bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Reliability of Initial Conditions for Dissipationless Cosmological Simulations
Authors: Knebe Alexander , Domínguez Alvaro 
Published: August 2003

AbstractWe present the study of ten random realisations of a density field characterised by a cosmological power spectrum P(k) at redshift z = 50. The reliability of such initial conditions for N-body simulations is tested with respect to their correlation properties. The power spectrum P(k) and the mass variance σM(r) do not show detectable deviations from the desired behaviour in the intermediate range of scales between the mean interparticle distance and the simulation volume. The estimator for ξ(r) is too noisy to detect any reliable signal at the initial redshift z = 50. The particle distributions are then evolved forward until z = 0. This allows us to explore the cosmic variance stemming from the random nature of the initial conditions. With cosmic variance we mean the fact that a simulation represents a single realisation of the stochastic initial conditions whereas the real Universe contains many realisations of regions of the size of the box; this problem affects most importantly the scales at about the fundamental mode. We study morphological descriptors of the matter distribution such as the genus, as well as the internal properties of the largest object(s) forming in the box. We find that the scatter is at least comparable to the scatter in the fundamental mode.
Constraining the Evolution of Young Radio-Loud AGN
Authors: Snellen I. A. G. , Mack K.-H. , Schilizzi R. T. , Tschager W. 
Published: August 2003

AbstractGPS and CSS radio sources are the objects of choice to investigate the evolution of young radio-loud AGN. Previous investigations, mainly based on number counts and source size distributions, indicate that GPS/CSS sources decrease significantly in radio power when evolving into old, extended objects. We suggest this is preceded by a period of increase in radio luminosity, which lasts as long as the radio source is confined within the core-radius of its host galaxy. We have selected a sample of nearby compact radio sources, unbiased by radio spectrum, to determine their luminosity function, size distribution, dynamical ages, and emission line properties in a complete and homogeneous way. First results indicate that the large majority of objects (>80%) exhibit classical GPS/CSS radio spectra, and show structures consistent with them being compact double or compact symmetric objects. This sample provides an ideal basis to further test and constrain possible evolution scenarios, and to investigate the relation between radio spectra and morphologies, orientation and Doppler boosting in samples of young radio-loud AGN, in an unbiased way.
GPS and CSS Sources — Theory and Modelling
Authors: Bicknell Geoffrey V. , Saxton Curtis J. , Sutherland Ralph S. 
Published: August 2003

AbstractWe review theoretical ideas that seem to be currently important for the physics of GPS and CSS radio sources. These include models for their evolution, the production of emission lines, and the origin of the low frequency turnover. We also describe the initial phases of a program of simulations that is aimed at understanding the radiative interactions between jets, lobes, and dense clouds in the nuclei of these objects.
VLBA Observations of Bright High Frequency Peakers
Authors: Tinti Sara , Dallacasa Daniele , Stanghellini Carlo , Celotti Annalisa 
Published: August 2003

AbstractThe anticorrelation between the turnover frequency in the radio spectrum and the projected linear size (indicative of the age in the currently favoured youth model) in powerful and intrinsically compact radio sources suggests that the youngest objects must have the highest turnover frequencies. We present preliminary results of new VLBA observations of a sample of sources peaking at frequencies higher than a few GHz, making them good candidates for being newly born sources. Our initial analysis deals with the morphological classification which allows us to study the contamination from beamed sources dominated by a single unresolved component.
Radio Spectral Variability of the Nearby GPS Galaxy PKS 1718–649
Authors: Tingay S. J. , de Kool M. 
Published: August 2003

AbstractData from new Australia Telescope Compact Array observations of a nearby gigahertz peaked spectrum radio source, PKS 1718–649, show significant variability both below and above the spectral turnover frequency during a nine month period. Simple models of synchrotron self-absorption (SSA) and free–free absorption (FFA) cannot explain the individual spectra or the spectral variability. Novel SSA or FFA models will need to be investigated in order to explain the complex variability in this source. Some potential explanations for the spectral variability are explored here but we can make no strong conclusion about which of SSA or FFA (or alternative mechanisms) causes the peaked spectrum in PKS 1718–649.
Deriving the Metallicity Distribution Function of Galactic Systems
Authors: Fenner Yeshe , Gibson Brad K. 
Published: August 2003

