J0041+3224: a new double–double radio galaxy

We report the discovery of a double–double radio galaxy (DDRG), J0041+3224, with the Giant Metrewave Radio Telescope (GMRT) and subsequent high-frequency observations with the Very Large Array (VLA). The inner and outer doubles are aligned within ∼4° and are reasonably collinear with the parent optical galaxy. The outer double has a steeper radio spectrum compared to the inner one. Using an estimated redshift of 0.45, the projected linear sizes of the outer and inner doubles are 969 and 171 kpc, respectively. The time-scale of interruption of jet activity has been estimated to be ∼20 Myr, similar to other known DDRGs. We have compiled a sample of known DDRGs, and have re-examined the inverse correlation between the ratio of the luminosities of the outer to the inner double and the size of the inner double, l _in. Unlike the other DDRGs with   l _in≳ 50 kpc  , the inner double of J0041+3224 is marginally more luminous than the outer one. The two DDRGs with   l _in≲  few kpc have a more luminous inner double than the outer one, possibly due to a higher efficiency of conversion of beam energy as the jets propagate through the dense interstellar medium. We have examined the symmetry parameters and found that the inner doubles appear to be more asymmetric in both its armlength and its flux density ratios compared to the outer doubles, although they appear marginally more collinear with the core than the outer double. We discuss briefly the possible implications of these trends.     

PSR J1453+1902 and the radio luminosities of solitary versus binary millisecond pulsars

We present 3 yr of timing observations for PSR J1453+1902, a 5.79-ms pulsar discovered during a 430-MHz drift-scan survey with the Arecibo telescope. Our observations show that PSR J1453+1902 is solitary and has a proper motion of  8 ±  2  mas yr⁻¹. At the nominal distance of 1.2 kpc estimated from the pulsar's dispersion measure, this corresponds to a transverse speed of  46 ± 11   km s⁻¹  , typical of the millisecond pulsar population. We analyse the current sample of 55 millisecond pulsars in the Galactic disc and revisit the question of whether the luminosities of isolated millisecond pulsars are different from their binary counterparts. We demonstrate that the apparent differences in the luminosity distributions seen in samples selected from 430-MHz surveys can be explained by small-number statistics and observational selection biases. An examination of the sample from 1400-MHz surveys shows no differences in the distributions. The simplest conclusion from the current data is that the spin, kinematic, spatial and luminosity distributions of isolated and binary millisecond pulsars are consistent with a single homogeneous population.     

Intermittent jet activity in the radio galaxy 4C 29.30?

We present radio observations at frequencies ranging from 240 to 8460 MHz of the radio galaxy 4C 29.30 (J0840+2949) using the Giant Metrewave Radio Telescope (GMRT), the Very Large Array (VLA) and the Effelsberg telescope. We report the existence of weak extended emission with an angular size of ∼520 arcsec (639 kpc) within which a compact edge-brightened double-lobed source with a size of 29 arcsec (36 kpc) is embedded. We determine the spectrum of the inner double from 240 to 8460 MHz and show that it has a single power-law spectrum with a spectral index of ∼0.8. Its spectral age is estimated to be ≲33 Myr. The extended diffuse emission has a steep spectrum with a spectral index of ∼1.3 and a break frequency ≲240 MHz. The spectral age is ≳200 Myr, suggesting that the extended diffuse emission is due to an earlier cycle of activity. We re-analyse archival X-ray data from Chandra and suggest that the X-ray emission from the hotspots consists of a mixture of non-thermal and thermal components, the latter being possibly due to gas which is shock heated by the jets from the host galaxy.     

The radio galaxy Centaurus B

Centaurus B (PKS B1343−601) is one of the brightest and closest radio galaxies, with flux density ∼250 Jy at 408 MHz and redshift 0.01215, but it has not been studied much because of its position (i) close to the Galactic plane (it is also known as G309.6+1.7 and Kes 19) and (ii) in the southern sky. It has recently been suggested as the centre of a highly obscured cluster behind the Galactic plane. We present radio observations made with the Australia Telescope Compact Array and Molonglo Observatory Synthesis Telescope to study the jets and lobes. The total intensity and polarization radio images of the FR I jets are used to determine the jet brightness and width variations, magnetic field structure and fractional polarization. The equipartition pressure calculated along the jets declines rapidly over the first 1 arcmin from the galaxy reaching a constant pressure of 10⁻¹³  h ^−4/7 Pa in the lobes blown in the intracluster medium.     

