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We present the results of the first successful observations of the Pie Town link with the Very Large Array at 74 MHz on Hercules A. The improvement in resolution from 25 to 10 arcsec resolves the helical- and ring-like features seen at higher frequencies. We also present new high dynamic range images of this powerful radio galaxy at 325 MHz. Our low-frequency observations confirm the multiple outburst interpretation of the spectral index differences at high frequencies. A comparison between our radio andROSATX-ray data does not reveal any association between the X-ray emission from the cluster and the radio lobes. There are no extra regions of radio emission at 74 MHz. [ABSTRACT FROM AUTHOR]

Abstract: Although the existence of asymmetrical profile of [OIII]λ5007 has been discovered for ages, its filiation and physics are poorly understood. Two new spectra of I ZWI taken on November 16, 2001 and on December 3, 2002 were compared with the spectra taken by BG92. Following results are obtained. (1) The certain variations of broad [OIII] during about 10 years separating the observations are identified. The inferred length scale of broad [OIII] emitting region ranges from 0.3 to 3pc. By assuming a Keplerian motion in line emitting region, the material emitting broad [OIII] is likely to be located at the transient emission line region, between BLR and NLR. (2) We find a positive relation between the FeII emission and flux of Hβ (or continuum). On the other hand, the parameter RFe decreases with ionizing continuum marginally. (3) We detect a low ionized NLR in I ZWI, because of the low flux ratios [OIII]n/Hβn (∼1.7). [Copyright &y& Elsevier]

We present results from a newXMM–Newtonobservation of the high-redshift quasar RX J1028.6– 0844 at a redshift of 4.276. The soft X-ray spectral flattening, as reported by a previous study withASCA, is confirmed to be present, with, however, a reduced column density when modelled by absorption. The inferred column density for absorption intrinsic to the quasar isfor cold matter, and higher for ionized gas. The spectral flattening shows remarkable similarity with that of two similar object, namely GB 1428+ 4217 and PMN J0525− 3343. The results improve upon those obtained from a previous short-exposure observation for RX J1028.6– 0844 withXMM–Newton. A comparative study of the twoXMM–Newtonobservations reveals a change in the power-law photon index fromto 1.5 on time-scales of about one year. A tentative excess emission feature in the rest-frame 5–10 keV band is suggested, which is similar to that marginally suggested for GB 1428+ 4217. [ABSTRACT FROM AUTHOR]

We present the results of a detailed spectral analysis of optically faint hard X-ray sources in theChandradeep fields selected on the basis of their high X-ray to optical flux ratio (X/O). The stacked spectra of high X/O sources in bothChandradeep fields, fitted with a single power-law model, are much harder than the spectrum of the X-ray background (XRB). The average slope is also insensitive to the 2–8 keV flux, being approximately constant aroundΓ≃ 1 over more than two decades, strongly indicating that high X/O sources represent the most obscured component of the XRB. For about half of the sample, a redshift estimate (in most of the cases a photometric redshift) is available from the literature. Individual fits of a few of the brightest objects and of stacked spectra in different redshift bins imply column densities in the range. A trend of increasing absorption towards higher redshifts is suggested. [ABSTRACT FROM AUTHOR]

We presentBVRIKimages and spectroscopic observations of thehost galaxy of the compact steep-spectrum (CSS) radio source MRC B1221−423. This is a youngradio source with double lobes lying well within the visible galaxy. The host galaxy is undergoing tidal interaction with a nearby companion, with shells, tidal tails and knotty star-forming regions all visible. We analyse the images of the galaxy and its companion pixel-by-pixel, first using colour–magnitude diagrams and then fitting stellar population models to the spectral energy distributions (SEDs) of each pixel. We also present medium-resolution spectroscopy of the system.The pixels separate cleanly in colour–magnitude diagrams, with pixels of different colours occupying distinct regions of the host galaxy and its companion. Fitting stellar population models to these colours, we have estimated the age of each population. We find three distinct groups of ages: an old populationin the outskirts of the host galaxy; an intermediate-age populationaround the nucleus and tidal tail, and a young populationin the nucleus and blue knots.The spectrum of the nucleus shows numerous strong emission lines, including[O i]λ6300,[O ]λ3727,[S ii]λλ6716, 6731, Hα and[N ii]λλ6548, 6583, characteristic of a low-ionization nuclear emission-line region (LINER) spectrum. The companion galaxy shows much narrower emission lines with very different line ratios, characteristic of a starburst galaxy.We have evidence for three distinct episodes of star formation in B1221−423. The correlation of age with position suggests the two most recent episodes were triggered by tidal interactions with the companion galaxy. The evidence points to the active galactic nucleus (AGN) in the centre of B1221−423 having been caught in the act of ignition. However, none of the components we have identified is as young as the radio source, implying that the delay between the interaction and the triggering of the AGN is at least. [ABSTRACT FROM AUTHOR]

