Emission-line Knots Research Articles

Testing Cluster Membership of Planetary Nebulae with High-precision Proper Motions. I. HST Observations of JaFu 1 Near the Globular Cluster Palomar 6

If a planetary nebula (PN) is shown to be a member of a star cluster, we obtain important new constraints on the mass and chemical composition of the PN’s progenitor star, which cannot be determined for PNe in the field. Cluster membership can be tested by requiring the projected separation between the PN and cluster to be within the tidal radius of the cluster, and the objects to have nearly identical radial velocities (RVs) and interstellar extinctions, and nearly identical proper motions (PMs). In an earlier study, we used PMs to confirm that three PNe, which had already passed the other tests, are highly likely to be members of Galactic globular clusters (GCs). For a fourth object, the PN JaFu 1, which lies in the Galactic bulge near the GC Palomar 6 on the sky and has a similar RV, the available PM measurement gave equivocal results. We have now obtained new high-resolution images of the central star of JaFu 1 with the Hubble Space Telescope (HST), which, combined with archival HST frames taken 14 and 16 yr earlier, provide a high-precision PM. Unfortunately, we find that the PM of the central star differs from that of the cluster with high statistical significance. Nevertheless, JaFu 1 is of astrophysical interest because its nucleus appears to be a member of the rare class of “EGB 6-type” central stars, which are associated with compact emission-line knots.

The MURALES survey

We observed the FR II radio galaxy 3C 459 (z = 0.22) with the MUSE spectrograph at the Very Large Telescope (VLT) as part of the MURALES project (a MUse RAdio Loud Emission line Snapshot survey). We detected diffuse nuclear emission and a filamentary ionized gas structure forming a one-sided, triangular-shaped region extending out to ∼80 kpc. The central emission line region is dominated by two compact knots of similar flux: the first (N1) cospatial with the radio core and the (N2) second located 1″.2 (5.3 kpc) to the SE. The two regions differ dramatically from the point of view of velocity (with an offset of ∼400 km s−1), line widths, and line ratios. This suggests that we are observing a dual AGN system formed by a radio loud AGN and type 2 QSO companion, which is the result of the recent merger that also produced its disturbed host morphology. The alternative possibility that N2 is just a bright emission line knot resulting from, for example, a jet-cloud interaction, is disfavored because of (1) the presence of a high ionization bicone whose apex is located at N2; (2) the observed narrow line widths; (3) its line luminosity (∼1042 erg s−1) typical of luminous QSOs; and (4) its location, which is offset from the jet path. The putative secondary AGN must be highly obscured, since we do not detect any emission in the Chandra and infrared Hubble Space Telescope images.

THE NUCLEUS OF THE PLANETARY NEBULA EGB 6 AS A POST-MIRA BINARY*

ABSTRACT EGB 6 is a faint, large, ancient planetary nebula (PN). Its central star, a hot DAOZ white dwarf (WD), is a prototype of a rare class of PN nuclei associated with dense, compact emission-line knots. The central star also shows excess fluxes in both the near-infrared (NIR) and mid-infrared (MIR). In a 2013 paper, we used Hubble Space Telescope (HST) images to show that the compact nebula is a point-like source, located 0.″16 (∼118 AU) from the WD. We attributed the NIR excess to an M dwarf companion star, which appeared to coincide with the dense emission knot. We now present new ground-based NIR spectroscopy, showing that the companion is actually a much cooler source with a continuous spectrum, apparently a dust-enshrouded low-luminosity star. New HST images confirm common proper motion of the emission knot and red source with the WD. The I-band, NIR, and MIR fluxes are variable, possibly on timescales as short as days. We can fit the spectral energy distribution (SED) with four blackbodies (the WD, a ∼1850 K NIR component, and MIR dust at 385 and 175 K). Alternatively, we show that the NIR/MIR SED is very similar to that of Class 0/I young stellar objects. We suggest a scenario in which the EGB 6 nucleus is descended from a wide binary similar to the Mira system, in which a portion of the wind from an AGB star was captured into an accretion disk around a companion star; a remnant of this disk has survived to the present time and is surrounded by gas photoionized by UV radiation from the WD.

