Session 5
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Keith Baxter and Paul Alexander
kmb23@mrao.cam.ac.uk
Mullard Radio Astronomy Observatory, Cambridge, England
We have constructed a new model for galactic structure based upon the principles of propagating star formation. Unlike previous simulations using this mechanism the model is fully self-gravitating (i.e., N-body), and thus imposes no a priori structure upon the galaxy. The model consists of halo, bulge and disk components, with masses and dimensions appropriate to the Milky Way. The simulation spontaneously forms a persistent 2 armed spiral structure, with disk heating being counteracted by star formation within the dissipative cloud component. We obtain a Schmidt-type law for the star formation rate, with the spiral arms thus acting as the focus for star formation. We have applied this model to the study of several interacting galaxy pairs, concentrating upon matching the morphology and dynamics of the system as observed in both the optical and HI bands.
Ilse M. van Bemmel and Peter D. Barthel
bemmel@astro.rug.nl
Kapteyn Institute for Astronomy, Groningen, The Netherlands
We present several explanations for the nature of the unusually high far-infrared emission seen by IRAS in 1983 in the quasars 3C47, 3C207 and 3C334. High resolution radio observations were carried out at cm and mm wavelengths to determine the radio core spectrum. Subsequently, this spectrum is extrapolated to the far-infrared in order to address the amount of non-thermal far-infrared emission, which may be enhanced by relativistic beaming. The extrapolated value of the far-infrared flux density is much lower than the observed one. Beaming is considered as one of the most important mechanisms for the difference between quasars and radio galaxies in the amount of far-infrared emission, but it is evident that it cannot explain the total far-infrared radiation observed in the three investigated quasars. There must be other mechanisms contributing to the emission. Several mechanisms are considered, but there are not enough data to make a distinction between the possibilities.
Stephen J. Curran
sjc@oso.chalmers.se
Onsala Space Observatory, 439 92 Onsala, Sweden
The Circinus galaxy, a type 2 Seyfert, is suspected to have a molecular gas ring structure with a diameter of ~ 500 pc. We have mapped the 12CO J = 2 -> 1 line which suggests that the molecular gas is orbiting the galaxy's nucleus in the form of a ring. To determine the geometry and kinematics of the ring structure, we have modelled different configurations using the de-convolved map as an initial estimate. The model takes the defined ring parameters, i.e. inner and outer radii, rotation curve across the ring, inclination angle and intensity of emission, and convolves the modelled ring with a synthesised telescope beam in order to provide modelled spectra. Comparing these with the observed spectra, our preliminary results suggest that a circumnuclear ring of ~ 500 pc diameter orbits the nucleus with non-Keplarian rotation. It is inclined nearly edge-on at an angle of ~ 80 deg. and has an associated conical outflow for which we plan further modelling in order to constrain its properties. Such a ring would be consistent with the dusty molecular torus expected from current unified models of active galactic nuclei, invoked to explain the observed differences between type 1 and type 2 Seyfert galaxies
Youri Dabrowski
youri@mrao.cam.ac.uk
Mullard Radio Astronomy Observatoty, Cambridge University, Great Britain
A decrement in the Cosmic Microwave Background (CMB) of -380 ± 64 micro Jy has been observed by the Ryle-Telescope towards a pair of, possibly lensed, quasars (PC1643+4631 A\&B) at red-shift z = 3.8 and separated by 198 arcsec. Assuming the decrement to be a Sunyaev-Zel'dovich (S-Z) effect from a galaxy cluster, this is indicative of a rich intervening cluster of total mass ~ 1015 solar masses, although, no X-ray cluster has yet been observed in that direction. Another similar situation has also been reported from observations with the VLA.
In order to investigate these problems, we present a new model for the formation of distant spherically symmetric clusters in an expanding Universe. Both the Universe and the collapsing cluster are governed by the same pressure-less fluid equations for which a uniform initial density profile is assumed. A simple perturbation imposed on the initial velocity field gives rise to an over-density which closely models real clusters. Computation of photon paths allows us to evaluate the gravitational effects on CMB photons passing through the evolving mass. The lensing properties of clusters are also considered so that the model can be applied to the PC1643+4631 A&B case to retrieve the S-Z flux decrement as well as the 198 arcsec separation.
Marek Gierlinski
gier@oa.uj.edu.pl
Jagiellonian University, Astronomical Observatory, Kraków, Poland
Since the dawn of history man has watched the skies. With his naked eye he was able to witness variety of celestial objects and events -- stars, planets, comets and meteors, the Moon, the Sun, and the Milky-Milky Way. When he invented the telescope his enhanced sight reached the deepest abyss of space. Then man discovered the utterly immense extent of the electromagnetic spectrum. The Radio Age begun in fifties unveiling abundance of the Nature mysteries -- radio activity of the Sun, pulsars, magnetic fields in space, active galaxies, jets, quasars, microwave background and the nearby radio station.
