Narrow-line Regions Of Seyfert Galaxies Research Articles

Outflow densities and ionization mechanisms in the NLRs of the prototypical Seyfert galaxies NGC 1068 and NGC 4151

ABSTRACT Despite being thought to play an important role in galaxy evolution, the true impact of outflows driven by active galactic nuclei (AGNs) on their host galaxies is unclear. In part, this may be because electron densities of outflowing gas are often underestimated: recent studies that use alternative diagnostics have measured much higher densities than those from commonly used techniques and consequently find modest outflow masses and kinetic powers. Furthermore, outflow ionization mechanisms – which are often used to probe acceleration mechanisms – are also uncertain. To address these issues, we have analysed archival HST/STIS spectra of the inner regions (r < 160 pc) of the nearby prototypical Seyfert galaxies NGC 1068 and NGC 4151, which show evidence of warm-ionized outflows driven by the central AGN. We derive high electron densities (103.6 < ne < 104.8 cm−3) using the transauroral [O ii] and [S ii] emission line ratios for the first time with spatially resolved observations. Moreover, we find evidence that the gas along the radio axis in NGC 1068 has a significant AGN-photoionized matter-bounded component, and there is evidence for shock-ionization and/or radiation-bounded AGN-photoionization along the radio axis in NGC 4151. We also note that the outflow extents are similar to those of the radio structures, consistent with acceleration by jet-induced shocks. Taken together, our investigation demonstrates the diversity of physical and ionization conditions in the narrow-line regions of Seyfert galaxies, and hence reinforces the need for robust diagnostics of outflowing gas densities and ionization mechanisms.

Do gas clouds in narrow-line regions of Seyfert galaxies come from their nuclei?

Abstract The narrow-line region (NLR) consists of gas clouds ionized by the strong radiation from the active galactic nucleus (AGN), distributed in the spatial scale of AGN host galaxies. The strong emission lines from the NLR are useful to diagnose physical and chemical properties of the interstellar medium in AGN host galaxies. However, the origin of the NLR is unclear; the gas clouds in NLRs may originally be in the host and photoionized by the AGN radiation, or they may be transferred from the nucleus with AGN-driven outflows. In order to study the origin of the NLR, we systematically investigate the gas density and velocity dispersion of NLR gas clouds using a large spectroscopic data set taken from the Sloan Digital Sky Survey. The [S ii] emission-line flux ratio and [O iii] velocity width of 9571 type-2 Seyfert galaxies and 110041 star-forming galaxies suggest that the gas density and velocity dispersion of NLR clouds in Seyfert galaxies (ne ≈ 194 cm−3 and $\sigma _{\rm [O\,{\small III}]} \approx 147\:$km s−1) are systematically larger than those of clouds in H ii regions of star-forming galaxies (ne ≈ 29 cm−3 and $\sigma _{\rm [O\,{\small III}]} \approx 58\:$km s−1). Interestingly, the electron density and velocity dispersion of NLR gas clouds are larger for Seyfert galaxies with a higher [O iii]/Hβ flux ratio, i.e., with a more active AGN. We also investigate the spatially-resolved kinematics of ionized gas clouds using the Mapping Nearby Galaxies at the Apache Point Observatory (MaNGA) survey data for 90 Seyfert galaxies and 801 star-forming galaxies. We find that the velocity dispersion of NLR gas clouds in Seyfert galaxies is larger than that in star-forming galaxies at a fixed stellar mass, at both central and off-central regions. These results suggest that gas clouds in NLRs come from the nucleus, probably through AGN outflows.