VLT FORS2 optical imaging and spectroscopy of nine luminous type 2 AGN at 0.3 < z < 0.6 – I. Ionized gas nebulae

We present optical imaging and long slit spectroscopic observations of 9 luminous type 2 AGNs within the redshift range 0.3<z<0.6 based on VLT-FORS2 data. Most objects (6/9) are high luminosity Seyfert 2, and three are type 2 quasars (QSO2), with our sample extending to lower luminosity than previous works. Seven out of nine objects (78%) show morphological evidence for interactions or mergers in the form of disturbed morphologies and/or peculiar features such as tidal tails, amorphous halos, or compact emission line knots. The detection rate of morphological evidence for interaction is consistent with those found during previous studies of QSO2 at similar z, suggesting that the merger rate is independent of AGN power at the high end of the AGN luminosity function. We find the emission line flux spatial profiles are often dominated by the often spatially unresolved central source. In addition, all but one of our sample is associated with much fainter, extended line emission. We find these extended emission line structures have a variety of origins and ionization mechanisms: star forming companions, tidal features, or extended ionized nebulae. AGN related processes dominate the excitation of the nuclear gas. Stellar photoionization sometimes plays a role in extended structures often related to mergers/interactions.

Carbon and oxygen abundances from recombination lines in low-metallicity star-forming galaxies. Implications for chemical evolution★

We present deep echelle spectrophotometry of the brightest emission-line knots of the star-forming galaxies He 2−10, Mrk 1271, NGC 3125, NGC 5408, POX 4, SDSS J1253−0312, Tol 1457−262, Tol 1924−416 and the H ii region Hubble V in the Local Group dwarf irregular galaxy NGC 6822. The data have been taken with the Very Large Telescope Ultraviolet-Visual Echelle Spectrograph in the 3100–10420 Å range. We determine electron densities and temperatures of the ionized gas from several emission-line intensity ratios for all the objects. We derive the ionic abundances of C2+ and/or O2+ from faint pure recombination lines in several of the objects, permitting to derive their C/H and C/O ratios. We have explored the chemical evolution at low metallicities analysing the C/O versus O/H, C/O versus N/O and C/N versus O/H relations for Galactic and extragalactic H ii regions and comparing with results for Galactic halo stars and damped Lyα systems. We find that H ii regions in star-forming dwarf galaxies occupy a different locus in the C/O versus O/H diagram than those belonging to the inner discs of spiral galaxies, indicating their different chemical evolution histories, and that the bulk of C in the most metal-poor extragalactic H ii regions should have the same origin than in halo stars. The comparison between the C/O ratios in H ii regions and in stars of the Galactic thick and thin discs seems to give arguments to support the merging scenario for the origin of the Galactic thick disc. Finally, we find an apparent coupling between C and N enrichment at the usual metallicities determined for H ii regions and that this coupling breaks in very low metallicity objects.

THE CENTRAL REGION OF THE NEARBY SEYFERT 2 GALAXY NGC 4945: A PAIR OF SPIRALS

NGC 4945 is a Seyfert 2 galaxy at a distance of 3.82 Mpc. Its relative proximity has permitted a detailed SMA study of the circumnuclear molecular gas in a galaxy exhibiting an AGN. Based on an analysis of the high-resolution velocity field of the central region (20" X 20", 1" = 19 pc), we demonstrate that the S-shaped structure of the isovelocity contours is well reproduced by the numerical results of a two dimensional hydrodynamical simulation. In particular, the velocity structure is represented by the bending produced by a shock along the spiral density waves, which are excited at the outer-inner Lindblad resonance by a fast rotating bar. The simulated density map reveals a pair of tightly wound spirals in the center which pass through most of the ring-like (claimed to be a circumnuclear starburst ring by other authors) high intensity region in the observations as well as intersect several Pa$\alpha$ emission line knots located outside the ring-like region. The calculated mass inflow rate at a scale of 50 pc is about three times the inferred mass accretion rate of the AGN of NGC 4945. We find that self-gravity of the gas is important and should be included in our model for NGC 4945. The model is compared with the gas orbit model discussed in Lim et al. (2009), and it is shown that the hydrodynamic model provides a better match to the observed position-velocity diagram and, hence, provides a more reliable prediction of the outer inner Lindblad resonance position.

