Broad Balmer Lines Research Articles

The massive stellar population in the young association LH 95 in the Large Magellanic Cloud

We present a spectroscopic study of the most massive stars in the young (4 Myr old) stellar cluster LH 95 in the Large Magellanic Cloud. This analysis allows us to complete the census of the stellar population of the system, previously investigated by us down to 0.4 solar masses with deep HST Advanced Camera for Surveys photometry. We perform spectral classification of the five stars in our sample, based on high resolution optical spectroscopy obtained with 2.2m MPG/ESO FEROS. We use complementary ground-based photometry, previously performed by us, to place these stars in the Hertzsprung-Russel diagram. We derive their masses and ages by interpolation from evolutionary models. The average ages and age spread of the most massive stars are found to be in general comparable with those previously derived for the cluster from its low mass PMS stars. We use the masses of the 5 sample stars to extend to the high-mass end the stellar initial mass function of LH 95 previously established by us. We find that the initial mass function follows a Salpeter relation down to the intermediate-mass regime at 2 Msun. The second most massive star in LH 95 shows broad Balmer line emission and infrared excess, which are compatible with a classical Be star. The existence of such a star in the system adds a constrain to the age of the cluster, which is well covered by our age and age spread determinations. The most massive star, a 60-70 Msun O2 giant is found to be younger (<1 Myr) than the rest of the population. Its mass in relation to the total mass of the system does not follow the empirical relation of the maximum stellar mass versus the hosting cluster mass, making LH 95 an exception to the average trend.

A SYSTEMATIC SEARCH FOR MASSIVE BLACK HOLE BINARIES IN THE SLOAN DIGITAL SKY SURVEY SPECTROSCOPIC SAMPLE

We present the results of a systematic search for massive black hole binaries in the Sloan Digital Sky Survey spectroscopic database. We focus on bound binaries, under the assumption that one of the black holes is active. In this framework, the broad lines associated to the accreting black hole are expected to show systematic velocity shifts with respect to the narrow lines, which trace the rest-frame of the galaxy. For a sample of 54586 quasars and 3929 galaxies at redshifts 0.1<z<1.5 we brute-force model each spectrum as a mixture of two quasars at two different redshifts. The spectral model is a data-driven dimensionality reduction of the SDSS quasar spectra based on a matrix factorization. We identified 32 objects with peculiar spectra. Nine of them can be interpreted as black hole binaries. This doubles the number of known black hole binary candidates. We also report on the discovery of a new class of extreme double-peaked emitters with exceptionally broad and faint Balmer lines. For all the interesting sources, we present detailed analysis of the spectra, and discuss possible interpretations.

3C 390.3: more stable evidence that the double-peaked broad Balmer lines originate from an accretion disc near a central black hole

In this manuscript, the structure of broad emission line regions (BLRs) of well-mapping double-peaked emitter (AGN with broad double-peaked low-ionization emission lines) 3C390.3 is studied. Besides the best fitted results for double-peaked broad optical balmer lines of 3C390.3 by theoretical disk model, we try to find another way to further confirm the origination of double-peaked line from accretion disk. Based on the long-period observed spectra in optical band around 1995 collected from AGN WATCH project, the theoretical disk parameters of disk-like BLRs supposed by elliptical accretion disk model (Eracleous et al. 1995) have been well determined. Through the theoretical disk-like BLRs, characters of observed light-curves of broad double-peaked H$\alpha$ of 3C390.3 can be well reproduced based on the reverberation mapping technique. Thus the accretion disk model is preferred as one better model for BLRs of 3C390.3. Furthermore, we can find that different disk parameters should lead to some different results about size of BLRs of 3C390.3 from the one measured through observational data, which indicates the measured disk parameters are significantly valid for 3C390.3. After that, the precession of theoretical elliptical disk-like BLRs being considered, we can find that the expected line profile in 2000 by theoretical model is consistent with the observed line profile by HST around 2000. Based on the results, we can further believe that the origination of broad double-peaked balmer emission lines of 3C390.3 are from accretion disk around central black hole.

