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We present Space Telescope Imaging Spectrograph emission-line spectra of the central regions of the spiral galaxies NGC 1300 and NGC 2748. From the derived kinematics of the nuclear gas we have found evidence for central supermassive black holes in both galaxies. The estimated mass of the black hole in NGC 1300 is 6.6 (+6.3, -3.2) x 10^7 solar masses and in NGC 2748 is 4.4 (+3.5, -3.6) x 10^7 solar masses (both at the 95% confidence level). These two black hole mass estimates contribute to the poorly sampled low-mass end of the nuclear black hole mass spectrum.

We present surface photometry for the central regions of a sample of 48 spiral galaxies (mostly unbarred and barred of types Sbc or Sc) observed with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. Surface brightness profiles were derived and modeled with a Nuker law. We also analyzed archival Wide Field Planetary Camera~2 images with a larger field of view, available for 18 galaxies in our sample. We modeled the extracted bulge surface brightness profiles with an exponential, a de Vaucouleurs or a Sersic profile. In agreement with previous studies, we find that bulges of Sbc galaxies fall into two categories: bulges well described by an exponential profile and those well described by an de Vaucouleurs profile. Only one galaxy requires the use of a more general Sersic profile to properly describe the bulge. Nuclear photometrically distinct components are found in ~55% of the galaxies. For those that we classify as star clusters based on their resolved extent we find absolute magnitudes that are brighter on average than those previously identified in spiral galaxies. This might be due to a bias in our sample toward star forming galaxies, combined with a trend for star forming galaxies to host brighter central clusters.

We describe an on-going HST program aimed at determining the relationship between the nuclear black hole mass and bulge mass in spiral galaxies. We have selected a volume limited sample of 54 nearby spiral galaxies for which we already have ground based emission line rotation curves, CCD surface photometry and radio maps. We are now obtaining HST/STIS longslit observations of each of the galaxies in the sample in order to determine the nuclear Halpha rotation curve at high (~0.1") spatial resolution. We will use these data to measure the unresolved dark mass concentration at the nucleus of each object. Here we show the first results from observations of objects in the sample., 4 pages, contributed talk at IAU Symposium 205 "Galaxies and their Constituents at the Highest Angular Resolutions", Manchester UK, August 2000. R. Schilizzi, S. Vogel, F. Paresce, M. Elvis eds, ASP Conf. Ser

We report the analysis of near-infrared (near-IR) imaging, polarimetric and spectroscopic observations of the powerful radio galaxy 3C 433 (z = 0.1016), obtained with the Hubble Space Telescope (HST) and the United Kingdom Infrared Telescope. The high spatial resolution of HST allows us to study the near-nuclear regions of the galaxy ( 10(4) km s(-1) (full width at half-maximum) to escape detection in our near-IR spectrum. Dichroic extinction is the most likely polarization mechanism because it is consistent with the various available extinction estimates. In this case, a highly ordered, coherent toroidal magnetic field must be present in the obscuring structure close to the nucleus.

The uncertainty surrounding the nature of the heating mechanism for the dust that emits at mid- to far-IR (MFIR) wavelengths in active galaxies limits our understanding of the links between active galactic nuclei (AGN) and galaxy evolution, as well as our ability to interpret the prodigious infrared and sub-mm emission of some of the most distant galaxies in the Universe. Here we report deep Spitzer observations of a complete sample of powerful, intermediate redshift (0.05 < z < 0.7) radio galaxies and quasars. We show that AGN power, as traced by [OIII]5007 emission, is strongly correlated with both the mid-IR (24 micron) and the far-IR (70 micron) luminosities, however, with increased scatter in the 70 micron correlation. A major cause of this increased scatter is a group of objects that falls above the main correlation and displays evidence for prodigious recent star formation activity at optical wavelengths, along with relatively cool MFIR colours. These results provide evidence that illumination by the AGN is the primary heating mechanism for the dust emitting at both 24 and 70 microns, with starbursts dominating the heating of the cool dust in only 20 -- 30% of objects. This implies that powerful AGN are not always accompanied by the type of luminous starbursts that are characteristic of the peak of activity in major gas-rich mergers.