3C 459: a highly asymmetric radio galaxy with a starburst

Multifrequency radio observations of the radio galaxy 3C 459 using MERLIN, VLA and the EVN and an optical Hubble Space Telescope ( HST ) image using the F702W filter are presented. The galaxy has a very asymmetric radio structure, a high infrared luminosity and a young stellar population. The eastern component of the double-lobed structure is brighter, much closer to the nucleus and is significantly less polarized than the western one. This is consistent with the jet on the eastern side interacting with dense gas, which could be due to a merged companion or dense cloud of gas. The HST image of the galaxy presented here exhibits filamentary structures and is compared with the MERLIN 5-GHz radio map. EVN observations of the prominent central component, which has a steep radio spectrum, show a strongly curved structure suggesting a bent or helical radio jet. The radio structure of 3C 459 is compared with other highly asymmetric, Fanaroff–Riley II radio sources, which are also good candidates for studying jet–cloud interactions. Such sources are usually of small linear size and it is possible that the jets are interacting with clouds of infalling gas that fuel the radio source.     

A radio study of neutral gas and dust in the radio galaxy 3C 293

We have observed broad H  i absorption in the radio galaxy 3C 293 using Multi-Element Radio Linked Interferometric Network (MERLIN) at 0.2-arcsec angular resolution and the Giant Meterwavelength Radio Telescope (GMRT) at arcsec resolution. Extensive H  i is found in absorption across the centre of this peculiar radio galaxy, allowing a detailed study of the dynamics of the neutral gas on linear scales down to ∼160 pc. In optical depth position–velocity diagrams across the central few kpc we detect a distinct velocity gradient of 179 km s⁻¹ arcsec⁻¹ associated with the broad absorption. This is interpreted as a ring of neutral gas rotating around the suspected position of the active galactic nucleus (AGN) . The radius of this high velocity gradient ring is found to be >0.74 arcsec (600 pc), implying an upper limit upon the enclosed mass of     , assuming a near edge-on disc with an inclination of i . The optical depth of H  i is mapped across the entire central region of 3C 293 showing enhancements of a factor of 4 in the areas that are co-spatial with dust lanes seen in Hubble Space Telescope ( HST ) imaging of this galaxy.     

A multifrequency study of possible relic lobes in giant radio sources

We present low-frequency observations with the Giant Metrewave Radio Telescope of three giant radio sources (GRSs: J0139+3957, J0200+4049 and J0807+7400) with relaxed diffuse lobes which show no hotspots and no evidence of jets. The largest of these three, J0200+4049, exhibits a depression in the centre of the western lobe, while J0139+3957 and J0807+7400 have been suggested earlier by Klein et al. and Lara et al., respectively, to be relic radio sources. We estimate the ages of the lobes. We also present Very Large Array observations of the core of J0807+7400, and determine the core radio spectra for all three sources. Although the radio cores suggest that the sources are currently active, we explore the possibility that the lobes in these sources are due to an earlier cycle of activity.     

A radio study of the superwind galaxy NGC 1482

We present multifrequency radio continuum as well as H  i observations of the superwind galaxy NGC 1482, with both the Giant Metrewave Radio Telescope (GMRT) and the Very Large Array (VLA). This galaxy has a remarkable hourglass-shaped optical emission-line outflow as well as bipolar soft X-ray bubbles on opposite sides of the galactic disc. The low-frequency, lower-resolution radio observations show a smooth structure. From the non-thermal emission, we estimate the available energy in supernovae, and examine whether this would be adequate to drive the observed superwind outflow. The high-frequency, high-resolution radio image of the central starburst region located at the base of the superwind bi-cone shows one prominent peak and more extended emission with substructure. This image has been compared with the infrared, optical red continuum, Hα, and soft and hard X-ray images from Chandra to understand the nature and relationship of the various features seen at different wavelengths. The peak of the infrared emission is the only feature that is coincident with the prominent radio peak, and possibly defines the centre of the galaxy.
The H  i observations with the GMRT show two blobs of emission on opposite sides of the central region. These are rotating about the centre of the galaxy and are located at ∼2.4 kpc from it. In addition, these observations also reveal a multicomponent H  i absorption profile against the central region of the radio source, with a total width of ∼250 km s⁻¹. The extreme blue- and redshifted absorption components are at 1688 and 1942 km s⁻¹, respectively, while the peak absorption is at 1836 km s⁻¹. This is consistent with the heliocentric systemic velocity of  1850 ± 20 km s⁻¹  , estimated from a variety of observations. We discuss possible implications of these results.     

