column density is similar to the case of a smooth torus, while a small number of clouds along the line of sight will smooth out the anisotropy of the reflection spectra and the fluorescent line Fe Kα. The smoothing effect is mild in the low column density case (N H = 1023 cm-2), whereas it is much more evident in the high column density case (N H = 1025 cm-2). Our model provides a quantitative tool for the spectral analysis of the clumpy torus. We suggest that the joint fits of the broad band spectral energy distributions of AGNs (from X-ray to infrared) should better constrain the structure of the torus.

Neuronal activity-regulated gene transcription: how are distant synaptic signals conveyed to the nucleus?

PubMed Central

Matamales, Miriam

2012-01-01

Synaptic activity can trigger gene expression programs that are required for the stable change of neuronal properties, a process that is essential for learning and memory. Currently, it is still unclear how the stimulation of dendritic synapses can be coupled to transcription in the nucleus in a timely way given that large distances can separate these two cellular compartments. Although several mechanisms have been proposed to explain long distance communication between synapses and the nucleus, the possible co-existence of these models and their relevance in physiological conditions remain elusive. One model suggests that synaptic activation triggers the translocation to the nucleus of certain transcription regulators localised at postsynaptic sites that function as synapto-nuclear messengers. Alternatively, it has been hypothesised that synaptic activity initiates propagating regenerative intracellular calcium waves that spread through dendrites into the nucleus where nuclear transcription machinery is thereby regulated. It has also been postulated that membrane depolarisation of voltage-gated calcium channels on the somatic membrane is sufficient to increase intracellular calcium concentration and activate transcription without the need for transported signals from distant synapses. Here I provide a critical overview of the suggested mechanisms for coupling synaptic stimulation to transcription, the underlying assumptions behind them and their plausible physiological significance. PMID:24327840

Neuronal activity-regulated gene transcription: how are distant synaptic signals conveyed to the nucleus?

PubMed

Matamales, Miriam

2012-12-19

Synaptic activity can trigger gene expression programs that are required for the stable change of neuronal properties, a process that is essential for learning and memory. Currently, it is still unclear how the stimulation of dendritic synapses can be coupled to transcription in the nucleus in a timely way given that large distances can separate these two cellular compartments. Although several mechanisms have been proposed to explain long distance communication between synapses and the nucleus, the possible co-existence of these models and their relevance in physiological conditions remain elusive. One model suggests that synaptic activation triggers the translocation to the nucleus of certain transcription regulators localised at postsynaptic sites that function as synapto-nuclear messengers. Alternatively, it has been hypothesised that synaptic activity initiates propagating regenerative intracellular calcium waves that spread through dendrites into the nucleus where nuclear transcription machinery is thereby regulated. It has also been postulated that membrane depolarisation of voltage-gated calcium channels on the somatic membrane is sufficient to increase intracellular calcium concentration and activate transcription without the need for transported signals from distant synapses. Here I provide a critical overview of the suggested mechanisms for coupling synaptic stimulation to transcription, the underlying assumptions behind them and their plausible physiological significance.

Neuronal activity-regulated gene transcription: how are distant synaptic signals conveyed to the nucleus?

PubMed

Matamales, Miriam

2012-01-01

Synaptic activity can trigger gene expression programs that are required for the stable change of neuronal properties, a process that is essential for learning and memory. Currently, it is still unclear how the stimulation of dendritic synapses can be coupled to transcription in the nucleus in a timely way given that large distances can separate these two cellular compartments. Although several mechanisms have been proposed to explain long distance communication between synapses and the nucleus, the possible co-existence of these models and their relevance in physiological conditions remain elusive. One model suggests that synaptic activation triggers the translocation to the nucleus of certain transcription regulators localised at postsynaptic sites that function as synapto-nuclear messengers. Alternatively, it has been hypothesised that synaptic activity initiates propagating regenerative intracellular calcium waves that spread through dendrites into the nucleus where nuclear transcription machinery is thereby regulated. It has also been postulated that membrane depolarisation of voltage-gated calcium channels on the somatic membrane is sufficient to increase intracellular calcium concentration and activate transcription without the need for transported signals from distant synapses. Here I provide a critical overview of the suggested mechanisms for coupling synaptic stimulation to transcription, the underlying assumptions behind them and their plausible physiological significance.

Rosetta/OSIRIS - Nucleus morphology and activity of comet 67P/Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Sierks, Holger; Barbieri, Cesare; Lamy, Philippe; Rickman, Hans; Rodrigo, Rafael; Koschny, Detlef

2015-04-01

ESA's Rosetta mission arrived on August 6, 2014, at target comet 67P/Churyumov-Gerasimenko after 10 years of cruise. OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) is the scientific imaging system onboard Rosetta. It comprises a Narrow Angle Camera (NAC) for nucleus surface and dust studies and a Wide Angle Camera (WAC) for the wide field coma investigations. OSIRIS imaged the nucleus and coma of the comet from the arrival throughout the mapping phase, PHILAE landing, early escort phase and close fly-by. The overview paper will discuss the surface morpholo-gy and activity of the nucleus as seen in gas, dust, and local jets as well as small scale structures in the local topography.

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.

Herschel spectroscopic observations of the compact obscured nucleus in Zw 049.057

NASA Astrophysics Data System (ADS)

Falstad, N.; González-Alfonso, E.; Aalto, S.; van der Werf, P. P.; Fischer, J.; Veilleux, S.; Meléndez, M.; Farrah, D.; Smith, H. A.

2015-08-01

Context. The luminous infrared galaxy Zw 049.057 contains a compact obscured nucleus where a considerable amount of the galaxy's luminosity is generated. This nucleus contains a dusty environment that is rich in molecular gas. One approach to probing this kind of environment and to revealing what is hidden behind the dust is to study the rotational lines of molecules that couple well with the infrared radiation emitted by the dust. Aims: We probe the physical conditions in the core of Zw 049.057 and establish the nature of its nuclear power source (starburst or active galactic nucleus). Methods: We observed Zw 049.057 with the Photodetector Array Camera and Spectrometer (PACS) and the Spectral and Photometric Imaging Receiver (SPIRE) onboard the Herschel Space Observatory in rotational lines of H2O, H218O, OH, 18OH, and [O I]. We modeled the unresolved core of the galaxy using a spherically symmetric radiative transfer code. To account for the different excitation requirements of the various molecular transitions, we use multiple components and different physical conditions. Results: We present the full high-resolution SPIRE FTS spectrum of Zw 049.057, along with relevant spectral scans in the PACS range. We find that a minimum of two different components (nuclear and extended) are required in order to account for the rich molecular line spectrum of Zw 049.057. The nuclear component has a radius of 10-30 pc, a very high infrared surface brightness (~1014L⊙kpc-2), warm dust (Td > 100 K), and a very large H2 column density (NH2 = 1024-1025 cm-2). The modeling also indicates high nuclear H2O (~5 × 10-6) and OH (~4 × 10-6) abundances relative to H2 as well as a low 16O/18O-ratio of 50-100. We also find a prominent infall signature in the [O I] line. We tentatively detect a 500 km s-1 outflow in the H2O 313 → 202 line. Conclusions: The high surface brightness of the core indicates the presence of either a buried active galactic nucleus or a very dense nuclear

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.

Trajectories of Cepheid variable stars in the Galactic nuclear bulge

NASA Astrophysics Data System (ADS)

Matsunaga, Noriyuki

2012-06-01

The central region of our Galaxy provides us with a good opportunity to study the evolution of galactic nuclei and bulges because we can observe various phenomena in detail at the proximity of 8 kpc. There is a hierarchical alignment of stellar systems with different sizes; from the extended bulge, the nuclear bulge, down to the compact cluster around the central supermassive blackhole. The nuclear bulge contains stars as young as a few Myr, and even hosts the ongoing star formation. These are in contrast to the more extended bulge which are dominated by old stars, 10Gyr. It is considered that the star formation in the nuclear bulge is caused by fresh gas provided from the inner disk. In this picture, the nuclear bulge plays an important role as the interface between the gas supplier, the inner disk, and the galactic nucleus. Kinematics of young stars in the nuclear bulge is important to discuss the star forming process and the gas circulation in the Galactic Center. We here propose spectroscopic observations of Cepheid variable stars, 25 Myr, which we recently discovered in the nuclear bulge. The spectra taken in this proposal will allow timely estimates of the systemic velocities of the variable stars.

Linking surface morphology, composition and activity on the 67P/Churyumov-Gerasimenko’s nucleus

NASA Astrophysics Data System (ADS)

Fornasier, Sonia; Hoang, Van Hong; Hasselmann, Pedro H.; Barucci, Maria Antonieta; Feller, Clement; Prasanna Deshapriya, Jasinghege Don; Keller, Horst Uwe; OSIRIS Team

2017-10-01

The Rosetta mission orbited around the comet 67P/Churyumov-Gerasimenko for more than 2 years, getting an incredible amount of unique data of the comet nucleus and inner coma. This has enabled us to study its activity continuously from 4 AU inbound to 3.6 AU outbound, including the perihelion passage at 1.25 AU.This work focuses on the identification of the regions sources of faint jets and outbursts, and on the study of their spectrophotometric properties, from observations acquired with the OSIRIS/NAC camera during the July-October 2015 period, i.e. close to perihelion. More than 150 jets of different intensities were identified directly on the nucleus from NAC color sequences acquired in 7-11 filters covering the 250-1000 nm wavelength range, and their spectrophotometric properties studied for the first time. Some spectacular outbursts appear dominated by water ice particles, while fainter jets often show colors redder than the nucleus and appear dominated by dusty particles. Some jets are very faint and were identified on the nucleus thanks to the unprecedented spatial and temporal resolution of the ROSETTA/OSIRIS observations. Some of them have an extremely short lifetime, appearing on the cometary surface during the color sequence observations, reaching their peak in flux and then vanishing in less than a couple of minutes.We will present the results on the location, duration, and colors of active sources on the 67P nucleus from the relatively low resolution (i.e. 6-10 m/pixel) images acquired close to the perihelion passage. Some of this active regions were observed and investigated in higher resolution (up to few dm per pixel) during other phases of the mission. These observations allow us to study the morphological and spectral evolution of the regions found to be active and to further investigate the link between morphology, composition, and activity on cometary nuclei.

The Galactic Bulge Radial Velocity/Abundance Assay

NASA Astrophysics Data System (ADS)

Rich, R. M.

2012-08-01

The Bulge Radial Velocity Assay (BRAVA) measured radial velocities for ˜ 9500 late-type giants in the Galactic bulge, predominantly from -10° < l < +10° and -2° < b < -10°. The project has discovered that the bulge exhibits cylindrical rotation characteristic of bars, and two studies of dynamics (Shen et al. 2010; Wang et al. 2012 MNRAS sub.) find that bar models- either N-body formed from an instability in a preexisting disk, or a self-consistent model- can account for the observed kinematics. Studies of the Plaut field at (l,b) = 0°, -8° show that alpha enhancement is found in bulge giants even 1 kpc from the nucleus. New infrared studies extending to within 0.25° = 35 pc of the Galactic Center find no iron or alpha gradient from Baade's Window (l,b) = 0.9°, -3.9° to our innermost field, in contrast to the marked gradient observed in the outer bulge. We consider the case of the remarkable globular cluster Terzan 5, which has a strongly bimodal iron and rm [α/Fe] within its members, and we consider evidence pro and con that the bulge was assembled from dissolved clusters. The Subaru telescope has the potential to contribute to study of the Galactic bulge, especially using the Hyper Superime-Cam and planned spectroscopic modes, as well as the high resolution spectrograph. The planned Jasmine satellite series may deliver a comprehensive survey of distances and proper motions of bulge stars, and insight into the origin and importance of the X-shaped bulge.

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.

Periodic mechanical stress activates EGFR-dependent Rac1 mitogenic signals in rat nucleus pulpous cells via ERK1/2

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

Gao, Gongming; Shen, Nan; Jiang, Xuefeng

2016-01-15

The mitogenic effects of periodic mechanical stress on nucleus pulpous cells have been studied extensively but the mechanisms whereby nucleus pulpous cells sense and respond to mechanical stimulation remain a matter of debate. We explored this question by performing cell culture experiments in our self-developed periodic stress field and perfusion culture system. Under periodic mechanical stress, rat nucleus pulpous cell proliferation was significantly increased (p < 0.05 for each) and was associated with increases in the phosphorylation and activation of EGFR, Rac1, and ERK1/2 (p < 0.05 for each). Pretreatment with the ERK1/2 selective inhibitor PD98059 reduced periodic mechanical stress-induced nucleus pulpous cell proliferationmore » (p < 0.05 for each), while the activation levels of EGFR and Rac1 were not inhibited. Proliferation and phosphorylation of ERK1/2 were inhibited after pretreatment with the Rac1 inhibitor NSC23766 in nucleus pulpous cells in response to periodic mechanical stress (p < 0.05 for each), while the phosphorylation site of EGFR was not affected. Inhibition of EGFR activity with AG1478 abrogated nucleus pulpous cell proliferation (p < 0.05 for each) and attenuated Rac1 and ERK1/2 activation in nucleus pulpous cells subjected to periodic mechanical stress (p < 0.05 for each). These findings suggest that periodic mechanical stress promotes nucleus pulpous cell proliferation in part through the EGFR-Rac1-ERK1/2 signaling pathway, which links these three important signaling molecules into a mitogenic cascade. - Highlights: • The mechanism involved in nucleus pulpous cells to respond to mechanical stimuli. • Periodic mechanical stress can stimulate the phosphorylation of EGFR. • EGFR activates Rac1 and leads to rat nucleus pulpous cell proliferation. • EGFR and Rac1 activate ERK1/2 mitogenic signals in nucleus pulpous cells. • EGFR-Rac1-ERK1/2 is constitutes at least one critical signal transduction pathway.« less

Causal relationships between neurons of the nucleus incertus and the hippocampal theta activity in the rat.

PubMed

Martínez-Bellver, Sergio; Cervera-Ferri, Ana; Luque-García, Aina; Martínez-Ricós, Joana; Valverde-Navarro, Alfonso; Bataller, Manuel; Guerrero, Juan; Teruel-Marti, Vicent

2017-03-01

The nucleus incertus is a key node of the brainstem circuitry involved in hippocampal theta rhythmicity. Synchronisation exists between the nucleus incertus and hippocampal activities during theta periods. By the Granger causality analysis, we demonstrated a directional information flow between theta rhythmical neurons in the nucleus incertus and the hippocampus in theta-on states. The electrical stimulation of the nucleus incertus is also able to evoke a phase reset of the hippocampal theta wave. Our data suggest that the nucleus incertus is a key node of theta generation and the modulation network. In recent years, a body of evidence has shown that the nucleus incertus (NI), in the dorsal tegmental pons, is a key node of the brainstem circuitry involved in hippocampal theta rhythmicity. Ascending reticular brainstem system activation evokes hippocampal theta rhythm with coupled neuronal activity in the NI. In a recent paper, we showed three populations of neurons in the NI with differential firing during hippocampal theta activation. The objective of this work was to better evaluate the causal relationship between the activity of NI neurons and the hippocampus during theta activation in order to further understand the role of the NI in the theta network. A Granger causality analysis was run to determine whether hippocampal theta activity with sensory-evoked theta depends on the neuronal activity of the NI, or vice versa. The analysis showed causal interdependence between the NI and the hippocampus during theta activity, whose directional flow depended on the different neuronal assemblies of the NI. Whereas type I and II NI neurons mainly acted as receptors of hippocampal information, type III neuronal activity was the predominant source of flow between the NI and the hippocampus in theta states. We further determined that the electrical activation of the NI was able to reset hippocampal waves with enhanced theta-band power, depending on the septal area

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.

A galactic maelstrom

NASA Image and Video Library

2015-08-31

This new NASA/ESA Hubble Space Telescope shows Messier 96, a spiral galaxy just over 35 million light-years away in the constellation of Leo (The Lion). It is of about the same mass and size as the Milky Way. It was first discovered by astronomer Pierre Méchain in 1781, and added to Charles Messier’s famous catalogue of astronomical objects just four days later. The galaxy resembles a giant maelstrom of glowing gas, rippled with dark dust that swirls inwards towards the nucleus. Messier 96 is a very asymmetric galaxy; its dust and gas is unevenly spread throughout its weak spiral arms, and its core is not exactly at the galactic centre. Its arms are also asymmetrical, thought to have been influenced by the gravitational pull of other galaxies within the same group as Messier 96. This group, named the M96 Group, also includes the bright galaxies Messier 105 and Messier 95, as well as a number of smaller and fainter galaxies. It is the nearest group containing both bright spirals and a bright elliptical galaxy (Messier 105).

The Second Nucleus of NGC 7727: Direct Evidence for the Formation and Evolution of an Ultracompact Dwarf Galaxy

NASA Astrophysics Data System (ADS)

Schweizer, François; Seitzer, Patrick; Whitmore, Bradley C.; Kelson, Daniel D.; Villanueva, Edward V.

2018-01-01

We present new observations of the late-stage merger galaxy NGC 7727, including Hubble Space Telescope/WFPC2 images and long-slit spectra obtained with the Clay telescope. NGC 7727 is relatively luminous ({M}V = ‑21.7) and features two unequal tidal tails, various bluish arcs and star clusters, and two bright nuclei 480 pc apart in projection. These two nuclei have nearly identical redshifts, yet are strikingly different. The primary nucleus, hereafter Nucleus 1, fits smoothly into the central luminosity profile of the galaxy and appears—at various wavelengths—“red and dead.” In contrast, Nucleus 2 is very compact, has a tidal radius of 103 pc, and exhibits three signs of recent activity: a post-starburst spectrum, an [O III] emission line, and a central X-ray point source. Its emission-line ratios place it among Seyfert nuclei. A comparison of Nucleus 2 ({M}V = ‑15.5) with ultracompact dwarf galaxies (UCDs) suggests that it may be the best case yet for a massive UCD having formed through tidal stripping of a gas-rich disk galaxy. Evidence for this comes from its extended star formation history, long blue tidal stream, and elevated dynamical-to-stellar-mass ratio. While the majority of its stars formed ≳ 10 {Gyr} ago, ∼1/3 formed during starbursts in the past 2 Gyr. Its weak active galactic nucleus activity is likely driven by a black hole of mass 3× {10}6-8 {M}ȯ . We estimate that the former companion’s initial mass was less than half that of then NGC 7727, implying a minor merger. By now this former companion has been largely shredded, leaving behind Nucleus 2 as a freshly minted UCD that probably moves on a highly eccentric orbit. Based in part on data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

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

Effects of cochlear ablation on choline acetyltransferase activity in the rat cochlear nucleus and superior olive.

PubMed

Jin, Yong-Ming; Godfrey, Donald A; Sun, Yizhe

2005-07-01

Using microdissection and quantitative microassay, choline acetyltransferase (ChAT) activity was mapped in the cochlear nucleus (CN) and in the source nuclei of the olivocochlear bundle, the lateral superior olive and ventral nucleus of the trapezoid body. In control rats, gradients of ChAT activity were found within the major subdivisions of the CN and in the lateral superior olive. These gradients correlated with the known tonotopic organizations, with higher activities corresponding to locations representing higher sound frequencies. No gradient was found in the ventral nucleus of the trapezoid body. In rats surviving 7 days or 1 or 2 months after cochlear ablation, ChAT activity was increased 1 month after ablation in the anteroventral CN by 30-50% in most parts of the lesion-side and by 40% in the contralateral ventromedial part. ChAT activity in the lesion-side posteroventral CN was increased by approximately 40-50% at all survival times. Little change was found in the dorsal CN. Decreases of ChAT activity were also found ipsilaterally in the lateral superior olive and bilaterally in the ventral nucleus of the trapezoid body. Our results suggest that cholinergic neurons are involved in plasticity within the CN and superior olive following cochlear lesions. Copyright 2005 Wiley-Liss, Inc.

GHRELIN ACTIVATES HYPOPHYSIOTROPIC CORTICOTROPIN-RELEASING FACTOR NEURONS INDEPENDENTLY OF THE ARCUATE NUCLEUS

PubMed Central

Cabral, Agustina; Portiansky, Enrique; Sánchez-Jaramillo, Edith; Zigman, Jeffrey M.; Perello, Mario

2016-01-01

Previous work has established that the hormone ghrelin engages the hypothalamic-pituitary-adrenal neuroendocrine axis via activation of corticotropin-releasing factor (CRF) neurons of the hypothalamic paraventricular nucleus (PVN). The neuronal circuitry that mediates this effect of ghrelin is currently unknown. Here, we show that ghrelin-induced activation of PVN CRF neurons involved inhibition of γ-aminobutyric acid (GABA) inputs, likely via ghrelin binding sites that were localized at GABAergic terminals within the PVN. While ghrelin activated PVN CRF neurons in the presence of neuropeptide Y (NPY) receptor antagonists or in arcuate nucleus (ARC)-ablated mice, it failed to do it so in mice with ghrelin receptor expression limited to ARC agouti gene related protein (AgRP)/NPY neurons. These data support the notion that ghrelin activates PVN CRF neurons via inhibition of local GABAergic tone, in an ARC-independent manner. Furthermore, these data suggest that the neuronal circuits mediating ghrelin’s orexigenic action vs. its role as a stress signal are anatomically dissociated. PMID:26874559

GALACTIC ANGULAR MOMENTUM IN THE ILLUSTRIS SIMULATION: FEEDBACK AND THE HUBBLE SEQUENCE

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

Genel, Shy; Fall, S. Michael; Snyder, Gregory F.

We study the stellar angular momentum of thousands of galaxies in the Illustris cosmological simulation, which captures gravitational and gas dynamics within galaxies, as well as feedback from stars and black holes. We find that the angular momentum of the simulated galaxies matches observations well, and in particular two distinct relations are found for late-type versus early-type galaxies. The relation for late-type galaxies corresponds to the value expected from full conservation of the specific angular momentum generated by cosmological tidal torques. The relation for early-type galaxies corresponds to retention of only ∼30% of that, but we find that those early-typemore » galaxies with low angular momentum at z = 0 nevertheless reside at high redshift on the late-type relation. Some of them abruptly lose angular momentum during major mergers. To gain further insight, we explore the scaling relations in simulations where the galaxy formation physics is modified with respect to the fiducial model. We find that galactic winds with high mass-loading factors are essential for obtaining the high angular momentum relation typical for late-type galaxies, while active galactic nucleus feedback largely operates in the opposite direction. Hence, feedback controls the stellar angular momentum of galaxies, and appears to be instrumental for establishing the Hubble sequence.« less

The 60 Month All-Sky Burst Alert Telescope Survey of Active Galactic Nucleus and the Anisotropy of Nearby AGNs

NASA Technical Reports Server (NTRS)

Ajello, M.; Alexander, D. M.; Greiner, J.; Madejeski, G. M.; Gehrels, N.; Burlon, D.

2014-01-01

Surveys above 10 keV represent one of the best resources to provide an unbiased census of the population of active galactic nuclei (AGNs). We present the results of 60 months of observation of the hard X-ray sky with Swift/Burst Alert Telescope (BAT). In this time frame, BAT-detected (in the 15-55 keV band) 720 sources in an all-sky survey of which 428 are associated with AGNs, most of which are nearby. Our sample has negligible incompleteness and statistics a factor of approx. 2 larger over similarly complete sets of AGNs. Our sample contains (at least) 15 bona fide Compton-thick AGNs and 3 likely candidates. Compton-thick AGNs represent approx. 5% of AGN samples detected above 15 keV. We use the BAT data set to refine the determination of the log N-log S of AGNs which is extremely important, now that NuSTAR prepares for launch, toward assessing the AGN contribution to the cosmic X-ray background. We show that the log N-log S of AGNs selected above 10 keV is now established to approx. 10% precision. We derive the luminosity function of Compton-thick AGNs and measure a space density of 7.9(+4.1/-2.9)× 10(exp -5)/cubic Mpc for objects with a de-absorbed luminosity larger than 2 × 10(exp 42) erg / s. As the BAT AGNs are all mostly local, they allow us to investigate the spatial distribution of AGNs in the nearby universe regardless of absorption. We find concentrations of AGNs that coincide spatially with the largest congregations of matter in the local (much < 85 Mpc) universe. There is some evidence that the fraction of Seyfert 2 objects is larger than average in the direction of these dense regions..

Influence of the active nucleus on the multiphase interstellar medium in NGC 1068

NASA Technical Reports Server (NTRS)

Bland-Hawthorn, Jonathan; Weisheit, Jon; Cecil, Gerald; Sokolowski, James

1993-01-01

The luminous spiral NGC 1068 has now been imaged from x-ray to radio wavelengths at comparably high resolution (approximately less than 5 in. FWHM). The bolometric luminosity of this well-known Seyfert is shared almost equally between the active nucleus and an extended 'starburst' disk. In an ongoing study, we are investigating the relative importance of the nucleus and the disk in powering the wide range of energetic activity observed throughout the galaxy. Our detailed analysis brings together a wealth of data: ROSAT HRI observations, VLA lambda lambda 6-20 cu cm and OVRO interferometry, lambda lambda 0.4-10.8 micron imaging, and Fabry-Perot spectrophotometry.

Momentum loss in proton-nucleus and nucleus-nucleus collisions

NASA Technical Reports Server (NTRS)

Khan, Ferdous; Townsend, Lawrence W.

1993-01-01

An optical model description, based on multiple scattering theory, of longitudinal momentum loss in proton-nucleus and nucleus-nucleus collisions is presented. The crucial role of the imaginary component of the nucleon-nucleon transition matrix in accounting for longitudinal momentum transfer is demonstrated. Results obtained with this model are compared with Intranuclear Cascade (INC) calculations, as well as with predictions from Vlasov-Uehling-Uhlenbeck (VUU) and quantum molecular dynamics (QMD) simulations. Comparisons are also made with experimental data where available. These indicate that the present model is adequate to account for longitudinal momentum transfer in both proton-nucleus and nucleus-nucleus collisions over a wide range of energies.

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.

Control of nucleus accumbens activity with neurofeedback

PubMed Central

Greer, Stephanie M.; Trujillo, Andrew J.; Glover, Gary H.; Knutson, Brian

2014-01-01

The nucleus accumbens (NAcc) plays critical roles in healthy motivation and learning, as well as in psychiatric disorders (including schizophrenia and attention deficit hyperactivity disorder). Thus, techniques that confer control of NAcc activity might inspire new therapeutic interventions. By providing second-to-second temporal resolution of activity in small subcortical regions, functional magnetic resonance imaging (fMRI) can resolve online changes in NAcc activity, which can then be presented as “neurofeedback.” In an fMRI-based neurofeedback experiment designed to elicit NAcc activity, we found that subjects could increase their own NAcc activity, and that display of neurofeedback significantly enhanced their ability to do so. Subjects were not as capable of decreasing their NAcc activity, however, and enhanced control did not persist after subsequent removal of neurofeedback. Further analyses suggested that individuals who recruited positive arousal affect were better able to increase NAcc activity in response to neurofeedback, and that NAcc neurofeedback also elicited functionally correlated activity in the medial prefrontal cortex. Together, these findings suggest that humans can modulate their own NAcc activity and that fMRI-based neurofeedback may augment their efforts. The observed association between positive arousal and effective NAcc control further supports an anticipatory affect account of NAcc function. PMID:24705203

Control of nucleus accumbens activity with neurofeedback.

PubMed

Greer, Stephanie M; Trujillo, Andrew J; Glover, Gary H; Knutson, Brian

2014-08-01

The nucleus accumbens (NAcc) plays critical roles in healthy motivation and learning, as well as in psychiatric disorders (including schizophrenia and attention deficit hyperactivity disorder). Thus, techniques that confer control of NAcc activity might inspire new therapeutic interventions. By providing second-to-second temporal resolution of activity in small subcortical regions, functional magnetic resonance imaging (fMRI) can resolve online changes in NAcc activity, which can then be presented as "neurofeedback." In an fMRI-based neurofeedback experiment designed to elicit NAcc activity, we found that subjects could increase their own NAcc activity, and that display of neurofeedback significantly enhanced their ability to do so. Subjects were not as capable of decreasing their NAcc activity, however, and enhanced control did not persist after subsequent removal of neurofeedback. Further analyses suggested that individuals who recruited positive aroused affect were better able to increase NAcc activity in response to neurofeedback, and that NAcc neurofeedback also elicited functionally correlated activity in the medial prefrontal cortex. Together, these findings suggest that humans can modulate their own NAcc activity and that fMRI-based neurofeedback may augment their efforts. The observed association between positive arousal and effective NAcc control further supports an anticipatory affect account of NAcc function. Copyright © 2014 Elsevier Inc. All rights reserved.

Launching of Active Galactic Nuclei Jets

NASA Astrophysics Data System (ADS)

Tchekhovskoy, Alexander

As black holes accrete gas, they often produce relativistic, collimated outflows, or jets. Jets are expected to form in the vicinity of a black hole, making them powerful probes of strong-field gravity. However, how jet properties (e.g., jet power) connect to those of the accretion flow (e.g., mass accretion rate) and the black hole (e.g., black hole spin) remains an area of active research. This is because what determines a crucial parameter that controls jet properties—the strength of large-scale magnetic flux threading the black hole—remains largely unknown. First-principles computer simulations show that due to this, even if black hole spin and mass accretion rate are held constant, the simulated jet powers span a wide range, with no clear winner. This limits our ability to use jets as a quantitative diagnostic tool of accreting black holes. Recent advances in computer simulations demonstrated that accretion disks can accumulate large-scale magnetic flux on the black hole, until the magnetic flux becomes so strong that it obstructs gas infall and leads to a magnetically-arrested disk (MAD). Recent evidence suggests that central black holes in jetted active galactic nuclei and tidal disruptions are surrounded by MADs. Since in MADs both the black hole magnetic flux and the jet power are at their maximum, well-defined values, this opens up a new vista in the measurements of black hole masses and spins and quantitative tests of accretion and jet theory.

The 2-79 keV X-ray Spectrum of the Circinus Galaxy with NuSTAR, XMM-Newton and Chandra: a Fully Compton-Thick Active Galactic Nucleus

DOE PAGES

Arevalo, P.; Bauer, F. E.; Puccetti, S.; ...

2014-07-30

Here, the Circinus galaxy is one of the closest obscured active galactic nuclei (AGNs), making it an ideal target for detailed study. Combining archival Chandra and XMM-Newton data with new NuSTAR observations, we model the 2-79 keV spectrum to constrain the primary AGN continuum and to derive physical parameters for the obscuring material. Chandra's high angular resolution allows a separation of nuclear and off-nuclear galactic emission. In the off-nuclear diffuse emission, we find signatures of strong cold reflection, including high equivalent-width neutral Fe lines. This Compton-scattered off-nuclear emission amounts to 18% of the nuclear flux in the Fe line region,more » but becomes comparable to the nuclear emission above 30 keV. The new analysis no longer supports a prominent transmitted AGN component in the observed band. We find that the nuclear spectrum is consistent with Compton scattering by an optically thick torus, where the intrinsic spectrum is a power law of photon index Γ = 2.2-2.4, the torus has an equatorial column density of N H = (6-10) × 10 24 cm –2, and the intrinsic AGN 2-10 keV luminosity is (2.3-5.1) × 10 42 erg s –1. These values place Circinus along the same relations as unobscured AGNs in accretion rate versus Γ and L X versus L IR phase space. NuSTAR's high sensitivity and low background allow us to study the short timescale variability of Circinus at X-ray energies above 10 keV for the first time. Here, the lack of detected variability favors a Compton-thick absorber, in line with the spectral fitting results.« less

Subthalamic nucleus activity optimizes maximal effort motor responses in Parkinson's disease.

PubMed

Anzak, Anam; Tan, Huiling; Pogosyan, Alek; Foltynie, Thomas; Limousin, Patricia; Zrinzo, Ludvic; Hariz, Marwan; Ashkan, Keyoumars; Bogdanovic, Marko; Green, Alexander L; Aziz, Tipu; Brown, Peter

2012-09-01

The neural substrates that enable individuals to achieve their fastest and strongest motor responses have long been enigmatic. Importantly, characterization of such activities may inform novel therapeutic strategies for patients with hypokinetic disorders, such as Parkinson's disease. Here, we ask whether the basal ganglia may play an important role, not only in the attainment of maximal motor responses under standard conditions but also in the setting of the performance enhancements known to be engendered by delivery of intense stimuli. To this end, we recorded local field potentials from deep brain stimulation electrodes implanted bilaterally in the subthalamic nuclei of 10 patients with Parkinson's disease, as they executed their fastest and strongest handgrips in response to a visual cue, which was accompanied by a brief 96-dB auditory tone on random trials. We identified a striking correlation between both theta/alpha (5-12 Hz) and high-gamma/high-frequency (55-375 Hz) subthalamic nucleus activity and force measures, which explained close to 70% of interindividual variance in maximal motor responses to the visual cue alone, when patients were ON their usual dopaminergic medication. Loud auditory stimuli were found to enhance reaction time and peak rate of development of force still further, independent of whether patients were ON or OFF l-DOPA, and were associated with increases in subthalamic nucleus power over a broad gamma range. However, the contribution of this broad gamma activity to the performance enhancements observed was only modest (≤13%). The results implicate frequency-specific subthalamic nucleus activities as substantial factors in optimizing an individual's peak motor responses at maximal effort of will, but much less so in the performance increments engendered by intense auditory stimuli.

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.

Detectability of galactic supernova neutrinos coherently scattered on xenon nuclei in XMASS

NASA Astrophysics Data System (ADS)

Abe, K.; Hiraide, K.; Ichimura, K.; Kishimoto, Y.; Kobayashi, K.; Kobayashi, M.; Moriyama, S.; Nakagawa, K.; Nakahata, M.; Norita, T.; Ogawa, H.; Sekiya, H.; Takachio, O.; Takeda, A.; Yamashita, M.; Yang, B. S.; Kim, N. Y.; Kim, Y. D.; Tasaka, S.; Liu, J.; Martens, K.; Suzuki, Y.; Fujita, R.; Hosokawa, K.; Miuchi, K.; Oka, N.; Onishi, Y.; Takeuchi, Y.; Kim, Y. H.; Lee, J. S.; Lee, K. B.; Lee, M. K.; Fukuda, Y.; Itow, Y.; Kegasa, R.; Kobayashi, K.; Masuda, K.; Takiya, H.; Uchida, H.; Nishijima, K.; Fujii, K.; Murayama, I.; Nakamura, S.; Xmass Collaboration

2017-03-01

The coherent elastic neutrino-nucleus scattering (CEvNS) plays a crucial role at the final evolution of stars. The detection of it would be of importance in astroparticle physics. Among all available neutrino sources, galactic supernovae give the highest neutrino flux in the MeV range. Among all liquid xenon dark matter experiments, XMASS has the largest sensitive volume and light yield. The possibility to detect galactic supernova via the CEvNS-process on xenon nuclei in the current XMASS detector was investigated. The total number of events integrated in about 18 s after the explosion of a supernova 10 kpc away from the Earth was expected to be from 3.5 to 21.1, depending on the supernova model used to predict the neutrino flux, while the number of background events in the same time window was measured to be negligible. All lead to very high possibility to detect CEvNS experimentally for the first time utilizing the combination of galactic supernovae and the XMASS detector. In case of a supernova explosion as close as Betelgeuse, the total observable events can be more than ∼ 104, making it possible to distinguish different supernova models by examining the evolution of neutrino event rate in XMASS.

CRTC2 activation in the suprachiasmatic nucleus, but not paraventricular nucleus, varies in a diurnal fashion and increases with nighttime light exposure.

