Low-luminosity Seyfert Galaxies Research Articles

Nature of UV Variability in NGC 4151 from IUE’s Intensive Monitoring Spectroscopic Data

The International Ultraviolet Explorer (IUE) satellite, launched in 1978 by NASA and ESA, has conducted highly successful long-term monitoring spectroscopic observations of many nearby (low-redshift) bright active galaxies, including NGC 1068, NGC 5548, NGC 7469, Fairall 9,MRK 335 and NGC 4151. Notably, IUE has monitored NGC 4151 more intensively than any other active galaxy, obtaining 414 spectra during its campaign from December 1 to 15, 1993. Here, we present results of our recent studies on the emission line and continuum variabilities characterised by the Rmax and Fvar parameters. From the analysis of the short timescale, intense monitoring data, we obtained Rmax values ranging between 2.14±0.02 and 1.62±0.01 corresponding to the UV continua 1270 Å, and 2705 Å, respectively. The corresponding Fvar values varied from 9.62±0.04% to 5.19±0.04 %. Furthermore, the Rmax values for the UV emission lines Lyα, C IV, He II, O III], C III] and Mg II have been found to be 4.09±0.06, 4.55±0.05, 13.65±0.68, 4.78±0.17, 2.76±0.02, respectively. The corresponding Fvar values obtained are 2.85±0.01 %, 26.51±0.06 %, 15.59±0.02 %, 48.93±1.79 %, 20.30±0.06% and 18.68±0.02 %, respectively. These results provide constraints on the amplitude of UV variability and the size of the broad-line region (BLR) in low luminosity Seyfert galaxies. The decreasing Fvar amplitudes of the UV continuum with respect to increasing wavelengths are significant results of the present study.

Short timescale UV variability study in NGC 4151 using IUE data

IUE has made very successful long term and intense short time-scale monitoring spectroscopic study of NGC 4151, a Seyfert 1 galaxy for over nearly 18 years from its launch in 1978 to 1996. The long-term observations have been useful in understanding the complex relation between UV continuum and emission line variability Seyfert galaxies. In this paper, we present the results of our studies on the short-timescale intense monitoring campaign of NGC 4151 undertaken during December 1–15, 1993. A most intense monitoring observation of NGC 4151 was carried out by IUE in 1993, when the source was at its historical high flux state with a shortest interval of 70 min between two successive observations. We present our results on emission line and continuum variability amplitudes characterized by $$F_{\mathrm{var}}$$ method. We found highest variability of nearly 8.3% at 1325 $$\AA $$ continuum with a smallest amplitude of 4% at 2725 $$\AA $$ . The relative variability amplitudes ( $$R_\mathrm{max}$$ ) have been found to be 1.372, 1.319, 1.302 and 1.182 at 1325, 1475, 1655 and 2725 $$\AA $$ continuum respectively. The continuum and emission line variability characteristics obtained in the present analysis are in very good agreement with the results obtained by Edelson et al. (1996) and Crenshaw et al. (1996) from the analysis of the same observational spectral data. The large amplitude rapid variability characteristics obtained in our study have been attributed to the continuum reprocessing of X-rays absorbed by the material in the accretion disk as proposed by Shakura and Sunyaev (1973). The continuum and emission light curves have shown four distinct high amplitude events of flux maxima during the intense monitoring campaign of 15 days, providing a good limit on the amplitude of UV variability and the BLR size in low luminosity Seyfert galaxies and are useful for constraining the continuum emission models. The decreasing $$F_{\mathrm{var}}$$ amplitude of UV continuum with respect to increasing wavelength obtained in the present study and consistent with similar observations by Edelson et al. (1996) and Crenshaw et al. (1996) is a significant result of the intense monitoring observations.