We present high-quality long-slit spectra for three nearby powerful radio galaxies– 3C 293, 3C 305 and PKS 1345+12. These were taken with the aim of characterizing the young stellar populations (YSP), and thereby investigating the evolution of the host galaxies, as well as the events that triggered the activity. Isochrone spectral synthesis modelling of the wide wavelength coverage spectra of nuclear and off-nuclear continuum-emitting regions have been used to estimate the ages, masses and luminosities of the YSP component, taking full account of reddening effects and potential contamination by activity-related components. We find that the YSP make a substantial contribution to the continuum flux in the off-nuclear regions on a radial scale of 1–20 kpc in all three objects. Moreover, in two objects we find evidence for reddened post-starburst stellar populations in the near-nuclear regions of the host galaxies. The YSP are relatively old (0.1–2 Gyr), massiveand make up a large proportion (∼1–50 per cent) of the total stellar mass in the regions of the galaxies sampled by the observations. Overall, these results are consistent with the idea that the nuclear activity of active galactic nuclei in some radio galaxies is triggered by major gas-rich mergers. Therefore, these radio galaxies form part of the subset of early-type galaxies that is evolving most rapidly in the local Universe. Intriguingly, the results also suggest that the radio jets are triggered relatively late in the merger sequence, and that there is an evolutionary link between radio galaxies and luminous/ultraluminous infrared galaxies. [ABSTRACT FROM AUTHOR]

We present the results of a 200-ksChandraobservation of part of the Groth Strip region, using the ACIS-I instrument. We present a relatively simple method for the detection of point sources and calculation of limiting sensitivities, which we argue is at least as sensitive and more self-consistent than previous methods presented in the literature. A total of 158 distinct X-ray sources are included in our point-source catalogue in the ACIS-I area. The number counts show a relative dearth of X-ray sources in this region. For example, at a flux limit of 10−15 erg cm−2 s−1, around 20 per cent more soft-band sources are detected in the HDF-N and almost 50 per cent more in the ELAIS-N1 field, which we have analysed by the same method for comparison. We find, however, that these differences are consistent with Poisson variations atsignificance, and therefore there is no evidence for cosmic variance based on these number counts alone. We determine the average spectra of the objects and find a marked difference between the soft-band-selected sources, which havetypical of unobscured active galactic nuclei (AGN), and the hard-band-selected sources, which have. Reassuringly, the sample as a whole has a mean spectrum of, the same as the X-ray background. None the less, our results imply that the fraction of sources with significant obscuration is only∼25 per cent, much less than predicted by standard AGN population synthesis models. This is confirmed by direct spectral fitting, with only a handful of objects showing evidence for absorption. After accounting for absorption, all objects are consistent with a mean intrinsic spectrum of, very similar to local Seyfert galaxies. The survey area is distinguished by having outstanding multiwaveband coverage. Comparison with these observations and detailed discussion of the X-ray source properties will be presented in future papers. [ABSTRACT FROM AUTHOR]

We analyse a group of radio sources, a subset of the 200-mJy sample, all of which have core–jet radio structures measured with very long baseline interferometry and have flat spectra stretching from the radio to the millimetre/submillimetre band. Thus the objects have most of the properties expected of blazars. However, they display varied optical properties ranging from‘Seyfert-like’ objects, through BL Lac objects, to‘normal’ elliptical galaxies. We investigate the distribution of synchrotron peak frequencies in their spectral energy distributions (SEDs) and find a broad distribution between 1012 and 1016 Hz. Our conclusion is that we should consider virtually all objects in the sample as blazars since much of the diversity in their classification based on traditional optical criteria arises from differences in the frequency at which the non-thermal emission begins to decline. Specifically, an object is only classified as BL Lac when its peak frequency falls in the near-infrared/optical range. We determine peak frequencies using the same method for objects from other blazar samples. An important result is that our objects do not follow the blazar spectral sequence proposed by Fossati et al. and Ghisellini et al. in which, on average, peak frequencies increase as the radio luminosity decreases. Most of our low radio luminosity sources have peaks in their SEDs at low frequencies, not at the expected high frequencies. We suggest that at least part of the systematic trend seen by Fossati et al. and Ghisellini et al. results from selection effects. [ABSTRACT FROM AUTHOR]

Abstract: We present results from the analysis of an XMM-Newton observation of the Seyfert 1 galaxy NGC 7469, the first high resolution X-ray spectrum of this source. The Reflection Grating Spectrometer (RGS) spectrum has several narrow absorption and emission lines of O, N, C and Ne, originating from gas at a range of ionisation parameters, from logξ∼1.6 to logξ∼−2 (where ξ has the units ergcms−1). We demonstrate that the ionisation state of the warm emitter is consistent with that of the high-ionisation phase of the warm absorber, and compare the warm absorber in this object with those in other sources. [Copyright &y& Elsevier]

