The Narrow-Line Region of NGC 4151: A Turbulent Cauldron (original) (raw)
Related papers
The Astrophysical Journal, 1999
We present the results from a detailed kinematic analysis of both groundbased, 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 Resolved Narrow‐Line Region in NGC 4151
The Astrophysical Journal, 2000
We present slitless spectra of the Narrow Line Region (NLR) in NGC 4151 from the Space Telescope Imaging Spectrograph (STIS) on HST, and investigate the kinematics and physical conditions of the emission line clouds in this region. Using medium resolution (∼ 0.5Å) slitless spectra at two roll angles and narrow band undispersed images, we have mapped the NLR velocity field from 1.2 kpc to within 13 pc (H • = 75 km s −1 Mpc −1) of the nucleus. The inner biconical cloud distribution exhibits recessional velocities relative to the nucleus to the NE and approaching velocities to the SW of the nucleus. We find evidence for at least two kinematic components in the NLR. One kinematic component is characterized by Low Velocities and Low Velocity Dispersions (LVLVD clouds: |v| < 400 km s −1 , and ∆v < 130 km s −1). This population extends through the NLR and their observed kinematics may be gravitationally associated with the host galaxy. Another component is characterized by High Velocities and High Velocity Dispersions (HVHVD clouds: 400 < |v| < ∼ 1700 km s −1 , ∆v ≥ 130 km s −1). This set of clouds is located within 1.1 (∼ 70 pc) of the nucleus and has radial velocities which are too high to be gravitational in origin, but show no strong correlation between velocity or velocity dispersion and the position of the radio knots. Outflow scenarios will be discussed as the driving mechanism for these HVHVD clouds. We also find clouds characterized by Low Velocities and High Velocity Dispersions (LVHVD clouds: |v| < 400 km s −1 , ∆v ≥ 130 km s −1). These clouds are located within 3.2 (∼ 200 pc) of the nucleus. It is not clear if the LVHVD clouds are HVHVD clouds whose low velocities are the results of projection effects. Within 3.2 (∼ 200 pc) of the nucleus, the [OIII]/Hβ ratio declines roughly linearly for both the High Velocity Dispersion (HVD) and LVLVD clouds. Since the ionization parameter is proportional to r −2 n −1 , it appears that the density, n, must decrease as ∼r −1 for the clouds within the inner ∼ 3.2. At distances further from the nucleus, the [OIII]/Hβ ratio is roughly constant.
The Astrophysical Journal, 2003
Sensitive high angular and linear resolution radio images of the 240-pc radio jet in NGC 4151, imaged at linear resolutions of 0.3 to 2.6 pc using the VLBA and phased VLA at λ21 cm, are presented and reveal for the first time a faint, highly collimated jet (diameter ∼ <1.4 pc) underlying discrete components, seen in lower -2resolution MERLIN and VLA images, that appear to be shock-like features associated with changes in direction as the jet interacts with small gas clouds within the central ∼100 pc of the galaxy. In addition, λ21-cm spectral line imaging of the neutral hydrogen in the nuclear region reveals the spatial location, distribution and kinematics of the neutral gas detected previously in a lower resolution MER-LIN study. Neutral hydrogen absorption is detected against component C4W (E+F) as predicted by Mundell et al, but the absorption, extending over 3 pc, is spatially and kinematically complex on sub-parsec scales, suggesting the presence of small, dense gas clouds with a wide range of velocities and column densities. The main absorption component matches that detected in the MERLIN study, close to the systemic velocity (998 km s −1 ) of the galaxy, and is consistent with absorption through a clumpy neutral gas layer in the putative obscuring torus, with higher velocity blue-and red-shifted systems with narrow linewidths also detected across E+F. In this region, average column densities are high, lying in the range 2.7 × 10 19 T S < N H < 1.7 × 10 20 T S cm −2 K −1 (T S is the spin temperature), with average radial velocities in the range 920 < V r < 1050 km s −1 . The spatial location and distribution of the absorbing gas across component E+F rules out component E as the location of the AGN (as suggested by Ulvestad et al.) and, in combination with the well-collimated continuum structures seen in component D, suggests that component D (possibly subcomponent D3) is the most likely location for the AGN. We suggest that components C and E are shocks produced in the jet as the plasma encounters, and is deviated by, dense clouds with diameters smaller than ∼1.4 pc.
