bluuebunny/crossref_metadata_2025 huggingface dataset:
8.1. Magnetic phenomena in galactic nuclei
Authors: Morris Mark
Published: July 2016

The magnetic environment of the Galactic nucleus contrasts sharply with that of the Galactic disk. The inner few hundred parsecs of our Galaxy appear to be dominated by a strong (~milligauss) and uniform dipole field which dominates the pressure within the central intercloud medium. An attractive hypothesis for the origin of the central vertical field is that it results from the concentration of protogalactic field by radial inflow of gas throughout the Galaxy's lifetime. The predominant orientation of the magnetic field within dense molecular clouds is parallel to the galactic plane, which can be understood in terms of the strong tidal shear to which these clouds are subjected. The contrasting geometries of the cloud and intercloud fields allow for magnetic field line reconnection at cloud surfaces, which, under the right circumstances, could produce the relativistic electrons which delineate the nonthermal radio filaments near the Galactic center with their synchrotron emission. The characteristics of the Galactic center “magnetosphere” should be generalizable to all gas-rich spiral galaxies. Inadequate spatial resolution currently prevents us from exploring magnetic fields in other galactic nuclei to the same depth as in the Galactic center, but existing evidence is consistent with similar magnetic geometries elsewhere.
8.3. Submillimeter polarimetry of Sagittarius A
Authors: Novak G. , Dotson J.L. , Renbarger T. , Dowell C.D. , Hildebrand R.H. , Schleuning D.A.
Published: July 2016

We present the first submillimeter polarimetric observations of Sagittarius A.
8.4. Properties of synchrotron emission and magnetic fields in the central region of M31
Authors: Hoernes P. , Beck R. , Berkhuijsen E.M.
Published: July 2016

At the centre of M31 the nonthermal spectral index between λ20 cm and λ6 cm is −0.2. It slowly decreases along the southern arm and the northern filaments visible in Hα, but perpendicular to these features it increases much faster. The magnetic field runs along the arm and the filaments. These phenomena suggest the existence of a mono-energetic source of relativistic electrons in the nucleus.
8.13. The dynamo effect in magnetohydrodynamic accretion onto a rotating black hole
Authors: Egi Masashi , Tomimatsu Akira , Takahashi Masaaki
Published: July 2016

A rotaing black hole has interesting features which can't be seen in nonrotating cases. The most characteristic one is to induce differential rotaions at angular velocity ω in inertial frames. Astrophysically it might have various impacts on its surrounding accretion plasmas. In a stationary and axisymmetric magnetohydrodynamic picture, it enables to directly extract the rotation energy of the black hole in the form of the outgoing Poynting flux. This process needs a condition ΩF(ΩH – ΩF) > 0 on the horizon r = rH, where ΩH ≡ ω|rH, and ΩF is the angular velocity of magnetosphere. However, it is not so clear how the extracted energy activates the magnetosphere. Recently, Kahnna and Camenzind (KC 1994,1995) proposed a possibility of a self-excitation mechanism of the electromagnetic fields, supported by a coupling between ω and the angular velocity of plasma Ω, through the magnetic diffusivity e of accretion plasmas. They called it ωΩ dynamo and tried to confirm this effect by numerical simulations. However no such growing cases were found in the initial conditions employed in the simulations (Brandenbrug 1996, KC 1996).
8.14. Magnetic fields in star-forming regions of our Galaxy
Authors: Hutawarakorn B. , Cohen R. J.
Published: July 2016

Masers provide a direct way of measuring magnetic fields in star-forming regions. OH ground-state masers at 18 cm wavelength exhibit strong circular polarization due to Zeeman splitting. The implied magnetic field strength is typically a few mG, which is sufficient for the field to be dynamically important, e.g. in channelling the observed bipolar outflows. Moreover there are indications that magnetic fields in maser regions are aligned with the large-scale Galactic magnetic field (Reid & Silverstein 1990), and that bipolar molecular outflows are also aligned with the local Galactic magnetic field (Cohen, Rowland & Blair 1984). Some theoretical work in fact suggests that the magnetic field is intimately connected with the origin of the molecular outflow (e.g. Pudritz & Norman 1983; Uchida & Shibata 1985). It is therefore important to investigate the magnetic field configuration in these regions in as much detail as possible.
9.2. Cores or cusps in elliptical galaxies: luminosity or environment?
Authors: de Jong Roelof S. , Davies Roger L. , Minchin Robert F. , Lucey John R. , Steel James
Published: July 2016

Two classes of elliptical galaxies are now recognised (Kormendy & Bender 1996). Luminous ellipticals rotate slowly (Davies et al. 1983and tend to have boxy isophotes. Ellipticals fainter than L∗ exhibit an increasing tendency to be rotationally supported and to possess a stellar disk component. This dichotomy led Bender, Burstein & Faber (1992) to suggest that the physical variable that controls the ultimate nature of a forming galaxy is the degree of gaseous dissipation that occurs in the final merger it experiences. Low luminosity systems experience more dissipative mergers which generate high rotation, disky end products. As bigger galaxies are formed, the mergers become increasingly stellar, producing the classical slow rotating ellipticals. They termed this the gas/stellar continuum. This global dichotomy is also reflected in the bimodality of core morphologies of the heterogeneous sample of local ellipticals observed with HST. The low luminosity disky galaxies have ‘hard’ cores with a steep slope in the luminosity profile at small radii, whereas the luminous galaxies have ‘soft’ cores with flat profiles at small radii (e.g. Faber et al. 1997).
9.8. Bars and black holes
Authors: Emsellem Eric
Published: July 2016