15-GHz radio emission from nearby low-luminosity active galactic nuclei

We present a sub-arcsec resolution radio imaging survey of a sample of 76 low-luminosity active galactic nuclei (LLAGN) that were previously not detected with the Very Large Array at 15 GHz. Compact, parsec-scale radio emission has been detected above a flux density of 40 μ Jy in 60% (45 of 76) of the LLAGN sample. We detect 20 out of 31 (64%) low-ionization nuclear emission-line region (LINER) nuclei, ten out of 14 (71%) low-luminosity Seyfert galaxies, and 15 out of 31 (48%) transition objects. We use this sample to explore correlations between different emission lines and the radio luminosity. We also populate the X-ray and the optical fundamental plane of black hole activity and further refine its parameters. We obtain a fundamental plane relation of log LR = 0.48 (±0.04) log LX + 0.79 (±0.03) log M and an optical fundamental plane relation of log LR = 0.63 (±0.05) log L[O III] + 0.67 (±0.03) log M after including all the LLAGN detected at high resolution at 15 GHz, and the best-studied hard-state X-ray binaries (luminosities are given in erg s−1 while the masses are in units of solar mass). Finally, we find conclusive evidence that the nuclear 15 GHz radio luminosity function (RLF) of all the detected Palomar Sample LLAGN has a turnover at the low-luminosity end, and is best-fitted with a broken power law. The break in the power law occurs at a critical mass accretion rate of 1.2 × 10−3 M⊙ yr−1, which translates to an Eddington ratio of ṁEdd ~ 5.1 × 10−5, assuming a black hole mass of 109 M⊙. The local group stands closer to the extrapolation of the higher-luminosity sources, and the classical Seyferts agree with the nuclear RLF of the LLAGN in the local universe.

Evidence for a truncated accretion disc in the low-luminosity Seyfert galaxy, NGC 7213?

We present the broad-band 0.6-150 keV Suzaku and Swift BAT spectra of the low luminosity Seyfert galaxy, NGC 7213. The time-averaged continuum emission is well fitted by a single powerlaw of photon index Gamma = 1.75 and from consideration of the Fermi flux limit we constrain the high energy cutoff to be 350 keV < E < 25 MeV. Line emission from both near-neutral iron K_alpha at 6.39 keV and highly ionised iron, from Fe_(xxv) and Fe_(xxvi), is strongly detected in the Suzaku spectrum, further confirming the results of previous observations with Chandra and XMM-Newton. We find the centroid energies for the Fe_(xxv) and Fe_(xxvi) emission to be 6.60 keV and 6.95 keV respectively, with the latter appearing to be resolved in the Suzaku spectrum. We show that the Fe_(xxv) and Fe_(xxvi) emission can result from a highly photo-ionised plasma of column density N_(H) ~ 3 x 10^(23) cm^(-2). A Compton reflection component, e.g., originating from an optically-thick accretion disc or a Compton-thick torus, appears either very weak or absent in this AGN, subtending < 1 sr to the X-ray source, consistent with previous findings. Indeed the absence of either neutral or ionised Compton reflection coupled with the lack of any relativistic Fe K signatures in the spectrum suggests that an inner, optically-thick accretion disc is absent in this source. Instead, the accretion disc could be truncated with the inner regions perhaps replaced by a Compton-thin Radiatively Inefficient Accretion Flow. Thus, the Fe_(xxv) and Fe_(xxvi) emission could both originate in ionised material perhaps at the transition region between the hot, inner flow and the cold, truncated accretion disc on the order of 10^(3) - 10^(4) gravitational radii from the black hole. The origin for the unresolved neutral Fe K_alpha emission is then likely to be further out, perhaps originating in the optical BLR or a Compton-thin pc-scale torus.

