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We present photometric and polarimetric measurements of gamma-ray burst (GRB) optical afterglows observed by the RINGO3 imaging polarimeter over its ∼7 yr lifetime mounted on the Liverpool Telescope. During this time, RINGO3 responded to 67 GRB alerts. Of these, 28 had optical afterglows and a further ten were sufficiently bright for photometric and polarimetric analysis (R ⪅ 17). We present high quality multicolour light curves of ten sources: GRB 130606A, GRB 130610A, GRB 130612A, GRB 140430A, GRB 141220A, GRB 151215A, GRB 180325A, GRB 180618A, GRB 190114C, and GRB 191016A and polarimetry for seven of these (excluding GRB 130606A, GRB 130610A, and GRB 130612A, which were observed before the polarimetry mode was fully commissioned). Eight of these ten GRBs are classical long GRBs, one sits at the short-long duration interface with a T 90 ∼ 4 s and one is a classical short, hard burst with extended emission. We detect polarization for GRB 190114C and GRB 191016A. While detailed analyses of several of these GRBs have been published previously, here we present a uniform re-reduction and analysis of the whole sample and investigation of the population in a broad context relative to the current literature. We use survival analysis to fully include the polarization upper limits in comparison with other GRB properties, such as temporal decay rate, isotropic energy, and redshift. We find no clear correlation between polarization properties and wider sample properties and conclude that larger samples of early time polarimetry of GRB afterglows are required to fully understand GRB magnetic fields. [ABSTRACT FROM AUTHOR]

All 280 of the statistically complete Palomar sample of nearby (<120 Mpc) galaxies δ > 20° have been observed at 1.5 GHz as part of the LeMMINGs e -MERLIN legacy survey. Here, we present Chandra X-ray observations of the nuclei of 213 of these galaxies, including a statistically complete sub-set of 113 galaxies in the declination range 40° <δ < 65°. We observed galaxies of all optical spectral types, including 'active' galaxies [e.g. low-ionization nuclear emission line regions (LINERs) and Seyferts] and 'inactive' galaxies like |${\rm H\, \small {II}}$| galaxies and absorption line galaxies (ALG). The X-ray flux limit of our survey is 1.65 × 10−14 erg s−1 cm−2 (0.3−10 keV). We detect X-ray emission coincident within 2 arcsec of the nucleus in 150/213 galaxies, including 13/14 Seyferts, 68/77 LINERs, 13/22 ALGs and 56/100 |${\rm H\, \small {II}}$| galaxies, but cannot completely rule out contamination from non-AGN processes in sources with nuclear luminosities |$\lesssim 10^{39}$|  erg s−1. We construct an X-ray Luminosity function (XLF) and find that the local galaxy XLF, when including all active galactic nucleus (AGN) types, can be represented as a single power law of slope −0.54 ± 0.06. The Eddington ratio of the Seyferts is usually 2−4 decades higher than that of the LINERs, ALGs, and |${\rm H\, \small {II}}$| galaxies, which are mostly detected with Eddington ratios |$\lesssim 10^{-3}$|⁠. Using [ |${\rm O\, \small {III}}$| ] line measurements and black hole masses from the literature, we show that LINERs, |${\rm H\, \small {II}}$| galaxies and ALGs follow similar correlations to low luminosities, suggesting that some 'inactive' galaxies may harbour AGN. [ABSTRACT FROM AUTHOR]