Evidence for radiation pressure compression in the X-ray narrow-line region of Seyfert galaxies

The observed spatial and kinematic overlap between soft X-ray emission and the Narrow Line Region (NLR) in obscured Active Galactic Nuclei (AGN) yields compelling evidence that relatively low-density gas co-exists with higher density gas on scales as large as 100s of pc. This is commonly interpreted as evidence for a constant gas pressure multiphase medium, likely produced by thermal instability. Alternatively, Radiation Pressure Compression (RPC) also leads to a density distribution, since a gas pressure (and hence density) gradient must arise within each cloud to counteract the incident ionising radiation pressure. RPC leads to a well-defined ionization distribution, and a Differential Emission Measure (DEM) distribution with a universal slope of $\sim-0.9$, weakly dependent on the gas properties and the illuminating radiation field. In contrast, a multiphase medium does not predict the form of the DEM. The observed DEMs of obscured AGN with XMM-Newton RGS spectra (the CHRESOS sample) are in striking agreement with the predicted RPC DEM, providing a clear signature that RPC is the dominant mechanism for the observed range of densities in the X-ray NLR. In contrast with the constant gas pressure multiphase medium, RPC further predicts an increasing gas pressure with decreasing ionization, which can be tested with future X-ray missions using density diagnostics.

Probing the Hot X-Ray Gas in the Narrow-line Region of Mrk 3

Abstract We study the prototypical Seyfert 2 galaxy, Markarian 3, based on imaging and high-resolution spectroscopy observations taken by Chandra. We construct a deconvolved X-ray image, which reveals the S-shaped morphology of the hot gas in the narrow-line region (NLR). While this morphology is similar to the radio and [O iii] emission, the distribution of the X-ray gas is broader than that obtained at these other wavelengths. By mapping the density and temperature distribution of the hot gas in the NLR, we demonstrate the presence of shocks toward the west ( ) and east ( ). Moreover, we compute the flux ratios between the [O iii] and 0.5–2 keV band X-ray luminosity and show that it is nonuniform in the NLR, with the western side of the NLR being more highly ionized. In addition, based on the Chandra grating data, we investigate the line ratios of the Si xiii triplet, which are not consistent with pure photoionization. Based on these results, we suggest that in the NLR of Mrk 3 both photoionization and collisional ionization act as excitation mechanisms. We conclude that the canonical picture, in which photoionization is solely responsible for exciting the interstellar medium in the NLR of Seyfert galaxies, may be overly simplistic. Given that weak and small-scale radio jets are commonly detected in Seyfert galaxies, it is possible that shock heating plays a non-negligible role in the NLR of these galaxies.

NEAR-INFRARED SPECTROSCOPY OF NEARBY SEYFERT GALAXIES: IS THERE EVIDENCE FOR SHOCK EXCITATION IN NARROW-LINE REGIONS?

ABSTRACT One of the important unsettled problems regarding active galactic nuclei (AGNs) is the major ionization mechanism of gas clouds in AGN narrow-line regions (NLRs). In order to investigate this issue, we present our J-band spectroscopic observations of a sample of 26 nearby Seyfert galaxies. In our study, we use the flux ratio of the following two forbidden emission lines, [Fe ii]1.257 μm and [P ii]1.188 μm, because it is known that this ratio is sensitive to the ionization mechanism. We obtain the [Fe ii]/[P ii] flux ratio or its lower limit for 19 objects. In addition to our data, we compile this flux ratio (or its lower limit) for 23 nearby Seyfert galaxies from the literature. Based on the collected data, we find that three Seyfert galaxies show very large lower limits of the [Fe ii]/[P ii] flux ratios (≳10): NGC 2782, NGC 5005, and Mrk 463. It is thus suggested that the contribution of the fast shock in the gas excitation is significantly large for them. However, more than half of the Seyfert galaxies in our sample show moderate [Fe ii]/[P ii] flux ratios (∼2), which is consistent with pure photoionization by power-law ionizing continuum emission. We also find that the [Fe ii]/[P ii] flux ratio shows no clear correlation with the radio loudness, suggesting that the radio jet is not the primary origin of shocks in NLRs of Seyfert galaxies.