Q2122-444: A NAKED ACTIVE GALACTIC NUCLEUS FULLY DRESSED

Based on previous spectral and temporal optical studies, Q2122-444 has been classified as a naked AGN or true type 2 AGN, that is, an AGN that genuinely lacks a broad line region (BLR). Its optical spectrum seemed to possess only narrow forbidden emission lines that are typical of type 2 (obscured) AGNs, but the long-term optical light curve, obtained from a monitoring campaign over more than two decades, showed strong variability, apparently ruling out the presence of heavy obscuration. Here, we present the results from a ~40 ks XMM-Newton observation of Q2122-444 carried out to shed light on the energetics of this enigmatic AGN. The X-ray analysis was complemented with ATCA radio data to assess the possible presence of a jet, and with new NTT/EFOSC2 optical spectroscopic data to verify the actual absence of a BLR. The higher-quality optical data revealed the presence of strong and broad Balmer lines that are at odds with the previous spectral classification of this AGN. The lack of detection of radio emission rules out the presence of a jet. The X-ray data combined with simultaneous UV observations carried out by the OM aboard XMM-Newton confirm that Q2122-444 is a typical type-1 AGN without any significant intrinsic absorption. New estimates of the black hole mass independently obtained from the broad Balmer lines and from a new scaling technique based on X-ray spectral data suggest that Q2122-444 is accreting at a relatively high rate in Eddington units.

Line profile and continuum variability in the very broad-line Seyfert galaxy Mrk 926

We present results of an intensive spectroscopic variability campaign of the very broad-line Seyfert 1 galaxy Mrk 926. Our aim is to investigate the broad-line region (BLR) by studying the intensity and line profile variations of this galaxy on short timescales. High signal-to-noise ratio(S/N) spectra were taken with the 9.2m Hobby-Eberly Telescope (HET) in identical conditions during two observing campaigns in 2004 and 2005. After the spectral reduction and internal calibration we achieved a relative flux accuracy of better than 1%. The rms profiles of the very broad Balmer lines have shapes that differ from their mean line profiles, consisting of two inner (v $\lesssim \pm{}$ 6000 km s$^{-1}$) and two outer (v $\gtrsim \pm{}$ 6000 km s$^{-1}$) line components in addition to a central component (v $\lesssim \pm{}$ 600 km s$^{-1}$). These outer and inner line segments varied with different amplitudes during our campaign. The radius of the BLR is very small with an upper limit of 2 light-days for the H$\beta$ BLR size. We derived an upper limit to the central black hole mass of $ M= 11.2 \times 10^{7} M_{\odot} $. The 2-D cross-correlation functions CCF($\tau$,$v$) of H$\beta$ and H$\alpha$ are flat within the error limits. The response of the Balmer line segments with respect to continuum variations is different in the outer and inner wings of H$\alpha$ and H$\beta$. This double structure in the response curves - of two separate inner and outer components - has also been seen in the rms line profiles. We conclude that the outer and inner line segments originate in different regions and/or under different physical conditions.

SPECTROPOLARIMETRIC EVIDENCE FOR A KICKED SUPERMASSIVE BLACK HOLE IN THE QUASAR E1821+643

We report spectropolarimetric observations of the quasar E1821+643 (z=0.297), which suggest that it may be an example of gravitational recoil due to anisotropic emission of gravitational waves following the merger of a supermassive black hole (SMBH) binary. In total flux, the broad Balmer lines are redshifted by ~1000 km/s relative to the narrow lines and have highly red asymmetric profiles, whereas in polarized flux the broad H_alpha line exhibits a blueshift of similar magnitude and a strong blue asymmetry. We show that these observations are consistent with a scattering model in which the broad-line region has two components, moving with different bulk velocities away from the observer and towards a scattering region at rest in the host galaxy. If the high velocity system is identified as gas bound to the SMBH, this implies that the SMBH is itself moving with a velocity ~2100 km/s relative to the host galaxy. We discuss some implications of the recoil hypothesis and also briefly consider whether our observations can be explained in terms of scattering of broad-line emission originating from the active component of an SMBH binary, or from an outflowing wind.

