MERLIN Images Research Articles

Dying radio galaxies in clusters

We present the study of five `dying' nearby radio galaxies belonging to the WENSS minisurvey and to the B2 bright catalogs: WNB1734+6407, WNB1829+6911, WNB1851+5707, B2 0120+33, and B2 1610+29. These sources have been selected on the basis of their extremely steep broad-band radio spectra. The modeling of the integrated spectra and the deep spectral index images obtained with the VLA confirmed that in these sources the central engine has ceased to be active for a significant fraction of their lifetime although their extended lobes have not yet completely faded away. We found that WNB1851+5707 is in reality composed by two distinct dying galaxies, which appear blend together as a single source in the WENSS. In the cases of WNB1829+6911 and B2 0120+33, the fossil radio lobes are seen in conjunction with a currently active core. A very faint core is detected also in a MERLIN image of WNB1851+5707a, one of the two dying sources composing WNB1851+5707. We found that all sources of our sample are located (at least in projection) at the center of an X-ray emitting cluster. Our results suggest that the duration of the dying phase for a radio source in cluster can be significantly higher with respect to that of a radio galaxy in the field. The simplest interpretation is that the low-frequency emission from the fading radio lobes last longer if their expansion is somewhat reduced or even stopped. Another possibility is that the occurrence of dying sources is higher in galaxy clusters. Radio sources in dense environment, like e.g. the center of cooling core clusters, may have a peculiar accretion mode which results in a bursting duty cycle sequence of active and quiescent periods. This result could have important implications for theories of the life cycles of radio sources and AGN feedback in clusters of galaxies but awaits confirmation from future observations of larger samples of objects.

Time course of dysregulation of calcium homeostasis in acutely isolated CA1 hippocampal pyramidal neurons after pilocarpine-induced Status Epilepticus

Glutamate induces excitotoxic damage to hippocampal pyramidal neurons in Status Epilepticus (SE) and epilepsy. In this study, we investigated time course of dysregulation of calcium homeostasis at various intervals after an episode of SE in acutely isolated CA1hippocampal pyramidal. For this purpose, male Sprague-Dawley rats (200 g) were subjected to pilocarpine-induced SE. The SE was blocked after 3 h with diazepam and MK-801. The CA1 pyramidal neurons were acutely isolated at 24 h, 48 h, 6 days, 10 days and one-month post-SE. The basal intracellular calcium levels [Ca++]i from individual neurons were determined by high speed image flourometery using Fura-2. Rise in neuronal [Ca++]i in response to 30 ?M glutamate (1 min) exposure was captured by Merlin image acquisition software. Calcium decay response curves were then constructed and compared with neurons from control animals at the same time points. The basal calcium levels in acutely isolated CA1 pyramidal neurons post SE were significantly higher (then control at different time points. The neurons studied at 24 h, 48 h, and 6 days were not able to restore calcium levels to normal after glutamate exposure. The neurons at 10 days and 1 month were gradually able to restore calcium levels to pre-glutamate levels. SE induced excitotoxic damage to the hippocampal pyramidal neurons that leads to neuronal death and disruption of calcium homeostasis. This is evidenced by an increase in basal [Ca++]i levels and inability to restore [Ca++]i to pre-glutamate levels after exposure. The neurons recover gradually over a period of 10 days after acute SE. This is the first direct evidence of dysregulation of calcium homeostasis in pyramidal neurons isolated from animals subjected to SE.

Forward modelling to determine the observational signatures of white-light imaging and interplanetary scintillation for the propagation of an interplanetary shock in the ecliptic plane

Recent coordinated observations of interplanetary scintillation (IPS) from the EISCAT, MERLIN, and STELab, and stereoscopic white-light imaging from the two heliospheric imagers (HIs) onboard the twin STEREO spacecraft are significant to continuously track the propagation and evolution of solar eruptions throughout interplanetary space. In order to obtain a better understanding of the observational signatures in these two remote-sensing techniques, the magnetohydrodynamics of the macro-scale interplanetary disturbance and the radio-wave scattering of the micro-scale electron-density fluctuation are coupled and investigated using a newly constructed multi-scale numerical model. This model is then applied to a case of an interplanetary shock propagation within the ecliptic plane. The shock could be nearly invisible to an HI, once entering the Thomson-scattering sphere of the HI. The asymmetry in the optical images between the western and eastern HIs suggests the shock propagation off the Sun–Earth line. Meanwhile, an IPS signal, strongly dependent on the local electron density, is insensitive to the density cavity far downstream of the shock front. When this cavity (or the shock nose) is cut through by an IPS ray-path, a single speed component at the flank (or the nose) of the shock can be recorded; when an IPS ray-path penetrates the sheath between the shock nose and this cavity, two speed components at the sheath and flank can be detected. Moreover, once a shock front touches an IPS ray-path, the derived position and speed at the irregularity source of this IPS signal, together with an assumption of a radial and constant propagation of the shock, can be used to estimate the later appearance of the shock front in the elongation of the HI field of view. The results of synthetic measurements from forward modelling are helpful in inferring the in-situ properties of coronal mass ejection from real observational data via an inverse approach.