Probing the physics of narrow-line regions of Seyfert galaxies

We have used the Wide Field Spectrograph (WiFeS) on the ANU 2.3m telescope at Siding Spring to observe the nearby, nearly face-on, Seyfert 2 galaxy, NGC 5427. We have obtained integral field spectroscopy of both the nuclear regions and the HII regions in the spiral arms. We have constrained the chemical abundance in the interstellar medium of the extended narrow line region (ENLR) by measuring the abundance gradient in the circum-nuclear \ion{H}{ii} regions to determine the nuclear chemical abundances, and to use these to in turn determine the EUV spectral energy distribution for comparison with theoretical models. We find a very high nuclear abundance, $\sim 3.0$ times solar, with clear evidence of a nuclear enhancement of N and He, possibly caused by massive star formation in the extended ($\sim 100$pc) central disk structure. The circum-nuclear narrow-line region spectrum is fit by a radiation pressure dominated photoionisation model model with an input EUV spectrum from a Black Hole with mass $5\times10^7 M_{\odot}$ radiating at $\sim 0.1$ of its Eddington luminosity. The bolometric luminosity is closely constrained to be $\log L_{\mathrm bol.} = 44.3\pm 0.1$ erg s$^{-1}$. The EUV spectrum characterised by a soft accretion disk and a harder component extending to above 15keV. The ENLR region is extended in the NW-SE direction. The line ratio variation in circum-nuclear spaxels can be understood as the result of mixing \ion{H}{ii} regions with an ENLR having a radius-invariant spectrum.

Spectral properties of the narrow-line region in Seyfert galaxies selected from the SDSS-DR7

Although the properties of the narrow-line region (NLR) of active galactic nuclei(AGN) have been deeply studied by many authors in the past three decades, many questions are still open. The main goal of this work is to explore the NLR of Seyfert galaxies by collecting a large statistical spectroscopic sample of Seyfert 2 and Intermediate-type Seyfert galaxies having a high signal-to-noise ratio in order to take advantage of a high number of emission-lines to be accurately measured. 2153 Seyfert 2 and 521 Intermediate-type Seyfert spectra were selected from Sloan Digital Sky Survey - Data Release 7 (SDSS-DR7) with a diagnostic diagram based on the oxygen emission-line ratios. All the emission-lines, broad components included, were measured by means of a self-developed code, after the subtraction of the stellar component. Physical parameters, such as internal reddening, ionization parameter, temperature, density, gas and stellar velocity dispersion were determined for each object. Furthermore, we estimated mass and radius of the NLR, kinetic energy of the ionized gas, and black-hole accretion rate. From the emission-line analysis and the estimated physical properties, it appears that the NLR is similar in Seyfert 2 and Intermediate-Seyfert galaxies. The only differences, lower extinction, gas kinematics in general not dominated by the host galaxy gravitational potential and higher percentage of [O III]5007 blue asymmetries in Intermediate-Seyfert can be ascribed to an effect of inclination of our line of sight with respect to the torus axis.

A 0.8–2.4μm spectral atlas of active galactic nuclei

Aims. We present a near-infrared spectral atlas of 47 active galactic nuclei (AGN) of all degrees of activity in the wavelength interval of 0.8-2.4 � m, including the fluxes of the observed emission lines. We ana lyze the spectroscopic properties of the continuum and emission line spectra of the sources. Methods. In order to exclude aperture and seeing effects we used near-infrared spectroscopy in the short cross-dispersed mode (SXD, 0.8−2.4� m), taking the JHK-bands spectra simultaneously. Results. We present the most extensive NIR spectral atlas of AGN to date. This atlas offers a suitable database for studying the continuum and line emission properties of these objects in a region full of interesting features. The shape of the continuum of QSOs and Sy 1’s are similar, being essentially flat in the H and K bands, while a strong vari ation is found in the J band. In Seyfert 2 galaxies, the contin uum in the Fλ×λ space smoothly decreases in flux from 1.2� m redwards in almost all sources. In J, it smoothly rises bluewards in some sources, while in others a small decrease in flux is observed. The spectra are do minated by strong emission features of Hi, Hei, Heii, [Siii] and by conspicuous forbidden lines of low and high ionization species. Molecular lines of H2 are common features of most objects. The absence of Oi and Feii lines in Seyfert 2 galaxies and the smaller FWHM of these lines relative to that of Hi in the Seyfert 1 give observational support to the fact that they are formed in the outermost portion of the broad-line region. The[Pii] and coronal lines are detected for all degrees of activity. The [Feii] 12570A/16436A line ratio becomes a reliable reddening indicator for the narrow-line region of Seyfert galaxies.