We present results from anXMM–Newtonobservation of the nearby Seyfert 2 galaxy NGC 5643. The nucleus exhibits a very flat X-ray continuum above 2 keV, together with a prominent Kα fluorescent iron line. This indicates heavy obscuration. We measure an absorbing column densityNH in the range, either directly covering the nuclear emission, or covering its Compton reflection. In the latter case, we might be observing a rather unusual geometry for the absorber, whereby reflection from the inner far side of a torus is in turn obscured by its near side outer atmosphere. The nuclear emission might be then either covered by a Compton-thick absorber, or undergoing a transient state of low activity. A second source (christened‘X-1’ in this paper) at the outskirts of the NGC 5643 optical surface outshines the nucleus in X-rays. If belonging to NGC 5643, it is the third brightestknown ultraluminous X-ray source. Comparison with past large aperture spectra of NGC 5643 unveils dramatic X-ray spectral changes above 1 keV. We interpret these as due to variability of the active nucleus and of source X-1 intrinsic X-ray powers by factors of≥10 and 5, respectively. [ABSTRACT FROM AUTHOR]

We have carried out extensive radio and optical follow-up of 176 sources from the 15-GHz 9th Cambridge survey. Optical identifications have been found for 155 of the radio sources; optical images are given with radio maps overlaid. The continuum radio spectrum of each source spanning the frequency range 1.4–43 GHz is also given.Two flux-limited samples are defined, one containing 124 sources complete to 25 mJy and one of 70 sources complete to 60 mJy. Between one-fifth and one-quarter of sources from these flux-limited samples display convex radio spectra, rising between 1.4 and 4.8 GHz. These rising-spectrum sources make up a much larger fraction of the radio source population at this high selection frequency than in lower frequency surveys.We find that by using non-simultaneous survey flux density measurements at 1.4 and 15 GHz to remove steep-spectrum objects, the efficiency of selecting objects with spectra rising between 1.4 and 4.8 GHz (as seen in simultaneous measurements) can be raised to 49 per cent without compromising the completeness of the rising-spectrum sample. [ABSTRACT FROM AUTHOR]

Analysis of Giant Metrewave Radio Telescope low frequency data for an X-shaped source, 3C 223.1 has revealed an unusual result as discussed earlier by Lal & Rao (2004). The radio morphologies of it at 240 and 610 MHz show a well-defined X-shaped structure with a pair of active jets along the north-south axis and a pair of wings along the east-west axis, that pass symmetrically through the undetected radio core. The wings (or low surface brightness jet) seem to have flatter spectral index with respect to the high surface brightness jet. This clearly shows the value of mapping the sample of X-shaped sources at low frequencies. Here we present our preliminary results for two more such sources. [ABSTRACT FROM AUTHOR]

XMM–Newton observations of five high-luminosity radio-quiet quasi-stellar objects (QSOs; Q 0144−3938, UM 269, PG 1634+706, SBS 0909+532 and PG 1247+267) are presented. Spectral energy distributions were calculated from the XMM–Newton European Photon Imaging Camera (EPIC) and Optical Monitor (OM) data, with bolometric luminosities estimated in the range from to for the sample, peaking in the ultraviolet. At least four of the QSOs show a similar soft excess, which can be well modelled by either one or two blackbody components, in addition to the hard X-ray power law. The temperatures of these blackbodies (∼100–500 eV) are too high to be direct thermal emission from the accretion disc, so Comptonization is suggested. Two populations of Comptonizing electrons, with different temperatures, are needed to model the broad-band spectrum. The hotter of these produces what is seen as the hard X-ray power law, while the cooler (∼0.25–0.5 keV) population models the spectral curvature at low energies. Only one of the QSOs shows evidence for an absorption component, while three of the five show neutral iron emission. Of these, PG 1247+267 seems to have a broad line (with an equivalent width of ∼250 eV), with a strong, associated reflection component , measured out to 30 keV in the rest frame of the QSO. Finally, it is concluded that the X-ray continuum shape of active galactic nuclei remains essentially constant over a wide range of black hole mass and luminosity. [ABSTRACT FROM AUTHOR]

High signal-to-noise ratio spectroscopy has established a redshift of for the source 2QZJ 215454.3−305654, originally selected from the 2dF/6dF QSO Redshift Surveys as one of 45 candidate BL Lacertae (BL Lac) objects displaying a featureless continuum at optical wavelengths. Radio observations using the Australia Telescope Compact Array at 1.4 GHz place a 3σ upper limit on the radio flux density of the object of ∼0.14 mJy. The radio-to-optical flux ratio of this object is thus more than seven times lower than the lowest such ratio observed in BL Lac objects. While the optical properties of 2QZJ 215454.3−305654 are consistent with a BL Lac identification, the lack of radio and/or X-ray emission is not. It is uncertain whether this object is an active galactic nucleus dominated by optical continuum emission from an accretion disc, or is similar to a BL Lac object with optical non-thermal emission from a relativistic jet. [ABSTRACT FROM AUTHOR]