Limited Mitochondrial Permeabilization Is an Early Manifestation of Palmitate-induced Lipotoxicity in Pancreatic β-Cells

Involvement of the mitochondrial permeability transition (MPT) pore in early stages of lipotoxic stress in the pancreatic beta-cell lines MIN6 and INS-1 was the focus of this study. Both long term (indirect) and acute (direct) effects of fatty acid (FA) application on beta-cell susceptibility to Ca(2+)-induced MPT induction were examined using both permeabilized and intact beta-cells. Long term exposure to moderate (i.e. below cytotoxic) levels of the saturated FA palmitate sensitized beta-cell mitochondria to MPT induced by Ca(2+). Long term exposure to palmitate was significantly a more efficient inducer of MPT than the unsaturated FA oleate, although upon acute application both caused similar MPT activation. Application of antioxidants, inhibitors of the ceramide pathway, or modifiers of membrane fluidity did not protect beta-cell mitochondria from FA exposure. However, significant protection was provided by co-application of the unsaturated FA oleate in a phosphatidylinositol 3-kinase-dependent manner. Characterization of MPT pore opening in response to moderate palmitate treatment revealed the opening of a unique form of MPT in beta-cells as it encompassed features of both low and high conductance MPT states. Specifically, this MPT showed solute selectivity, characteristic of a low conductance MPT; however, it affected mitochondrial respiration and membrane potential in a way typical of a high conductance MPT. Activation of the full-size/high conductance form of MPT required application of high levels of FA that reduced growth and initiated apoptosis. These findings suggest that in the beta-cell, MPTs can act as both initiators of cell death and as versatile modulators of cell metabolism, depending on the mode of the MPT pore induced.

Subarcsec optical and radio obsercations of the gravitationally lensed systmen B1422 + 23.1

Optical observations of the multiple-component gravitational lens candidate B1422+23.1 using the 2.5m Nordic Optical Telescope and a MERLIN image at 1658 MHz are presented. The radio image at L-band and B, V, R and I band images with a 0.6 arcsec seeing resolve the components. These observations show that the brightness ratio of the components at optical bands is similar to those at radio bands. This strengthens the case for a gravitational lens hypothesis for the source. Keywords : keyword; Gravitational lensing quasar, radio map, optical image Nigerian Journal of Physics Vol. 18 (2) 2006: pp. 191-196

Six months of mass outflow and inclined rings in the ejecta of V1494 Aql

V1494 Aql was a very fast nova which reached a visual maximum of mv≃ 4.0 by the end of 1999 December 3. We report observations from 4 to 284 d after discovery, including submillimetre- and centimetre-band fluxes, a single MERLIN image and optical spectroscopy in the 410 to 700 nm range. The extent of the radio continuum emission is consistent with a recent lower distance estimate of 1.6 kpc. We conclude that the optical and radio emission arises from the same expanding ejecta. We show that these observations are not consistent with simple kinematical spherical shell models used in the past to explain the rise and fall of the radio flux density in these objects. The resolved remnant structure is consistent with an inclined ring of enhanced density within the ejecta. Optical spectroscopy indicates likely continued mass ejection for over 195 d, with the material becoming optically thin in the visible sometime between 195 and 285 d after outburst.

Polarization and kinematic studies of SS 433 indicate a continuous and decelerating jet