We report the earliest ever detection of optical polarization from a GRB forward shock (GRB 141220A), measured |$129.5{-}204.3\,$| s after the burst using the multicolour RINGO3 optical polarimeter on the 2-m fully autonomous robotic Liverpool Telescope. The temporal decay gradient of the optical light curves from |$86\,$| to |$\sim 2200\,$| s post-burst is typical of classical forward shocks with α = 1.091 ± 0.008. The low-optical polarization |$P_{ BV} = 2.8 _{- 1.6} ^{+ 2.0} \, {{\ \rm per\ cent}}$| (2 σ) at mean time |$\sim 168\,$| s post-burst is compatible with being induced by the host galaxy dust (⁠|$A_{V, {\rm HG}}= 0.71 \pm 0.15 \,$| mag), leaving low polarization intrinsic to the GRB emission itself – as theoretically predicted for forward shocks and consistent with previous detections of low degrees of optical polarization in GRB afterglows observed hours to days after the burst. The current sample of early-time polarization data from forward shocks suggests polarization from (a) the Galactic and host galaxy dust properties (i.e. |$P \sim 1-3{{\ \rm per\ cent}}$|⁠), (b) contribution from a polarized reverse shock (GRB deceleration time, jet magnetization) or (c) forward shock intrinsic polarization (i.e. |$P \le 2{{\ \rm per\ cent}}$|⁠), which depends on the magnetic field coherence length-scale and the size of the observable emitting region (burst energetics, circumburst density). [ABSTRACT FROM AUTHOR]

NGC 3393, a nearby Seyfert 2 galaxy with nuclear radio jets, large-scale and nuclear bars, and a posited secondary supermassive black hole, provides an interesting laboratory to test the physics of inflows and outflows. Here we present and analyse the molecular gas [ALMA observations of CO J:2-1 emission over a field of view (FOV) of 45 arcsec × 45 arcsec, at 0 $${^{\prime\prime}_{.}}$$ 56 (143 pc) spatial and 5 km s−1 spectral resolution), ionized gas and stars (GEMINI–GMOS/IFU; over an FOV of 4 arcsec × 5 arcsec, at 0 $${^{\prime\prime}_{.}}$$ 62 (159 pc) spatial and 23 km s−1 spectral resolution) in NGC 3393. The ionized gas emission, detected over the complete GEMINI–GMOS FOV, has three identifiable kinematic components. A narrow (σ < 115 km s−1) component present in the complete FOV, which is consistent with rotation in the galaxy disc. A broad (σ > 115 km s−1) redshifted component, detected near the NE and SW radio lobes; which we interpret as a radio jet-driven outflow. And a broad (σ > 115 km s−1) blueshifted component that shows high velocities in a region perpendicular to the radio jet axis; we interpret this as an equatorial outflow. The CO J:2-1 emission is detected in spiral arms on 5–20 arcsec scales, and in two disturbed circumnuclear regions. The molecular kinematics in the spiral arms can be explained by rotation. The highly disturbed kinematics of the inner region can be explained by perturbations induced by the nuclear bar and interactions with the large scale bar. We find no evidence for, but cannot strongly rule out, the presence of the posited secondary black hole. [ABSTRACT FROM AUTHOR]

We present high-sensitivity eMERLIN radio images of the Seyfert galaxy NGC4151 at 1.51 GHz. We compare the new eMERLIN images to those from archival MERLIN observations in 1993 to determine the change in jet morphology in the 22 yr between observations. We report an increase by almost a factor of 2 in the peak flux density of the central core component, C4, thought to host the black hole, but a probable decrease in some other components, possibly due to adiabatic expansion. The core flux increase indicates an active galactic nucleus (AGN) that is currently active and feeding the jet. We detect no significant motion in 22 yr between C4 and the component C3, which is unresolved in the eMERLIN image. We present a spectral index image made within the 512MHz band of the 1.51 GHz observations. The spectrum of the core, C4, is flatter than that of other components further out in the jet. We use HST emission-line images (H α, [OIII] and [O II]) to study the connection between the jet and the emission-line region. Based on the changing emission-line ratios away from the core and comparison with the eMERLIN radio jet, we conclude that photoionization from the central AGN is responsible for the observed emission-line properties further than 4 arcsec (360 pc) from the core, C4. Within this region, a body of evidence (radio-line co-spatiality, low [O III]/H α and estimated fast shocks) suggests additional ionization from the jet. [ABSTRACT FROM AUTHOR]