In this paper, we cross-correlate the FIRST (Faint Images of the Radio Sky at Twenty centimeters) 1.4-GHz radio survey with a wide-field (1.6 deg2) shallow [ ] XMM–Newton survey. We find 12 X-ray/radio matches representing 4 per cent of the X-ray-selected sample. Most of them are found to be associated with active galactic nuclei (a total of nine) on the basis of the observed optical spectra (three), radio morphology (two) or X-ray/optical properties (four), whereas one radio source is identified with an X-ray-selected cluster. We also find two sources associated with low-redshift galaxies with narrow emission line optical spectra, X-ray luminosity , radio luminosity density and , suggesting ‘normal’ star-forming galaxies. We argue that radio surveys combined with X-ray samples could provide a powerful tool for identifying X-ray-selected ‘normal’ galaxies powered by stellar processes. Finally, radio-loud and radio-quiet systems in the present sample have mean X-ray spectral properties consistent with . [ABSTRACT FROM AUTHOR]

We address the question of why low-luminosity radio sources with similar flat radio spectra show a range of optical activity. The investigation is based on the spectral energy distributions (SEDs) of objects from the 200-mJy sample. We gathered new data from the VLA at 43 GHz, from SCUBA in the JCMT at 2000, 1350 and 850 μm, and from the ISOPHOT instrument on ISO at 170, 90, 60 and 25 μm. There is considerable diversity amongst the SEDs of the objects: there are objects with steep broad-band spectra between centimetre and millimetre bands (14 per cent of the sample); there are those with flat broad-band spectra over most of the spectral range (48 per cent of the sample); and there are those which show pronounced submillimetre/infrared excesses (27 per cent of the sample). Some objects of the first group have two-sided radio morphology, indicating that their parsec-scale emission is not dominated by beamed jet emission. Amongst the objects that have smooth broad-band spectra from the radio to the infrared, there are passive elliptical galaxies as well as the expected BL Lacertae objects. The most pronounced submillimetre/infrared excesses are shown by the broad-emission-line objects. [ABSTRACT FROM AUTHOR]

We present the analysis and results from a series of XMM–Newton observations of the distant blazar PMN J0525−3343 at a redshift of 4.4. The X-ray spectrum shows a spectral flattening below ∼1 keV, confirming earlier results from ASCA and BeppoSAX . The spectrum is well fitted by a power-law continuum with either a spectral break or absorption; no sharp features are apparent in the spectrum. No variability is seen in the individual light curves, although there is evidence of small longer-term variations (∼ months in the blazar frame) in both flux and (0.1–2.4)/(2–10) keV flux ratio. Very low levels of optical–UV extinction and the lack of any evidence of a Lyman-limit system at the quasar redshift rule out neutral absorption and we argue that the most plausible explanation is the presence of a warm, ionized absorber. Very strong C iv absorption in the optical spectrum already implies the presence of highly ionized material along the line of sight. Warm absorber models using the photoionization code cloudy are consistent with both the X-ray and C iv data, yielding a column density and ionization parameter . [ABSTRACT FROM AUTHOR]

We present initial results from a follow-up of the 9C survey, complete to 25 mJy at 15 GHz, designed to assemble and investigate a sample of young radio sources. We have made radio continuum maps of 111 sources at frequencies spanning 1.4–43 GHz, and classified them according to their radio size and spectral index between 1.4 and 4.8 GHz. We find that selection at 15 GHz is twice as efficient at picking Gigahertz Peaked Spectrum (GPS) sources as selection at ∼5 GHz. Optical follow-up has now begun; imaging of GPS and compact steep spectrum sources suggests that a significant fraction of the host galaxies have close companions or disturbed morphologies. [Copyright &y& Elsevier]

We summarise the properties of the absorbing haloes around two high-redshift radio galaxies studied with the VLT-UVES echelle spectrograph. The absorbers in 0943−242 (z=2.92) exhibit little further structure compared with previous data—the main absorber still has N(HI)≃1019 cm−2—reinforcing the picture in which the absorbing gas occupies a smooth shell beyond the emission line halo. In 0200+015 (z=2.23) the main absorber now splits into two spatially-resolved systems with N(HI)≃4×1014 cm−2, one of which has strong CIV absorption, implying a metallicity of Z≃10 Z◎. We explain the differences between the two sources with an evolutionary scenario, invoking interaction with the expanding radio source and metal enrichment via a starburst superwind. [Copyright &y& Elsevier]