The broad line regions of NGC 4151
Arxiv preprint astro-ph/9602074, 1996
We estimate the properties of clouds that form as a result of the interaction of the surface of a disc embedded in a supersonic outflow and heated by external irradiation. We find two regions where short-lived clouds are injected into the outflow and accelerated by ram pressure. We indentify these with a broad line region and an intermediate line region. We compute the line strengths and profiles from a model of the cloud dynamics and compare the results with the observations of the nearest Seyfert galaxy NGC 4151, which, in its various luminosity states, has provided a large amount of emission line data. We show that the model parameters for this galaxy are constrained by just the CIV λ1549 line profile in the high luminosity state of the nucleus. We review briefly some of the data on broad line ratios, profiles, profile variations and transfer functions and show how much (if not all) of this data can be accounted for in the model. We also indicate how the X-ray data can be fitted into this picture.
Hst foc spectroscopy of the nlr of ngc 4151. I. gas kinematics
1999
We present the results from a detailed kinematic analysis of both groundbased, 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 1 Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.
Jet-Cloud Interactions and the Brightening of the Narrow-Line Region in Seyfert Galaxies
The Astrophysical Journal, 1997
We study the kinematical and brightness evolution of emission line clouds in the narrow line region (NLR) of Seyfert galaxies during the passage of a jet. We derive a critical density above which a cloud remains radiative after compression by the jet cocoon. The critical density depends mainly on the cocoon pressure. Super-critical clouds increase in emission line brightness, while sub-critical clouds generally are highly overheated reducing their luminosity below that of the intercloud medium. Due to the pressure stratification in the bow-shock of the jet, a cylindrical structure of nested shells develops around the jet. The most compact and brightest compressed clouds surround the cloud-free channel of the radio jet. To support our analytical model we present a numerical simulation of a supersonic jet propagating into a clumpy NLR. The position-velocity diagram of the simulated Hα emission shows total line widths of the order of 500 km s −1 with large-scale variations in the radial velocities of the clouds due to the stratified pressure in the bow-shock region of the jet. Most of the luminosity is concentrated in a few dense clouds surrounding the jet. These morphological and kinematic signatures are all found in the well observed NLR of NGC 1068 and other Seyfert galaxies.
X‐Ray and Optical Variability in NGC 4051 and the Nature of Narrow‐Line Seyfert 1 Galaxies
The Astrophysical Journal, 2000
We report on the results of a three-year program of coordinated X-ray and optical monitoring of the narrow-line Seyfert 1 galaxy NGC 4051. The rapid continuum variations observed in the X-ray spectra are not detected in the optical, although the time-averaged X-ray and optical continuum fluxes are well-correlated. Variations in the flux of the broad Hβ line are found to lag behind the optical continuum variations by 6 days (with an uncertainty of 2-3 days), and combining this with the line width yields a virial mass estimate of ∼ 1.1 × 10 6 M ⊙ , at the very low end of the distribution of AGN masses measured by line reverberation. Strong variability of He ii λ4686 is also detected, and the response time measured is similar to that of Hβ, but with a much larger uncertainty. The He ii λ4686 line is almost five times broader than Hβ, and it is strongly blueward asymmetric, as are the high-ionization UV lines recorded in archival spectra of NGC 4051. The data are consistent with the Balmer lines arising in a low to moderate inclination disk-like configuration, and the high-ionization lines arising in an outflowing wind, of which we observe preferentially the near side. Previous observations of the narrow-line region morphology of this source suggest that the system is inclined by ∼ 50 o , and if this is applicable to the broad Hβ-emitting region, a central mass of ∼ 1.4 × 10 6 M ⊙ can be inferred. During the third year of monitoring, both the X-ray continuum and the He ii λ4686 line went into extremely low states, although the optical continuum and the Hβ broad line were both still present and 6 Deceased.