THE GEOMETRY OF MASS OUTFLOWS AND FUELING FLOWS IN THE SEYFERT 2 GALAXY MRK 3

We present a study of the resolved emission-line regions and an inner dust/gas disk in the Seyfert 2 galaxy Mrk 3, based on Hubble Space Telescope observations. We show that the extended narrow-line region (ENLR), spanning ~4 kpc, is defined by the intersection of the ionizing bicone of radiation from the AGN and the inner disk, which is not coplanar with the large-scale stellar disk. This intersection leads to different position and opening angles of the ENLR compared to the narrow-line region (NLR). A number of emission-line arcs in the ENLR appear to be continuations of dust lanes in the disk, supporting this geometry. The NLR, which consists of outflowing emission-line knots spanning the central ~650 pc, is in the shape of a backwards S. This shape may arise from rotation of the gas, or it may trace the original fueling flow close to the nucleus that was ionized after the AGN turned on.

Exploring the Inner Narrow-Line Regions of Seyfert Galaxies

In HST/STIS optical spectra of Seyfert galaxies, there is often a bright knot of [O iii] emission in the inner NLR. In the case of the Seyfert 1 galaxy NGC 4151, we have shown that the emission-line gas may be associated with the mass outflow detected in absorption in UV spectra, which suggests that we are probing regions close to the AGN. Here we present results for the luminous Seyfert 2 galaxy Mrk 573. The spectra reveal the presence of lines from a wide range of ionization states (see Figure 1), which is indicative of the heterogeneous nature of the emission-line gas. As in our studies of other Seyfert galaxies, including NGC 1068, NGC 4151, and Mrk 3, there is evidence for emission from low-ionization gas outside the nominal emission-line bicone. Finally, based on photoionization modeling, we find that the central emission-line knot in Mrk 573 is some tens of parsecs from the AGN, similar to other Seyfert 2 galaxies, which suggests that the material that is obscuring the central AGN in Seyfert 2s must have a similar radial extent.

PHYSICAL CONDITIONS IN THE INNER NARROW-LINE REGION OF THE SEYFERT 2 GALAXY MARKARIAN 573

We have examined the physical conditions within a bright emission-line knot in the inner narrow-line region (NLR) of the Seyfert 2 galaxy Mrk 573 using optical spectra and photoionization models. The spectra were obtained with the Hubble Space Telescope/Space Telescope Imaging Spectrograph with the G430L and G750M gratings. Comparing the spatial emission-line profiles, we found [Fe X] 6734 barely resolved, [O III] 5007 centrally peaked, but broader than [Fe X], and [O II] 3727 the most extended. The spectra reveal that [Fe X] is broader in velocity width and blue-shifted compared with lines from less ionized species. Our estimate of the bolometric luminosity indicates that the active galactic nucleus (AGN) is radiating at or above its Eddington Luminosity, which is consistent with its identification as a hidden Narrow-Line Seyfert 1. We were able to successfully match the observed emission line ratios with a three-component photoionization model. Two components, one to account for the [O III] emission and another in which the [Fe X] arises, are directly ionized by the AGN, while [O II] forms in a third component, which is ionized by a heavily absorbed continuum. Based on our assumed ionizing continuum and the model parameters, we determined that the two directly-ionized components are ~ 55 pc from the AGN. We have found similar radial distances for the central knots in the Seyfert 2 galaxies Mrk 3 and NGC 1068, but much smaller radial distances for the inner NLR in the Seyfert 1 galaxies NGC 4151 and NGC 5548. Although in general agreement with the unified model, these results suggest that the obscuring material in Seyfert galaxies extends out to at least tens of parsecs from the AGN.