AbstractThe chemical evolution of the Milky Way is investigated using a dual-phase metal-enriched infall model in which primordial gas fuels the earliest epoch of star formation, followed by the ongoing formation of stars from newly accreted gas. The latest metallicity distribution of local K-dwarfs is reproduced by this model, which allows the Galactic thin disk to form from slightly metal-enriched gas with α-element enhancement. Our model predicts ages for the stellar halo and thin disk of 12.5 and 7.4 Gyr respectively, in agreement with empirically determined values. The model presented in this paper is compared with a similar dual-phase infall model from Chiappini et al. (2001). We discuss a degeneracy that enables both models to recover the K-dwarf metallicity distribution while yielding different star formation histories.The metallicity distribution function (MDF) of K-dwarfs is proposed to be more directly comparable to chemical evolution model results than the G-dwarf distribution because lower mass K-dwarfs are less susceptible to stellar evolutionary effects. The K-dwarf MDF should consequently be a better probe of star formation history and provide a stronger constraint to chemical evolution models than the widely used G-dwarf MDF. The corrections that should be applied to a G-dwarf MDF are quantified for the case of the outer halo of NGC 5128.
Hi Absorption in GPS/CSS Sources
Authors: Pihlström Ylva , Conway John , Vermeulen Rene 
Published: August 2003

AbstractCombining our own observations with data from the literature, we consider the incidence of HI absorption in gigahertz peaked spectrum (GPS) and compact steep spectrum (CSS) sources. Here we present our preliminary results, where we find that the smaller GPS sources (<1 kpc) on average have larger HI column densities than the larger CSS sources (>1 kpc). Both a spherical and an axi-symmetric gas distribution, with a radial power law density profile, can be used to explain this anti-correlation between projected linear size and HI column density. Since most detections occur in galaxy classified objects, we argue that if the unified schemes apply to the GPS/CSS sources, a disk distribution for the HI is more likely.
Weak CSS Sources from the FIRST Survey
Authors: Marecki Andrzej , Niezgoda Jacek , Włodarczak Jacek , Kunert Magdalena , Spencer Ralph E. , Kus Andrzej J. 
Published: August 2003

AbstractWe report early results of an observational campaign targeted on a sample of compact steep spectrum sources selected from the FIRST survey which are significantly weaker than those investigated before. The selection criteria and procedure are given in detail. We present here an assortment of MERLIN and VLBI observations and make some general comments based on the morphologies of the sources presented.
Location of Weak CSS Sources on the Evolutionary Path of Radio-Loud AGN
Authors: Marecki Andrzej , Spencer Ralph E. , Kunert Magdalena 
Published: August 2003

AbstractAccording to the currently accepted paradigm compact steep spectrum (CSS) sources are precursors of larger/older objects and gigahertz peaked spectrum (GPS) sources may be earlier stages of CSS sources. In this paper we confront this paradigm with the outcome of recent observations of CSS sources that are significantly weaker than those known before. In particular we claim that not all CSS sources must end up as large scale objects; if the activity phase of an AGN's central engine is shorter than the lifetime of a large scale radio source (up to ˜108 yr) the radio source associated with such an AGN decays earlier, e.g. at the CSS stage. We point out that a theory of thermal–viscous instabilities in the accretion disks of AGN may explain many features of radio sources at all stages of their evolution.
X-ray Emission from Gigahertz Peaked/Compact Steep Spectrum Sources
Authors: Siemiginowska Aneta , Aldcroft Thomas L. , Bechtold Jill , Brunetti Gianfranco , Elvis Martin , Stanghellini Carlo 
Published: August 2003

AbstractThe high spatial resolution of the Chandra X-ray Observatory allows us to study the environment of GPS/CSS sources to within an arcsec of the strong compact core. We present the discovery of X-ray jets in two GPS quasars, PKS1127–145 and B2 0738+313, indicating that X-ray emission associated with the relativistic plasma is present at large distances from the GPS nucleus. We also discuss first results from Chandra observations of our GPS/CSS sample. We find that six out of ten sources show intrinsic absorption at a level which may be sufficient to confine the GPS source.
Proper Motions in Compact Symmetric Objects
Authors: Polatidis A. G. , Conway J. E. 
Published: August 2003

