高红移耀变体4C 38.41光学多波段光变性质

4C 38.41是一颗红移为1.813、可分类为平谱射电类星体的耀变体,使用一台85 cm望远镜在2018年2月22日至26日期间对其进行了光学V和R波段测光观测,得到两个波段的准同时数据.基于这些数据分析了该源在不同光变时标下的光变特性.结果表明:这颗源在观测期间处于较弱的活动状态, V和R波段星等(V, R)总变化均约为0.20等.在天内时标下,其中3晚探测到了该源的天内光变,另有一晚可能存在天内光变.此外,通过色指数和时延分析发现4C 38.41在不同时标下都展现越亮越红行为,与大多数平谱射电类星体类似,但在最后一晚4C 38.41在颜色-星等图上呈现出v字形,即首先展现越亮越红行为,然后转变为越亮越蓝行为,这可能是由该源的辐射在吸积盘主导和喷流主导之间的转换造成的.此外在第2晚探测到了V、R波段之间的时延,这是首次在高红移耀变体中探测到不同光学波段光变之间的时延,可以用随机同步辐射小结构模型来解释.     

A radio and optical study of Molonglo radio sources

We present multi-wavelength radio observations with the Very Large Array, and narrow- and broad-band optical observations with the 2.5-m telescope at the Las Campanas Observatory, of a well-defined sample of high-luminosity Fanaroff–Riley class II radio galaxies and quasars, selected from the Molonglo Reference Catalogue 1-Jy sample. These observations were carried out as part of a programme to investigate the effects of orientation and environment on some of the observed properties of these sources. We examine the dependence of the Liu–Pooley relationship, which shows that radio lobes with flatter radio spectra are less depolarized, on size, identification and redshift, and show that it is significantly stronger for smaller sources, with the strength of the relationship being similar for both radio galaxies and quasars. In addition to Doppler effects, there appear to be intrinsic differences between the lobes on opposite sides. We discuss the asymmetry in brightness and location of the hotspots, and present estimates of the ages and velocities from matched-resolution observations in the L and C bands. Narrow- and broad-band optical images of some of these sources were made to study their environments and correlate with the symmetry parameters. An extended emission-line region is seen in a quasar, and in four of the objects possible companion galaxies are seen close to the radio axis.     

Correlated Radio-Optical Variations on Intraday Timescales

Correlated radio-optical variations on intraday timescales have been observed (e.g. In BLO 0716 714) and such radio intraday variability is suggested to have an intrinsic ori- gin. Recently, multi-wavelength observations, simultaneous at radio, mm-submm, optical and hard X-rays, of 0716 714, show that during a period of intraday/interday variations at ra- dio and mm wavelengths, the apparent brightness temperature of the source exceeded the Compton-limit (～1012 K) by 2--4 orders of magnitude, but no Compton catastrophe (or no high luminosity of inverse-Compton radiation) was detected. It is also found that the intra- day/interday variations at mm-submm wavelengths are consistent with the evolutionary be- havior of a standard synchrotron source and for the intraday/interday variations at centimeter wavelengths opacity effects can play a significant role, which is consistent with the interpreta- tion suggested previously by Qian et al. Thus the apparent high brightness temperatures may probably be explained in terms of Doppler boosting effects due to bulk relativistic motion of the source. We will argue a scenario to simulate the correlations between the radio and optical variations on intraday timescales observed in BLO 0716 714 in terms of a relativistic shock propagating through a jet with a dual structure.     