The Structure of Narrow-Line Region in LINERs

Low-ionization nuclear emission regions (LINERs) are present in a large fraction of local galaxies, while their connection to the more luminous active galactic nuclei (AGN) remains elusive. We analyze the narrow band images obtained by the Hubble Space Telescope (HST) in Hα+[NII] and/or [OIII] band for 23 LINERs and low luminosity Seyfert galaxies in the sample of the Palomar Optical Spectroscopic Survey of nearby galaxies in an attempt to resolve the structure of Narrow Emission Line Regions (NLRs) of these objects. In all cases, NLRs are well resolved and their morphology differs from object to object. Clumps, linear structure, spiral arms or a ring are detected in a large fraction of the objects, while there is no significant difference between Seyfert galaxies and LINERs. We find that the NLR size and the narrow line luminosity are strongly correlated for both LINERs and low luminosity Seyfert galaxies, and that the size of Hα+[NII] emission line region scales with Hα luminosity as RNLR∝LHα0.44±0.06, consistent with an extension of the NLR size-luminosity relation defined for luminous Seyfert galaxies and quasars, to two orders of magnitude lower in luminosity and to lower activity levels. Our results suggest that NLRs in LINERs are similar to those of Seyfert galaxies, and they are powered by the central active galactic nucleus.

The morphology of minor axis gaseous outflows in edge-on Seyfert galaxies

Context. Spiral galaxies often have extended outflows that permeate beyond the region of the disk. Such outflows have been seen both in starburst galaxies, actively star forming galaxies and galaxies with an AGN. In the latter galaxies it is unknown whether the large-scale outflows are driven by star formation activity or purely by the active nucleus. Aims. The aim of our investigation is to study the frequency of extended minor-axis outflows in edge-on Seyfert galaxies to investigate the role of the AGN, the circumnuclear environment and star formation activity within the disk regions, and their importance for IGM enrichment on large scales. Methods. We obtained optical narrowband imaging observations of a distance limited, northern hemisphere sample of 14 edge-on Seyfert spiral galaxies. Because of the distance-limited nature of the sample, it is restricted to relatively low-luminosity Seyfert galaxies. The data were obtained with BUSCA attached to the 2.2 m telescope at the Calar Alto observatory. Narrowband imaging in two different ionizational stages (H α and [O iii] ) was performed to attempt a discrimination between processes associated with the active nucleus and those connected to star forming activity within the disk. The median 3- σ sensitivities for detection of high-latitude extended emission in the sample galaxies are $3.6\times10^{-17}$ erg s -1 cm -2 arcsec -2 for the H α images and $6.9\times10^{-17}$ erg s -1 cm -2 arcsec -2 for the [O iii] images. We use the data to study the distribution of extraplanar emission with respect to the AGN and the underlying disk H ii regions. Results. The H α morphology of the Seyfert galaxies is usually complex, but only in three out of 14 galaxies did we find evidence for minor axis disk outflows. At the sensitivity of our observations [O iii] emission is generally detected only in the nuclear region. For Ark 79 we present the first evidence of a secondary nuclear component, best visible in the [O iii] image, which has a linear separation from the primary nucleus of about 850 pc. Conclusions. Overall, our results show that extraplanar emission of similar brightness and extent as in the previously known cases of NGC 3079 and NGC 4388 is not common in Seyfert galaxies of otherwise similar properties. Comparison with our previous results shows that for nearby edge-on spiral galaxies star formation may be a more powerful mechanism for producing DIG than AGN activity. While in general AGN activity undoubtedly plays some role in driving minor-axis outflows, this probably requires higher AGN luminosities than are encountered in our small distance-limited sample.

Long-term optical photometric monitoring of the quasar SDSS J153259.96−003944.1

We report optical Cousins R- and I-band monitoring observations of the high-redshift (z = 4.67) quasi-stellar object (QSO) SDSS J 153259.96-003944.1 which does not show detectable emission lines in its optical spectrum. We show this object varies with a maximum amplitude of ∼0.4 mag over 1 yr and 3 months of monitoring. Combined with two other epochs of photometric data available in the literature, we show the object has gradually faded by ∼0.9 mag during the period 1998 June-2001 April. A linear least-squares fit to all available observations gives a slope of ∼0.35 mag yr -1 which translates to ∼1.9 mag yr -1 in the rest frame of the quasar. Such a variability is higher than that typically seen in QSOs but consistent with that of BL Lacs, suggesting that the optical continuum is Doppler boosted. Alternatively, within photometric errors, the observed light curve is also consistent with the object going through a microlensing event. Photoionization model calculations show the mass of the broad line region to be a few tens of M ○. similar to that of low-luminosity Seyfert galaxies, but ∼2 orders of magnitude less than that of luminous quasars. Further frequent photometric/spectroscopic monitoring is needed to support or refute the different alternatives discussed here about the nature of SDSS J153259.96-003944.1.

