bluuebunny/crossref_metadata_2025 huggingface dataset:
Cosmic Rays from Regions of Star Formation I. The Carina Complex
Authors: Montmerle T. , Paul J. A. , Cassé M.
Published: July 2016

Within the error circle of the COS-B gamma-ray source at ℓ = 288°, b = 0° lies the Carina Nebula, one of the most active regions of star formation known, housing several OB associations and Wolf-Rayet stars (WRS), and perhaps also a supernova remnant (SNR). As a region containing intense mass-losing stars it belongs to the same species as the Rho Oph cloud (but much more active), suggested to be associated with the gamma-ray source at ℓ = 353°, b = +16° (Paul et al., this conference). As a group of OB association linked with a SNR, it belongs to the same species as “SNOB's” (Montmerle, 1979), possibly identified with about half of the COS-B sources. We suggest that the source at ℓ = 288°, b = 0° should be identified with the Carina complex. In this case the source would be at ≃ 2.7 kpc and its gamma-ray luminosity would be ≃ 2.1035 erg s−1. It is suggestive that the nearest aggregate of stars, gas and dust (Rho Oph) and the richest one (Carina) are both in the direction of a gamma-ray source. The Carina complex is noted in particular for the compact star clusters Tr 14, Tr 16 and Cr 228 (Humphreys, 1978), altogether comprising 6 of the 7 O3 stars observed in the Galaxy. It is also remarkable that 3 WRS are associated with the complex. All 3 WRS are of the WN7 type, having the highest mass-loss rate of WRS (≃ 10−4 M⊙ yr−1). Even more remarkable is the presence of the strange Carina object which sheds mass at the extraordinary rate of 10−3 to 0.075 M⊙ yr−1, with a velocity of ≃ 600 km s−1. Moreover, according to radio (Jones, 1973) and optical (Elliot, 1979) data, there seems to be a SNR buried in the Nebula. However, it is not seen at X-ray wavelengths by the Einstein observatory (Seward et al., 1979). This could be explained if the SNR has a luminosity Lx < 1034 erg s−1, since it could then be conceivably hidden by the unstructured, diffuse X-background. The molecular cloud associated with the Carina Nebula has been observed in the lines of H2CO and OH (Dickel, 1974). The cloud has a derived mass of ≲ 105 M⊙, typical of other molecular clouds.
Cosmic Rays from Regions of Star Formation II. The OB Associations
Authors: Cassé M. , Montmerle T. , Paul J. A.
Published: July 2016

Supersonic stellar winds have recently been proposed as active agents of cosmic-ray acceleration. We try to insert this potential acceleration mechanism in its general astrophysical context. Among galactic objects, OB associations have the narrowest latitude distribution, resembling to that of gamma-ray sources. Here we focus on the bulk rate of kinetic energy deposition in molecular clouds through stellar winds of individual stars pertaining to OB associations. Assuming that a minute fraction of this mechanical energy can be transferred to suprathermal particles, we examine whether OB associations are detectable high-energy gamma-ray sources, owing to the interaction of accelerated particles with the dense molecular cloud still present close to young and massive stars. The 3 factors that govern the gamma-ray “visibility” of a given OB association are i) the rate of kinetic energy deposition , where the summation is done on all mass-losing stars; is the mass-loss rate for the star i and Vi is the terminal velocity of its stellar wind;(ii) the distance of the OB association;(iii) the angular extent of the association.
Cosmic Rays from Regions of Star Formation III. The Role of T-Tauri Stars in the Rho Oph Cloud
Authors: Paul J. A. , Cassé M. , Montmerle T.
Published: July 2016

It has long been expected that gamma-ray astronomy will visualize the mysterious cosmic-ray (CR) sources. Indeed, on the basis of COS-B observations, it has been proposed that CR acceleration within the Rho Oph cloud complex (ROCC) is required to account for its gamma-ray luminosity (Cassé and Paul, 1980, herein after CP, Bignami and Morfill, 1980). However, Issa et al. (1980) have suggested that the size of the ROCC has been underestimated by a factor ≃2, and that the cloud mass is a factor ≃ 4 higher than given by Myers et al. (1978), making unnecessary CR acceleration and trapping in the cloud interior.
Shock Structure including Cosmic Ray Acceleration
Authors: Drury L. O'C. , Völk H.J.
Published: July 2016

The backreaction of shock accelerated cosmic rays (CR) on the hydrodynamic flow is studied in a simple macroscopic modeL introduced by Axford et al. (1977): the fluid is isentropic except at discontinuities and the energy of the scattering wave field is neglected. With gas density p , velocity u, pressure pQ and a constant specific heat ratio γQ we have in the one dimensional steady state:
THE COMPOSITION OF PLANETARY ATMOSPHERES
Authors: Encrenaz Th. , Combes M.
Published: July 2016

During the past 10 years, great progress has been made in our knowledge of the planetary atmospheres, mainly due to the recent development of infrared techniques and space astronomy.
THE LARGE SCALE INFRARED EMISSION IN THE GALACTIC PLANE—OBSERVATIONS
Authors: Okuda H.
Published: July 2016

For a long time, the inner region of our Galaxy has been veiled by strong interstellar extinction in visible light. The situation has been greatly improved by recent exploration in the infrared region, where the interstellar extinction becomes practically negligible.
INFRARED STUDIES OF STAR-FORMING REGIONS - SUMMARY
Authors: Zuckerman B.
Published: July 2016