Morphology and surface brightness evolution of z∼1.1 radio galaxies

We use K '-band (2.1-μm) imaging to investigate the angular size and morphology of 10 6C radio galaxies, at redshifts 1≤ z ≤1.4. Two radio galaxies appear to be undergoing mergers, another contains, within a single envelope, two intensity peaks aligned with the radio jets, while the other seven appear consistent with being normal ellipticals in the K band.
Intrinsic half-light radii are estimated from the areas of each radio galaxy image above a series of thresholds. The 6C galaxy radii are found to be significantly smaller than those of the more radio-luminous 3CR galaxies at similar redshifts. This would indicate that the higher mean K -band luminosity of the 3CR galaxies reflects a difference in the size of the host galaxies, and not solely a difference in the power of the active nuclei.
The size–luminosity relation of the z ∼1.1 6C galaxies indicates a 1.0–1.6 mag enhancement of their rest frame R -band surface brightness relative to either local ellipticals of the same size or FRII radio galaxies at z <0.2. The 3CR galaxies at z ∼1.1 show a comparable enhancement in surface brightness. The mean radius of the 6C galaxies suggests that they evolve into ellipticals of L ∼ L * luminosity, and is consistent with their low-redshift counterparts being relatively small FRII galaxies ∼25 times lower in radio luminosity, or small FRI galaxies ∼1000 times lower in radio luminosity. Hence the 6C radio galaxies appear to undergo as much optical and radio evolution as the 3CR galaxies.     

Long-term optical and X-ray variability of the Seyfert galaxy Markarian 79

We present the results of concurrent X-ray and optical monitoring of the Seyfert 1 galaxy Mrk 79 over a period of more than 5 yr. We find that on short to medium time-scales (days to a few tens of days) the 2–10 keV X-ray and optical u - and V -band fluxes are significantly correlated, with a delay between the bands consistent with 0 d. We show that most of these variations may be well reproduced by a model where the short-term optical variations originate from reprocessing of X-rays by an optically thick accretion disc. The optical light curves, however, also display long time-scale variations over thousands of days, which are not present in the X-ray light curve. These optical variations must originate from an independent variability mechanism and we show that they can be produced by variations in the (geometrically) thin disc accretion rate as well as by varying reprocessed fractions through changes in the location of the X-ray corona.     

Radio–optical alignments in a low radio luminosity sample

We present an optically based study of the alignment between the radio axes and the optical major axes of eight z ∼0.7 radio galaxies in a 7C sample. The radio galaxies in this sample are ≈20 times less radio‐luminous than 3C galaxies at the same redshift, and are significantly less radio-luminous than any other well-defined samples studied to date. Using Nordic Optical Telescope images taken in good seeing conditions at rest frame wavelengths just longward of the 4000-Å break, we find a statistically significant alignment effect in the 7C sample. Furthermore, in two cases where the aligned components are well separated from the host we have been able to confirm spectroscopically that they are indeed at the same redshift as the radio galaxy. However, a quantitative analysis of the alignment in this sample and in a corresponding 3C sample from HST archival data indicates that the percentage of aligned flux may be lower and of smaller spatial scale in the 7C sample. Our study suggests that alignments on the 50-kpc scale are probably closely related to the radio luminosity, whereas those on the 15‐kpc scale are not. We discuss these results in the context of popular models for the alignment effect.     

NICMOS images of JVAS/CLASS gravitational lens systems

We present Hubble Space Telescope ( HST ) infrared images of four gravitational lens systems from the JVAS/CLASS gravitational lens survey and compare the new infrared HST pictures with previously published WFPC2 HST optical images and radio maps. Apart from the wealth of information that we get from the flux ratios and accurate positions and separations of the components of the lens systems, which we can use as inputs for better constraints on the lens models, we are able to discriminate between reddening and optical/radio microlensing as the possible cause of differences observed in the flux ratios of the components across the three wavelength bands. Substantial reddening has been known to be present in the lens system B1600+434 and has been further confirmed by the present infrared data. In the two systems B0712+472 and B1030+074 microlensing has been pinpointed as the main cause of the flux ratio discrepancy both in the optical/infrared and in the radio, the radio possibly caused by the substructure revealed in the lensing galaxies. In B0218+357, however, the results are still not conclusive. If we are actually seeing the two 'true' components of the lens system then the flux ratio differences are attributed to a combination of microlensing and reddening or are alternatively the result of some variability in at least one of the images. Otherwise the second 'true' component of B0218+357 may be completely absorbed by a molecular cloud and the anomalous flux density ratios and large difference in separation between the optical/infrared and radio that we see can be explained by emission either from a foreground object or from part of the lensing galaxy.     