Asymmetrical structure of ionization and kinematics in the Seyfert galaxy NGC 5033

We present integral field spectroscopy of NGC 5033, a low luminosity Seyfert galaxy. The observations were made with INTEGRAL, a fiber based system operating at the WHT. The intensity map of the H emission line represents a spiral or ring-like pattern of HII regions. On the contrary, the [OIII] intensity map morphology is markedly anisotropic. The strong morphological differences imply that the [ OIII] emitters represent highly ionized gas illuminated by the central source. The [ OIII] map morphology is compatible with a biconical structure of ionization induced by strong extinction in the galaxy disc that also obscures half of the spheroidal stellar bulge. We identify the spectrum corresponding to the Seyfert 1 nucleus from the presence of H broad emission lines. This spectrum is located in a region where strong extinction is expected but exhibits the bluest spectral energy distribution. The Seyfert 1 nucleus seems to be off center with respect to the stellar rotation center. This result has been also found in other Seyfert galaxies and interpreted in terms of a past merger. The off centering could indicate the presence of nonsymmetric departures in the gravitational potential which could be fueling the active nucleus. The kinematics of the [ OIII] emitters show important deviations at a kpc scale with respect to the stellar velocity field and show features related to the asymmetrical morphology of the high ionization region.

ChandraSnapshot Observations of Low‐Luminosity Active Galactic Nuclei with a Compact Radio Source

The results of Chandra snapshot observations of 11 LINERs (Low-Ionization Nuclear Emission-line Regions), three low-luminosity Seyfert galaxies, and one HII-LINER transition object are presented. Our sample consists of all the objects with a flat or inverted spectrum compact radio core in the VLA survey of 48 low-luminosity AGNs (LLAGNs) by Nagar et al. (2000). An X-ray nucleus is detected in all galaxies except one and their X-ray luminosities are in the range 5x10^38 to 8x10^41 erg/s. The X-ray spectra are generally steeper than expected from thermal bremsstrahlung emission from an advection-dominated accretion flow (ADAF). The X-ray to Halpha luminosity ratios for 11 out of 14 objects are in good agreement with the value characteristic of LLAGNs and more luminous AGNs, and indicate that their optical emission lines are predominantly powered by a LLAGN. For three objects, this ratio is less than expected. Comparing with properties in other wavelengths, we find that these three galaxies are most likely to be heavily obscured AGN. We use the ratio RX = \nu L\nu (5 GHz)/LX, where LX is the luminosity in the 2-10 keV band, as a measure of radio loudness. In contrast to the usual definition of radio loudness (RO = L\nu(5 GHz)/L\nu(B)), RX can be used for heavily obscured (NH >~ 10^23 cm^-2, AV>50 mag) nuclei. Further, with the high spatial resolution of Chandra, the nuclear X-ray emission of LLAGNs is often easier to measure than the nuclear optical emission. We investigate the values of RX for LLAGNs, luminous Seyfert galaxies, quasars and radio galaxies and confirm the suggestion that a large fraction of LLAGNs are radio loud.

X‐Ray Properties of LINERs and Low‐Luminosity Seyfert Galaxies Observed withASCA. I. Observations and Results