PubMed

Highland, Julie A; Weiser, Michael J; Hinds, Laura R; Spencer, Robert L

2014-10-01

Entrainment of the intrinsic suprachiasmatic nucleus (SCN) molecular clock to the light-dark cycle depends on photic-driven intracellular signal transduction responses of SCN neurons that converge on cAMP response element-binding protein (CREB)-mediated regulation of gene transcription. Characterization of the CREB coactivator proteins CREB-regulated transcriptional coactivators (CRTCs) has revealed a greater degree of differential activity-dependent modulation of CREB transactivational function than previously appreciated. In confirmation of recent reports, we found an enrichment of crtc2 mRNA and prominent CRTC2 protein expression within the SCN of adult male rats. With use of a hypothalamic organotypic culture preparation for initial CRTC2-reactive antibody characterization, we found that CRTC2 immunoreactivity in hypothalamic neurons shifted from a predominantly cytoplasmic profile under basal culture conditions to a primarily nuclear localization (CRTC2 activation) 30 min after adenylate cyclase stimulation. In adult rat SCN, we found a diurnal variation in CRTC2 activation (peak at zeitgeber time of 4 h and trough at zeitgeber time of 16-20 h) but no variation in the total number of CRTC2-immunoreactive cells. There was no diurnal variation of CRTC2 activation in the hypothalamic paraventricular nucleus, another site of enriched CRTC2 expression. Exposure of rats to light (50 lux) for 30 min during the second half of their dark (nighttime) phase produced CRTC2 activation. We observed in the SCN a parallel change in the expression of a CREB-regulated gene (FOS). In contrast, nighttime light exposure had no effect on CRTC2 activation or FOS expression in the paraventricular nucleus, nor did it affect corticosterone hormone levels. These results suggest that CRTC2 participates in CREB-dependent photic entrainment of SCN function. Copyright © 2014 the American Physiological Society.

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.

Gas Flows in Dual Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Mueller Sanchez, Francisco; Comerford, Julia M.; Davies, Richard; Treister, Ezequiel; Privon, George C.; Nevin, Becky

2018-06-01

Dual Active Galactic Nuclei (AGN) are the Rosetta stone to understand the role of galaxy mergers in triggering nuclear activity and regulating black hole (BH) and galaxy growth. But very little is known about the physical processes required to effectively trigger AGN activity and regulate the growth of the two BHs. The work I will present here characterizes for the first time the properties of the stars, gas (molecular, ionized, and highly-ionized) and dust in all the confirmed dual AGN at z < 0.05, using Keck/OSIRIS, VLT/SINFONI, SOFIA/FORCAST, and HST data. I will focus on the interplay between the several complex processes observed in dual AGN, using as an example the prototypical merger system NGC 6240: vigorous star formation, two AGNs, outflowing winds of ionized gas, rippling dust and gas lanes, and tidal tails. In this galaxy, we observe for the first time a dual outflow of different species of gas: an AGN-driven outflow of highly-ionized gas to the northeast and a starburst-driven outflow of ionized hydrogen to the northwest. This shows that stellar feedback and supermassive black hole feedback can work in tandem to regulate the stellar growth of a galaxy after a merger event. These results open a new door to studies of dual AGN and AGN pairs in general, and enable dual AGN to be used, for the first time, for studies of galaxy evolution.

Formation, structure, and evolution of boiling nucleus and interfacial tension between bulk liquid phase and nucleus

NASA Astrophysics Data System (ADS)

Wang, Xiao-Dong; Peng, Xiao-Feng; Tian, Yong; Wang, Bu-Xuan

2005-05-01

In this paper, the concept of the molecular free path is introduced to derive a criterion distinguishing active molecules from inactive molecules in liquid phase. A concept of the critical aggregation concentration (CAC) of active molecules is proposed to describe the physical configuration before the formation of a nucleus during vapor-liquid phase transition. All active molecules exist as monomers when the concentration of active molecules is lower than CAC, while the active molecules will generate aggregation once the concentration of the active molecules reaches CAC. However, these aggregates with aggregation number, N, smaller than five can steadily exist in bulk phase. The other excess active molecules can only produce infinite aggregation and form a critical nucleus of vapor-liquid phase transition. Without any outer perturbation the state point of CAC corresponds to the critical superheated or supercooled state. Meanwhile, a model of two-region structure of a nucleus is proposed to describe nucleus evolution. The interfacial tension between bulk liquid phase and nucleus is dependent of the density gradient in the transition region and varies with the structure change of the transition region. With the interfacial tension calculated using this model, the predicted nucleation rate is very close to the experimental measurement. Furthermore, this model and associated analysis provides solid theoretical evidences to clarify the definition of nucleation rate and understand nucleation phenomenon with the insight into the physical nature.

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

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.

Normalizing motor-related brain activity: subthalamic nucleus stimulation in Parkinson disease.

PubMed

Grafton, S T; Turner, R S; Desmurget, M; Bakay, R; Delong, M; Vitek, J; Crutcher, M

2006-04-25

To test whether therapeutic unilateral deep brain stimulation (DBS) of the subthalamic nucleus (STN) in patients with Parkinson disease (PD) leads to normalization in the pattern of brain activation during movement execution and control of movement extent. Six patients with PD were imaged off medication by PET during performance of a visually guided tracking task with the DBS voltage programmed for therapeutic (effective) or subtherapeutic (ineffective) stimulation. Data from patients with PD during ineffective stimulation were compared with a group of 13 age-matched control subjects to identify sites with abnormal patterns of activation. Conjunction analysis was used to identify those areas in patients with PD where activity normalized when they were treated with effective stimulation. For movement execution, effective DBS caused an increase of activation in the supplementary motor area (SMA), superior parietal cortex, and cerebellum toward a more normal pattern. At rest, effective stimulation reduced overactivity of SMA. Therapeutic stimulation also induced reductions of movement related "overactivity" compared with healthy subjects in prefrontal, temporal lobe, and basal ganglia circuits, consistent with the notion that many areas are recruited to compensate for ineffective motor initiation. Normalization of activity related to the control of movement extent was associated with reductions of activity in primary motor cortex, SMA, and basal ganglia. Effective subthalamic nucleus stimulation leads to task-specific modifications with appropriate recruitment of motor areas as well as widespread, nonspecific reductions of compensatory or competing cortical activity.

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.

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.

Luminosity and redshift dependence of the covering factor of active galactic nuclei viewed with WISE and Sloan digital sky survey

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

Toba, Y.; Matsuhara, H.; Oyabu, S.

2014-06-10

In this work, we investigate the dependence of the covering factor (CF) of active galactic nuclei (AGNs) on the mid-infrared (MIR) luminosity and the redshift. We constructed 12 and 22 μm luminosity functions (LFs) at 0.006 ≤z ≤ 0.3 using Wide-field Infrared Survey Explorer (WISE) data. Combining the WISE catalog with Sloan Digital Sky Survey (SDSS) spectroscopic data, we selected 223,982 galaxies at 12 μm and 25,721 galaxies at 22 μm for spectroscopic classification. We then identified 16,355 AGNs at 12 μm and 4683 AGNs at 22 μm by their optical emission lines and cataloged classifications in the SDSS. Followingmore » that, we estimated the CF as the fraction of Type 2 AGN in all AGNs whose MIR emissions are dominated by the active nucleus (not their host galaxies) based on their MIR colors. We found that the CF decreased with increasing MIR luminosity, regardless of the choice of Type 2 AGN classification criteria, and the CF did not change significantly with redshift for z ≤ 0.2. Furthermore, we carried out various tests to determine the influence of selection bias and confirmed that similar dependences exist, even when taking these uncertainties into account. The luminosity dependence of the CF can be explained by the receding torus model, but the 'modified' receding torus model gives a slightly better fit, as suggested by Simpson.« less

Descending projections from the nucleus accumbens shell excite activity of taste-responsive neurons in the nucleus of the solitary tract in the hamster.

PubMed

Li, Cheng-Shu; Lu, Da-Peng; Cho, Young K

2015-06-01

The nucleus of the solitary tract (NST) and the parabrachial nuclei (PbN) are the first and second relays in the rodent central taste pathway. A series of electrophysiological experiments revealed that spontaneous and taste-evoked activities of brain stem gustatory neurons are altered by descending input from multiple forebrain nuclei in the central taste pathway. The nucleus accumbens shell (NAcSh) is a key neural substrate of reward circuitry, but it has not been verified as a classical gustatory nucleus. A recent in vivo electrophysiological study demonstrated that the NAcSh modulates the spontaneous and gustatory activities of hamster pontine taste neurons. In the present study, we investigated whether activation of the NAcSh modulates gustatory responses of the NST neurons. Extracellular single-unit activity was recorded from medullary neurons in urethane-anesthetized hamsters. After taste response was confirmed by delivery of sucrose, NaCl, citric acid, and quinine hydrochloride to the anterior tongue, the NAcSh was stimulated bilaterally with concentric bipolar stimulating electrodes. Stimulation of the ipsilateral and contralateral NAcSh induced firings from 54 and 37 of 90 medullary taste neurons, respectively. Thirty cells were affected bilaterally. No inhibitory responses or antidromic invasion was observed after NAcSh activation. In the subset of taste cells tested, high-frequency electrical stimulation of the NAcSh during taste delivery enhanced taste-evoked neuronal firing. These results demonstrate that two-thirds of the medullary gustatory neurons are under excitatory descending influence from the NAcSh, which is a strong indication of communication between the gustatory pathway and the mesolimbic reward pathway. Copyright © 2015 the American Physiological Society.

Activation of the cerebellar cortex and the dentate nucleus in a prism adaptation fMRI study.

PubMed

Küper, Michael; Wünnemann, Meret J S; Thürling, Markus; Stefanescu, Roxana M; Maderwald, Stefan; Elles, Hans G; Göricke, Sophia; Ladd, Mark E; Timmann, Dagmar

2014-04-01

During prism adaptation two types of learning processes can be distinguished. First, fast strategic motor control responses are predominant in the early course of prism adaptation to achieve rapid error correction within few trials. Second, slower spatial realignment occurs among the misaligned visual and proprioceptive sensorimotor coordinate system. The aim of the present ultra-highfield (7T) functional magnetic resonance imaging (fMRI) study was to explore cerebellar cortical and dentate nucleus activation during the course of prism adaptation in relation to a similar visuomotor task without prism exposure. Nineteen young healthy participants were included into the study. Recently developed normalization procedures were applied for the cerebellar cortex and the dentate nucleus. By means of subtraction analysis (early prism adaptation > visuomotor, early prism adaptation > late prism adaptation) we identified ipsilateral activation associated with strategic motor control responses within the posterior cerebellar cortex (lobules VIII and IX) and the ventro-caudal dentate nucleus. During the late phase of adaptation we observed pronounced activation of posterior parts of lobule VI, although subtraction analyses (late prism adaptation > visuomotor) remained negative. These results are in good accordance with the concept of a representation of non-motor functions, here strategic control, within the ventro-caudal dentate nucleus. Copyright © 2013 Wiley Periodicals, Inc.

Actomyosin contractility rotates the cell nucleus.

PubMed

Kumar, Abhishek; Maitra, Ananyo; Sumit, Madhuresh; Ramaswamy, Sriram; Shivashankar, G V

2014-01-21

The cell nucleus functions amidst active cytoskeletal filaments, but its response to their contractile stresses is largely unexplored. We study the dynamics of the nuclei of single fibroblasts, with cell migration suppressed by plating onto micro-fabricated patterns. We find the nucleus undergoes noisy but coherent rotational motion. We account for this observation through a hydrodynamic approach, treating the nucleus as a highly viscous inclusion residing in a less viscous fluid of orientable filaments endowed with active stresses. Lowering actin contractility selectively by introducing blebbistatin at low concentrations drastically reduced the speed and coherence of the angular motion of the nucleus. Time-lapse imaging of actin revealed a correlated hydrodynamic flow around the nucleus, with profile and magnitude consistent with the results of our theoretical approach. Coherent intracellular flows and consequent nuclear rotation thus appear to be an intrinsic property of cells.

Constraints on two active galactic nuclei in the merger remnant cosmos J100043.15+020637.2

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

Wrobel, J. M.; Comerford, J. M.; Middelberg, E., E-mail: jwrobel@nrao.edu, E-mail: julie.comerford@colorado.edu, E-mail: middelberg@astro.rub.de

2014-02-20

COSMOS J100043.15+020637.2 is a merger remnant at z = 0.36 with two optical nuclei, NW and SE, offset by 500 mas (2.5 kpc). Prior studies suggest two competing scenarios for these nuclei: (1) SE is an active galactic nucleus (AGN) lost from NW due to a gravitational-wave recoil. (2) NW and SE each contain an AGN, signaling a gravitational-slingshot recoil or inspiralling AGNs. We present new images from the Very Large Array (VLA) at a frequency ν = 9.0 GHz and a FWHM resolution θ = 320 mas (1.6 kpc), and the Very Long Baseline Array (VLBA) at ν =more » 1.52 GHz and θ = 15 mas (75 pc). The VLA imaging is sensitive to emission driven by AGNs and/or star formation, while the VLBA imaging is sensitive only to AGN-driven emission. No radio emission is detected at these frequencies. Folding in prior results, we find: (a) The properties of SE and its adjacent X-ray feature resemble those of the Type 1 AGN in NGC 4151, albeit with a much higher narrow emission-line luminosity. (b) The properties of NW are consistent with it hosting a Compton-thick AGN that warms ambient dust, photoionizes narrow emission-line gas, and is free-free absorbed by that gas. Finding (a) is consistent with scenarios (a) and (b). Finding (b) weakens the case for scenario (a) and strengthens the case for scenario (b). Follow-up observations are suggested.« less

Molecular Gas Feeding the Circumnuclear Disk of the Galactic Center

NASA Astrophysics Data System (ADS)

Hsieh, Pei-Ying; Koch, Patrick M.; Ho, Paul T. P.; Kim, Woong-Tae; Tang, Ya-Wen; Wang, Hsiang-Hsu; Yen, Hsi-Wei; Hwang, Chorng-Yuan

2017-09-01

The interaction between a supermassive black hole (SMBH) and the surrounding material is of primary importance in modern astrophysics. The detection of the molecular 2 pc circumnuclear disk (CND) immediately around the Milky Way SMBH, SgrA*, provides a unique opportunity to study SMBH accretion at subparsec scales. Our new wide-field CS(J = 2 - 1) map toward the Galactic center (GC) reveals multiple dense molecular streamers that originated from the ambient clouds 20 pc further out, and that are connected to the central 2 pc of the CND. These dense gas streamers appear to carry gas directly toward the nuclear region and might be captured by the central potential. Our phase-plot analysis indicates that these streamers show a signature of rotation and inward radial motion with progressively higher velocities as the gas approaches the CND and finally ends up corotating with the CND. Our results might suggest a possible mechanism of gas feeding the CND from 20 pc around 2 pc in the GC. In this paper, we discuss the morphology and the kinematics of these streamers. As the nearest observable Galactic nucleus, this feeding process may have implications for understanding the processes in extragalactic nuclei.

Infrared fine-structure line diagnostics of shrouded active galactic nuclei

NASA Technical Reports Server (NTRS)

Voit, G. M.

1992-01-01

The ultraluminous far-IR galaxies revealed by IRAS, quasar-like in luminosity but smothered in molecular gas, probably conceal either immense starbursts or luminous active nuclei. In both scenarios, these objects ought to produce copious infrared fine-structure emission with several lines comparable to H-beta in luminosity. We show how these lines, if detected, can be used to determine the electron densities and far-IR obscurations of shrouded photoionized regions and to constrain the shape and ionization parameter of the ionizing spectra. The presence of Ne v emission in particular will distinguish shrouded AGNs from shrouded starbursts. Since all active galaxies photoionize at least some surrounding material, these diagnostics can also be applied to active galaxies in general and will aid in studying how an active nucleus interacts with the interstellar medium of its host galaxy.

Actomyosin contractility rotates the cell nucleus

PubMed Central

Kumar, Abhishek; Maitra, Ananyo; Sumit, Madhuresh; Ramaswamy, Sriram; Shivashankar, G. V.

2014-01-01

The cell nucleus functions amidst active cytoskeletal filaments, but its response to their contractile stresses is largely unexplored. We study the dynamics of the nuclei of single fibroblasts, with cell migration suppressed by plating onto micro-fabricated patterns. We find the nucleus undergoes noisy but coherent rotational motion. We account for this observation through a hydrodynamic approach, treating the nucleus as a highly viscous inclusion residing in a less viscous fluid of orientable filaments endowed with active stresses. Lowering actin contractility selectively by introducing blebbistatin at low concentrations drastically reduced the speed and coherence of the angular motion of the nucleus. Time-lapse imaging of actin revealed a correlated hydrodynamic flow around the nucleus, with profile and magnitude consistent with the results of our theoretical approach. Coherent intracellular flows and consequent nuclear rotation thus appear to be an intrinsic property of cells. PMID:24445418

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.

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.

Modulation of the subthalamic nucleus activity by serotonergic agents and fluoxetine administration.

PubMed

Aristieta, A; Morera-Herreras, T; Ruiz-Ortega, J A; Miguelez, C; Vidaurrazaga, I; Arrue, A; Zumarraga, M; Ugedo, L

2014-05-01

Within the basal ganglia, the subthalamic nucleus (STN) is the only glutamatergic structure and occupies a central position in the indirect pathway. In rat, the STN receives serotonergic input from the dorsal raphe nucleus and expresses serotonergic receptors. This study examined the consequences of serotonergic neurotransmission modulation on STN neuron activity. In vivo single-unit extracellular recordings, HPLC determination, and rotarod and bar test were performed in control, 4-chloro-DL-phenylalanine methyl ester hydrochloride- (pCPA, a serotonin synthesis inhibitor) and chronically fluoxetine-treated rats. The pCPA treatment and the administration of serotonin (5-HT) receptor antagonists increased number of bursting neurons in the STN. The systemic administration of the 5-HT(1A) agonist, 8-OH-DPAT, decreased the firing rate and increased the coefficient of variation of STN neurons in pCPA-treated rats but not in control animals. Additionally, microinjection of 8-OH-DPAT into the STN reduced the firing rate of STN neurons, while microinjection of the 5-HT(2C) agonist, Ro 60-0175, increased the firing rate in both control and fluoxetine-treated animals. Finally, the fluoxetine challenge increased the firing rate of STN neurons in fluoxetine-treated rats and induced catalepsy. Our results indicate that the depletion and the blockage of 5-HT modify STN neuron firing pattern. STN neuron activity is under the control of 5-HT(1A) and 5-HT(2C) receptors located both inside and outside the STN. Finally, fluoxetine increases STN neuron activity in chronically fluoxetine-treated rats, which may explain the role of this nucleus in fluoxetine-induced extrapyramidal side effects.

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.

Gamma-ray and X-ray emission from the Galactic centre: hints on the nuclear star cluster formation history

NASA Astrophysics Data System (ADS)

Arca-Sedda, Manuel; Kocsis, Bence; Brandt, Timothy D.

2018-06-01

The Milky Way centre exhibits an intense flux in the gamma and X-ray bands, whose origin is partly ascribed to the possible presence of a large population of millisecond pulsars (MSPs) and cataclysmic variables (CVs), respectively. However, the number of sources required to generate such an excess is much larger than what is expected from in situ star formation and evolution, opening a series of questions about the formation history of the Galactic nucleus. In this paper we make use of direct N-body simulations to investigate whether these sources could have been brought to the Galactic centre by a population of star clusters that underwent orbital decay and formed the Galactic nuclear star cluster (NSC). Our results suggest that the gamma ray emission is compatible with a population of MSPs that were mass segregated in their parent clusters, while the X-ray emission is consistent with a population of CVs born via dynamical interactions in dense star clusters. Combining observations with our modelling, we explore how the observed γ ray flux can be related to different NSC formation scenarios. Finally, we show that the high-energy emission coming from the galactic central regions can be used to detect black holes heavier than 105M⊙ in nearby dwarf galaxies.

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

[Local GABA-ergic modulation of serotonergic neuron activity in the nucleus raphe magnus].

PubMed

Iniushkin, A N; Merkulova, N A; Orlova, A O; Iniushkina, E M

2009-07-01

In voltage-clamp experimental on slices of the rat brainstem the effects of 5-HT and GABA on serotonergic neurons of nucleus raphe magnus were investigated. Local applications of 5-HT induced an increase in IPCSs frequency and amplitude in 45% of serotonergic cells. The effect suppressed by the blocker of fast sodium channels tetradotoxin. Antagonist of GABA receptor gabazine blocked IPSCs in neurons both sensitive and non-sensitive to 5-HT action. Applications of GABA induced a membrane current (I(GABA)), which was completely blocked by gabazine. The data suggest self-control of the activity of serotonergic neurons in nucleus raphe magnus by negative feedback loop via local GABAergic interneurons.

A Comparison of the X-Ray Emission from Tidal Disruption Events with those of Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Auchettl, Katie; Ramirez-Ruiz, Enrico; Guillochon, James

2018-01-01

One of the main challenges of current tidal disruption events (TDEs) studies is that emission arising from active galactic nucleus (AGN) activity may potentially mimic the expected X-ray emission of a TDE. Here we compare the X-ray properties of TDEs and AGNs to determine a set of characteristics that would allow us to discriminate between flares arising from these two objects. We find that at peak, TDEs are brighter than AGNs found at similar redshifts. However, compared to pre-flare upper limits, highly variable AGNs can produce flares of a similar order of magnitude as those seen from X-ray TDEs. Nevertheless, TDEs decay significantly more monotonically, and their emission exhibits little variation in spectral hardness as a function of time. We also find that X-ray TDEs are less absorbed, and their emission is much softer than the emission detected from AGNs found at similar redshifts. We derive the X-ray luminosity function (LF) for X-ray TDEs using the events from Auchettl et al. Interestingly, our X-ray LF closely matches the theoretically derived LF by Milosavljević et al., which assumes a higher TDE rate currently estimated from observations. Using our results and the results of Stone & Metzger, we estimate a TDE rate of (0.7–4.7) × 10‑4 year‑1 per galaxy, higher than current observational estimates. We find that TDEs can contribute significantly to the LF of AGNs for z ≲ 0.4, while there is no evidence that TDEs influence the growth of 106–7 M ⊙ BHs. However, BHs < 106 M ⊙ can grow from TDEs arising from super-Eddington accretion without contributing significantly to the observed AGN LF at z = 0.

Chronic methamphetamine exposure significantly decreases microglia activation in the arcuate nucleus.

PubMed

Lloyd, Steven A; Corkill, Beau; Bruster, Matthew C; Roberts, Rick L; Shanks, Ryan A

2017-07-01

Methamphetamine is a powerful psychostimulant drug and its use and abuse necessitates a better understanding of its neurobiobehavioral effects. The acute effects of binge dosing of methamphetamine on the neurons in the CNS are well studied. However, the long-term effects of chronic, low-dose methamphetamine are less well characterized, especially in other cell types and areas outside of the major dopamine pathways. Mice were administered 5mg/kg/day methamphetamine for ten days and brain tissue was analyzed using histochemistry and image analysis. Increased microglia activity in the striatum confirmed toxic effects of methamphetamine in this brain region using this dosing paradigm. A significant decrease in microglia activity in the arcuate nucleus of the hypothalamus was observed with no effect noted on dopamine neurons in the arcuate nucleus. Given the importance of this area in homeostatic and neuroendocrine regulation, the current study highlights the need to more fully understand the systemic effects of chronic, low-dose methamphetamine use. The novel finding of microglia downregulation after chronic methamphetamine could lead to advances in understanding neuroinflammatory responses towards addiction treatment and protection from psychostimulant-induced neurotoxicity. Copyright © 2017 Elsevier B.V. All rights reserved.

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 onset of galactic winds in early-type galaxies

NASA Technical Reports Server (NTRS)

Jones, Christine

1992-01-01

We completed the spectral analysis of 31 early-type galaxies to investigate whether their x-ray emission was predominantly due to thermal bremsstrahlung from a hot gaseous corona or emission from discrete, galactic sources such as x-ray binaries. If a corona dominates the x-ray emission, its spectra is expected to be relatively cool (0.5 - 1 keV) compared to the harder emission associated with x-ray binaries in our galaxy, the Magellanic Clouds and M31. While it is generally accepted that the x-ray emission in luminous E and S0 galaxies arises from hot coronae, the status of hot gas in lower luminosity (and hence lower mass) galaxies is less clear. Calculations show that, for a given supernova rate, a critical galaxy luminosity (mass) exists below which the gas cannot be gravitationally confined and a galactic wind is predicted to be effective in expelling gas from the galaxy. Since significant mass (a dark halo) is required to hold a hot, gaseous corona around a galaxy, we expect that the faintest, smallest galaxies will not have a hot corona, but their x-ray emission will be dominated by galactic sources or by an active galactic nuclei. In the sample we tested which spanned the absolute magnitude range from -21.5 to -19.5, we found that except for two galaxies whose x-ray emission was dominated by an active nucleus, that the others were consistent with emission from hot gas. We also found that there is a correlation between gas temperature and galaxy magnitude (mass), such that the brighter, more luminous galaxies have hotter gas temperatures. Thus even at relatively faint magnitudes, the dominant emission from early-type galaxies appears to be hot gas. We also carried out an investigation of the x-ray surface brightness distribution of the x-ray emission for about 100 early type galaxies to determine whether the x-ray emission from galaxies are extended. Extended x-ray emission is expected if the emission is due to a hot gaseous corona. We determined the ratio

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.

The Dense Molecular Gas and Nuclear Activity in the ULIRG IRAS 13120-5453

NASA Astrophysics Data System (ADS)

Privon, G. C.; Aalto, S.; Falstad, N.; Muller, S.; González-Alfonso, E.; Sliwa, K.; Treister, E.; Costagliola, F.; Armus, L.; Evans, A. S.; Garcia-Burillo, S.; Izumi, T.; Sakamoto, K.; van der Werf, P.; Chu, J. K.

2017-02-01

We present new Atacama Large Millimeter/submillimeter Array Band 7 (˜340 GHz) observations of the dense gas tracers HCN, HCO+, and CS in the local, single-nucleus, ultraluminous infrared galaxy IRAS 13120-5453. We find centrally enhanced HCN (4-3) emission, relative to HCO+ (4-3), but do not find evidence for radiative pumping of HCN. Considering the size of the starburst (0.5 kpc) and the estimated supernovae rate of ˜1.2 yr-1, the high HCN/HCO+ ratio can be explained by an enhanced HCN abundance as a result of mechanical heating by the supernovae, though the active galactic nucleus and winds may also contribute additional mechanical heating. The starburst size implies a high ΣIR of 4.7 × 1012 L ⊙ kpc-2, slightly below predictions of radiation-pressure limited starbursts. The HCN line profile has low-level wings, which we tentatively interpret as evidence for outflowing dense molecular gas. However, the dense molecular outflow seen in the HCN line wings is unlikely to escape the Galaxy and is destined to return to the nucleus and fuel future star formation. We also present modeling of Herschel observations of the H2O lines and find a nuclear dust temperature of ˜40 K. IRAS 13120-5453 has a lower dust temperature and ΣIR than is inferred for the systems termed “compact obscured nuclei (CONs)” (such as Arp 220 and Mrk 231). If IRAS 13120-5453 has undergone a CON phase, we are likely witnessing it at a time when the feedback has already inflated the nuclear ISM and diluted star formation in the starburst/active galactic nucleus core.

Luminous Infrared Galaxies. III. Multiple Merger, Extended Massive Star Formation, Galactic Wind, and Nuclear Inflow in NGC 3256

NASA Astrophysics Data System (ADS)

Lípari, S.; Díaz, R.; Taniguchi, Y.; Terlevich, R.; Dottori, H.; Carranza, G.

2000-08-01

We report detailed evidence for multiple merger, extended massive star formation, galactic wind, and circular/noncircular motions in the luminous infrared galaxy NGC 3256, based on observations of high-resolution imaging (Hubble Space Telescope, ESO NTT), and extensive spectroscopic data (more than 1000 spectra, collected at Estación Astrofísica de Bosque Alegre, Complejo Astronómico el Leoncito, Cerro Tololo InterAmerican Observatory, and IUE observatories). We find in a detailed morphological study (resolution ~15 pc) that the extended massive star formation process detected previously in NGC 3256 shows extended triple asymmetrical spiral arms (r~5 kpc), emanating from three different nuclei. The main optical nucleus shows a small spiral disk (r~500 pc), which is a continuation of the external one and reaches the very nucleus. The core shows blue elongated structure (50 pc×25 pc) and harbors a blue stellar cluster candidate (r~8 pc). We discuss this complex morphology in the framework of an extended massive star formation driven by a multiple merger process (models of Hernquist et al. and Taniguchi et al.). We study the kinematics of this system and present a detailed Hα velocity field for the central region (40''×40'' rmax~30''~5 kpc), with a spatial resolution of 1" and errors of +/-15 km s-1. The color and isovelocity maps show mainly (1) a kinematic center of circular motion with ``spider'' shape, located between the main optical nucleus and the close (5") mid-IR nucleus and (2) noncircular motions in the external parts. We obtained three ``sinusoidal rotation curves'' (from the Hα velocity field) around position angle (P.A.) ~55°, ~90°, and ~130°. In the main optical nucleus we found a clear ``outflow component'' associated with galactic winds plus an ``inflow radial motion.'' The outflow component was also detected in the central and external regions (r<=5-6 kpc). The main axis of the inflow region (P.A.~80deg) is practically perpendicular to the

The Man behind the Curtain: X-Rays Drive the UV through NIR Variability in the 2013 Active Galactic Nucleus Outburst in NGC 2617

NASA Astrophysics Data System (ADS)

Shappee, B. J.; Prieto, J. L.; Grupe, D.; Kochanek, C. S.; Stanek, K. Z.; De Rosa, G.; Mathur, S.; Zu, Y.; Peterson, B. M.; Pogge, R. W.; Komossa, S.; Im, M.; Jencson, J.; Holoien, T. W.-S.; Basu, U.; Beacom, J. F.; Szczygieł, D. M.; Brimacombe, J.; Adams, S.; Campillay, A.; Choi, C.; Contreras, C.; Dietrich, M.; Dubberley, M.; Elphick, M.; Foale, S.; Giustini, M.; Gonzalez, C.; Hawkins, E.; Howell, D. A.; Hsiao, E. Y.; Koss, M.; Leighly, K. M.; Morrell, N.; Mudd, D.; Mullins, D.; Nugent, J. M.; Parrent, J.; Phillips, M. M.; Pojmanski, G.; Rosing, W.; Ross, R.; Sand, D.; Terndrup, D. M.; Valenti, S.; Walker, Z.; Yoon, Y.

2014-06-01

After the All-Sky Automated Survey for SuperNovae discovered a significant brightening of the inner region of NGC 2617, we began a ~70 day photometric and spectroscopic monitoring campaign from the X-ray through near-infrared (NIR) wavelengths. We report that NGC 2617 went through a dramatic outburst, during which its X-ray flux increased by over an order of magnitude followed by an increase of its optical/ultraviolet (UV) continuum flux by almost an order of magnitude. NGC 2617, classified as a Seyfert 1.8 galaxy in 2003, is now a Seyfert 1 due to the appearance of broad optical emission lines and a continuum blue bump. Such "changing look active galactic nuclei (AGNs)" are rare and provide us with important insights about AGN physics. Based on the Hβ line width and the radius-luminosity relation, we estimate the mass of central black hole (BH) to be (4 ± 1) × 107 M ⊙. When we cross-correlate the light curves, we find that the disk emission lags the X-rays, with the lag becoming longer as we move from the UV (2-3 days) to the NIR (6-9 days). Also, the NIR is more heavily temporally smoothed than the UV. This can largely be explained by a simple model of a thermally emitting thin disk around a BH of the estimated mass that is illuminated by the observed, variable X-ray fluxes.

The man behind the curtain: X-rays drive the UV through NIR variability in the 2013 active galactic nucleus outburst in NGC 2617

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

Shappee, B. J.; Kochanek, C. S.; Stanek, K. Z.

2014-06-10

After the All-Sky Automated Survey for SuperNovae discovered a significant brightening of the inner region of NGC 2617, we began a ∼70 day photometric and spectroscopic monitoring campaign from the X-ray through near-infrared (NIR) wavelengths. We report that NGC 2617 went through a dramatic outburst, during which its X-ray flux increased by over an order of magnitude followed by an increase of its optical/ultraviolet (UV) continuum flux by almost an order of magnitude. NGC 2617, classified as a Seyfert 1.8 galaxy in 2003, is now a Seyfert 1 due to the appearance of broad optical emission lines and a continuummore » blue bump. Such 'changing look active galactic nuclei (AGNs)' are rare and provide us with important insights about AGN physics. Based on the Hβ line width and the radius-luminosity relation, we estimate the mass of central black hole (BH) to be (4 ± 1) × 10{sup 7} M {sub ☉}. When we cross-correlate the light curves, we find that the disk emission lags the X-rays, with the lag becoming longer as we move from the UV (2-3 days) to the NIR (6-9 days). Also, the NIR is more heavily temporally smoothed than the UV. This can largely be explained by a simple model of a thermally emitting thin disk around a BH of the estimated mass that is illuminated by the observed, variable X-ray fluxes.« less

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?

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.

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.

Astrophysical bags - A new paradigm for active galactic nuclei?

NASA Technical Reports Server (NTRS)

Wilson, Thomas L.

1992-01-01

Active galaxies are believed to consist of a compact nucleus, the standard model for which is a massive black hole or a cluster of black holes. A different paradigm is considered here, deriving from quark confinement theory in QCD. It is an 'astrophysical bag', modelled after the 'hadron bags' of particle physics which have already been studied in astrophysics as quark stars. Another interpretation of the cosmological constant in general relativity, and possibly a new quasar redshift formula, are introduced. As a highly-energetic object, this model may resolve the baryonic matter problem for fuelling AGN accretion processes which black hole paradigms cannot account for. Here, baryons, cosmic rays, and neutrinos are free.

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.

Molecular Gas Feeding the Circumnuclear Disk of the Galactic Center

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

Hsieh, Pei-Ying; Koch, Patrick M.; Ho, Paul T. P.

The interaction between a supermassive black hole (SMBH) and the surrounding material is of primary importance in modern astrophysics. The detection of the molecular 2 pc circumnuclear disk (CND) immediately around the Milky Way SMBH, SgrA*, provides a unique opportunity to study SMBH accretion at subparsec scales. Our new wide-field CS( J = 2 − 1) map toward the Galactic center (GC) reveals multiple dense molecular streamers that originated from the ambient clouds 20 pc further out, and that are connected to the central 2 pc of the CND. These dense gas streamers appear to carry gas directly toward themore » nuclear region and might be captured by the central potential. Our phase-plot analysis indicates that these streamers show a signature of rotation and inward radial motion with progressively higher velocities as the gas approaches the CND and finally ends up corotating with the CND. Our results might suggest a possible mechanism of gas feeding the CND from 20 pc around 2 pc in the GC. In this paper, we discuss the morphology and the kinematics of these streamers. As the nearest observable Galactic nucleus, this feeding process may have implications for understanding the processes in extragalactic nuclei.« less

Magnetospheric Gamma-Ray Emission in Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Katsoulakos, Grigorios; Rieger, Frank M.

2018-01-01

The rapidly variable, very high-energy (VHE) gamma-ray emission from active galactic nuclei (AGNs) has been frequently associated with non-thermal processes occurring in the magnetospheres of their supermassive black holes. The present work aims to explore the adequacy of different gap-type (unscreened electric field) models to account for the observed characteristics. Based on a phenomenological description of the gap potential, we estimate the maximum extractable gap power L gap for different magnetospheric setups, and study its dependence on the accretion state of the source. L gap is found in general to be proportional to the Blandford–Znajek jet power L BZ and a sensitive function of gap size h, i.e., {L}{gap}∼ {L}{BZ}{(h/{r}g)}β , where the power index β ≥slant 1 is dependent on the respective gap setup. The transparency of the vicinity of the black hole to VHE photons generally requires a radiatively inefficient accretion environment and thereby imposes constraints on possible accretion rates, and correspondingly on L BZ. Similarly, rapid variability, if observed, may allow one to constrain the gap size h∼ c{{Δ }}t. Combining these constraints, we provide a general classification to assess the likelihood that the VHE gamma-ray emission observed from an AGN can be attributed to a magnetospheric origin. When applied to prominent candidate sources these considerations suggest that the variable (day-scale) VHE activity seen in the radio galaxy M87 could be compatible with a magnetospheric origin, while such an origin appears less likely for the (minute-scale) VHE activity in IC 310.