Massive black holes are now thought to be present at the centre of a fair fraction of nearby galaxies. The origin of these central dark masses is still unknown, although tentative explanations have been proposed in an attempt to reconcile non-active galaxies with AGNs and quasars. The activity of a galaxy may then mostly depend on the efficiency of gas accretion onto the central dark object. It is important to note that many of the galaxies which are today candidates for the presence of a massive black hole are spirals. In this context, bars should play an important role in the evolution (and formation?) of a central mass, since (1) they are present in a significant fraction of spirals, (2) they may be efficient drivers of gas accretion. If indeed most of present day galaxies hosts a central dark mass, then bars and black holes should coexist in a significant fraction of them. We examine here the cases of 3 edge-on galaxies which are candidates for the presence of a central black holes: NGC 4570, NGC 3115 and M 104.
9.10. The cause of the spectral turnover in the GPS source 0108+388: free-free absorption or SSA?
Authors: Marr J. M. , Crawford F. , Taylor G. B.
Published: July 2016

The radio source 0108 + 388 is a canonical example of a class of extragalactic radio sources, referred to as Gigahertz-Peaked Spectrum (GPS) sources, whose spectra peak at high frequencies. There are two competing models for the cause of the high frequency turnover: free-free absorption (f-f) of the lower frequency radiation by ionized gas in the host galaxies (e.g. van Breugel 1984), or synchrotron self-absorption (SSA) due to exceptionally large magnetic fields, (e.g. Hodges, Mutel, & Phillips 1984).
9.12. Global disk oscillations and kinematics of mega-maser sources
Authors: Okazaki A.T.
Published: July 2016

Megamasers provide a powerful tool to probe the innermost few parsecs of active galactic nuclei (AGNs). In particular, for AGNs with large inclination angles, only maser sources enable to directly study the structure and dynamics of the region inside the supposed obscuring tori, which are considered to be optically thick from the infrared to the X-ray bands. For example, the VLBI observations of the water megamaser sources at the center of NGC 4258 have provided not only the compelling evidence for the presence of a central supermassive black hole but also the detailed information on the spatial and velocity distribution of the maser sources (Miyoshi et al. 1995; Nakai et al. 1995).
9.16. A sub-parsec accretion disk in NGC 4261
Authors: Jones D.L. , Wehrle A.E.
Published: July 2016

We observed the nuclear region of NGC 4261 (3C270) with the VLBA to determine the morphology of the central radio source on parsec scales. Our highest angular resolution image at 8.4 GHz shows a very narrow gap in emission just east of the radio core (on the counterjet side), which we interpret as an absorption feature caused by a small, dense inner accretion disk whose width is less than 0.1 parsec. If the inclination of this inner disk is close to that of the much larger-scale disk imaged by HST, it becomes optically thin to 8.4 GHz radiation at a deprojected radius of about 0.8 pc. September 1997 VLBA observations at higher frequencies should allow us to determine the radial electron density distribution of the inner disk.
9.17. Accretion disk winds driven by the disk radiation field under radiation drag
Authors: Tajima Y. , Fukue J.
Published: July 2016

The radiative winds from a geometrically thin accretion disk are studied. The effect of radiation drag which causes in the intense radiation fields around the accretion disk is examined recently. Then, we numerically consider the radiatively-accelerated accretion-disk winds which consist of ionized gas particles, taking into account radiation drag of the order ofv/c.
10.7. Absorption columns with bright X-ray sources near the galactic center: — mass estimation in the Galactic center region
Authors: Sakano Masaaki , Nishiuchi Mamiko , Maeda Yoshitomo , Koyama Katsuji , Yokogawa Jun
Published: July 2016

We report the column density distribution to the Galactic Center region using the X-ray binary observations with the X-ray satellite ASCA, and demonstrate a new method of the total mass determination near the Galactic Center. The column densities are given by a simple form as a function of the angular distance from the Galactic Plane. Assuming a disklike mass distribution of 500 pc radius, we estimate the total mass to be ~ 6 × 107M⊙.
11.2. The nature of compact radio cores in galaxies
Authors: Falcke H.
Published: July 2016

Compact radio cores, which are often assumed to mark the presence of a super-massive black hole, are not only found in the nuclei of powerful quasars but also in nearby galaxies. While in quasars they are typically associated with relativistic jets, the nature of those cores in low-luminosity AGN is less clear. Here, I will briefly mention some of the recent theories (ADAFs or jets) and observations of the latter class of objects.
11.3. The black hole grazer
Authors: Taniguchi Y. , Kaburaki O.
Published: July 2016

We propose an alternative model for the powering of active galactic nuclei (AGN), based on the assumption that all AGN have experienced mergers. In our model (Kaburaki and Taniguchi 1996; Taniguchi and Kaburaki 1996), a close pair of super-massive black holes (the black hole grazer) orbit one another in a plane roughly perpendicular to the galactic center magnetic field. The orbital motion induces surface charges on the black holes which produce an electric field. This field is strong enough to cause pair creation so that the Roche lobe of the binary system is filled with pair plasmas. Rigid-body rotation of the Roche-lobe magnetosphere drives electrodynamically a powerful synchrotron jet emanating from the center of mass of the binary. Furthermore, a pair of equatorial jets flow from the outer Lagrangian points of the binary system. Although these jets are not so collimated, they interact with the accreting gas ring formed around the orbital plane of the binary, causing broad line regions or H2O maser emission regions (Taniguchi et al. 1996). In addition to the primary jet, two secondary jets are also driven by local accretion disks around the two black holes. The interaction among the primary and the secondary jets may explain detailed jet morphology observed by VLBI facilities.
11.5. Pregalactic production of heavy elements by quasars
Authors: Collin Suzy , Huré Jean-Marc
Published: July 2016