AbstractWe discuss recent measurements of proper motions of the hotspots of compact symmetric objects (CSOs). Source expansion has been detected in 10 CSOs so far and all these objects are very young (≤ 3 × 103 yr). In a few sources ages have also been estimated from energy supply and spectral ageing arguments and these estimates are comparable. This argues that these sources are close to equipartition and that standard spectral ageing models apply. Proper motion studies are now constraining hotspot accelerations, side-to-side motions, and differences in hotspot advance speeds between the two hotspots of a source. Although most CSOs are young sources their evolution is unclear. There is increasing evidence that in some objects the CSO structure represents a new phase of activity within a recurrent source.
Two-Sided Radio Jets in B1524–136
Authors: Mantovani F. , Bondi M. , Saikia D. J. , Junor W. , Salter C. J. , Ricci R. 
Published: August 2003

AbstractWe present global VLBI and VLBA observations of the compact steep spectrum quasar B1524–136. These observations reveal well-defined radio jets on both sides of the active nucleus. Also, the overall radio structure appears highly distorted and asymmetric with the counter-jet exhibiting several oscillations. A possible scenario is one in which jet and counter-jet are inclined at about 25° and 75° to the line of sight respectively and an environment which is dense on the jet side. Possible implications of these results are discussed.
Radio Properties of GPS and CSS Sources: Galaxies versus Quasars
Authors: Stanghellini Carlo 
Published: August 2003

AbstractOn the basis of the different radio properties (especially different radio morphologies) between GPS galaxies and GPS quasars, I suggest that GPS galaxies are a more homogeneous class mainly consisting of compact symmetric objects, while the majority of GPS quasars are an intrinsically different type of radio source, similar to the common flat spectrum radio sources. For CSS radio sources the difference between galaxies and quasars is less evident. This is interpreted as a bias correlated with size: samples of smaller objects are more likely to be contaminated by unrelated objects. This is consistent also with the high percentage of blazar/quasar objects present in a sample of the even smaller HFP radio sources.
The Impact of the Early Stages of Radio Source Evolution on the ISM of the Host Galaxies
Authors: Morganti R. , Tadhunter C. N. , Oosterloo T. A. , Holt J. , Tzioumis A. , Wills K. 
Published: August 2003

AbstractThe study of both neutral and ionised gas in young radio sources is providing key information on the effect the radio plasma has on the ISM of these objects. We present results obtained for the compact radio sources PKS 1549–79, 4C 12.50 and PKS 1814–63 and for the intermediate-size radio galaxy 3C 459. At least in the first two, low ionisation optical emission lines and HI absorption appear to be associated with the extended, but relatively quiescent, dusty cocoon surrounding the nucleus. The [OIII] lines are, on the other hand, mostly associated with the region of interaction between the radio plasma and the ISM, indicating a fast outflow from the centre. A case of fast outflow (up to ∼1000 km s-1) is also observed in HI in the radio source 4C 12.50. As the radio source evolves, any obscuring material along the radio axis is swept aside until, eventually, cavities (of the same kind as observed e.g. in Cygnus A) are hollowed out on either side of the nucleus. We may witness this phase in the evolution of a radio source in the radio galaxy 3C 459.
Radio-Excess IRAS Galaxies: Low Power CSS/GPS Sources?
Authors: Drake Catherine L. , McGregor Peter J. , Bicknell Geoffrey V. , Dopita Michael A. 
Published: August 2003

AbstractAmongst our sample of radio-excess IRAS galaxies, we have identified compact steep spectrum radio sources that fall into the classes of CSS or GPS sources, but have not previously been identified as such. The sample includes objects that have radio powers as low as ˜1022 W Hz−1. We suggest that these are low-power analogues of CSS and GPS sources, with weaker radio jets. These may be precursors to FR I radio galaxies or may ‘fade’ into radio-quiet galaxies.
Symmetry Parameters of CSS Sources: Evidence of Fuelling?
Authors: Saikia D. J. , Jeyakumar S. , Mantovani F. , Salter C. J. , Spencer R. E. , Thomasson P. , Wiita P. J. 
Published: August 2003