On the Nature of Seyfert Galaxies with High [Oiii] λ5007 Blueshifts

We have studied the properties of Seyfert galaxies with high [O III] ?5007 blueshifts (blue outliers), originally identified because of their strong deviation from the -->MBH ? ? relation of normal, narrow-line Seyfert 1 (NLS1) and broad-line Seyfert 1 (BLS1) galaxies. These blue outliers turn out to be important test beds for models of the narrow-line region (NLR), for mechanisms of driving large-scale outflows, for links between NLS1 galaxies and radio galaxies, and for orientation-dependent NLS1 models. We report the detection of a strong correlation of line blueshift with ionization potential in each galaxy, including the measurement of coronal lines with radial velocities up to 500-1000 km s -->?1, and we confirm a strong correlation between [O III] blueshift and line width. All [O III] blue outliers have narrow widths of their broad Balmer lines and high Eddington ratios. While the presence of nonshifted low-ionization lines signifies the presence of a classical outer quiescent NLR in blue outliers, we also report the absence of any second, nonblueshifted [O III] component from a classical inner NLR. These results place tight constraints on NLR models. We favor a scenario in which the NLR clouds are entrained in a decelerating wind, which explains the strong stratification and the absence of a zero-blueshift inner NLR of blue outliers. The origin of the wind remains speculative at this time (collimated radio plasma, thermal winds, or radiatively accelerated clouds). It is perhaps linked to the high Eddington ratios of blue outliers. Similar, less powerful winds could be present in all Seyfert galaxies, but would generally only affect the coronal line region (CLR), or level off even before reaching the CLR. Similarities between blue outliers in NLS1 galaxies and (compact) radio sources are briefly discussed.

A Recoiling Supermassive Black Hole in the Quasar SDSS J092712.65+294344.0?

We present SDSSJ092712.65+294344.0 as the best candidate to date for a recoiling supermassive black hole (SMBH). SDSSJ0927+2943 shows an exceptional optical emission-line spectrum with two sets of emission lines: one set of very narrow emission lines, and a second set of broad Balmer and broad high-ionization forbidden lines which are blueshifted by 2650 km\s relative to the set of narrow emission lines. This observation is most naturally explained if the SMBH was ejected from the core of the galaxy, carrying with it the broad-line gas while leaving behind the bulk of the narrow-line gas. We show that the observed properties of SDSSJ0927+2943 are consistent with predictions and expectations from recent numerical relativity simulations which demonstrate that SMBHs can receive kicks up to several thousand km\s due to anisotropic emission of gravitational waves during the coalescence of a binary. Our detection of a strong candidate for a rapidly recoiling SMBH implies that kicks large enough to remove SMBHs completely from their host galaxies do occur, with important implications for models of black hole and galaxy assembly at the epoch of structure formation, and for recoil models.

Broad Lyα emission from supernova remnants in young galaxies

Context. Charge transfer (or exchange) reactions between hydrogen atoms and protons in collisionless shocks of supernova remnants (SNRs) are a natural way of producing broad Balmer, Lyman, and other lines of hydrogen. Aims. We wish to quantify the importance of shock-induced, non-thermal hydrogen emission from SNRs in young galaxies. Methods. We present a method estimating the luminosity of broad (~1000 km s -1 ) Ly α , Ly β , Ly γ , H β and P α lines, as well as the broad and narrow luminosities of the two-photon (2 γ ) continuum, from existing measurements of the H α flux. We consider cases of $\beta=0.1$ and 1, where $\beta \equiv T_{\rm e}/T_{\rm p}$ is the ratio of electron-to-proton temperatures. We examine a modest sample of 8 proximate, Balmer-dominated SNRs from our Galaxy and the Large Magellanic Cloud. The expected broad Ly α luminosity per object is at most ~10 36 erg s -1 . The 2 γ continuum luminosities are comparable to the broad H α and Ly α ones. We restrict our analysis to homogenous and static media. Results. Differences in the Ly α /H α and Ly β /H α luminosity ratios between the $\beta=0.1$ and 1 cases are factors ~2 for shock velocities $1000 \lesssim v_{\rm s} \lesssim 4000$ km s -1 , thereby providing a direct and unique way to measure β . In principle, broad, “non-radiative” Ly α from SNRs in young galaxies can be directly observed in the optical range of wavelengths. However, by taking the different rates between core collapse and thermonuclear supernovae into consideration, as well as the duration we expect to observe such Ly α emission from SNRs, we expect their contribution to the total Ly α luminosity from $z \sim 3$ to 5 galaxies to be negligibly small (~0.001%), compared to the radiative shock mechanism described by Shull & Silk (1979). Although broad, non-thermal Ly α emission has never been observed, these photons are produced in SNRs. Hence, the non-radiative Ly α luminosity is a part of the intrinsic Ly α spectrum of young galaxies.