We present radio images of SS 433 taken in 1987 at 1.5, 5, 8 and 15 GHz using the VLA in A configuration, and taken at four more recent epochs at 5 or 1.6 GHz using MERLIN. The extremely sensitive 5-GHz VLA image appears to be inconsistent with the ballistic kinematic model predictions. However, the inclusion of a deceleration term of0.02c per period (162.375 d) or the use of a slower constant velocity of 0.225c gives a good agreement with the observations. This slower ejection velocity is not consistent with existing measurements of the jet velocity on subarcsecond scales. The images also show a depolarization region surrounding the radio core of SS 433, with an extent ∼0.5 arcsec at 5 GHz. This depolarization region is present even at our highest observing frequency of 15 GHz. The MERLIN images confirm the presence of depolarization at four separate observing epochs. The depolarizing medium is likely to be an ionized cloud of gas associated with the stellar wind of the normal star, although we cannot rule out thermal gas in the jet material co-existing with the relativistic electrons which emit via the synchrotron mechanism. Outside the depolarizing region the jets are highly linearly polarized (up to 20 per cent). We find a rotation measure of 119 ± 16 rad m -2 for the extended jets, consistent with previous lower-frequency studies. After correcting for foreground Faraday rotation we find an alignment between the implied magnetic field orientation and the kinematic locus. This can be explained by the stretching of the plasma tube along the kinematic locus as a result of differential motion. We also transform the rest-frame angles defining the apparent electric field direction to the observer's frame and show that, after allowing for Lorentz contraction, projection and light travel delays, the observer also sees the electric field perpendicular to the plasma tube. The observed alignment of the jet magnetic field and direction suggests that the jet consists of a continuous plasma tube with longitudinal magnetic field (as proposed for the jets emitted by quasars) and not of an unconnected series of plasmons.

A relativistic helical jet in theγ-ray AGN 1156+295

We present the results of a number of high resolution radio observations of the AGN 1156+295. These include multi-epoch and multi-frequency VLBI, VSOP, MERLIN and VLA observations made over a period of 50 months. The 5 GHz MERLIN images trace a straight jet extending to similar to2 at PAsimilar to-18degrees. Extended low brightness emission was detected in the MERLIN observation at 1.6 GHz and the VLA observation at 8.5 GHz with a bend of similar to90degrees at the end of the 2 arcsec jet. A region of similar diffuse emission is also seen about 2 arcsec south of the radio core. The VLBI images of the blazar reveal a core-jet structure with an oscillating jet on a milli-arcsecond (mas) scale which aligns with the arcsecond jet at a distance of several tens of milli-arcseconds from the core. This probably indicates that the orientation of the jet structure is close to the line of sight, with the northern jet being relativistically beamed toward us. In this scenario the diffuse emission to the north and south is not beamed and appears symmetrical. For the northern jet at the mas scale, proper motions of 13.7+/-3.5, 10.6+/-2.8, and 11.8+/-2.8 c are measured in three distinct components of the jet (q(0)=0.5, H-0=65 km s(-1) Mpc(-1) are used through out this paper). Highly polarised emission is detected on VLBI scales in the region in which the jet bends sharply to the north-west. The spectral index distribution of the source shows that the strongest compact component has a flat spectrum, and the extended jet has a steep spectrum. A helical trajectory along the surface of a cone was proposed based on the conservation laws for kinetic energy and momentum to explain the observed phenomena, which is in a good agreement with the observed results on scales of 1 mas to 1 arcsec.

Hints for a fast precessing relativistic radio jet in LS I +61°303

Here we discuss two consecutive MERLIN observations of the X-ray binary LS I +61 303. The first observation shows a double-sided jet extending up to about 200 AU on both sides of a central source. The jet shows a bent S-shaped structure similar to the one displayed by the well-known precessing jet of SS 433. The precession suggested in the first MERLIN image becomes evident in the second one, showing a one-sided bent jet significantly rotated with respect to the jet of the day before. We conclude that the derived precession of the relativistic (beta=0.6) jet explains puzzling previous VLBI results. Moreover, the fact that the precession is fast could be the explanation of the never understood short term (days) variability of the associated gamma-ray source 2CG 135+01 / 3EG J0241+6103.

VLA and MERLIN observations of RZ Cassiopeiae

We present radio interferometric observations of the Algol-type binary system RZ Cassiopeiae made with the VLA and MERLIN arrays at 6 cm over an incomplete orbital cycle of the system (1.195 d). We detected RZ Cas with both instruments. The images were unresolved in both cases, with angular extents comparable to the synthesized beams. The peak flux density in the VLA image was 1.14 mJy beam−1 and in the MERLIN image it was 0.93 mJy beam−1. The derived brightness temperatures are 4.02 × 108 and 4.35 × 108 K and the effective electron energies are 0.347 and 0.346 MeV for the MERLIN and VLA data respectively. The radio light curve shows an interesting modulation centred close to the primary eclipse which seems to correlate with ASCA SIS observations of the system. The results can be interpreted as an emitting region on the outer hemisphere of the cool component aligned along the centroid axis of the binary system.