The Connection between the Narrow‐Line Region and the UV Absorbers in Seyfert Galaxies

We present evidence that the outflowing UV absorbers in Seyfert 1 galaxies arise primarily in their inner narrow (emission) line regions (NLRs), based on similarities in their locations, kinematics, and physical conditions. 1) Hubble Space Telescope observations show that nearly all Seyfert galaxies have bright, central knots of [O III] emission in their NLRs with radii of tens of parsecs. These sizes are consistent with most previous estimates of the distances of UV (and X-ray) absorbers from their central continuum sources, and a recently obtained reliable distance of ~25 pc for a UV absorber in the Seyfert 1 galaxy NGC 3783. 2) The nuclear emission-line knots in a sample of 10 Seyfert galaxies have velocity widths of 300 - 1100 km/s (half-width at zero intensity), similar to the radial velocities of most UV absorbers. The highest radial velocity for a Seyfert UV absorber to date is only -2100 km/s, which is much lower than typical broad-line region (BLR) velocities. There is also mounting evidence that the NLR clouds are outflowing from the nucleus, like the UV absorbers. 3) If our hypothesis is correct, then the NLR must have a component with a high global covering factor (Cg) of the continuum source and BLR, to match that found from previous surveys of UV absorbers (Cg = 0.5 - 1.0). Using STIS spectra of NGC 4151, obtained when the continuum and BLR fluxes were low, we find evidence for optically thin gas in its nuclear emission-line knot. We are able to match the line ratios from this gas with photoionization models that include a component with Cg ~ 1 and an ionization parameter and hydrogen column density that are typical of UV absorbers.

Probing the Kinematics of the Narrow-Line Region in Seyfert Galaxies with Slitless Spectroscopy: Observational Results

We present slitless spectra of 10 Seyfert galaxies observed with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. The spectra cover the [OIII] 4959, 5007 emission lines at a spectral resolving power of ~9000 and a spatial resolution of 0.1. We compare the slitless spectra with previous HST narrow-band images to determine the velocity shifts and dispersions of the bright emission-line knots in the narrow-line regions (NLRs) of these Seyferts. Many knots are spatially resolved with sizes of tenths of arcsecs, corresponding to tens of pcs, and yet they appear to move coherently with radial velocities between zero and +/- 1200 km/s with respect to the systemic velocities of their hostgalaxies. The knots also show a broad range in velocity dispersion, ranging from ~30 km/s (the velocity resolution) to ~1000 km/s FWHM. Most of the Seyfert galaxies in this sample show an organized flow pattern, with radial velocities near zero at the nucleus (defined by the optical continuum peak) and increasing to maximum blueshifts and redshifts within ~1'' of the nucleus, followed by a decline to the systemic velocity. The emission-line knots also follow a general trend of decreasing velocity dispersion with increasing distance. In the Seyfert 2 galaxies, the presence of blueshifts and redshifts on either side of the nucleus indicates that rotation alone cannot explain the observed radial velocities, and that radial outflow plays an important role. Each of the Seyfert galaxies in this sample (with the exception of Mrk 3) shows a bright, compact (FWHM < 0.5) [O III] knot at the position of its optical nucleus. These nuclear emission-line knots have radial-velocity centroids near zero, but they typically have the highest velocity dispersions.

The Centaurus A Northern Middle Lobe as a Buoyant Bubble

We model the northern middle radio lobe of Centaurus A (NGC 5128) as a buoyant bubble of plasma deposited by an intermittently active jet. The extent of the rise of the bubble and its morphology imply that the ratio of its density to that of the surrounding ISM is less than 10-2, consistent with our knowledge of extragalactic jets and minimal entrainment into the precursor radio lobe. Using the morphology of the lobe to date the beginning of its rise through the atmosphere of Cen A, we conclude that the bubble has been rising for approximately 140 Myr. This timescale is consistent with that proposed by Quillen and coworkers for the settling of postmerger gas into the presently observed large-scale disk in NGC 5128, suggesting a strong connection between the delayed reestablishment of radio emission and the merger of NGC 5128 with a small gas-rich galaxy. This suggests a connection, for radio galaxies in general, between mergers and the delayed onset of radio emission. In our model, the elongated X-ray emission region discovered by Feigelson and coworkers, part of which coincides with the northern middle lobe, is thermal gas that originates from the interstellar medium below the bubble and that has been uplifted and compressed. The large-scale jet appearing in the radio images of Morganti and coworkers may be the result of the same pressure gradients that cause the uplift of the thermal gas, acting on much lighter plasma, or may represent a jet that did not turn off completely when the northern middle lobe started to buoyantly rise. We propose that the adjacent emission-line knots (the outer filaments) and star-forming regions result from the disturbance, in particular the thermal trunk, caused by the bubble moving through the extended atmosphere of NGC 5128.