We have obtained Integral Field Spectroscopy for 23 spiral bulges using INTEGRAL on the William Herschel Telescope and SPIRAL on the Anglo-Australian Telescope. This is the first 2D survey directed solely at the bulges of spiral galaxies. Eleven galaxies of the sample do not have previous measurements of the stellar velocity dispersion (sigma*). These data are designed to complement our Space Telescope Imaging Spectrograph program for estimating black hole masses in the range 10^6-10^8M_sun using gas kinematics from nucleated disks. These observations will serve to derive the stellar dynamical bulge properties using the traditional Mgb and CaII triplets. We use both Cross Correlation and Maximum Penalized Likelihood to determine projected sigma* in these systems and present radial velocity fields, major axis rotation curves, curves of growth and sigma* fields. Using the Cross Correlation to extract the low order 2D stellar dynamics we generally see coherent radial rotation and irregular velocity dispersion fields suggesting that sigma* is a non-trivial parameter to estimate., Comment: 11 pages, 30 figures, accepted for publication in ApJS

We have obtained HST/STIS long slit spectroscopy of the aligned emission line nebulae in three compact steep spectrum (CSS) radio sources - 3C67, 3C 277.1, and 3C 303.1. We find systematic offsets (similar to 300 - 500 km s(-1)) of the emission line velocities on one or both sides of the radio sources. We also see evidence for broad lines (FWHM similar to 500 km s(-1)) and complex emission line profiles. In 3C 303.1 the data are consistent with multiple components and possibly split lines. The amplitude of the velocity variations is not so large as to exclude gravitationally-induced motions. However, the complex kinematics, the lack of a signature of Keplerian rotation, and the association of the velocity variations with the radio lobes are consistent with the observed similar to 300-500 km s(-1) velocities being driven by the expansion of the radio source. Acceleration of the clouds by the bow shock is plausible given the estimated densities in the clouds and the velocities observed in the much smaller compact symmetric objects and with expansion velocities estimated from spectral ageing. This conclusion is unchanged if we consider the scenario in which the cloud acceleration is dominated by the post bow shock flow.

We have obtained Hubble Space Telescope Space Telescope Imaging Spectrograph long-slit spectroscopy of the aligned emission-line nebulae in three compact steep-spectrum radio sources: 3C 67, 277.1, and 303.1. We find systematic offsets (~300–500 km s-1) of the emission-line velocities on one or both sides of the radio sources. We also see evidence for broad lines (FWHM ~ 500 km s-1) and complex emission-line profiles. In 3C 303.1 the data are consistent with multiple components and possibly split lines. The amplitude of the velocity variations is not so large as to exclude gravitationally induced motions. However, the complex kinematics, the lack of a signature of Keplerian rotation, and the association of the velocity variations with the radio lobes are consistent with the motions being driven by the expansion of the radio source. These kinematic signatures are consistent with an interaction between the expanding radio lobe and the emission-line clouds in which the clouds have been accelerated to velocities ~300–500 km s-1. Acceleration of the clouds by the bow shock is plausible given the estimated densities in the clouds and the velocities observed in the much smaller compact symmetric objects and with expansion velocities estimated from spectral aging.

We present optical spectropolarimetric observations of three radio-loud broad-line active galactic nuclei: 3C 332, 3C 351 and 4C 73.18, together with new observations of 3C 390.3, which we observed previously. Intrinsically polarized broad Hα emission was detected in 3C 332 and 3C 390.3 at levels of ∼3 per cent and ∼1 per cent, respectively. Significant polarization was not detected in 3C 351, while the polarization measured in 4C 73.18 (∼1 per cent) is consistent with foreground contamination by the galactic interstellar medium. Although 3C 332 and 3C 390.3 both exhibit ‘double-peaked’ broad Hα line profiles, their polarization properties differ significantly. The polarized Hα emission in 3C 332 has a similar profile to that seen in total flux and the continuum and line emission is polarized at 70° to the axis of the radio source. In 3C 390.3, however, the double peaks seen in total flux are suppressed in polarized flux and the Hα line and continuum are polarized at ∼5° to the axis of the radio emission. Comparison of these new observations of 3C 390.3 with data obtained 2 years previously reveals significant variations in both total and polarized flux. The implications of these observations for the relationship between the geometry of the broad-line region and that of the scattering medium are discussed. We argue that models in which the Hα emission arises in a relativistically rotating disc cannot easily explain the observed polarization properties of 3C 332 and, in particular, 3C 390.3. We consider instead a model in which the line emission originates in a bipolar outflow and present calculations showing that the observed polarization properties of 3C 390.3 can be broadly explained by scattering from the inner wall of an obscuring torus, while those of 3C 332 are consistent with scattering by particles situated above the poles of the torus. We outline a scheme in which either toroidal or polar scattering dominates in a given object, depending on the orientation of its radio jet axis to our line of sight.