Relation between blue/ultraviolet continuum shape and the ratio of radio-to-optical emission for B3-VLA quasars

The low-frequency radio luminosity is believed to be an indicator of jet power, while the optical/ultraviolet (UV) emission is probably from accretion discs in the nuclei of steep-spectrum radio quasars. We present a correlation between the ratio of radio-to-optical luminosities and the continuum spectral index in blue/UV bands, which might indicate that the continuum shape in blue/UV bands is related to the ratio of jet to accretion power. The results may imply that the spectra and structure of accretion discs are probably affected by the interactions between jets and discs.     

Magnetic and optical spiral arms in the galaxy NGC 6946

The spiral pattern in the nearby spiral galaxy NGC 6946 has been studied using the wavelet transformation technique, applied to galaxy images in polarized and total non-thermal radio emission at λλ 3.5 and 6.2 cm, in broadband red light, in the λ 21.1 cm H  i line and in the optical Hα line. Well-defined, continuous spiral arms are visible in polarized radio emission and red light, where we can isolate a multi-armed pattern in the range of galactocentric distances 1.5–12 kpc, consisting of four long arms and one short spiral segment. The 'magnetic arms' (visible in polarized radio emission) are localized almost precisely between the optical arms. Each magnetic arm is similar in length and pitch angle to the preceding optical arm (in the sense of galactic rotation) and can be regarded as its phase-shifted image. Even details like a bifurcation of an optical arm have their phase-shifted counterparts in the magnetic arms. The average relative amplitude of the optical spiral arms (the stellar density excess over the azimuthal average) grows with galactocentric radius up to 0.3–0.7 at r ≃5 kpc, decreases by a factor of two at r =5–6 kpc and remains low at 0.2–0.3 in the outer parts of the galaxy. By contrast, the magnetic arms have a constant average relative amplitude (the excess in the regular magnetic field strength over the azimuthal average) of 0.3–0.6 in a wide radial range r =1.5–12 kpc. We briefly discuss implications of our findings for theories of galactic magnetic fields.     

The infrared jet in 3C 66B

We present images of infrared (IR) emission from the radio jet in 3C 66B. Data at three wavelengths (4.5, 6.75 and 14.5 μm) were obtained using the Infrared Space Observatory . The 6.75-μm image clearly shows an extension aligned with the radio structure. The jet was also detected in the 14.5-μm image, but not at 4.5 μm. The radio–infrared–optical spectrum of the jet can be interpreted as synchrotron emission from a population of electrons with a high-energy break of 4×10¹¹ eV. We place upper limits on the IR flux from the radio counter-jet. A symmetrical, relativistically beamed twin-jet structure is consistent with our results if the jets consist of multiple components.     

PKS 1117+146: a new large compact symmetric object

We present 23-GHz MERLIN observations of the high-luminosity radio galaxy PKS 1117+146. The radio image obtained from these data shows, for the first time, a central weak component (designated C) that we identify as the core of the radio galaxy, and two outer components (designated N and S) which are the hotspots of the extended lobes observed at lower frequencies. Extended emission in components C and S is an indication of a possible jet connecting the core to the strongest component. The overall optical and radio properties of PKS 1117+146 are consistent with the source being classified as a compact symmetric object (CSO). We discuss this hypothesis, which would make PKS 1117+146 the largest CSO known so far.     

The magnetic field and geometry of the oblique shock in the jet of 3C 346

We investigate the brightest regions of the kpc-scale jet in the powerful radio galaxy 3C 346, using new optical Hubble Space Telescope ( HST ) ACS/F606W polarimetry together with Chandra X-ray data and 14.9 and 22.5 GHz Very Large Array (VLA) radio polarimetry. The jet shows a close correspondence between optical and radio morphology, while the X-ray emission shows a  0.80 ± 0.17 kpc  offset from the optical and radio peak positions. Optical and radio polarimetry show the same apparent magnetic field position angle and fractional polarization at the brightest knot, where the jet undergoes a large kink of almost 70° in the optical and radio images. The apparent field direction here is well aligned with the new jet direction, as predicted by earlier work that suggested the kink was the result of an oblique shock. We have explored models of the polarization from oblique shocks to understand the geometry of the 3C 346 jet, and find that the upstream flow is likely to be highly relativistic  (β_u= 0.91^+0.05_−0.07)  , where the plane of the shock front is inclined at an angle of  η= 51°± 11°  to the upstream flow which is at an angle  θ= 14⁺⁸₋₇  deg to our line of sight. The actual deflection angle of the jet in this case is only 22°.     