We address the following questions. Is it possible that the heavy elements observed in high redshift quasars are formed in the vicinity of the black hole? And in this case do quasars produce, mainly during their growing phase, the first heavy elements which enrich the intergalactic medium and the protogalaxies?
11.9. Jets from time-dependent accretion flows onto a black hole
Authors: Nobuta Koji , Hanawa Tomoyuki
Published: July 2016

It is widely believed that accretion onto a black hole is the origin of X- and γ-ray emission and jets emerging from AGNs. Since the X- and γ-rays are highly variable, the accretion is also expected to be variable. We investigate highly variable hydrodynamical accretion with numerical simulations.
11.14. Massive black hole binaries in galactic nuclei
Authors: Makino Junichiro
Published: July 2016

Many large ellipticals were believed to have large, flat core, of which the radius is typically a few percents of the effective radius (e.g., Lauer, 1985). However, HST observations (e.g., Lauer et al., 1995) have revealed that they are not flat cores at all. The “cores” observed by HST are actually very shallow central density cusps (ρ ~ r−0.5~–1). Such a shallow cusp poses a serious problem to almost any scenario of the formation of ellipticals. If these ellipticals do not have central black holes (MBHs), we are faced with very strange structure with the velocity dispersion decreasing inward. Neither dissipationless/dissipational collapse nor merging have been able to make such a density distribution.
11.15. The effect of a central massive black hole on the gas fueling
Authors: Fukuda H. , Habe A. , Wada K.
Published: July 2016

Nuclear activities in galaxies, such as nuclear starbursts or AGNs, are supposed to be induced by gas fueling into nuclear regions of galaxies. Non-axisymmetric gravitational potential caused by a stellar bar is a convincing mechanism for triggering gas fueling (Phinney 1994). However, numerical simulations have shown that the bar can not force the gas to accrete toward the galactic center beyond the inner Lindblad resonance (ILR). As a mechanism to overcome the ILR barrier, the double barred structure (Friedli & Martinet 1993), or the self-gravity of gas (Wada & Habe 1992, 1995; Elmegreen 1994) are proposed.
11.16. On the origin of density cusp in galactic nuclei by central black hole
Authors: Nakano T. , Fukushige T. , Makino J.
Published: July 2016

We investigated the dynamical reaction of the central region of galaxies to a falling massive black hole by N-body simulations. As the initial galaxy model, we used an isothermal King model and placed a massive black hole at around the half-mass radius of the galaxy. We found that the central core of the galaxy is destroyed by the heating due to the black hole and a very weak density cusp (ρ ∝ r−α, with α ∼ 0.5) is formed around the center. This result is consistent with recent observations of large elliptical galaxies by Hubble Space Telescope (Lauer et al. 1995; Byun et al. 1996; Gebhardt et al. 1996; Faber et al. 1996; Kormendy et al. 1996). The radius of the weak cusp region is large for large black hole mass. The velocity of the stars become tangentially anisotropic in the inner region, while in the outer region the stars have radially anisotropic velocity dispersion. Our result naturally explains the mechanism of the formation of the weak cusp found in the previous simulations of galaxy merging, and implies that the weak cusp observed in large elliptical galaxies may be formed by the heating process by sinking black holes during merging events.
11.18. The magnetic switch and the FR I/FR II break
Authors: Meier D.L. , Godon P. , Edgington S. , Payne D.G. , Lind K.R.
Published: July 2016

It is proposed that the Fanaroff and Riley division between class I and class II radio sources may be due to phenomena occurring in the coronae of magnetized accretion disks around black holes.
12.1. The central regions of the Galaxy and galaxies: a brief summary
Authors: Combes F.
Published: July 2016

This symposium has revealed considerable new progress on nuclei of galaxies over the last three years. In this talk, I will try to point out the advances since the last meeting on exactly the same subject held three years ago at Ringberg Castle in Germany (see “The Nuclei of Normal Galaxies: Lessons from the Galactic Center”, ed. R. Genzel & A. Harris, Kluwer).
Introductory Remarks
Authors: Woltjer L.
Published: July 2016

Those of us who were around a few decades ago, frequently became initiated into cosmology by a very clear and concise small book, written by Herman Bondi, entitled “Cosmology” (1952/1960). It is interesting to see the list of chapter headings:Physics and CosmologyThe Cosmological PrincipleObservational Evidence:The background light of the sky(Olbers' paradox)The problem of inertia(Mach's principle)Observations of distant nebulae(isotropy, m < 19, z < 0.2)Astrophysical and geophysical data(ages, abundances)Microphysics and Cosmology(large numbers)Theories:Newtonian CosmologyRelativistic Cosmology(Friedmann/Lemaitre models)Steady State CosmologyMilne/Eddington/Dirac/Jordan.
Backgrounds and the Big Bang: Some Extracts from Their History
Authors: Trimble Virginia
Published: July 2016