Matrix mechanics controls FHL2 movement to the nucleus to activate p21 expression

PubMed Central

Nakazawa, Naotaka; Sathe, Aneesh R.; Shivashankar, G. V.; Sheetz, Michael P.

2016-01-01

Substrate rigidity affects many physiological processes through mechanochemical signals from focal adhesion (FA) complexes that subsequently modulate gene expression. We find that shuttling of the LIM domain (domain discovered in the proteins, Lin11, Isl-1, and Mec-3) protein four-and-a-half LIM domains 2 (FHL2) between FAs and the nucleus depends on matrix mechanics. In particular, on soft surfaces or after the loss of force, FHL2 moves from FAs into the nucleus and concentrates at RNA polymerase (Pol) II sites, where it acts as a transcriptional cofactor, causing an increase in p21 gene expression that will inhibit growth on soft surfaces. At the molecular level, shuttling requires a specific tyrosine in FHL2, as well as phosphorylation by active FA kinase (FAK). Thus, we suggest that FHL2 phosphorylation by FAK is a critical, mechanically dependent step in signaling from soft matrices to the nucleus to inhibit cell proliferation by increasing p21 expression. PMID:27742790

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.

Photoproduction of lepton pairs in proton-nucleus and nucleus-nucleus collisions at RHIC and LHC energies

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

Moreira, B. D.; Goncalves, V. P.; De Santana Amaral, J. T.

2013-03-25

In this contribution we study coherent interactions as a probe of the nonlinear effects in the Quantum Electrodynamics (QED). In particular, we study the multiphoton effects in the production of leptons pairs for proton-nucleus and nucleus-nucleus collisions for heavy nuclei. In the proton-nucleus we assume the ultrarelativistic proton as a source of photons and estimate the photoproduction of lepton pairs on nuclei at RHIC and LHC energies considering the multiphoton effects associated to multiple rescattering of the projectile photon on the proton of the nucleus. In nucleus - nucleus colllisions we consider the two nuclei as a source of photons.more » As each scattering contributes with a factor {alpha}Z to the cross section, this contribution must be taken into account for heavy nuclei. We consider the Coulomb corrections to calculate themultiple scatterings and estimate the total cross section for muon and tau pair production in proton-nucleus and nucleus-nucleus collisions at RHIC and LHC energies.« less

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.

Higgs-boson production in nucleus-nucleus collisions

NASA Technical Reports Server (NTRS)

Norbury, J. W.; Townsend, L. W. (Principal Investigator)

1990-01-01

Cross-section calculations are presented for the production of intermediate-mass Higgs bosons produced in ultrarelativistic nucleus-nucleus collisions via two-photon fusion. The calculations are performed in position space using Baur's method for folding together the Weizsacker-Williams virtual-photon spectra of the two colliding nuclei. It is found that two-photon fusion in nucleus-nucleus collisions is a plausible way of finding intermediate-mass Higgs bosons at the Superconducting Super Collider or the CERN Large Hadron Collider.

Higgs-Boson Production in Nucleus-Nucleus Collisions

NASA Technical Reports Server (NTRS)

Norbury, John W.

1992-01-01

Cross section calculations are presented for the production of intermediate-mass Higgs bosons produced in ultrarelativistic nucleus-nucleus collisions via two photon fusion. The calculations are performed in position space using Baur's method for folding together the Weizsacker-Williams virtual-photon spectra of the two colliding nuclei. It is found that two photon fusion in nucleus-nucleus collisions is a plausible way of finding intermediate-mass Higgs bosons at the Superconducting Super Collider or the CERN Large Hadron Collider.

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.

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

Infrared fine-structure line diagnostics of shrouded active galactic nuclei

NASA Technical Reports Server (NTRS)

Voit, G. M.

1993-01-01

Far-infrared spectroscopy of celestial objects will improve dramatically in the coming decade, allowing astronomers to use fine-structure line emission to probe photoionized regions obscured in the optical band by thick clouds of dust. The ultraluminous far-IR galaxies revealed by IRAS, quasar-like in luminosity but smothered in molecular gas, probably conceal either immense starbursts or luminous active nuclei. In both scenarios, these objects ought to produce copious infrared fine-structure emission with several lines comparable to H(beta) in luminosity. This paper shows how these lines, if detected, can be used to determine the electron densities and far-IR obscurations of shrouded photoionized regions and to constrain the shape and ionization parameter of the ionizing spectra. The presence of (Ne V) emission in particular will distinguish shrouded AGN's from shrouded starbursts. Since all active galaxies photoionize at least some surrounding material, these diagnostics can also be applied to active galaxies in general and will aid in studying how an active nucleus interacts with the interstellar medium of its host galaxy.

Subthalamic nucleus gamma activity increases not only during movement but also during movement inhibition

PubMed Central

Fischer, Petra; Pogosyan, Alek; Herz, Damian M; Cheeran, Binith; Green, Alexander L; Fitzgerald, James; Aziz, Tipu Z; Hyam, Jonathan; Little, Simon; Foltynie, Thomas; Limousin, Patricia; Zrinzo, Ludvic; Brown, Peter; Tan, Huiling

2017-01-01

Gamma activity in the subthalamic nucleus (STN) is widely viewed as a pro-kinetic rhythm. Here we test the hypothesis that rather than being specifically linked to movement execution, gamma activity reflects dynamic processing in this nucleus. We investigated the role of gamma during fast stopping and recorded scalp electroencephalogram and local field potentials from deep brain stimulation electrodes in 9 Parkinson’s disease patients. Patients interrupted finger tapping (paced by a metronome) in response to a stop-signal sound, which was timed such that successful stopping would occur only in ~50% of all trials. STN gamma (60–90 Hz) increased most strongly when the tap was successfully stopped, whereas phase-based connectivity between the contralateral STN and motor cortex decreased. Beta or theta power seemed less directly related to stopping. In summary, STN gamma activity may support flexible motor control as it did not only increase during movement execution but also during rapid action-stopping. DOI: http://dx.doi.org/10.7554/eLife.23947.001 PMID:28742498

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.

High energy nucleus-nucleus collisions

NASA Technical Reports Server (NTRS)

Wosiek, B.

1986-01-01

Experimental results on high energy nucleus-nucleus interactions are presented. The data are discussed within the framework of standard super-position models and from the point-of-view of the possible formation of new states of matter in heavy ion collisions.

Active galactic nuclei: what's in a name?

NASA Astrophysics Data System (ADS)

Padovani, P.; Alexander, D. M.; Assef, R. J.; De Marco, B.; Giommi, P.; Hickox, R. C.; Richards, G. T.; Smolčić, V.; Hatziminaoglou, E.; Mainieri, V.; Salvato, M.

2017-08-01

Active galactic nuclei (AGN) are energetic astrophysical sources powered by accretion onto supermassive black holes in galaxies, and present unique observational signatures that cover the full electromagnetic spectrum over more than twenty orders of magnitude in frequency. The rich phenomenology of AGN has resulted in a large number of different "flavours" in the literature that now comprise a complex and confusing AGN "zoo". It is increasingly clear that these classifications are only partially related to intrinsic differences between AGN and primarily reflect variations in a relatively small number of astrophysical parameters as well the method by which each class of AGN is selected. Taken together, observations in different electromagnetic bands as well as variations over time provide complementary windows on the physics of different sub-structures in the AGN. In this review, we present an overview of AGN multi-wavelength properties with the aim of painting their "big picture" through observations in each electromagnetic band from radio to γ -rays as well as AGN variability. We address what we can learn from each observational method, the impact of selection effects, the physics behind the emission at each wavelength, and the potential for future studies. To conclude, we use these observations to piece together the basic architecture of AGN, discuss our current understanding of unification models, and highlight some open questions that present opportunities for future observational and theoretical progress.

Metals in the circumgalactic medium are out of ionization equilibrium due to fluctuating active galactic nuclei

NASA Astrophysics Data System (ADS)

Segers, Marijke C.; Oppenheimer, Benjamin D.; Schaye, Joop; Richings, Alexander J.

2017-10-01

We study the effect of a fluctuating active galactic nucleus (AGN) on the abundance of circumgalactic O VI in galaxies selected from the Evolution and Assembly of GaLaxies and their Environments simulations. We follow the time-variable O VI abundance in post-processing around four galaxies - two at z = 0.1 with stellar masses of M* ˜ 1010 M⊙ and M* ˜ 1011 M⊙, and two at z = 3 with similar stellar masses - out to impact parameters of twice their virial radii, implementing a fluctuating central source of ionizing radiation. Due to delayed recombination, the AGN leave significant 'AGN proximity zone fossils' around all four galaxies, where O VI and other metal ions are out of ionization equilibrium for several megayears after the AGN fade. The column density of O VI is typically enhanced by ≈0.3-1.0 dex at impact parameters within 0.3Rvir, and by ≈0.06-0.2 dex at 2Rvir, thereby also enhancing the covering fraction of O VI above a given column density threshold. The fossil effect tends to increase with increasing AGN luminosity, and towards shorter AGN lifetimes and larger AGN duty cycle fractions. In the limit of short AGN lifetimes, the effect converges to that of a continuous AGN with a luminosity of (fduty/100 per cent) times the AGN luminosity. We also find significant fossil effects for other metal ions, where low-ionization state ions are decreased (Si IV, C IV at z = 3) and high-ionization state ions are increased (C IV at z = 0.1, Ne viii, Mg x). Using observationally motivated AGN parameters, we predict AGN proximity zone fossils to be ubiquitous around M* ˜ 1010-11 M⊙ galaxies, and to affect observations of metals in the circumgalactic medium at both low and high redshifts.

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

The Dense Molecular Gas and Nuclear Activity in the ULIRG IRAS 13120–5453

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

Privon, G. C.; Treister, E.; Aalto, S.

2017-02-01

We present new Atacama Large Millimeter/submillimeter Array Band 7 (∼340 GHz) observations of the dense gas tracers HCN, HCO{sup +}, and CS in the local, single-nucleus, ultraluminous infrared galaxy IRAS 13120–5453. We find centrally enhanced HCN (4–3) emission, relative to HCO{sup +} (4–3), but do not find evidence for radiative pumping of HCN. Considering the size of the starburst (0.5 kpc) and the estimated supernovae rate of ∼1.2 yr{sup −1}, the high HCN/HCO{sup +} ratio can be explained by an enhanced HCN abundance as a result of mechanical heating by the supernovae, though the active galactic nucleus and winds maymore » also contribute additional mechanical heating. The starburst size implies a high Σ{sub IR} of 4.7 × 10{sup 12} L {sub ⊙} kpc{sup −2}, slightly below predictions of radiation-pressure limited starbursts. The HCN line profile has low-level wings, which we tentatively interpret as evidence for outflowing dense molecular gas. However, the dense molecular outflow seen in the HCN line wings is unlikely to escape the Galaxy and is destined to return to the nucleus and fuel future star formation. We also present modeling of Herschel observations of the H{sub 2}O lines and find a nuclear dust temperature of ∼40 K. IRAS 13120–5453 has a lower dust temperature and Σ{sub IR} than is inferred for the systems termed “compact obscured nuclei (CONs)” (such as Arp 220 and Mrk 231). If IRAS 13120–5453 has undergone a CON phase, we are likely witnessing it at a time when the feedback has already inflated the nuclear ISM and diluted star formation in the starburst/active galactic nucleus core.« less

In situ fluorescence activation of DNA-silver nanoclusters as a label-free and general strategy for cell nucleus imaging.

PubMed

Li, Duo; Qiao, Zhenzhen; Yu, Yanru; Tang, Jinlu; He, Xiaoxiao; Shi, Hui; Ye, Xiaosheng; Lei, Yanli; Wang, Kemin

2018-01-25

A facile, general and turn-on nucleus imaging strategy was first developed based on in situ fluorescence activation of C-rich dark silver nanoclusters by G-rich telomeres. After a simple incubation without washing, nanoclusters could selectively stain the nucleus with intense red luminescence, which was confirmed using fixed/living cells and several cell lines.

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.

Individuals with more severe depression fail to sustain nucleus accumbens activity to preferred music over time.

PubMed

Jenkins, Lisanne M; Skerrett, Kristy A; DelDonno, Sophie R; Patrón, Víctor G; Meyers, Kortni K; Peltier, Scott; Zubieta, Jon-Kar; Langenecker, Scott A; Starkman, Monica N

2018-05-30

We investigated the ability of preferred classical music to activate the nucleus accumbens in patients with Major depressive disorder (MDD). Twelve males with MDD and 10 never mentally ill male healthy controls (HC) completed measures of anhedonia and depression severity, and listened to 90-second segments of preferred classical music during fMRI. Compared to HCs, individuals with MDD showed less activation of the left nucleus accumbens (NAcc). Individuals with MDD showed attenuation of the left NAcc response in later compared to earlier parts of the experiment, supporting theories that MDD involves an inability to sustain reward network activation. Counter intuitively, we found that NAcc activity during early music listening was associated with greater depression severity. In whole-brain analyses, anhedonia scores predicted activity in regions within the default mode network, supporting previous findings. Our results support theories that MDD involves an inability to sustain reward network activation. It also highlights that pleasant classical music can engage critical neural reward circuitry in MDD. Copyright © 2018 Elsevier B.V. All rights reserved.

MOLECULAR GAS DISK STRUCTURES AROUND ACTIVE GALACTIC NUCLEI

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

Wada, Keiichi; Papadopoulos, Padeli P.; Spaans, Marco

We present new high-resolution numerical simulations of the interstellar medium (ISM) in a central R {<=} 32 parsecs region around a supermassive black hole (1.3 x 10{sup 7} M{sub sun}) at a galactic center. Three-dimensional hydrodynamic modeling of the ISM (Wada and Norman 2002) with the nuclear starburst now includes tracking of the formation of molecular hydrogen (H{sub 2}) out of the neutral hydrogen phase as a function of the evolving ambient ISM conditions with a finer spatial resolution (0.125 pc). In a quasi-equilibrium state, mass fraction of H{sub 2} is about 0.4 (total H{sub 2} mass is {approx_equal}1.5 xmore » 10{sup 6} M{sub sun}) of the total gas mass for the uniform far ultra-violet (FUV) with G {sub 0} = 10 in Habing unit. As shown in the previous model, the gas forms an inhomogeneous disk, whose scale height becomes larger in the outer region. H{sub 2} forms a thin nuclear disk in the inner {approx_equal}5 pc, which is surrounded by molecular clouds swelled up toward h {approx}< 10 pc. The velocity field of the disk is highly turbulent in the torus region, whose velocity dispersion is {approx_equal}20 km s{sup -1} on average. Average supernova (SN) rate of {approx_equal}5 x 10{sup -5} yr{sup -1} is large enough to energize these structures. Gas column densities toward the nucleus larger than 10{sup 22} cm{sup -2} are observed if the viewing angle is smaller than {theta} {sub v} {approx_equal} 50 deg. from the edge-on. However, the column densities are distributed over almost two orders of magnitude around the average for any given viewing angle due to the clumpy nature of the torus. For a stronger FUV (G {sub 0} = 100), the total H{sub 2} mass in an equilibrium is only slightly smaller ({approx_equal}0.35), a testimony to the strong self-shielding nature of H{sub 2}, and the molecular gas is somewhat more concentrated in a midplane. Other properties of the ISM are not very sensitive either to the FUV intensity or the SN rate. Finally, the

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.

Galaxy mergers moulding the circum-galactic medium - I. The impact of a major merger

NASA Astrophysics Data System (ADS)

Hani, Maan H.; Sparre, Martin; Ellison, Sara L.; Torrey, Paul; Vogelsberger, Mark

2018-03-01

Galaxies are surrounded by sizeable gas reservoirs which host a significant amount of metals: the circum-galactic medium (CGM). The CGM acts as a mediator between the galaxy and the extragalactic medium. However, our understanding of how galaxy mergers, a major evolutionary transformation, impact the CGM remains deficient. We present a theoretical study of the effect of galaxy mergers on the CGM. We use hydrodynamical cosmological zoom-in simulations of a major merger selected from the Illustris project such that the z = 0 descendant has a halo mass and stellar mass comparable to the Milky Way. To study the CGM we then re-simulated this system at a 40 times better mass resolution, and included detailed post-processing ionization modelling. Our work demonstrates the effect the merger has on the characteristic size of the CGM, its metallicity, and the predicted covering fraction of various commonly observed gas-phase species, such as H I, C IV, and O VI. We show that merger-induced outflows can increase the CGM metallicity by 0.2-0.3 dex within 0.5 Gyr post-merger. These effects last up to 6 Gyr post-merger. While the merger increases the total metal covering fractions by factors of 2-3, the covering fractions of commonly observed UV ions decrease due to the hard ionizing radiation from the active galactic nucleus, which we model explicitly. Our study of the single simulated major merger presented in this work demonstrates the significant impact that a galaxy interaction can have on the size, metallicity, and observed column densities of the CGM.

Active Galactic Nuclei and X-ray Ovservations

NASA Astrophysics Data System (ADS)

Vasylenko, A. A.; Zhdanov, V. I.; Fedorova, E. V.

2016-11-01

Active galactic nuclei (AGN) are the brightest objects in the Universe and their brightness is mainly caused by accretion of m atter onto supermassive black holes (SMBH). This is the common reason of the AGN activity. However, every AGN has differences and fine features, which are the subject of an intensive investigation. The occurrence of such highly-relativistic objects as SMBH residing at the AGN core makes them an excellent laboratory for testing the fundamental physical theories. The X-rays and gamma-rays generated in a corona of an accretion disc around SMBH yield valuable information for these tests, the radiation in the range of 1-100 keV being at present the most informative source. However, there are a number of obstacles for such a study due to different physical processes that complicate the interpretation of observations in different bands of the electromagnetic radiation. In this paper, we review the current concepts concerning the structure of AGNs with a focus on the central part of these objects th at require relativistic theories for their understanding. The basic notions of the unified AGN schemes are considered; some modifications are reviewed. The paper contains the following sections. I. Introduction; II. Observational manifestations and classification of galaxies with active nuclei (II.A. Optical observations; II.B. Radio observations; II.C. X-ray data; II.D Infrared data; II.E. AGN anatomy with multywave data); III. AGN "central machine"; III.A. Black holes; III.B. Accretion disc types; III.C. Corona; III.D. AGN unified scheme); IV. Simulation X-ray AGN spectra (IV.A. The power-law contimuum and the exponential cut-off; IV.B. The absorption of X-rays; IV.C. Reflection; IV.D. Fe K a line; IV.E. Spin paradigm); V. AGN as a laboratory to test the fundamental interactions (V.A. Strong gravitational fields; V.B. Dynamic dark energy near compact astrophysical objects

THE COMPLEX NORTH TRANSITION REGION OF CENTAURUS A: A GALACTIC WIND

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

Neff, Susan G.; Eilek, Jean A.; Owen, Frazer N., E-mail: susan.g.neff@nasa.gov

2015-04-01

We present deep GALEX images of NGC 5128, the parent galaxy of Centaurus A. We detect a striking “weather ribbon” of far-UV (FUV) and Hα emission which extends more than 35 kpc northeast of the galaxy. This ribbon is associated with a knotty ridge of radio/X-ray emission and is an extension of the previously known string of optical emission-line filaments. Many phenomena in the region are too short-lived to have survived transit out from the inner galaxy; something must be driving them locally. We also detect FUV emission from the galaxy’s central dust lane. Combining this with previous radio andmore » far-IR measurements, we infer an active starburst in the central galaxy which is currently forming stars at ∼2 M{sub ☉} yr{sup −1}, and has been doing so for 50–100 Myr. If the wind from this starburst is enhanced by energy and mass driven out from the active galactic nucleus, the powerful augmented wind can be the driver needed for the northern weather system. We argue that both the diverse weather system, and the enhanced radio emission in the same region, result from the wind’s encounter with cool gas left by one of the recent merger/encounter events in the history of NGC 5128.« less

The Potential for Cubesats to Determine Black Holes Masses in Nearby Active Galactic Nuclei and Contribute to Other Time Domain Science

NASA Astrophysics Data System (ADS)

Gorjian, Varoujan; Ardila, David R.; Barth, Aaron J.; Janson, Siegfried; Kochanek, Christopher S.; Malkan, Matthew Arnold; Peterson, Bradley M.; Rowen, Darren; Seager, Sara; Shkolnik, Evgenya L.

2016-01-01

A 3U (30cmx10cmx10cm) CubeSat with a 9cm diameter aperture telescope can deliver unprecedented time domain coverage in the ultraviolet (UV) for the purposes of Active Galactic Nucleus (AGN) reverberation mapping to determine supermassive black hole (SMBH) masses. SMBH's reside at the centers of most, if not all, massive galaxies and accretion onto those black holes generates a great deal of emission peaking in the UV. These accretion disks are also surrounded by a nearby, fast moving gas region called the Broad Line Region (BLR). As light pulses generated near the black hole spread out, they first illuminate the accretion disk, and then the BLR. For a sample of bright AGN, a dedicated cubesat can follow these changes in brightness on a daily basis for up to 100 days from low Earth orbit. With such monitoring of changes in the accretion disk and then the BLR, an accurate distance between the two regions can be determined. Combining this UV coverage with optical emission-line spectroscopy from the ground allows for a direct measurement of the mass of the central black hole. This exchange of time resolution for spatial resolution can also be used to determine the structure of the central region of the AGN. Ground-based photometric and spectroscopic measurements will complement the UV by tracing the optically emitting and hence cooler regions of the AGN to provide one of the best measurements of supermassive black hole masses.In addition to the primary science mission, the long observing campaigns and the large field of view required to get comparison stars for relative photometry allow for other competitive science. We have identified UV activity in M dwarfs as ancillary science that can be addressed with such a cubesat. This activity will have a strong impact on the habitability of any possible planet around the star.

CHANDRA OBSERVATIONS OF GALAXY ZOO MERGERS: FREQUENCY OF BINARY ACTIVE NUCLEI IN MASSIVE MERGERS

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

Teng, Stacy H.; Schawinski, Kevin; Urry, C. Megan

We present the results from a Chandra pilot study of 12 massive galaxy mergers selected from Galaxy Zoo. The sample includes major mergers down to a host galaxy mass of 10{sup 11} M{sub Sun} that already have optical active galactic nucleus (AGN) signatures in at least one of the progenitors. We find that the coincidences of optically selected active nuclei with mildly obscured (N{sub H} {approx}< 1.1 Multiplication-Sign 10{sup 22} cm{sup -2}) X-ray nuclei are relatively common (8/12), but the detections are too faint (<40 counts per nucleus; f{sub 2-10keV} {approx}< 1.2 Multiplication-Sign 10{sup -13} erg s{sup -1} cm{sup -2})more » to reliably separate starburst and nuclear activity as the origin of the X-ray emission. Only one merger is found to have confirmed binary X-ray nuclei, though the X-ray emission from its southern nucleus could be due solely to star formation. Thus, the occurrences of binary AGNs in these mergers are rare (0%-8%), unless most merger-induced active nuclei are very heavily obscured or Compton thick.« less

Glutamatergic projection from the nucleus incertus to the septohippocampal system.

PubMed

Cervera-Ferri, Ana; Rahmani, Yasamin; Martínez-Bellver, Sergio; Teruel-Martí, Vicent; Martínez-Ricós, Joana

2012-05-31

Recent findings support a relevant role of the nucleus incertus in the control of the hippocampal activity through the modulation of theta rhythm. Previous studies from our group have shown that this nucleus is a critical relay between reticularis pontis oralis and the medial septum/diagonal band, regarded as the main activator and the pacemaker of the hippocampal oscillations, respectively. Besides, the nucleus incertus is highly linked to activated states related to the arousal response. The neurotransmission of the nucleus incertus, however, remains uncertain. Only GABA and the neuromodulator relaxin 3 are usually considered to be involved in its contribution to the septohippocampal system. In this work, we have analyzed the existence of an excitatory projection from the nucleus incertus to the medial septum. We have found a group of glutamatergic neurons in the nucleus incertus projecting to the medial septum. Moreover, we were able to describe a segregated distribution of calbindin and calretinin neurons. While calretinin expression was restricted to the nucleus incertus pars compacta, calbindin positive neurons where observed both in the pars dissipata and the pars compacta of the nucleus. The present work provides innovative data supporting an excitatory component in the pontoseptal pathway. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.

Cholinergic Oculomotor Nucleus Activity Is Induced by REM Sleep Deprivation Negatively Impacting on Cognition.

PubMed

Santos, Patrícia Dos; Targa, Adriano D S; Noseda, Ana Carolina D; Rodrigues, Lais S; Fagotti, Juliane; Lima, Marcelo M S

2017-09-01

Several efforts have been made to understand the involvement of rapid eye movement (REM) sleep for cognitive processes. Consolidation or retention of recognition memories is severely disrupted by REM sleep deprivation (REMSD). In this regard, pedunculopontine tegmental nucleus (PPT) and other brainstem nuclei, such as pontine nucleus (Pn) and oculomotor nucleus (OCM), appear to be candidates to take part in this REM sleep circuitry with potential involvement in cognition. Therefore, the objective of this study was to investigate a possible association between the performance of Wistar rats in a declarative memory and PPT, Pn, and OCM activities after different periods of REMSD. We examined c-Fos and choline acetyltransferase (ChaT) expressions as indicators of neuronal activity as well as a familiarity-based memory test. The animals were distributed in groups: control, REMSD, and sleep rebound (REB). At the end of the different REMSD (24, 48, 72, and 96 h) and REB (24 h) time points, the rats were immediately tested in the object recognition test and then the brains were collected. Results indicated that OCM neurons presented an increased activity, due to ChaT-labeling associated with REMSD that negatively correlated (r = -0.32) with the cognitive performance. This suggests the existence of a cholinergic compensatory mechanism within the OCM during REMSD. We also showed that 24 h of REMSD impacted similarly in memory, compared to longer periods of REMSD. These data extend the notion that REM sleep is influenced by areas other than PPT, i.e., Pn and OCM, which could be key players in both sleep processes and cognition.

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.

Neurons of human nucleus accumbens.

PubMed

Sazdanović, Maja; Sazdanović, Predrag; Zivanović-Macuzić, Ivana; Jakovljević, Vladimir; Jeremić, Dejan; Peljto, Amir; Tosevski, Jovo

2011-08-01

Nucleus accumbens is a part of the ventral striatum also known as a drug active brain region, especially related with drug addiction. The aim of the study was to investigate the Golgi morphology of the nucleus accumbens neurons. The study was performed on the frontal and sagittal sections of 15 human brains by the Golgi Kopsch method. We classified neurons in the human nucleus accumbens according to their morphology and size into four types: type I--fusiform neurons; type II--fusiform neurons with lateral dendrite, arising from a part of the cell body; type III--pyramidal-like neuron; type IV--multipolar neuron. The medium spiny neurons, which are mostly noted regarding to the drug addictive conditions of the brain, correspond to the type IV--multipolar neurons. Two regions of human nucleus accumbens could be clearly recognized on Nissl and Golgi preparations each containing different predominant neuronal types. Central part of nucleus accumbens, core region, has a low density of impregnated neurons with predominant type III, pyramidal-like neurons, with spines on secondary branches and rare type IV, multipolar neurons. Contrary to the core, peripheral region, shell of nucleus, has a high density of impregnated neurons predominantly contained of type I and type IV--multipolar neurons, which all are rich in spines on secondary and tertiary dendritic branches. Our results indicate great morphological variability of human nucleus accumbens neurons. This requires further investigations and clarifying clinical significance of this important brain region.

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.

A Snapshot of the Continuous Emission of the Active Galactic Nucleus in NGC 3783 from Gamma-Ray to Radio Wavelengths

NASA Technical Reports Server (NTRS)

Alloin, D.; Santos-Lleo, M.; Peterson, B. M.; Wamsteker, W.; Altieri, B.; Brinkmann, W.; Clavel, J.; Crenshaw, D. M.; George, I. M.; Glass, I. S.;

Sexual behavior induction of c-Fos in the nucleus accumbens and amphetamine-stimulated locomotor activity are sensitized by previous sexual experience in female Syrian hamsters.

PubMed

Bradley, K C; Meisel, R L

2001-03-15

Dopamine transmission in the nucleus accumbens can be activated by drugs, stress, or motivated behaviors, and repeated exposure to these stimuli can sensitize this dopamine response. The objectives of this study were to determine whether female sexual behavior activates nucleus accumbens neurons and whether past sexual experience cross-sensitizes neuronal responses in the nucleus accumbens to amphetamine. Using immunocytochemical labeling, c-Fos expression in different subregions (shell vs core at the rostral, middle, and caudal levels) of the nucleus accumbens was examined in female hamsters that had varying amounts of sexual experience. Female hamsters, given either 6 weeks of sexual experience or remaining sexually naive, were tested for sexual behavior by exposure to adult male hamsters. Previous sexual experience increased c-Fos labeling in the rostral and caudal levels but not in the middle levels of the nucleus accumbens. Testing for sexual behavior increased labeling in the core, but not the shell, of the nucleus accumbens. To validate that female sexual behavior can sensitize neurons in the mesolimbic dopamine pathway, the locomotor responses of sexually experienced and sexually naive females to an amphetamine injection were then compared. Amphetamine increased general locomotor activity in all females. However, sexually experienced animals responded sooner to amphetamine than did sexually naive animals. These data indicate that female sexual behavior can activate neurons in the nucleus accumbens and that sexual experience can cross-sensitize neuronal responses to amphetamine. In addition, these results provide additional evidence for functional differences between the shell and core of the nucleus accumbens and across its anteroposterior axis.

Observing the Super-Massive Black Hole of the Galactic center with Simbol-X .

NASA Astrophysics Data System (ADS)

Goldwurm, A.

The Center of our Galaxy is one of the prime objective of the Simbol-X mission. This region of several square degrees around the dynamical center of the galaxy hosts a large variety of high energy sources and violent phenomena that involve different non-thermal processes contributing to the hard X-ray emission from the region. Here we present in detail the case for the observation of Sgr A*, the super-massive black hole of the galactic nucleus, with Simbol-X, stressing on the presently open questions and on the crucial measurements that will be performed in the hard X-ray domain with this formation-flying hard X-ray focussing telescope expected to flight in the next decade.

Optical monitoring of Active Galactic Nuclei from ARIES

NASA Astrophysics Data System (ADS)

Gopal-Krishna; Wiita, Paul Joseph

2018-04-01

This overview provides a historical perspective highlighting the pioneering role which the fairly modest observational facilities of ARIES have played since the 1990s in systematically characterizing the optical variability on hour-like time scale (intra-night optical variability, or INOV) of several major types of high-luminosity Active Galactic Nuclei (AGN). Such information was previously available only for blazars. Similar studies have since been initiated in at least a dozen countries, giving a boost to AGN variability research. Our work has, in particular, provided strong indication that mild INOV occurs in radio-quiet QSOs (amplitude up to 3 – 5 % and duty cycle 10%) and, moreover, has demonstrated that similarly mild INOV is exhibited even by the vast majority of radio-loud quasars which possess powerful relativistic jets (even including many that are beamed towards us). The solitary outliers are blazars, the tiny strongly polarized subset of powerful AGN, which frequently exhibit a pronounced INOV. Among the blazars, BL Lac objects often show a bluer-when-brighter chromatic behavior, while the flat spectrum radio quasars seem not to. Quantifying any differences of INOV among the major subclasses of non-blazar type AGNs will require dedicated monitoring programs using 2 - 3 metre class telescopes.

X-ray Reverberation Mapping in Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Kara, Erin

2018-01-01

Active Galactic Nuclei can produce as much or more electromagnetic and kinetic luminosities than the combined stellar luminosity of an entire galaxy. The energy output from AGN comes from the gravitational potential energy of the infalling material and the rotational energy of the black hole, both of which are released very close to the black hole. Therefore, probing the relativistic region of the inner accretion flow is essential to understanding how AGN work and effect their environments. In this talk, I will present a new technique for probing these relativistic environments: X-ray reverberation mapping. Similar to Optical reverberation mapping, where time delays of days or weeks between the continuum and Broad Line Region lines map out centiparsec scales, X-ray reverberation reveals time delays of tens of seconds, which map out microparsec scales in the accretion flow—well beyond the spatial resolution power of any instrument. This technique has been discovered in the past decade, so I will give a brief overview of how the measurements are made, and highlight some recent discoveries, which allow us to map the gas falling on to the black hole and measure the effects of strongly curved spacetime close to the event horizon.

Nucleus and nucleus-cytoskeleton connections in 3D cell migration

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

Liu, Lingling, E-mail: liulingling2012@163.com; Luo, Qing, E-mail: qing.luo@cqu.edu.cn; Sun, Jinghui, E-mail: sunjhemail@163.com

Cell migration plays an important role in many physiological and pathological settings, ranging from embryonic development to cancer metastasis. Currently, accumulating data suggest that cells migrating in three-dimensional (3D) environments show well-defined differences compared to their well-established two-dimensional (2D) counterparts. During 3D migration, the cell body and nucleus must deform to allow cellular passage through the available spaces, and the deformability of the relatively rigid nucleus may constitute a limiting step. Here, we highlight the key evidence regarding the role of the nuclear mechanics in 3D migration, including the molecular components that govern the stiffness of the nucleus and reviewmore » how the nuclear dynamics are connected to and controlled by cytoskeleton-based migration machinery. Intriguingly, nuclear movement must be coordinated with the cytoskeletal dynamics at the leading and trailing edges, which in turn impact the cytoplasmic dynamics that affect the migration efficiency. Thus, we suggest that alterations in the nuclear structure may facilitate cellular reorganizations that are necessary for efficient migration. - Graphical abstract: Schematic representations of a cell migrating on a 2D substrate and a cell migrating in a 3D extracellular matrix environment. (A) Nucleus-cytoskeleton connections are essential to 3D migration. Mechanical signals are transduced by integrins at the cell surface and channeled to cytoskeletal proteins, which generates prestress. The nucleus-cytoskeleton connections can either act as a stable skeleton to anchor the nuclei or provide active force to move the nuclei. The LINC complex is responsible for the nucleo-cytoskeletal coupling. Nesprins connect the cytoskeletal proteins to the inner nuclear membrane proteins SUN1 and SUN2. The SUN proteins connect to the lamins that form the lamina, which attaches to the chromatin. This physical connectivity transmits the mechanical signals from

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.

A (Si VI) (1.92 micrometer) coronal line survey of galactic nuclei

NASA Astrophysics Data System (ADS)

Marconi, A.; Moorwood, A. F. M.; Salvati, M.; Oliva, E.

1994-11-01

We present the results of a (Si VI) lambda 1.962 emission line survey of active, starburst and IRAS luminous galaxies. The line was only detected in known Seyfert type 1 and 2 nuclei confirming previous suggestions that (Si VI) is related to Seyfert activity. By modeling the formation of (Si VI) and (Fe VIII) lambda 6087 we find further strong evidence that these lines arise in gas photoionized by the active nucleus although collisional ionization e.g. by shock fronts may be important in some galaxies exhibiting (Fe VII) much greater than (Si VI). Our failure to detect (Si VI) in the IRAS ultraluminous galaxies does not exclude the possible presence of obscured Active Galactic Nuclei (AGNs), particularly as some of the known Seyferts were also not detected. Molecular hydrogen lines (a by-product of our spectra) are common in all galaxy types including several IRAS ultraluminous galaxies whose H2 equivalent widths (Wlambda less that 20 A) are 'normal'and much lower than the extreme value (Wlambda approximately = 70 A) found in NGC 6240 and NGC 1275. 'Bare' Seyferts have Wlambda(H2) less than 1 A and a factor greater than or approximately 10 lower than starbursts, and we do not confirm previous claims of H2 line emission in the quasar 3C273. Although the ratio of H2 to (Si VI) emission varies over a wide range it does not appear to provide a useful indicator of activity type or to impose constraints on the He excitation mechanism.