The Nuclear Regions of the Seyfert Galaxy NGC 4151: Parsec‐Scale HiAbsorption and a Remarkable Radio Jet

Sensitive high angular and linear resolution radio images of the 240-pc radio jet in NGC4151, imaged at linear resolutions of 0.3 to 2.6 pc using the VLBA and phased VLA at 21 cm, are presented and reveal for the first time a faint, highly collimated jet (diameter <1.4 pc) underlying discrete components, seen in lower resolution MERLIN and VLA images, that appear to be shock-like features associated with changes in direction as the jet interacts with small gas clouds within the central 100 pc of the galaxy. In addition, 21-cm spectral line imaging of the neutral hydrogen in the nuclear region reveals the spatial location, distribution and kinematics of the neutral gas detected previously in a lower resolution MERLIN study. Neutral hydrogen absorption is detected against component C4W (E+F) as predicted by Mundell et al, but the absorption, extending over 3 pc, is spatially and kinematically complex on sub-parsec scales, suggesting the presence of small, dense gas clouds with a wide range of velocities and column densities. The main absorption component matches that detected in the MERLIN study and is consistent with absorption through a clumpy neutral gas layer in the putative obscuring torus, with higher velocity blue- and red-shifted systems with narrow linewidths also detected across E+F. The spatial location and distribution of the absorbing gas across component E+F rules out component E as the location of the AGN (as suggested by Ulvestad et al.) and, in combination with the well-collimated continuum structures seen in component D, suggests that component D is the most likely location for the AGN. We suggest that components C and E are shocks produced in the jet as the plasma encounters, and is deviated by, dense clouds with diameters smaller than ~1.4 pc. (Abridged)

The symbiotic star CH Cygni - III. A precessing radio jet

VLA, MERLIN and Hubble Space Telescope imaging observations of the extended regions of the symbiotic system CH Cygni are analysed. These extensions are evidence of a strong collimation mechanism, probably an accretion disc surrounding the hot component of the system. Over 16 yr (between 1985 and 2001) the general trend is that these jets are seen to precess. Fitting a simple ballistic model of matter ejection to the geometry of the extended regions suggests a period of 6520 ′ 150 d, with a precession cone opening angle of 35° ′ 1°. This period is of the same order as that proposed for the orbital period of the outer giant in the system, suggesting a possible link between the two. Anomalous knots in the emission, not explained by the simple model, are believed to be the result of older, slower moving ejecta, or possibly jet material that has become disrupted through sideways interaction with the surrounding medium.

The orientation of the Seyfert nucleus in Markarian 348

Multi-frequency observations of Mrk 348 are presented consisting of 2 epochs of MERLIN data at 5 GHz, ISOPHOT data at 170, 90, 60 and 25 micron, NOT images at U, B, R and I bands and data at 1350 micron from the archive for SCUBA. The new optical images reveal a disrupted arm that ends towards the eastern companion of Mrk 348, consistent with the hypothesis that Mrk 348 and its companion form an interacting system. 5 GHz MERLIN imaging shows that only one of the radio components of Mrk 348 is polarized (%P=5). The broadband spectrum of Mrk 348 is flat between the radio and millimetre bands, suggesting that synchrotron emission extends to high frequencies. Mrk 348 has many of the characteristics of a radio-loud object. We discuss the orientation of the radio axis of Mrk 348 with respect to the line of sight. We conclude that the evidence is conflicting, and the geometry in Mrk 348 is not well-described by a simple edge-on or face-on model.

Hα, SCUBA and MERLIN imaging of NGC 4490

We describe Ha, SCUBA and MERLIN imaging of the interacting galaxy pair NGC 4490 and 4485. We detect an Ha filament emerging from the disc of NGC 4490 to a projected distance of 3 kpc which has counterparts in both the radio continuum and Hi. The HI counterpart extends to a projected distance of ∼ 30 kpc from NGC 4490 and we argue that this is evidence that the giant HI envelope in this system has its origins in star formation. We use SCUBA and radio continuum data to attempt to place constraints on the distribution of dust with respect to the star forming regions. This analysis is limited by the lack of an independent estimate of the dust temperature, something that both 'SIRTF' and 'SOFIA' will be able to provide, however we find some evidence that most obscuring dust is not located within HII regions themselves.

Mass Loss and Jet Outflow in the Orion Nebula Proplyd LV 2

We have obtained Hubble Space Telescope (HST) Space Telescope Imaging Spectrometer high-resolution spectra of the Orion proplyd LV 2 in the C III doublet at 1906.68 and 1908.73 ?. New images at the 6 cm wavelength with MERLIN complement earlier HST images at a similar spatial resolution. This object is one of the closest proplyds to ?1 Ori C, the source of the photoionizing and photoevaporating radiation. Combining the spectra with the HST images and detailed theoretical models has allowed a determination of the mass-loss rate as 8.2 ? 10-7 M? yr-1 ?10%. This rate of mass loss is used to address the conundrum of the continued existence of proplyds. Even though they should be photoevaporated in only about 105 yr, there is no evidence for their destruction. It is concluded that the only explanation is that the age of ?1 Ori C is less than 105 yr. These spectra and previously unpublished ground-based spectra in [O III] also show the presence of a monopolar microjet, redshifted by about 100 km s-1 with respect to the systemic velocity. This jet is more visible in the 6 cm MERLIN images than in HST images, and this image together with the spectra are used to determine the flow parameters for the jet. Our spectra also include the stand-off shock that lies between LV 2 and ?1 Ori C. This is the result of the high-velocity wind coming from the hot star ?1 Ori C with the low-velocity wind coming from the proplyd. As expected, this shock is at rest with respect to the two objects.

