Compact Steep Spectrum Quasar Research Articles

Extragalactic Radio Quasars: Consequences of the Luminosity/ Redshift Relationship

We have used both analytical and statistical methods to show some plausible consequences of the luminosity/redshift relationships for compact steep spectrum (CSS) quasars and the more extended extragalactic radio (EGR) quasars. From the analytical methods (or theory), we find that luminosity shows an inverse dependence on the redshift; while from the statistical (empirical) the converse is the case for both CSS quasars and their extended counterparts. We know that luminosity selection effects may play some role in the empirical results. However, we find that the magnitudes of departure of the two empirical results from the theoretical result are staggering – the difference for the extended EGR quasars far outweighs that of the CSS quasars. We may state categorically that this discrepancy may simply be a sign of a factor in the intergalactic medium (IGM) that appears to cause the anomaly in the extended EGR quasars. This is because sources with similar powers are expected to produce similar luminosities; and besides, central engines of the more extended EGR quasars have roughly similar powers with the CSS central engines. However, our results show great difference between their radiated powers (luminosities). A likely explanation of this is that the irregularity may be a signature of dark/vacuum energy. It simply indicates that among other factors, dark energy may constitute a factor which influences luminosities of the more extended EGR quasars. The components (jets and lobes) of the more extended EGR quasars lie in the intergalactic medium (IGM). This medium is more of a vacuum than the interstellar medium (ISM) in which the components of the CSS sources are located. Therefore, dark energy is expected to show more effect in the IGM than in the ISM. Besides, we estimate percentage influence caused by luminosity selection effect and that caused by the presumed dark/vacuum energy. The estimates are respectively, and . These results show that intrinsically, dark/vacuum energy influences extended EGR quasars’ luminosities by about times more than the observational bias caused by luminosity selection effects.

On Cosmic Epochand Linear Size/Luminosity Evolution of Compact Steep Spectrum Sources

We have used analytical methods in this paper to obtain a mathematical relation that describes relationship between the linear size of compact steep spectrum (CSS) sources and their redshift. Result shows that the source linear size has an inverse power-law dependence on the redshift. Moreover, for the purpose of obtaining an empirical relation that shows relationship between the liner size and the redshift, we carry out simple linear regression analyses on the observed linear sizes of the CSS sources in our sample against their respective observed redshifts. Results of the analyses indicate that the linear sizes of the quasars have direct power law relationship with their respective redshifts; while the converse is the case for their galaxy counterparts. Their correlation coefficients are marginal. In comparison with the obtained theoretical relation, we notice that for the CSS quasars, the linear size–redshift data show an inverse correlation. This is comparable with the theoretical relation. So, it suggests that the dynamical evolution of the source linear sizes may have some cosmological effects on it. However, the converse is the case for the CSS galaxies – the correlation is direct. The possible explanation for this difference is that quasars are observed at higher redshifts than their galaxy counterparts. Hence, the cosmological effects are expected to be more pronounced on the quasars. Furthermore, we use analytical methods again to obtain a theoretical relation that shows relationship between luminosity and redshift. The relation indicates that luminosity of a radio source has an inverse power-law relationship with redshift. This suggestively implies that the intrinsic luminosity of a radio source may be modified by cosmological evolution. Moreover, for the purpose of obtaining an empirical relation for comparison with the theory, we carry out linear regression analysis of observed luminosities against observed redshifts of the CSS quasars and galaxies in our sample. Results show that luminosities have excellent direct power-law relationship with redshifts. However, this is in contradiction to the obtained theory which shows inverse relationship between the two parameters. This excellent direct correlation has been attributable by some authors to strong luminosity selection effects in which samples with high luminosities are found at high redshifts. Therefore, if the selection effects are taken care of, we may be able to see the comparability of the theory with the empirical relation. Hence, we conclude that source radiated power may have some cosmological implications just like we saw in the size/redshift relation.

Radio polarimetry of compact steep spectrum sources at sub-arcsecond resolution

Aims - We report new Very Large Array polarimetric observations of Compact Steep-Spectrum (CSS) sources at 8.4, 15, and 23GHz. Methods - Using multi-frequency VLA observations we have derived sub-arcsecond resolution images of the total intensity, polarisation, and rotation measure (RM) distributions. Results heading - We present multi-frequency VLA polarisation observations of CSS sources. About half of the sources are point-like even at the resolution of about 0.1x0.1 arcseconds. The remaining sources have double or triple structure. Low values for the percentage of polarised emission in CSS sources is confirmed. On the average, quasars are more polarised than galaxies. A wide range of RM values have been measured. There are clear indications of very large RMs up to 5\,585 rad m**(-2). CSS galaxies are characterized by RM values that are larger than CSS quasars. The majority of the objects show very large values of RM. Conclusions - The available data on sub-arcsecond-scale rest-frame RM estimates for CSS sources show that these have a wide range of values extending up to about 36,000 rad m**(-2). RM estimates indicate an overall density of the magneto-ionic medium larger than classical radio sources.