The first astronomical background firmly established was that of cosmic rays. Photons at various wavelengths came later; and in some bands we have not year clearly peeled away all the sources to see a true background, if one even exists. All known backgrounds are astrophysically important and at least several cosmologically so. The path by which the standard hot big bang came to be generally regarded as standard is littered with the detritus of mistaken impressions, misunderstandings, and missed opportunities.
Fluctuations in the Microwave Sky
Authors: Partridge R. B.
Published: July 2016

This paper reviews the great progress recently made in searches for and the characterization of anisotropies in the cosmic microwave background. We now have secure detections on some angular scales and improved upper limits on others. As the sensitivity of such searches increases, understanding sources of foreground noise (e.g., Galactic and extragalactic radio emission) becomes more important. Also reviewed are the contributions aperture synthesis (interferometric) observations can make in characterizing cosmic background fluctuations and foreground sources of noise. Some recent results from the Very Large Array at λ = 3.6 cm are given; these set a limit δT/T ≲ 1.4 × 10−5on fluctuations at θ ~ 80′. Recent work on the Sunyaev-Zel'dovich effect is summarized.
Cold Material in Distant Radio Galaxies
Authors: Röttgering Huub
Published: July 2016

Dust, H I and molecular gas must be important components of distant radio galaxies. Recent observations to detect these constituents are discussed.
Galaxy Formation: ISOCAM Counts
Authors: Cesarsky C.J. , Elbaz D.
Published: July 2016

Detailed observations in the optical do not allow to discriminate between the following scenarii of galaxy formation:

- synchronous formation at large redshift (z > 7).

- hierarchical merging, down to z ≤ 1, of proto-galactic lumps formed at very high redshift (≈ 10).

- galaxy formation at low z (≈ 2-5), but partially obscured by dust.

More than 1500 galaxies in a field of 2.6′ × 4.6′ were detected by Tyson (1988) with CCD images in the B band. These deep counts of galaxies revealed the presence of an unexpectedly large population of blue galaxies, corresponding to a number excess of 3 to 5 times more galaxies at B > 23 than one can expect from the local luminosity function. These objects lie apparently at moderate redshift (z = 0.3 for B = 23–24) as shown by spectroscopy of B-selected galaxies (Collesset al.1990).
Observations of Diffuse IR Background Radiation by IRTS and IRIS
Authors: Okuda H.
Published: July 2016

Diffuse background radiation is integrated light which is consisted of various components of interplanetary, stellar, interstellar, galactic and intergalactic origins as well as cosmic background radiation, the remnant of the pre-galactic phenomena in the early history of the universe.
Degree Scale Anisotropy: Current Status
Authors: Lubin P.M.
Published: July 2016

The Cosmic Background Radiation gives us one of the few probes into the density perturbations in the early universe that should later lead to the formation of structure we now observe. Recent advances in degree scale anisotropy measurements have allowed us to begin critically testing cosmological models. Combined with the larger scale measurements from COBE we are now able to directly compare data and theory. These measurements promise future progress in understanding structure formation. Because of the extreme sensitivities needed (1-10 ppm) and the difficulties of foreground sources, these measurements require not only technological advances in detector and measurement techniques, but multi spectral measurements and careful attention to low level systematic errors. This field is advancing rapidly and is in a true discovery mode. Our own group has been involved in a series of eleven experiments over the last six years using the ACME (Advanced Cosmic Microwave Explorer) payload which has made measurements at angular scales from 0.3 to 3 degrees and over a wavelength range from 1 to 10 mm. The recent data from these and other measurements will be reviewed as well as some of the challenges and potential involved in these and future measurements.
The Hubble Parameter - A Status Report at EPOCH 1994.5
Authors: Van Den Bergh Sidney
Published: July 2016

New observations obtained during the last two years have slightly shifted the balance of evidence towards larger values of Ho. A compilation of recent determinations shows reasonable agreement and suggests that Ho≳ 75 km s−1Mpc−1.
The Local Velocity Field and the Hubble Constant
Authors: Tammann G. A. , Sandage Allan
Published: July 2016

The methods are reviewed that give a distance modulus to the core of the Virgo cluster of m - M = 31.64 ± 0.08 (D = 21.3 ± 0.8 Mpc). It is shown that the cosmic velocity of the cluster core is 1179 ± 17 km s−1, which, when combined with the distance gives Ho= 55 ± 3 km s−1Mpc−1from the Virgo cluster data alone. Nine independent methods are reviewed that confirm that Ho= 50 ± 2. Discussion is made why all methods that are said to give the short distance scale (Ho~ 85) are incorrect.
Large-Scale Flows in the Local Universe
Authors: Mathewson D.S. , Ford V.L.
Published: July 2016

Peculiar velocity measurements of 2500 southern spiral galaxies show large-scale flows in the direction of the Hydra-Centaurus clusters which fully participate in the flow themselves. The flow is not uniform over this region and seems to be associated with the denser regions which participate in the flow of amplitude about 400km/s. In the less dense regions the flow is small or non-existent. This makes the flow quite asymmetric and inconsistent with that expected from large-scale, parallel streaming flow that includes all galaxies out to 6000km/s as previously thought. The flow cannot be modelled by a Great Attractor at 4300km/s or the Centaurus clusters at 3500km/s. Indeed, from the density maps derived from the redshift surveys of “optical” and IRAS galaxies, it is difficult to see how the mass concentrations can be responsible particularly as they themselves participate in the flow. These results bring into question the generally accepted reason for the peculiar velocities of galaxies that they arise solely as a consequence of infall into the dense regions of the universe. To the N. of the Great Attractor region, the flow increases and shows no sign of diminishing out to the redshift limit of 8000km/s in this direction. We may have detected flow in the nearest section of the Great Wall.
Spiral Galaxies and the Peculiar Velocity Field
Authors: Giovanelli Riccardo , Haynes Martha P. , Chamaraux Pierre , Da Costa Luiz N. , Freudling Wolfram , Salzer John J. , Wegner Gary
Published: July 2016