Population calcium imaging of spontaneous respiratory and novel motor activity in the facial nucleus and ventral brainstem in newborn mice

PubMed Central

Persson, Karin; Rekling, Jens C

2011-01-01

Abstract The brainstem contains rhythm and pattern forming circuits, which drive cranial and spinal motor pools to produce respiratory and other motor patterns. Here we used calcium imaging combined with nerve recordings in newborn mice to reveal spontaneous population activity in the ventral brainstem and in the facial nucleus. In Fluo-8 AM loaded brainstem–spinal cord preparations, respiratory activity on cervical nerves was synchronized with calcium signals at the ventrolateral brainstem surface. Individual ventrolateral neurons at the level of the parafacial respiratory group showed perfect or partial synchrony with respiratory nerve bursts. In brainstem–spinal cord preparations, cut at the level of the mid-facial nucleus, calcium signals were recorded in the dorsal, lateral and medial facial subnuclei during respiratory activity. Strong activity initiated in the dorsal subnucleus, followed by activity in lateral and medial subnuclei. Whole-cell recordings from facial motoneurons showed weak respiratory drives, and electrical field potential recordings confirmed respiratory drive to particularly the dorsal and lateral subnuclei. Putative facial premotoneurons showed respiratory-related calcium signals, and were predominantly located dorsomedial to the facial nucleus. A novel motor activity on facial, cervical and thoracic nerves was synchronized with calcium signals at the ventromedial brainstem extending from the level of the facial nucleus to the medulla–spinal cord border. Cervical dorsal root stimulation induced similar ventromedial activity. The medial facial subnucleus showed calcium signals synchronized with this novel motor activity on cervical nerves, and cervical dorsal root stimulation induced similar medial facial subnucleus activity. In conclusion, the dorsal and lateral facial subnuclei are strongly respiratory-modulated, and the brainstem contains a novel pattern forming circuit that drives the medial facial subnucleus and cervical motor

Optical, Near-IR, and Sub-mm IFU Observations of the Nearby Dual Active Galactic Nuclei MRK 463

NASA Astrophysics Data System (ADS)

Treister, Ezequiel; Privon, George C.; Sartori, Lia F.; Nagar, Neil; Bauer, Franz E.; Schawinski, Kevin; Messias, Hugo; Ricci, Claudio; U, Vivian; Casey, Caitlin; Comerford, Julia M.; Muller-Sanchez, Francisco; Evans, Aaron S.; Finlez, Carolina; Koss, Michael; Sanders, David B.; Urry, C. Megan

2018-02-01

We present optical and near-IR Integral Field Unit (IFU) and ALMA band 6 observations of the nearby dual active galactic nuclei (AGNs) Mrk 463. At a distance of 210 Mpc, and a nuclear separation of ∼4 kpc, Mrk 463 is an excellent laboratory to study the gas dynamics, star formation processes and supermassive black hole (SMBH) accretion in a late-stage gas-rich major galaxy merger. The IFU observations reveal a complex morphology, including tidal tails, star-forming clumps, and emission-line regions. The optical data, which map the full extent of the merger, show evidence for a biconical outflow and material outflowing at >600 km s‑1, both associated with the Mrk 463E nucleus, along with large-scale gradients likely related to the ongoing galaxy merger. We further find an emission-line region ∼11 kpc south of Mrk 463E that is consistent with photoionization by an AGN. Compared to the current AGN luminosity, the energy budget of the cloud implies a luminosity drop in Mrk 463E by a factor of 3–20 over the last 40,000 years. The ALMA observations of 12CO(2–1) and adjacent 1 mm continuum reveal the presence of ∼109 M ⊙ in molecular gas in the system. The molecular gas shows velocity gradients of ∼800 km s‑1 and ∼400 km s‑1 around the Mrk 463E and 463W nuclei, respectively. We conclude that, in this system, the infall of ∼100s M ⊙ yr‑1 of molecular gas is in rough balance with the removal of ionized gas by a biconical outflow being fueled by a relatively small, <0.01% of accretion onto each SMBH.

THE OBSCURED FRACTION OF ACTIVE GALACTIC NUCLEI IN THE XMM-COSMOS SURVEY: A SPECTRAL ENERGY DISTRIBUTION PERSPECTIVE

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

Lusso, E.; Hennawi, J. F.; Richards, G. T.

2013-11-10

The fraction of active galactic nucleus (AGN) luminosity obscured by dust and re-emitted in the mid-IR is critical for understanding AGN evolution, unification, and parsec-scale AGN physics. For unobscured (Type 1) AGNs, where we have a direct view of the accretion disk, the dust covering factor can be measured by computing the ratio of re-processed mid-IR emission to intrinsic nuclear bolometric luminosity. We use this technique to estimate the obscured AGN fraction as a function of luminosity and redshift for 513 Type 1 AGNs from the XMM-COSMOS survey. The re-processed and intrinsic luminosities are computed by fitting the 18 bandmore » COSMOS photometry with a custom spectral energy distribution fitting code, which jointly models emission from hot dust in the AGN torus, from the accretion disk, and from the host galaxy. We find a relatively shallow decrease of the luminosity ratio as a function of L{sub bol}, which we interpret as a corresponding decrease in the obscured fraction. In the context of the receding torus model, where dust sublimation reduces the covering factor of more luminous AGNs, our measurements require a torus height that increases with luminosity as h ∝ L{sub bol}{sup 0.3-0.4}. Our obscured-fraction-luminosity relation agrees with determinations from Sloan Digital Sky Survey censuses of Type 1 and Type 2 quasars and favors a torus optically thin to mid-IR radiation. We find a much weaker dependence of the obscured fraction on 2-10 keV luminosity than previous determinations from X-ray surveys and argue that X-ray surveys miss a significant population of highly obscured Compton-thick AGNs. Our analysis shows no clear evidence for evolution of the obscured fraction with redshift.« less

[Comparative study of effects of cortical nucleus of amygdala and pyriform cortex on activity of bulbar respiratory neurons in cats].

PubMed

Nersesian, L B; Eganova, V S; Pogosian, N L; Avetisian, I N

2011-01-01

Comparative microelectrophysiological study of character and peculiarities of effects of the cortical nucleus of amygdala and of the periamygdalar area of pyriform cortex on impulse activity was performed on the same single functionally identified respiratory medullar neurons. A high reactivity of bulbar respiratory neurons on stimulation is established in both studied limbic structures. There is established the qualitatively different character of their response reactions at stimulation of the cortical amygdala nucleus and the periamygdalar cortex. The cortical amygdala nucleus has been shown to produce on the activity of medullar respiratory neurons both facilitating and inhibitory action with predominance of the activating one (without topographical orderliness). The effect of periamygdalar cortex at stimulation of various parts was characterized by topographic differentiation. The suppressing reactions of neurons in the majority of cases were recorded at stimulation of the rostral area of periamygdalar cortex, whereas the excitatory reactions--at stimulation of its caudal part. Functional organization of respiratory control of the studied limbic system structures is discussed.

THE MULTIPHASE STRUCTURE AND POWER SOURCES OF GALACTIC WINDS IN MAJOR MERGERS

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

Rupke, David S. N.; Veilleux, Sylvain, E-mail: drupke@gmail.com

2013-05-01

Massive, galaxy-scale outflows are known to be ubiquitous in major mergers of disk galaxies in the local universe. In this paper, we explore the multiphase structure and power sources of galactic winds in six ultraluminous infrared galaxies (ULIRGs) at z < 0.06 using deep integral field spectroscopy with the Gemini Multi-Object Spectrograph (GMOS) on Gemini North. We probe the neutral, ionized, and dusty gas phases using Na I D, strong emission lines ([O I], H{alpha}, and [N II]), and continuum colors, respectively. We separate outflow motions from those due to rotation and tidal perturbations, and find that all of themore » galaxies in our sample host high-velocity flows on kiloparsec scales. The properties of these outflows are consistent with multiphase (ionized, neutral, and dusty) collimated bipolar winds emerging along the minor axis of the nuclear disk to scales of 1-2 kpc. In two cases, these collimated winds take the form of bipolar superbubbles, identified by clear kinematic signatures. Less collimated (but still high-velocity) flows are also present on scales up to 5 kpc in most systems. The three galaxies in our sample with obscured QSOs host higher velocity outflows than those in the three galaxies with no evidence for an active galactic nucleus. The peak outflow velocity in each of the QSOs is in the range 1450-3350 km s{sup -1}, and the highest velocities (2000-3000 km s{sup -1}) are seen only in ionized gas. The outflow energy and momentum in the QSOs are difficult to produce from a starburst alone, but are consistent with the QSO contributing significantly to the driving of the flow. Finally, when all gas phases are accounted for, the outflows are massive enough to provide negative feedback to star formation.« less

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.

Coalescence Effects on Neutron Production in High Energy Nucleus-Nucleus Collisions

DTIC Science & Technology

2001-08-01

25/Jun/2001 THESIS 1 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER COALESCENCE EFFECTS ON NEUTRON PRODUCTION IN HIGH- ENERGY NUCLEUS-NUCLEUS COLLISIONS 5b... Energy Nucleus-Nucleus Collisions." I have examined the final copy of this thesis for form and content and recommend that it be accepted in partial...School COALESCENCE EFFECTS ON NEUTRON PRODUCTION IN HIGH ENERGY NUCLEUS-NUCLEUS COLLISIONS A Thesis Presented for the Master of Science Degree The

On the functional anatomy of the nucleus of the optic tract-dorsal terminal nucleus commissural connection in the opossum (Didelphis marsupialis aurita).

PubMed

Vargas, C D; Volchan, E; Hokoç, J N; Pereira, A; Bernardes, R F; Rocha-Miranda, C E

1997-01-01

Immunocytochemical methods revealed the presence of GABA in cell bodies and terminals in the nucleus of the optic tract-dorsal terminal nucleus, the medial terminal nucleus, the lateral terminal nucleus and the interstitial nucleus of the superior fasciculus of the opossum (Didelphis marsupialis aurita). Moreover, after unilateral injections of rhodamine beads in the nucleus of the optic tract-dorsal terminal nucleus complex and processing for GABA, double-labelled cells were detected in the ipsilateral complex, up to 400 microns from the injected site, but not in the opposite. Analysis of the distributions of GABAergic and retrogradely-labelled cells throughout the contralateral nucleus of the optic tract-dorsal terminal nucleus showed that the highest density of GABAergic and rhodamine-labelled cells overlapped at the middle third of the complex. Previous electrophysiological data obtained in the opossum had suggested the existence, under certain conditions, of an inhibitory action between the nucleus of the optic tract-dorsal terminal nucleus of one side over the other. The absence of GABAergic commissural neurons may imply that this inhibition is mediated by an excitatory commissural pathway that activates GABAergic interneurons.

Stronger activation of SREBP-1a by nucleus-localized HBx

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

Wu, Qi; Qiao, Ling; Yang, Jian

2015-05-08

We previously showed that hepatitis B virus (HBV) X protein activates the sterol regulatory element-binding protein-1a (SREBP-1a). Here we examined the role of nuclear localization of HBx in this process. In comparison to the wild-type and cytoplasmic HBx, nuclear HBx had stronger effects on SREBP-1a and fatty acid synthase transcription activation, intracellular lipid accumulation and cell proliferation. Furthermore, nuclear HBx could activate HBV enhancer I/X promoter and was more effective on up-regulating HBV mRNA level in the context of HBV replication than the wild-type HBx, while the cytoplasmic HBx had no effect. Our results demonstrate the functional significance of themore » nucleus-localized HBx in regulating host lipogenic pathway and HBV replication. - Highlights: • Nuclear HBx is more effective on activating SREBP-1a and FASN transcription. • Nuclear HBx is more effective on enhancing intracellular lipid accumulation. • Nuclear HBx is more effective on enhancing cell proliferation. • Nuclear HBx up-regulates HBV enhancer I/X promoter activity. • Nuclear HBx increases HBV mRNA level in the context of HBV replication.« less

Diffuse γ-ray emission from misaligned active galactic nuclei

DOE PAGES

Di Mauro, M.; Calore, F.; Donato, F.; ...

2013-12-20

Active galactic nuclei (AGNs) with jets seen at small viewing angles are the most luminous and abundant objects in the γ-ray sky. AGNs with jets misaligned along the line of sight appear fainter in the sky but are more numerous than the brighter blazars. Here, we calculate the diffuse γ-ray emission due to the population of misaligned AGNs (MAGNs) unresolved by the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (Fermi). Furthermore, a correlation between the γ-ray luminosity and the radio-core luminosity is established and demonstrated to be physical by statistical tests, as well as compatible with uppermore » limits based on Fermi-LAT data for a large sample of radio-loud MAGNs. We constrain the derived γ-ray luminosity function by means of the source-count distribution of the radio galaxies detected by the Fermi-LAT. We finally calculate the diffuse γ-ray flux due to the whole MAGN population. These results demonstrate that MAGNs can contribute from 10% up to nearly the entire measured isotropic gamma-ray background. We evaluate a theoretical uncertainty on the flux of almost an order of magnitude.« less

Aspects of Supermassive Black Hole Growth in Nearby Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Lena, Davide

Super-massive black holes (SBHs) have long been identified as the engines of active galactic nuclei (AGNs) and are now considered to play a key role in galaxy evolution. In this dissertation I present results from two observational studies conducted on nearby AGNs with the aim of furthering our understanding of SBH growth and their interplay with the host galaxies. The first study is an observational search for SBHs spatially offset from the center of their host galaxies. Such offsets can be considered signatures of gravitational recoil following the coalescence of an SBH binary system (formed in the aftermath of a galaxy merger) due to emission of gravitational waves. The study is based on a photometric analysis of fourteen nearby elliptical galaxies observed with the Hubble Space Telescope. I find that parsec-scale offsets are common. However, while these are individually consistent with residual gravitational recoil oscillations, there is a high probability that larger offsets than those actually observed should have been found in the sample as a whole. There are a number of possible explanations for this result: the galaxy merger rate may be lower than current estimates; SBH-binaries may reach the merger stage with a configuration which minimizes recoil velocities; or the SBH oscillations are more quickly damped than predicted. In the second study I use integral field spectroscopy obtained with the Gemini South telescope to investigate the kinematics of the circum-nuclear ionized gas in two active galaxies: NGC 1386, a Seyfert 2, and NGC 1365, a Seyfert 1. The goal of the study is to investigate outflows in low-luminosity AGNs, and the mechanisms channeling gas (the SBH fuel) from the inner kiloparsec down to a few tens of parsecs from the SBH. I find that the dominant kinematic components can be explained as a combination of rotation in the large-scale galactic disk and compact outflows along the axis of the AGN "radiation cone". However, in the case of NGC

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.

An infrared jet in Centaurus A (NGC 5128): Evidence for interaction between the active nucleus and the interstellar medium

NASA Technical Reports Server (NTRS)

Joy, Marshall; Harvey, P. M.; Tollestrup, E. V.; Mcgregor, P. J.; Hyland, A. R.

1990-01-01

In the present study, higher resolution near infrared images of the visually-obscured central region of Centaurus A were obtained in order to investigate the effects of the active nucleus on the surrounding galaxy. Researchers present J(1.25 microns), H(1.65 microns), and K(2.2 microns) images of the central 40 seconds of the galaxy, taken with the Univ. of Texas InSb array camera on the Anglo Australian 3.9 meter telescope. These images reveal a jet extending approx. 10 arcseconds to the northeast of the nucleus at the same position angle as the x ray and radio jets. The infrared jet is most prominent at the shortest wavelength (1.25 microns), where its brightness surpasses that of the nucleus. The blue appearance of the infrared jet is remarkable considering the heavy obscuration that is evident at visual wavelengths. The amount of reddening in the vicinity of the jet is determined from the measured colors of the stellar core of the galaxy, and this value is used to generate an extinction-corrected energy distribution. In contrast to previously studied optical and infrared jets in active nuclei, the short-wavelength prominence of the Cen A jet indicates that it cannot be attributed to synchrotron emission from a beam of relativistic electrons. The remaining viable mechanisms involve an interaction between the interstellar medium and the active nucleus: the infrared radiation from the jet may be due to emission from interstellar gas that has been entrained and heated by the flow of relativistic particles from the nucleus; alternatively, luminous blue stars may have been created by compression of interstellar material by the relativistic plasma. To investigate these proposed mechanisms, near-infrared spectroscopic studies of Cen A are in progress to look for collisionally excited molecular hydrogen emission lines and recombination lines from ionized gas.

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.

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.

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.

Structural dynamics of the cell nucleus

PubMed Central

Wiegert, Simon; Bading, Hilmar

2011-01-01

Neuronal morphology plays an essential role in signal processing in the brain. Individual neurons can undergo use-dependent changes in their shape and connectivity, which affects how intracellular processes are regulated and how signals are transferred from one cell to another in a neuronal network. Calcium is one of the most important intracellular second messengers regulating cellular morphologies and functions. In neurons, intracellular calcium levels are controlled by ion channels in the plasma membrane such as NMDA receptors (NMDARs), voltage-gated calcium channels (VGCCs) and certain α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) as well as by calcium exchange pathways between the cytosol and internal calcium stores including the endoplasmic reticulum and mitochondria. Synaptic activity and the subsequent opening of ligand and/or voltage-gated calcium channels can initiate cytosolic calcium transients which propagate towards the cell soma and enter the nucleus via its nuclear pore complexes (NPCs) embedded in the nuclear envelope. We recently described the discovery that in hippocampal neurons the morphology of the nucleus affects the calcium dynamics within the nucleus. Here we propose that nuclear infoldings determine whether a nucleus functions as an integrator or detector of oscillating calcium signals. We outline possible ties between nuclear mophology and transcriptional activity and discuss the importance of extending the approach to whole cell calcium signal modeling in order to understand synapse-to-nucleus communication in healthy and dysfunctional neurons. PMID:21738832

Finding Distant Galactic HII Regions

NASA Astrophysics Data System (ADS)

Anderson, L. D.; Armentrout, W. P.; Johnstone, B. M.; Bania, T. M.; Balser, Dana S.; Wenger, Trey V.; Cunningham, V.

2015-12-01

The WISE Catalog of Galactic H ii Regions contains ˜2000 H ii region candidates lacking ionized gas spectroscopic observations. All candidates have the characteristic H ii region mid-infrared morphology of WISE 12 μ {{m}} emission surrounding 22 μ {{m}} emission, and additionally have detected radio continuum emission. We here report Green Bank Telescope hydrogen radio recombination line and radio continuum detections in the X-band (9 GHz; 3 cm) of 302 WISE H ii region candidates (out of 324 targets observed) in the zone 225^\\circ ≥slant {\\ell }≥slant -20^\\circ , | {\\text{}}b| ≤slant 6^\\circ . Here we extend the sky coverage of our H ii region Discovery Survey, which now contains nearly 800 H ii regions distributed across the entire northern sky. We provide LSR velocities for the 302 detections and kinematic distances for 131 of these. Of the 302 new detections, 5 have ({\\ell },{\\text{}}b,v) coordinates consistent with the Outer Scutum-Centaurus Arm (OSC), the most distant molecular spiral arm of the Milky Way. Due to the Galactic warp, these nebulae are found at Galactic latitudes >1° in the first Galactic quadrant, and therefore were missed in previous surveys of the Galactic plane. One additional region has a longitude and velocity consistent with the OSC but lies at a negative Galactic latitude (G039.183-01.422 -54.9 {km} {{{s}}}-1). With Heliocentric distances >22 kpc and Galactocentric distances >16 kpc, the OSC H ii regions are the most distant known in the Galaxy. We detect an additional three H ii regions near {\\ell }≃ 150^\\circ whose LSR velocities place them at Galactocentric radii >19 kpc. If their distances are correct, these nebulae may represent the limit to Galactic massive star formation.

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

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.

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.

Implications of gamma band activity in the pedunculopontine nucleus

PubMed Central

Garcia-Rill, E.; Luster, B.; D’Onofrio, S.; Mahaffey, S.; Bisagno, V.; Urbano, F. J.

2015-01-01

The fact that the pedunculopontine nucleus (PPN) is part of the reticular activating system places it in a unique position to modulate sensory input and fight-or-flight responses. Arousing stimuli simultaneously activate ascending projections of the PPN to the intralaminar thalamus to trigger cortical high frequency activity and arousal, as well as descending projections to reticulospinal systems to alter posture and locomotion. As such, the PPN has become a target for deep brain stimulation (DBS) for the treatment of Parkinson’s disease (PD), modulating gait, posture, and higher functions. This article describes the latest discoveries on PPN physiology and the role of the PPN in a number of disorders. It has now been determined that high frequency activity during waking and REM sleep is controlled by two different intracellular pathways and two calcium channels in PPN cells. Moreover, there are three different PPN cell types that have one or both calcium channels and may be active during waking only, REM sleep only, or both. Based on the new discoveries, novel mechanisms are proposed for insomnia as a waking disorder. In addition, neuronal calcium sensor protein-1 (NCS-1), which is over expressed in schizophrenia and bipolar disorder, may be responsible for the dysregulation in gamma band activity in at least some patients with these diseases. Recent results suggest that NCS-1 modulates PPN gamma band activity and that lithium acts to reduce the effects of over expressed NCS-1, accounting for its effectiveness in bipolar disorder. PMID:26597124

Cometary activity and nucleus modelling: a new approach

NASA Astrophysics Data System (ADS)

Möhlmann, D.

1996-06-01

The phenomena of comet splittings with an average frequency of about one splitting per 100 years and comet (Chen and Jewitt, Icarus108, 265-271, 1994), and the restriction of cometary activity to well-defined small areas at the almost passive and mantle covered surface (Keller et al., ESA SP-250, Vol. II, pp. 363-364, 1986) are at present driving challenges to models of structure and evolution of comet nuclei. Extending the presently discussed models by incorporating lateral subsurface transport of sublimed volatiles, there appears the possibility that the places of sublimation are different from those of activity (the so-called active areas). Then, there is no necessity to distinguish between different surface properties at active and passive areas, assuming, e.g. an uncovered icy surface at active areas. Active areas are simply the very local "source sites" where the accumulated subsurface flows from distant regions reach the surface. The pressure driven subsurface flows of volatiles may not only leave the comet at its surface, they may penetrate via cracks, etc. also deeply into the nucleus. There they can cause a further growth of cracks and also new cracks. This can be a cause for the observed regular splittings. Furthermore, actual models (Kührt and Keller, Icarus109, 121-132, 1994; Skorov and Rickman, Planet. Space Sci.43, 1587-1594, 1995) of the gas transport through porous comet surface crusts can be interpreted as to give first indications for thermodynamical parameters in heat conducting and porous cometary crusts which are appropriate for 1 AU conditions to permit the temporary existence of a layer with fluid subsurface water within these crusts. This exciting result of the possible temporary existence of subsurface warm water in comets which approach the Sun within about 1 AU makes a cometary subsurface chemistry much more efficient than expected hitherto.

Observing the Next Galactic Supernova

NASA Astrophysics Data System (ADS)

Adams, Scott M.; Kochanek, C. S.; Beacom, John F.; Vagins, Mark R.; Stanek, K. Z.

2013-12-01

No supernova (SN) in the Milky Way has been observed since the invention of the optical telescope, instruments for other wavelengths, neutrino detectors, or gravitational wave observatories. It would be a tragedy to miss the opportunity to fully characterize the next one. To aid preparations for its observations, we model the distance, extinction, and magnitude probability distributions of a successful Galactic core-collapse supernova (ccSN), its shock breakout radiation, and its massive star progenitor. We find, at very high probability (sime 100%), that the next Galactic SN will easily be detectable in the near-IR and that near-IR photometry of the progenitor star very likely (sime 92%) already exists in the Two Micron All Sky Survey. Most ccSNe (98%) will be easily observed in the optical, but a significant fraction (43%) will lack observations of the progenitor due to a combination of survey sensitivity and confusion. If neutrino detection experiments can quickly disseminate a likely position (~3°), we show that a modestly priced IR camera system can probably detect the shock breakout radiation pulse even in daytime (64% for the cheapest design). Neutrino experiments should seriously consider adding such systems, both for their scientific return and as an added and internal layer of protection against false triggers. We find that shock breakouts from failed ccSNe of red supergiants may be more observable than those of successful SNe due to their lower radiation temperatures. We review the process by which neutrinos from a Galactic ccSN would be detected and announced. We provide new information on the EGADS system and its potential for providing instant neutrino alerts. We also discuss the distance, extinction, and magnitude probability distributions for the next Galactic Type Ia supernova (SN Ia). Based on our modeled observability, we find a Galactic ccSN rate of 3.2^{+7.3}_{-2.6} per century and a Galactic SN Ia rate of 1.4^{+1.4}_{-0.8} per century for a

On the physical environment in the nucleus of Centaurus A /NGC 5128/

NASA Technical Reports Server (NTRS)

Beall, J. H.; Rose, W. K.

1980-01-01

A model is proposed for the radio and X-ray variability of the nucleus of Centaurus A in which an adiabatically expanding plasma containing a power-law distribution of relativistic electrons produces the radio flux by synchrotron emission, and the X-ray flux by inverse Compton scattering of an ambient distribution of thermal photons. The variability of Centaurus A is shown to be consistent with the expansion of an initially opaque, hot (1000-10,000 K) plasma which eventually becomes optically thin. Radio flares without corresponding X-ray flares are possible in this model because the plasma density decreases during the expansion, allowing radio radiation previously absorbed or suppressed to be observed. Some consequences of the model for the physical environment in galactic nuclei are discussed.

Understanding the spectral hardenings and radial distribution of Galactic cosmic rays and Fermi diffuse γ rays with spatially-dependent propagation

NASA Astrophysics Data System (ADS)

Guo, Yi-Qing; Yuan, Qiang

2018-03-01

Recent direct measurements of Galactic cosmic ray spectra by balloon/space-borne detectors reveal spectral hardenings of all major nucleus species at rigidities of a few hundred GV. The all-sky diffuse γ -ray emissions measured by the Fermi Large Area Telescope also show spatial variations of the intensities and spectral indices of cosmic rays. These new observations challenge the traditional simple acceleration and/or propagation scenario of Galactic cosmic rays. In this work, we propose a spatially dependent diffusion scenario to explain all these phenomena. The diffusion coefficient is assumed to be anticorrelated with the source distribution, which is a natural expectation from the charged particle transportation in a turbulent magnetic field. The spatially dependent diffusion model also gives a lower level of anisotropies of cosmic rays, which are consistent with observations by underground muons and air shower experiments. The spectral variations of cosmic rays across the Galaxy can be properly reproduced by this model.

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.

Galactic politics

NASA Image and Video Library

2015-12-07

Only rarely does an astronomical object have a political association. However, the spiral galaxy NGC 7252 acquired exactly that when it was given an unusual nickname. In December 1953, the US President Dwight D. Eisenhower gave a speech advocating the use of nuclear power for peaceful purposes. This  “Atoms for Peace” speech was significant for the scientific community, as it brought nuclear research into the public domain, and NGC 7252, which has a superficial resemblance to an atomic nucleus surrounded by the loops of electronic orbits, was dubbed the Atoms for Peace galaxy in honour of this. These loops are well visible in a wider field of view image. This nickname is quite ironic, as the galaxy’s past was anything but peaceful. Its peculiar appearance is the result of a collision between two galaxies that took place about a billion years ago, which ripped both galaxies apart. The loop-like outer structures, likely made up of dust and stars flung outwards by the crash, but recalling orbiting electrons in an atom, are partly responsible for the galaxy’s nickname. This NASA/ESA Hubble Space Telescope image shows the inner parts of the galaxy, revealing a pinwheel-shaped disc that is rotating in a direction opposite to the rest of the galaxy. This disc resembles a spiral galaxy like our own galaxy, the Milky Way, but is only about 10 000 light-years across — about a tenth of the size of the Milky Way. It is believed that this whirling structure is a remnant of the galactic collision. It will most likely have vanished in a few billion years’ time, when NGC 7252 will have completed its merging process.

Comprehensive model for the nucleus of Periodic Comet Tempel 2 and its activity

NASA Technical Reports Server (NTRS)

Sekanina, Zdenek

1991-01-01

A comprehensive synergistic physical model for the nucleus of Periodic Comet Tempel 2 was developed on the basis of observations carried out in 1988. The model includes the best possible estimates of the comet's bulk properties (including the dimensions and the approximate shape), information on its state of rotation, and the characterization of its activity. The model is shown to be consistent with all lines of evidence that are currently available, including relevant information from earlier apparitions.

FERMI Observations of TeV-Selected Active Galactic Nuclei

DOE PAGES

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

2009-12-04

Here, we report on observations of TeV-selected active galactic nuclei (AGNs) made during the first 5.5 months of observations with the Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope (Fermi). In total, 96 AGNs were selected for study, each being either (1) a source detected at TeV energies (28 sources) or (2) an object that has been studied with TeV instruments and for which an upper limit has been reported (68 objects). The Fermi observations show clear detections of 38 of these TeV-selected objects, of which 21 are joint GeV-TeV sources, and 29 were not in the thirdmore » EGRET catalog. For each of the 38 Fermi-detected sources, spectra and light curves are presented. Most can be described with a power law of spectral index harder than 2.0, with a spectral break generally required to accommodate the TeV measurements. Based on an extrapolation of the Fermi spectrum, we identify sources, not previously detected at TeV energies, which are promising targets for TeV instruments. Finally, evidence for systematic evolution of the γ-ray spectrum with redshift is presented and discussed in the context of interaction with the extragalactic background light.« less

Galactic cosmic ray composition

NASA Technical Reports Server (NTRS)

Meyer, J. P.

1986-01-01

An assessment is given of the galactic cosmic ray source (GCRS) elemental composition and its correlation with first ionization potential. The isotopic composition of heavy nuclei; spallation cross sections; energy spectra of primary nuclei; electrons; positrons; local galactic reference abundances; comparison of solar energetic particles and solar coronal compositions; the hydrogen; lead; nitrogen; helium; and germanium deficiency problems; and the excess of elements are among the topics covered.

The Structure of Active Galactic Nuclei

NASA Technical Reports Server (NTRS)

Kriss, Gerard A.

1997-01-01

We are continuing our systematic investigation of the nuclear structure of nearby active galactic nuclei (AGN). Upon completion, our study will characterize hypothetical constructs such as narrow-line clouds, obscuring tori, nuclear gas disks. and central black holes with physical measurements for a complete sample of nearby AGN. The major scientific goals of our program are: (1) the morphology of the NLR; (2) the physical conditions and dynamics of individual clouds in the NLR; (3) the structure and physical conditions of the warm reflecting gas; (4) the structure of the obscuring torus; (5) the population and morphology of nuclear disks/tori in AGN; (6) the physical conditions in nuclear disks; and (7) the masses of central black holes in AGN. We will use the Hubble Space Telescope (HST) to obtain high-resolution images and spatially resolved spectra. Far-UV spectroscopy of emission and absorption in the nuclear regions using HST/FOS and the Hopkins Ultraviolet Telescope (HUT) will help establish physical conditions in the absorbing and emitting gas. By correlating the dynamics and physical conditions of the gas with the morphology revealed through our imaging program, we will be able to examine mechanisms for fueling the central engine and transporting angular momentum. The kinematics of the nuclear gas disks may enable us to measure the mass of the central black hole. Contemporaneous X-ray observations using ASCA will further constrain the ionization structure of any absorbing material. Monitoring of variability in the UV and X-ray absorption will be used to determine the location of the absorbing gas, possibly in the outflowing warm reflecting gas, or the broad-line region, or the atmosphere of the obscuring torus. Supporting ground-based observations in the optical, near-IR, imaging polarimetry, and the radio will complete our picture of the nuclear structures. With a comprehensive survey of these characteristics in a complete sample of nearby AGN, our

The Halo Occupation Distribution of Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Chatterjee, Suchetana; Nagai, D.; Richardson, J.; Zheng, Z.; Degraf, C.; DiMatteo, T.

2011-05-01

We investigate the halo occupation distribution of active galactic nuclei (AGN) using a state-of-the-art cosmological hydrodynamic simulation that self-consistently incorporates the growth and feedback of supermassive black holes and the physics of galaxy formation (DiMatteo et al. 2008). We show that the mean occupation function can be modeled as a softened step function for central AGN and a power law for the satellite population. The satellite occupation is consistent with weak redshift evolution and a power law index of unity. The number of satellite black holes at a given halo mass follows a Poisson distribution. We show that at low redshifts (z=1.0) feedback from AGN is responsible for higher suppression of black hole growth in higher mass halos. This effect introduces a bias in the correlation between instantaneous AGN luminosity and the host halo mass, making AGN clustering depend weakly on luminosity at low redshifts. We show that the radial distribution of AGN follows a power law which is fundamentally different from those of galaxies and dark matter. The best-fit power law index is -2.26 ± 0.23. The power law exponent do not show any evolution with redshift, host halo mass and AGN luminosity within statistical limits. Incorporating the environmental dependence of supermassive black hole accretion and feedback, our formalism provides the most complete theoretical tool for interpreting current and future measurements of AGN clustering.

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.

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.

Eye movements and abducens motoneuron behavior after cholinergic activation of the nucleus reticularis pontis caudalis.

PubMed

Márquez-Ruiz, Javier; Escudero, Miguel

2010-11-01

the aim of this work was to characterize eye movements and abducens (ABD) motoneuron behavior after cholinergic activation of the nucleus reticularis pontis caudalis (NRPC). six female adult cats were prepared for chronic recording of eye movements (using the scleral search-coil technique), electroencephalography, electromyography, ponto-geniculo-occipital (PGO) waves in the lateral geniculate nucleus, and ABD motoneuron activities after microinjections of the cholinergic agonist carbachol into the NRPC. unilateral microinjections of carbachol in the NRPC induced tonic and phasic phenomena in the oculomotor system. Tonic effects consisted of ipsiversive rotation to the injected side, convergence, and downward rotation of the eyes. Phasic effects consisted of bursts of rhythmic rapid eye movements directed contralaterally to the injected side along with PGO-like waves in the lateral geniculate and ABD nuclei. Although tonic effects were dependent on the level of drowsiness, phasic effects were always present and appeared along with normal saccades when the animal was vigilant. ABD motoneurons showed phasic activities associated with ABD PGO-like waves during bursts of rapid eye movements, and tonic and phasic activities related to eye position and velocity during alertness. the cholinergic activation of the NRPC induces oculomotor phenomena that are somewhat similar to those described during REM sleep. A precise comparison of the dynamics and timing of the eye movements further suggests that a temporal organization of both NRPCs is needed to reproduce the complexity of the oculomotor behavior during REM sleep.

Strongly Magnetized Accretion Disks in Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Begelman, Mitchell

Accretion disks likely provide the conduit for fueling active galactic nuclei (AGN), linking the black hole's immediate surroundings to the host galaxy's nuclear star cluster, and possibly beyond. Yet detailed AGN disk models fail to explain several of the most basic observational features of AGN: How do the outer regions of the disk avoid stalling as a result of wholesale gravitational fragmentation? What regulates the amount of star formation that is inferred to accompany accretion in some AGN? Why is the broad emission line region a ubiquitous feature of luminous AGN? What processes create and maintain the so-called "dusty torus"? Analytic work suggests that vertical pressure support of the disk primarily by a toroidal magnetic field, rather than by gas or radiation pressure, can readily resolve these problems. And recent numerical simulations have indicated that such a strong toroidal field is the inevitable consequence of the magnetorotational instability (MRI) when a disk accumulates a modest amount of net magnetic flux, thus providing a sound theoretical basis for strongly magnetized disks. We propose an analytic and computational study of such disks in the AGN context, focusing on: (1) The basic physical properties of strongly magnetized AGN disks. We will focus on the competition between field generation and buoyancy, improving on previous work by considering realistic equations of state, dissipative processes and radiative losses. We will use global simulations to test the limiting magnetic fields that can be produced by MRIdriven accretion disk dynamos and explore the driving mechanisms of disk winds and the resulting levels of mass, angular momentum and energy loss. (2) Gravitational fragmentation and star formation in strongly magnetized disks. We will determine how a strong field reduces and regulates gravitational fragmentation, by both lowering the disk density and creating a stratified structure in which star formation near the equator can co

Nucleus accumbens hyperpolarization-activated cyclic nucleotide-gated channels modulate methamphetamine self-administration in rats.