Merlin water maser observations of the Seyfert 2 galaxy Mrk 348

MERLIN images of Mrk 348 at 22 GHz show H2O maser emission at 0.02–0.11 Jy, within ∼ 0.8 pc of the nucleus. This is the first direct confirmation that molecular material exists close to the Seyfert 2 nucleus. Mrk 348 was observed one month after Falcke et al. (2000) first identified the maser in single-dish spectra. The peak maser flux density has increased about threefold. The masing region is ≲ 0.6 pc in radius. The flux density of radio continuum emission from the core has been rising for about 2 years. The maser-core separation is barely resolved but at the 3σ significance level maser and continuum peaks are not coincident along the line of sight. The masers lie in the direction of the northern radio lobes and probably emanate from material shocked by a jet with velocity close to c although direct maser amplification of the core by masers tracing a Keplerian disc is not completely ruled out.

PMN J0134−0931: A Gravitationally Lensed Quasar with Unusual Radio Morphology

The radio-loud quasar J0134-0931 was discovered to have an unusual morphology during our search for gravitational lenses. In Very Large Array and MERLIN images, there are five compact components with a maximum separation of 07. All of these components have the same spectral index from 5 to 43 GHz. In a Very Long Baseline Array image at 1.7 GHz, a curved arc of extended emission joins two of the components in a manner suggestive of gravitational lensing. At least two of the radio components have near-infrared counterparts. We argue that this evidence implies that J0134-0931 is a gravitational lens, although we have not been able to devise a plausible model for the foreground gravitational potential. Like several other radio-loud lenses, the background source has an extraordinarily red optical counterpart.

MERLIN imaging of the maser flare in Markarian 348

MERLIN images of Mrk 348 at 22 GHz show water maser emission at 0.02 - 0.11 Jy, within approximately 0.8 pc of the nucleus. This is the first direct confirmation that molecular material exists close to the Seyfert 2 nucleus. Mrk 348 was observed in 2000 May one month after Falcke et al. (2000) first identified the maser in single-dish spectra. The peak maser flux density has increased about threefold. The masing region is < 0.6 pc in radius. The flux density of radio continuum emission from the core has been rising for about 2 years. The maser-core separation is barely resolved but at the 3 sigma significance level they are not coincident along the line of sight. The masers lie in the direction of the northern radio lobes and probably emanate from material shocked by a jet with velocity close to c. The correlation between the radio continuum increase and maser flare is explained as arising from high level nuclear activity through a common excitation mechanism although direct maser amplification of the core by masers tracing a Keplerian disc is not completely ruled out.

The Ejecta of Classical Novae

Classical novae are interacting binary stars in which a thermonuclear runaway in material accreted onto a white dwarf from a companion red dwarf results in the ejection of around 10−4M⊙ at hundreds to thousands of kilometres per second. Recent Hubble Space Telescope and MERLIN imaging of the expanding ejecta from several classical novae are presented. In general the ejecta are clumpy but often display coherent structures, most notably equatorial rings of enhanced emission encircling prolate ellipsoidal shells. Physical mechanisms (including the common envelope phase and anisotropic irradiation of the shell) which may result in the generation of these structures are discussed.

A Nearly Symmetric Double-Image Gravitational Lens

We report the discovery of a new double-image gravitational lens, resulting from our search for lenses in the southern sky. Radio source PMN J2004-1349 is composed of two compact components separated by 113 in VLA, MERLIN, and VLBA images. The components have a flux ratio of 1:1 at radio frequencies ranging from 5 to 22.5 GHz. The I-band optical counterpart is also an equal double, with roughly the same separation and position angle as the radio double. Upon subtraction of the components from the I-band image, we identify a dim pattern of residuals as the lens galaxy. While the present observations are sufficient to establish that PMN J2004-1349 is a gravitational lens, additional information will be necessary (such as the redshifts of the galaxy and quasar and precise astrometry and photometry of the lens galaxy) before constructing detailed mass models.