We present the result obtained from a study, based on long-slit spectroscopy, of the kinematics and ionization mechanisms of the line-emitting gas for a sample of four high/intermediate-redshift radio galaxies. In two of the galaxies (3C352 and 3C435A) the radio sources are of the same scale as the emission-line regions, whereas in the other two (3C34 and 3C330) the radio sources are extended on a larger scale than the emission-line structures. We see evidence for shock-acceleration of the emission-line gas in the extended regions of all the galaxies, even in the largest radio sources of our sample, in which the radio hot spots have passed the extended gas of the galaxies. The extended regions present highly disturbed kinematics (line-splitting and/or underlying broad components), which are difficult to explain if we do not consider a strong interaction between the radio-emitting components and the ambient gas. However, the dominant ionization mechanism of the line-emitting gas remains uncertain. We have compared the optical diagnostic line ratios of the galaxies in our sample with both AGN-photoionization and shock-ionization models. We find a lack of consistency in explaining the main ionization mechanism of the emission-line gas. This suggest that, if the extended regions are shock-ionized, some of the assumptions implicit in the shock models may need to be reconsidered. In addition, we have investigated the nebular continuum cointribution to the UV excess in the galaxies of our sample. We find a substantial nebular emission contribution to the UV continuum in all the cases. However, after the subtraction iof the nebular component, a significant UV excess remains in the extended nebulae of most of the objects.

We used the near infrared spectrometer ISAAC at the ESO 'Very Large Telescope' to map the velocity field of Centaurus A (NGC 5128) at several position angles and locations in the central 20" of the galaxy. The high spatial resolution (~0.5") velocity fields from both ionized and molecular gas (PaBeta, [FeII], BrGamma, and H2) are not compromised by either excitation effects or obscuration. We identify three distinct kinematical systems: (i) a rotating 'nuclear disk' of ionized gas, confined to the inner 2", the counterpart of the PaAlpha feature previously revealed by HST/NICMOS imaging; (ii) a ring-like system with a ~6" inner radius detected only in H2, likely the counterpart of the 100pc-scale structure detected in CO by other authors; (iii) a normal extended component of gas rotating in the galactic potential. The nuclear disk is in keplerian rotation around a central mass concentration, dark (M/L>20 Msun/LsunK) and point-like at the spatial resolution of the data (R15deg) is M=2(+3.0;-1.4) 10^8 Msun. The ring-like system is probably characterized by non-circular motions; a 'figure-of-8' pattern observed in the H2 position-velocity diagram might provide kinematical evidence for the presence of a nuclear bar., 43 pages, 19 figures, Astrophysical Journal in press, higher quality figures available at http://www.arcetri.astro.it/~marconi/pubs.html

We report results from HST/NICMOS 2 micron imaging polarimetry of the central region of Centaurus A. In the vicinity of the nucleus we observe a complex polarization structure which we explain by a combination of scattering of nuclear light and dichroic polarization associated with the dust lane. The scattered nuclear radiation is found in an angular region which extends over ~ 70 degrees and thus it does not originate from a highly collimated beam, but is associated with more omni-directional nuclear illumination. These observations also show the presence of an unresolved, highly polarized (P = 11.1 %) nuclear source whose polarization angle PA = 148.2 degrees is perpendicular to the jet axis. We set an upper limit of 0.04'' (~0.8 pc) to its extent. The observed nuclear polarization is naturally accounted for if we are observing scattered light from an otherwise obscured nucleus provided that both the scattering region and the occulting torus are extremely compact, with an outer radius of less than ~ 1 pc. Alternatively, we might be directly seeing the infrared counterpart of the radio core, similar to those found in other low luminosity radio-galaxies observed with HST. We discuss these results in the framework of the FRI / BL Lac unifying model.

‘The definitive version is available at www.blackwell-synergy.com.’ Copyright Blackwell Publishing. DOI: 10.1046/j.1365-8711.2000.03045.x [Full text of this article is not available in the UHRA]