We report results of a redshift-independent distance measurement survey that extends to all sky and out to a redshift of approximately 7500 km s−1. Tully–Fisher (TF) distances for a homogeneous sample of 1600 late spiral galaxies are used to analyze the peculiar velocity field. We find large peculiar velocities in the neighborhood of superclusters, such as Perseus–Pisces (PP) and Hydra–Centaurus, but the main clusters embedded in those regions appear to be virtually at rest in the CMB reference frame. We find no compelling evidence for large-scale bulk flows, whereby the Local Group, Hydra–Cen and PP would share a motion of several hundred km s−1with respect to the CMB. Denser sampling in the PP region allows a clear detection of infall and backflow motions, which can be used to map the mass distribution in the supercluster and to obtain an estimate of the cosmological density parameter.
Formation of the Supercluster-Void Network
Authors: Einasto J.
Published: July 2016

Already first redshift surveys, made 10 – 15 years ago, demonstrated that galaxies and clusters of galaxies are located along patchy sheets and filaments, and the space between is empty. Sheets and filaments form large aggregates – superclusters of galaxies. Between superclusters there are large voids with no clusters at all, in such supervoids we observe only poor galaxy filaments (Lindneret al.1994).
Cosmological Applications of Gravitational Lensing
Authors: Schneider Peter
Published: July 2016

It was recognized very early that the gravitational lens effect can be used as an efficient cosmological tool. Of the many researchers who foresaw the use of lensing, F. Zwicky and S. Refsdal should be explicitly mentioned. The perhaps most accurate predictions and foresights by these two authors are as follows: Zwicky estimated the probability that a distant object is multiply imaged to be about 1/400, and thus that the observation of this effect is “a certainty” [73] – his value, which was obtained by a very crude reasoning, is in fact very close to current estimates of the lensing probability of high-redshift QSOs. He predicted that the magnification caused by gravitational light deflection will allow a “deeper look” into the universe –in fact, the spectroscopy of very faint galaxies which are imaged into giant luminous arcs have yielded spectral information which would be very difficult to obtain without these ‘natural telescopes’. And third, Zwicky saw that gravitational lenses may be used to determine the mass of distant extragalactic objects[72] – in fact, the mass determination of clusters masses from giant luminous arcs is as least as accurate as other methods, but does not rely on special assumptions (like spherical symmetry, virial or thermal equilibrium) inherent in other methods, and the determination of the mass within the inner 0.9 arcseconds of the lensing galaxy in the quadruple QSO 2237+0305 to within 2% [52] is the most accurate extragalactic mass determination known. Refsdal predicted the use of gravitational lenses for determining cosmological parameters and for testing cosmological theories [48][49] – we shall return to these issues below.
The X-Ray Background
Authors: Hasinger G.
Published: July 2016

The recent progress in the measurement and understanding of the X-ray background is reviewd here. Particular emphasis is put on a discussion of the partially discrepant measurement of the X-ray background spectrum in the 0.5-3 keV range. New and important constraints on large scale structure are obtained from measurements of the smoothness of the XRB. Recently the first discovery of a signal in the angular correlation function of the XRB could be announced. Finally, various X-ray surveys and their identification content is summarized. The role of optically inactive galaxies as a major contributor to the faint X-ray source population which might produce a substantial fraction of the XRB is clarified.
The Cosmological Diffuse γ-Ray Background: Myth or Reality?
Authors: Laurent P.
Published: July 2016

This paper is by no means a critical review of what have been thought, calculated or written about the cosmological diffuse γ-ray background. More simply, it is intended to tell its story, in order to answer a may be more historical than astronomical question:

“How ideas about the cosmological diffuse γ-ray background has evolved since the beginning of the space era ?”
The Quasi-Steady State Cosmology
Authors: Hoyle F. , Burbidge G. , Narlikar J.V.
Published: July 2016

At IAU Symposium No. 168 the presentation was divided into two parts:

I.

Theoretical Foundations and

II.

Observational Facts and Consequences
A Panel Discussion of “Major Unsolved Problems of Cosmology”
Authors: Kondo Yoji
Published: July 2016

I would first like to ask my distinguished co-panelists to introduce themselves briefly. I will then ask each to make a five-minute comment on “major unsolved problems of cosmology”. It will be followed by discussions among the panelists and also with the audience.
Fundamental Observational Problems
Authors: Arp H.
Published: July 2016

Almost all of cosmology and extragalactic astronomy are built on the assumption that redshifts are caused by recession velocities and hence measure distances. Evidence has been accumulating since 1966, however, that high redshift quasars and other active objects violate this assumption and are associated with nearby, relatively low redshift galaxies (For recent reviews see Arp 1987; 1992a, 1994a,b and the present conference).
Redshifts of Unknown Origin
Authors: Burbidge G.
Published: July 2016