PubMed

Cao, Dan-Ni; Song, Rui; Zhang, Shu-Zhuo; Wu, Ning; Li, Jin

2016-08-01

Methamphetamine addiction is believed to primarily result from increased dopamine release and the inhibition of dopamine uptake. Some evidence suggests that hyperpolarization-activated cyclic nucleotide-gated (HCN) channels play important roles in the functional modulation of dopaminergic neurons and the pathophysiology of related diseases. However, little is known about the effects of HCN channels on methamphetamine addiction. The present study investigated the role of brain HCN channels in methamphetamine addiction. Acute intracerebroventricular (i.c.v.) injection or bilateral intra-accumbens microinjections of non-selective HCN channel blocker ZD7288 (0.3125 and 0.625 μg) significantly reduced both methamphetamine (0.0125 or 0.05 mg/kg/infusion)-induced self-administration under fixed ratio 2 reinforcement and the breakpoint of methamphetamine (0.05 mg/kg/infusion) under progressive ratio reinforcement in rats. Moreover, compared with i.c.v. injection, bilateral intra-accumbens microinjections of ZD7288 exerted stronger inhibitory effects, suggesting that blockade of HCN channels in the nucleus accumbens reduced the reinforcing effects of and motivation for methamphetamine. We also found that ZD7288 (0.625 and 1.25 μg, i.c.v.) significantly decreased methamphetamine (1 mg/kg, intraperitoneal (i.p.))-induced hyperactivity with no effect on the spontaneous activity in rats. Finally, in vivo microdialysis experiments showed that the HCN channel blockade using ZD7288 (0.625 and 1.25 μg, i.c.v.) decreased methamphetamine (1 mg/kg, i.p.)-induced elevation of extracellular dopamine levels in the nucleus accumbens. These results indicate that HCN channels in the nucleus accumbens are involved in the reinforcing properties of methamphetamine and highlight the importance of HCN channels in the regulation of dopamine neurotransmission underlying methamphetamine addiction.

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.

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.

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

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.

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

Velocity field and physical conditions in the active lenticular galaxy NGC 3998

NASA Technical Reports Server (NTRS)

Blackman, C. P.; Wilson, A. S.; Ward, M. J.

1983-01-01

A rotating and expanding flattened distribution of gas is suggested by measurements of the emission line velocity field for the line elliptical/lenticular galaxy NGC 3998, using seven long slit spectrograms in five position angles. Expanding material kinetic energy values of 10 to the 53rd to 10 to the 54th ergs, together with the flat spectrum radio source and nucleus X-ray emission, indicate pronounced nuclear activity. Spectrophotometry of the galactic nucleus shows emission line strengths typical of shocks rather than of photoionization, and line ratios indicate a postshock temperature of 60,000 K and a preshock density of 25 particles/cu cm. Both the stars and the ionized gas of the galaxy have central velocity dispersions of 260 km/s. In view of the high rotational velocity of the stars, NGC 3998 is a lenticular rather than elliptical galaxy.

RESOLVING THE BRIGHT HCN(1–0) EMISSION TOWARD THE SEYFERT 2 NUCLEUS OF M51: SHOCK ENHANCEMENT BY RADIO JETS AND WEAK MASING BY INFRARED PUMPING?

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

Matsushita, Satoki; Trung, Dinh-V-; Boone, Frédéric

2015-01-20

We present high angular resolution observations of the HCN(1-0) emission (at ∼1'' or ∼34 pc), together with CO J = 1-0, 2-1, and 3-2 observations, toward the Seyfert 2 nucleus of M51 (NGC 5194). The overall HCN(1-0) distribution and kinematics are very similar to that of the CO lines, which have been indicated as the jet-entrained molecular gas in our past observations. In addition, high HCN(1-0)/CO(1-0) brightness temperature ratio of about unity is observed along the jets, similar to that observed at the shocked molecular gas in our Galaxy. These results strongly indicate that both diffuse and dense gases are entrained bymore » the jets and outflowing from the active galactic nucleus. The channel map of HCN(1-0) at the systemic velocity shows a strong emission right at the nucleus, where no obvious emission has been detected in the CO lines. The HCN(1-0)/CO(1-0) brightness temperature ratio at this region reaches >2, a value that cannot be explained considering standard physical/chemical conditions. Based on our calculations, we suggest infrared pumping and possibly weak HCN masing, but still requiring an enhanced HCN abundance for the cause of this high ratio. This suggests the presence of a compact dense obscuring molecular gas in front of the nucleus of M51, which remains unresolved at our ∼1'' (∼34 pc) resolution, and consistent with the Seyfert 2 classification picture.« less

Cell Biology of the Caenorhabditis elegans Nucleus

PubMed Central

Cohen-Fix, Orna; Askjaer, Peter

2017-01-01

Studies on the Caenorhabditis elegans nucleus have provided fascinating insight to the organization and activities of eukaryotic cells. Being the organelle that holds the genetic blueprint of the cell, the nucleus is critical for basically every aspect of cell biology. The stereotypical development of C. elegans from a one cell-stage embryo to a fertile hermaphrodite with 959 somatic nuclei has allowed the identification of mutants with specific alterations in gene expression programs, nuclear morphology, or nuclear positioning. Moreover, the early C. elegans embryo is an excellent model to dissect the mitotic processes of nuclear disassembly and reformation with high spatiotemporal resolution. We review here several features of the C. elegans nucleus, including its composition, structure, and dynamics. We also discuss the spatial organization of chromatin and regulation of gene expression and how this depends on tight control of nucleocytoplasmic transport. Finally, the extensive connections of the nucleus with the cytoskeleton and their implications during development are described. Most processes of the C. elegans nucleus are evolutionarily conserved, highlighting the relevance of this powerful and versatile model organism to human biology. PMID:28049702

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)

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).

AGN ACTIVITY AND IGM HEATING IN THE FOSSIL CLUSTER RX J1416.4+2315

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

Miraghaei, H.; Khosroshahi, H. G.; Abbassi, S.

2015-12-15

We study active galactic nucleus (AGN) activity in the fossil galaxy cluster RX J1416.4+2315. Radio observations were carried out using the Giant Metrewave Radio Telescope at two frequencies, 1420 and 610 MHz. A weak radio lobe that extends from the central nucleus is detected in the 610 MHz map. Assuming the radio lobe originated from the central AGN, we show that the energy injection into the intergalactic medium is only sufficient to heat up the central 50 kpc within the cluster core, while the cooling radius is larger (∼130 kpc). In the hardness ratio map, three low energy cavities havemore » been identified. No radio emission is detected for these regions. We evaluated the power required to inflate the cavities and showed that the total energy budget is sufficient to offset the radiative cooling. We showed that the initial conditions would change the results remarkably. Furthermore, the efficiency of the Bondi accretion in powering the AGN has been estimated.« 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 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 Nuclei, Host Star Formation, and the Far Infrared

NASA Astrophysics Data System (ADS)

Draper, Aden R.; Ballantyne, D. R.

2011-05-01

Telescopes like Herschel and the Atacama Large Millimeter/submillimeter Array (ALMA) are creating new opportunities to study sources in the far infrared (FIR), a wavelength region dominated by cold dust emission. Probing cold dust in active galaxies allows for study of the star formation history of active galactic nuclei (AGN) hosts. The FIR is also an important spectral region for observing AGN which are heavily enshrouded by dust, such as Compton thick (CT) AGN. By using information from deep X-ray surveys and cosmic X-ray background synthesis models, we compute Cloudy photoionization simulations which are used to predict the spectral energy distribution (SED) of AGN in the FIR. Expected differential number counts of AGN and their host galaxies are calculated in the Herschel bands. The expected contribution of AGN and their hosts to the cosmic infrared background (CIRB) is also computed. Multiple star formation scenarios are investigated using a modified blackbody star formation SED. It is found that FIR observations at 350 and 500 um are an excellent tool in determining the star formation history of AGN hosts. Additionally, the AGN contribution to the CIRB can be used to determine whether star formation in AGN hosts evolves differently than in normal galaxies. AGN and host differential number counts are dominated by CT AGN in the Herschel-SPIRE bands. Therefore, X-ray stacking of bright SPIRE sources is likely to disclose a large fraction of the CT AGN population.

Obscuration-dependent Evolution of Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Buchner, Johannes; Georgakakis, Antonis; Nandra, Kirpal; Brightman, Murray; Menzel, Marie-Luise; Liu, Zhu; Hsu, Li-Ting; Salvato, Mara; Rangel, Cyprian; Aird, James; Merloni, Andrea; Ross, Nicholas

2015-04-01

We aim to constrain the evolution of active galactic nuclei (AGNs) as a function of obscuration using an X-ray-selected sample of ~2000 AGNs from a multi-tiered survey including the CDFS, AEGIS-XD, COSMOS, and XMM-XXL fields. The spectra of individual X-ray sources are analyzed using a Bayesian methodology with a physically realistic model to infer the posterior distribution of the hydrogen column density and intrinsic X-ray luminosity. We develop a novel non-parametric method that allows us to robustly infer the distribution of the AGN population in X-ray luminosity, redshift, and obscuring column density, relying only on minimal smoothness assumptions. Our analysis properly incorporates uncertainties from low count spectra, photometric redshift measurements, association incompleteness, and the limited sample size. We find that obscured AGNs with N H > 1022 cm-2 account for {77}+4-5% of the number density and luminosity density of the accretion supermassive black hole population with L X > 1043 erg s-1, averaged over cosmic time. Compton-thick AGNs account for approximately half the number and luminosity density of the obscured population, and {38}+8-7% of the total. We also find evidence that the evolution is obscuration dependent, with the strongest evolution around N H ≈ 1023 cm-2. We highlight this by measuring the obscured fraction in Compton-thin AGNs, which increases toward z ~ 3, where it is 25% higher than the local value. In contrast, the fraction of Compton-thick AGNs is consistent with being constant at ≈35%, independent of redshift and accretion luminosity. We discuss our findings in the context of existing models and conclude that the observed evolution is, to first order, a side effect of anti-hierarchical growth.

Variability in nucleus accumbens activity mediates age-related suboptimal financial risk taking

PubMed Central

Samanez-Larkin, Gregory R.; Kuhnen, Camelia M.; Yoo, Daniel J.; Knutson, Brian

2010-01-01

As human life expectancy continues to rise, financial decisions of aging investors may have an increasing impact on the global economy. In this study, we examined age differences in financial decisions across the adult life span by combining functional neuroimaging with a dynamic financial investment task. During the task, older adults made more suboptimal choices than younger adults when choosing risky assets. This age-related effect was mediated by a neural measure of temporal variability in nucleus accumbens activity. These findings reveal a novel neural mechanism by which aging may disrupt rational financial choice. PMID:20107069

Activity Parameters of Subthalamic Nucleus Neurons Selectively Predict Motor Symptom Severity in Parkinson's Disease

PubMed Central

Gulberti, Alessandro; Zittel, Simone; Tudor Jones, Adam A.; Fickel, Ulrich; Münchau, Alexander; Köppen, Johannes A.; Gerloff, Christian; Westphal, Manfred; Buhmann, Carsten; Hamel, Wolfgang; Engel, Andreas K.

2014-01-01

Parkinson's disease (PD) is a heterogeneous disorder that leads to variable expression of several different motor symptoms. While changes in firing rate, pattern, and oscillation of basal ganglia neurons have been observed in PD patients and experimental animals, there is limited evidence linking them to specific motor symptoms. Here we examined this relationship using extracellular recordings of subthalamic nucleus neurons from 19 PD patients undergoing surgery for deep brain stimulation. For each patient, ≥10 single units and/or multi-units were recorded in the OFF medication state. We correlated the proportion of neurons displaying different activities with preoperative Unified Parkinson's Disease Rating Scale subscores (OFF medication). The mean spectral power at sub-beta frequencies and percentage of units oscillating at beta frequencies were positively correlated with the axial and limb rigidity scores, respectively. The percentage of units oscillating at gamma frequency was negatively correlated with the bradykinesia scores. The mean intraburst rate was positively correlated with both bradykinesia and axial scores, while the related ratio of interspike intervals below/above 10 ms was positively correlated with these symptoms and limb rigidity. None of the activity parameters correlated with tremor. The grand average of all the significantly correlated subthalamic nucleus activities accounted for >60% of the variance of the combined bradykinetic-rigid and axial scores. Our results demonstrate that the occurrence of alterations in the rate and pattern of basal ganglia neurons could partly underlie the variability in parkinsonian phenotype. PMID:24790198

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

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

The Nucleus Accumbens and Pavlovian Reward Learning

PubMed Central

Day, Jeremy J.

2011-01-01

The ability to form associations between predictive environmental events and rewarding outcomes is a fundamental aspect of learned behavior. This apparently simple ability likely requires complex neural processing evolved to identify, seek, and utilize natural rewards and redirect these activities based on updated sensory information. Emerging evidence from both animal and human research suggests that this type of processing is mediated in part by the nucleus accumbens and a closely associated network of brain structures. The nucleus accumbens is required for a number of reward-related behaviors, and processes specific information about reward availability, value, and context. Additionally, this structure is critical for the acquisition and expression of most Pavlovian stimulus-reward relationships, and cues that predict rewards produce robust changes in neural activity in the nucleus accumbens. While processing within the nucleus accumbens may enable or promote Pavlovian reward learning in natural situations, it has also been implicated in aspects of human drug addiction, including the ability of drug-paired cues to control behavior. This article will provide a critical review of the existing animal and human literature concerning the role of the NAc in Pavlovian learning with non-drug rewards and consider some clinical implications of these findings. PMID:17404375

Ionized Absorbers in Active Galactic Nuclei and Very Steap Soft X-Ray Quasars

NASA Technical Reports Server (NTRS)

Fiore, Fabrizio; White, Nicholas (Technical Monitor)

2000-01-01

Steep soft X-ray (0.1-2 keV) quasars share several unusual properties: narrow Balmer lines, strong Fe II emission, large and fast X-ray variability, and a rather steep 2-10 keV spectrum. These intriguing objects have been suggested to be the analogues of Galactic black hole candidates in the high, soft state. We present here results from ASCA observations for two of these quasars: NAB 0205 + 024 and PG 1244 + 026. Both objects show similar variations (factor of approximately 2 in 10 ks), despite a factor of approximately 10 difference in the 0.5-10 keV luminosity (7.3 x 10(exp 43) erg/s for PG 1244 + 026 and 6.4 x 10(exp 44) erg/s for NAB 0205 + 024, assuming isotropic emission, H(sub 0) = 50.0 and q(sub 0) = 0.0). The X-ray continuum of the two quasars flattens by 0.5-1 going from the 0.1-2 keV band towards higher energies, strengthening recent results on another half-dozen steep soft X-ray active galactic nuclei. PG 1244 + 026 shows a significant feature in the '1-keV' region, which can be described either as a broad emission line centered at 0.95 keV (quasar frame) or as edge or line absorption at 1.17 (1.22) keV. The line emission could be a result of reflection from a highly ionized accretion disc, in line with the view that steep soft X-ray quasars are emitting close to the Eddington luminosity. Photoelectric edge absorption or resonant line absorption could be produced by gas outflowing at a large velocity (0.3-0.6 c).

Constraining the size of the dusty torus in Active Galactic Nuclei: An Optical/Infrared Reverberation Lag Study

NASA Astrophysics Data System (ADS)

Vazquez, Billy

The dusty torus is the key component in the Active Galactic Nuclei (AGN) Unification Scheme that explains the spectroscopic differences between Seyfert galaxies of types 1 and 2. The torus dust is heated by the nuclear source and emits the absorbed energy in the infrared (IR); but because of light travel times, the torus IR emission responds to variations of the nuclear ultraviolet/optical continuum with a delay that corresponds to the size of the emitting region. The results from a mid-infrared (MIR) monitoring campaign using the Spitzer Space Telescope and optical ground-based telescopes (B and V band imaging), which spanned over 2 years and covered a sample of 12 Seyfert galaxies, are presented. The aim was to constrain the distances from the nucleus to the regions in the torus emitting at wavelengths of 3.6 microm and 4.5 microm. MIR light curves showing the variability characteristics of these AGN are presented and the effects of photometric uncertainties on the time-series analysis of the light curves are discussed. Significant variability was observed in the IR light curves of 10 of 12 objects, with relative amplitudes ranging from ˜10% to ˜100% from their mean flux. The "reverberation lags" between the 3.6 microm and 4.5 microm IR bands were determined for the entire sample and between the optical and MIR bands for NGC6418. In NGC6418, the 3.6 microm and 4.5 microm fluxes lagged behind those of the optical continuum by 47.5+2.0-1.9) days and 62.5+2.5-2.9 days, respectively. This is consistent with the inferred lower limit to the sublimation radius for pure graphite grains at T=1800 K but smaller by a factor of 2 than the lower limit for dust grains with a "standard" interstellar medium (ISM) composition. There is evidence that the lags increased following approximately by a factor of 2 increase in luminosity, consistent with an increase in the sublimation radius.

Actomyosin Pulls to Advance the Nucleus in a Migrating Tissue Cell

PubMed Central

Wu, Jun; Kent, Ian A.; Shekhar, Nandini; Chancellor, T.J.; Mendonca, Agnes; Dickinson, Richard B.; Lele, Tanmay P.

2014-01-01

The cytoskeletal forces involved in translocating the nucleus in a migrating tissue cell remain unresolved. Previous studies have variously implicated actomyosin-generated pushing or pulling forces on the nucleus, as well as pulling by nucleus-bound microtubule motors. We found that the nucleus in an isolated migrating cell can move forward without any trailing-edge detachment. When a new lamellipodium was triggered with photoactivation of Rac1, the nucleus moved toward the new lamellipodium. This forward motion required both nuclear-cytoskeletal linkages and myosin activity. Apical or basal actomyosin bundles were found not to translate with the nucleus. Although microtubules dampen fluctuations in nuclear position, they are not required for forward translocation of the nucleus during cell migration. Trailing-edge detachment and pulling with a microneedle produced motion and deformation of the nucleus suggestive of a mechanical coupling between the nucleus and the trailing edge. Significantly, decoupling the nucleus from the cytoskeleton with KASH overexpression greatly decreased the frequency of trailing-edge detachment. Collectively, these results explain how the nucleus is moved in a crawling fibroblast and raise the possibility that forces could be transmitted from the front to the back of the cell through the nucleus. PMID:24411232

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).

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.

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

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.

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} galactic stellar disks, even without extensive interferometric mapping. We find no preference among published disk maser candidates to lie in high-inclination galaxies. This provides independent support for conclusions that in late-type galaxies, central engine accretion disks and galactic plane orientations are not

c-Met must translocate to the nucleus to initiate calcium signals.

PubMed

Gomes, Dawidson A; Rodrigues, Michele A; Leite, M Fatima; Gomez, Marcus V; Varnai, Peter; Balla, Tamas; Bennett, Anton M; Nathanson, Michael H

2008-02-15

Hepatocyte growth factor (HGF) is important for cell proliferation, differentiation, and related activities. HGF acts through its receptor c-Met, which activates downstream signaling pathways. HGF binds to c-Met at the plasma membrane, where it is generally believed that c-Met signaling is initiated. Here we report that c-Met rapidly translocates to the nucleus upon stimulation with HGF. Ca(2+) signals that are induced by HGF result from phosphatidylinositol 4,5-bisphosphate hydrolysis and inositol 1,4,5-trisphosphate formation within the nucleus rather than within the cytoplasm. Translocation of c-Met to the nucleus depends upon the adaptor protein Gab1 and importin beta1, and formation of Ca(2+) signals in turn depends upon this translocation. HGF may exert its particular effects on cells because it bypasses signaling pathways in the cytoplasm to directly activate signaling pathways in the nucleus.

PREFACE: Galactic Center Workshop 2006

NASA Astrophysics Data System (ADS)

Schödel, Rainer; Bower, Geoffrey C.; Muno, Michael P.; Nayakshin, Sergei; Ott, Thomas

2006-12-01

We are pleased to present the proceedings from the Galactic Center Workshop 2006—From the Center of the Milky Way to Nearby Low-Luminosity Galactic Nuclei. The conference took place in the Physikzentrum, Bad Honnef, Germany, on 18 to 22 April 2006. It is the third workshop of this kind, following the Galactic Center Workshops held 1998 in Tucson, Arizona, and 2002 in Kona, Hawaii. The center of the Milky Way is the only galactic nucleus of a fairly common spiral galaxy that can be observed in great detail. With a distance of roughly 8 kpc, the resolution that can currently be achieved is of the order 40 mpc/8000 AU in the X-ray domain, 2 mpc/400 AU in the near-infrared, and 0.01 mpc/1 AU with VLBI in the millimeter domain. This is two to three orders of magnitude better than for any comparable nearby galaxy, making thus the center of the Milky Way thetemplate object for the general physical interpretation of the phenomena that can be observed in galactic nuclei. We recommend the summary article News from the year 2006 Galactic Centre workshopby Mark Morris and Sergei Nayakshin—who also gave the summary talk of the conference—to the reader in order to obtain a first, concise overview of the results presented at the workshop and some of the currently most exciting—and debated—developments in recent GC research. While the workshops held in 1998 and 2002 were dedicated solely to the center of the Milky Way, the field of view was widened in Bad Honnef to include nearby low-luminosity nuclei. This new feature followed the realization that not only the GC serves as a template for understanding extragalactic nuclei, but that the latter can also provide the context and broader statistical base for understanding the center of our Milky Way. This concerns especially the accretion and emission processes related to the Sagittarius A*, the manifestation of the super massive black hole in the GC, but also the surprising observation of great numbers of massive, young

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.

Continuum radiation from active galactic nuclei: A statistical study

NASA Technical Reports Server (NTRS)

Isobe, T.; Feigelson, E. D.; Singh, K. P.; Kembhavi, A.

1986-01-01

The physics of the continuum spectrum of active galactic nuclei (AGNs) was examined using a large data set and rigorous statistical methods. A data base was constructed for 469 objects which include radio selected quasars, optically selected quasars, X-ray selected AGNs, BL Lac objects, and optically unidentified compact radio sources. Each object has measurements of its radio, optical, X-ray core continuum luminosity, though many of them are upper limits. Since many radio sources have extended components, the core component were carefully selected out from the total radio luminosity. With survival analysis statistical methods, which can treat upper limits correctly, these data can yield better statistical results than those previously obtained. A variety of statistical tests are performed, such as the comparison of the luminosity functions in different subsamples, and linear regressions of luminosities in different bands. Interpretation of the results leads to the following tentative conclusions: the main emission mechanism of optically selected quasars and X-ray selected AGNs is thermal, while that of BL Lac objects is synchrotron; radio selected quasars may have two different emission mechanisms in the X-ray band; BL Lac objects appear to be special cases of the radio selected quasars; some compact radio sources show the possibility of synchrotron self-Compton (SSC) in the optical band; and the spectral index between the optical and the X-ray bands depends on the optical luminosity.

Vestibular signals in the parasolitary nucleus.

PubMed

Barmack, N H; Yakhnitsa, V

2000-06-01

Vestibular primary afferents project to secondary vestibular neurons located in the vestibular complex. Vestibular primary afferents also project to the uvula-nodulus of the cerebellum where they terminate on granule cells. In this report we describe the physiological properties of neurons in a "new" vestibular nucleus, the parasolitary nucleus (Psol). This nucleus consists of 2,300 GABAergic neurons that project onto the ipsilateral inferior olive (beta-nucleus and dorsomedial cell column) as well as the nucleus reticularis gigantocellularis. These olivary neurons are the exclusive source of vestibularly modulated climbing fiber inputs to the cerebellum. We recorded the activity of Psol neurons during natural vestibular stimulation in anesthetized rabbits. The rabbits were placed in a three-axis rate table at the center of a large sphere, permitting vestibular and optokinetic stimulation. We recorded from 74 neurons in the Psol and from 23 neurons in the regions bordering Psol. The activity of 72/74 Psol neurons and 4/23 non-Psol neurons was modulated by vestibular stimulation in either the pitch or roll planes but not the horizontal plane. Psol neurons responded in phase with ipsilateral side-down head position or velocity during sinusoidal stimulation. Approximately 80% of the recorded Psol neurons responded to static roll-tilt. The optimal response planes of evoked vestibular responses were inferred from measurement of null planes. Optimal response planes usually were aligned with the anatomical orientation of one of the two ipsilateral vertical semicircular canals. The frequency dependence of null plane measurements indicated a convergence of vestibular information from otoliths and semicircular canals. None of the recorded neurons evinced optokinetic sensitivity. These results are consistent with the view that Psol neurons provide the vestibular signals to the inferior olive that eventually reached the cerebellum in the form of modulated climbing fiber

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.

HIV-1 Nef protein in the nucleus influences adipogenesis as well as viral transcription through the peroxisome proliferator-activated receptors.

PubMed

Otake, Kaori; Omoto, Shinya; Yamamoto, Takuya; Okuyama, Harumi; Okada, Hidechika; Okada, Noriko; Kawai, Masahiro; Saksena, Nitin K; Fujii, Yoichi R

2004-01-23

Although the HIV-1 Nef protein (27 kDa) localizes primarily in cytoplasm, there is considerable evidence suggesting its occasional localization in the nucleus. Nef is known to play an important role in transcriptional events and viral replication, but the actual target of Nef in the nucleus remains to be identified. To examine the functional roles of Nef in the nucleus and its possible interactions with other unknown factors in the nucleus. High-density microarray analysis was used to screen directly the unique functions of Nef on host gene transcription. The nuclear localization of Nef and its effects on the expression of peroxisome proliferator-activated receptors (PPAR) was examined using PPAR promoter/reporter assay and immunoblotting. A long terminal repeat/reporter assay was used to investigated the effects of Nef and PPAR on viral transcription. Nef in the nucleus suppressed PPAR gamma expression and reduced fatty acid levels in human T and macrophage cell lines. Expression of Nef or PPAR suppressed viral replication; the effect of PPAR gamma or retinoid X receptor-alpha on viral replication were reduced by coexpression of Nef in MT(-)4 T cells. Nef may be involved in both viral replication and the wasting syndrome associated with AIDS.

Galactic conformity and central/satellite quenching, from the satellite profiles of M* galaxies at 0.4 < z < 1.9 in the UKIDSS UDS

NASA Astrophysics Data System (ADS)

Hartley, W. G.; Conselice, C. J.; Mortlock, A.; Foucaud, S.; Simpson, C.

2015-08-01

We explore the redshift evolution of a curious correlation between the star formation properties of central galaxies and their satellites (`galactic conformity') at intermediate to high redshift (0.4 < z < 1.9). Using an extremely deep near-infrared survey, we study the distribution and properties of satellite galaxies with stellar masses, log(M*/M⊙) > 9.7, around central galaxies at the characteristic Schechter function mass, M ˜ M*. We fit the radial profiles of satellite number densities with simple power laws, finding slopes in the range -1.1 to -1.4 for mass-selected satellites, and -1.3 to -1.6 for passive satellites. We confirm the tendency for passive satellites to be preferentially located around passive central galaxies at 3σ significance and show that it exists to at least z ˜ 2. Meanwhile, the quenched fraction of satellites around star-forming galaxies is consistent with field galaxies of equal stellar masses. We find no convincing evidence for a redshift-dependent evolution of these trends. One simple interpretation of these results is that only passive central galaxies occupy an environment that is capable of independently shutting off star formation in satellite galaxies. By examining the satellites of higher stellar mass star-forming galaxies (log(M*/M⊙) > 11), we conclude that the origin of galactic conformity is unlikely to be exclusively due to the host dark matter halo mass. A halo-mass-independent correlation could be established by either formation bias or a more physical connection between central and satellite star formation histories. For the latter, we argue that a star formation (or active galactic nucleus) related outburst event from the central galaxy could establish a hot halo environment which is then capable of quenching both central and satellite galaxies.

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.;

Low-mass Active Galactic Nuclei on the Fundamental Plane of Black Hole Activity

NASA Astrophysics Data System (ADS)

Qian, Lei; Dong, Xiao-Bo; Xie, Fu-Guo; Liu, Wenjuan; Li, Di

2018-06-01

It is widely known that in active galactic nuclei (AGNs) and black hole X-ray binaries (BHXBs), there is a tight correlation among their radio luminosity (L R ), X-ray luminosity (L X), and BH mass ({M}BH}), the so-called “fundamental plane” (FP) of BH activity. Yet the supporting data are very limited in the {M}BH} regime between stellar mass (i.e., BHXBs) and 106.5 {M}ȯ (namely, the lower bound of supermassive BHs in common AGNs). In this work, we developed a new method to measure the 1.4 GHz flux directly from the images of the VLA FIRST survey, and apply it to the type-1 low-mass AGNs in the Dong et al. sample. As a result, we obtained 19 new low-mass AGNs for FP research with both {M}BH} estimates ({M}BH} ≈ 105.5–6.5 {M}ȯ ), reliable X-ray measurements, and (candidate) radio detections, tripling the number of such candidate sources in the literature. Most (if not all) of the low-mass AGNs follow the standard radio/X-ray correlation and the universal FP relation fitted with the combined data set of BHXBs and supermassive AGNs by Gültekin et al.; the consistency in the radio/X-ray correlation slope among those accretion systems supports the picture that the accretion and ejection (jet) processes are quite similar in all accretion systems of different {M}BH}. In view of the FP relation, we speculate that the radio loudness { \\mathcal R } (i.e., the luminosity ratio of the jet to the accretion disk) of AGNs depends not only on Eddington ratio, but probably also on {M}BH}.

[Ultrasonic measurements of fetal thalamus, caudate nucleus and lenticular nucleus in prenatal diagnosis].

PubMed

Yang, Ruiqi; Wang, Fei; Zhang, Jialing; Zhu, Chonglei; Fan, Limei

2015-05-19

To establish the reference values of thalamus, caudate nucleus and lenticular nucleus diameters through fetal thalamic transverse section. A total of 265 fetuses at our hospital were randomly selected from November 2012 to August 2014. And the transverse and length diameters of thalamus, caudate nucleus and lenticular nucleus were measured. SPSS 19.0 statistical software was used to calculate the regression curve of fetal diameter changes and gestational weeks of pregnancy. P < 0.05 was considered as having statistical significance. The linear regression equation of fetal thalamic length diameter and gestational week was: Y = 0.051X+0.201, R = 0.876, linear regression equation of thalamic transverse diameter and fetal gestational week was: Y = 0.031X+0.229, R = 0.817, linear regression equation of fetal head of caudate nucleus length diameter and gestational age was: Y = 0.033X+0.101, R = 0.722, linear regression equation of fetal head of caudate nucleus transverse diameter and gestational week was: R = 0.025 - 0.046, R = 0.711, linear regression equation of fetal lentiform nucleus length diameter and gestational week was: Y = 0.046+0.229, R = 0.765, linear regression equation of fetal lentiform nucleus diameter and gestational week was: Y = 0.025 - 0.05, R = 0.772. Ultrasonic measurement of diameter of fetal thalamus caudate nucleus, and lenticular nucleus through thalamic transverse section is simple and convenient. And measurements increase with fetal gestational weeks and there is linear regression relationship between them.

Outflow and Accretion Physics in Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

McGraw, Sean Michael

2016-09-01

This dissertation focuses on placing observational constraints on outflows and accretion disks in active galactic nuclei (AGN) for the purpose of better understanding the physics of super-massive black holes (SMBHs) and their evolution with the host galaxy over cosmic time. Quasar outflows and their importance in SMBH-host galaxy co-evolution can be further understood by analyzing broad absorption lines (BALs) in rest-frame UV spectra that trace a range of wind conditions. We quantify the properties of the flows by conducting BAL variability studies using multiple-epoch spectra acquired primarily from MDM Observatory and from the Sloan Digital Sky Survey. Iron low-ionization BALs (FeLoBALs) are a rare type of outflow that may represent a transient phase in galaxy evolution, and we analyze the variations in 12 FeLoBAL quasars with redshifts between 0.7 ≤ z ≤ 1.9 and rest frame timescales between ˜10 d to 7.6 yr. We investigate BAL variability in 71 quasar outflows that exhibit P V absorption, a tracer of high column density gas (i.e. NH ≥ 1022 cm -2), in order to quantify the energies and momenta of the flows. We also characterize the variability patterns of 26 quasars with mini-BALs, an interesting class of absorbers that may represent a distinct phase in the evolution of outflows. Low-luminosity AGN (LLAGN) are important objects to study since their prominence in the local Universe suggest a possible evolution from the quasar era, and their low radiative outputs likely indicate a distinct mode of accretion onto the SMBH. We probe the accretion conditions in the LLAGN NGC 4203 by estimating the SMBH mass, which is obtained by modeling the 2-dimensional velocity field of the nebular gas using spectra from the Hubble Space Telescope. We detect significant BAL and mini-BAL variability in a subset of quasars from each of our samples, with measured rest-frame variability time-scales from days to years and over multiple years on average. Variable wavelength

Corona accretion in active galactic nuclei and the observational test

NASA Astrophysics Data System (ADS)

Qiao, E.; Liu, B.; Taam, R.; Yuan, W.

2017-10-01

In this talk, we propose a new accretion model, in which the matter is accreted initially in the form of a vertically extended, hot gas (corona) to the central supermassive black hole by capturing the interstellar medium or the stellar wind in active galactic nuclei (AGNs). In this scenario, when the initial mass accretion rate is greater than about 0.01 \\dot M_{Edd}, at a critical radius r_{d}, part of the hot gas begins to condense on to the equatorial disc plane of the black hole, forming an inner cold accretion disc. Then, the matter is accreted in the form of a disc-corona structure extending down to the ISCO of the black hole. We calculate the theoretical structure and the corresponding emergent spectra of the model. It is shown that the model can naturally explain the origin of the X-ray emission in AGNs. Meanwhile the model predicts a new geometry of the accretion flow, which can very well explain some observations, such as the correlation between the hard X-ray slope Γ and the reflection scaling factor R found in AGNs. Finally, we discuss the potential applications of the model to high mass X-ray binaries.

The suppression of star formation by powerful active galactic nuclei.

PubMed

Page, M J; Symeonidis, M; Vieira, J D; Altieri, B; Amblard, A; Arumugam, V; Aussel, H; Babbedge, T; Blain, A; Bock, J; Boselli, A; Buat, V; Castro-Rodríguez, N; Cava, A; Chanial, P; Clements, D L; Conley, A; Conversi, L; Cooray, A; Dowell, C D; Dubois, E N; Dunlop, J S; Dwek, E; Dye, S; Eales, S; Elbaz, D; Farrah, D; Fox, M; Franceschini, A; Gear, W; Glenn, J; Griffin, M; Halpern, M; Hatziminaoglou, E; Ibar, E; Isaak, K; Ivison, R J; Lagache, G; Levenson, L; Lu, N; Madden, S; Maffei, B; Mainetti, G; Marchetti, L; Nguyen, H T; O'Halloran, B; Oliver, S J; Omont, A; Panuzzo, P; Papageorgiou, A; Pearson, C P; Pérez-Fournon, I; Pohlen, M; Rawlings, J I; Rigopoulou, D; Riguccini, L; Rizzo, D; Rodighiero, G; Roseboom, I G; Rowan-Robinson, M; Sánchez Portal, M; Schulz, B; Scott, D; Seymour, N; Shupe, D L; Smith, A J; Stevens, J A; Trichas, M; Tugwell, K E; Vaccari, M; Valtchanov, I; Viero, M; Vigroux, L; Wang, L; Ward, R; Wright, G; Xu, C K; Zemcov, M

2012-05-09

The old, red stars that constitute the bulges of galaxies, and the massive black holes at their centres, are the relics of a period in cosmic history when galaxies formed stars at remarkable rates and active galactic nuclei (AGN) shone brightly as a result of accretion onto black holes. It is widely suspected, but unproved, that the tight correlation between the mass of the black hole and the mass of the stellar bulge results from the AGN quenching the surrounding star formation as it approaches its peak luminosity. X-rays trace emission from AGN unambiguously, whereas powerful star-forming galaxies are usually dust-obscured and are brightest at infrared and submillimetre wavelengths. Here we report submillimetre and X-ray observations that show that rapid star formation was common in the host galaxies of AGN when the Universe was 2-6 billion years old, but that the most vigorous star formation is not observed around black holes above an X-ray luminosity of 10(44) ergs per second. This suppression of star formation in the host galaxy of a powerful AGN is a key prediction of models in which the AGN drives an outflow, expelling the interstellar medium of its host and transforming the galaxy's properties in a brief period of cosmic time.