The first direct detection of gravitational waves was made in 2015 September with the Advanced LIGO detectors. By prior arrangement, a worldwide collaboration of electromagnetic follow-up observers were notified of candidate gravitational wave events during the first science run, and many facilities were engaged in the search for counterparts. Three alerts were issued to the electromagnetic collaboration over the course of the first science run, which lasted from 2015 September to 2016 January. Two of these alerts were associated with the gravitational wave events since named GW150914 and GW151226. In this paper we provide an overview of the Liverpool Telescope contribution to the follow-up campaign over this period. Given the hundreds of square degree uncertainty in the sky position of any gravitational wave event, efficient searching for candidate counterparts required survey telescopes with large (∼degrees) fields of view. The role of the Liverpool Telescope was to provide followup classification spectroscopy of any candidates. We followed candidates associated with all three alerts, observing 1, 9 and 17 candidates respectively. We classify the majority of the transients we observed as supernovae. No counterparts were identified, which is in line with expectations given that the events were classified as black hole–black hole mergers. However these searches laid the foundation for similar follow-up campaigns in future gravitational wave detector science runs, in which the detection of neutron star merger events with observable electromagnetic counterparts is much more likely. [ABSTRACT FROM AUTHOR]

ABSTRACT Follow-up observations of large numbers of gamma-ray burst (GRB) afterglows, facilitated by the Swift satellite, have produced a large sample of spectral energy distributions and light curves, from which their basic micro- and macro-physical parameters can in principle be derived. However, a number of phenomena have been observed that defy explanation by simple versions of the standard fireball model, leading to a variety of new models. Polarimetry can be a major independent diagnostic of afterglow physics, probing the magnetic field properties and internal structure of the GRB jets. In this paper we present the first high-quality multi-night polarimetric light curve of a Swift GRB afterglow, aimed at providing a well-calibrated data set of a typical afterglow to serve as a benchmark system for modelling afterglow polarization behaviour. In particular, our data set of the afterglow of GRB 091018 (at redshift z = 0.971) comprises optical linear polarimetry ( R band, 0.13-2.3 d after burst); circular polarimetry ( R band) and near-infrared linear polarimetry ( Ks band). We add to that high-quality optical and near-infrared broad-band light curves and spectral energy distributions as well as afterglow spectroscopy. The linear polarization varies between 0 and 3 per cent, with both long and short time-scale variability visible. We find an achromatic break in the afterglow light curve, which corresponds to features in the polarimetric curve. We find that the data can be reproduced by jet break models only if an additional polarized component of unknown nature is present in the polarimetric curve. We probe the ordered magnetic field component in the afterglow through our deep circular polarimetry, finding Pcirc < 0.15 per cent (2σ), the deepest limit yet for a GRB afterglow, suggesting ordered fields are weak, if at all present. Our simultaneous R- and Ks-band polarimetry shows that dust-induced polarization in the host galaxy is likely negligible. [ABSTRACT FROM AUTHOR]

ABSTRACT We report the detection of a faint optical flash by the 2-m Faulkes Telescope North simultaneously with the second of two prompt γ-ray pulses in INTEGRAL gamma-ray burst (GRB) 080603A, beginning at trest= 37 s after the onset of the GRB. This optical flash appears to be distinct from the subsequent emerging afterglow emission, for which we present comprehensive broad-band radio to X-ray light curves to 13 d post-burst and rigorously test the standard fireball model. The intrinsic extinction towards GRB 080603A is high ( A V, z= 0.8 mag), and the well-sampled X-ray-to-near-infrared spectral energy distribution is interesting in requiring an LMC2 extinction profile, in contrast to the majority of GRBs. Comparison of the γ-ray and extinction-corrected optical flux densities of the flash rules out an inverse-Compton origin for the prompt γ-rays; instead, we suggest that the optical flash could originate from the inhomogeneity of the relativistic flow. In this scenario, a large velocity irregularity in the flow produces the prompt γ-rays, followed by a milder internal shock at a larger radius that would cause the optical flash. Flat γ-ray spectra, roughly F∝ν−0.1, are observed in many GRBs. If the flat spectrum extends down to the optical band in GRB 080603A, the optical flare could be explained as the low-energy tail of the γ-ray emission. If this is indeed the case, it provides an important clue to understanding the nature of the emission process in the prompt phase of GRBs and highlights the importance of deep ( R > 20 mag), rapid follow-up observations capable of detecting faint, prompt optical emission. [ABSTRACT FROM AUTHOR]