Narrowband Ly α imaging has been carried out around eight radio galaxies at 2 to search for (proto-)cluster galaxies at the same redshift. Subsequent spectroscopy has led to the discovery of six protoclusters at redshifts z=2.2, 2.9, 2.9, 3.1, 3.2 and 4.1, with velocity dispersions between 300 km s−1 and 1000 km s−1. The estimated masses are in the range 1014–1016 M⊙, comparable to the mass of present day rich clusters of galaxies. [Copyright &y& Elsevier]

Keck LRISp optical spectropolarimetry and VLT ISAAC NIR spectroscopy of an overlapping sample of z∼2.5 radio galaxies has provided a set of uniquely high quality spectra stretching from Ly α to Hα. The measurement of emission and absorption line strengths, continuum polarization and SED allow us to quantify the various emission and scattering mechanisms that comprise the observed spectra. We identify this epoch as critical in the chemical evolution of massive spheroids and show that, while star formation must be very active, most of the UV/optical radiation we see from these luminous sources derives from the AGN. [Copyright &y& Elsevier]

Powerful radio galaxies often display enhanced optical/UV continuum emission and extended emission line regions, elongated and aligned with the radio jet axis. The expansion of the radio source strongly affects the gas clouds in the surrounding IGM, and the kinematic and ionization properties of the extended emission line regions display considerable variation over the lifetime of individual sources, as well as with cosmic epoch. We present the results of deep rest-frame UV and optical imaging and UV spectroscopy of high redshift 6C radio galaxies. The interdependence of the host galaxy and radio source properties are discussed, considering: (i) the relative contribution of shocks associated with the expanding radio source to the observed emission line gas kinematics, and their effect on the ionization state of the gas; (ii) the similarities and differences between the morphologies of the host galaxies and aligned emission for a range of radio source powers; and (iii) the influence of radio power on the strength of the observed alignment effect. [Copyright &y& Elsevier]

ABSTRACT We discuss the properties of a small sample of type 2 Seyfert galaxies whose X-ray spectra changed appearance on time-scales of years, becoming reflection-dominated from Compton-thin, or vice versa. A reflection-dominated spectrum is usually taken as evidence of Compton-thick absorption, but we instead argue that such a spectrum is due to a temporary switching-off of the nuclear radiation. The observations discussed here may help to explain mismatches between optical and X-ray classifications, and provide new strong and direct evidence for the presence of more than one cold circumnuclear region in type 2 Seyfert galaxies. [ABSTRACT FROM AUTHOR]

ABSTRACT We report on the X-ray, optical, near-infrared, submillimetre and radio properties of five extremely red objects (EROs) selected at X-ray wavelengths by XMM-Newton in the Lockman Hole field. They all have enough counts in the X-ray band to allow spectral fitting: four are most probably obscured, Compton-thin active galactic nuclei (AGNs) with redshift-dependent absorbing column densities of 10[sup 22]–10[sup 24] cm[sup -2], whilst the fifth is best fitted by a thermal spectrum and is likely to be a massive elliptical galaxy in a deep gravitational potential. Their optical/near-infrared colours and sizes suggest that X-ray selected EROs comprise a mixture of dusty ‘starburst’ galaxies and non-dusty galaxies that are dominated by either starlight or light from an active nucleus. The colour diagnostics are supported by the submillimetre and radio data; the two AGNs with ‘starburst’ colours have submillimetre or radio flux densities that imply large star formation rates, whilst those with ‘elliptical’ colours do not. The one source detected in the submillimetre waveband has narrow emission lines at a redshift of 1.45. Although the bulk of its radio emission originates from processes other than star formation, it is most probably a radio-quiet ultraluminous infrared galaxy. [ABSTRACT FROM AUTHOR]

ABSTRACT We use long-slit spectroscopic optical data to derive the properties of the extended emitting gas and the nuclear luminosity of a sample of 18 Seyfert 2 galaxies. From the emission-line luminosities and ratios we derive the density, reddening and mass of the ionized gas as a function of distance up to 2–4 kpc from the nucleus. Taking into account the geometric dilution of the nuclear radiation, we derive the radial distribution of covering factors and the minimum rate of ionizing photons emitted by the nuclear source. This number is an order of magnitude larger than that obtained from the rate of ionizing photons ‘intercepted’ by the gas and measured from the Hα luminosity. A calibration is proposed to recover this number from the observed luminosity. The He iiλ4686/Hβ line ratio was used to calculate the slope of the ionizing spectral energy distribution (SED), which in combination with the number of ionizing photons allows the calculation of the hard X-ray luminosities. These luminosities are consistent with those derived from X-ray spectra in the eight cases for which such data are available and recover the intrinsic X-ray emission in Compton-thick cases. Our method can thus provide reliable estimates of the X-ray fluxes in Seyfert 2 galaxies for the cases where it is not readily available. We also use the ionizing SED and luminosity to predict the infrared luminosity under the assumption that it is dominated by reprocessed radiation from a dusty torus, and find a good agreement with the observed IRAS luminosities. [ABSTRACT FROM AUTHOR]