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.

Study of the Extended Narrow‐Line Region in the Host Galaxy of the Lensed QSO 2237+0305 (z= 1.69)

The detection of spatially extended line emission in multiply imaged QSOs offers a new possibility to study the properties (kinematics and structure) of the ionized gas in the host galaxies of high-redshift QSOs. We have studied the arc of extended emission detected in Q2237+0305, finding that it arises from the core of the C III] λ1909 emission line and that the emission in the wings is compact. From the morphology of the emission-line profiles we have identified an additional narrow emission line component affecting the core of the spectra in the region of the arc (around component D). The kinematic analysis shows that the extended narrow-line region (NLR) exhibits broadening similar to that of NLRs in Seyfert galaxies and that its mean velocity is consistent with galaxy rotation. We model the shape of the arc and thus derive qualitative lower and upper limits for the source of ionized gas in the host galaxy of the QSO. Thus, thanks to the lensing, we resolve kinematically and spatially an extended NLR of the quasar host that is likely photoionized by the central engine.

Science with NIFS, Australia's First Gemini Instrument

AbstractThe Near-infrared Integral Field Spectrograph (NIFS) will beAustralia’s first Gemini instrument. NIFS is a near-infrared, imaging spectrograph that will be used with the ALTAIR facility adaptive optics system on Gemini North to perform near-diffraction-limited imaging spectroscopy over a 3·0″ × 3·0″ field of view with 0·1″ wide slitlets and a spectral resolving power of ˜5300. NIFS will operate in the wavelength range from 0·94–2·50 µm where ALTAIR delivers its greatest gains. Its primary purpose is to study moderate-surface-brightness structures around discrete objects that are revealed at high spatial resolution by ALTAIR. NIFS will address a wide range of science from studies of Galactic star formation and the Galactic centre to the nature of disk galaxies at z ˜ 1. Studies of the demographics of massive black holes in galactic nuclei and studies of the excitation conditions in the inner narrow-line regions of Seyfert galaxies have been identified as two core NIFS programs. These and other science drivers for NIFS are discussed.

The Effect of Intrinsic Ultraviolet Absorbers on the Ionizing Continuum and Narrow Emission Line Ratios in Seyfert Galaxies

We explore the effects of UV-absorbing material on the shape of the EUV continuum radiation emitted by the active galactic nucleus and on the relative strengths of emission lines, formed in the narrow-line regions of Seyfert galaxies, excited by this continuum. Within a sample of Seyfert 1.5 galaxies, objects with flatter soft X-ray slopes tend to have lower values of He II ?4686/H?, which implies a correlation between the observed spectral energy distribution of the ionizing continuum and the narrow emission line strengths. Objects with the flattest soft X-ray continua tend to possess high-column density UV absorption, and it is plausible that the differences in narrow emission line ratios among these galaxies are an indication of the effects of absorbing material internal to the narrow-line region, rather than intrinsic differences in continuum shape. We have generated a set of photoionization models to examine the effect of a range of UV absorbers on the ionizing continuum and, hence, the resulting conditions in a typical narrow-line cloud. Our results indicate that a low-ionization UV absorber with large covering factor will indeed produce the combination of narrow-line ratios and soft X-ray spectral characteristics observed in several Seyfert 1.5 galaxies. Our results also suggest that low-ionization UV absorption may be more common than currently believed.