We present a comprehensive multiwavelength temporal and spectral analysis of the ‘fast rise exponential decay’ GRB 070419A. The early-time emission in the γ-ray and X-ray bands can be explained by a central engine active for at least 250 s, while at late times the X-ray light curve displays a simple power-law decay. In contrast, the observed behaviour in the optical band is complex (from 102 up to 106 s). We investigate the light-curve behaviour in the context of the standard forward/reverse shock model; associating the peak in the optical light curve at ∼450 s with the fireball deceleration time results in a Lorenz factor at this time. In contrast, the shallow optical decay between 450 and 1500 s remains problematic, requiring a reverse shock component whose typical frequency is above the optical band at the optical peak time for it to be explained within the standard model. This predicts an increasing flux density for the forward shock component until , inconsistent with the observed decay of the optical emission from . A highly magnetized fireball is also ruled out due to unrealistic microphysic parameters and predicted light-curve behaviour that is not observed. We conclude that a long-lived central engine with a finely tuned energy injection rate and a sudden cessation of the injection is required to create the observed light curves, consistent with the same conditions that are invoked to explain the plateau phase of canonical X-ray light curves of γ-ray bursts. [ABSTRACT FROM AUTHOR]

We present the results of an analysis of a well-selected sample of galaxies with active and inactive galactic nuclei from the Sloan Digital Sky Survey, in the range . The SDSS galaxy catalogue was split into two classes of active galaxies, Type 2 active galactic nuclei (AGN) and composites, and one set of inactive, star-forming/passive galaxies. For each active galaxy, two inactive control galaxies were selected by matching redshift, absolute magnitude, inclination, and radius. The sample of inactive galaxies naturally divides into a red and a blue sequence, while the vast majority of AGN hosts occur along the red sequence. In terms of Hα equivalent width (EW), the population of composite galaxies peaks in the valley between the two modes, suggesting a transition population. However, this effect is not observed in other properties such as the colour–magnitude space or colour–concentration plane. Active galaxies are seen to be generally bulge-dominated systems, but with enhanced Hα emission compared to inactive red-sequence galaxies. AGN and composites also occur in less dense environments than inactive red-sequence galaxies, implying that the fuelling of AGN is more restricted in high-density environments. These results are therefore inconsistent with theories in which AGN host galaxies are a ‘transition’ population. We also introduce a systematic 3D spectroscopic imaging survey, to quantify and compare the gaseous and stellar kinematics of a well-selected, distance-limited sample of up to 20 nearby Seyfert galaxies, and 20 inactive control galaxies with well-matched optical properties. The survey aims to search for dynamical triggers of nuclear activity and address outstanding controversies in optical/infrared imaging surveys. [ABSTRACT FROM AUTHOR]