When Gareth Wynn-Williams first asked me to give this summary talk he specifically requested that I be “provocative.” Having already been to Hawaii three times I realized how much easier it is to be laid back rather than provocative here - indeed, I but rarely rise above the ground energy state. So, the prospect of giving this talk has so terrified me that I have been sitting in the front row taking notes for two days now - something I have never done at any meeting. I even sought out the advice of an expert summarizer and first row sitter, my colleague Virginia Trimble, who advised me not to worry, but to simply “tell them what they should have said but didn't.”
INFRARED STUDIES OF THE STELLAR CONTENT IN EXTRAGALACTIC SYSTEMS
Authors: Aaronson Marc
Published: July 2016

Normal galaxies emit most of their radiation longward of one micron, and many problems related to our understanding of galaxy formation and evolution can be fruitfully addressed with measurements at near-infrared wavelengths. Such problems include the make-up of the red stellar population, the star formation rate, the initial mass function, metallicity effects, and mass-to-light ratio. How these various quantities depend on morphological type, on total mass (or absolute magnitude), on radial position, and on environment is also of great interest. In this review recent infrared observations of extragalactic stars, star clusters, and galaxies having important bearing on these questions are discussed. Particular emphasis is placed on new evidence for the presence of a finite intermediate age population in early-type systems. This evidence comes from observations of intermediate age stars in many Magellanic Cloud globular clusters, observations of such stars in at least one nearby dwarf spheroidal (Fornax), the difficulties of fitting theoretical isochrone models to the red V-K colors of E and SO galaxies, and the differences in the infrared color-magnitude relations for the Virgo and Coma clusters.

“It is not very bright to measure a blue magnitude for a red object.”

– Vera Rubin
Parsec-Scale Structure of Compact Radio Sources
Authors: Zensus J. A.
Published: July 2016

High-dynamic range imaging and monitoring with Very Long Baseline Interferometry have considerably increased our knowledge of the parsec-scale properties of compact radio sources. I review some of the properties of individual sources in areas where particular progress has been made in the last few years.
The Sub-Parsec Scale Jets of AGN
Authors: Krichbaum T.P. , Alef W. , Witzel A.
Published: July 2016

With an angular resolutions of 0.05–0.2 mas, millimeter-VLBI1 observations (at 22, 43, and 86 GHz) allow to investigate the very central –sub-parsec scale – regions of active galactic nuclei (AGN), which are self-absorbed at lower frequencies. Here we briefly present preliminary results from recent observations of Cygnus A at 22 & 43 GHz, which reveal evidence for subluminal motion in jet and counter-jet, and 86 GHz VLBI observations of two extreme γ – blazars, suggesting a tight correlation between their γ – ray activity and the generation of jets.
Monitoring the Jet in Centaurus A at 0.1 Parsec Resolution
Authors: Preston R.A. , Tingay S.J. , Jauncey D.L. , Reynolds J.E. , Lovell J.E.J. , Mcculloch P.M. , Tzioumis A.K. , Costa M.E. , Murphy D.W. , Meier D.L. , Jones D.L. , Clay R.W. , Edwards P.G. , Ellingsen S.P. , Ferris R.H. , Gough R.G. , Harbison P. , Jones P.A. , King E.A. , Kemball A.J. , Migenes V. , Nicolson G.D. , Sinclair M.W. , Van OMMEN T.D. , Wark R.M. , White G.L.
Published: July 2016

Centaurus A is the closest active extragalactic radio source, at a distance of approximately 3.5 Mpc, and is identified with the peculiar elliptical galaxy NGC 5128. As such it is a very important target for observations of the small-scale (sub-parsec) and large-scale (kpc) structures in extragalactic jets. Here we present Mk-II VLBI observations made at 8.4 GHz over a 4.3 year period from early 1991 until mid-1995, as well as a 4.8 GHz observation that was co-eval with one of the 8.4 GHz observations. All of the observations were made with the SHEVE array except for the last observation which was made with the VLBA. The dual-frequency observations identify the core of the radio source, while the multi-epoch observations show the complex structural evolution at a resolution of 0.1 pc. Subluminal motion of ≈ 0.15c is evident. Structural changes are observed on time scales shorter than four months.
Constraints on the accretion region in NGC 1275 from VLBA observations of the counterjet
Authors: Walker R.C. , Romney J.D. , Vermeulen R.C. , Dhawan V. , Kellermann K.I.
Published: July 2016

A northern feature, that is most likely related to a counterjet, was found on parsec scales in 3C 84 (which is in NGC 1275) in “First Science” observations on the VLBA1 at 8.4 GHz (Walker et al., 1994) and in Global VLBI observations at 22 GHz (Vermeulen et al., 1994). The jet/counterjet length ratio, brightness ratio at 22 GHz, and speeds, as measured over many years with VLBI, fit a simple beaming model with symmetric jets oriented at 30–50 degrees to the line-of-sight and traveling at a speed of 0.3–0.5 times the speed of light. These ranges allow for Hubble constants of between 50 and 100 km s–1 Mpc–1. The brightness of the counterjet at 8.4 GHz was very much lower than expected with this model, assuming that the spectral indices in the near and far side jets are similar. This was interpreted as the result of free-free absorption in an ionized medium that lies in front of the counterjet but not in front of the near-side jet. An accretion disk or torus has an appropriate geometry to show this effect (for an analysis, see Levinson et al., 1995).
CSS versus Large Size Sources
Authors: Fanti R. , Spencer R. E.
Published: July 2016