This paper presents a comprehensive study of the X-ray properties of low-ionization nuclear emission-line regions (LINERs) and low-luminosity Seyfert galaxies based on observations obtained with the ASCA satellite. We analyzed data of 53 observations of 21 LINERs and 17 low-luminosity Seyferts. X-ray emission has been detected in all but one object. The X-ray luminosities in the 2-10 keV band range from 4 × 1039 to 5 × 1041 ergs s-1, which are 1-3 orders of magnitude smaller than in classical Seyfert galaxies. The X-ray spectra of most objects are well described by a canonical model which consists of (1) a soft component from a thermal plasma with kT < 1 keV and (2) a hard component represented by a power law with a photon index of Γ ≈ 1.8 or thermal bremsstrahlung emission with kT ≈ 10 keV. Several objects do not require the soft thermal component, and their continua are well fitted by a single power-law model. Some objects show heavy absorption with column densities in excess of 1023 cm-2. We detect in several objects Fe K line emission with equivalent widths ranging from 50 eV to 2 keV. Variability on timescales less than a day is uncommon in our sample. By comparing multiple observations made with ASCA or with published 2-10 keV observations from other satellites, we show that at least eight objects are variable on timescales of a week to several years. We find that the morphologies of many objects, both in the soft and hard bands, are consistent with being pointlike relative to the telescope point-spread function; a few are clearly extended in either or both energy bands. The second paper of this series will discuss the physical interpretation of the X-ray emission and its implications for low-luminosity active galactic nuclei.

Active nucleus in a post-starburst galaxy: KUG 1259+280

We report the discovery of an active nucleus in a post-starburst galaxy, KUG 1259+280, based on its X-ray and optical characteristics. The X-ray source in KUG 1259+280 was detected during a search for ultrasoft sources in the ROSAT pointings. High-resolution X-ray imaging observations with ROSAT HRI show that X-ray emission from KUG 1259+280 is unresolved. X-ray emission from KUG 1259+280 is highly variable; an episode in which X-ray intensity changed by a factor ∼2.5 within ∼1300 s has been detected. ROSAT PSPC spectra of this galaxy are found to be well represented by a steep power law of photon index ΓX∼4.25, and a change in the absorbing column within ∼1 d is indicated. The rest frame intrinsic X-ray luminosity of KUG 1259+280 is found to be ∼3.6–4.7×1042 erg s−1, similar to that of low-luminosity Seyfert galaxies. The mass of the central massive object within KUG 1259+280 is estimated to be in the range 105–107 M⊙. The optical spectrum of the nuclear region of the galaxy is complex and shows Balmer absorption and collisionally excited lines of [O iii] and [N ii]. The presence of forbidden emission lines and the absence of Balmer emission lines in the spectrum of KUG 1259+280 could be the result of photoionization by a diluted power-law continuum modified by enhanced stellar absorption owing to a post-starburst event. Estimated Balmer line strengths free of stellar absorptions and forbidden line strengths indicate the nucleus of KUG 1259+280 to be low-ionization nuclear emission region (LINER) like in nature. However, the low-ionization forbidden line [O i] λ6300 usually present in LINER spectra is not detected in the spectrum of KUG 1259+280. X-ray characteristics—variability, point-like appearance, luminosity and steepness of spectrum—indicate that the nucleus in KUG 1259+280 is active and perhaps like that of narrow-line Seyfert type 1 galaxies.

Hard X‐Ray Emission and the Ionizing Source in LINERs

We report X-ray fluxes in the 2-10 keV band from LINERs (low-ionization nuclear emission-line regions) and low-luminosity Seyfert galaxies obtained with the ASCA satellite. Observed X-ray luminosities are in the range between 4 x 10(exp 39) and 5 x 10(exp 41) ergs/s, which are significantly smaller than that of the classical low-luminosity Seyfert 1 galaxy NGC 4051. We found that X-ray luminosities in 2-10 keV of LINERs with broad H.alpha emission in their optical spectra (LINER 1s) are proportional to their Ha luminosities. This correlation strongly supports the hypothesis that the dominant ionizing source in LINER 1s is photoionization by hard photons from low-luminosity AGNs. On the other hand, the X-ray luminosities of most LINERs without broad H.alpha emission (LINER 2s) in our sample are lower than LINER 1s at a given H.alpha luminosity. The observed X-ray luminosities in these objects are insufficient to power their H.alpha luminosities, suggesting that their primary ionizing source is other than an AGN, or that an AGN, if present, is obscured even at energies above 2 keV.