We present a multiwavelength study of GRB 060108 – the 100th gamma-ray burst discovered by Swift. The X-ray flux and light curve (three segments plus a flare) detected with the X-ray Telescope are typical of Swift long bursts. We report the discovery of a faint optical afterglow detected in deep BVRi′-band imaging obtained with the Faulkes Telescope North beginning 2.75 min after the burst. The afterglow is below the detection limit of the Ultraviolet/Optical Telescope within 100 s of the burst, while is evident in K-band images taken with the United Kingdom Infrared Telescope 45 min after the burst. The optical light curve is sparsely sampled. Observations taken in the R and i′ bands can be fitted either with a single power-law decay in flux, where , or with a two-segment light curve with an initial steep decay , flattening to a slope . A marginal evidence for rebrightening is seen in the i′ band. Deep R-band imaging obtained ∼12 d post-burst with the Very Large Telescope reveals a faint, extended object at the location of the afterglow. Although the brightness is compatible with the extrapolation of the slow decay with index α2, significant flux is likely due to a host galaxy. This implies that the optical light curve had a break before 12 d, akin to what observed in the X-rays. We derive the maximum photometric redshift for GRB 060108. We find that the spectral energy distribution at 1000 s after the burst, from the optical to the X-ray range, is best fitted by a simple power law, , with and a small amount of extinction. The optical to X-ray spectral index confirms GRB 060108 to be one of the optically darkest bursts detected. Our observations rule out a high redshift as the reason for the optical faintness of GRB 060108. We conclude that a more likely explanation is a combination of an intrinsic optical faintness of the burst, a hard optical to X-ray spectrum and a moderate amount of extinction in the host galaxy. [ABSTRACT FROM AUTHOR]

First using a sample of 32 gamma-ray bursts (GRBs) with known redshift and then a sample of 551 BATSE GRBs with derived pseudo-redshift, the time variability/peak luminosity correlation ( V versus L), originally found by Reichart et al. using a sample of 18 GRBs, was tested. For both samples the correlation is still found is but less relevant because of a much higher spread of the data. Assuming a straight line in the log L–log V plane , both Guidorzi et al. and Guidorzi found that the line slope for both samples is much lower than that derived by Reichart et al.: and , to be compared with by Reichart et al. Reichart & Nysewander discuss our results and attribute the different slope to the fact that we do not take into account the variance of the sample in the fit (also called the slop), and demonstrate that, using the method presented by Reichart, the expanded data set in the log L–log V plane is still well described by a line with slope . Here we compare the results of two methods accounting for the slope of the sample: the method implemented by Reichart and that by D'Agostini. We demonstrate that the first method provides an inconsistent estimate of the parameter when the sample variance is comparable to the interval of values covered by the GRB variability. We also demonstrate that, using the second method, the slope of the log L–log V correlation is still consistent with that derived by us earlier and inconsistent with that derived by Reichart & Nysewander. Finally we discuss the implications on the interpretations proposed for the V– L correlation and show that our results are in agreement with the peak energy/variability correlation found by Lloyd-Ronning & Ramirez-Ruiz and the peak energy/peak luminosity correlation found by Yonetoku et al. and Ghirlanda et al. [ABSTRACT FROM AUTHOR]

We report test results of the correlation between the time variability and the peak luminosity of gamma-ray bursts (GRBs), using a larger sample (32) of GRBs with known redshift than that available to Reichart et al., and using as a variability measure that introduced by these authors. The results are puzzling. Assuming an isotropic-equivalent peak luminosity, as had Reichart et al., a correlation is still found, but it is less relevant and inconsistent with a power law as previously reported. Assuming as the peak luminosity that corrected for GRB beaming for a subset of 16 GRBs with known beaming angle, the correlation becomes slightly less significant. [ABSTRACT FROM AUTHOR]

We have determined the structure and kinematics of ionized gas in the weak oval bar of the archetypal Seyfert 1 galaxy, NGC 4151, using the TAURUS Fabry–Perot interferometer to simultaneously map the distribution and kinematics of Hβ emission. We also present broad-band ultraviolet imaging of the host galaxy, obtained withXMM–Newton, which shows the detailed distribution of star formation in the bar and in the optically faint outer spiral arms. We compare the distribution and kinematics of ionized gas with that previously determined in neutral hydrogen by Mundell&Shone; we suggest that the distribution of bright, patchy ultraviolet emission close to the H ishocks is consistent with ionization by star clusters that have formed in compressed pre-shock gas. These clusters then travel ballistically through the gaseous shock to ionize gas downstream along the leading edge of the bar. In addition, we detect, for the first time, ionized gas within the shock itself, which is streaming to smaller radii in the same manner as the neutral gas. [ABSTRACT FROM AUTHOR]