The LBDS Hercules sample of mJy radio sources at 1.4 GHz – I. Multicolour photometry

The results are presented of an extensive programme of optical and infrared imaging of radio sources in a complete subsample of the Leiden–Berkeley Deep Survey. The LBDS Hercules sample consists of 72 sources observed at 1.4 GHz, with flux densities S _1.41.0 mJy, in a 1.2 deg² region of Hercules. This sample is almost completely identified in the g , r , i and K bands, with some additional data available at J and H . The magnitude distributions peak at r ≃22 mag, K ≃16 mag and extend down to r ≃26 mag, K ≃21 mag. The K -band magnitude distributions for the radio galaxies and quasars are compared with those of other radio surveys. At S _1.4 GHz≲1 Jy, the K -band distribution does not change significantly with radio flux density. The sources span a broad range of colours, with several being extremely red ( r − K ≳6). Though small, this is the most optically complete sample of mJy radio sources available at 1.4 GHz, and is ideally suited for studying the evolution of the radio luminosity function out to high redshifts.     

UV and optical emission lines from the z∼ 2.6 radio galaxy 0828+193: spatially resolved measurements

We present an investigation into the spatial variation of the rest-frame ultraviolet (UV) and optical line and continuum emission along the radio axis of the z ∼ 2.6 radio galaxy 0828+193, using long-slit spectra from the Keck II and Subaru telescopes. Line brightnesses, line ratios and electron temperatures are examined, and their relationship with the arm-length asymmetry of the radio source is also investigated. We find that on the side of the nucleus with the shortest radio lobe, the gas covering factor is higher, and the ionization parameter is lower. The contrasts in environmental density required to explain the asymmetries in the line brightness and the radio arm-length asymmetries are in fair agreement with each other. These results add further weight to the conclusion of McCarthy, van Breugel & Kapahi – lobe distance asymmetries in powerful radio sources are the result of an asymmetry in the environmental density.
We also note that the brightness of both the UV and optical continuum emission shows a similar spatial asymmetry to that shown by the line emission. While the UV continuum asymmetry can be wholly explained by the expected asymmetry in the nebular continuum, the optical continuum asymmetry cannot. We argue that, at least at optical wavelengths, the starlight and/or the scattered light must also be strongly spatially asymmetric.     

HST and UKIRT imaging observations of z∼ 1 6C radio galaxies – II. Galaxy morphologies and the alignment effect

Powerful radio galaxies often display enhanced optical/ultraviolet emission regions, elongated and aligned with the radio jet axis. The aim of this series of papers is to investigate separately the effects of radio power and redshift on the alignment effect, together with other radio galaxy properties. In this second paper, we present a deeper analysis of the morphological properties of these systems, including both the host galaxies and their surrounding aligned emission.
The host galaxies of our 6C subsample are well described as de Vaucouleurs ellipticals, with typical scale sizes of  ∼10 kpc  . This is comparable to the host galaxies of low- z radio sources of similar powers, and also the more powerful 3CR sources at the same redshift. The contribution of nuclear point source emission is also comparable, regardless of radio power.
The 6C alignment effect is remarkably similar to that seen around more powerful 3CR sources at the same redshift in terms of extent and degree of alignment with the radio source axis, although it is generally less luminous. The bright, knotty features observed in the case of the z ∼ 1 3CR sources are far less frequent in our 6C subsample; neither do we observe such strong evidence for evolution in the strength of the alignment effect with radio source size/age. However, we do find a very strong link between the most extreme alignment effects and emission-line region properties indicative of shocks, regardless of source size/age or power. In general, the 6C alignment effect is still considerably stronger than that seen around lower redshift galaxies of similar radio powers. Cosmic epoch is clearly just as important a factor as radio power: although aligned emission is observed on smaller scales at lower redshifts, the processes which produce the most extreme features simply no longer occur, suggesting considerable evolution in the properties of the extended haloes surrounding the radio source.     