A large fraction of the sources in flux density limited radio samples have angular sizes < 2 arcsec (and hence projected linear sizes ≤ 10–15 kpc for H0 = 100 Km/(sec Mpc), and steep (α > 0.5, S∝ v–α) high frequency spectra (Kapahi, 1981; Peacock and Wall 1982). The proportion of these Compact Steep–spectrum Sources (CSSs) is high (15–30% depending on the selection frequency) amongst distant (z > 0.2) radio sources of high power, both galaxies and quasars. We include in this class the GHz Peaked Spectrum Radio Sources (GPS), sub–kpc objects whose radio spectra are peaked at GHz frequencies (see, e.g., O'Dea et al, 1991).
2.23 and 8.29 GHz Observations of CSS-GPS Candidates
Authors: Dallacasa D. , Bondi M. , Mantovani F. , Alef W.
Published: July 2016

Compact Steep-Spectrum (CSS) and GHz-Peaked Spectrum (GPS) radio sources are intrinsically small objects (Fanti et al. 1990) with high frequency steep spectra (α > 0.5 with S∝ v–α), found at moderate or high redshifts (z>0.2 but many objects have z>1.5). Their characteristics have been interpreted in terms of youth (e.g. Fanti et al. 1995) or “frustration” (e.g. van Breugel et al. 1984). Their radio spectra turn over at tens or a few hundreds of MHz (CSS) or at higher frequencies (GPS), interpreted as due to synchrotron self-absorption. They represent a significant fraction of flux limited catalogues (15–30 %, depending on the frequency).
NLR Kinematics in CSS Radio Sources
Authors: Gelderman Richard
Published: July 2016

Compact Steep-Spectrum (CSS) radio sources are defined by their powerful yet subgalactic radio structure. High resolution radio interferometers reveal subarcsecond double, triple, and core-jet radio morphologies resembling miniature FR II sources. There are three promising scenarios for how such powerful radio sources could be so intrinsically small: 1) they are young sources which have not had time to grow large, 2) they are confined sources with exceptionally dense gas in the host which either smothers an existing source or frustrates its initial growth, or 3) they are enhanced sources with an intrinsic power much lower than one might expect based on their radio luminosity. To investigate these scenarios, we are continuing a comprehensive optical study of a sample of Compact Steep Spectrum objects.
Multi-frequency VLBI Observations of the Gravitational Lens B0218+357
Authors: Porcas R. W. , Patnaik A. R.
Published: July 2016

The gravitational lens system B0218+357 comprises 2 image components (A and B) and a radio ‘Einstein Ring’ (Patnaik et al, 1993). The redshift of the lens galaxy is 0.6847 (Browne et al, 1994) and that of the imaged source 0.96 (preliminary result; Lawrence et al, 1995). The separation of A and B, which are both flat-spectrum radio sources, is only 0.335 arcsec, leading to the hope that the lens is a single galaxy with a relatively simple mass distribution. Refsdal pointed out (1964) that a model of such a distribution, and a measurement of the time difference along the two image paths, leads to an estimate of the Hubble constant, independent of the usual steps in the distance ladder. B0218+357 is one of only a few lensed systems well suited for such measurements. A preliminary value of 12 days has been measured for the A-B time delay, derived from a comparison of the percentage polarisation variations of the images at 15GHz, using the VLA (Corbett et al, 1995).
EVN Phase-Referenced Observations of 1308+328
Authors: Rioja María José , Porcas Richard W. , Machalski Jerzy
Published: July 2016

Machalski and Engels (1994) have drawn attention to the recent outburst in the extragalactic radio source 1308+328. We observed it with VLBI at 2.3 and 8.4 GHz in February 1995, using the EVN, and including antennas at Seshan, Kashima, Hartebeesthoek and Ny-Alesund, all of which provided long baselines. During these observations we switched every few minutes between 1308+328 and the nearby compact source 1308+326, 14 arcmin away. This allowed us to determine a precise relative separation between these sources at both frequencies using phase referencing techniques, and provided a useful comparison between source sizes. We found that the target source, 1308+328, is considerably more compact than the reference source 1308+326, the latter being resolved (correlated flux decreased by 50 %) at 8.4 GHz at 250 million wavelengths. In contrast, 1308+328 appears completely unresolved at this resolution (Fig 1), corresponding to a source size < 0.5 mas.
The relativistic Jet in M84
Authors: Wrobel J.M. , Walker R.C. , Bridle A.H.
Published: July 2016

The elliptical galaxy M84 (NGC 4374, UGC 07494) hosts an FR-I radio continuum source (Laing & Bridle 1987, MNRAS, 228, 557) and a dusty, warped optical emission line “disk” (Baumet al.1988, ApJS, 68, 643; Goudfrooijet al.1994, A&ApS, 105, 341). HST imaging shows that the inner dust distribution is not relaxed, but filamentary and complex (Jaffeet al.1994, AJ, 108, 1567). M84 is a member of the Virgo Cluster, at which distance 1 arcsec = 73 pc independent of Hubble's constant (Jacobyet al.1990, ApJ, 356, 332). Our VLA imaging, at 6 cm with a resolution of 500 mas (36 pc) FWHM, shows that the two large-scale jets in M84 are initially asymmetric: the ratioRIof the intensity of the northern main jet to the southern counterjet exceeds unity. However, these jets symmetrize(RI≃1) by a projected nuclear offsetrp≃ 13 arcsec (950 pc). Is this VLA symmetrization trend consistent with Doppler boosting in a decelerating, but initially relativistic, jet? To test this, we obtained preliminary VLBA images of M84 at 18 cm and 4 cm, with resolutions of 11 mas (0.80 pc) and 1.9 mas (0.14 pc), respectively, and used them to evaluateRIon pc scales for comparison withRIon 100-pc (VLA) scales.
The parsec-scale nucleus and jets of Hydra A
Authors: Taylor Gregory B.
Published: July 2016