We present the results of neutral hydrogen (HI) observations of the NGC 5044 and NGC 1052 groups, as part of a GEMS (Group Evolution Multiwavelength Study) investigation into the formation and evolution of galaxies in nearby groups. Two new group members have been discovered during a wide-field HI imaging survey conducted using the ATNF Parkes telescope. These results, as well as those from follow-up H I synthesis and optical imaging, are presented here. J1320 – 1427, a new member of the NGC 5044 group, has an HI mass of MHI = 1.05 × 109 M and MHI/LL = 1.65 M/L, with a radial velocity of v = 2750 km s-1. The optical galaxy is characterized by two regions of star formation, surrounded by an extended, diffuse halo. J0249–0806, the new member of the NGC 1052 group, has MHI = 5.4 × 108 M, MHI/LR = 1.13 M/L and v= 1450 km s-l. The optical image reveals a low-surface-brightness galaxy. We interpret both of these galaxies as irregular type, with J0249 – 0806 possibly undergoing first infall into the NGC 1052 group. [ABSTRACT FROM AUTHOR]

In this paper, we present new results from an extensive set of Hubble Space Telescope (HST) and ground-based observations of the Seyfert galaxy NGC 2110. The HST data sets include Wide Field Planetary Camera 2 (WFPC2) observations as well as the first high-spatial resolution spectroscopy ([OI], [NII], Hα and [SII] lines) of this galaxy obtained using the Space Telescope Imaging Spectrograph (STIS). The ground-based data are three-dimensional (x, y, λ) spectrographic observations obtained using the integral field spectrograph OASIS on the Canada—France—Hawaii Telescope, complemented by near-infrared long-slit spectroscopy obtained using NIRSPEC on the Keck-II telescope. The OASIS observations cover regions containing both stellar absorption lines and major optical emission lines. The NIRSPEC observations cover the H and K bands. Combined with archival HST observations, the WFPC2 data provide us with a high-spatial resolution extinction map. The OASIS data allowed bidimensional mapping of the stellar and gaseous kinematics, as well as of the spectral properties of the ionized gas. These results are compared to those obtained in the near-infrared with NIRSPEC/Keck. Last, we used the STIS data to probe the ionized gas kinematics and properties in the inner 4 arcsec along PA = 156° at unprecedented spatial resolution. Our two-dimensional (2D) map of the stellar velocity field and the near-infrared stellar velocity profile are symmetric about the nucleus, confirming the results of previous long-slit observations. The asymmetry of the velocity field of the ionized gas is present at the same level for visible and near-infrared lines, indicating this is not a reddening effect. Multiple Gaussian firing of the emission-line profile allowed the contributions of the broad and a narrow components to he disentangled. The intensity peak of the [OIII] narrow component is located north of the nucleus, indicating that the bulk of the narrow [OIII] emission comes from the jet-like structure (Mulchaey et al.) and not from the nucleus itself. We suggest that the northern arm is the anomalous one, contrary to what has been claimed earlier. Last, we also show that the elongated region of high gas velocity dispersion located close to the nucleus and discovered by González Delgado et al. is intrinsic to the narrow component. [ABSTRACT FROM AUTHOR]