Probably the biggest problem in cosmology is one that many people don't even think about or want to think about. It has to do with the nature of the redshifts of astronomical bodies.
Future Cosmic Microwave and Cosmic Infrared Background Measurements
Authors: Mather John C.
Published: July 2016

Cosmic microwave and infrared background radiation (CMBR and CIBR) measurements in the near future have the potential to greatly advance our knowledge of the early universe. New instrument and space technology will soon enable much better measurements of both.
On the Use of COBE Results
Authors: Melek M.
Published: July 2016

The aim of this brief report is to find a lower limit of the Hubble parameter using the COBE's detected fluctuations in the temperature of the CMBR.
Is the Early Universe Fractal?
Authors: de Gouveia Dal Pino E. M. , Hetem A. , Horvath J. E. , Villela T.
Published: July 2016

It is generally believed that onverylarge scales the distribution of matter in the universe is homogeneous and effectively all the existing theoretical approaches are based on this assumption. However, recent re-analysis of galaxy-galaxy and cluster-cluster correlations by Coleman and Pietronero (1992, hereafter CP) and Luo and Schramm (1992, hereafter LS) indicates that the distribution of the visible matter in the universe is fractal or multifractal up to the present observed limits (~100 h−1Mpc for H0= 100 h km s−1Mpc−1and 0.5≤h≤1) without any evidence for homogenization on those scales. The fractal dimension obtained from these analyses is D ~ 1.2 - 1.3 (CP; LS).
A Fractal Model of the Universe: Do Large Galaxies Interact by Quasar Exchange ?
Authors: Driessen P.
Published: July 2016

A fractal universe model has been proposed elsewhere (Driessen, 1991, 1994), based on the assumption of perfect self-similarity between some definite scales, and in particular between particles and galaxies. Its motivation rested essentially on two ideas: first, if striving for unification is justified, then the fractal idea makes sense, for in this case one single theory of particles could encompass all self-similar structures at once. Secondly, it could be demonstrated that, provided some reasonable hypothesis were made about the structure of spiral galaxy cores, they came back to the same topological state after two complete revolutions (Driessen, 1991). These ideas combined suggested that spiral galaxies might correspond to electrons on the cosmic scale. The main test of the coherence of the fractal picture was then to discover if other galaxy types and quasars do find a place in this model. Now, a small group of dissident has sustained for years that QSOs (or at least a certain class of QSOs) are local objects emitted by galaxies. This class would contain very small (d ≈ 0.3 kpc), faint (Mv≈ −12), and most often radio-quiet objects with large (non cosmological) excess redshift. The analogy between the two statements “electrons emit photons” and “galaxies emit QSOs” hinted that QSOs embody cosmic scale photons, and entails that galaxies experience quasar exchange interactions. It was claimed further that galaxy clusters reproduce atomic and molecular-like systems with one or a few central giant ellipticals (the cosmic scale nuclei) interacting via quasar exchange with their satellite spirals (the cosmic scale electrons). The flock of dwarf galaxies around large ellipticals and spirals would result from condensation of dusty gas clouds entrained by ejected QSOs.
Powerful Extended Radio Sources: A Goldmine for Cosmology
Authors: Daly R. A.
Published: July 2016

The radio properties of powerful extended radio sources may be used to study the environments of the sources, the source energetics, a characteristic length-scale that can be used as a cosmological tool, and the relation between radio galaxies and radio loud quasars. Thus, these sources offer a rich variety of diagnostics, both direct and indirect, of the cosmological model that describes our universe. They, indeed, are a goldmine for cosmology.

Perhaps the most significant result of the investigations mentioned here is the use of the radio properties of the sources to estimate the ambient gas density in the vicinity of the radio lobe. As discussed below, the ambient gas densities estimated using the strong shock jump conditions across the radio lobe indicate that these sources lie in relatively dense gaseous environments, similar to the intracluster medium found in clusters of galaxies at low redshift. Thus, the observations suggest that at least some clusters with their intracluster medium in place exist at high redshift.
Projected Clustering Around 1 < Z < 2 Radiogalaxies
Authors: Martínez-González E. , Benítez N. , González-Serrano J. I. , Cayón L.
Published: July 2016

We have taken deepR-band images of fields around five radiogalaxies: 0956+47, 1217+36, 3C256, 3C324 and 3C294 with 1 <z< 2. We found a statistically significant excess of bright (19.5 <R< 22) galaxies on scales of 2 arcmin around the radiogalaxies. The excess has been determined empirically to be at ≳99.5% level. It is remarkable that this excess is not present for 22 <R< 23.75 galaxies within the same area, suggesting that the excess is not physically associated to the galaxies but due to intervening groups and then related to gravitational lensing.
Clusters and Voids in General Galaxy Field
Authors: Anosova J. , Iyer S. , Varma R.K.
Published: July 2016

In our previous works (Anosova 1987, Anosova, Iyer, Varma 1994), we developed a new method for determination of the structure of a clustered distribution. In this work, we apply this method studying the observed distribution of galaxies in the Universe.
A Dedicated Quasar Monitoring Telescope
Authors: Borgeest U. , Schramm K.-J. , Von Linde J.
Published: July 2016