But there were more things in heaven and earth, than were dreamt of in the philosophy. The new era opened when Wilhelm Röntgen discovered X-rays. Since seventies, X-ray satellites have explored the hidden skies, opening our sightless eyes to the brand-new Universe.
In this talk I will persuade all radio astronomers of the superiority of X-rays over radio waves. I will prove that X-ray astronomy is more challenging, more satisfying, more profitable, and more expensive -- simply is the best. I will cause you to change your profession...
Pekka Heinamaki, M. Valtonen and S. Mikkola
pekheina@utu.fi
Tuorla Observatory, Finland
According to our present knowledge galaxy mergers as well as black holes in the nuclei of galaxies are common. If the time between galaxy mergers is assumed to be about 109 years, black hole binaries occur more than once in Hubble time. Under favourable conditions evolution like this may lead to the formation of systems with three or four black holes.These kind of systems are chaotic and typically very unstable. Dynamical interaction of black holes in galaxy center lead typically to ejections and escapes from the galaxy nucleus. This is called the slingshot prosess (Saslaw, Valtonen & Aarseth 1974). We have studied possibility that this prosess may be responsible for the observed the properties of some radio galaxies.
Because we are working with chaotic system, it can be studied only by numerical computer simulations and statistical calculations. This needs lot of data and computer time. Large number of cases with different initial values have been studied and results of calculations are compared to the samples of radiogalaxies and quasars by Potash & Wardle (1979), Gower and Hutchings (1984), Rogora el al. (1986) and Macklin (1981).Our studies suggests that the observations of one- and two-sided radiogalaxies can be quite well explained by ejected black holes from galaxy nucleus.
Julia Hutchison and Tim Cawthorne
j.m.hutchison@uclan.ac.uk
Department of Physics, Astronomy and Maths, University of Central Lancashire, Great Britain
Studies of the magnetic fields of jets in quasars have shown that the fields tend to lie parallel to the jet on kilo-parsec scales. Parsec-scale observations, however, show that the magnetic fields can be misaligned to the jet by as much as 30-40 degrees. One such case of misalignment is quasar 4C71.07 (0836+710) where previous VLBI observations at 6cm showed the implied magnetic field direction at 30 degrees to the jet structure. To determine whether the origin of the misalignment was Faraday rotation, due to intervening gas in the narrow line region, dual-frequency VLBI polarization sensitive observations at 6 cm and 3.6 cm were made at two epochs.
The results show that only small changes in polarization position angle occur between the two frequencies, certainly not the ~ 30 degrees needed to align the field with the jet. Three explanations for the misalignment are proposed: 1) a helical magnetic field structure occurs throughout the jet 2) the jet 'wiggles' and the polarization is seen when the jet has a favourable orientation to the observer 3) the source is gravitationally lensed.
Marek Jamrozy
jamrozy@oa.uj.edu.pl
Astronomical Observatory of the Jagiellonian University, Poland
Further investigation of the cosmological evolution of radio sources is presented. The number counts of sources of various morphological types to the 1.4 GHz flux density limit of about 200 mJy are compiled from the literature. These counts are extended to about 20 mJy using the recent deep VLA surveys at this frequency: NVSS (Condon et al. 1996) and FIRST (Becker et al. 1995), and compared with predictions of the existing evolutionary models.
Dmitry Krivitsky and Victor Kontorovich
kriv@ira.kharkov.ua
Institute of Radio Astronomy, Kharkov, Ukraine
Appearance of quasars and other AGN as a result of galaxy mergers is investigated in the framework of a phenomenological approach which relates the quasar luminosity function to the galaxy mass function. Quasars are assumed to be short-lived, the luminosity of a quasar is controlled by the masses and angular momenta of the merged galaxies which have formed the quasar (the masses and momenta determine the amount of mass which loses its angular momentum and can fall to the centre). Comparison of the calculated luminosity function with the observational data by Boyle et al. (MNRAS, 1988, 235, 935) allows us to determine the model parameters (galaxy number density and the fraction of mass which actually falls to the centre) as functions of the redshift in the range z = 0.5 to 2. We show that the merger model can explain the shape and time dependence of the quasar luminosity function. The obtained fraction of mass which falls to the centre decreases with time, which probably resembles decreasing of the amount of gas in galaxies; the density contrast increases with time, probably, due to the rise of the large-scale structure.