Sensitive, high-resolution VLBA observations of the nuclear region of Hydra A are presented at 1.3, 5 and 15 GHz. Hydra A (3C218) is an outstanding example of a high-luminosity FRI radio galaxy embedded within a cooling flow cluster. VLA observations by Taylor & Perley (1993) have demonstrated extremely high (>5000 radians m–2) Faraday rotation measures (RMs) and a striking RM and depolarization asymmetry between the northern and southern radio lobes. In view of this asymmetry on the kpc-scale Hydra A appears remarkably symmetric on the pc-scale in the radio continuum. Hydra A is also unusual in that the 21 cm atomic Hydrogen line is seen in absorption against the nucleus.
FR I Jets in Southern Radio Galaxies
Authors: Jones Paul A. , Lloyd Ben D.
Published: July 2016

Sources flagged as extended or multiple in the Molonglo Reference Catalogue (MRC, Large et al. 1981, 1991), south of δ = −30°, were observed with the Molonglo Observatory Synthesis Telescope (MOST) with a resolution of 44 arcsec at 843 MHz (Jones and McAdam 1992) to give a sample of 193 southern extended sources. Optical identifications were made using the UKST bJ sky survey. We are now using the Australia Telescope Compact Array (ATCA) near Narrabri in Australia to study a subsample of Fanaroff-Riley class I radio galaxies and fit models to the jets.
High-Frequency Study of Low and Intermediate Luminosity Radio Galaxies
Authors: Gregorini L. , Parma P. , Klein U. , Mack K.-H.
Published: July 2016

All the information on the morphology, spectral index and polarization properties of low and intermediate luminosity radio galaxies were collected in an intermediate frequency range, and some of the basic questions to be elucidated with such measurements are still unanswered. We therefore decided to extend the study of their characteristics towards higher frequencies. From the B2 and 4C catalogue we selected 26 radio galaxies for which VLA or WSRT data are available. These sources were observed at 10.6 GHz using the Effelsberg 100-m telescope (Gregorini & al. 1992; Mack & al. 1994; Klein & al. 1995).
The Jets in FRII Radio Galaxies with z < 0.3
Authors: Hardcastle Martin
Published: July 2016

If we believe that jets trace the energy transport in radio sources, we might in principle expect to see them in every classical double radio galaxy with compact hot spots. Until recently the detection rate of jets in FRII radio galaxies has been low, although most FRII quasars have bright one-sided jets. However, it seems likely that this is due to lack of sensitivity. Black et al. (1992) found jets in up to 70% of a sample of FRII galaxies with z < 0.15. We have observed the FRII sources in Laing et al. (1983) with 0.15 < z < 0.3 and discuss results from the combined samples.
An Atlas of Extragalactic Radio Sources
Authors: Leahy J.P. , Bridle A.H. , Strom R.G.
Published: July 2016

Our Atlas of Extragalactic Radio Sources will present high-quality images of the nearer half of “3CRR”, the sample defined by Laing, Riley & Longair (1983). This is the best-studied complete sample of extragalactic radio sources. All 173 members have secure redshifts and most have been imaged in the radio at high resolution. There is also copious information on their optical line emission, and many have been detected in the sub-mm, FIR, and in X-rays. 3CRR is widely used as a baseline against which fainter, higher-redshift samples can be compared to define the evolution of the population (e.g. Neeser et al. 1995; Law-Green, this conference).
A Multi-radio-frequency Study of a RQQ
Authors: Blundell K.M. , Lacy M.
Published: July 2016

1821+643 is exceptionally bright at optical wavelengths with MB ≈ −27 (Hutchings & Neff 1991), at a redshift of only 0.297. It is however, a radio-quiet quasar (RQQ) as can be demonstrated by considering e.g., the ratio of the luminosity in [Oiii]λ5007 to the radio luminosity (Lacy, Rawlings, & Hill 1992). In contrast with other radio-quiet quasars however, E 1821+643 is located in a very rich cluster (Lacy et al. 1992) and is purported to reside in a gE host galaxy (Hutchings & Neff 1991). The full-resolution 8 GHz map is seen in Fig. 1. A bright unresolved core is seen with extended emission to the north-west (feature B). Features A and C are accurately diametrically opposed on either side of the core and therefore suggestive of jets; this is further supported by the alignment of features C, D and E.
Circumnuclear Disks in Radio-Quiet Active Galaxies
Authors: Wilson A. S.
Published: July 2016

In this paper, I review some of the evidence for gaseous circumnuclear disks in radio-quiet active galaxies (Seyfert galaxies and LINER's). Results from observations of Fe Kα lines, H2O megamasers, extended structures seen in near infrared observations and ionization cones are discussed.
What Powers Ultra-Luminous IRAS Galaxies?
Authors: Partridge R.B. , Marr J. , Crawford T. , Strauss M.
Published: July 2016

I report here centimeter–wavelength observations carried out at the Very Large Array (VLA) to help resolve two questions. First, what is the source of the far infrared (FIR) emission in infrared-luminous IRAS galaxies, active nuclei or more widely distributed star formation? And what physics underlies the tight correlation (Helou et al., 1985) between FIR and radio flux? To test potential answers to these questions, we believe it is important to study the most luminous IRAS galaxies. We selected 39 for study from the ultraluminous catalog of Strauss et al.(1990 and 1992). All sources had FIR luminosity ≥ 1011.4 L⊙. Radio wavelength observations of these systems provide several advantages. First, in the radio there is no obscuration, so we can “see” the active galactic nuclei, if present. Radio spectral indices can distinguish between synchrotron and thermal emission. And finally, observations at the VLA provide sub–kpc resolution. We observed these sources with the VLA in its C configuration. At 1460 MHz, the effective resolution was ≃ 15″; and ≃ 4″ at 4860 MHz. We made follow-up observations on 24 sources in the A configuration with resolution at 4860 MHz of ≃ 0″.5 (or 300–800 h–1 pc for these sources).
Optical–Radio Connections AGN Illumination or Jet/cloud Interactions?
Authors: Tadhunter Clive N.
Published: July 2016