Probing the Dusty Accretion Torus of Seyfert Galaxies

We show that the IRAS colors of Seyfert galaxies can be understood in terms of a model in which we see emission by hot dust near its sublimation temperature emitting a spectrum that varies little from object to object. For objects observed through the dusty accretion torus, which is optically thick at 12 μm, this dust emission is absorbed to various degrees. In addition, in many objects, this spectrum is veiled by a component produced by a circumnuclear starburst. The hidden broad-line objects all lie along the reddening line in IRAS color-color plots, and the dust extinction at 12 μm lies in the range 0.5-2.5, which implies an H I column density of ~5 × 1022 cm-2 for the hot circumnuclear dust located at about 3 pc from the central engine. For these objects we can also estimate the true luminosities of the central active nuclei from the dereddened IR fluxes. If the simple accretion flow model is correct, then typical accretion rates are on the order of 10 M☉ yr-1. The radiation pressure of the central active galactic nucleus acting on the inner portions of the dust torus is likely to play a critical role in controlling the accretion flow toward the nucleus and in forming the ionization cones seen in the narrow-line regions of Seyfert galaxies.

Jet-Cloud Interactions and the Brightening of the Narrow-Line Region in Seyfert Galaxies

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. Supercritical clouds increase in emission-line brightness, while subcritical clouds generally are highly overheated, reducing their luminosity below that of the intercloud medium. As a result of 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.

Radio Outflows and the Origin of the Narrow-Line Region in Seyfert Galaxies

We present the results of Hubble Space Telescope medium-band imaging of four Seyfert 2 galaxies, Mrk 573, Mrk 348, Mrk 3, and Mrk 78, which show extended radio emission, and ground based Johnson A images of Mrk 3 and Mrk 78 obtained with the William Herschel Telescope. Together these two data sets allow us to investigate the relationship between the narrow-line region (NLR) emission structure, the radio structure, and the large-scale morphology of the host galaxy. In all four objects there is a close association between the NLR emission-line morphology and that of the radio emission. Furthermore, it appears that the NLR takes a different form depending on the structure of the radio emission. The emission-line regions associated with the radio lobes are shell-like or bow shock-like, while those associated with the jets are linear. In Mrk 573, the emission-line ratios [O III]/[O II] and [O III]/Hα show only a slow increase with radius between the bow shocks ([O III]/[O II] ~3 and [O III]/Hα ~ 1.5, r &lt; 2") and the outer filaments [O III]/[O II] ~ 4 and [O III]/Hα ~ 2.2" &lt;r &lt;4"). A similar, but more substantial, trend for increasing ionization with radius is seen in Mrk 78 ([O III]/[O II] ~ 1.4 in the core and [O III]/[O II]~ 2.9 in the western lobe). In the case of Mrk 573, it appears that a local source of ionization is required to explain the observed ionization structure. We interpret these results as strong evidence that the line-emitting gas is compressed by the shocks created by the passage of the radio- emitting outflow. The increase in the density due to the shocks causes the line emission to be highly enhanced in the region in which this interaction occurs. The shell-like morphology of the emission-line gas associated with the radio lobes is formed by the sweeping-up of material by the ejected and expanding lobes, while the linear structure associated with the jets arises due to the lateral expansion of hot gas around the jet axis. There is no evidence for an unresolved bright core which could be identified as the active nucleus in any of these galaxies. From this, we conclude that the nucleus must be hidden along our line of sight. In all four objects, an absorption lane crossing the nuclear region has been detected. In Mrk 348, Mrk 573, and Mrk 3, the typical scale height of the dust lane is less than 50 pc, while in Mrk 78 it is ~180 pc. We suggest that these dust lanes are associated with the obscuring torus which occults the Seyfert nucleus. Three of the objects (Mrk 573, Mrk 3, and Mrk 78) show large-scale stellar bars, and Mrk 573 also shows an inner bar oriented nearly perpendicular to the outer bar. We discuss the relationship between the bars and the orientation of the NLR.