Under the auspices of Sjur Refsdal, 25 astrophysicists and engineers from Germany and Scandinavia have founded a non-profit association, aiming at the use of an intelligent telescope for quasar monitoring in the optical (Borgeest et al. 1993). Beyond a better understanding of the physics in quasars, the scientific goals are determining the cosmic distance scale at large redshifts and constraining the nature of Dark Matter, both using the gravitational lens effect. Thus, targets of special interest are the multiply lensed quasars and some well-known violently variable blazars. The optical photometry will in part be carried out simultaneously to observations with, e.g., ISO, ROSAT, CGRO and various radio telescopes. For the first time, a complete quasar sample will be monitored continuously, namely a sub-sample of the all-sky 1 Jy catalogue (5 GHz). Since we will collect about 106photometric data points during the programme, Megaphot has been chosen as name for the association. Members from Hamburg and Bochum intend to test the 1.5 m Hexapod Telescope (HPT) astronomically in the very near future. The HPT hardware was developed and built byVertex Antennentechnik, Duisburgtogether with theRuhr-Universität, BochumandCarl Zeiss, Jena;the intelligent software and weather control requires still some work. When working well, the system will be placed at a site with excellent astronomical conditions. After a few years of exclusive quasar monitoring, it will be used as a German photometry telescope.
Complex Theory of Gravitational Lenses Part II: Cluster-Lensing: Statistics of the Arclet Distribution
Authors: Schramm T. , Kayser R.
Published: July 2016

Applying the complex formalism of Part I we investigate the transformation of the ellipticity and orientation distribution of elliptical background sources by local lensing. One important result is that we can apply the techniques from Part I directly in most parts of the cluster field from which we can also reconstruct the distribution of the background sources, without further information. Knowing the distribution we can apply the techniques from Part I everywhere.
Gravitational Macrolensing and Quasar Spectra
Authors: Khmil S.V.
Published: July 2016

Gravitational microlensing, i.e. lensing by stars in a foreground galaxy, can affect not only the radiation flux observed from quasars (Chang and Refsdal, 1979) but also the spectral line profiles (Nemiroff, 1988; Schneider and Wambsganss, 1990). As a rule, in contrast to it, gravitational macrolensing, i.e. lensing by a whole galaxy or a cluster of galaxies, affects only the radiation flux; differences in image spectra arise mainly from source variability and travel time delays between images. However, if the source, the lens, and the observer are in motion relative to one another, then an additional shift in the source's image spectrum occurs due to the aberration of light (Birkinshaw and Gull, 1983; Khmil, 1988 and references therein). Here we consider the special case of intrinsic motions in the source and study their influence on spectra of macroimages.
Peaks and Periodicities in the Redshift Distribution of Quasi-Stellar Object
Authors: Duari D. , Dasgupta P. , Narlikar J. V.
Published: July 2016

There have been claims from time to time that there are periodicities in the redshift distribution of QSOs. These claims are examined from various statistical angles for a sample of 2164 QSO redshifts, with redshifts lying in the range 0.025 – 4.43 taken from the latest compilation (1993) by Hewitt & Burbidge. We have not included QSOs whose redshifts were obtained by ‘grism’ technique, because of a possible selection effect (Scott 1991). For our analysis we use several staistical techniques, including the Burbidge - O'Dell type Power spectrum analysis (1972), the Rayleigh test, the Kolmogorov-Smirnov test, and the so called ‘Comb-tooth’ template test. the tests are not inter related and have the advantage of checking the claim for nonuniformity of the distribution from various independent angles. We have also carried out Monte Carlo simulations of the redshift distribution of QSOs to check for any systematic effect that can give rise to a spurious periodic effect.
Do Massive Neutrinos Ionize Intergalactic HI?
Authors: Roos M. , Bowyer S. , Lampton M. , Peltoniemi J. T.
Published: July 2016

The radiative decay of massive relic 30eV neutrinos could explain several observational puzzles including the missing dark matter in the universe and the anomalous degree of ionization of interstellar matter in the Galaxy. We note that various non-standard particle physics models with extended scalar sector or minimal supersymmetry have sufficient freedom to accommodate such neutrinos. We discuss observational constraints in the immediate Solar neighborhood, in nearby regions of low interstellar absorption, in the Galactic halo, in clusters of galaxies, and in extragalactic space. Although some observations have been interpreted as ruling out this picture, we note that this is true only for models in which extreme concentrations of neutrinos occur in clusters of galaxies. An instrument is under development to measure the cosmic diffuse EUV background in the local Solar neighborhood, for flight on the Spanish Minisat satellite platform. This instrument will have the capability of providing a definitive test of the radiative neutrino decay hypothesis.
Stability of Cosmological Models
Authors: Wanas M. I. , Bakry MA
Published: July 2016

The stability problem in cosmology is studied using the equations of geodesic deviation. General conditions for stability are obtained. The method is applied to a number of cosmological models, resulting from different field theories. The results are compared with those obtained from FRW -models.
Cosmological Simulations with Smoothed Particle Hydrodynamics
Authors: Abadi Mario G. , Lambas Diego G. , Tissera Patricia B.
Published: July 2016

We have developed and tested a code that computes the evolution of a mixed system of gas and dark matter in expanding world models. The gravitational forces are calculated with the Adaptative P3M algorithms developed by H. Couchmann, 1993. The calculation of gas forces follow the standard SPH formalism (Monaghan, 1989).
Convective Overshooting to Drive g-Modes in γ Dor Stars
Authors: Li Y.
Published: July 2016