Resolved Spectroscopy of the Narrow‐Line Region in NGC 1068. III. Physical Conditions in the Emission‐Line Gas

The physical conditions in the inner narrow-line region (NLR) of the Seyfert 2 galaxy NGC 1068 are examined using ultraviolet and optical spectra and photoionization models. The spectra were taken with the Hubble Space Telescope Space Telescope Imaging Spectrograph (STIS), through the 01 ? 520 slit, covering the full STIS 1200-10000 ? waveband. The slit was centered on a position 014 north of the optical continuum peak (or hot spot) at a position angle of 202?, bisecting the brighter part of the biconical emission-line region. We have measured the emission-line fluxes for a region extending 38 northeast (~270 pc) to 18 southwest (~130 pc) of this point. The emission lines on each side show evidence of two principal kinematic components, one blueshifted with respect to the systemic velocity and the other redshifted (the kinematics were discussed in a separate paper). Based on the photoionization modeling results, we find that the physical conditions vary among these four quadrants. (1) The emission-line gas in the blueshifted northeast quadrant is photoionized by the hidden central source out to ~100 pc, at which point we find evidence of another source of ionizing radiation, which may be due to fast (~1000 km s-1) shocks resulting from the interaction of the emission-line knots and the interstellar medium. Interestingly, this occurs at approximately the location where the knots begin to show signs of deceleration. (2) The gas in the redshifted northeast quadrant is photoionized by continuum radiation that has been heavily absorbed by gas within ~30 pc of the central source. We find no strong evidence of the effects of shocks in this component. (3) The redshifted emission-line gas in the southwest quadrant is photoionized by unabsorbed continuum from the central source, similar to that in the inner ~100 pc of the blueshifted northeast quadrant. Finally, (4) the emission-line spectrum of the blueshifted southwest quadrant appears to be the superposition of highly ionized, tenuous component within the ionization cone and gas outside the cone, the latter photoionized by scattered continuum radiation. There are several implications of this complicated physical scenario. First, the hidden active nucleus is the dominant source of ionizing radiation in the inner NLR. The absorption of continuum radiation along the line of sight to the redshifted northeast quadrant may result from the intersection of the ionization cone and the plane of the host galaxy. Finally, the evidence for shock-induced continuum radiation at the point where the emission-line knots begin to decelerate indicates that the deceleration is due to the interaction of emission-line knots with slower moving gas, such as the interstellar medium of NGC 1068.

A Kinematic Model for the Narrow-Line Region in NGC 4151

We present a simple kinematic model for the narrow-line region (NLR) of the Seyfert 1 galaxy NGC 4151, based on our previous observations of extended [O III] emission with the Space Telescope Imaging Spectrograph. The model is similar to a biconical radial outflow model developed for the Seyfert 2 galaxy NGC 1068, except that the bicone axis is tilted much more into our line of sight (40? out of the plane of the sky instead of 5?), and the maximum space velocities are lower (750 km s-1 instead of 1300 km s-1). We find evidence for radial acceleration of the emission-line knots to a distance of 160 pc, followed by deceleration that approaches the systemic velocity at a distance of 290 pc (for a distance to NGC 4151 of 13.3 Mpc). Other similarities to the kinematics of NGC 1068 are (1) there are a number of high-velocity clouds that are not decelerated, suggesting that the medium responsible for the deceleration is patchy, and (2) the bicone in NGC 4151 is at least partially evacuated along its axis. Together, these two Seyfert galaxies provide strong evidence for radial outflow (e.g., due to radiation and/or wind pressure) and against gravitational motion or expansion away from the radio jets as the principal kinematic component in the NLR.