Radio-loud Narrow-Line Type 1 Quasars

We present the first systematic study of (non-radio-selected) radio-loud narrow-line Seyfert 1 (NLS1) galaxies. Cross-correlation of the Catalogue of Quasars and Active Nuclei with several radio and optical catalogs led to the identification of ~11 radio-loud NLS1 candidates, including four previously known ones. This study almost triples the number of known radio-loud NLS1 galaxies if all candidates are confirmed. Most of the radio-loud NLS1 galaxies are compact, steep-spectrum sources accreting close to or above the Eddington limit. The radio-loud NLS1 galaxies of our sample are remarkable in that they occupy a previously rarely populated regime in NLS1 multiwavelength parameter space. While their [O III]/Hβ and Fe II/Hβ intensity ratios almost cover the whole range observed in NLS1 galaxies, their radio properties extend the range of radio-loud objects to those with small widths of the broad Balmer lines. Their black hole masses are generally at the upper observed end among NLS1 galaxies but are still unusually small in view of the radio loudness of the sources. Among the radio-detected NLS1 galaxies, the radio index R is distributed quite smoothly up to the critical value of R 10 and covers about 4 orders of magnitude in total. Statistics show that ~7% of the NLS1 galaxies are formally radio-loud, while only 2.5% exceed a radio index R > 100. Implications for NLS1 models are discussed. Several mechanisms are considered as explanations for the radio loudness of the NLS1 galaxies and for the lower frequency of radio-loud galaxies among NLS1 galaxies than among quasars. While properties of most sources (with two to three exceptions) generally do not favor relativistic beaming, the combination of accretion mode and spin may explain the observations.

Profile variability of the H$\mathsf{\alpha}$ and H$\mathsf{\beta}$ broad emission lines in NGC 5548

Between 1996 and 2002, we have carried out a spectral monitoring program for the Seyfert galaxy NGC 5548 with the 6 m and 1 m telescopes of SAO (Russia) and with the 2.1 m telescope of Guillermo Haro Observatory (GHO) at Cananea, Mexico. High quality spectra with S/N > 50 in the continuum near Ha and Hβ were obtained, covering the spectral range ∼(4000-7500) A with a (4.5 to 15) A-resolution. We found that both the flux in the lines and the continuum gradually decreased, reaching minimum values during May-June 2002. In the minimum state, the wings of Hβ and Ha became extremely weak, corresponding to a Sy1.8 type, not to a Syl, as observed previously when the nucleus was brighter. The line profiles were decomposed into variable and constant components. The variable broad component is well correlated with the continuum variation. It consists of a double peaked structure with radial velocities ∼±1000 km s -1 relative to the narrow component. A constant component, whose presence is independent of the continuum flux variations, shows only narrow emission lines.The mean, rms, and the averaged over years, observed and difference line profiles of Hβ and Ha reveal the same double peaked structure. The relative intensity of these peaks changes with time. During 1996, the red peak was the brightest, while in 1998-2002, the blue peak became the brighter one. Their radial velocities vary in the ∼(500-1200) km s -1 range. In 2000-2002 a distinct third peak appeared in the red wing of Ha and Hβ line profiles. The radial velocity of this feature decreased between 2000 and 2002: from the observed profiles, from ∼+(2500-2600) km s -1 to ∼+2000 km s -1 and is clearly seen on the difference profiles. The fluxes of the various parts of the line profiles are well correlated with each other and also with the continuum flux. The blue and red parts of the line profiles at the same radial velocities vary in an almost identical manner. Shape changes of the different parts of the broad line are not correlated with continuum variations and, apparently, are not related to reverberation effects. Changes of the integral Balmer decrement are, on average, anticorrelated with the continuum flux variations. This is probably due to an increasing role of collisional excitation as the ionizing flux decreases. The behavior of the Balmer decrement of the various parts of the line profiles was different in 1996-2000 as compared with the 2001 behavior. Our results favor the formation of the broad Balmer lines in a turbulent accretion disc with large and moving optically thick inhomogeneities, capable of reprocessing the central source continuum.