Results of Detailed Modeling of the Narrow-Line Region of Seyfert Galaxies

We present model line profiles of [O II] lambda3727, [Ne III] lambda3869, [O I] lambda5007, [Fe VII] lambda6087, [Fe X] lambda6374, [O I] lambda6300, H(alpha) lambda6563, and [S 2] lambda6731. The profiles presented here illustrate explicitly the pronounced effects that collisional de-excitation, and that spatial variations in both the ionization parameter and cloud column density, have on Narrow-Line Region (NLR) model profiles. The above effects were included only qualitatively in a previous analytical treatment by Moore and Cohen. By making a direct correspondence between these model profiles and the analytical model profiles of Moore and Cohen, and by comparing with the observed profiles presented in a companion paper and also with those presented elsewhere in the literature, we strengthen some of the conclusions of Moore and Cohen. Most notably, we argue for constant ionization parameter, uniformly accelerated outflow of clouds that are individually stratified in ionization, and the interpretation of emission-line width correlations with ionization potential as a column density effect. For comparison with previous observational studies, such as our own in a companion paper, we also calculate profile parameters for some of the models, and we present and discuss the resulting line width correlations with critical density (n(sub cr)) and Ionization Potential (IP). Because the models we favor are those that produce extended profile wings as observed in high spectral resolution studies, the line width correlations of our favoured models are of particular interest. Line width correlations with n(sub cr) and/or IP result only if the width parameter is more sensitive to extended profile wings than is the Full Width at Half-Maximum (FWHM). Correlations between FWHM and n(sub cr) and/or IP result only after convolving the model profiles with a broad instrumental profile that simulates the lower spectral resolution used in early observational studies. The model in agreement with the greatest number of observational considerations has electron density decreasing outward from n(sub e) approx. equals 10(exp 6)/cu cm to n(sub e) approx. equals 10(exp 2)/cu cm and, due to collisional de-excitation effects in the lowest velocity clouds, it generates broad flat-topped profile peaks in the lines of lowest critical density (e.g., [O II] lambda3727 and [S II] lambda(lambda)6716, 6731). Because the observed profile peaks of both low and high critical density lines are often very similar, our favored model requires a contribution to NLR emission-line spectra from low-velocity, low-density, and low-ionization gas not included in the model NLR.

IUE Spectra and photoionization models of the Seyfert 2 glaxies NGC 7674 and I ZW 92

The physical conditions in the narrow-line regions of two Seyfert 2 galaxies, NGC 7674 and I Zw 92, are examined using IUE spectra, published optical spectra and multifrequency observations, and photoionization models. For each Seyfert galaxy, the emission-line fluxes were dereddened using the He II lambda(1640)/lambda(4686) ratio. Photoionization models were calculated using a power-law index determined from the He II lambda(4686)/H-beta ratio; the index is very similar to that obtained from a fit to the observed multifrequency continuum from the infrared to the X-rays. The models were calculated in a way that minimized the number of assumptions, and given the uncertainties in the reddening corrections, the calculated ratios match nearly all of the dereddened ratios successfully. a multicomponent model (three components with different densities and ionization parameters) was required to fit the spectrum of I Zw 92, whereas a single component was sufficient for NGC 7674. The CNO abundances are close to solar, although a reduced abundance of up to one-third solar for one or more of the heavy elements is possible. In contrast to a previous study of Mrk 3, dust inside the narrow-line region (NLR) louds was not required to fit the spectra of these two Seyfert galaxies, although the emission lines experience considerable reddening from external dust. Higher signal-to-noise spectra in the UV are essential for placing further restrictions on the reddening and physical conditions in the narrow-line regions of Seyfert galaxies.