NGC 3516 displays the strongest intrinsic blueshifted UV absorption lines of any Seyfert 1 galaxy. In this paper, we report on UV spectrophotometric monitoring data obtained over a period of 11 months using the Hubble Space Telescope Faint Object Spectrograph (HST/FOS). The observations were at ~2 A resolution and covered the wavelength range 1150-3300 A. During the (HST/FOS) observation period, the UV continuum showed a factor of 5 variation, spanning almost the entire range in continuum flux seen in over 15 yr of IUE data. The broad (FWHM ~ 10,000 km s-1) high-ionization emission lines (HILs) of Lyα λ1215, C IV λ1549, N V λ1240, and He II λ1640 showed significant variation (a factor of ~2), while the low-ionization lines (LILs) of Mg II λ2798 and Fe II showed no significant variation (less than 7%) within the signal-to-noise ratio of our data. No significant variability was detected in the narrow (FWHM ~ 1000 km s-1) emission line strengths over the course of our campaign. The profile shapes of the HILs also display significant variation, with the largest flux changes occurring in the core of the line, blueward of line center, a picture generally consistent with a kinematically radial outflowing broad-line region. Interestingly, the profile shapes of Lyα and C IV are identical, suggesting a common kinematic origin for these lines. This is supported by an absence of variation in their respective line ratios despite significant flux changes. Perhaps even more surprisingly, at high continuum levels the profile shapes of C IV and Mg II are indistinguishable. Moreover, although the Mg II emission-line flux varies on longer timescales (~years), the profile shape of the Mg II emission line appears invariant on timescales of a decade. Our spectra clearly show narrow (FWHM ~ 200-500 km s-1) intrinsic absorption lines of highly ionized species (e.g., Lyα λ1215, N V λ1240, Si IV λ1397, and C IV λ1549), but we do not observe the higher velocity C IV absorption-line component seen in the historic (pre-1989) IUE/SWP spectra. The absence of a detectable variation in the narrow absorption line strengths over the course of our observing campaign (11 months) suggests absorption in ions close to their peak in fractional abundance. We find no evidence for a change in the strength of the narrow absorption lines, suggesting that the absorbing gas remains stable on timescales of at least 20 months. The line widths and ionization state of the intrinsic absorbers are found to be consistent with a narrow-line region origin for the absorbing gas.

Derivation of accurate polarization information about an astronomical target is a vital tool for investigation of astrophysical processes. Use of large area detectors for imaging and spectroscopy has become commonplace, and frequently such instruments offer a polarization capability. Processing of polarimetric data, however, is nontrivial, especially when the polarimeter is far from ideal. Here we present an overview of the analysis procedures needed to properly process polarimetry data that comprise a series of images of an object taken through a given set of polarizers, such as the imaging instruments on the Hubble Space Telescope (HST). The analysis can also be used for other types of polarization data, such as spectra. We consider only linear polarization, not circular. The polarizers do not need to be perfect polarizers, although it is important that their characteristics be well established. From an input data set of n intensities (or, equivalently, fluxes) and their errors, assumed independent between observations, corresponding to a set of observations through n polarizers (not necessarily identical or perfect), we show how to derive the Stokes parameters and their covariance matrix both for the special case of n = 3 and for general n.We then discuss how to derive higher level parameters such as polarization degree and position angle and their associated uncertainties and indicate ways to "debias" the positive definite polarization degree. We present tests of our analysis using Monte Carlo simulations. Finally, we show the achievable accuracy for various levels of polarization and signal-to-noise ratio for typical cases, which should be useful for observation design. The techniques allow accurate recovery of polarization information from several of the instruments on board the HST as well as estimates of the uncertainties in the results.

We present the results from a detailed kinematic analysis of both ground-based, and Hubble Space Telescope/Faint Object Camera long-slit spectroscopy at sub-arcsec spatial resolution, of the narrow-line region of NGC 4151. In agreement with previous work, the extended emission gas (R > 4") is found to be in normal rotation in the galactic plane, a behaviour that we were able to trace even across the nuclear region, where the gas is strongly disturbed by the interaction with the radio jet, and connects smoothly with the large scale rotation defined by the neutral gas emission. The HST data, at 0.029" spatial resolution, allow us for the first time to truly isolate the kinematic behaviour of the individual clouds in the inner narrow-line region. We find that, underlying the perturbations introduced by the radio ejecta, the general velocity field can still be well represented by planar rotation down to a radius of ~ 0.5" (30 pc), distance at which the rotation curve has its turnover. The most striking result that emerges from our analysis is that the galaxy potential derived fitting the rotation curve changes from a "dark halo" at the ENLR distances to dominated by the central mass concentration in the NLR, with an almost Keplerian fall-off in the 1"< R < 4" interval. The observed velocity of the gas at 0.5" implies a mass of M ~ 10E9 M(sol) within the inner 60 pc. The presence of a turnover in the rotation curve indicates that this central mass concentration is extended. The first measured velocity point (outside the region saturated by the nucleus) would imply an enclosed mass of ~ 5E7 M(sol) within R ~ 0.15" (10 pc) which represents an upper limit to any nuclear point mass.