Many of the most important discoveries in the study of extragalactic radio sources have resulted from investigations of the relationships between optical and radio properties. The optical/radio connections include: correlations between optical emission line luminosity and radio power; alignments between optical/UV and radio structures; and UV excesses in the spectral energy distributions of radio galaxies compared with normal early-type galaxies.
Weak Radio Galaxies: Narrow-Band Optical Imaging
Authors: Carrillo René , Cruz-González Irene
Published: July 2016

Previous studies show that: a) radio galaxies and radio-loud quasars have emission-line gas (ELG) which is extended on scales of tenths of kiloparsecs; b) there is convincing evidence that the kinematics and excitation of the very extended emission-line gas is governed by its interaction with the outflowing radio plasma; c) the evidence for an interaction is weaker in some radio galaxies. It is argued that the ionization of the ELG may be predominantly produced by the nuclear ultraviolet continuum and the kinematics of the gas due to the gravitational potential of the host galaxy, but it is not yet known whether there is a physical relationship between the ELG and the extended radio jets.
Soft X-Ray Properties of a Complete Sample of Radio Sources
Authors: Siebert J. , Brinkmann W. , Morganti R. , Tadhunter C.N. , Danziger I.J. , Fosbury R.A.E. , Alighieri S. Di Serego
Published: July 2016

We investigate the X–ray properties of a complete sample of 88 radio sources derived from the Wall & Peacock 2–Jy sample. We find that Lx correlates well with core radio luminosity for all object classes, whereas the Lx – Ltotal is probably introduced by sample selection effects. Further, evidence for an anisotropic X–ray component in broad line radio galaxies is reported. A full description of the results will be given elsewhere (Siebert et al. 1996).
X-Ray Spectral Properties of Radio Galaxies
Authors: Inoue H.
Published: July 2016

X-ray spectral properties of radio galaxies are reviewed in comparison with those of Seyfert galaxies, mainly based on results from Japanese X-ray astronomy satellites, Ginga and ASCA.
Gamma-Ray Emission from Extragalactic Radio Sources: EGRET Observations of Active Galactic Nuclei
Authors: Michelson Peter F.
Published: July 2016

The Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Gamma-Ray Observatory is an imaging high-energy telescope with sensitivity from approximately 20 MeV to 30 GeV. EGRET has observed more than 129 sources during more than 4 years of operation. Among these sources, 51 have been identified with active galaxies. A common characteristic of the AGN sources is that they are all radio-loud, flat radio spectrum sources. Many of them are seen as superluminal radio sources as well. The gamma-ray emission characteristics of these sources are reviewed and some of the proposed emission models are discussed.
The Radio-Gamma-Ray Connection: the Radio Properties of Gamma-Ray-Bright Blazars
Authors: Aller M. F. , Aller H. D. , Hughes P. A.
Published: July 2016

Forty AGN have been detected at high significance level by EGRET in the γ-ray band. Previous studies based on radio observations near or at the times of the EGRET detections suggest that there is a causal connection between individual events in these two wavebands. Here we examine the question of whether the cm-λ and the γ-ray activity are related.
AGN Statistics of Simultaneous Radio and Gamma Ray Observations
Authors: Mücke A. , Pohl M. , Kanbach G. , Reich P. , Reich W. , Schlickeiser R.
Published: July 2016

In this paper we present first results of a statistical analysis of correlated variability behaviour of flat-spectrum radio quasars (FSRQ) on the basis of EGRET data and cm-wavelength monitoring data. We use EGRET observations obtained between April 1991 to September 1993 and multifrequency radio observations at 2.8cm, 6cm and 11cm taken with the 100-m-Effelsberg Telescope parallel to the CGRO observations. In the following discussion the observed FSRQ which have not been detected by EGRET yet, are referred to as ‘candidates’ in contrast to the detected ones, called ‘EGRET-sources’. The methods used in this paper are described in more detail in Mücke et al. (1996).
Optical Monitoring of Gamma-Ray Loud Blazars
Authors: Raiteri C.M. , Ghisellini G. , Villata M. , DE FRANCESCO G. , Bosio S. , Latini G. , Chiumiento G. , Lanteri L. , Massone G. , Racioppi F. , Smart R.L.
Published: July 2016

The observations by the Compton Gamma Ray Observatory (CGRO) have shown that highly variable and radio-loud quasars emit a significant fraction of their energy in the γ band. According to the Inverse Compton model, the γ-ray emission is due to upscattering of soft (IR-optical-UV) photons by high energy particles. Optical monitoring is thus of great value in providing information on the mechanisms that rule the production of the seed photons for the γ-ray radiation and on the γ-ray emission itself. In particular, detection of variability correlations between optical and γ-ray emissions would be a crucial test for the theoretical predictions.
Radio Sources in Clusters of Galaxies
Authors: Owen F.N.
Published: July 2016

Since the Albuquerque IAU meeting, most of the advances in the understanding of radio sources in clusters has come from combining radio observations with x-ray and optical data. The x-ray images from Einstein and ROSAT have been particularly important because they have allowed us to see the external medium with which the radio sources co-exist and interact. I will cover three examples of such work in this review.
Morphologies in Mpc-Size Radio Galaxies
Authors: Saripalli L. , Subrahmanyan R. , Hunstead R. W.
Published: July 2016