Bowshocks and the formation of the narrow-line region of Seyfert galaxies

Considerable evidence exists for a relationship between the optical narrow-line region (the NLR) and the nuclear non-thermal radio emission in Seyfert galaxies. In a previous paper we introduced a model for the NLR, which we here develop and describe more fully, in which the linear motions of the radio components drive bowshocks into the ambient nuclear medium. The cooled shocked gas, photoionized by the UV nuclear continuum, produces the optical NLR emission. The radio components may take the form of bubbles of plasma ejected from the nucleus, or may represent the working surfaces of jets

A study of the structure and kinematics of the narrow-line region in Seyfert galaxies. III - Individual objects

view Abstract Citations (112) References (190) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Study of the Structure and Kinematics of the Narrow-Line Region in Seyfert Galaxies. III. Individual Objects Veilleux, Sylvain Abstract This is the third paper in a series discussing the results of a high-resolution study of the narrow-line profiles in 16 Seyfert galaxies. In this paper the objects in the sample are analyzed individually. The high spectral resolution, excellent signal-to-noise ratio, and broad wavelength coverage of the data allow a detailed comparison of the emission-line profiles in each galaxy through proNe ratio and decomposition techniques. Substructure is observed in the narrow-line profiles of all but one of the objects in the sample (Mrk 359). A direct relationship between the radio structure and these emission-line components appears to exist in at least six objects. Evidence for ionization/density stratification of the gas in the narrow-line region (NLR) was discovered or confirmed in 4 (ionization)/5 (density) of the 11 objects in the sample for which a multispecies analysis was possible. Stronger evidence for stratification is observed in the objects whose emission lines present a minimum of profile substructure. The results of profile ratios suggest that the blueward asymmetry, observed in the profiles of at least 10 of the 16 galaxies in the sample, is caused by dust within the line-emitting clouds or by the effects of an occulting (i.e., highly optically thick) component located near the nucleus. The gas producing the blue wing generally is more highly ionized than the rest of the gas. A multi-component model of the NLR is proposed to attempt to tie together the results of Papers I, II, and III and of previous kinematic studies. Publication: The Astrophysical Journal Pub Date: March 1991 DOI: 10.1086/169765 Bibcode: 1991ApJ...369..331V Keywords: Galactic Nuclei; Galactic Structure; Seyfert Galaxies; Spectral Line Width; Emission Spectra; Markarian Galaxies; Signal To Noise Ratios; Astrophysics; GALAXIES: INTERNAL MOTIONS; GALAXIES: NUCLEI; GALAXIES: SEYFERT; LINE PROFILES full text sources ADS | data products NED (16) SIMBAD (13) Related Materials (2) Part 1: 1991ApJS...75..357V Part 2: 1991ApJS...75..383V

A Study of the Structure and Kinematics of the Narrow-Line Region in Seyfert Galaxies. II. Analysis of the Line-Profile Parameters

view Abstract Citations (81) References (64) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Study of the Structure and Kinematics of the Narrow-Line Region in Seyfert Galaxies. II. Analysis of the Line-Profile Parameters Veilleux, Sylvain Abstract The results of the analysis of the line profiles presented in Paper I are reported. It is shown that the line-profile parameters derived from low- resolution data are often greatly affected by the finite width of the instrumental profile. These resolution effects generally result in overestimates of the line widths and underestimates of the line asymmetries. In spite of these important systematic errors, many of the results of low-resolution studies are confirmed in the high-resolution data. The narrow-line profiles of Seyfert galaxies have a stronger base relative to core than a Gaussian. Most of the emission lines present a blueward asymmetry in a lower portion of their profile. The widths of all of the emission lines are correlated with the emission-line/infrared/radio luminosities. None of the profile parameters correlates strongly with the reddening, ionization level, temperature, or density of the gas producing the narrow emission lines. The host galaxy probably plays a role in the kinematics of some of the gas in the narrow-line region. There is a tendency for galaxies with early morphological types to have broader and stubbier line profiles than objects of later types. A correlation is also observed between the [O III] line width and the luminosity of the galactic bulge. Publication: The Astrophysical Journal Supplement Series Pub Date: February 1991 DOI: 10.1086/191535 Bibcode: 1991ApJS...75..383V Keywords: GALAXIES: INTERNAL MOTIONS; GALAXIES: NUCLEI; GALAXIES: SEYFERT; LINE PROFILES full text sources ADS | data products SIMBAD (16) NED (16) Related Materials (2) Part 1: 1991ApJS...75..357V Part 3: 1991ApJ...369..331V