ABSTRACTWe present sensitive, high-resolution observations of neutral hydrogen (HI) in the unusually gas-rich, oval distortion of the Seyfert galaxy NGC 4151. The gas dynamics of the oval are found to be consistent with those of a kinematically weak bar, fully confirming previous suggestions for the presence of a fat bar, and, for the first time, individual gaseous features in the bar are spatially resolved. In particular, the two bright regions close to the leading edges of the bar in NGC 4151 exhibit kinematics strikingly similar to the signature of bar shocks seen in gas-dynamical simulations, and demonstrate how strong the gaseous response may be even in such a weak bar potential. The residual velocity field, showing deviations from circular motion, is largely consistent with streaming in a bar potential, and, in addition, clearly shows that inflow is concentrated in narrow regions originating in the shocks. This inflow may represent an early stage in the fuelling process of the AGN. The presence and properties of the shocks in NGC 4151 indicate that, in addition to the x1 orbits, the family of x2 orbits exists and is of significant extent in the bar of NGC 4151, with gas streaming from the shocks making the transition between the two families. We therefore suggest that the circumnuclear ellipse, identified optically by previous authors and associated with gas flowing in x2 orbits, has formed as a natural consequence of the gas flows in the bar without the requirement for a second, inner bar. Observations of HI were previously thought to be ill-suited to the study of bar shocks because of limitations in angular resolution and sensitivity. However, our observations show that, following recent instrumental enhancements, such measurements are now feasible, albeit at the limits of instrumental capability. [ABSTRACT FROM AUTHOR]

ABSTRACTWe present sensitive, high angular resolution (6× 5 arcsec2) λ 21-cm observations of the neutral hydrogen in the nearby barred Seyfert galaxy, NGC 4151. These HI observations, obtained using the VLA in B configuration, are the highest resolution of this galaxy to date, and reveal hitherto unprecedented detail in the distribution and kinematics of the HI on sub-kiloparsec scales. A complete analysis and discussion of the HI data are presented and the global properties of the galaxy are related to the bar dynamics presented in Paper I. HI absorption, consistent with previous studies, is detected against the radio continuum nucleus and shows two components -- a deep absorption component, centred at 987 ± 1 km s-1 and width 87 ± 3 km s-1, and a weaker component, redshifted to 1096 ± 6 km s-1 with a width of 35 ± 15 km s-1. An alternative fit is also presented. In addition to the absorption, a high velocity cloud is detected in emission, coincident with the nucleus. This cloud is redshifted by 260 km s-1 from systemic, has an HI mass of 2.3 × 107 M⊙, and corresponds to outflow on the far side of the nucleus. Contrary to previous studies, no HI bridge is detected reaching from the shocks directly across the nucleus. Instead, the gas streams from the shocks on to smaller orbits and forms fingers of HI that wind around the nucleus, consistent with predictions from general numerical simulations of bars. These fingers correspond closely with dust arcs seen in optical studies and resemble nuclear features seen by others in weak barred galaxies such as M100. A new rotation curve is presented, extending to within 8 arcsec of the nucleus and showing a turnover at a radius of ∼35 arcsec, which was previously undetected in lower resolution studies. The corresponding resonance curve and the properties of the shocks (Paper I) yield a bar pattern speed of 24.5 ± 3.7 km s-1 and one inner Lindblad resonance (ILR) at a radius of 2.8 ± 0.6 kpc. Our observations, however, do not rule out the possibility of an inner ILR. [ABSTRACT FROM AUTHOR]

We have used MERLIN to observe neutral hydrogen absorption against the central region of the ultraluminous infrared galaxy (ULIRG) galaxy Mrk 273 with an angular resolution of 0.2 arcsec. This represents a factor of 5 increase in resolution compared with previous work. Absorption has been resolved against two of three radio continuum components. A Hubble Space Telescope (HST) image reveals a complex central region composed of clumpy emission obscured by dust lanes. We find that the northern and south-eastern radio components are associated with two optical components. The alignment supports the idea that Mrk 273 has a double nucleus due to a recent galactic merger event. Broad, strong and spatially varying absorption is seen against the northern radio component with a velocity gradient of 1990±50 km s-1 kpc-1. The absorption resolves into six discrete components with an average column density of 1.7×1022 atom cm-2. We propose that the absorption is due to a clumpy ring or disc of neutral gas of radius ∼250 pc rotating around a central starburst. In addition to the broad component, narrow absorption (<100 km s-1) is detected against the northern and south-eastern components. Absorption is not detected against the weak (2 mJy) south-western component. We propose that the narrow absorption is due to quiescent gas in a large-scale dust lane that coincides with these regions of narrow absorption. [ABSTRACT FROM AUTHOR]