Resolved Spectroscopy of the Narrow-Line Region in NGC 1068: Kinematics of the Ionized Gas.

We have determined the radial velocities of the [O iii]-emitting gas in the inner narrow-line region of the Seyfert 2 galaxy NGC 1068, along a slit at position angle 202 degrees, from STIS observations at a spatial resolution of 0&farcs;1 and a spectral resolving power of lambda&solm0;Deltalambda approximately 1000. We use these data to investigate the kinematics of the narrow-line region within 6&arcsec; ( approximately 430 pc) of the nucleus. The emission-line knots show evidence for radial acceleration to a projected angular distance of 1&farcs;7 in most cases, followed by deceleration that approaches the systemic velocity at a projected distance of approximately 4&arcsec;. We find that a simple kinematic model of biconical radial outflow can match the general trend of observed radial velocities. In this model, the emitting material is evacuated along the bicone axis, and the axis is inclined 5 degrees out of the plane of the sky. The acceleration of the emission-line clouds provides support for dynamical models that invoke radiation and/or wind pressure. We suggest that the deceleration of the clouds is due to their collision with a patchy and anistropically distributed ambient medium.

The extended emission-line region of the Seyfert galaxy Mrk 573

We present the results of observations of the extended emission-line region of the Seyfert 2 galaxy Mrk 573, obtained using the WFPC2 on board HST and the TIGER integral field spectrograph on the CFHT. We describe and use a new ‘guided’ deconvolution technique in which the spatial resolution of the TIGER data cubes is improved, allowing us to obtain the [O iii] gaseous kinematics with an unprecedented spatial resolution of ≃0.35 arcsec. The HST images outline the detailed complex structure of the central ∼3 kpc of this galaxy in [O iii] and Hα+[N ii], with strings of knots and a system of arcs straddling the nucleus. The [O iii]/(Hα+[N ii]) map shows that, taken together, all these individual features define a double wedge form with sharp edges, consistent with an ionization cone. The ‘linear’ radio structure is closely associated with the strings of emission-line knots, with the north-west radio lobe lying inside one of the arcs. Strong velocity perturbations are found in the vicinity of all of the radio components, witnessing the interaction between the radio ejecta and the ambient material. The spectral and kinematical properties of the different components of the emission-line region of Mrk 573 are discussed. The emission-line knots, associated with the radio knots and the velocity perturbations, probably trace the deflection of the radio jet by clouds. The inner arcs may represent radiative bow shocks driven by the weakened radio jets. The similar structure of each of these arcs in the different emission lines, and the absence of any strong kinematic perturbation in the arcs themselves, indicates that they are not photoionizing shocks. Instead, the arcs are photoionized by an external source of radiation. The same conclusion is reached for the outer arcs, which mark the transition between the narrow-line and extended narrow-line regions of Mrk 573. We use the measured variation of the ionization parameter and gas density to derive the flux of ionizing photons as a function of distance from the nucleus. We find that, unless the ionizing photon flux of the compact central source has decreased by a factor of 10 over the last 4000 yr, a model in which all the ionizing photons originate in the central source is excluded. Instead, we speculate that fast shocks, possibly associated with the jet/cloud interactions, may provide the required spatially extended source of ionizing photons.

