The Resolved Narrow‐Line Region in NGC 4151 (original) (raw)
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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.
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.
Kinematical analysis of the ionized gas in the nuclear region of NGC 4214
Arxiv preprint astro-ph/ …, 1998
We present in this paper a detailed study of the kinematical properties of the ionized gas around the young massive star clusters in the nucleus of NGC 4214. The analysis is based on bidimensional spectroscopical data, allowing to derive the spatial variation of different properties (intensity, velocity and width / line splitting) of the emission lines Hα and [O III] λ5007 along the nuclear region. We have found that the Giant H II region around the two most massive clusters in NGC 4214 (A and B) is resolved into two clearly separated regions. We have not detected superbubbles with the properties we would expect according to the evolutionary state of the stellar clusters, but just a partial ring feature around the most massive one and two expanding shells around cluster B. The first expanding shell seems to have experienced blowout, whereas the second one is still complete. A possible explanation to this phenomenon is that the most massive stars in a starburst spend a large fraction of their lives buried inside their original molecular clouds. Champagne flows might have formed at the borders of the regions, especially on the SE complex, explaining the existence of the diffuse ionized gas around the galaxy. As a consequence of these results we postulate that NGC 4214 is indeed a dwarf spiral galaxy, with a thin (∼ 200 pc) disk that inhibits the formation of large scale structures in the ISM. The mechanical input deposited by the star formation complexes, in a variety of physical processes that include the free expanding bubbles liberated after blowout and photoevaporation of the parent clouds, have succeeded in generating the structures now detected far from the disk, giving place to the large-scale structure which now enriches the optical appearance of the galaxy.
The Astrophysical Journal, 2011
We report ultraviolet spectra of Galactic high-velocity clouds (HVCs) in Complex C, taken by the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST), together with new 21 cm spectra from the Green Bank Telescope. The wide spectral coverage and higher signal-to-noise ratio, compared to previous HST spectra, provide better velocity definition of the HVC absorption, additional ionization species (including high ions), and improved abundances in this halo gas. Complex C has a metallicity of 10%-30% solar and a wide range of ions, suggesting dynamical and thermal interactions with hot gas in the Galactic halo. Spectra in the COS medium-resolution G130M (1133-1468 Å) and G160M (1383-1796 Å) gratings detect ultraviolet absorption lines from eight elements in low-ionization states (O i, N i, C ii, S ii, Si ii, Al ii, Fe ii, P ii) and three elements in intermediate-and high-ionization states (Si iii, Si iv, C iv, N v). Our four active galactic nucleus sight lines toward Mrk 817, Mrk 290, Mrk 876, and PG 1259+593 have high-velocity H i and O vi column densities, log N H i = 19.39-20.05 and log N O vi = 13.58-14.10, with substantial amounts of kinematically associated photoionized gas. The high-ion abundance ratios are consistent with cooling interfaces between photoionized and collisionally ionized gas: N(C iv)/N(O vi) ≈ 0.3-0.5, N(Si iv)/N(O vi) ≈ 0.05-0.11, N(N v)/N(O vi) ≈ 0.07-0.13, and N(Si iv)/N(Si iii) ≈ 0.2.
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.
Compact H i Clouds at High Forbidden Velocities in the Inner Galaxy
The Astrophysical Journal, 2006
The VLA Galactic Plane Survey (VGPS) of the first Galactic quadrant was searched for H I emission with velocities well above the maximum velocity allowed by Galactic rotation. A sample of 17 small fast-moving clouds was identified. The distribution of the ensemble of clouds in longitude and velocity indicates that the clouds are part of the Galactic disk, despite their large forbidden velocity. The median angular diameter of the clouds detected in the VGPS is 3. ′ 4. These clouds would not be noticed in previous low resolution surveys because of strong beam dilution. Assuming each cloud is located at the tangent point, a median cloud has a diameter of 10 pc, H I mass of 60 M ⊙ , and a velocity more than 25 km s −1 beyond the local terminal velocity derived from 12 CO observations. Three clouds
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.
The Narrow-Line Region of NGC 4151: A Turbulent Cauldron
The Astrophysical Journal, 1997
We present the first results of the Hubble Space Telescope/Faint Object Camera long-slit spectroscopy of the inner 8 of the Narrow Line Region of NGC 4151 at a spatial resolution of 0 .029. The emission gas is characterized by an underlying general orderly behaviour, consistent with galactic rotation, over which are superposed kinematically distinct and strongly localized emission structures. High velocity components shifted up to ∼ 1500 km s −1 from the systemic velocity are seen, associated with individual clouds located preferentially along the edges of the radio knots. Off-nuclear blue continuum emission is also observed, associated with the brightest emission line clouds. Emission line ratios like [Ne III] λ3869/[O II] λ3727, and [O II] λ3727/Hβ are observed to vary substantially between individual clouds. We advance the general picture that, as in other Seyfert galaxies observed with HST (e.g. NGC 1068, Mrk 573), the interaction of the radio jet with the ambient gas strongly influences both the morphology and the physical conditions of the NLR.
Velocity structure of the 50 pc long NGC 6334 filamentary cloud
Astronomy and Astrophysics, 2022
Context. The interstellar medium is observed to be organized in filamentary structures, and in neutral (H I) and ionized (H II) bubbles. The expanding nature of these bubbles shapes the surrounding medium and possibly plays a role in the formation and evolution of the interstellar filaments. The impact of the expansion of these bubbles on the interstellar medium is not well understood. Aims. Our aim is to describe the kinematics of a filamentary molecular cloud forming high-mass stars and hosting multiple H II regions in order to study the possible environmental impact on the properties of molecular filaments. Methods. We present APEX 13 CO and C 18 O(2−1) mapping observations of the 10 × 50 pc NGC 6334 molecular cloud complex. We investigated the gas velocity structure along and across the 50 pc long cloud and toward velocity-coherent filaments (VCFs). Results. The NGC 6334 complex is observed to have a coherent velocity structure smoothly varying by ∼5 km s −1 over its 50 pc elongation parallel to the Galactic plane. We identify a sample of 75 VCFs in the C 18 O(2−1) position-position-velocity cube and present the properties of 47 VCFs with a length ≳1 pc (five beams). We measure a large number of velocity gradients along the VCFs. The amplitudes of these velocity gradients and the velocity dispersion measured along the crests increase with the column density of the VCFs. We derive the column density and velocity power spectra of the VCFs. These power spectra are well represented with power laws showing similar slopes for the two quantities (with a mean of about −2), although some differ by up to a factor of 2. The position velocity diagrams perpendicular to three VCFs (selected from different physical environments) show the V-shaped velocity pattern corresponding to a bent structure in velocity space with the filament at the tip of the V surrounded by an extended structure connected to it with a velocity gradient. This velocity structure is qualitatively similar to that resulting from numerical simulations of filament formation from large-scale compression from propagating shock fronts. In addition, the radial profiles perpendicular to these VCFs hint to small-scale internal impacts from neighboring H II bubbles on two of them, while the third is mostly unaffected. Conclusions. The observed opposite curvature in velocity space (V-and Λ-shaped) toward the VCFs points to various origins of large-scale external compressions from propagating H I bubbles. This suggests the plausible importance of multiple H I compressions, separated in space and time, in the formation and evolution of molecular clouds and their star formation history. These atomic compressions due to past and distant star formation events are complemented by the impact of H II bubbles from present time and local star formation activity.