We present intermediate-resolution optical spectropolarimetry of the radio-loud quasar 4C 74.26. Large variations in both the degree and position angle of polarization are observed across the broad H α line. After continuum subtraction, we find that in polarized flux this feature is redshifted by ≈ 2000 km s-1 relative to its median wavelength in total flux. We show that the H α polarization can be explained by scattering in a high-speed outflow which, if it is directed along the axis of the radio jet, must have a velocity ≥ 5000 km s-1 in order to account for the observed redshift. The polarization position angle is not precisely orthogonal to that of the radio source, suggesting that the scattering outflow is either inhomogeneous, or somewhat misaligned with the jet axis.

During the 1996 HST/FOS monitoring campaign of the Seyfert 1 galaxy NGC 3516, the UV continuum showed a factor of 5 variation; correspondingly the strongest broad UV emission lines (e.g. Ly-alpha, CIV) displayed somewhat weaker, though still significant variations (a factor of 2). In contrast, no variation was detected in the strong broad MgII+UV FeII emission-line complex. While historically the flux in the broad MgII emission line has varied (a factor of 2 within a few years), the profile shape has not been observed to change over the past decade. In contrast, the high ionization lines (HILs) show both emission-line flux and profile changes on relatively short timescales, which appear to be correlated with changes in the continuum level. Significantly, on 1996, February 21, the profile shapes of the HILs (e.g. Ly-alpha, CIV) and low ionization lines (LILs, e.g. MgII) were identical, at which time the continuum level was at its highest. These results impose stringent constraints upon viable kinematic models of the BLR in NGC 3516, some of which we discuss below.

Infrared-imaging observations that span the wavelength range of 0.8-2.35 μm have been obtained for the archetypal powerful radio galaxy Cygnus A using the Near-Infrared Camera and Multiobject Spectrograph on board the Hubble Space Telescope. At 2.25 μm, the images are dominated by the presence of a nuclear point source (FWHM < 021), whose flux is a factor of ~4 times less than the limits deduced from previous ground-based studies. The observations also reveal an edge-brightened biconical structure centered on the point source, which is strikingly similar to those observed around young stellar objects. The high polarization and orientation of the bicone relative to the radio axis lead us to conclude that it is an illuminated structure, while the edge brightening provides evidence that the bicone is defined as much by outflows in the nuclear regions as by the polar diagram of the illuminating quasar radiation field. A further implication of our observations is that not all of the anisotropy in the nuclear radiation field is caused by extinction on a scale less than 100 pc in the torus; some of the anisotropy must be generated by absorption and scattering in the dust lane on a 1 kpc scale.

Original article can be found at: www3.interscience.wiley.com Copyright Blackwell Publishing / Royal Astronomical Society. DOI: 10.1046/j.1365-8711.1998.01586.x [Full text of this article is not available in the UHRA]

We report HST NICMOS observations of the central region of NGC 5128 at 2.2mic and in Paschen Alpha (PA). The continuum images show extended emission typical of an elliptical galaxy and a strong unresolved central source we identify as the nucleus of the galaxy. Its position is consistent with ground-based IR and radio data, and with the peak of reddening found with WF/PC-1. In PA, we detect a prominent elongated structure, centered on the nucleus, extended by ~2" at a position angle of 33deg, and with a major to minor axis ratio of ~2. We interpret this as an inclined, ~40 parsec diameter, thin nuclear disk of ionized gas rather than a jet-gas cloud interaction. We do see several weaker PA features, some of which may be circumnuclear gas clouds shocked by the X-ray/radio jet. The disk is one of the smallest ever observed at the nucleus of an AGN. It is not perpendicular to the jet, but consistent with being oriented along the major axis of the bulge. If it represents the warped outer portion of an accretion disk around a black hole, we conclude that even on the scale of a few parsecs, the disk is dominated by the galaxy gravitational potential and not directly related to the symmetry axis of the AGN., 9 pages, 5 figures, Astrophysical Journal Letters in press

Original article can be found at: www3.interscience.wiley.com Copyright Blackwell Publishing / Royal Astronomical Society. DOI: 10.1046/j.1365-8711.1998.01420.x [Full text of this article is not available in the UHRA]