Radio Sources in Low‐Luminosity Active Galactic Nuclei. I. VLA Detections of Compact, Flat‐Spectrum Cores

We report a high-resolution (02), 15 GHz survey of a sample of 48 low-luminosity active galactic nuclei with the Very Large Array. Compact radio emission has been detected above a flux density of 1.1 mJy in 57% (17 of 30) of low-ionization nuclear emission-line region (LINER) nuclei and low-luminosity Seyfert galaxies. The 2 cm radio power is significantly correlated with the emission-line ([O I] λ6300) luminosity. Using radio fluxes at other frequencies from the literature, we find that at least 15 of the 18 detected radio cores have a flat to inverted spectrum (α ≥ -0.3, Sν ∝ να). While the present observations are consistent with the radio emission originating in star-forming regions (the brightness temperatures are ≥102.5-4.5 K), higher resolution radio observations of 10 of the detected sources, reported in an accompanying paper, show that the cores are very compact (1 pc), of high brightness temperature (Tb 108 K), and probably synchrotron self-absorbed, ruling out a starburst origin. Thus, our results suggest that at least 50% of low-luminosity Seyfert galaxies and LINERs in the sample are accretion powered, with the radio emission presumably coming from jets or advection-dominated accretion flows. We have detected only 1 of 18 transition (i.e., LINER + H II) nuclei observed, indicating that their radio cores are significantly weaker than those of pure LINERs. Compact 2 cm radio cores are found in both type 1 (i.e., with broad Hα) and type 2 (without broad Hα) nuclei. There is weak evidence, limited in significance by small numbers, that low-luminosity active galactic nuclei with compact radio cores exhibit radio ejecta preferentially aligned along the rotation axis of the galaxy disk. If this result were confirmed by a larger sample, it would lend support to the idea that the misalignment of accretion disks with the galaxy stellar disk in more luminous Seyfert galaxies is a result of radiation-pressure-induced warping of their accretion disks.

High-resolution X-ray imaging observations of two low-luminosity Seyfert galaxies

Results from observations of two nearby, low X-ray luminosity Seyfert-type galaxies, namely NGC 1365 and NGC 4051, using the ROSAT High Resolution Imager (HRI), are presented. The observations, carried out with the aim of detecting and resolving the extranuclear (beyond the central 5–10 arcsec) X-ray emission, show evidence for an extended component of ≃2 kpc size in NGC 1365 and NGC 4051. The extended component contains 56±8 per cent of the total observed flux in the case of NGC 1365, and 21±6 per cent in the case of NGC 4051. In NGC 1365, the extended X-ray emission shows a component aligned with the inner disc structure, another as wings or ears along the east and west direction aligned with the inner spiral arms, and an elongated edge-brightened structure (‘chimney’) breaking out of the disc in the north-west direction. The extended soft X-ray component around the nucleus of NGC 4051 is cospatial with the disc of the galaxy. It also shows an elongation coincident with a ‘banana’-like feature in the north-east seen in the 6-cm radio band. Extensions are also seen towards the south and south-east of the nucleus. Starburst activity driving strong winds through the disc of NGC 1365 can account for most of the extended soft X-ray emission in it. In the case of NGC 4051, extended X-ray emission probably owes its origin to both nuclear activity and starburst-induced activity. The nuclear component of NGC 4051 shows strong soft X-ray variability, with X-ray intensity changing by a factor of 2–3 on a time-scale of a few 100 s. The power spectrum of the variability has been extended to higher frequencies compared with previous observations, and has now reached the true Poissonian noise level of the source. At lower frequencies the power spectrum is best characterized by a power law and a Gaussian. The power-law slope of ≃−1.8 is consistent with the previous low-energy observations with EXOSAT, and the presence of a Gaussian feature signifies the persistence of a quasi-periodic oscillation that was also seen earlier with EXOSAT. During its low intensity and low variability state, however, the extended component of soft X-ray emission dominates the flux in NGC 4051. A list of X-ray sources, some of which are new, detected in the field of view of the HRI during the observations is also presented.