Does a continuous solid nucleus exist in comets.

NASA Technical Reports Server (NTRS)

Lyttleton, R. A.

1972-01-01

The implication of actual cometary observations for the physical nature of comets is briefly reviewed, bringing out the complete conflict with observation of the ice-dust solid nucleus model put forward in recent years as representing the fundamental structure of comets. That under increasing solar heat the nucleus develops an expanding atmosphere is inconsistent with the well-established phenomenon that the coma contracts with decreasing distance from the sun. Several comets remaining always beyond Mars have nevertheless been strongly active and produced fine tails. That some comets show at times a star-like point of light is readily explicable on the dust-cloud structure and by no means establishes that a solid nucleus exists. With the nucleus-area corresponding not to a small solid mass but to an optical phenomenon, there would be no reason to expect that it would describe a precise dynamical orbit. On the hypothesis of a nucleus, it is necessary to postulate further some internal jet-propulsion mechanism to account for the orbital deviations.

On the 10 μm Silicate Feature in Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Nikutta, Robert; Elitzur, Moshe; Lacy, Mark

2009-12-01

The 10 μm silicate feature observed with Spitzer in active galactic nuclei (AGNs) reveals some puzzling behavior. It (1) has been detected in emission in type 2 sources, (2) shows broad, flat-topped emission peaks shifted toward long wavelengths in several type 1 sources, and (3) is not seen in deep absorption in any source observed so far. We solve all three puzzles with our clumpy dust radiative transfer formalism. Addressing (1), we present the spectral energy distribution (SED) of SST1721+6012, the first type 2 quasar observed to show a clear 10 μm silicate feature in emission. Such emission arises in models of the AGN torus easily when its clumpy nature is taken into account. We constructed a large database of clumpy torus models and performed extensive fitting of the observed SED. We find that the cloud radial distribution varies as r -1.5 and the torus contains 2-4 clouds along radial equatorial rays, each with optical depth at visual ~60-80. The source bolometric luminosity is ~3 × 1012 Lsun. Our modeling suggests that lsim35% of objects with tori sharing these characteristics and geometry would have their central engines obscured. This relatively low obscuration probability can explain the clear appearance of the 10 μm emission feature in SST1721+6012 together with its rarity among other QSO2. Investigating (2), we also fitted the SED of PG1211+143, one of the first type 1 QSOs with a 10 μm silicate feature detected in emission. Together with other similar sources, this QSO appears to display an unusually broadened feature whose peak is shifted toward longer wavelengths. Although this led to suggestions of non-standard dust chemistry in these sources, our analysis fits such SEDs with standard galactic dust; the apparent peak shifts arise from simple radiative transfer effects. Regarding (3), we find additionally that the distribution of silicate feature strengths among clumpy torus models closely resembles the observed distribution, and the feature

A New Compton-thick AGN in our Cosmic Backyard: Unveiling the Buried Nucleus in NGC 1448 with NuSTAR

NASA Astrophysics Data System (ADS)

Annuar, A.; Alexander, D. M.; Gandhi, P.; Lansbury, G. B.; Asmus, D.; Ballantyne, D. R.; Bauer, F. E.; Boggs, S. E.; Boorman, P. G.; Brandt, W. N.; Brightman, M.; Christensen, F. E.; Craig, W. W.; Farrah, D.; Goulding, A. D.; Hailey, C. J.; Harrison, F. A.; Koss, M. J.; LaMassa, S. M.; Murray, S. S.; Ricci, C.; Rosario, D. J.; Stanley, F.; Stern, D.; Zhang, W.

2017-02-01

NGC 1448 is one of the nearest luminous galaxies (L 8-1000μm > 109 L ⊙) to ours (z = 0.00390), and yet the active galactic nucleus (AGN) it hosts was only recently discovered, in 2009. In this paper, we present an analysis of the nuclear source across three wavebands: mid-infrared (MIR) continuum, optical, and X-rays. We observed the source with the Nuclear Spectroscopic Telescope Array (NuSTAR), and combined these data with archival Chandra data to perform broadband X-ray spectral fitting (≈0.5-40 keV) of the AGN for the first time. Our X-ray spectral analysis reveals that the AGN is buried under a Compton-thick (CT) column of obscuring gas along our line of sight, with a column density of N H(los) ≳ 2.5 × 1024 cm-2. The best-fitting torus models measured an intrinsic 2-10 keV luminosity of L {}2-10,{int} = (3.5-7.6) × 1040 erg s-1, making NGC 1448 one of the lowest luminosity CTAGNs known. In addition to the NuSTAR observation, we also performed optical spectroscopy for the nucleus in this edge-on galaxy using the European Southern Observatory New Technology Telescope. We re-classify the optical nuclear spectrum as a Seyfert on the basis of the Baldwin-Philips-Terlevich diagnostic diagrams, thus identifying the AGN at optical wavelengths for the first time. We also present high spatial resolution MIR observations of NGC 1448 with Gemini/T-ReCS, in which a compact nucleus is clearly detected. The absorption-corrected 2-10 keV luminosity measured from our X-ray spectral analysis agrees with that predicted from the optical [O III]λ5007 Å emission line and the MIR 12 μm continuum, further supporting the CT nature of the AGN.

A thalamic input to the nucleus accumbens mediates opiate dependence.

PubMed

Zhu, Yingjie; Wienecke, Carl F R; Nachtrab, Gregory; Chen, Xiaoke

2016-02-11

Chronic opiate use induces opiate dependence, which is characterized by extremely unpleasant physical and emotional feelings after drug use is terminated. Both the rewarding effects of a drug and the desire to avoid withdrawal symptoms motivate continued drug use, and the nucleus accumbens is important for orchestrating both processes. While multiple inputs to the nucleus accumbens regulate reward, little is known about the nucleus accumbens circuitry underlying withdrawal. Here we identify the paraventricular nucleus of the thalamus as a prominent input to the nucleus accumbens mediating the expression of opiate-withdrawal-induced physical signs and aversive memory. Activity in the paraventricular nucleus of the thalamus to nucleus accumbens pathway is necessary and sufficient to mediate behavioural aversion. Selectively silencing this pathway abolishes aversive symptoms in two different mouse models of opiate withdrawal. Chronic morphine exposure selectively potentiates excitatory transmission between the paraventricular nucleus of the thalamus and D2-receptor-expressing medium spiny neurons via synaptic insertion of GluA2-lacking AMPA receptors. Notably, in vivo optogenetic depotentiation restores normal transmission at these synapses and robustly suppresses morphine withdrawal symptoms. This links morphine-evoked pathway- and cell-type-specific plasticity in the paraventricular nucleus of the thalamus to nucleus accumbens circuit to opiate dependence, and suggests that reprogramming this circuit holds promise for treating opiate addiction.

The different neighbours around Type-1 and Type-2 active galactic nuclei

NASA Astrophysics Data System (ADS)

Villarroel, Beatriz; Korn, Andreas J.

2014-06-01

One of the most intriguing open issues in galaxy evolution is the structure and evolution of active galactic nuclei (AGN) that emit intense light believed to come from an accretion disk near a super massive black hole. To understand the zoo of different AGN classes, it has been suggested that all AGN are the same type of object viewed from different angles. This model--called AGN unification--has been successful in predicting, for example, the existence of hidden broad optical lines in the spectrum of many narrow-line AGN. But this model is not unchallenged and it is debatable whether more than viewing angle separates the so-called Type-1 and Type-2 AGN. Here we report the first large-scale study that finds strong differences in the galaxy neighbours to Type-1 and Type-2 AGN with data from the Sloan Digital Sky Survey (SDSS; ref. ) Data Release 7 (DR7; ref. ) and Galaxy Zoo. We find strong differences in the colour and AGN activity of the neighbours to Type-1 and Type-2 AGN and in how the fraction of AGN residing in spiral hosts changes depending on the presence or not of a neighbour. These findings suggest that an evolutionary link between the two major AGN types might exist.

The Cool Stellar Populations of Early-Type Galaxies and the Galactic Bulge

NASA Astrophysics Data System (ADS)

Houdashelt, Mark Lee

1995-01-01

Red (6800-9200 A) and near-infrared (K-band) spectra have been obtained for 34 early-type galaxies in the Virgo cluster, the Coma cluster and the field. The strengths of the Ca II triplet (lambdalambda 8498, 8542, 8662 A), the Na I doublet ( lambdalambda8183, 8195 A), the Mg I lambda8807 A line, and molecular bands of TiO and VO were measured from the red spectra. Absorption due to the CO band with bandhead at 2.29 mu m was measured from the near-infrared spectra. The behavior of the spectral indices was examined for the Virgo galaxy nuclei as functions of luminosity and color. Overall, the CO, TiO and Na I indices were found to be stronger in redder and brighter galaxies. The Mg I and the Ca II triplet lines did not vary significantly among galaxies of different color or brightness. These trends are consistent with a change in chemical composition producing the well-known color-magnitude relation for early -type galaxies. No significant differences were detected among galaxies of similar luminosity in the Virgo cluster, the Coma cluster and the field. To simulate the stellar population changes implied by the radial color gradients observed in early-type galaxies, models were constructed to represent the integrated light of the Galactic bulge as a function of latitude. A field in Baade's Window (BW) was studied first and the stellar population there was found to be quite inhomogeneous. The BW model indicated that the integrated light of BW is giant -dominated, and the BW spectral energy distribution is very similar to that of the nucleus of a low-luminosity early -type galaxy. From models of BW and a field at b = -8^circ, radial gradients were estimated for the Galactic bulge and compared to the changes which occur along a luminosity sequence of early -type galaxies in the Virgo cluster. This comparison showed that: (1) the Na I and I(8197) indices increase steeply with redder colors in the Virgo galaxies but appear to decrease with color in the Galactic bulge

Rosetta/OSIRIS: Nucleus morphology and activity of comet 67P/Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Sierks, Holger

2015-08-01

Introduction: The Rosetta mission of the European Space Agency arrived on August 6, 2014, at the target comet 67P/Churyumov-Gerasimenko after 10 years of cruise. OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) is the scientific imaging system onboard Rosetta. It comprises a Narrow Angle Camera (NAC) for broad-band nucleus surface and dust studies and a Wide Angle Camera (WAC) for the wide field coma investigations.OSIRIS images the nucleus and the coma of comet 67P/C-G from the arrival throughout early mapping phase, PHILAE landing, and escort phase with close fly-by beginning of the year 2015.The team paper presents the surface morphology and activity of the nucleus as seen in gas, dust, and local jets and the larger scale coma studied by OSIRIS.Acknowledgements: OSIRIS was built by a consortium led by the Max-Planck-Institut für Sonnensystemforschung, Göttingen, Germany, in collaboration with CISAS, University of Padova, Italy, the Laboratoire d'Astrophysique de Marseille, France, the Instituto de Astrofísica de Andalucia, CSIC, Granada, Spain, the Scientific Support Office of the European Space Agency, Noordwijk, The Netherlands, the Instituto Nacional de Técnica Aeroespacial, Madrid, Spain, the Universidad Politéchnica de Madrid, Spain, the Department of Physics and Astronomy of Uppsala University, Sweden, and the Institut für Datentechnik und Kommunikationsnetze der Technischen Universität Braunschweig, Germany.Additional Information: The OSIRIS team is H. Sierks, C. Barbieri, P. Lamy, R. Rodrigo, D. Koschny, H. Rickman, J. Agarwal, M. A'Hearn, I. Bertini, F. Angrilli, M. A. Barucci, J. L. Bertaux, G. Cremonese, V. Da Deppo, B. Davidsson, S. Debei, M. De Cecco, S. Fornasier, M. Fulle, O. Groussin, C. Güttler, P. Gutierrez, S. Hviid, W. Ip, L. Jorda, H. U. Keller, J. Knollenberg, R. Kramm, E. Kührt, M. Küppers, L. Lara, M. Lazzarin, J. J. Lopez, S. Lowry, S. Marchi, F. Marzari, H. Michalik, S. Mottola, G. Naletto, N. Oklay, L

Radio observations of active galactic nuclei with mm-VLBI

NASA Astrophysics Data System (ADS)

Boccardi, B.; Krichbaum, T. P.; Ros, E.; Zensus, J. A.

2017-11-01

Over the past few decades, our knowledge of jets produced by active galactic nuclei (AGN) has greatly progressed thanks to the development of very-long-baseline interferometry (VLBI). Nevertheless, the crucial mechanisms involved in the formation of the plasma flow, as well as those driving its exceptional radiative output up to TeV energies, remain to be clarified. Most likely, these physical processes take place at short separations from the supermassive black hole, on scales which are inaccessible to VLBI observations at centimeter wavelengths. Due to their high synchrotron opacity, the dense and highly magnetized regions in the vicinity of the central engine can only be penetrated when observing at shorter wavelengths, in the millimeter and sub-millimeter regimes. While this was recognized already in the early days of VLBI, it was not until the very recent years that sensitive VLBI imaging at high frequencies has become possible. Ongoing technical development and wide band observing now provide adequate imaging fidelity to carry out more detailed analyses. In this article, we overview some open questions concerning the physics of AGN jets, and we discuss the impact of mm-VLBI studies. Among the rich set of results produced so far in this frequency regime, we particularly focus on studies performed at 43 GHz (7 mm) and at 86 GHz (3 mm). Some of the first findings at 230 GHz (1 mm) obtained with the Event Horizon Telescope are also presented.

Galactic Train Wrecks

NASA Image and Video Library

2011-05-25

This montage combines observations from NASA Spitzer Space Telescope and NASA Galaxy Evolution Explorer GALEX spacecraft showing three examples of colliding galaxies from a new photo atlas of galactic train wrecks.

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

Super-massive binary black holes and emission lines in active galactic nuclei

NASA Astrophysics Data System (ADS)

Popović, Luka Č.

2012-02-01

It is now agreed that mergers play an essential role in the evolution of galaxies and therefore that mergers of supermassive black holes (SMBHs) must have been common. We see the consequences of past supermassive binary black holes (SMBs) in the light profiles of so-called 'core ellipticals' and a small number of SMBs have been detected. However, the evolution of SMBs is poorly understood. Theory predicts that SMBs should spend a substantial amount of time orbiting at velocities of a few thousand kilometers per second. If the SMBs are surrounded by gas observational effects might be expected from accretion onto one or both of the SMBHs. This could result in a binary Active Galactic Nucleus (AGN) system. Like a single AGN, such a system would emit a broad band electromagnetic spectrum and broad and narrow emission lines. The broad emission spectral lines emitted from AGNs are our main probe of the geometry and physics of the broad line region (BLR) close to the SMBH. There is a group of AGNs that emit very broad and complex line profiles, showing two displaced peaks, one blueshifted and one redshifted from the systemic velocity defined by the narrow lines, or a single such peak. It has been proposed that such line shapes could indicate an SMB system. We discuss here how the presence of an SMB will affect the BLRs of AGNs and what the observational consequences might be. We review previous claims of SMBs based on broad line profiles and find that they may have non-SMB explanations as a consequence of a complex BLR structure. Because of these effects it is very hard to put limits on the number of SMBs from broad line profiles. It is still possible, however, that unusual broad line profiles in combination with other observational effects (line ratios, quasi-periodical oscillations, spectropolarimetry, etc.) could be used for SMBs detection. Some narrow lines (e.g., [O III]) in some AGNs show a double-peaked profile. Such profiles can be caused by streams in the Narrow

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

Purinergic A2b Receptor Activation by Extracellular Cues Affects Positioning of the Centrosome and Nucleus and Causes Reduced Cell Migration*

PubMed Central

Ou, Young; Chan, Gordon; Zuo, Jeremy; Rattner, Jerome B.; van der Hoorn, Frans A.

2016-01-01

The tight, relative positioning of the nucleus and centrosome in mammalian cells is important for the regulation of cell migration. Under pathophysiological conditions, the purinergic A2b receptor can regulate cell motility, but the underlying mechanism remains unknown. Expression of A2b, normally low, is increased in tissues experiencing adverse physiological conditions, including hypoxia and inflammation. ATP is released from such cells. We investigated whether extracellular cues can regulate centrosome-nucleus positioning and cell migration. We discovered that hypoxia as well as extracellular ATP cause a reversible increase in the distance between the centrosome and nucleus and reduced cell motility. We uncovered the underlying pathway: both treatments act through the A2b receptor and specifically activate the Epac1/RapGef3 pathway. We show that cells lacking A2b do not respond in this manner to hypoxia or ATP but transfection of A2b restores this response, that Epac1 is critically involved, and that Rap1B is important for the relative positioning of the centrosome and nucleus. Our results represent, to our knowledge, the first report demonstrating that pathophysiological conditions can impact the distance between the centrosome and nucleus. Furthermore, we identify the A2b receptor as a central player in this process. PMID:27226580

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.

On the Jet Properties of γ-Ray-loud Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Chen, Liang

2018-04-01

Based on broadband spectral energy distributions (SEDs), we estimate the jet physical parameters of 1392 γ-ray-loud active galactic nuclei (AGNs), the largest sample so far. The (SED) jet power and magnetization parameter are derived for these AGNs. Out of these sources, the accretion disk luminosity of 232 sources and (extended) kinetic jet powers of 159 sources are compiled from archived papers. We find the following. (1) Flat-spectrum radio quasars (FSRQs) and BL Lacs are well separated by {{Γ }}=-0.127{log}{L}γ +8.18 in the γ-ray luminosity versus photon index plane with a success rate of 88.6%. (2) Most FSRQs present a (SED) jet power larger than the accretion power, which suggests that the relativistic jet-launching mechanism is dominated by the Blandford–Znajek process. This result confirms previous findings. (3) There is a significant anticorrelation between jet magnetization and a ratio of the (SED) jet power to the (extended) kinetic jet power, which, for the first time, provides supporting evidence for the jet energy transportation theory: a high-magnetization jet may more easily transport energy to a large scale than a low-magnetization jet.

The Second Catalog Of Active Galactic Nuclei Detected By The Fermi Large Area Telescope

DOE PAGES

Ackermann, M.

2011-12-02

The second catalog of active galactic nuclei (AGNs) detected by the Fermi Large Area Telescope (LAT) in two years of scientific operation is presented. The Second LAT AGN Catalog (2LAC) includes 1017 γ-ray sources located at high Galactic latitudes (|b| > 10°) that are detected with a test statistic (TS) greater than 25 and associated statistically with AGNs. However some of these are affected by analysis issues and some are associated with multiple AGNs. Consequently we define a clean sample which includes 886 AGNs, comprising 395 BL Lacertae objects (BL Lacs), 310 flat-spectrum radio quasars (FSRQs), 157 candidate blazars ofmore » unknown type (i.e., with broad-band blazar characteristics but with no optical spectral measurement yet), eight misaligned AGNs, four narrow-line Seyfert 1 (NLS1s), 10 AGNs of other types and two starburst galaxies. Where possible, the blazars have been further classified based on their spectral energy distributions (SEDs) as archival radio, optical, and X-ray data permit. While almost all FSRQs have a synchrotron-peak frequency < 10 14 Hz, about half of the BL Lacs have a synchrotron-peak frequency > 10 15 Hz. The 2LAC represents a significant improvement relative to the First LAT AGN Catalog (1LAC), with 52% more associated sources. The full characterization of the newly detected sources will require more broad-band data. 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. The general trends observed in 1LAC are confirmed.« less

THE SECOND CATALOG OF ACTIVE GALACTIC NUCLEI DETECTED BY THE FERMI LARGE AREA TELESCOPE

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

Ackermann, M.; Ajello, M.; Allafort, A.

The second catalog of active galactic nuclei (AGNs) detected by the Fermi Large Area Telescope (LAT) in two years of scientific operation is presented. The second LAT AGN catalog (2LAC) includes 1017 {gamma}-ray sources located at high Galactic latitudes (|b| > 10 Degree-Sign ) that are detected with a test statistic (TS) greater than 25 and associated statistically with AGNs. However, some of these are affected by analysis issues and some are associated with multiple AGNs. Consequently, we define a Clean Sample which includes 886 AGNs, comprising 395 BL Lacertae objects (BL Lac objects), 310 flat-spectrum radio quasars (FSRQs), 157more » candidate blazars of unknown type (i.e., with broadband blazar characteristics but with no optical spectral measurement yet), 8 misaligned AGNs, 4 narrow-line Seyfert 1 (NLS1s), 10 AGNs of other types, and 2 starburst galaxies. Where possible, the blazars have been further classified based on their spectral energy distributions (SEDs) as archival radio, optical, and X-ray data permit. While almost all FSRQs have a synchrotron-peak frequency <10{sup 14} Hz, about half of the BL Lac objects have a synchrotron-peak frequency >10{sup 15} Hz. The 2LAC represents a significant improvement relative to the first LAT AGN catalog (1LAC), with 52% more associated sources. The full characterization of the newly detected sources will require more broadband data. Various properties, such as {gamma}-ray fluxes and photon power-law spectral indices, redshifts, {gamma}-ray luminosities, variability, and archival radio luminosities and their correlations are presented and discussed for the different blazar classes. The general trends observed in 1LAC are confirmed.« less

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 (90degGalactic sources but also of general use: optimum photometry in crowded fields using advanced techniques for overlapping sources, rigorous astrometry and 95% error circles for combining X-ray images or matching to optical/IR images, and application of quantile analysis for spectral analysis of faint sources. We apply these techniques to 15 anti-Galactic center observations (of 14 distinct fields), in which we have detected 921 X-ray point sources. We present logN-logS distributions and quantile analysis to show that in the hard band (2-8 keV) active galactic nuclei dominate the sources. Complete analysis of all ChaMPlane anti-Galactic center fields will be given in a subsequent paper, followed by papers on sources in the Galactic center and bulge regions.

Pitch angle of galactic spiral arms

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

Michikoshi, Shugo; Kokubo, Eiichiro, E-mail: michiko@mail.doshisha.ac.jp, E-mail: kokubo@th.nao.ac.jp

2014-06-01

One of the key parameters that characterizes spiral arms in disk galaxies is a pitch angle that measures the inclination of a spiral arm to the direction of galactic rotation. The pitch angle differs from galaxy to galaxy, which suggests that the rotation law of galactic disks determines it. In order to investigate the relation between the pitch angle of spiral arms and the shear rate of galactic differential rotation, we perform local N-body simulations of pure stellar disks. We find that the pitch angle increases with the epicycle frequency and decreases with the shear rate and obtain the fittingmore » formula. This dependence is explained by the swing amplification mechanism.« less

The distances of the Galactic Novae

NASA Astrophysics Data System (ADS)

Ozdonmez, Aykut; Guver, Tolga; Cabrera-Lavers, Antonio; Ak, Tansel

2016-07-01

Using location of the RC stars on the CMDs obtained from the UKIDSS, VISTA and 2MASS photometry, we have derived the reddening-distance relations towards each Galactic nova for which at least one independent reddening measurement exists. We were able to determine the distances of 72 Galactic novae and set lower limits on the distances of 45 systems. The reddening curves of the systems are presented. These curves can be also used to estimate reddening or the distance of any source, whose location is close to the position of the nova in our sample. The distance measurement method in our study can be easily applicable to any source, especially for ones that concentrated along the Galactic plane.

Virally mediated increased neurotensin 1 receptor in the nucleus accumbens decreases behavioral effects of mesolimbic system activation.

PubMed

Cáceda, Ricardo; Kinkead, Becky; Owens, Michael J; Nemeroff, Charles B

2005-12-14

Dopamine receptor agonist and NMDA receptor antagonist activation of the mesolimbic dopamine system increases locomotion and disrupts prepulse inhibition of the acoustic startle response (PPI), paradigms frequently used to study both the pharmacology of antipsychotic drugs and drugs of abuse. In rats, virally mediated overexpression of the neurotensin 1 (NT1) receptor in the nucleus accumbens antagonized d-amphetamine- and dizocilpine-induced PPI disruption, hyperlocomotion, and D-amphetamine-induced rearing. The NT receptor antagonist SR 142948A [2-[[5-(2,6-dimethoxyphenyl)-1-(4-N-(3-dimethylaminopropyl)-N-methylcarbamoyl)-2-isopropylphenyl)-1H-pyrazole-3-carbonyl]amino] adamantane-2-carboxylic acid, hydrochloride] blocked inhibition of dizocilpine-induced hyperlocomotion mediated by overexpression of the NT1 receptor. Together, these results suggest that increased nucleus accumbens NT neurotransmission, via the NT1 receptor, can decrease the effects of activation of the mesolimbic dopamine system and disruption of the glutamatergic input from limbic cortices, resembling the action of the atypical antipsychotic drug clozapine. In contrast to clozapine, virally mediated overexpression of the NT1 receptor in the nucleus accumbens had prolonged protective effects (up to 4 weeks after viral injection) without perturbing baseline PPI and locomotor behaviors. These data further confirm the NT1 receptor as the receptor mediating the antistimulant- and antipsychotic-like properties of NT and provide rationale for the development of NT1 receptor agonists as novel antipsychotic drugs. In addition, the NT1 receptor vector might be a valuable tool for understanding the mechanism of action of antipsychotic drugs and drugs of abuse and may have potential therapeutic applications.

Inhibition of oxytocin and vasopressin neuron activity in rat hypothalamic paraventricular nucleus by relaxin-3-RXFP3 signalling.

PubMed

Kania, Alan; Gugula, Anna; Grabowiecka, Agnieszka; de Ávila, Camila; Blasiak, Tomasz; Rajfur, Zenon; Lewandowski, Marian H; Hess, Grzegorz; Timofeeva, Elena; Gundlach, Andrew L; Blasiak, Anna

2017-06-01

Relaxin-3 is a stress-responsive neuropeptide that acts at its cognate receptor, RXFP3, to alter behaviours including feeding. In this study, we have demonstrated a direct, RXFP3-dependent, inhibitory action of relaxin-3 on oxytocin and vasopressin paraventricular nucleus (PVN) neuron electrical activity, a putative cellular mechanism of orexigenic actions of relaxin-3. We observed a Gα i/o -protein-dependent inhibitory influence of selective RXFP3 activation on PVN neuronal activity in vitro and demonstrated a direct action of RXFP3 activation on oxytocin and vasopressin PVN neurons, confirmed by their abundant expression of RXFP3 mRNA. Moreover, we demonstrated that RXFP3 activation induces a cadmium-sensitive outward current, which indicates the involvement of a characteristic magnocellular neuron outward potassium current. Furthermore, we identified an abundance of relaxin-3-immunoreactive axons/fibres originating from the nucleus incertus in close proximity to the PVN, but associated with sparse relaxin-3-containing fibres/terminals within the PVN. The paraventricular nucleus of the hypothalamus (PVN) plays an essential role in the control of food intake and energy expenditure by integrating multiple neural and humoral inputs. Recent studies have demonstrated that intracerebroventricular and intra-PVN injections of the neuropeptide relaxin-3 or selective relaxin-3 receptor (RXFP3) agonists produce robust feeding in satiated rats, but the cellular and molecular mechanisms of action associated with these orexigenic effects have not been identified. In the present studies, using rat brain slices, we demonstrated that relaxin-3, acting through its cognate G-protein-coupled receptor, RXFP3, hyperpolarized a majority of putative magnocellular PVN neurons (88%, 22/25), including cells producing the anorexigenic neuropeptides, oxytocin and vasopressin. Importantly, the action of relaxin-3 persisted in the presence of tetrodotoxin and glutamate/GABA receptor

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.

Lipid-binding proteins modulate ligand-dependent trans-activation by peroxisome proliferator-activated receptors and localize to the nucleus as well as the cytoplasm.

PubMed

Helledie, T; Antonius, M; Sorensen, R V; Hertzel, A V; Bernlohr, D A; Kølvraa, S; Kristiansen, K; Mandrup, S

2000-11-01

Peroxisome proliferator-activated receptors (PPARs) are activated by a variety of fatty acids, eicosanoids, and hypolipidemic and insulin-sensitizing drugs. Many of these compounds bind avidly to members of a family of small lipid-binding proteins, the fatty acid-binding proteins (FABPs). Fatty acids are activated to CoA esters, which bind with high affinity to the acyl-CoA-binding protein (ACBP). Thus, the availability of known and potential PPAR ligands may be regulated by lipid-binding proteins. In this report we show by transient transfection of CV-1 cells that coexpression of ACBP and adipocyte lipid-binding protein (ALBP) exerts a ligand- and PPAR subtype-specific attenuation of PPAR-mediated trans-activation, suggesting that lipid-binding proteins, when expressed at high levels, may function as negative regulators of PPAR activation by certain ligands. Expression of ACBP, ALBP, and keratinocyte lipid-binding protein (KLBP) is induced during adipocyte differentiation, a process during which PPARgamma plays a prominent role. We present evidence that endogenous ACBP, ALBP, and KLBP not only localize to the cytoplasm but also exhibit a prominent nuclear localization in 3T3-L1 adipocytes. In addition, forced expression of ACBP, ALBP, and KLBP in CV-1 cells resulted in a substantial accumulation of all three proteins in the nucleus. These results suggest that lipid-binding proteins, contrary to the general assumption, may exert their action in the nucleus as well as in the cytoplasm.

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.

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.

Galactic bulge population II Cepheids in the VVV survey: period-luminosity relations and a distance to the Galactic centre

NASA Astrophysics Data System (ADS)

Bhardwaj, A.; Rejkuba, M.; Minniti, D.; Surot, F.; Valenti, E.; Zoccali, M.; Gonzalez, O. A.; Romaniello, M.; Kanbur, S. M.; Singh, H. P.

2017-09-01

Context. Multiple stellar populations of different ages and metallicities reside in the Galactic bulge that trace its structure and provide clues to its formation and evolution. Aims: We present the near-infrared observations of population II Cepheids in the Galactic bulge from VISTA Variables in the Vía Láctea (VVV) survey. The JHKs photometry together with optical data from Optical Gravitational Lensing Experiment (OGLE) survey provide an independent estimate of the distance to the Galactic centre. The old, metal-poor and low-mass population II Cepheids are also investigated as useful tracers for the structure of the Galactic bulge. Methods: We identify 340 population II Cepheids in the VVV survey Galactic bulge catalogue based on their match with the OGLE-III Catalogue. The single-epoch JH and multi-epoch Ks observations complement the accurate periods and optical (VI) mean-magnitudes from OGLE. The sample consisting of BL Herculis and W Virginis subtypes is used to derive period-luminosity relations after correcting mean-magnitudes for the extinction. Our Ks-band period-luminosity relation, Ks = -2.189(0.056) [log (P)-1] + 11.187(0.032), is consistent with published work for BL Herculis and W Virginis variables in the Large Magellanic Cloud. Results: We present a combined OGLE-III and VVV catalogue with periods, classification, mean magnitudes, and extinction for 264 Galactic bulge population II Cepheids that have good-quality Ks-band light curves. The absolute magnitudes for population II Cepheids and RR Lyraes calibrated using Gaia and Hubble Space Telescope parallaxes, together with calibrated magnitudes for Large Magellanic Cloud population II Cepheids, are used to obtain a distance to the Galactic centre, R0 = 8.34 ± 0.03(stat.) ± 0.41(syst.), which changes by with different extinction laws. While noting the limitation of small number statistics, we find that the present sample of population II Cepheids in the Galactic bulge shows a nearly spheroidal

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).

STIS Observations of the Intrinsic UV Absorption in the Dwarf Seyfert Nucleus of NGC 4395

NASA Astrophysics Data System (ADS)

Kraemer, Steven

2002-07-01

The Sd IV dwarf galaxy NGC 4395 is one of the nearest {d 4.2 Mpc} and least luminous {L_bol 10^41 ergs s^-1} examples of Seyfert 1 galaxies. Furthermore, it is the only known example of an active nucleus within a bulgeless, extreme late-type galaxy. This unique object possesses all of the classic Seyfert 1 properties in miniature, including broad and narrow emission lines and highly variable X-ray emission, presumably powered by a small {few x 10^4 M_odot} black hole. Furthermore, we have discovered evidence for blueshifted, intrinsic absorption lines in the UV {C IV LambdaLambda1548.2, 1550.8}, while X-ray spectra show the presence of bound-free edges from O VII and O VIII. We propose HST/STIS echelle observations to determine the properties {ionization states, column densities, velocity coverages, covering factors} of the intrinsic UV absorbers in NGC 4395. Due to the high covering factor of its narrow-line emission, NGC 4395 offers the best case for testing the connection between the absorbers and the narrow-line region {NLR}. Furthermore, an empirical comparison of its absorption properties with those in higher luminosity active galactic nuclei {AGN} will provide valuable constraints on dynamical models of the absorbers, which make predictions that are strongly dependent on luminosity and/or central black hole mass.

Formation of Offset and Dual Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Barrows, Scott; Comerford, Julia M.; Greene, Jenny E.

2018-06-01

Galaxy mergers are effective mechanisms for triggering accretion onto supermassive black holes (SMBHs) and thereby powering active galactic nuclei (AGN). In the merger scenario, when the SMBH from only one galaxy is accreting we observe a spatially offset AGN, and when the SMBHs from both galaxies are accreting we observe a dual AGN. Understanding the merger conditions that lead to the formation of offset AGN versus dual AGN is fundamental to informing models of hierarchical SMBH growth and the physics leading to the accretion of matter onto SMBHs. However, while the role of galaxy mergers for AGN triggering has been well-studied, the efficiency with which these events trigger offset AGN versus dual AGN is currently unclear. One reason for this gap in knowledge can be attributed to the observational difficulties in distinguishing between offset and dual AGN since doing so requires high spatial resolution, especially in the small separation regime where merger-driven AGN triggering is most likely to occur. To overcome this hurdle, we have utilized the spatial resolution of the Chandra X-ray Observatory to develop a unique sample of AGN hosted by late-stage galaxy mergers. Moreover, we have recently acquired Hubble Space Telescope imaging for a subset of these systems to examine the role that their merger morphologies play in SMBH growth and the formation of offset and dual AGN. We find that offset AGN are predominately found in minor mergers, whereas dual AGN are usually hosted by major mergers and galaxies with large morphological asymmetries. Furthermore, in both offset and dual AGN, the rate of SMBH growth increases toward more major mergers and larger morphological asymmetries. These results are in agreement with numerical simulations predicting that merger morphology is a relevant parameter governing SMBH merger-driven growth, and these results are the first to observationally confirm these trends at small pair separations.

Hidden Active Galactic Nuclei in Early-type Galaxies

NASA Astrophysics Data System (ADS)

Paggi, Alessandro; Fabbiano, Giuseppina; Civano, Francesca; Pellegrini, Silvia; Elvis, Martin; Kim, Dong-Woo

2016-06-01

We present a stacking analysis of the complete sample of early-type galaxies (ETGs) in the Chandra COSMOS (C-COSMOS) survey, to explore the nature of the X-ray luminosity in the redshift and stellar luminosity ranges 0\\lt z\\lt 1.5 and {10}9\\lt {L}K/{L}⊙ \\lt {10}13. Using established scaling relations, we subtract the contribution of X-ray binary populations to estimate the combined emission of hot ISM and active galactic nuclei (AGNs). To discriminate between the relative importance of these two components, we (1) compare our results with the relation observed in the local universe {L}X,{gas}\\propto {L}K4.5 for hot gaseous halos emission in ETGs, and (2) evaluate the spectral signature of each stacked bin. We find two regimes where the non-stellar X-ray emission is hard, consistent with AGN emission. First, there is evidence of hard, absorbed X-ray emission in stacked bins including relatively high z (˜1.2) ETGs with average high X-ray luminosity ({L}X {- {LMXB}}≳ 6× {10}42 {{erg}} {{{s}}}-1). These luminosities are consistent with the presence of highly absorbed “hidden” AGNs in these ETGs, which are not visible in their optical-IR spectra and spectral energy distributions. Second, confirming the early indication from our C-COSMOS study of X-ray detected ETGs, we find significantly enhanced X-ray luminosity in lower stellar mass ETGs ({L}K≲ {10}11{L}⊙ ), relative to the local {L}X,{gas}\\propto {L}K4.5 relation. The stacked spectra of these ETGs also suggest X-ray emission harder than expected from gaseous hot halos. This emission is consistent with inefficient accretion {10}-5-{10}-4{\\dot{M}}{Edd} onto {M}{BH}˜ {10}6-{10}8 {M}⊙ .