We have obtained Hubble Space Telescope Faint Object Camera (FOC) f/48 long-slit spectroscopy of the inner 4'' of the narrow-line region (NLR) of NGC 1068 between 3500 and 5400 A with a spectral resolution of 1.78 A pixel-1. At a spatial scale of 00287 pixel-1 these data provide an order-of-magnitude improvement in resolution over previous ground-based spectra and allow us to trace the interaction between the radio jet and the gas in the NLR. Our results show that within ±05 of the radio jet the emission lines are kinematically disturbed and split into two components whose velocity separation is 1500 km s-1. The filaments associated with the radio lobe also show a redshifted kinematic disturbance on the order of 300 km s-1, which is probably a consequence of the expansion of the radio plasma. Furthermore, the material enveloping the radio jet is in a much higher ionization state than that of the surrounding NLR gas. The highest excitation is coincident with the jet axis, where emission in the coronal line of [Fe VII] λ3769 is detected and the He II λ4686 is strong but where [O II] λ3727 is depressed. This large localized increase in ionization on the jet axis is accompanied by the presence of an excess continuum. Because the electron density is substantially larger in the jet compared with the surrounding NLR, these results can be explained only if there is a more intense ionizing continuum associated with the jet. This can be accomplished in a variety of ways, which include an intrinsically anisotropic nuclear radiation field, a reduced gas covering factor, or the presence of a local ionization source. The morphology, kinematics, and, possibly, the ionization structure of the NLR in the vicinity of the jet of NGC 1068 are a direct consequence of the interaction with the radio outflow.

Original article can be found at: www3.interscience.wiley.com Copyright Blackwell Publishing / Royal Astronomical Society. DOI: 10.1046/j.1365-8711.1998.01243.x [Full text of this article is not available in the UHRA]

We present spectroscopic observations of the extended emission-line region (EELR) aligned with the radio axis of the powerful radio galaxy 3C 171. The results obtained from a detailed analysis of the observational data show that shocks induced by jet-cloud interactions have a dramatic effect on the extended line-emitting gas. The evidence for shocks includes (1) close radio-optical associations; (2) ionization minima coincident with both radio hot spots; (3) high-velocity (~500 km s-1) line splitting displaced by ~2'' (10 kpc) (a Hubble constant of H0 = 50 km s-1 and a decleration parameter of q0 are assumed throughout this paper) behind the hot spots on either side of the nucleus, spatially associated with the two inner radio knots; (4) large line widths in the extended gas (FWHM ~ 1300 km s-1); and (5) an anticorrelation between line width and ionization state in the extended gas. Given that shocks clearly determine the morphology, kinematics, and physical conditions of the extended line-emitting gas, shock ionization is a possible alternative to AGN photoionization in the EELR. The high [O III] temperatures and low He II/Hβ ratios in the EELR provide evidence that local ionization by shocks is indeed important. A pronounced UV continuum excess is also detected in the extended line-emitting regions. From the measured strength of the Balmer lines, it is found that the extended UV continuum is dominated by nebular continuum emission from the warm gas. There is no evidence whatsoever for jet-induced star formation. The properties of 3C 171—in particular the alignment of the optical line and UV-continuum emission with the radio axis, and the extreme emission-line kinematics in the extended gas—are similar to those observed in high-redshift radio galaxies. This supports the hypothesis that jet-induced shocks determine the distribution, kinematics, physical conditions, and ionization of the EELR in the powerful radio galaxies observed at high redshifts.

The core of OMC-1 has been imaged with the Near-Infrared Camera and Multiobject Spectrometer (NICMOS) on board the Hubble Space Telescope at 02 resolution in 1% filters at 2.12 and 2.15 μm, revealing intricate structures in both continuum and shocked molecular hydrogen line emission. Numerous H2-emitting clumps surrounding the BN/KL region have been resolved for the first time, several of which exhibit prototypical bow-shock morphologies with V-shaped tips. We interpret these to be lower excitation analogs of similar structures ~2' northwest of the core observed with ground-based telescopes. Many of the elongated H2 structures and bow-shock features appear to radiate outward from a region within a few arcseconds of radio source I, which suggests that the H2 energetics are dominated by one or more outflow sources in this region. However, the orientations of some features are unrelated to this apparent outflow pattern. The deeply embedded, suspected outflow source I remains undetected at 2 μm, although two faint new continuum sources have been detected within ~1'' of it. The newly resolved H2 features with bow-shock morphologies are located in regions previously identified as bow shocks by highly blueshifted components in their line profiles. In contrast, regions of H2 emission that are diffuse in the NICMOS image have broad, smooth line profiles. Several continuum features have an arclike appearance, which suggests interactions of winds with the ambient medium. At least 40 stellar or protostellar continuum sources have been detected, including at least one proplyd and four pairs of binary stars.