AbstractThe compact steep spectrum (CSS) and gigahertz peaked spectrum (GPS) sources are widely believed to be young radio sources, with ages ≤106yr. If the activity in the nucleus is fuelled by the supply of gas, one might find evidence of this gas by studying the structural and polarisation characteristics of CSS sources and their evolution through this gas. In this paper we discuss some of the possible ‘smoking-gun’ evidence of this gas which may have triggered and fuelled the radio source.
The Polarised Bent Jet of 3C 43
Authors: Mantovani F. , Junor W. , Saikia D. J. , Salter C. J. 
Published: August 2003

AbstractRadio observations of linear polarisation provide a useful probe of the physical conditions in the gaseous environments of compact steep spectrum (CSS) sources. Here, we present polarimetric VLBA observations at 8.4 GHz of the CSS quasar 3C 43. The jet in this source curves gently up to about 220 mas from the core, at which point it bends sharply, probably due to a jet–cloud encounter. Regions of polarised emission are detected along the jet, while the core component shows no significant polarisation.
III Zw 2: Evolution of a Radio Galaxy in a Nutshell
Authors: Brunthaler A. , Falcke H. , Bower G. C. , Aller M. F. , Aller H. D. , Teräsranta H. , Krichbaum T. P. 
Published: August 2003

AbstractIII Zw 2 shows dramatic radio outbursts roughly every five years. Here we present the light curves and VLBA observations of the latest flare with an excellent time sampling. We have detected superluminal motion with a lower limit for the apparent expansion speed of 1.25±0.09 c at 43 GHz. Spectral and spatial evolution are closely linked and the evolution of III Zw 2 in a turnover frequency vs. linear size diagram is similar to the correlation for GPS and CSS sources. Before and after this rapid expansion we observe a period of virtually no expansion. However, at 15 GHz III Zw 2 shows a constant slow expansion (∼0.6 c). The difference is qualitatively explained by optical depth effects in an ‘inflating-balloon model’, describing the evolution of radio lobes on an ultra-compact scale. The stop-and-go behaviour could be explained by a jet interacting with a molecular cloud or the molecular torus.
A Dynamical Model for the Evolution of Hot Spots in Powerful Radio Sources
Authors: Perucho M. , Martí J. M. 
Published: August 2003

AbstractCompact symmetric objects are considered the young counterparts of large doubles according to advance speeds measured or inferred from spectral ageing. Here we present a simple power law model for the CSO/FR II evolution based on the study of sources with well defined hot spots. The luminosity of the hot spots is estimated under minimum energy conditions. The advance of the source is considered to proceed in ram pressure equilibrium with the ambient medium. Finally, we also assume that the jets feeding the hot spots are relativistic and have a time dependent power. Comparison with observational data points to an interpretation of the CSO–FR II evolution in terms of decreasing jet power with time.
Luminosity Evolution of Double Radio Sources
Authors: Carvalho Joel C. , O'Dea Christopher P. 
Published: August 2003

AbstractWe have recently developed a detailed analytical model for powerful radio sources based on the results of a series of 2-D numerical hydrodynamical simulations. Here we make use of the model results to investigate the radio source luminosity evolution. Changes in the radio spectrum due to radiation losses were calculated in two different scenarios for energy gains/losses: Kardashev–h;Pacholczyk (KP) and ‘continuous injection’ (CI). The magnetic field was calculated in two limiting cases: (1) assuming equipartition of energy between relativistic particles and fields and (2) magnetic flux conservation inside the cocoon. The effect of the surrounding medium was taken into account by considering three different ambient density profiles. The evolutionary tracks were plotted in a power–diameter (P-D) diagram and compared with the predictions of self-similar models. In general, the evolutionary tracks cannot be represented by a simple power law and have a complex form that is most probably the result of the nonself-similar evolution of the source.
Dense Plasma Torus in the GPS Galaxy NGC 1052
Authors: Kameno Seiji , Inoue Makoto , Wajima Kiyoaki , Sawada-Satoh Satoko , Shen Zhi-Qiang 
Published: August 2003