ABSTRACT An analysis is presented of the power spectrum of X-ray variability of the bright Seyfert 1 galaxy Mrk 766 as observed by XMM–Newton. Over the 0.2–10 keV energy range the power spectral density (PSD) is well-represented by a power-law with a slope of α[sub low]≈ 1 at low frequencies, breaking to a slope of α[sub hi]= 2.8[sup +0.2][sub -0.4] at a frequency f[sub br]≈ 5 × 10[sup -4] Hz . As has been noted before, this broken power-law PSD shape is similar to that observed in the Galactic black hole candidate Cygnus X-1. If it is assumed that Mrk 766 shows a power spectrum similar in form to that of Cyg X-1, and that the break time-scale scales linearly with black hole mass, then the mass of the black hole in Mrk 766 is inferred to be ≲ 5 × 10[sup 5] M[sub ⊙] . This rather low mass would mean Mrk 766 radiates above the Eddington limit. The coherence between different energy bands is significantly below unity implying that variations in the different energy bands are rather poorly correlated. The low coherence can be explained in the framework of standard Comptonization models if the properties of the Comptonizing medium are rapidly variable or if there are several distinct emission sites. [ABSTRACT FROM AUTHOR]

Integral-field spectroscopic observations are presented for three powerful radio galaxies, namely 3C 277.3 (Coma A; z = 0.0857), 3C 171 (z = 0.2384) and 3C 265 (z = 0.811), which are known to be undergoing jet-cloud interactions. The morphology, kinematics and ionization of the gas in the emission-line structure of these sources are mapped and analysed. One-dimensional spectra are also extracted and integrated over the different emission-line regions in each galaxy. In two of the galaxies (3C 277.3 and 3C 171) the radio sizes are of similar extent to the emission-line structure. For these, enhanced emission-line regions are found associated with the radio structures, in addition to complex kinematics and low ionization states close to the radio hotspots, indicating that jet-induced shocks disturb and ionize the gas. Interestingly, the bright — presumably shock-ionized — emission-line region coincident with the radio jet knot in 3C 277.3 shows quiescent kinematics and high ionization state. Possible explanations for this puzzling result are proposed. The images of 3C 171 and 3C 265 indicate that the lateral expansion of the cocoon has a significant effect on the kinematics and ionization of the gas, showing for the first time that the effects of the radio source are felt far from the jet axis. In addition, the presence of a stellar-photoionized H II region is detected in the extended emission-line nebula of the radio galaxy 3C 277.3. [ABSTRACT FROM AUTHOR]

Using the cross-spectral method, we confirm the existence of the X-ray hard lags discovered with cross-correlation function technique during a large flare of Mrk 421 observed with BeppoSAX. For the 0.1-2 versus 2-10 keV light curves, both methods suggest sub-hour hard lags. In the time domain, the degree of hard lag, i.e. the amplitude of the 3.2-10 keV photons lagging the lower energy ones, tends to increase with the decreasing energy. In the Fourier frequency domain, by investigating the cross-spectra of the 0.1-2/2-10 keV and the 2-3.2/3.210 keV pairs of light curves, the flare also shows hard lags at the lowest frequencies. However, with the present data, it is impossible to constrain the dependence of the lags on frequencies even though the detailed simulations demonstrate that the hard lags at the lowest frequencies probed by the flare are not an artefact of sparse sampling, Poisson and red noise. As a possible interpretation, the implication of the hard lags is discussed in the context of the interplay between the (diffusive) acceleration and synchrotron cooling of relativistic electrons responsible for the observed X-ray emission. The energy-dependent hard lags are in agreement with the expectation of an energy-dependent acceleration time-scale. The inferred magnetic field (B ∼ 0.11 G) is consistent with the value inferred from the spectral energy distributions of the source. Future investigations with higher quality data that show whether or not the time-lags are energy-/frequency-dependent will provide a new constraint on the current models of the TeV blazars. [ABSTRACT FROM AUTHOR]

Abstract We present a large sample of H - and K -band spectra of 32 optically line-luminous central cluster galaxies. We find significant rovibrational H 2 emission in 23 of these galaxies as well as H recombination and/or [Fe ii] emission in another five. This represents a fourfold increase in the number of molecular line detections known. A number of the detections are of extended emission (5–20 kpc). In several objects we find significant [Si vi] emission that appears to correlate with the strength of high ionization lines in the optical (e.g. [O iii]). This comprehensive sample builds on previous work and confirms that warm (1000–2500 K) molecular hydrogen is present wherever there is ionized material in the cores of cooling flows and in most cases it also coincides with CO molecular line emission. [ABSTRACT FROM AUTHOR]