Hubble Space Telescope (HST)/WFPC2 imaging has been used to investigate the emission-line structure of the narrow-line region (NLR) of the Seyfert 2 galaxy NGC 1068 and its relationship to the extended radio emission. We find that the morphology and the ionization properties of the NLR of NGC 1068 are dominated by the interaction with the radio jet, in full agreement with similar results obtained for other Seyfert galaxies with extended radio emission. The emission lines originate in two distinct regions: a large-scale cocoon enveloping the northeastern radio lobe and a small-scale broken network of filaments and knots surrounding the radio jet. The material along the radio jet, although denser than the surrounding gas, is in a much higher ionization state than the remainder of the NLR. We believe that this requires the presence of a source of ionizing radiation that locally dominates over the nuclear emission, e.g., free-free emission from the gas heated by the interaction with the radio jet. At a distance of approximately 4'' (~300 pc) from the nucleus, corresponding to the transition in the radio structure from jetlike to lobelike, the ionization structure of the NLR shows a sharp and well-defined boundary between an inner low-ionization zone and an outer higher ionization zone. This ionization change is easily explained if there is a density increase where the jet enters the lobe, presumably due to the compression of the backflowing radio cocoon at the jet working surface. A color image reveals the presence of a nuclear dust lane projected onto the location of the hidden nucleus. Nuclear dust lanes appear to be ubiquitous in Seyfert 2 galaxies observed with HST and can be naturally associated with the material responsible for the obscuration of the active nucleus.

We present a velocity-resolved data cube of the distribution of the V= 1-0 S(1) line of molecular hydrogen from the source OMC-1. With", 1.5-arcsec spatial and 14 km S-1 velocity resolution, obtained with a scanning Fabry-Perot interferometer, it provides the most extensive data base yet obtained on both the distribution and the dynamics of the shocked molecular gas in this source. The line profiles are broad and generally smooth allover the source, with total extent (FWZI) up to '" 150 km S-1. We have identified, however, two distinct components to the line profiles which have different spatial distributions. Over the entire source, strong emission from a central velocity component is present, close to the ambient cloud velocity, while emission from high-velocity components (both red and blueshifted) is confined to discrete condensations. The central velocity component peaks, on average, at VLSR '" + 12 km s-\ with an average FWHM of '" 37 km s-\ but shows subtle variation across the source. In particular, the strongest emission region, Peak 1 to the north-west, is both slightly blueshifted and broader than the secondary Peak 2 to the south-east of OMC-1. We interpret this emission as the result of an isotropic steady wind from the IRc2 complex being loosely collimated by a disc, so that it flows close to the plane of the sky but with Peak 1 pointing slightly towards us and interacting with ambient molecular gas to excite the molecular hydrogen emission. In addition, high-velocity emission components (centred at '" - 35 km S-1 and + 40 km S-1 with FWHM of '" 30 km S-1) are found in discrete locations, primarily along an emission ridge running north along the Peak 1 region and towards the circumstellar disc about the IRc2 complex. We develop an analytical shock model to demonstrate that these discrete emission knots closely resemble the emission expected from partially resolved bow shocks. We ascribe these features to additional 'bullets' to those identified by Allen & Burton in [Fe II] at greater distances from the source, but which have been revealed by their interaction with dense, ambient molecular gas. They likely originate from a temporally limited event ~ 1000 yr ago. We provide new estimates on the energetics and the momenta of all the bullets, and speculate on their origin.

We present 6- and I8-cm MERLIN maps ofthe radio structure in the Seyfert galaxy Markarian 6, along with [0 III] and V-band images and a long-slit spectrum of this object. The 6-cm map combines high resolution with high sensitivity, and reveals a collimated jet on a scale of '" 1 arcsec: one of the best examples of a radio jet yet seen in a Seyfert nucleus and remarkably similar to the structure in Markarian 3. On larger scales the I8-cm map shows features suggestive of shells or bubbles on either side of the radio jet. These are much larger than known supernova remnants and appear to be unique to this object; we discuss several possibilities for their origin. Our optical images show an elongated extended narrow-line region (ENLR) structure with knots and linear features. The ENLR is misaligned with the large­ scale radio axis, and we examine the relationship between these two emission regions. Finally, we discuss the implications of the complex structures in this object for current models of Seyfert nuclei.