The radio jets in B2 0755+379

We present and discuss observations of the radio galaxy 0755+379 made with the VLA at 1.4 and 5.0 GHz and with MERLIN at 1.7 GHz. These data allow us to image the radio jets over two orders of magnitude in linear size and to investigate the hypothesis that jets in low-luminosity radio galaxies start with velocities close to c and then slow down to subrelativistic speeds. We apply a model for an adiabatically expanding relativistic jet to the observed surface brightness and derive velocity profiles along the jet for various assumed starting conditions. We show that these profiles are consistent with the observed jet/counter-jet brightness ratios provided that the angle to the line of sight θ ≃27°. The inferred velocity at a distance of 0.5 kpc from the nucleus is ≃0.9 c . Finally, we show that the predicted velocity at 10 kpc from the nucleus is consistent with that obtained independently from energy-balance arguments.     

Radio jet interactions in the radio galaxy PKS 2152–699

We present radio observations of the radio galaxy PKS 2152–699 obtained with the Australia Telescope Compact Array. The much higher resolution and signal-to-noise ratio of the new radio maps reveal the presence of a bright radio component about 10 arcsec north-east of the nucleus. This lies close to the highly ionized cloud previously studied in the optical and here shown in a broad-band red snapshot image with the HST PC 2. It suggests that PKS 2152–699 may be a jet/cloud interaction similar to 3C 277.3. This could cause the change in the position angle (of ∼ 20°) of the radio emission from the inner to the outer regions. On the large scale, the source has Fanaroff & Riley type II morphology although the presence of the two hotspots in the centres of the lobes is unusual. The northern lobe shows a particularly relaxed structure while the southern one has an edge-brightened, arc-like structure.     

H i and radio continuum study of the isolated SBa Seyfert galaxy NGC 3783

NGC 3783 is a nearby SBa, type 1 Seyfert galaxy. We present H  i and radio continuum images of the galaxy made with the Australia Telescope Compact Array (ATCA). We find that NGC 3783 has an H  i mass of 8.4×10⁹ M_⊙, an H  i diameter of 1.9 D ₀ ( D ₀=37 kpc for h =0.5), and a nuclear depression in the H  i surface density. The H  i rotation curve is dominated by differential rotation, with little evidence of warping. The rotation curve suggests a mass-to-light ratio M L _B =7.2 and a bar-pattern speed of 19±7 km s⁻¹ kpc⁻¹. The total mass of gas in the inner 50 arcsec is ≳10 per cent of the dynamical mass, and consistent with models that require significant gas content to fuel the Seyfert nucleus. There is no evidence that the nuclear activity in NGC 3783 is being stimulated by an interaction or merger: it may be a self-generated, perhaps bar-driven, process.     

85-GHz BIMA observations of the double-hotspot radio galaxy 3C 20

We present 85-GHz observations of the archetypal double-hotspot radio source 3C 20 made with the BIMA millimetre array. The resolution of BIMA allows us to separate the two components of the eastern hotspot. By comparing the BIMA observations with existing VLA data, we show that the spectra of the two hotspot components are very similar, despite the clear differences in their radio structure and their wide separation. We discuss the implications for models of double hotspot formation. Weak emission from the lobes of 3C 20 is detected at 85 GHz, at a level consistent with the predictions of standard spectral ageing models.     

A search for optical polarization from the narrow-line Seyfert 1 galaxy RE J1034+396

We present spectropolarimetry data on RE J1034+396, an ultra-soft X-ray narrow-line Seyfert 1 galaxy, and find an upper limit of ∼ 0.4 to the linear polarization in the optical band. This suggests that there is no synchrotron emission in this AGN, and thus it is unlikely that RE J1034+396 is related to BL Lac objects. Furthermore, any other polarization arising from transmission through dust, or reflection from dust and electrons, must be cancelled out by geometrical effects or diluted to a high degree by unpolarized radiation.