The origin of rovibrational H[sub 2] emission in the central galaxies of cooling flow clusters is poorly understood. Here we address this issue using data from our near-infrared spectroscopic survey of 32 of the most line-luminous such systems, presented in the companion paper by Edge et al. We consider excitation by X-rays from the surrounding intracluster medium (ICM), ultraviolet (UV) radiation from young stars, and shocks. The v = 1-0 K-band lines with upper levels within 10[sup 4] K of the ground state appear to be mostly thermalized (implying gas densities ... 10[sup 5] cm[sup -3]), with the excitation temperature typically exceeding 2000 K, as found earlier by Jaffe, Bremer & van der Werf. Together with the lack of strong v = 2-0 lines in the H-band, this rules out UV radiative fluorescence. Using the CLOUDY photoionization code, we deduce that the H[sub 2] lines can originate in a population of dense clouds, exposed to the same hot (T ∼ 50000 K) stellar continuum as the lower density gas which produces the bulk of the forbidden optical line emission in the Hα-luminous systems. This dense gas may be in the form of self-gravitating clouds deposited directly by the cooling flow, or may instead be produced in the high-pressure zones behind strong shocks. Furthermore, the shocked gas is likely to be gravitationally unstable, so collisions between the larger clouds may lead to the formation of globular clusters. [ABSTRACT FROM AUTHOR]

Presents the spectroscopic results from a small-area faint K-excess survey. Production of complete samples of QSOs from the effects of reddening and extinction; Use of photometric catalogue; Identification of galactic stars.

Focuses on the spectroscopic observations of the emission-line outflows of the radio galaxy PKS1549-79. Evolution of the radio-sources; Analysis of the high-ionization forbidden lines; Discussion of the kinematics of the emission lines.

We have surveyed 188 ROSAT Position Sensitive Proportional Counter (PSPC) fields for X-ray sources with hard spectra (α<0.5); such sources must be major contributors to the X-ray background at faint fluxes. In this paper we present optical identifications for 62 of these sources: 28 active galactic nuclei (AGN) which show broad lines in their optical spectra (BLAGN), 13 narrow emission line galaxies (NELGs), five galaxies with no visible emission lines, eight clusters and eight Galactic stars. The BLAGN, NELGs and galaxies have similar distributions of X-ray flux and spectra. Their ROSAT spectra are consistent with their being AGN obscured by columns of 20.5< log(NH/cm-2)<23. The hard spectrum BLAGN have a distribution of X-ray to optical ratios which is similar to that found for AGN from soft X-ray surveys (1<αOX<2). However, a relatively large proportion (15 per cent) of the BLAGN, NELGs and galaxies are radio loud. This could be because the radio jets in these objects produce intrinsically hard X-ray emission, or if their hardness is caused by absorption, it could be because radio-loud objects are more X-ray luminous than radio-quiet objects. The eight hard sources identified as clusters of galaxies are the brightest, and softest group of sources and hence clusters are unlikely to be an important component of the hard, faint population. We propose that BLAGN are likely to constitute a significant fraction of the faint, hard, 0.5–2 keV population and could be important to reproducing the shape of the X-ray background, because they are the most numerous type of object in our sample (comprising almost half the identified sources), and because all our high redshift (z>1) identified hard sources have broad lines. [ABSTRACT FROM AUTHOR]

We present the first results of our follow-up programme of optical imaging and spectroscopy of a deep 12-μm survey conducted with the ISO satelliteQ1. We find that the objects are typically of fairly low redshift (z∼0.1–0.2), but with a tail that extends to high redshifts. The highest redshift object is a previously unknown quasar at z=1.2. The sample of objects for which spectroscopy has been obtained forms a complete subsample of the original survey with an R-band magnitude limit of 19.6. We are thus able to use accessible volume methods to determine the luminosity function. We find that the luminosity function is close to the low-redshift 12-μm luminosity function determined by IRASQ1, but with a possible excess at the highest luminosities, which also correspond to the highest redshifts. This excess is compatible with the rapid luminosity evolution of L ∝ (1+z)[sup 4.5] claimed by Xu Q1and suggested by ElbazQ1 et al. on the basis of number counts. These conclusions remain tentative because of small number statistics at the highest redshifts. Almost all of the galaxies in this survey are emission line objects. We use the spectra to determine emission line diagnostics for the underlying ionization source. We find that the majority of objects have H ii region-like spectra (roughly 2/3) but there is a significant fraction (about 1/3) that contain an active galactic nucleus (AGN)Q2. This confirms suspicions that deep mid-IR surveys will be a powerful way to find obscured AGN. Part of the survey area has been imaged deeply by the INT Wide Field Camera. Nearly all 12-μm sources in this area, down to the 3σ sensitivity limit of the original ISO survey, have good optical identifications, the faintest being at R=23. The prospects are thus good for obtaining complete spectroscopy for this sample. With such data we should be able to make a clear measurement of the evolution rate of this population and determine the role of obscured AGN in the mid-infrared. [ABSTRACT FROM AUTHOR]