Evidence for cospatial optical and radio polarized emission in active galactic nuclei

We investigate the relationship between the optical and radio emission of active galactic nuclei (AGN) by analysing optical and 15+22+43 GHz Very Long Baseline Array (VLBA) polarization observations simultaneous to within a day for 11 BL Lacertae (BL Lac) objects and the blazar 3C279. We have determined and corrected for the Faraday rotation measures in the very long baseline interferometry (VLBI) cores, enabling us to compare the intrinsic (zero-wavelength) VLBI-core polarization angles and the optical polarization angles χ_opt. A clear alignment between these two angles emerges in the transition toward higher radio frequencies, and a prominent peak at 0° is visible in the distribution of |χ_opt−χ_43 GHz|. This correlation implies that the magnetic-field orientations in the regions giving rise to the optical and radio polarization are the same, and can be easily understood if the radio and optical polarization are roughly cospatial. It is difficult to rule out the possibility that they arise in different regions in a straight jet with a uniform magnetic-field structure, but this seems less likely, since the VLBI jets of AGN are often bent on parsec-scales. This may suggest that much or all of the strong optical polarization in these sources arises in the inner radio jets, possibly associated with the formation and emergence of compact new VLBI components.     

Neutral hydrogen gas distribution and kinematics in NGC 7479

We have investigated the effects of a bar and an asymmetric spiral structure on the neutral hydrogen distribution and kinematics in the strongly barred spiral galaxy NGC 7479. The strongest 21-cm line emission at 1-kpc resolution comes from the western spiral arm which appears to be slightly inclined to the plane of the main disc. In contrast, the area within the radius of the bar is devoid of 21-cm line emission. The radio continuum emission at 21 cm follows the bar dust lanes, but beyond 3 kpc from the nucleus the radio continuum emission has a peculiar morphology, unlike that of optical and near-infrared images. We did not detect any low surface brightness gas-rich companions in the near neighbourhood of NGC 7479. This leads us to propose that the strong western spiral arm was created in a recent minor merger.     

The cluster environments of the z ∼ 1 3CR radio galaxies

An analysis of the environments around a sample of 28 3CR radio galaxies with redshifts 0.6< z <1.8 is presented, based primarily upon K -band images down to K ∼20 taken using the UK Infrared Telescope (UKIRT). A net overdensity of K -band galaxies is found in the fields of the radio galaxies, with the mean excess counts being comparable to that expected for clusters of Abell Class 0 richness. A sharp peak is found in the angular cross-correlation amplitude centred on the radio galaxies that, for reasonable assumptions about the luminosity function of the galaxies, corresponds to a spatial cross-correlation amplitude between those determined for low-redshift Abell Class 0 and 1 clusters.
These data are complemented by J -band images also from UKIRT, and by optical images from the Hubble Space Telescope . The fields of the lower redshift ( z ≲0.9) radio galaxies in the sample generally show well-defined near-infrared colour–magnitude relations with little scatter, indicating a significant number of galaxies at the redshift of the radio galaxy; the relations involving colours at shorter wavelengths than the 4000 Å break show considerably greater scatter, suggesting that many of the cluster galaxies have low levels of recent or on-going star formation. At higher redshifts the colour–magnitude sequences are less prominent owing to the increased field galaxy contribution at faint magnitudes, but there is a statistical excess of galaxies with the very red infrared colours ( J − K ≳1.75) expected of old cluster galaxies at these redshifts.
Although these results are appropriate for the mean of all of the radio galaxy fields, there exist large field-to-field variations in the richness of the environments. Many, but certainly not all, powerful z ∼1 radio galaxies lie in (proto)cluster environments.     

Properties of BL Lac Objects with Redshift < 0.2

We present a large sample which includes 82 BL Lac objects with redshifts below 0.2 from recent literature. We find strong correlations in both flux and luminosity between the radio (5 GHz) and optical bands (5500 A). The correlations in other bands are very weak. Five TeV BL Lacs and two suspect sources are found to have similar properties as high-frequency-peaked BL Lacs (HBLs). Our results suggest that both the radio and optical emissions are from the same radiation mech anism in the SSC model. The TeV BL Lac candidates should be HBLs or HBL-like objects with small redshifts.