Jacek Niezgoda
jacmalt@astro.uni.torun.pl
Torun Center for Astronomy, Poland
Gigahertz Peaked Spectrum (GPS) radio sources have simple convex radio spectra with steep spectral indices at high frequencies and spectral turnovers near 1 GHz. These sources tend to have very compact radio structure (~10–100 milliarcsec or 10–1000 pc) and large radio luminosity (Lradio ~ 1045 erg s-1) comparable to the most powerful quasars. The host object of GPSs is a heterogenous mix of radio galaxies and quasars. VLBI imaging of GPS sources show that some (almost exclusively quasars) exhibit a complex morphology. Others, termed compact doubles (almost exclusively galaxies), show two components of similar flux density. The small extents of the GPS sources, coupled with their high brightness temperatures (TB ~ 1010 K) make them candidates for young, burgeoning, powerful radio galaxies. The known radio properties of GPS are consistent with a scenario in which these sources represent the very early stages (t ~ 104 years) in the development of powerful, classical double radio sources. The alternative hypothesis is that GPS are smothered radio sources by a very dense and clumpy Interstellar Medium in the nucleus of the host galaxy.
A new sample of GPS sources found using the MERLIN survey at 408 MHz is presented. The sample is based on Patnaik's list (Patnaik et al. 1992), containing compact radio sources in the range 35 deg. < delta
< 75 deg. with fluxes > 200 mJy at 8.4 GHz and a flat spectrum. A large number of "new" sources makes our catalogue ideally suited for statistical surveys of GPS sources.Izabela Owsianik1, and John E. Conway2
iza@astro.uni.torun.pl
1Torun Center for Astronomy, Poland
2Onsala Space Observatory, Sweden
Compact Symmetric Objects have high luminosity radio emission regions located on both sides of the central activity on scales < 1000 pc, which are thought to be free of beaming effects. Detailed theories of the "youth model" of compact sources show that CSO's can be related by evolution to the slightly larger Compact Symmetric Sources (CSS), which then evolve into classical doubles. An obvious way to distinguish between competing models is to try to measure or set limits on the growth in overall size of CSO's and so determine their ages directly.
We present the results of multi-epoch global VLBI observations of the CSO 0710+439 at 5 GHz. Recent analysis of data spread over 13 years shows strong evidence for the advance of the northern hotspot at a speed of 0.24 h-1 c. The Southern hotspot seems to be stationary within the errors (< 0.176 h-1 c). Since the Northern and Southern hotspots are approximately the same distance from the core, we argue that the advance speeds of the hotspots must vary perhaps due to periodic encounters with clouds. Estimated apparent velocity suggests source age of 1000's years and therefore a strong evidence for the "youth" models of CSO's.
Marco Pedani1, Gavril Grueff1,2
pedani@astbo1.bo.cnr.it
1Istituto di Radioastronomia del C.N.R., Italy
2Universitá degli studi di Bologna, Italy
A new 408 Mhz survey, down to a limit flux of 0.1 Jy, has been completed using the ''Northern Cross'' radiotelescope in Bologna. We observed a sky strip just along the Celestial Equator, with Declination range -2 deg. -- 2 deg., that will be easily accessible also to the new 8 mt class telescopes (VLT). Because of the beam size of our telescope ( 3' x 7' at these declinations ), in order to obtain more precise radio positions, we performed a cross-correlation with the sources also present in the NVSS maps at 1.4 Ghz ( 45" beam size ) actually availabe.
These positions have been used to search for the optical counterparts of USS ( ultra steep spectrum ) sources with a spectral index alpha1400408 < -1.0, usually considered as good HZRG ( high redshift radio galaxies ) candidates. At the present we have selected a sample of 42 USS sorces of which 7 have an optical counterpart on the POSS-I plates ( limit mr =20.0 ), while 35 are Empty Fields.
Bong Won Sohn and Uli Klein
bwsohn@astro.uni-bonn.de
Radioastronomical Institute of the Bonn University, Germany
We present depolarisation (DP) and rotation measure (RM) maps of 5 intermediate or low luminosity and 2 giant radio galaxies by using 3 or 4 frequencies data between 326 MHz or 1.4 GHz and 10.6 GHz. These results show strong correlation with the morphologies of the radio galaxies. All 7 selected objects have well defined two radio lobes in high-resolution maps. The bent structure of jet (precession?) and the projection (Laing-Garrington) effect are the dominant factors, which determine the large-scale polarisation properties. Core/Lobe contrast is dominant in the results of the bent-jet sources and Lobe/Lobe asymmetries (jetsideness) which are well known in powerful (3C) radio sources are detected in the maps of well collimated jet sources. From Burn (1966)'s and Laing (1988)'s works, we suggest possible explanations of the RM and DP maps with internal and faraday foreground materials.Michael Thierbach, Reinhard Schlickeiser, and Richard
Wielebinski
thierb@mpifr-bonn.mpg.de
Max-Planck Institut für Radioastronomie, Germany
We present the reduction of X-ray data of the clusters of galaxies A85, A665 and Cl0016+16 measured by the ROSAT satellite (PSPC) and its implication for the Sunyaev-Zeldovich (SZ) effect. We calculate the expected diminution of the microwave background radiation at radio wavelength from the X-ray data. We derive expected central diminutions Delta TR,max -(580±230) microK for A85, -(440±180) microK for A665 and -(810±680) microK for Cl0016+16.