We present optical spectra of the nuclei of seven luminous (P[sub 178 MHz]&gsim;10[sup 25] W Hz[sup -1] Sr[sup -1]) nearby (z<0.08) radio galaxies, which mostly correspond to the FR II class. In two cases, Hydra A and 3C 285, the Balmer and λ4000-Å break indices constrain the spectral types and luminosity classes of the stars involved, revealing that the blue spectra are dominated by blue supergiant and/or giant stars. The ages derived for the last burst of star formation in Hydra A are between 7 and 40 Myr, and in 3C 285 about 10 Myr. The rest of the narrow-line radio galaxies (four) have a λ4000-Å break and metallic indices consistent with those of elliptical galaxies. The only broad-line radio galaxy in our sample, 3C 382, has a strong featureless blue continuum and broad emission lines that dilute the underlying blue stellar spectra. We are able to detect the Ca ii triplet in absorption in the seven objects, with good quality data for only four of them. The strengths of the absorptions are similar to those found in normal elliptical galaxies, but these values are consistent both with stellar populations of roughly similar ages (as derived from the Balmer absorption and break strengths) andQ2 with mixed young+old populations. [ABSTRACT FROM AUTHOR]

This paper describes an investigation of the early evolution of extragalactic radio sources using samples of faint and bright gigahertz peaked spectrum (GPS) and compact steep spectrum (CSS) radio galaxies. Correlations found between their peak frequency, peak flux density and angular size provide strong evidence that synchrotron self-absorption is the cause of the spectral turnovers, and indicate that young radio sources evolve in a self-similar way. In addition, the data seem to suggest that the sources are in equipartition while they evolve. If GPS sources evolve to large size radio sources, their redshift dependent birth-functions should be the same. Therefore, since the lifetimes of radio sources are thought to be short compared to the Hubble time, the observed difference in redshift distribution between GPS and large size sources must be due to a difference in slope of their luminosity functions. We argue that this slope is strongly affected by the luminosity evolution of the individual sources. A scenario for the luminosity evolution is proposed in which GPS sources increase in luminosity and large-scale radio sources decrease in luminosity with time. This evolution scenario is expected for a ram-pressure confined radio source in a surrounding medium with a King profile density. In the inner parts of the King profile, the density of the medium is constant and the radio source builds up its luminosity, but after it grows large enough the density of the surrounding medium declines and the luminosity of the radio source decreases. A comparison of the local luminosity function (LLF) of GPS galaxies with that of extended sources is a good test for this evolution scenario. Unfortunately, only a handful of GPS sources are known at low redshift, and an LLF can only be derived, assuming that their cosmological number density evolution is similar to that of steep spectrum sources. The LLF derived in this way is shown to be in good agreement with the proposed evolution scenario. However, the uncertainties are large, and larger, homogeneously selected samples of GPS sources are needed. [ABSTRACT FROM AUTHOR]

We present the data and analysis of VLBI observations at 1.6, 5 and 15 GHz of a sample of faint gigahertz peaked spectrum (GPS) sources selected from the Westerbork Northern Sky Survey. The 5-GHz observations involved a global array of 16 stations and yielded data on the total sample of 47 sources. A subsample of 26 GPS sources with peak frequencies and/or peak flux densities was observed with the VLBA at 15 GHz. A second subsample of 29 sources, with was observed at 1.6 GHz using a 14-station global VLBI array. In this way, 44 of the 47 sources (94 per cent) in the sample were observed above and at or below their spectral peak. Spectral decomposition allowed us to identify three, 11, seven and two objects as compact symmetric objects, compact doubles, core–jet and complex sources, respectively. However, many of the sources classified as compact double or core–jet sources show only two components making their classification rather tentative. This may explain why the strong morphological dichotomy of GPS quasars and galaxies found for radio-bright GPS sources is not as clear in this faint sample. [ABSTRACT FROM AUTHOR]

Low-luminosity AGNs (LLAGNs) are a very important class of sources since they occur in a significant fraction of local galaxies. Their spectra differ significantly from the canonical luminous AGNs, most notably by the absence of the ‘big blue bump’. Up until now there is no model which can explain the spectra of LLAGNs. Taking NGC 4258 as an example, we propose a coupled jet-disk model for some LLAGNs. [Copyright &y& Elsevier]