The Suppression of Star Formation by Powerful Active Galactic Nuclei

NASA Technical Reports Server (NTRS)

Dwek, E.

2012-01-01

The old, red stars that constitute the bulges of galaxies, and the massive black holes at their centres, are the relics of a period in cosmic history when galaxies formed stars at remarkable rates and active galactic nuclei (AGN) shone brightly as a result of accretion onto black holes. It is widely suspected, but unproved, that the tight corre1ation between the mass of the black hole and the mas. of the stellar bulge results from the AGN quenching the surrounding star formation as it approaches its peak luminosity. X-rays trace emission from AGN unambiguously, whereas powerful star-forming ga1axies are usually dust-obscured and are brightest at infrared and submillimeter wavelengths. Here we report submillimetre and X-ray observations that show that rapid star formation was common in the host galaxies of AGN when the Universe was 2-6 billion years old, but that the most vigorous star formation is not observed around black holes above an X-ray luminosity of 10(exp 44) ergs per second. This suppression of star formation in the host galaxy of a powerful AGN is a key prediction of models in which the AGN drives an outflow, expe11ing the interstellar medium of its host and transforming the galaxy's properties in a brief period of cosmic time.

Nucleus Ruber of Actinopterygians.

PubMed

Nakayama, Tomoya; Miyajima, Satoshi; Nishino, Hirotaka; Narita, Junya; Abe, Hideki; Yamamoto, Naoyuki

2016-01-01

Nucleus ruber is known as an important supraspinal center that controls forelimb movements in tetrapods, and the rubral homologue may serve similar functions in fishes (motor control of pectoral fin). However, two apparently different structures have been identified as 'nucleus ruber' in actinopterygians. One is nucleus ruber of Goldstein (1905) (NRg), and the other nucleus ruber of Nieuwenhuys and Pouwels (1983) (NRnp). It remains unclear whether one of these nuclei (or perhaps both) is homologous to tetrapod nucleus ruber. To resolve this issue from a phylogenetic point of view, we have investigated the distribution of tegmental neurons retrogradely labeled from the spinal cord in eight actinopterygian species. We also investigated the presence/absence of the two nuclei with Nissl- or Bodian-stained brain section series of an additional 28 actinopterygian species by comparing the morphological features of candidate rubral neurons with those of neurons revealed by the tracer studies. Based on these analyses, the NRg was identified in all actinopterygians investigated in the present study, while the NRnp appears to be absent in basal actinopterygians. The phylogenetic distribution pattern indicates that the NRg is the more likely homologue of nucleus ruber, and the NRnp may be a derived nucleus that emerged during the course of actinopterygian evolution. © 2016 S. Karger AG, Basel.

Purinergic A2b Receptor Activation by Extracellular Cues Affects Positioning of the Centrosome and Nucleus and Causes Reduced Cell Migration.

PubMed

Ou, Young; Chan, Gordon; Zuo, Jeremy; Rattner, Jerome B; van der Hoorn, Frans A

2016-07-15

The tight, relative positioning of the nucleus and centrosome in mammalian cells is important for the regulation of cell migration. Under pathophysiological conditions, the purinergic A2b receptor can regulate cell motility, but the underlying mechanism remains unknown. Expression of A2b, normally low, is increased in tissues experiencing adverse physiological conditions, including hypoxia and inflammation. ATP is released from such cells. We investigated whether extracellular cues can regulate centrosome-nucleus positioning and cell migration. We discovered that hypoxia as well as extracellular ATP cause a reversible increase in the distance between the centrosome and nucleus and reduced cell motility. We uncovered the underlying pathway: both treatments act through the A2b receptor and specifically activate the Epac1/RapGef3 pathway. We show that cells lacking A2b do not respond in this manner to hypoxia or ATP but transfection of A2b restores this response, that Epac1 is critically involved, and that Rap1B is important for the relative positioning of the centrosome and nucleus. Our results represent, to our knowledge, the first report demonstrating that pathophysiological conditions can impact the distance between the centrosome and nucleus. Furthermore, we identify the A2b receptor as a central player in this process. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

Higher Landing Accuracy in Expert Pilots is Associated with Lower Activity in the Caudate Nucleus

PubMed Central

Adamson, Maheen M.; Taylor, Joy L.; Heraldez, Daniel; Khorasani, Allen; Noda, Art; Hernandez, Beatriz; Yesavage, Jerome A.

2014-01-01

The most common lethal accidents in General Aviation are caused by improperly executed landing approaches in which a pilot descends below the minimum safe altitude without proper visual references. To understand how expertise might reduce such erroneous decision-making, we examined relevant neural processes in pilots performing a simulated landing approach inside a functional MRI scanner. Pilots (aged 20–66) were asked to “fly” a series of simulated “cockpit view” instrument landing scenarios in an MRI scanner. The scenarios were either high risk (heavy fog–legally unsafe to land) or low risk (medium fog–legally safe to land). Pilots with one of two levels of expertise participated: Moderate Expertise (Instrument Flight Rules pilots, n = 8) or High Expertise (Certified Instrument Flight Instructors or Air-Transport Pilots, n = 12). High Expertise pilots were more accurate than Moderate Expertise pilots in making a “land” versus “do not land” decision (CFII: d′ = 3.62±2.52; IFR: d′ = 0.98±1.04; p<.01). Brain activity in bilateral caudate nucleus was examined for main effects of expertise during a “land” versus “do not land” decision with the no-decision control condition modeled as baseline. In making landing decisions, High Expertise pilots showed lower activation in the bilateral caudate nucleus (0.97±0.80) compared to Moderate Expertise pilots (1.91±1.16) (p<.05). These findings provide evidence for increased “neural efficiency” in High Expertise pilots relative to Moderate Expertise pilots. During an instrument approach the pilot is engaged in detailed examination of flight instruments while monitoring certain visual references for making landing decisions. The caudate nucleus regulates saccade eye control of gaze, the brain area where the “expertise” effect was observed. These data provide evidence that performing “real world” aviation tasks in an fMRI provide objective data regarding the

Higher landing accuracy in expert pilots is associated with lower activity in the caudate nucleus.

PubMed

Adamson, Maheen M; Taylor, Joy L; Heraldez, Daniel; Khorasani, Allen; Noda, Art; Hernandez, Beatriz; Yesavage, Jerome A

2014-01-01

The most common lethal accidents in General Aviation are caused by improperly executed landing approaches in which a pilot descends below the minimum safe altitude without proper visual references. To understand how expertise might reduce such erroneous decision-making, we examined relevant neural processes in pilots performing a simulated landing approach inside a functional MRI scanner. Pilots (aged 20-66) were asked to "fly" a series of simulated "cockpit view" instrument landing scenarios in an MRI scanner. The scenarios were either high risk (heavy fog-legally unsafe to land) or low risk (medium fog-legally safe to land). Pilots with one of two levels of expertise participated: Moderate Expertise (Instrument Flight Rules pilots, n = 8) or High Expertise (Certified Instrument Flight Instructors or Air-Transport Pilots, n = 12). High Expertise pilots were more accurate than Moderate Expertise pilots in making a "land" versus "do not land" decision (CFII: d' = 3.62 ± 2.52; IFR: d' = 0.98 ± 1.04; p<.01). Brain activity in bilateral caudate nucleus was examined for main effects of expertise during a "land" versus "do not land" decision with the no-decision control condition modeled as baseline. In making landing decisions, High Expertise pilots showed lower activation in the bilateral caudate nucleus (0.97 ± 0.80) compared to Moderate Expertise pilots (1.91 ± 1.16) (p<.05). These findings provide evidence for increased "neural efficiency" in High Expertise pilots relative to Moderate Expertise pilots. During an instrument approach the pilot is engaged in detailed examination of flight instruments while monitoring certain visual references for making landing decisions. The caudate nucleus regulates saccade eye control of gaze, the brain area where the "expertise" effect was observed. These data provide evidence that performing "real world" aviation tasks in an fMRI provide objective data regarding the relative expertise of pilots and brain regions involved

Molecular diagnostics of Galactic star-formation regions

NASA Astrophysics Data System (ADS)

Loenen, Edo; Baan, Willem; Spaans, Marco

2007-10-01

We propose a sensitive spectral survey of Galactic star-formation regions. Using the broadband correlator at two different frequencies, we expect to detect the (1-0) transition of CO, CN, HNC, HCN, HCO+, and HCO and various of their isotopes lines, as well as the (12-11) and (10-9) transitions of HC3N. The purpose of these observations is to create a consistent (public) database of molecular emission from galactic star-formation regions. The data will be interpreted using extensive physical and chemical modeling of the whole ensemble of lines, in order to get an accurate description of the molecular environment of these regions. In particular, this diagnostic approach will describe the optical depths, the densities, and the radiation fields in the medium and will allow the establishment of dominant temperature gradients. These observations are part of a program to study molecular emission on all scales, going from individual Galactic star-formation regions, through resolved nearby galaxies, to unresolved extra-galactic emission.

Parameters of Six Selected Galactic Potential Models

NASA Astrophysics Data System (ADS)

Bajkova, Anisa; Bobylev, Vadim

2017-11-01

This paper is devoted to the refinement of the parameters of the six three-component (bulge, disk, halo) axisymmetric Galactic gravitational potential models on the basis of modern data on circular velocities of Galactic objects located at distances up to 200 kpc from the Galactic center. In all models the bulge and disk are described by the Miyamoto-Nagai expressions. To describe the halo, the models of Allen-Santillán (I), Wilkinson-Evans (II), Navarro- Frenk-White (III), Binney (IV), Plummer (V), and Hernquist (VI) are used. The sought-for parameters of potential models are determined by fitting the model rotation curves to the measured velocities, taking into account restrictions on the local dynamical matter density p⊙ - 0.1M⊙ pc-3 and the vertical force |Kz=1.1|/2πG = 77M⊙ pc-2. A comparative analysis of the refined potential models is made and for each of the models the estimates of a number of the Galactic characteristics are presented.

Visual stimulation synchronizes or desynchronizes the activity of neuron pairs between the caudate nucleus and the posterior thalamus.

PubMed

Rokszin, Alice; Gombköto, Péter; Berényi, Antal; Márkus, Zita; Braunitzer, Gábor; Benedek, György; Nagy, Attila

2011-10-18

Recent morphological and physiological studies have suggested a strong relationship between the suprageniculate nucleus (Sg) of the posterior thalamus and the input structure of the basal ganglia, the caudate nucleus (CN) of the feline brain. Accordingly, to clarify if there is a real functional relationship between Sg and CN during visual information processing, we investigated the temporal relations of simultaneously recorded neuronal spike trains of these two structures, looking for any significant cross-correlation between the spiking of the simultaneously recorded neurons. For the purposes of statistical analysis, we used the shuffle and jittering resampling methods. Of the recorded 288 Sg-CN neuron pairs, 26 (9.2%) showed significantly correlated spontaneous activity. Nineteen pairs (6.7%) showed correlated activity during stationary visual stimulation, while 21 (7.4%) pairs during stimulus movement. There was no overlap between the neuron pairs that showed cross-correlated spontaneous activity and the pairs that synchronized their activity during visual stimulation. Thus visual stimulation seems to have been able to synchronize, and also, by other neuron pairs, desynchronize the activity of CN and Sg. In about half of the cases, the activation of Sg preceded the activation of CN by a few milliseconds, while in the other half, CN was activated earlier. Our results provide the first piece of evidence for the existence of a functional cooperation between Sg and CN. We argue that either a monosynaptic bidirectional direct connection should exist between these structures, or a common input comprising of parallel pathways synchronizing them. Copyright © 2011 Elsevier B.V. All rights reserved.

The third catalog of active galactic nuclei detected by the Fermi large area telescope

DOE PAGES

Ackermann, M.; Ajello, M.; Atwood, W. B.; ...

2015-08-25

We present the third catalog of active galactic nuclei (AGNs) detected by the Fermi-LAT (3LAC). It is based on the third Fermi-LAT catalog (3FGL) of sources detected between 100 MeV and 300 GeV with a Test Statistic greater than 25, between 2008 August 4 and 2012 July 31. The 3LAC includes 1591 AGNs located at high Galactic latitudes (more » $$| b| \\gt 10^\\circ $$), a 71% increase over the second catalog based on 2 years of data. There are 28 duplicate associations, thus 1563 of the 2192 high-latitude gamma-ray sources of the 3FGL catalog are AGNs. Most of them (98%) are blazars. About half of the newly detected blazars are of unknown type, i.e., they lack spectroscopic information of sufficient quality to determine the strength of their emission lines. Based on their gamma-ray spectral properties, these sources are evenly split between flat-spectrum radio quasars (FSRQs) and BL Lacs. The most abundant detected BL Lacs are of the high-synchrotron-peaked (HSP) type. There were about 50% of the BL Lacs that had no measured redshifts. A few new rare outliers (HSP-FSRQs and high-luminosity HSP BL Lacs) are reported. The general properties of the 3LAC sample confirm previous findings from earlier catalogs. The fraction of 3LAC blazars in the total population of blazars listed in BZCAT remains non-negligible even at the faint ends of the BZCAT-blazar radio, optical, and X-ray flux distributions, which hints that even the faintest known blazars could eventually shine in gamma-rays at LAT-detection levels. Furthermore, the energy-flux distributions of the different blazar populations are in good agreement with extrapolation from earlier catalogs.« less

Dynamic, mechanical integration between nucleus and cell- where physics meets biology.

PubMed

Dickinson, Richard B; Neelam, Srujana; Lele, Tanmay P

2015-01-01

Nuclear motions like rotation, translation and deformation suggest that the nucleus is acted upon by mechanical forces. Molecular linkages with the cytoskeleton are thought to transfer forces to the nuclear surface. We developed an approach to apply reproducible, known mechanical forces to the nucleus in spread adherent cells and quantified the elastic response of the mechanically integrated nucleus-cell. The method is sensitive to molecular perturbations and revealed new insight into the function of the LINC complex. While these experiments revealed elastic behaviors, turnover of the cytoskeleton by assembly/disassembly and binding/unbinding of linkages are expected to dissipate any stored mechanical energy in the nucleus or the cytoskeleton. Experiments investigating nuclear forces over longer time scales demonstrated the mechanical principle that expansive/compressive stresses on the nuclear surface arise from the movement of the cell boundaries to shape and position the nucleus. Such forces can shape the nucleus to conform to cell shapes during cell movements with or without myosin activity.

Dynamic, mechanical integration between nucleus and cell- where physics meets biology

PubMed Central

Dickinson, Richard B; Neelam, Srujana; Lele, Tanmay P

2015-01-01

Nuclear motions like rotation, translation and deformation suggest that the nucleus is acted upon by mechanical forces. Molecular linkages with the cytoskeleton are thought to transfer forces to the nuclear surface. We developed an approach to apply reproducible, known mechanical forces to the nucleus in spread adherent cells and quantified the elastic response of the mechanically integrated nucleus-cell. The method is sensitive to molecular perturbations and revealed new insight into the function of the LINC complex. While these experiments revealed elastic behaviors, turnover of the cytoskeleton by assembly/disassembly and binding/unbinding of linkages are expected to dissipate any stored mechanical energy in the nucleus or the cytoskeleton. Experiments investigating nuclear forces over longer time scales demonstrated the mechanical principle that expansive/compressive stresses on the nuclear surface arise from the movement of the cell boundaries to shape and position the nucleus. Such forces can shape the nucleus to conform to cell shapes during cell movements with or without myosin activity. PMID:26338356

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.

Direct observation of nanoparticle-cancer cell nucleus interactions.

PubMed

Dam, Duncan Hieu M; Lee, Jung Heon; Sisco, Patrick N; Co, Dick T; Zhang, Ming; Wasielewski, Michael R; Odom, Teri W

2012-04-24

We report the direct visualization of interactions between drug-loaded nanoparticles and the cancer cell nucleus. Nanoconstructs composed of nucleolin-specific aptamers and gold nanostars were actively transported to the nucleus and induced major changes to the nuclear phenotype via nuclear envelope invaginations near the site of the construct. The number of local deformations could be increased by ultrafast, light-triggered release of the aptamers from the surface of the gold nanostars. Cancer cells with more nuclear envelope folding showed increased caspase 3 and 7 activity (apoptosis) as well as decreased cell viability. This newly revealed correlation between drug-induced changes in nuclear phenotype and increased therapeutic efficacy could provide new insight for nuclear-targeted cancer therapy.

The anterior and posterior pedunculopontine tegmental nucleus are involved in behavior and neuronal activity of the cuneiform and entopeduncular nuclei.

PubMed

Jin, X; Schwabe, K; Krauss, J K; Alam, M

2016-05-13

Loss of cholinergic neurons in the mesencephalic locomotor region, comprising the pedunculopontine nucleus (PPN) and the cuneiform nucleus (CnF), is related to gait disturbances in late stage Parkinson's disease (PD). We investigate the effect of anterior or posterior cholinergic lesions of the PPN on gait-related motor behavior, and on neuronal network activity of the PPN area and basal ganglia (BG) motor loop in rats. Anterior PPN lesions, posterior PPN lesions or sham lesions were induced by stereotaxic microinjection of the cholinergic toxin AF64-A or vehicle in male Sprague-Dawley rats. First, locomotor activity (open field), postural disturbances (Rotarod) and gait asymmetry (treadmill test) were assessed. Thereafter, single-unit and oscillatory activities were measured in the non-lesioned area of the PPN, the CnF and the entopeduncular nucleus (EPN), the BG output region, with microelectrodes under urethane anesthesia. Additionally, ECoG was recorded in the motor cortex. Injection of AF64-A into the anterior and posterior PPN decreased cholinergic cell counts as compared to naive controls (P<0.001) but also destroyed non-cholinergic cells. Only anterior PPN lesions decreased the front limb swing time of gait in the treadmill test, while not affecting other gait-related parameters tested. Main electrophysiological findings were that anterior PPN lesions increased the firing activity in the CnF (P<0.001). Further, lesions of either PPN region decreased the coherence of alpha (8-12 Hz) band between CnF and motor cortex (MCx), and increased the beta (12-30 Hz) oscillatory synchronization between EPN and the MCx. Lesions of the PPN in rats had complex effects on oscillatory neuronal activity of the CnF and the BG network, which may contribute to the understanding of the pathophysiology of gait disturbance in PD. Copyright © 2016 IBRO. Published by Elsevier Ltd. All rights reserved.

Effects of intense tone exposure on choline acetyltransferase activity in the hamster cochlear nucleus.

PubMed

Jin, Yong-Ming; Godfrey, Donald A; Wang, Jie; Kaltenbach, James A

2006-01-01

Choline acetyltransferase (ChAT) activity has been mapped in the cochlear nucleus (CN) of control hamsters and hamsters that had been exposed to an intense tone. ChAT activity in most CN regions of hamsters was only a third or less of the activity in rat CN, but in granular regions ChAT activity was similar in both species. Eight days after intense tone exposure, average ChAT activity increased on the tone-exposed side as compared to the opposite side, by 74% in the anteroventral CN (AVCN), by 55% in the granular region dorsolateral to it, and by 74% in the deep layer of the dorsal CN (DCN). In addition, average ChAT activity in the exposed-side AVCN and fusiform soma layer of DCN was higher than in controls, by 152% and 67%, respectively. Two months after exposure, average ChAT activity was still 53% higher in the exposed-side deep layer of DCN as compared to the opposite side. Increased ChAT activity after intense tone exposure may indicate that this exposure leads to plasticity of descending cholinergic innervation to the CN, which might affect spontaneous activity in the DCN that has been associated with tinnitus.

Perceptual decision related activity in the lateral geniculate nucleus

PubMed Central

Jiang, Yaoguang; Yampolsky, Dmitry; Purushothaman, Gopathy

2015-01-01

Fundamental to neuroscience is the understanding of how the language of neurons relates to behavior. In the lateral geniculate nucleus (LGN), cells show distinct properties such as selectivity for particular wavelengths, increments or decrements in contrast, or preference for fine detail versus rapid motion. No studies, however, have measured how LGN cells respond when an animal is challenged to make a perceptual decision using information within the receptive fields of those LGN cells. In this study we measured neural activity in the macaque LGN during a two-alternative, forced-choice (2AFC) contrast detection task or during a passive fixation task and found that a small proportion (13.5%) of single LGN parvocellular (P) and magnocellular (M) neurons matched the psychophysical performance of the monkey. The majority of LGN neurons measured in both tasks were not as sensitive as the monkey. The covariation between neural response and behavior (quantified as choice probability) was significantly above chance during active detection, even when there was no external stimulus. Interneuronal correlations and task-related gain modulations were negligible under the same condition. A bottom-up pooling model that used sensory neural responses to compute perceptual choices in the absence of interneuronal correlations could fully explain these results at the level of the LGN, supporting the hypothesis that the perceptual decision pool consists of multiple sensory neurons and that response fluctuations in these neurons can influence perception. PMID:26019309

The dynamic landscape of the cell nucleus.

PubMed

Austin, Christopher M; Bellini, Michel

2010-01-01

While the cell nucleus was described for the first time almost two centuries ago, our modern view of the nuclear architecture is primarily based on studies from the last two decades. This surprising late start coincides with the development of new, powerful strategies to probe for the spatial organization of nuclear activities in both fixed and live cells. As a result, three major principles have emerged: first, the nucleus is not just a bag filled with nucleic acids and proteins. Rather, many distinct functional domains, including the chromosomes, resides within the confines of the nuclear envelope. Second, all these nuclear domains are highly dynamic, with molecules exchanging rapidly between them and the surrounding nucleoplasm. Finally, the motion of molecules within the nucleoplasm appears to be mostly driven by random diffusion. Here, the emerging roles of several subnuclear domains are discussed in the context of the dynamic functions of the cell nucleus.

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.

Multiple Mechanisms Cooperate to Constitutively Exclude the Transcriptional Co-Activator YAP from the Nucleus During Murine Oogenesis1

PubMed Central

Abbassi, Laleh; Malki, Safia; Cockburn, Katie; Macaulay, Angus; Robert, Claude; Rossant, Janet; Clarke, Hugh J.

2016-01-01

Reproduction depends on the generation of healthy oocytes. Improving therapeutic strategies to prolong or rescue fertility depends on identifying the inter- and intracellular mechanisms that direct oocyte development under physiological conditions. Growth and proliferation of multiple cell types is regulated by the Hippo signaling pathway, whose chief effectors are the transcriptional co-activator YAP and its paralogue WWTR1. To resolve conflicting results concerning the potential role of Hippo in mammalian oocyte development, we systematically investigated the expression and localization of YAP in mouse oocytes. We report that that YAP is expressed in the germ cells beginning as early as Embryonic Day 15.5 and subsequently throughout pre- and postnatal oocyte development. However, YAP is restricted to the cytoplasm at all stages. YAP is phosphorylated at serine-112 in growing and fully grown oocytes, identifying a likely mechanistic basis for its nuclear exclusion, and becomes dephosphorylated at this site during meiotic maturation. Phosphorylation at serine-112 is regulated by a mechanism dependent on cyclic AMP and protein kinase A, which is known to be active in oocytes prior to maturation. Growing oocytes also contain a subpopulation of YAP, likely dephosphorylated, that is able enter the oocyte nucleus, but it is not retained there, implying that oocytes lack the cofactors required to retain YAP in the nucleus. Thus, although YAP is expressed throughout oocyte development, phosphorylation-dependent and -independent mechanisms cooperate to ensure that it does not accumulate in the nucleus. We conclude that nuclear YAP does not play a significant physiological role during oocyte development in mammals. PMID:26985001

Wet disc contraction to galactic blue nuggets and quenching to red nuggets

NASA Astrophysics Data System (ADS)

Dekel, A.; Burkert, A.

2014-02-01

We study the origin of high-redshift, compact, quenched spheroids (red nuggets) through the dissipative shrinkage of gaseous discs into compact star-forming systems (blue nuggets). The discs, fed by cold streams, undergo violent disc instability that drives gas into the centre (along with mergers). The inflow is dissipative when its time-scale is shorter than the star formation time-scale. This implies a threshold of ˜0.28 in the cold-to-total mass ratio within the disc radius. For the typical gas fraction ˜0.5 at z ˜ 2, this threshold is traced back to a maximum spin parameter of ˜0.05, implying that ˜half the star-forming galaxies contract to blue nuggets, while the rest form extended stellar discs. Thus, the surface density of blue galaxies is expected to be bimodal about ˜109 M⊙ kpc-2, slightly increasing with mass. The blue nuggets are expected to be rare at low z when the gas fraction is low. The blue nuggets quench to red nuggets by complementary internal and external mechanisms. Internal quenching by a compact bulge, in a fast mode and especially at high z, may involve starbursts, stellar and active galactic nucleus feedback, or Q-quenching. Quenching due to hot-medium haloes above 1012 M⊙ provides maintenance and a slower mode at low redshift. These predictions are confirmed in simulations and are consistent with observations at z = 0-3.

Pedunculopontine nucleus electric stimulation alleviates akinesia independently of dopaminergic mechanisms.

PubMed

Jenkinson, Ned; Nandi, Dipankar; Oram, Rebecca; Stein, John F; Aziz, Tipu Z

2006-04-24

The symptom of Parkinson's disease that is most disabling and difficult to treat is akinesia. We have previously shown that low-frequency stimulation of the pedunculopontine nucleus can alleviate such akinesia in a macaque rendered Parkinsonian using 1-methyl 4-phenyl 1,2,3,6-tetrahydropyridine. Here, we have extended that study to show that adding stimulation of the pedunculopontine nucleus to levodopa treatment in this Parkinsonian monkey increased its motor activity significantly more than levodopa alone. This additivity suggests that pedunculopontine nucleus stimulation may improve movement by acting at a site downstream from where levodopa therapy affects the basal ganglia.

Activation of D2 dopamine receptor-expressing neurons in the nucleus accumbens increases motivation

PubMed Central

Soares-Cunha, Carina; Coimbra, Barbara; David-Pereira, Ana; Borges, Sonia; Pinto, Luisa; Costa, Patricio; Sousa, Nuno; Rodrigues, Ana J.

2016-01-01

Striatal dopamine receptor D1-expressing neurons have been classically associated with positive reinforcement and reward, whereas D2 neurons are associated with negative reinforcement and aversion. Here we demonstrate that the pattern of activation of D1 and D2 neurons in the nucleus accumbens (NAc) predicts motivational drive, and that optogenetic activation of either neuronal population enhances motivation in mice. Using a different approach in rats, we further show that activating NAc D2 neurons increases cue-induced motivational drive in control animals and in a model that presents anhedonia and motivational deficits; conversely, optogenetic inhibition of D2 neurons decreases motivation. Our results suggest that the classic view of D1–D2 functional antagonism does not hold true for all dimensions of reward-related behaviours, and that D2 neurons may play a more prominent pro-motivation role than originally anticipated. PMID:27337658

Light ion components of the galactic cosmic rays: Nuclear interactions and transport theory

NASA Technical Reports Server (NTRS)

Cucinotta, F. A.; Townsend, L. W.; Wilson, J. W.; Shinn, J. L.; Badhwar, G. D.; Dubey, R. R.

1996-01-01

Light nuclei are present in the primary galactic cosmic rays (GCR) and are produced in thick targets due to projectile or target fragmentation from both nucleon and heavy induced reactions. In the primary GCR, He-4 is the most abundant nucleus after H-1. However, there are also a substantial fluxes of H-2 and He-3. In this paper we describe theoretical models based on quantum multiple scattering theory for the description of light ion nuclear interactions. The energy dependence of the light ion fragmentation cross section is considered with comparisons of inclusive yields and secondary momentum distributions to experiments described. We also analyze the importance of a fast component of lights ions from proton and neutron induced target fragementation. These theoretical models have been incorporated into the cosmic ray transport code HZETRN and will be used to analyze the role of shielding materials in modulating the production and the energy spectrum of light ions.

Galactic-scale civilization

NASA Technical Reports Server (NTRS)

Kuiper, T. B. H.

1980-01-01

Evolutionary arguments are presented in favor of the existence of civilization on a galactic scale. Patterns of physical, chemical, biological, social and cultural evolution leading to increasing levels of complexity are pointed out and explained thermodynamically in terms of the maximization of free energy dissipation in the environment of the organized system. The possibility of the evolution of a global and then a galactic human civilization is considered, and probabilities that the galaxy is presently in its colonization state and that life could have evolved to its present state on earth are discussed. Fermi's paradox of the absence of extraterrestrials in light of the probability of their existence is noted, and a variety of possible explanations is indicated. Finally, it is argued that although mankind may be the first occurrence of intelligence in the galaxy, it is unjustified to presume that this is so.

Fusion cross sections for reactions involving medium and heavy nucleus-nucleus systems

NASA Astrophysics Data System (ADS)

Atta, Debasis; Basu, D. N.

2014-12-01

Existing data on near-barrier fusion excitation functions of medium and heavy nucleus-nucleus systems have been analyzed by using a simple diffused-barrier formula derived assuming the Gaussian shape of the barrier-height distributions. The fusion cross section is obtained by folding the Gaussian barrier distribution with the classical expression for the fusion cross section for a fixed barrier. The energy dependence of the fusion cross section, thus obtained, provides good description to the existing data on near-barrier fusion and capture excitation functions for medium and heavy nucleus-nucleus systems. The theoretical values for the parameters of the barrier distribution are estimated which can be used for fusion or capture cross-section predictions that are especially important for planning experiments for synthesizing new superheavy elements.

Electromagnetic Nucleus - Nucleus Cross Sections Using Energy Dependent Branching Ratios

NASA Astrophysics Data System (ADS)

Adamczyk, Anne; Norbury, John

2009-11-01

Energy dependent branching ratios, derived from Weisskopf-Ewing theory, are presented and compared to an energy independent formalism, developed by Norbury, Townsend, and Westfall. The energy dependent branching ratio formalism is more versatile since it allows for not only neutron and proton emission, but also alpha particle, deuteron, helion, and triton emission. A new theoretical method for calculating electromagnetic dissociation (EMD) nucleus - nucleus cross sections, with energy dependent branching ratios, is introduced. Comparisons of photonuclear and nucleus - nucleus cross sections, using energy dependent and independent branching ratios, to experiment are presented. Experimental efforts, by various groups, have focused on measuring cross sections for proton and neutron emission, because proton and neutron emission is generally more probable than heavier particle emission. Consequently, comparisons of energy dependent and independent branching ratios to experiment are made for photoneutron and photoproton cross sections. EMD cross sections for single neutron, proton, and alpha particle removal are calculated and compared to experimental data for a variety of projectile, target, and energy combinations. Results indicate that using energy dependent branching ratios yields better estimates.

Relationship between cortical state and spiking activity in the lateral geniculate nucleus of marmosets

PubMed Central

Pietersen, Alexander N.J.; Cheong, Soon Keen; Munn, Brandon; Gong, Pulin; Solomon, Samuel G.

2017-01-01

Key points How parallel are the primate visual pathways? In the present study, we demonstrate that parallel visual pathways in the dorsal lateral geniculate nucleus (LGN) show distinct patterns of interaction with rhythmic activity in the primary visual cortex (V1).In the V1 of anaesthetized marmosets, the EEG frequency spectrum undergoes transient changes that are characterized by fluctuations in delta‐band EEG power.We show that, on multisecond timescales, spiking activity in an evolutionary primitive (koniocellular) LGN pathway is specifically linked to these slow EEG spectrum changes. By contrast, on subsecond (delta frequency) timescales, cortical oscillations can entrain spiking activity throughout the entire LGN.Our results are consistent with the hypothesis that, in waking animals, the koniocellular pathway selectively participates in brain circuits controlling vigilance and attention. Abstract The major afferent cortical pathway in the visual system passes through the dorsal lateral geniculate nucleus (LGN), where nerve signals originating in the eye can first interact with brain circuits regulating visual processing, vigilance and attention. In the present study, we investigated how ongoing and visually driven activity in magnocellular (M), parvocellular (P) and koniocellular (K) layers of the LGN are related to cortical state. We recorded extracellular spiking activity in the LGN simultaneously with local field potentials (LFP) in primary visual cortex, in sufentanil‐anaesthetized marmoset monkeys. We found that asynchronous cortical states (marked by low power in delta‐band LFPs) are linked to high spike rates in K cells (but not P cells or M cells), on multisecond timescales. Cortical asynchrony precedes the increases in K cell spike rates by 1–3 s, implying causality. At subsecond timescales, the spiking activity in many cells of all (M, P and K) classes is phase‐locked to delta waves in the cortical LFP, and more cells are phase�

ORIGINS OF SCATTER IN THE RELATIONSHIP BETWEEN HCN 1-0 AND DENSE GAS MASS IN THE GALACTIC CENTER

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

Mills, Elisabeth A. C.; Battersby, Cara, E-mail: elisabeth.mills@sjsu.edu

We investigate the correlation of HCN 1-0 with gas mass in the central 300 pc of the Galaxy. We find that on the ∼10 pc size scale of individual cloud cores, HCN 1-0 is well correlated with dense gas mass when plotted as a log–log relationship. There is ∼0.75 dex of scatter in this relationship from clouds like Sgr B2, which has an integrated HCN 1-0 intensity of a cloud less than half its mass, and others that have HCN 1-0 enhanced by a factor of 2–3 relative to clouds of comparable mass. We identify the two primary sources ofmore » scatter to be self-absorption and variations in HCN abundance. We also find that the extended HCN 1-0 emission is more intense per unit mass than in individual cloud cores. In fact the majority (80%) of HCN 1-0 emission comes from extended gas with column densities below 7 × 10{sup 22} cm{sup −2}, accounting for 68% of the total mass. We find variations in the brightness of HCN 1-0 would only yield a ∼10% error in the dense gas mass inferred from this line in the Galactic center. However, the observed order of magnitude HCN abundance variations, and the systematic nature of these variations, warn of potential biases in the use of HCN as dense gas mass tracer in more extreme environments such as an active galactic nucleus and shock-dominated regions. We also investigate other 3 mm tracers, finding that HNCO is better correlated with mass than HCN, and might be a better tracer of cloud mass in this environment.« less

Alpha oscillations in the pedunculopontine nucleus correlate with gait performance in parkinsonism

PubMed Central

Thevathasan, Wesley; Pogosyan, Alek; Hyam, Jonathan A.; Jenkinson, Ned; Foltynie, Tom; Limousin, Patricia; Bogdanovic, Marko; Zrinzo, Ludvic; Green, Alexander L.; Aziz, Tipu Z.

2012-01-01

The pedunculopontine nucleus, a component of the reticular formation, is topographically organized in animal models and implicated in locomotor control. In Parkinson's disease, pedunculopontine nucleus stimulation is an emerging treatment for gait freezing. Local field potentials recorded from pedunculopontine nucleus electrodes in such patients have demonstrated oscillations in the alpha and beta frequency bands, reactive to self-paced movement. Whether these oscillations are topographically organized or relevant to locomotion is unknown. Here, we recorded local field potentials from the pedunculopontine nucleus in parkinsonian patients during rest and unconstrained walking. Relative gait speed was assessed with trunk accelerometry. Peaks of alpha power were present at rest and during gait, when they correlated with gait speed. Gait freezing was associated with attenuation of alpha activity. Beta peaks were less consistently observed across rest and gait, and did not correlate with gait speed. Alpha power was maximal in the caudal pedunculopontine nucleus region and beta power was maximal rostrally. These results indicate a topographic distribution of neuronal activity in the pedunculopontine nucleus region and concur with animal data suggesting that the caudal subregion has particular relevance to gait. Alpha synchronization, proposed to suppress ‘task irrelevant’ distraction, has previously been demonstrated to correlate with performance of cognitive tasks. Here, we demonstrate a correlation between alpha oscillations and improved gait performance. The results raise the possibility that stimulation of caudal and rostral pedunculopontine nucleus regions may differ in their clinical effects. PMID:22232591

Evolution of the Oort Cloud under Galactic Perturbations

NASA Astrophysics Data System (ADS)

Higuchi, A.; Kokubo, E.; Mukai, T.