The Origin of the Narrow‐Line Region of Markarian 3: An Overpressured Jet Cocoon

We have obtained Hubble Space Telescope (HST) Faint Object Camera (FOC) f/48 long-slit optical spectroscopy of the inner 2'' of the narrow-line region (NLR) of the Seyfert 2 galaxy Mrk 3 with a spatial resolution of 006. Spectra were taken in six locations with the slit approximately perpendicular to the radio axis. In the region cospatial with the radio jet, where the brightest emission line knots are located, the velocity field is highly perturbed, showing two velocity systems separated by as much as 1700 km s-1. In several locations the split lines form almost complete velocity ellipsoids, implying that we are seeing an expanding shell of gas. The diameter of this shell (~200 pc) is much larger than the width of the radio jet (d<15 pc). We interpret this to be the consequence of the rapid expansion of a cocoon of hot gas, shocked and heated by the radio-emitting outflow, which compresses and accelerates the ambient gas. The cocoon mediates the energy exchange between jets and the line-emitting gas. The gas motions within the NLR of Mrk 3 are therefore clearly dominated by the interaction between the jets and the interstellar medium; the NLR itself is essentially a cylindrical shell expanding supersonically. With its current size of 200 pc, the cocoon has expanded to several disk scale heights. Because of the external gas density stratification, the hot gas located above the plane of the disk blows out into the halo, puncturing the bubble and fracturing the velocity ellipsoids. The system is effectively momentum driven. From the size and velocity of the expanding region, we derive an upper limit to the age of the radio source of 1.5?105 yr, and a lower limit for the jet power of 2?1042 ergs s-1, required to inflate the cocoon; we estimate that the jet minimum advance speed is 3?10-3 pc yr-1. The total kinetic energy of the high-velocity gas associated with the radio jet can be estimated as ~6?1054 ergs, comparable to the total energy carried by the jet over its lifetime; this quantitatively supports the idea that the NLR gas is accelerated by the jet. Radio outflows are associated with at least 50% of Seyfert galaxies with typical sizes smaller than a few kpc. If the advance speed of Mrk 3 is representative of the Seyfert population, then these sources must also be short lived and are probably recurrent. Evidence that this is indeed the case is provided by the fact that the expansion timescale derived for NGC 1068 is comparable to that seen in Mrk 3. The jet kinetic luminosity of Mrk 3 is between 2 and 3 orders of magnitude smaller than that derived for radio-loud AGNs with similar emission-line luminosity. On the other hand, the fraction of jet power dissipated in radio emission is similar. We speculate that the main distinction between radio-quiet and radio-loud active galactic nuclei can be ascribed to a difference in jet power rather than to a different efficiency in synchrotron emission production.

Unveiling the Hidden Nucleus of IC 5063 with NICMOS

We present high-resolution near-infrared images of the Seyfert 2 galaxy IC 5063 obtained using the Near-Infrared Camera and Multiobject Spectrometer (NICMOS) in broadband filters at 1.1, 1.6, and 2.2 μm (FWHM ≈ 021 at 2.2 μm). The images show a very red, unresolved point source at the center of the galaxy, confirming the existence of the obscured active nucleus inferred from previous ground-based studies. The 2.2 μm flux, supplemented with ground-based L'-band observations, suggests thermal emission equivalent to a blackbody at a temperature of 720 K. We ascribe the emission not to direct light from the nucleus, but to hot dust in the inner part of the torus. The 1.6 μm emission is only minimally affected by the hot dust emission. The luminosity of the central source producing most of the 1.6 μm emission, not corrected for extinction, is 1.5×1041 ergs s−1, integrated over the F160W filter only. We also present lower spatial resolution images of IC 5063 obtained with NICMOS in the emission lines of [Fe II] λ1.644 μm, Paα λ1.8756 μm, and H2 λ2.1218 μm. These images reveal a linear emission morphology comprised of two bright knots, separated by 18 on either side of a central knot that is at the location of the continuum nucleus. A comparison with high-resolution radio continuum maps shows that there is a one-to-one spatial correspondence between the radio lobes and the emission-line knots, directly implying that the [Fe II] and H2 emission is created by fast shocks produced by the advancing radio jets. The asymmetry in the [Fe II]/H2 ratio may suggest a difference in either the shock velocities or the molecular mass on the two sides of the nucleus.