From considerations of kinetic energy input from turbulent convection into g-mode pulsation, we show that g-mode pulsation may obtain enough energy from the turbulence to overcome damping in the stellar interior. The development of thick convective envelope in the stellar models requires a small value of the convection parameter α = 1.2 to ensure the low mass limit of the γ Dor stars' instability strip to be in agreement with the observations.
Measurements of the Apparent Solar Diameter with Astrolabe at Observatório Nacional—1997/2000
Authors: Andrei A. H. , Reis Neto E. , Penna J. L. , de Almeida W. G. , d'Ávila V. A. , Puliaev S. P. , Jilinski E. G.
Published: July 2016

The metrological qualities render the modified CCD solar astrolabe a very reliable instrument for the difficult conditions of solar diameter measurements. At O.N. an average value of 959”.04 ± 0”.01 is found, for λ = 563.5nm, and an effective bandpass of 168nm. To improve the signal to noise ratio, the images are treated for flat field. This includes distortions brought about by the COHU 4710 camera, the astrolabe optics, and by the system of filters that cut down the incoming solar light. The extensive series observed (over 12000 independent measures) is examined, using a CLEAN periodogram algorithm. The outcome shows periods reconcilable with the solar activity and geometry of observation.
MDI-SOHO Measures of Solar Radius Variation
Authors: Emilio M. , Kuhn J. R. , Bush R. I. , Scherrer P.
Published: July 2016

Is the Solar Radius a constant? Ground experiments show evidence of possible variations in the visual solar semi diameter that are correlated with the solar activity. Those measurements are limited by the Earth's atmospheric turbulance. It is importance to accurately determine the solar radius variations because of their implication for stellar structure and possible relation to the terrestrial climate. Here we report on data from a space experiment (MDI-SOHO) used to detect solar diameter fluctuations. We stabilish a superior limit for changes in the solar radius.
Quadrupole Mode of the Sun's Poloidal Magnetic Field: on the Possibility of Exciting by Turbulent Dynamo Mechanism
Authors: Kryvodubskyj V. N.
Published: July 2016

On the base of turbulent dynamo model with allowance for newer helioseismic measurements of the Sun's inner rotation it is shown that the physical conditions in deep layers of the solar convection zone in near-pole domain are favourable for exciting of quadrupole mode of poloidal magnetic field near maximum phase of 23-rd solar cycle
Magnetic Pumping at the Base of the Solar Convection Zone
Authors: Tobias S. M. , Brummell N. H. , Toomre J.
Published: July 2016

The transport of magnetic flux from the convection zone into the stably-stratified tachocline is a key component of the proposed interface scenario for the solar dynamo. In this paper we give a summary of the results from three-dimensional numerical experiments (detailed in Tobias et al. 2000) of pumping of magnetic flux by turbulent, penetrative convection. We also list how the efficiency of pumping depends on the parameters of the convection.
New Inferences on the Sun from High-degree Modes: The External Layers and the Equation of State
Authors: Di Mauro M. P. , Christensen-Dalsgaard J.
Published: July 2016

We investigate the structure of the Sun by helioseismic inversion of a set of p-mode frequencies which include new precise observations of modes with high degree obtained from the MDI instrument on the SOHO satellite. Such data have the potential to improve the resolution of the solar structure in the near-surface region, to test the equation of state and constrain the envelope helium abundance.
Stellar Prominences
Authors: Collier Cameron A.
Published: July 2016

I review recent observational and theoretical progress in the study of condensations of cool material trapped in the coronae of rapidly rotating stars. Such condensations were discovered over a decade ago, producing transient moving absorption features in the optical Balmerseries lines. These condensations appear to be in a physical state similar to that of solar prominence material, in the sense that they are sufficiently cool and dense to contain substantial amounts of neutral hydrogen. The strong coronal magnetic fields of the stars in which they occur serve both to confine and to insulate the cool material. The coronal condensations (sometimes dubbed “slingshot prominences”) form at a variety of distances from the star, but are observed to favour formation sites near the Keplerian co-rotation radius. Simple support models involving purely dipolar fields can explain the existence of stable mechanical equilibria for sheet-like prominences in the equatorial plane. More complex field configurations show a wider variety of stable formation sites, both inside the co-rotation radius and out of the stellar equatorial plane.
Chromospheric Heating in the Late Gradual Flare Phase
Authors: Czaykowska A. , Alexander D.
Published: July 2016

Upflows of several tens of km/s have been observed by SOHO-CDS in the late gradual phase of the M6.8 two-ribbon flare on April 29, 1998. These upflows observed in EUV lines formed at coronal temperatures are interpreted as chromospheric evaporation which fills the post-flare loops with hot plasma. In order to achieve chromospheric evaporation, the chromospheric plasma has to be heated to coronal temperatures. The energy for this heating process is assumed to be provided by magnetic reconnection. The mechanism which transports the energy from the reconnection site to the chromosphere must be either thermal or non-thermal. We compare the observed upflow velocities with the velocities derived by different chromospheric heating models in order to decide which mechanism might account for the chromospheric heating. From non-thermal models we take the electron energy flux necessary to achieve the observed velocities and calculate the expected hard X-ray counts in Yohkoh/HXT for non-thermal thick-target Bremsstrahlung generated by this electron flux. We conclude that energetic (> 15keV) non-thermal electrons are unlikely to cause the chromospheric heating since a significant number of HXT counts are expected from the resulting electron energy flux but not observed. Recent thermal conduction models seem to be more appropriate for explaining the observations.