2005-08-01

The Oort cloud is a spherical comet reservoir surrounding the solar system. There is general agreement that the Oort cloud comets are the residual planetesimals of planet formation. The standard scenario of the Oort cloud formation consists of two dynamical stages: (1) giant planets raise the aphelia of planetesimals to the outer region of the solar system and (2) the galactic tide, passing stars, and giant molecular clouds pull up their perihelia out of the planetary region and randomize their inclinations. Here we show the orbital evolution of planetesimals due to the galactic tide. Planetesimals with large aphelion distances change their perihelion distances toward the outside of the planetary region by the galactic tide and become members of the Oort cloud. We consider only the vertical component of the galactic tide because it is dominant compared to other components. Then, under such an axi-symmetric assumption, some planetesimals may show the librations around ω (argument of perihelion)=π /2 or 3π /2 (the Kozai mechanism). The alternate increases of eccentricity and inclination of the Kozai mechanism are effective to form the Oort cloud. Using the secular perturbation theory, we can understand the motion of the planetesimals analytically. We applied the Kozai mechanism to the galactic tide and found that the galactic tide raise perihelia and randomize inclinations of planetesimals with semimajor axes larger than ˜ 103 AU in 5Gyr. We take into account time evolution of the local galactic density, which is thought to be denser in the early stage of the sun than the current one. This work was supported by the 21st Century COE Program Origin and Evolution of Planetary Systems of the Ministry of Education, Culture, Sports, Science, and Technology, Japan, and JSPS Research Fellowship for Young Scientists.

Black hole masses in active galactic nuclei

NASA Astrophysics Data System (ADS)

Denney, Kelly D.

2010-11-01

We present the complete results from two, high sampling-rate, multi-month, spectrophotometric reverberation mapping campaigns undertaken to obtain either new or improved Hbeta reverberation lag measurements for several relatively low-luminosity active galactic nuclei (AGNs). We have reliably measured the time delay between variations in the continuum and Hbeta emission line in seven local Seyfert 1 galaxies. These measurements are used to calculate the mass of the supermassive black hole at the center of each of these AGNs. We place our results in context to the most current calibration of the broad-line region (BLR) RBLR-L relationship, where our results remove many outliers and significantly reduce the scatter at the low-luminosity end of this relationship. A detailed analysis of the data from our high sampling rate, multi-month reverberation mapping campaign in 2007 reveals that the Hbeta emission region within the BLRs of several nearby AGNs exhibit a variety of kinematic behaviors. Through a velocity-resolved reverberation analysis of the broad Hbeta emission-line flux variations in our sample, we reconstruct velocity-resolved kinematic signals for our entire sample and clearly see evidence for outflowing, infalling, and virialized BLR gas motions in NGC 3227, NGC 3516, and NGC 5548, respectively. Finally, we explore the nature of systematic errors that can arise in measurements of black hole masses from single-epoch spectra of AGNs by utilizing the many epochs available for NGC 5548 and PG1229+204 from reverberation mapping databases. In particular, we examine systematics due to AGN variability, contamination due to constant spectral components (i.e., narrow lines and host galaxy flux), data quality (i.e., signal-to-noise ratio, S/N), and blending of spectral features. We investigate the effect that each of these systematics has on the precision and accuracy of single-epoch masses calculated from two commonly-used line-width measures by comparing these

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

Meson-nucleus potentials and the search for meson-nucleus bound states

NASA Astrophysics Data System (ADS)

Metag, V.; Nanova, M.; Paryev, E. Ya.

2017-11-01

Recent experiments studying the meson-nucleus interaction to extract meson-nucleus potentials are reviewed. The real part of the potentials quantifies whether the interaction is attractive or repulsive while the imaginary part describes the meson absorption in nuclei. The review is focused on mesons which are sufficiently long-lived to potentially form meson-nucleus quasi-bound states. The presentation is confined to meson production off nuclei in photon-, pion-, proton-, and light-ion induced reactions and heavy-ion collisions at energies near the production threshold. Tools to extract the potential parameters are presented. In most cases, the real part of the potential is determined by comparing measured meson momentum distributions or excitation functions with collision model or transport model calculations. The imaginary part is extracted from transparency ratio measurements. Results on K+ ,K0 ,K- , η ,η‧ , ω, and ϕ mesons are presented and compared with theoretical predictions. The interaction of K+ and K0 mesons with nuclei is found to be weakly repulsive, while the K- , η ,η‧ , ω and ϕ meson-nucleus potentials are attractive, however, with widely different strengths. Because of meson absorption in the nuclear medium the imaginary parts of the meson-nucleus potentials are all negative, again with a large spread. An outlook on planned experiments in the charm sector is given. In view of the determined potential parameters, the criteria and chances for experimentally observing meson-nucleus quasi-bound states are discussed. The most promising candidates appear to be the η and η‧ mesons.

Polarization of the diffuse galactic light.

NASA Technical Reports Server (NTRS)

Sparrow, J. G.; Ney, E. P.

1972-01-01

Polarization measurements made from the satellite OSO-5 show that the polarized intensity in the direction of the Scutum arm of the Galaxy is different in intensity and direction of the polarization from that observed due to the zodiacal light. The observations are consistent with polarized diffuse galactic light superposed on the zodiacal light. The results are interpreted in terms of a model in which the galactic starlight is scattered by interstellar dust.

Parabrachial origin of calcitonin gene-related peptide-immunoreactive axons innervating Meynert's basal nucleus.

PubMed

Knyihár-Csillik, E; Boncz, I; Sáry, G; Nemcsók, J; Csillik, B

1999-06-01

Meynert's basal nucleus is innervated by calcitonin gene-related peptide (CGRP)-immunoreactive axons synapsing with cholinergic principal cells. Origin of CGRP-immunopositive axons was studied in the albino rat. Since beaded axons containing the nicotinic acetylcholine receptor (nAChR) are also present in the basal nucleus, the microstructural arrangement raises the question whether or not an interaction between CGRP and nAChR exists like in the neuromuscular junction. We found that electrolytic lesion of the parabrachial nucleus results in degeneration of CGRP-immunoreactive axons in the ipsilateral nucleus basalis and induces shrinkage of principal cholinergic neurons while the contralateral nucleus basalis remains intact. Electrolytic lesions in the thalamus, caudate-putamen, and hippocampus did not induce alterations in Meynert's basal nucleus. Disappearance of CGRP after lesions of the parabrachial nucleus does not impair presynaptic nAChR in the basal nucleus, suggesting that, unlike in the neuromuscular junction, CGRP is not involved in the maintenance of nAChR in the basal forebrain. It is concluded that the parabrachial nucleus is involved in the activation of the nucleus basalis-prefrontal cortex system, essential in gnostic and mnemonic functions. Copyright 1999 Academic Press.

Computer program for parameterization of nucleus-nucleus electromagnetic dissociation cross sections

NASA Technical Reports Server (NTRS)

Norbury, John W.; Townsend, Lawrence W.; Badavi, Forooz F.

1988-01-01

A computer subroutine parameterization of electromagnetic dissociation cross sections for nucleus-nucleus collisions is presented that is suitable for implementation in a heavy ion transport code. The only inputs required are the projectile kinetic energy and the projectile and target charge and mass numbers.

The Galactic Magnetic Field and its lensing of Ultrahigh Energy and Galactic Cosmic Rays

NASA Astrophysics Data System (ADS)

Farrar, Glennys

2015-08-01

It has long been recognized that magnetic fields play an important role in many astrophysical environments, but the magnetic field strength and structure has only been quantitatively determined for relatively few systems beyond our solar system.Our understanding of the Galactic magnetic field (GMF) has improved tremendously in recent years. The Jansson-Farrar (2012) (JF12) GMF model is the most realistic and comprehensive model available. It was constrained by fitting all-sky Faraday Rotation Measures of ~40k extragalactic sources, simultaneously with WMAP polarized (Q,U) and total synchrotron emission maps - together providing a total of more than 10,000 independent datapoints, each with measured astrophysical variance. In addition to disk and toroidal halo components, a previously overlooked coherent poloidal halo field proves to be necessary to account for the RM, Q and U data. Moreover a “striated” random component is needed in addition to a fully random component, in both disk and halo.The talk will give a concise review of the JF12 model and its derivation, with emphasis on which features of the GMF are well or poorly established. I will show that the data unambiguously demand a large scale coherent component to the halo field which is a diverging-spiral centered on the Galactic center, with field lines running from Southern to Northern hemispheres. The puzzles posed by the large scale coherent halo and disk magnetic fields, and their possible origins, will be discussed.Having a good model of the Galactic magnetic field is crucial for determining the sources of UHECRs, for modeling the transport of Galactic CRs (the halo field provides a heretofore-overlooked escape route for by diffusion along its field lines), and for calculating the background to dark matter and CMB-cosmology studies. I will present new results on the lensing effect of the GMF on UHECRs, which produces multiple images and dramatic magnification and demagnification that varies with

Nucleus-nucleus interactions between 20 and 65 GeV per nucleon

NASA Technical Reports Server (NTRS)

Burnett, T. H.; Derrickson, J. H.; Fountain, W. F.; Meegan, C. A.; Parnell, T. A.; Roberts, F. E.; Watts, J. W.; Oda, H.; Takahashi, Y.; Jones, W. V.

1987-01-01

A hybrid electronic-counter/emulsion-chamber instrument was exposed to high-energy cosmic rays on a balloon. The data on 105 nucleus-nucleus collisions in the energy range 20-65 GeV/nucleon and for incident nuclear charges Zp in the range of 22 to 28 are presented. Inclusive characteristics of particle production on different targets (plastic, emulsion, and lead) are shown and compared with models based on the superposition of nucleon-nucleus interactions. Features of a subset of the more central collisions with a plastic target and some characteristics of individual events with the highest multiplicity of produced particles are described.

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 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.

Elucidation of the anatomy of a satiety network: Focus on connectivity of the parabrachial nucleus in the adult rat.

PubMed

Zséli, Györgyi; Vida, Barbara; Martinez, Anais; Lechan, Ronald M; Khan, Arshad M; Fekete, Csaba

2016-10-01

We hypothesized that brain regions showing neuronal activation after refeeding comprise major nodes in a satiety network, and tested this hypothesis with two sets of experiments. Detailed c-Fos mapping comparing fasted and refed rats was performed to identify candidate nodes of the satiety network. In addition to well-known feeding-related brain regions such as the arcuate, dorsomedial, and paraventricular hypothalamic nuclei, lateral hypothalamic area, parabrachial nucleus (PB), nucleus of the solitary tract and central amygdalar nucleus, other refeeding activated regions were also identified, such as the parastrial and parasubthalamic nuclei. To begin to understand the connectivity of the satiety network, the interconnectivity of PB with other refeeding-activated neuronal groups was studied following administration of anterograde or retrograde tracers into the PB. After allowing for tracer transport time, the animals were fasted and then refed before sacrifice. Refeeding-activated neurons that project to the PB were found in the agranular insular area; bed nuclei of terminal stria; anterior hypothalamic area; arcuate, paraventricular, and dorsomedial hypothalamic nuclei; lateral hypothalamic area; parasubthalamic nucleus; central amygdalar nucleus; area postrema; and nucleus of the solitary tract. Axons originating from the PB were observed to closely associate with refeeding-activated neurons in the agranular insular area; bed nuclei of terminal stria; anterior hypothalamus; paraventricular, arcuate, and dorsomedial hypothalamic nuclei; lateral hypothalamic area; central amygdalar nucleus; parasubthalamic nucleus; ventral posterior thalamic nucleus; area postrema; and nucleus of the solitary tract. These data indicate that the PB has bidirectional connections with most refeeding-activated neuronal groups, suggesting that short-loop feedback circuits exist in this satiety network. J. Comp. Neurol. 524:2803-2827, 2016. © 2016 Wiley Periodicals, Inc. © 2016 Wiley

The Galactic Nova Rate Revisited

NASA Astrophysics Data System (ADS)

Shafter, A. W.

2017-01-01

Despite its fundamental importance, a reliable estimate of the Galactic nova rate has remained elusive. Here, the overall Galactic nova rate is estimated by extrapolating the observed rate for novae reaching m≤slant 2 to include the entire Galaxy using a two component disk plus bulge model for the distribution of stars in the Milky Way. The present analysis improves on previous work by considering important corrections for incompleteness in the observed rate of bright novae and by employing a Monte Carlo analysis to better estimate the uncertainty in the derived nova rates. Several models are considered to account for differences in the assumed properties of bulge and disk nova populations and in the absolute magnitude distribution. The simplest models, which assume uniform properties between bulge and disk novae, predict Galactic nova rates of ˜50 to in excess of 100 per year, depending on the assumed incompleteness at bright magnitudes. Models where the disk novae are assumed to be more luminous than bulge novae are explored, and predict nova rates up to 30% lower, in the range of ˜35 to ˜75 per year. An average of the most plausible models yields a rate of {50}-23+31 yr-1, which is arguably the best estimate currently available for the nova rate in the Galaxy. Virtually all models produce rates that represent significant increases over recent estimates, and bring the Galactic nova rate into better agreement with that expected based on comparison with the latest results from extragalactic surveys.

Fermi-LAT high-z active galactic nuclei and the extragalactic background light

NASA Astrophysics Data System (ADS)

Armstrong, Thomas; Brown, Anthony M.; Chadwick, Paula M.

2017-10-01

Observations of distant gamma-ray sources are hindered by the presence of the extragalactic background light (EBL). In order to understand the physical processes that result in the observed spectrum of sources, it is imperative that a good understanding of the EBL is included. In this work, an investigation into the imprint of the EBL on the observed spectra of high-redshift Fermi-LAT active galactic nuclei is presented. By fitting the spectrum below ˜10 GeV, an estimation of the unabsorbed intrinsic source spectrum is obtained; by applying this spectrum to data up to 300 GeV, it is then possible to derive a scaling factor for different EBL models. A second approach uses five sources (PKS 0426-380, 4C +55.17, Ton 116, PG 1246+586 and RBS 1432) that were found to exhibit very high energy (VHE) emission (Eγ > 100 GeV). Through Monte Carlo simulations, it is shown that the observation of VHE photons, despite the large distances of these objects, is consistent with current EBL models. Many of these sources would be observable with the upcoming ground-based observatory, the Cherenkov Telescope Array, leading to a better understanding of the EBL.

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.

HOT-DUST-POOR TYPE 1 ACTIVE GALACTIC NUCLEI IN THE COSMOS SURVEY

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

Hao Heng; Elvis, Martin; Civano, Francesca

2010-11-20

We report a sizable class of type 1 active galactic nuclei (AGNs) with unusually weak near-infrared (1-3 {mu}m) emission in the XMM-COSMOS type 1 AGN sample. The fraction of these 'hot-dust-poor' AGNs increases with redshift from 6% at low redshift (z < 2) to 20% at moderate high redshift (2 < z < 3.5). There is no clear trend of the fraction with other parameters: bolometric luminosity, Eddington ratio, black hole mass, and X-ray luminosity. The 3 {mu}m emission relative to the 1 {mu}m emission is a factor of 2-4 smaller than the typical Elvis et al. AGN spectral energymore » distribution (SED), which indicates a 'torus' covering factor of 2%-29%, a factor of 3-40 smaller than required by unified models. The weak hot dust emission seems to expose an extension of the accretion disk continuum in some of the source SEDs. We estimate the outer edge of their accretion disks to lie at (0.3-2.0) x 10{sup 4} Schwarzschild radii, {approx}10-23 times the gravitational stability radii. Formation scenarios for these sources are discussed.« less

Dusty Winds in Active Galactic Nuclei: Reconciling Observations with Models

NASA Astrophysics Data System (ADS)

Hönig, Sebastian F.; Kishimoto, Makoto

2017-04-01

This Letter presents a revised radiative transfer model for the infrared (IR) emission of active galactic nuclei (AGNs). While current models assume that the IR is emitted from a dusty torus in the equatorial plane of the AGNs, spatially resolved observations indicate that the majority of the IR emission from ≲100 pc in many AGNs originates from the polar region, contradicting classical torus models. The new model CAT3D-WIND builds upon the suggestion that the dusty gas around the AGNs consists of an inflowing disk and an outflowing wind. Here, it is demonstrated that (1) such disk+wind models cover overall a similar parameter range of observed spectral features in the IR as classical clumpy torus models, e.g., the silicate feature strengths and mid-IR spectral slopes, (2) they reproduce the 3-5 μm bump observed in many type 1 AGNs unlike torus models, and (3) they are able to explain polar emission features seen in IR interferometry, even for type 1 AGNs at relatively low inclination, as demonstrated for NGC3783. These characteristics make it possible to reconcile radiative transfer models with observations and provide further evidence of a two-component parsec-scale dusty medium around AGNs: the disk gives rise to the 3-5 μm near-IR component, while the wind produces the mid-IR emission. The model SEDs will be made available for download.

Dusty Winds in Active Galactic Nuclei: Reconciling Observations with Models

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

Hönig, Sebastian F.; Kishimoto, Makoto, E-mail: S.Hoenig@soton.ac.uk

2017-04-01

This Letter presents a revised radiative transfer model for the infrared (IR) emission of active galactic nuclei (AGNs). While current models assume that the IR is emitted from a dusty torus in the equatorial plane of the AGNs, spatially resolved observations indicate that the majority of the IR emission from ≲100 pc in many AGNs originates from the polar region, contradicting classical torus models. The new model CAT3D-WIND builds upon the suggestion that the dusty gas around the AGNs consists of an inflowing disk and an outflowing wind. Here, it is demonstrated that (1) such disk+wind models cover overall amore » similar parameter range of observed spectral features in the IR as classical clumpy torus models, e.g., the silicate feature strengths and mid-IR spectral slopes, (2) they reproduce the 3–5 μ m bump observed in many type 1 AGNs unlike torus models, and (3) they are able to explain polar emission features seen in IR interferometry, even for type 1 AGNs at relatively low inclination, as demonstrated for NGC3783. These characteristics make it possible to reconcile radiative transfer models with observations and provide further evidence of a two-component parsec-scale dusty medium around AGNs: the disk gives rise to the 3–5 μ m near-IR component, while the wind produces the mid-IR emission. The model SEDs will be made available for download.« less

An Iwasawa-Taniguchi effect for Compton-thick active galactic nuclei

NASA Astrophysics Data System (ADS)

Boorman, Peter G.; Gandhi, Poshak; Baloković, Mislav; Brightman, Murray; Harrison, Fiona; Ricci, Claudio; Stern, Daniel

2018-07-01

We present the first study of an Iwasawa-Taniguchi/`X-ray Baldwin' effect for Compton-thick active galactic nuclei (AGN). We report a statistically significant anticorrelation between the rest-frame equivalent width (EW) of the narrow core of the neutral Fe Kα fluorescence emission line, ubiquitously observed in the reflection spectra of obscured AGN, and the mid-infrared 12 μ m continuum luminosity (taken as a proxy for the bolometric AGN luminosity). Our sample consists of 72 Compton-thick AGN selected from pointed and deep-field observations covering a redshift range of z ˜ 0.0014-3.7. We employ a Monte Carlo-based fitting method, which returns a Spearman's Rank correlation coefficient of ρ = - 0.28 ± 0.12, significant to 98.7 per cent confidence. The best-fitting found is log(EW_{Fe Kα }) ∝ -0.08± 0.04 log(L_{12 {μ } m}), which is consistent with multiple studies of the X-ray Baldwin effect for unobscured and mildly obscured AGN. This is an unexpected result, as the Fe Kα line is conventionally thought to originate from the same region as the underlying reflection continuum, which together constitute the reflection spectrum. We discuss the implications this could have if confirmed on larger samples, including a systematic underestimation of the line-of-sight X-ray obscuring column density and hence the intrinsic luminosities and growth rates for the most luminous AGN.

Direct Observation of Nanoparticle-Cancer Cell Nucleus Interactions

PubMed Central

Dam, Duncan Hieu M.; Lee, Jung Heon; Sisco, Patrick N.; Co, Dick T.; Zhang, Ming; Wasielewski, Michael R.; Odom, Teri W.

2012-01-01

We report the direct visualization of interactions between drug-loaded nanoparticles and the cancer cell nucleus. Nanoconstructs composed of nucleolin-specific aptamers and gold nanostars were actively transported to the nucleus and induced major changes to the nuclear phenotype via nuclear envelope invaginations near the site of the construct. The number of local deformations could be increased by ultra-fast, light-triggered release of the aptamers from the surface of the gold nanostars. Cancer cells with more nuclear envelope folding showed increased caspase 3 and 7 activity (apoptosis) as well as decreased cell viability. This newly revealed correlation between drug-induced changes in nuclear phenotype and increased therapeutic efficacy could provide new insight for nuclear-targeted cancer therapy. PMID:22424173

Neuronal plasticity in the hedgehog supraoptic nucleus during hibernation.

PubMed

Sanchez-Toscano, F; Caminero, A A; Machin, C; Abella, G

1989-01-01

The purpose of the present study was to identify processes of plasticity in the receptive field of neurosecretory neurons of the supraoptic nucleus during hibernation in the hedgehog, in order to correlate them with the increased neurosecretory activity observed in this nucleus during this annual period. Using the Rapid Golgi method, a quantitative study was conducted in the receptive field of bipolar and multipolar neurons (the main components of the nucleus). Results indicate a generalized increase in the following characteristics: (1) number of dendritic spines per millimeter along the dendritic shafts; (2) degree of branching in the dendritic field; and (3) dendritic density around the neuronal soma. These data demonstrate modification of the dendritic field in the supraoptic nucleus during hibernation, a change undoubtedly related to functional conditions. Since the observed changes affect structures such as dendritic spines which are directly related to the arrival of neural afferences, the discussion is centered on the types of stimuli which may be responsible for the observed processes.

The reorientation of cell nucleus promotes the establishment of front-rear polarity in migrating fibroblasts.

PubMed

Maninová, Miloslava; Klímová, Zuzana; Parsons, J Thomas; Weber, Michael J; Iwanicki, Marcin P; Vomastek, Tomáš

2013-06-12

The establishment of cell polarity is an essential step in the process of cell migration. This process requires precise spatiotemporal coordination of signaling pathways that in most cells create the typical asymmetrical profile of a polarized cell with nucleus located at the cell rear and the microtubule organizing center (MTOC) positioned between the nucleus and the leading edge. During cell polarization, nucleus rearward positioning promotes correct microtubule organizing center localization and thus the establishment of front-rear polarity and directional migration. We found that cell polarization and directional migration require also the reorientation of the nucleus. Nuclear reorientation is manifested as temporally restricted nuclear rotation that aligns the nuclear axis with the axis of cell migration. We also found that nuclear reorientation requires physical connection between the nucleus and cytoskeleton mediated by the LINC (linker of nucleoskeleton and cytoskeleton) complex. Nuclear reorientation is controlled by coordinated activity of lysophosphatidic acid (LPA)-mediated activation of GTPase Rho and the activation of integrin, FAK (focal adhesion kinase), Src, and p190RhoGAP signaling pathway. Integrin signaling is spatially induced at the leading edge as FAK and p190RhoGAP are predominantly activated or localized at this location. We suggest that integrin activation within lamellipodia defines cell front, and subsequent FAK, Src, and p190RhoGAP signaling represents the polarity signal that induces reorientation of the nucleus and thus promotes the establishment of front-rear polarity. Copyright © 2013 Elsevier Ltd. All rights reserved.

Constraining the contribution of active galactic nuclei to reionization

NASA Astrophysics Data System (ADS)

Hassan, Sultan; Davé, Romeel; Mitra, Sourav; Finlator, Kristian; Ciardi, Benedetta; Santos, Mario G.

2018-01-01

Recent results have suggested that active galactic nuclei (AGN) could provide enough photons to reionize the Universe. We assess the viability of this scenario using a semi-numerical framework for modelling reionization, to which we add a quasar contribution by constructing a Quasar Halo Occupancy Distribution (QHOD) based on Giallongo et al. observations. Assuming a constant QHOD, we find that an AGN-only model cannot simultaneously match observations of the optical depth τe, neutral fraction and ionizing emissivity. Such a model predicts τe too low by ∼2σ relative to Planck constraints, and reionizes the Universe at z ≲ 5. Arbitrarily increasing the AGN emissivity to match these results yields a strong mismatch with the observed ionizing emissivity at z ∼ 5. If we instead assume a redshift-independent AGN luminosity function yielding an emissivity evolution like that assumed in Madau & Haardt model, then we can match τe albeit with late reionization; however, such evolution is inconsistent with observations at z ∼ 4-6 and poorly motivated physically. These results arise because AGN are more biased towards massive haloes than typical reionizing galaxies, resulting in stronger clustering and later formation times. AGN-dominated models produce larger ionizing bubbles that are reflected in ∼×2 more 21 cm power on all scales. A model with equal part galaxies and AGN contribution is still (barely) consistent with observations, but could be distinguished using next-generation 21 cm experiments such as Hydrogen Epoch of Reionization Array and SKA-low. We conclude that, even with recent claims of more faint AGN than previously thought, AGN are highly unlikely to dominate the ionizing photon budget for reionization.

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.

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.

Double-peaked broad line emission from the LINER nucleus of NGC 1097

NASA Technical Reports Server (NTRS)

Storchi-Bergmann, Thaisa; Baldwin, Jack A.; Wilson, Andrew S.

1993-01-01

We report the recent appearance of a very broad component in the H-alpha and H-beta emission lines of the weakly active nucleus of the Sersic-Pastoriza galaxy NGC 1097. The FWZI of the broad component is about 21,000 km/s, and its profile is double-peaked; the presence of a blue, featureless continuum in the nucleus is also suggested. The broad component was first observed in H-alpha in November 2, 1991, and confirmed 11 months later. The H-alpha profile and flux did not change in this time interval. Comparison with previously published spectral data indicates that the broad lines have only recently appeared. Together with the relatively high X-ray luminosity and the compact nuclear radio source, our results characterize the presence of a Seyfert 1 nucleus in a galaxy which had previously shown only LINER characteristics. Obscuring material along our line of sight to the nucleus appears to have recently cleared, permitting a direct view of the active nucleus. We discuss two possible structures for the broad line region, biconical outflow and an accretion disk, that could give rise to the observed profile.

Convergence of limb, visceral, and vertical semicircular canal or otolith inputs onto vestibular nucleus neurons

NASA Technical Reports Server (NTRS)

Jian, B. J.; Shintani, T.; Emanuel, B. A.; Yates, B. J.

2002-01-01

The major goal of this study was to determine the patterns of convergence of non-labyrinthine inputs from the limbs and viscera onto vestibular nucleus neurons receiving signals from vertical semicircular canals or otolith organs. A secondary aim was to ascertain whether the effects of non-labyrinthine inputs on the activity of vestibular nucleus neurons is affected by bilateral peripheral vestibular lesions. The majority (72%) of vestibular nucleus neurons in labyrinth-intact animals whose firing was modulated by vertical rotations responded to electrical stimulation of limb and/or visceral nerves. The activity of even more vestibular nucleus neurons (93%) was affected by limb or visceral nerve stimulation in chronically labyrinthectomized preparations. Some neurons received non-labyrinthine inputs from a variety of peripheral sources, including antagonist muscles acting at the same joint, whereas others received inputs from more limited sources. There was no apparent relationship between the spatial and dynamic properties of a neuron's responses to tilts in vertical planes and the non-labyrinthine inputs that it received. These data suggest that non-labyrinthine inputs elicited during movement will modulate the processing of information by the central vestibular system, and may contribute to the recovery of spontaneous activity of vestibular nucleus neurons following peripheral vestibular lesions. Furthermore, some vestibular nucleus neurons with non-labyrinthine inputs may be activated only during particular behaviors that elicit a specific combination of limb and visceral inputs.

Convergence of limb, visceral, and vertical semicircular canal or otolith inputs onto vestibular nucleus neurons.

PubMed

Jian, B J; Shintani, T; Emanuel, B A; Yates, B J

2002-05-01

The major goal of this study was to determine the patterns of convergence of non-labyrinthine inputs from the limbs and viscera onto vestibular nucleus neurons receiving signals from vertical semicircular canals or otolith organs. A secondary aim was to ascertain whether the effects of non-labyrinthine inputs on the activity of vestibular nucleus neurons is affected by bilateral peripheral vestibular lesions. The majority (72%) of vestibular nucleus neurons in labyrinth-intact animals whose firing was modulated by vertical rotations responded to electrical stimulation of limb and/or visceral nerves. The activity of even more vestibular nucleus neurons (93%) was affected by limb or visceral nerve stimulation in chronically labyrinthectomized preparations. Some neurons received non-labyrinthine inputs from a variety of peripheral sources, including antagonist muscles acting at the same joint, whereas others received inputs from more limited sources. There was no apparent relationship between the spatial and dynamic properties of a neuron's responses to tilts in vertical planes and the non-labyrinthine inputs that it received. These data suggest that non-labyrinthine inputs elicited during movement will modulate the processing of information by the central vestibular system, and may contribute to the recovery of spontaneous activity of vestibular nucleus neurons following peripheral vestibular lesions. Furthermore, some vestibular nucleus neurons with non-labyrinthine inputs may be activated only during particular behaviors that elicit a specific combination of limb and visceral inputs.

Investigating The Nuclear Activity Of Barred Spirals: The case of NGC 1672

NASA Astrophysics Data System (ADS)

Jenkins, Leigh; Brandt, N.; Colbert, E.; Levan, A.; Roberts, T.; Ward, M.; Zezas, A.

2008-03-01

We present new results from Chandra and XMM-Newton X-ray observations of the nearby barred spiral galaxy NGC1672. It shows dramatic nuclear and extra-nuclear star formation activity, including starburst regions located either end of its prominent bar. Using new X-ray imaging and spectral information, together with supporting multiwavelength data, we show for the first time that NGC1672 possesses a faint, hard, central X-ray source surrounded by a circumnuclear starburst ring that dominates the X-ray emission in the region, presumably triggered and sustained by gas and dust driven inwards along the galactic bar. The faint central source may represent low-level AGN activity, or alternatively emission associated with star-formation in the nucleus. More generally, we present some preliminary results on a Chandra archival search for low-luminosity AGN activity in barred galaxies.

Galactic Surveys in the Gaia Era

NASA Astrophysics Data System (ADS)

Wyse, Rosemary F. G.

2018-04-01

The final astrometric data from the Gaia mission will transform our view of the stellar content of the Galaxy, particularly when complemented with spectroscopic surveys providing stellar parameters, line-of-sight kinematics and elemental abundances. Analyses with Gaia DR1 are already demonstrating the insight gained and the promise of what is to come with future Gaia releases. I present a brief overview of results and puzzles from recent Galactic Archaeology surveys for context, focusing on the Galactic discs.

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.

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.

Star formation inside a galactic outflow.

PubMed

Maiolino, R; Russell, H R; Fabian, A C; Carniani, S; Gallagher, R; Cazzoli, S; Arribas, S; Belfiore, F; Bellocchi, E; Colina, L; Cresci, G; Ishibashi, W; Marconi, A; Mannucci, F; Oliva, E; Sturm, E

2017-04-13

Recent observations have revealed massive galactic molecular outflows that may have the physical conditions (high gas densities) required to form stars. Indeed, several recent models predict that such massive outflows may ignite star formation within the outflow itself. This star-formation mode, in which stars form with high radial velocities, could contribute to the morphological evolution of galaxies, to the evolution in size and velocity dispersion of the spheroidal component of galaxies, and would contribute to the population of high-velocity stars, which could even escape the galaxy. Such star formation could provide in situ chemical enrichment of the circumgalactic and intergalactic medium (through supernova explosions of young stars on large orbits), and some models also predict it to contribute substantially to the star-formation rate observed in distant galaxies. Although there exists observational evidence for star formation triggered by outflows or jets into their host galaxy, as a consequence of gas compression, evidence for star formation occurring within galactic outflows is still missing. Here we report spectroscopic observations that unambiguously reveal star formation occurring in a galactic outflow at a redshift of 0.0448. The inferred star-formation rate in the outflow is larger than 15 solar masses per year. Star formation may also be occurring in other galactic outflows, but may have been missed by previous observations owing to the lack of adequate diagnostics.

Detection of sulfur in the galactic center

NASA Technical Reports Server (NTRS)

Herter, T.; Briotta, D. A., Jr.; Gull, G. E.; Shure, M. A.; Houck, J. R.

1983-01-01

A strong detection at the S III forbidden 18.71 micron line is reported for the galactic center region, Sgr A West. A line flux of 1.7 + or - 0.2 x 10 to the -17th W/sq cm is found for a 20 inch beam size measurement centered on IRS 1. A preliminary analysis indicates that the S III abundance relative to hydrogen is consistent with the cosmic abundance of sulfur, 0.000016, if a filling factor of unity within the known clumps is assumed. However, the sulfur abundance in the galactic center may be as much as a factor of 3 overabundant if a filling factor of 0.03 is adopted, a value found to hold for some galactic H II regions.

MSG-Evoked c-Fos Activity in the Nucleus of the Solitary Tract Is Dependent upon Fluid Delivery and Stimulation Parameters

PubMed Central

Thompson, John A.

2016-01-01

The marker of neuronal activation, c-Fos, can be used to visualize spatial patterns of neural activity in response to taste stimulation. Because animals will not voluntarily consume aversive tastes, these stimuli are infused directly into the oral cavity via intraoral cannulae, whereas appetitive stimuli are given in drinking bottles. Differences in these 2 methods make comparison of taste-evoked brain activity between results that utilize these methods problematic. Surprisingly, the intraoral cannulae experimental conditions that produce a similar pattern of c-Fos activity in response to taste stimulation remain unexplored. Stimulation pattern (e.g., constant/intermittent) and hydration state (e.g., water-restricted/hydrated) are the 2 primary differences between delivering tastes via bottles versus intraoral cannulae. Thus, we quantified monosodium glutamate (MSG)-evoked brain activity, as measured by c-Fos, in the nucleus of the solitary tract (nTS; primary taste nucleus) across several conditions. The number and pattern of c-Fos neurons in the nTS of animals that were water-restricted and received a constant infusion of MSG via intraoral cannula most closely mimicked animals that consumed MSG from a bottle. Therefore, in order to compare c-Fos activity between cannulae-stimulated and bottle-stimulated animals, cannulated animals should be water restricted prior to stimulation, and receive taste stimuli at a constant flow. PMID:26762887

Introducing CGOLS: The Cholla Galactic Outflow Simulation Suite

NASA Astrophysics Data System (ADS)

Schneider, Evan E.; Robertson, Brant E.

2018-06-01

We present the Cholla Galactic OutfLow Simulations (CGOLS) suite, a set of extremely high resolution global simulations of isolated disk galaxies designed to clarify the nature of multiphase structure in galactic winds. Using the GPU-based code Cholla, we achieve unprecedented resolution in these simulations, modeling galaxies over a 20 kpc region at a constant resolution of 5 pc. The simulations include a feedback model designed to test the effects of different mass- and energy-loading factors on galactic outflows over kiloparsec scales. In addition to describing the simulation methodology in detail, we also present the results from an adiabatic simulation that tests the frequently adopted analytic galactic wind model of Chevalier & Clegg. Our results indicate that the Chevalier & Clegg model is a good fit to nuclear starburst winds in the nonradiative region of parameter space. Finally, we investigate the role of resolution and convergence in large-scale simulations of multiphase galactic winds. While our largest-scale simulations show convergence of observable features like soft X-ray emission, our tests demonstrate that simulations of this kind with resolutions greater than 10 pc are not yet converged, confirming the need for extreme resolution in order to study the structure of winds and their effects on the circumgalactic medium.