X-Ray Properties of LINERs and Low Luminosity Seyfert Galaxies Observed with ASCA

We present ASCA spectra of low luminosity AGNs with X-ray luminosities of 1040-41 ergs s−1. Their X-ray continua are very similar to Seyfert galaxies. Although iron K emissin centered at 6.4 keV or 6.7 keV is detected from a few objects, iron K emission is weak on average. Possible reasons for variety of iron line properties are discussed.

X-Ray Observations of Low-Luminosity Active Galactic Nuclei

AbstractThrough X-ray observations with ASCA, low-luminosity active galactic nuclei have been found in at least seven near-by spiral galaxies. Some of them exhibit very intense, and possibly broad, Fe-K emission lines. Their time variability is relatively insignificant, in contrast to lowluminosity Seyfert galaxies.

Faint object spectrograph observations of the low-luminosity Seyfert galaxy NGC 1566

view Abstract Citations (23) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Faint Object Spectrograph Observations of the Low-Luminosity Seyfert Galaxy NGC 1566 Kriss, G. A. ; Hartig, G. F. ; Armus, L. ; Blair, William P. ; Caganoff, S. ; Dressel, L. Abstract FOS observations of the Seyfert galaxy NGC 1566 show it to possess the broad lines characteristic of a typical Seyfert 1 galaxy, even in states of very low luminosity. The continuum, however, is steep (f_v_~v^- 1.5^) with no suggestion of the ultraviolet excess seen in higher luminosity AGNs. The broad emission lines have symmetric profiles, but are redshifted by 200-1000 km s^-1^ relative to the systemic velocity. The broad-line ratios indicate a low ionization parameter, and the strength of lines such as Fe II, Mg II, and the Balmer continuum relative to the UV continuum supports models for X-ray heating of the broad-line cloud interiors. The sharp core of the HST point response function gives a significant advantage over ground-based telescopes for observations of low luminosity active galaxies, despite the spherical aberration of the primary mirror. The high contrast of the active nucleus over the surrounding starlight permits observers to use the small apertures of the FOS to reject most of the contaminating starlight that frustrates ground-based observations and to obtain nearly simultaneous spectra spanning the full UV and optical wavelength range. Publication: The Astrophysical Journal Pub Date: August 1991 DOI: 10.1086/186105 Bibcode: 1991ApJ...377L..13K Keywords: Active Galactic Nuclei; Faint Objects; Luminosity; Seyfert Galaxies; Spectrographs; Ultraviolet Spectra; Balmer Series; Emission Spectra; Line Shape; Line Spectra; Astronomy; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 1566; GALAXIES: NUCLEI; GALAXIES: SEYFERT; ULTRAVIOLET: SPECTRA full text sources ADS | data products SIMBAD (3) NED (1) MAST (1) ESA (1)

The hydrodynamic effects of nuclear active galaxy winds on host galaxies

view Abstract Citations (60) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The hydrodynamic effects of nuclear active galaxy winds on host galaxies Schiano, A. V. R. Abstract The hydrodynamic effects of a powerful thermal wind in active nuclei on the low-density gas component of a model galactic interstellar medium are investigated. The model ISM is based on properties of the Milky Way and other nearby "nonactive" galaxies. The wind is assumed to be highly supersonic with spherical symmetry and constant power. The wind power is varied from low-luminosity Seyfert galaxies to QSOs (1042 < Lw < 1046ergs s-1. The propagation of the wind into the low-density gas is studied using the Kompaneets approximation to a strong explosion in an exponential atmosphere. The near isobaricity of the shocked wind and ISM gases is used to determine the motion of the wind "bubble" for a variety of ISM gas distributions. The results show that for typical ISM pressures the extent of the wind can range from 1 to 10 kpc for wind powers of 1042 - 1046ergs s-1 in a time scale of less than 107yr. Publication: The Astrophysical Journal Pub Date: December 1985 DOI: 10.1086/163680 Bibcode: 1985ApJ...299...24S Keywords: Active Galaxies; Astronomical Models; Galactic Evolution; Galactic Nuclei; Interstellar Gas; Seyfert Galaxies; Emission Spectra; Hydrodynamics; Quasars; Shock Fronts; Spiral Galaxies; Astrophysics full text sources ADS |