The extended radio structures or lobes found in edge-brightened radio galaxies represent interactions with the ambient medium over the source lifetimes. Their study probes the temporal evolution in the radio sources and the properties of the ambient medium encountered at different locations. Previous studies (Leahy & Williams, 1984; Leahy et al., 1989) involved radio galaxies with sizes ≃ 400 kpc, and revealed radio morphologies with a variety of off-axis distortions that could be interpreted as due to different ways in which the lobes interact with the galactic halos. Such studies are lacking for radio galaxies having Megaparsec sizes, which extend to distances well beyond the observed galactic halos and are suspected of evolving in a different regime (Baldwin, 1982). Towards learning the evolution of radio galaxies in this size regime, we have carried out a study of a complete sample of Mpc-size radio galaxies; details are presented in Subrahmanyan, Saripalli & Hunstead (to appear in MNRAS, 1996).
Towards a Complete Sample of Giant Radio Galaxies at z > 0.4
Authors: Schoenmakers A.P. , Röttgering H. , Van Der Laan H. , De Bruyn A.G.
Published: July 2016

Giant Radio Galaxies are the largest radio sources associated with galaxies. They have linear sizes exceeding 1 Mpc (e.g. Saripalli et al., 1986). They used to be known only at redshifts below 0.2, and it has been argued that this was not only due to a selection effect, but that there is a real cutoff in the space distribution of these objects (e.g. Gopal-Krishna & Wiita, 1987). Recently, a small number of giants have been found at redshifts largely exceeding 0.3, indicating that such a cutoff does not exist (e.g. Cotter et al., 1995).
Evolution of Powerful Extended Radio Sources: Implications for Cosmology and Cosmogony
Authors: Daly R. A.
Published: July 2016

Powerful extended radio sources are observed out to relatively large redshift. They may be used to study the properties and redshift evolution of the gaseous environment in the vicinity of each source, the active galactic nucleus (AGN), and the source size. This information may then be used to study and constrain cosmological and cosmogonical models. It is interesting to note that the rate of change of quantities with redshift allows constraints to be placed on global cosmological parameters and on models of structure formation and evolution that are completely independent of those inferred using the cosmic microwave background or local dynamical studies, and thus provide an important complement to these studies. The method does require that we understand the physics of the sources well enough to account for intrinsic source evolution. The physics of powerful extended radio sources that propagate supersonically appears to be relatively straight-forward. We have used the radio properties of the sources to deduce the ambient gas density, the beam power of the AGN, the characteristic time a particular AGN is on, and a characteristic source size that allows the sources to be used to probe global cosmological parameters. We plan to use the radio properties of the sources to deduce the ambient gas temperature, which will be combined with the ambient gas density to constrain cosmogonical models, that is, models of structure formation and evolution.
The Environments of Radio Galaxies
Authors: Pesce J.E. , Falomo R. , Fasano G. , Scarpa R.
Published: July 2016

In the unified schemes of AGNs BL Lac objects are believed to be Fanaroff-Riley (FR) type I radio galaxies with a relativistic jet aligned to the observer's line of sight (e.g. Urry & Padovani 1995). Kollgaard et al. (1992) and Owen et al. (1995) suggest some FR II sources can also be BL Lac parents. Clearly, isotropic properties such as the galaxy environment of both beamed and unbeamed objects should be identical.
Electron Transport in the Coma Cluster
Authors: Kirk J.G. , Duffy P. , Dendy R.O.
Published: July 2016

The inner regions of the Coma cluster of galaxies contain a source of diffuse synchrotron emission (‘Coma C’) which has a linear dimension of at least 500 kpc. There has been interest in the question of where the relativistic electrons responsible for this emission originate, and how they are transported through the intra-cluster medium (Tribble, 1993). It is widely thought that one or more of the radio galaxies in the centre of the cluster provides a likely source for particles which then diffuse out into the halo (Giovannini et al., 1993); a process which depends critically on the structure of this field in the intra-cluster medium. Recent observations of the emission from NGC4869 (Feretti et al., 1995), which occupies a central position in the Coma cluster, indicate the presence of a magnetic field which is both stronger (B ≈ 8μ G) and tangled on much shorter scales ≲ 1 kpc than had been thought previously (Kim et al., 1990). These new results suggest not only a shorter cooling time for energetic electrons, but also a slower rate of diffusive transport. In this paper we show the constraints that the new observations place on transport theories of the relativistic electrons.
Coma Cluster: CR Acceleration and Gamma-Ray Production
Authors: Dogiel A.V.
Published: July 2016

The Coma cluster is situated near to the North Pole and its galactic coordinates are: l≃ 50° and b≃87°. The distance to the cluster is about 138 Mpc. Observations in soft X-rays (see e.g. Briel, 1992) discovered there the thermal emission from the diffuse hot intracluster gas whose density and temperature are: n≃ 3 · 10–3 cm–3 and T≃ 108K. Measurements of hard X-ray flux from Coma showed controversial detection in different experiments (see Bazzano et al. 1990 and Rephaeli et al. 1994).
The Environment of Hercules A
Authors: Gizani N.A.B. , Leahy J.P.
Published: July 2016

The bright radio galaxy Hercules A (z = 0.154), has power P178MHz = 8 × 1026 W Hz–1sr–1 and although this puts it well above the FR break, its structure is intermediate between Fanaroff and Riley classes I and II. With a linear size of 334 kpc (for H0 = 100 kms–1Mpc–1), Hercules A possesses an unusual jet-dominated morphology and no compact hotspots. The western jet shows partial or full ring-like features that form a linear sequence heading from the core to the lobes and follow an inner jet.
A2241: Clusters with Head-Tails at X-Rays
Authors: Norci L. , Feretti L. , Meurs E.J.A.
Published: July 2016