The location of the hidden nucleus of NGC 1068

We present HST polarization observations of NGC 1068 obtained with the Faint Object Camera in the ultraviolet (λ ∼ 2700–3700 Å), and the Wide Field Planetary Camera in the visual (λ ∼ 5000–6000 Å), at a resolution of 0.″06 and 0.″08, respectively. The UV continuum polarization is very high, peaking at ∼ 60% in the vicinity of the emission line knot 4″.5 NE of the nucleus. To a high degree of precision the polarization vectors show the centro-symmetric pattern expected from scattering from a point source. By locating the centre of symmetry of this pattern we have determined the location of the hidden nuclear source, to an accuracy of ±0.″05, which lies 0.″65 South of the emission peak and 0.″35 South of the 12.4μ peak. A pair of highly polarized clouds ( P ∼ 45% in the UV) lies close to the position of the scattered nuclear source and correspond to the “ twin cresent” object seen in FOC [OIII] images. The WF/PC-I polarization images contain contributions from both the optical continuum and emission lines. Generally, the large scale polarization structure is dominated by scattered [O III] emission from knot B, except at the edge of the cavity when other NLR knots contribution. However, scattered continuum from the nucleus dominates the polarization in a narrow linear region stetching from the “ hidden nucleus” to knot B, suggesting that there is a component to the nuclear light which is highly collimated.

HST Imaging Polarimetry of NGC 1068

view Abstract Citations (58) References (36) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS HST Imaging Polarimetry of NGC 1068 Capetti, A. ; Axon, D. J. ; Macchetto, F. ; Sparks, W. B. ; Boksenberg, A. Abstract We present the results of high-quality pre-refurbishment HST imaging polarimetry of NGC 1068 obtained with the Faint Object Camera in the ultraviolet ( 2700-3700 A), and the Wide Field Planetary Camera in the visual (λ ∼ 5000-6000 Å), with resolutions of 0".06 and 0".08, respectively. The polarization of the UV continuum is very high, peaking at ∼60% in the vicinity of the emission line knot 4'S NE of the nucleus. To a high degree of precision the polarization vectors show the centro-symmetric pattern expected from scattering from a point source. By locating the centre of symmetry of this pattern we have determined the location of the hidden nuclear source, to an accuracy of ±0".05 which lies 0".6 south of the emission peak. A pair of highly polarized clouds (P ∼ 45% in the UV) lies close to the position of the scattered nuclear source. The degree of polarization after correction for dilution is close to 100%, indicating that this is a reflection image. These clouds are associated with the "twin-crescent" object, a ringlike or double-jet like feature. Their peculiar properties suggests that they are related to the hidden nucleus. They probably represent reflection clouds produced by an expanding bipolar structure, or a jet. The hidden nucleus would lie at its center. The WF/PC-I polarization images contain contributions from both optical continuum and emission lines. However, these two components are spatially separated. The continuum polarization dominates in a quasilinear region starting at the location of the "hidden nucleus" and including the continuum peak, knot B. The nature of this pattern suggest that the nuclear light might be collimated. The large-scale polarization structure is dominated by scattered line emission. The source of this scattered [O III] emission is predominantly the bright observed region of line emission in the NLR, knot B. Therefore, scattering is also very important for narrow lines and this must be taken into account when trying to understand the kinematics and morphology of the NLR. The nuclear radiation cone is only partly filled with scatterers; the minimum angular extent is from PA -15 to PA +55, corresponding to an opening angle greater than 700, but it is probably as large as 100°. It is difficult to establish the precise association between radio and optical emission because of the relatives errors between the respective reference frames. Adopting the registration of Evans et al. leads to the conclusion that there is no significant radio emission from the nucleus. This maybe because the radio nucleus is radio quiet, or, as both the theoretical model of the torus and the X-ray data imply, the column density in front of the nucleus is sufficient that free-free absorption obscures it even at centimeter wavelengths. Alternatively, if the flat spectrum southern radio component is assumed to be the nucleus, then there appears to be no direct spatial correspondence between the radio and the emission line structures. Publication: The Astrophysical Journal Pub Date: June 1995 DOI: 10.1086/175775 Bibcode: 1995ApJ...446..155C Keywords: GALAXIES: INDIVIDUAL NGC NUMBER: NGC 1068; GALAXIES: SEYFERT; POLARIZATION; ULTRAVIOLET: GALAXIES full text sources ADS | data products SIMBAD (1) NED (1) MAST (1) ESA (1)