AbstractWe report results from nearly simultaneous pentachromatic VLBI observations towards a nearby GPS galaxy NGC 1052. The observations at 1.6 and 4.8 GHz with the VSOP, and at 2.3, 8.4, and 15.4 GHz with VLBA, provide linear resolutions of ∼0.1 pc. Convex spectra of a double-sided jet imply that synchrotron emission is obscured through foreground cold dense plasma, in terms of free–free absorption (FFA). We found a central condensation of the plasma which covers about 0.1 and 1 pc of the approaching and receding jets, respectively. A simple model with a geometrically thick plasma torus perpendicular to the jets is established to explain the asymmetric distribution of FFA opacities.
A Population Study of Faint Compact Steep Spectrum Radio Sources: Self-Similar Growth
Authors: Tschager Wolfgang , Schilizzi Richard , Röttgering Huub , Snellen Ignas , Miley George , Perley Rick 
Published: August 2003

AbstractThe main topic of this contribution is the investigation of the morphological self-similarity of the growth process during the gigahertz peaked spectrum (GPS) and compact steep spectrum (CSS) phase of evolving radio galaxies. By investigating a new sample of faint CSS radio sources we establish that self-similar evolution must hold for peaked spectrum sources over a wide range of luminosities as well as physical sizes. Thus, we argue that self-similarity should be regarded as an essential, intrinsic characteristic of the growth process of young radio sources, and be treated as such, and not merely as a supplementary constraint for evolution models.
High Frequency Peakers
Authors: Dallacasa Daniele 
Published: August 2003

AbstractThere is quite a clear anticorrelation between the intrinsic peak frequency and the overall radio source size in compact steep spectrum (CSS) and gigahertz peaked spectrum (GPS) radio sources. This feature is interpreted in terms of synchrotron self-absorption (although free–free absorption may play a role as well) of the radiation emitted by a small radio source which is growing within the inner region of the host galaxy. This leads to the hypothesis that these objects are young and that the radio source is still developing/expanding within the host galaxy itself.Very young radio sources must have the peak in their radio spectra occurring above a few tens of gigahertz, and for this reason they are termed high frequency peakers (HFPs). These newly born radio sources must be very rare given that they spend very little time in this stage. Ho = 100 km s−1 Mpc−1 and qo = 0.5 are used throughout this paper.
Jet–Cloud Interactions in Compact Steep Spectrum Radio Sources
Authors: O'Dea C. P. , Vries W. H. de , Koekemoer A. M. , Baum S. A. , Axon D. J. , Barthel P. D. , Capetti A. , Fanti R. , Gelderman R. , Morganti R. , Tadhunter C. N. 
Published: August 2003

AbstractWe have obtained HST/STIS long slit spectroscopy of the aligned emission line nebulae in three compact steep spectrum (CSS) radio sources — 3C 67, 3C 277.1, and 3C 303.1. We find systematic offsets (˜300–500 kms) of the emission line velocities on one or both sides of the radio sources. We also see evidence for broad lines (FWHM ˜500 kms) and complex emission line profiles. In 3C 303.1 the data are consistent with multiple components and possibly split lines. The amplitude of the velocity variations is not so large as to exclude gravitationally-induced motions. However, the complex kinematics, the lack of a signature of Keplerian rotation, and the association of the velocity variations with the radio lobes are consistent with the observed ˜300–500 kms velocities being driven by the expansion of the radio source. Acceleration of the clouds by the bow shock is plausible given the estimated densities in the clouds and the velocities observed in the much smaller compact symmetric objects and with expansion velocities estimated from spectral ageing. This conclusion is unchanged if we consider the scenario in which the cloud acceleration is dominated by the post bow shock flow.
Rotation Measure and Opacity Asymmetry in 2134+004
Authors: Mutoh M. , Inoue M. , Kameno S. , Asada K. 
Published: August 2003

AbstractBased on the free–free absorption (FFA) model of gigahertz peaked spectrum (GPS) sources, we explain both Faraday rotation asymmetry and opacity asymmetry consistently between two components of a GPS quasar 2134+004. The FFA model assumes dense plasma around the central core to produce FFA, and the difference of path lengths in the plasma toward each component could cause these asymmetries. The component that is closer to the observer has a shorter path length, and consequently, smaller opacity of FFA and lower Faraday rotation. In a simple case, the ratio of Faraday rotation between two components is a function of the ratio of path length, and is the same as the ratio of opacity. Then these two ratios are shown to be essentially the same by our observations. We could thus distinguish between near-side and far-side components by the asymmetries.