A ROSAT PSPC image of the galaxy cluster Abell 2241 has been obtained, showing X-ray emission from the intracluster medium and from individual objects. The brightness distribution of the cluster gas is used to assess the physical conditions at the location of two tailed radio galaxies (in A2241E and A2241W, at different redshifts). Together with radio and X-ray information on the two galaxies themselves the results are of relevance to the question of energy equipartition in radio sources.
ASCA observations of clusters of galaxies
Authors: Yamashita Koujun
Published: July 2016

X-ray emissions from clusters are most likely originated from a thin hot plasma in a collisional ionization equilibrium. The optical depth of continuum component is order of 10–3, whereas that of emission lines is around unity. Present emission models used for spectral fitting can not estimate this effect, so that the determination of elemental abundances seems to include large uncertainty. The high resolution spectroscopy with ASCA gives a clue to investigate the physical state of hot intracluster gas and a impact to reconsider the basic atomic processes. This is important issue to deeply understand the structure, formation and evolution of clusters, and the origin of intracluster gas.
Unified Schemes for Extragalactic Radio Sources
Authors: Krishna Gopal
Published: July 2016

The most widely discussed class of unified schemes for radio-loud extragalactic sources attempts to interpret their seemingly disparate types as the same objects seen from different directions. The orientation dependence is attributed to relativistic beaming of the nonthermal jet and, possibly, anisotropic obscuration/re-radiation of the nuclear emission by a circum-nuclear distribution of dusty material with polar openings, possibly a torus. Although alternative approaches have been mooted for unifying radio galaxies (RGs) and quasars (QSRs) by incorporating a strong jet-environment interaction, or temporally decaying nuclear prominence, the orientation based unified scheme, thanks to its rich predictive potential, has been subjected to a multitude of observational tests and its pros and cons have been discussed extensively in recent reviews. Here we briefly address some recent developments, including the claim that the radio size measurements of powerful RGs and QSRs are incompatible with orientation being the primary distinction between them. On balance, it seems that while the basic orientation picture can broadly explain the bulk of the observations, its viability could be much enhanced by taking into consideration the (inevitable) temporal evolution of radio sources.
The Unification of Radio-Loud AGN
Authors: Urry C. M. , Padovani Paolo
Published: July 2016

In a recent review paper we summarized the current status of unification of radio-loud AGN (Urry & Padovani 1995 PASP 107, 803), connecting high-luminosity (FR II) radio galaxies with quasars, and low-luminosity (FR I) radio galaxies with BL Lac objects. Unified schemes are motivated by the knowledge that AGN appearance depends strongly on orientation (Fig. 1): optical/UV light from the centers of many AGN is obscured by circumnuclear matter, and in radio-loud AGN, bipolar relativistic jets beam light along the jet axes. Understanding these radiation anisotropics allows us to unify apparently distinct classes of AGN that differ primarily because of orientation.

Our review described the classification and general properties of AGN and summarized the evidence for anisotropic emission caused by circumnuclear obscuration and relativistic beaming. We outlined the evidence, both observed isotropic properties and statistical arguments, for connecting FR IIs with quasars and FR Is with BL Lacs. The population statistics (with beaming) are in accordance with available data and suggest γ ≃ 5 for low-luminosity AGN and γ ≃ 10 for high-luminosity AGN. The distinctions between X-ray-selected and radio-selected BL Lac objects, and between BL Lacs and flat-spectrum variable quasars, still not understood, provide clues to the underlying physics of blazars. Our review discussed several possible problems and complications, and concluded with a list of the ten questions we believe are the most pressing in this field.
Composite Optical Spectra of Radio Quasars
Authors: Baker Joanne C. , Hunstead Richard W.
Published: July 2016

Primarily to illustrate the effects of orientation on the optical properties of radio-loud quasars, we have created a set of composite optical spectra (see also Baker & Hunstead 1995). Optical spectra drawn from the 408-MHz Molonglo Quasar Sample (MQS) have been coadded in four sets according to R, the ratio of radio core-to-lobe flux, which is used as an orientation indicator (eg. Orr & Browne 1982). Compact steep-spectrum (CSS) quasars (see review by Fanti, this volume) have been combined separately, revealing for the first time many distinguishing features in their average spectra.
On the X-Ray Emission from the Powerful Radio galaxies
Authors: Brunetti G. , Setti G. , Comastri A.
Published: July 2016

There is a growing evidence that radio loud quasars and powerful FR II radio galaxies belong to the same population. While X-ray observations of low redshift radio galaxies generally support the unified scheme relating the FR II radio galaxies to the radio quasars, nevertheless detailed studies of the X-ray properties of distant radio galaxies are made difficult due to both the low sensitivity of X-ray-satellites and to the emission of the hot intracluster gas in which they are normally embedded. We point out that significant fluxes of X-rays are produced in the strong radio galaxies by the Inverse Compton (IC) process. In the framework of the unified scheme the radio galaxies are pervaded both by an intense radiation flux from the misdirected hidden quasar and the cosmic microwave background radiation flux (CMB). From the standpoint of IC computation the far and near-IR emissions of the hidden quasar are of particular importance.
Energy Transport in Radio Galaxies and Quasars: A Workshop Theory Review
Authors: Hardee Philip E.
Published: July 2016

A workshop on the dynamics, emission and morphology associated with the highly collimated outflows seen in radio galaxies and quasars was held at The University of Alabama in Tuscaloosa in September of 1995. Complete workshop proceedings will be published in the ASP Conference Series. This workshop review covers the theoretical developments and problems discussed at the workshop.
Supersonic Jets and Lobe Morphologies
Authors: Ferrari A. , Massaglia S. , Bodo G.
Published: July 2016