DISCOVERY OF THE DISTURBED RADIO MORPHOLOGY IN THE INTERACTING BINARY QUASAR FIRST J164311.3+315618

We report the high-resolution radio observations and the subsequent analysis of the radio-loud compact steep spectrum quasar FIRST J164311.3+315618, one of the members of a binary system. The second component of the system is a radio-quiet active galactic nucleus. The projected separation of this pair is 23 (15 kpc); it is one of the smallest-known-separation binary quasars. The multi-band images of this binary system made with the Hubble Space Telescope show that the host galaxy of the radio-loud quasar is highly disturbed. The radio observations presented here were made with the Multi-Element Radio-Linked interferometer network (MERLIN) at 1.66 GHz and 5 GHz. We show that the radio morphology of FIRST J164311.3+315618 is complex on both frequencies and exhibits four components that indicate the intermittent activity with a possible rapid change of the jet direction and/or restarting of the jet due to the interaction with the companion. The radio components that are no longer powered by the jet can quickly fade away. We suggest that this makes the potential distortions of the radio structure short-lived phenomena. Our numerical simulations show that the influence of the companion can lead to prolonged current and future activities. FIRST J164311.3+315618 is an unusual and statistically very rare low redshift binary quasar wherein the first close encounter is probably just taking place.

X‐Ray Properties of the Gigahertz Peaked and Compact Steep Spectrum Sources

We present Chandra X-ray Observatory observations of gigahertz peaked-spectrum (GPS) and compact steep spectrum (CSS) radio sources. The Chandra sample contains 13 quasars and 3 galaxies, with measured 2-10 keV X-ray luminosities within 1042-1046 erg s−1. We detect all of the sources, five of which are observed in X-rays for the first time. We study the X-ray spectral properties of the sample. The measured absorption columns in the quasars are different from those in the galaxies in that the quasars show no absorption (with limits ~1021 cm−2), while the galaxies have large absorption columns (>1022 cm−2) consistent with previous findings. The median photon index of the sources with a high signal-to-noise ratio is Γ = 1.84 ± 0.24, which is larger than the typical index of radio-loud quasars. The arcsec resolution of the Chandra telescope allows us to investigate extended X-ray emission and to look for diffuse components and X-ray jets. We found X-ray jets in two quasars (PKS 1127–145 and B2 0738+32), and an X-ray cluster surrounding a CSS quasar (3C 186; z = 1.1). We detected a possible binary structure in galaxy 0941–080 and an extended diffuse emission in galaxy PKS B1345+125. We discuss our results in the context of X-ray emission processes and radio source evolution. We conclude that the X-ray emission in these sources is most likely unrelated to a relativistic jet, although the sources' radio loudness may suggest a high radiative efficiency for the jet power in these sources.

Interactions of jets with inhomogeneous cloudy media

We present two-dimensional slab-jet simulations of jets in inhomogeneous media consisting of a tenuous hot medium populated with a small filling factor by warm, dense clouds. The simulations are relevant to the structure and dynamics of sources such as gigahertz peak spectrum and compact steep spectrum (CSS) radio galaxies, high-redshift radio galaxies and radio galaxies in cooling flows. The jets are disrupted to a degree depending upon the filling factor of the clouds. With a small filling factor, the jet retains some forward momentum but also forms a halo or bubble around the source. At larger filling factors channels are formed in the cloud distribution through which the jet plasma flows and a hierarchical structure consisting of nested lobes and an outer enclosing bubble results. We suggest that the CSS quasar 3C 48 is an example of a low filling factor jet-interstellar medium interaction while M87 may be an example of the higher filling factor type of interaction. Jet disruption occurs primarily as a result of Kelvin-Helmholtz instabilities driven by turbulence in the radio cocoon not through direct jet-cloud interactions, although there are some examples of these. In all radio galaxies whose morphology may be the result of jet interactions with an inhomogeneous interstellar medium we expect that the dense clouds will be optically observable as a result of radiative shocks driven by the pressure of the radio cocoon. We also expect that the radio galaxies will possess faint haloes of radio-emitting material well beyond the observable jet structure.