Astrophysical Journal, 2002
Using the STIS spectrograph on HST we have obtained a grid of [O III]λλ4959,5007 and Hβ emission-line spectra at 0. 05 × 0. 19 and 60 km s −1 (FWHM) resolution that covers much of the NLR of NGC 1068. We find emitting knots that have blueshifted radial velocities up to 3200 km s −1 relative to galaxy systemic, are 70 − 150 pc NE of the nucleus and up to 40 pc from the radio jet, emit several percent of the NLR line flux but no significant continuum, span a small fraction of the sky as seen from the nucleus, coincide with a region of enhanced IR coronal-line emission, show gradients in radial velocities of up to 2000 km s −1 in 7 pc, span velocity extents averaged over 0. 1 × 0. 2 regions of up to 1250 km s −1 , have ionization parameter U 0.1, and ionized masses ∼ 200 M /n e,4 (n e,4 = 10 4 cm −3 ). The brightest parts of the blueshifted knots are often kinematically contiguous with more massive clouds nearer the jet that are moving with velocities of ≤ 1300 km s −1 relative to galaxy systemic. However, some knots at 1. 5 − 2. 5 radii appear as bright points in a broken shell of radius ∼ 0. 55 (40 pc) that is expanding at up to 1500 km s −1 , implying a dynamical age of ∼ 1.3 × 10 4 yrs. Between 2. 5-4. 5 from the nucleus, emission is redshifted relative to systemic, a pattern that we interpret as gas in the galaxy disk being pushed away from us by the NE radio lobe. We argue that the blueshifted knots are ablata from disintegrating molecular clouds that are being photoionized by the AGN, and are being accelerated radiatively by the AGN or mechanically by the radio jet. In their kinematic properties, the knots resemble the associated absorbers seen projected on the UV continua of some AGN.
Molecular Gas Kinematics and Line Diagnostics in Early-type Galaxies: NGC 4710 & NGC 5866
We present interferometric observations of CO lines (12CO(1-0, 2-1) and 13CO(1-0, 2-1)) and dense gas tracers (HCN(1-0), HCO+(1-0), HNC(1-0) and HNCO(4-3)) in two nearby edge-on barred lenticular galaxies, NGC~4710 and NGC~5866, with most of the gas concentrated in a nuclear disc and an inner ring in each galaxy. We probe the physical conditions of a two-component molecular interstellar medium in each galaxy and each kinematic component by using molecular line ratio diagnostics in three complementary ways. First, we measure the ratios of the position-velocity diagrams of different lines, second we measure the ratios of each kinematic component's integrated line intensities as a function of projected position, and third we model these line ratios using a non-local thermodynamic equilibrium radiative transfer code. Overall, the nuclear discs appear to have a tenuous molecular gas component that is hotter, optically thinner and with a larger dense gas fraction than that in the inner rings, suggesting more dense clumps immersed in a hotter more diffuse molecular medium. This is consistent with evidence that the physical conditions in the nuclear discs are similar to those in photo-dissociation regions. A similar picture emerges when comparing the observed molecular line ratios with those of other galaxy types. The physical conditions of the molecular gas in the nuclear discs of NGC4710 and NGC5866 thus appear intermediate between those of spiral galaxies and starbursts, while the star formation in their inner rings is even milder.
Gas Cloud Kinematics near the Nucleus of NGC 4151
The Astrophysical Journal, 1998
We report early observations with Space Telescope Imaging Spectrometer (STIS) of the nuclear region of NGC 4151. Direct images in [O ii] and [O iii] and slitless medium-dispersion spectral images of the Hb to [O iii] region were obtained. A slitless UV spectral image was taken of the C iv 1550 Å region. We present radial velocities and line ratios of ∼40 clouds resolved in the narrow-line region (NLR). The kinematics suggest outflow within a biconical region about the nucleus, centered on the radio axis and viewed near the edge of the cones. A few high-velocity clouds are seen that do not fit this simple picture. Line ratios indicate that the NLR gas is photoionized by the central continuum source and that there may be a density gradient in the NLR. These observations are being followed by an extensive STIS program on NGC 4151.