Since the pioneering work by Norman et al. (1982), many numerical studies have been devoted to the analysis of the propagation of a supersonic jet shot into an ambient medium (see Massaglia, Bodo & Ferrari 1995, hereinafter Paper I, and references therein). In spite of these strong efforts many aspects of this problem are still not well understood. This is due to the complexity of the jet-cocoon structure: in fact, the cocoon excites perturbations to the jet flow, which in turn can be amplified by the Kelvin–Helmholtz mechanism and induce a strong activity of the jet's head that affects the cocoon structure. Thus a complex feedback loop mechanism establishes between jet and cocoon which make the dynamics of the interaction very complex.
Numerical Simulations of Extragalactic Jets in an Inhomogeneous Environment
Authors: Higgins Steve , O'BRIEN TIM , Dunlop James
Published: July 2016

We have simulated the passage of an extragalactic jet through a medium containing an ensemble of cool, dense clouds. The hydrodynamic code uses the second-order Godunov method of Falle (Falle 1991, van Leer 1979) in three-dimensional, cartesian coordinates. We have estimated the synchrotron emissivity and used this to produce synthetic radio maps. The results are reminiscent of structures seen in many extragalactic radio sources.
Comparative Study of Extragalactic Radio Sources from “Double Jet” models
Authors: Dole H. , Sol H. , Vicente L.
Published: July 2016

It seems now important to consider bulk velocity gradients inside jets (Blandford, 1993; Biretta et al, 1995) and recent results from tomography technique suggest the presence of different components in radio sources (Rudnick, this symposium). A few jet models take explicitly into account two components with different bulk velocities (Smith, Raine, 1985; Baker et al, 1988; Sol et al, 1989; Achatz et al, 1990). A fast beam comes from the vicinity of the black hole while a slower collimated wind is emitted by the accretion disk. When stable, the two components can survive along the jet. If a fast instability develops at a distance Dc from core, the beam is destroyed over some relaxation length. Its energy and momentum are transmitted to the wind. Apparent change in the flow regime such as slowing down, decollimation, local bending or discontinuity in surface brightness is the expected observational signature of such critical zones on radio maps. The exact appearance of the zone depends on the parameters of the two flows and on their interaction regime.
Simulation of the Variable Multifrequency Radio Emission and Structure of the Quasar 2145+067
Authors: Kovalev Y.Y.
Published: July 2016

Here are reported new successful results of analysis for jet in the strong radial magnetic field of an active galactic nuclei, suggested in.
The NRAO VLA D-Array Sky Survey (NVSS)
Authors: Cotton W. D. , Condon J. J. , Yin Q. F. , Perley R. A. , Broderick J. J.
Published: July 2016

Early large scale radio surveys of the sky were made with instruments with poor imaging quality and were limited to measuring positions and brightnesses of discrete sources. In recent decades radio interferometric arrays have dramatically increased their speed, sensitivity and ability to image the sky and several large scale radio surveys are currently being made with imaging instruments. One of these surveys is discussed in this paper.
The Distant DRAGNs Survey
Authors: Law-Green J. D. B.
Published: July 2016

DRAGNs (Double Radio sources Associated with Galactic Nuclei, Leahy 1991) are the class of powerful extragalactic radio sources thought to be produced by the interaction of a jet with the ambient medium. They exhibit strong cosmological evolution in comoving number density; at z ≃ 2 the “classical double” FR II DRAGNs were ≃ 1000 times as common as they are now (Dunlop & Peacock 1990).

To understand this, systematic studies of complete DRAGN samples at low and high z and differing levels of flux density are required, in order to resolve the P – z ambiguity. The Distant DRAGNs Survey is a long-term project to image with the VLA and MERLIN, matched samples of DRAGNs at high redshift.
Imaging of Extragalactic Radio Sources with the VSOP Space VLBI Mission
Authors: Murphy D.W.
Published: July 2016

In September 1996 the first dedicated VLBI spacecraft, VSOP, will be launched. This Japanese spacecraft operating in conjunction with ground-based VLBI arrays such as the EVN or VLBA will enable observers to routinely undertake VLBI observations with maximum baseline lengths of 2.6 Earth diameters and a resolution of 55 μas at the highest operating frequency of 22 GHz. In this paper we present a brief overview of the imaging capability of the VSOP mission together with an example of an imaging simulation.
A nuclear Luminosity Function for Seyferts
Authors: Meurs E.J.A.
Published: July 2016

Relations between various classes of AGN should show up when examining their LFs. For Seyfert galaxies, such studies have been affected by the prevalence of (essentially) integrated magnitudes. Proper nuclear magnitudes have been determined in an effort of CCD imaging, which enable an appropriate comparison with QSOs.
On the Cosmological Evolution of Radio Quiet and Radio Loud Quasars
Authors: Machalski J.
Published: July 2016

This contribution gives further insight into the problem of an ‘evolution’ of the function G(> R) [R is the ratio between radio and optical luminosity of a QSO] suggested by Visnovsky et al.(1992,ApJ,391,560), and recently by Schmidt et al.(1995,AJ,109,473). Using the Optical Luminosity Function for optically selected quasars derived by Boyle et al.(1988,MNRAS, 235,935), and evolving (cf. Schmidt et al. 1995) or non-evolving (cf. Marshall 1987,ApJ,316,84) G(> R) function, an evolutionary function E(z) for the population of both radio quiet and radio loud quasars is determined by modelling the distributions of redshift n(z), as well as counts of apparent optical blue magnitude n(B) and radio 5 GHz flux density n(S) in samples with different radio and optical limits, respectively, and fitting them to the available observational data.