We present a study of the velocity profiles of the v=l-0 S(1) transition of molecular hydrogen (H2) towards the star forming region of OMC-1. A three dimensional data cube is presented which displays the spatial distribution as well as the velocity structure of the H2 emission. A brief description of the data acquisition, reduction and analysis is given.The three dimensional aspect of the data has allowed us to re-examine the kinematic nature of the region. The results reveal a number of isolated sources which posses asymmetric velocity profiles which can be modelled by bow C-shocks. The implication is that these sources are compact knots of material which were involved in some explosive event, possibly associated with the luminous source IRc2, and are ploughing into the dense molecular disk around IRc2. It is likely that these bullets are associated with those discovered by Allen & Burton (1993).

We have obtained long slit spectra of 3C 67 and 3C 277.1 with the HST/STIS spectrograph. We present our preliminary results on the diagnostic emission line ratios along the radio source axes in 3C 67 and 3C 277.1.

We analyze Chandra observations of diffuse soft X-ray emission associated with a complete sample of 3CR radio galaxies at z < 0.3. In this paper we focus on the properties of the spectroscopic sub-classes of high excitation galaxies (HEGs) and broad line objects (BLOs). Among the 33 HEGs we detect extended (or possibly extended) emission in about 40% of the sources; the fraction is even higher (8/10) restricting the analysis to the objects with exposure times larger than 10 ks. In the 18 BLOs, extended emission is seen only in 2 objects; this lower detection rate can be ascribed to the presence of their bright X-ray nuclei that easily outshine any genuine diffuse emission. A very close correspondence between the soft X-ray and optical line morphology emerges. We also find that the ratio between [O III] and extended soft X-ray luminosity is confined within a factor of 2 around a median value of 5. Both results are similar to what is seen in Seyfert galaxies. We discuss different processes that could explain the soft X-ray emission and conclude that the photoionization of extended gas, coincident with the narrow line region, is the favored mechanism., Comment: 15 pages, 11 figures. Accepted for publication on A&A

We have used the enhanced MERLIN at 5 GHz to image the central 700 pc of the nearby starburst galaxy M82. We detect in excess of 40 discrete sources, all of which are resolved by the MERLIN 50-mas (0.75-pc) beam. The observations confirm that most of the discrete sources are supernova remnants. Several show complete shells, and many more show structure consistent with partial shells. We have measured the sizes, flux densities and radio brightnesses of 23 of the sources, and show that they follow a surface brightness/diameter relation consistent with that found in the LMC and Galactic remnants. The cumulative number as a function of diameter appears to increase linearly to diameters of at least 3 pc, and indicates a supernova rate of 0.05 per year if the shells are expanding at 5000 km s −1

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We report the discovery of a two-armed mini-spiral structure within the inner kiloparsec of the E0 LINER/Seyfert 1 galaxy Arp102B. The arms are observed in H-alpha emission and located East and West of the nucleus, extending up to about 1 kpc from it. We use narrow-band imaging from the Hubble Space Telescope Advanced Camera for Surveys, in combination with archival VLA radio images at 3.6 and 6 cm to investigate the origin of the nuclear spiral. From the H-alpha luminosity of the spiral, we obtain an ionized gas mass of the order of one million solar masses. One possibility is that the nuclear spiral represents a gas inflow triggered by a recent accretion event which has replenished the accretion disk, giving rise to the double-peaked emission-line profiles characteristic of Arp102B. However, the radio images show a one-sided curved jet which correlates with the eastern spiral arm observed in the H-alpha image. A published milliarcsecond radio image also shows one-sided structure at position angle about 40 degrees, approximately aligned with the inner part of the eastern spiral arm. The absence of a radio counter-part to the western spiral arm is tentatively interpreted as indicating that the jet is relativistic, with an estimated speed of 0.45c. Estimates of the jet kinetic energy and the ionizing luminosity of the active nucleus indicate that both are capable of ionizing the gas along the spiral arms. We conclude that, although the gas in the nuclear region may have originated in an accretion event, the mini-spiral is most likely the result of a jet-cloud interaction rather than an inflowing stream., Comment: 9 pages, 5 figures, accepted for publication in ApJ

We report the detection of strong, broad Hα emission seen in polarized flux from the early-type radio galaxy IC 5063. This suggests that the galaxy has a broad-line region which is obscured from our direct view, with the broad-line radiation being scattered into our line of sight by scatterers outside the obscuring regions. A model has been developed to estimate the dilution by starlight of the intrinsic polarization, and to correct for interstellar polarization. The FWHM of the broad Hα is 3400 km s −1 , well within the range covered by typical Seyfert 1 galaxies