Jets: an environmental impact statement

We review our recent work on the interaction of jets with the interstellar medium of both classical double and young radio galaxies. We propose explanations for the intriguing radio morphology of Hercules A and Pictor A in terms of the complex structure produced near the terminal shock in the jet. This also has ramifications for the interpretation of the high energy emission from Pictor A. Gigahertz Peak Spectrum (GPS) and Compact Steep Spectrum (CSS) sources are now believed to be young radio galaxies in which the jets are interacting with an inhomogeneous interstellar medium. Two dimensional slab-jet simulations of jets interacting with a clumpy interstellar medium show the way in which radiative shocks are driven into the clouds and how the jet is disrupted. There are interesting morphological comparisons between one of our simulations and the GPS source 4C31.05 and the large scale structure of M87. Another simulation with a lower filling factor, resembles the CSS quasar 3C48.

The Faraday screen near the nucleus of the CSS quasar 3C 138

Compact Steep Spectrum (CSS) sources are known to show strong optical line emission (Gelderman & Whittle 1994) which is generally considered to be due to the interaction between the radio jet and the ISM. This argument is strengthened by the HST observations of Axon et al. (2000) which show this emission is frequently associated with the radio jet. Previous observations of the CSS quasar 3C 138 (Cotton et al. 1997) have shown that the bulk of the jet has very low amounts of Faraday rotation whereas the inner jet shows very high Faraday rotation (≈−5000 rad m −2 ). The inner jet is dominated by moving components which allows observing the fine scale of the Faraday screen as the components move behind it. We report the results of such a monitoring campaign which indicated that there is structure in the Faraday screen on the pc and possibly sub pc scale. Motions of the polarized component slowed dramatically during the course of these observations, limiting the region probed. The observations also strongly suggest that the polarized emission from the inner jet is seen through limited holes in a dense Faraday screen. In this case, the observed variations in Faraday rotation are possibly the result of jet-ISM interactions.

Two-Sided Radio Jets in B1524–136

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.

The Polarised Bent Jet of 3C 43

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.

Optical‐Radio Alignment in Compact Steep‐Spectrum Radio Sources

We discuss Hubble Space Telescope (HST) WFPC2 observations through the broad red filter F702W of 30 3CR sources from the Compact Steep Spectrum (CSS) radio source sample, and present 11 new HST/WFPC2 images through linear ramp filters (LRF), isolating either rest-frame CO nl 3727 Angstrom or [O III] 5007 Angstrom radiation. In nearly all the CSS galaxies, we find high surface brightness emission that is aligned with the radio axis. The strong nuclear PSF prevents us from detecting such aligned light at similar levels in most of the CSS quasars. However, a comparison between CSS galaxies and quasars with PSF signatures removed reveals no inconsistency with the viewing angle unification scheme. The alignment effect in CSS sources is not a strong function of redshift, and is seen over the entire redshift range of the sample (0.2 less than or similar to z less than or similar to 1.5). Our analysis of the LRF images and complementary KPNO spectroscopy reveals that the aligned light is predominantly emission-line gas. These observations demonstrate the existence of dense gas in the host galaxies of CSS sources, strongly interacting with the expanding radio sources. Assuming such a shock interaction, cooling-time arguments suggest that lobe expansion speeds of greater than or similar to 1000 km s(-1) and ambient densities of similar to 1 cm(-3) are consistent with the observed offset between the leading edge of the radio lobe and the optical line emission.

Effects of dense medium surrounding galactic-sized radio sources

In this paper, I have analysed the subarcsecond polarization structure of two high-z compact steep-spectrum quasars. Morphology suggests that the jets are interacting strongly with intergalactic medium. Models of bending by ram pressure equilibrium in a cooling flow and alignment of magnetic field lines by jet-IGM shock suggest that the CSS jets are light, supersonic and mildly relativistic. Particle energy index variations along the jet suggests replenishment triggered by such interactions.

Compact steep spectrum sources and linear size evolution

It is shown that the fraction (f) of compact steep spectrum (CSS) galaxies in a combined Peacock & Wall (1981, MNRAS, 194) and Wall & Peacock (1985, MNRAS, 216) sample increases with redshift for Z > 0.2 according to the relation f ∞ (1 + Z ) 2.1 , with a cutoff for Z < 0.2. The fraction of CSS quasars, however, remains fairly constant with redshift. It is concluded that for galaxies, the variation of f with Z could give rise to the effect of linear size evolution in the angular diameter-redshift relation for an inhomogeneous sample, whereas for quasars non-random orientation can give rise to the same effect

Images of four compact steep-spectrum quasars with a resolution of 20 milliarcseconds at 329.1 MHz

Four compact steep-spectrum quasars (3C 48, 3C 147, 3C 309.1, and 3C 380) have been mapped with a resolution of 20 mas at 329 MHz. The structures of all four objects are asymmetric and complex, but they are shown here to be consistent with a basic one-sided jet morphology. In this, they are quite similar to other classes of radio sources; however, their small scales and convoluted structures suggest that in these objects, other factors such as the interaction with the interstellar medium and/or variations in the initial jet direction significantly affect the morphology. 43 refs.