XMM-Newton discovery of a Compton-thick AGN in the GPS galaxy Mkn 668

We report the XMM-Newton discovery of the first Compton-thick obscured AGN in a Broad Line Radio Galaxy, the Gigahertz Peaked-Spectrum source Mkn 668 (OQ+208). The remarkably flat 2-10 keV X-ray spectrum (observed photon index, Γ � 0.7), with a prominent iron Kα fluorescent emission line, is a clear signature of a Compton-reflection dominated spectrum. Mkn 688 represents a remarkable example of discrepancy between X-ray spectral properties and optical classification, as its optical spectrum is characterized by broad and asymmetric Balmer lines. The obscuring matter is constrained to be located within the radio hotspots, in turn separated by about 10 pc. If the jets are piercing their way through a Compton-thick medium pervading the nuclear environment, one could be largely underestimating the radio activity dynamical age determined from the observed hotspot recession velocity. The soft X-ray spectrum is dominated by a much steeper component, which may be due to nuclear continuum electron scattering, or inverse Compton of the - remarkably large - far infrared emission. Soft X-rays are suppressed by a further Compton-thin (NH ∼ 10 21 cm −2 ) absorbing system, that we identify with matter responsible for free-free absorption of the radio lobes.

A Candidate of a Type 2 Quasi‐stellar Object atz = 0.9: Large X‐Ray Absorption with a Strong Broad Hα Emission Line

Deep hard X-ray and near-infrared observations of a type 2 radio-quiet quasi-stellar object (QSO) candidate at z = 0.9, AX J08494+4454, are reported. The 0.5-10 keV Chandra X-Ray Observatory spectrum of AX J08494+4454 is hard and is explained well with a power-law continuum absorbed by a hydrogen column density of (2.3 ± 1.1) × 1023 cm-2. The 2-10 keV luminosity of the object is estimated to be 7.2 × 1044 ergs s-1, after correcting the absorption, and reaches hard X-ray luminosities of QSOs. The large X-ray absorption and the large intrinsic luminosity support the original identification of AX J08494+4454 as a type 2 radio-quiet QSO. Nevertheless, the deep Subaru/IRCS J-band spectroscopic observation suggests the presence of a strong broad Hα emission line from AX J08494+4454. If real, the broad Hα emission line has a velocity width of 9400 ± 1000 km s-1, which corresponds to a typical broad Balmer line velocity width of a luminous QSO. The existence of the strong broad Hα line means that the object is not a type 2 QSO but a luminous cousin of a Seyfert 1.9 galaxy in the source-frame optical spectrum. The Balmer decrement of broad lines and the broad Hα emission to the hard X-ray luminosity ratio suggest that the nucleus is affected by dust extinction with an AV of 1-3 mag in the optical wavelength. Optical colors and faint optical magnitudes of AX J08494+4454 are consistent with the model. The estimated amount of dust extinction is much smaller than that expected from the X-ray column density (AV = 130 ± 60 mag).

NGC 3065: A Certified LINER with Broad, Variable Balmer Lines

Motivated by the X-ray properties of the galaxy NGC 3065, we have obtained new optical spectra that reveal that it has a low-ionization nuclear emission-line region (LINER) as well as broad Balmer emission lines, establishing it as an active galactic nucleus. We also examined an older spectrum from the CfA Redshift Survey that lacks broad Balmer lines, indicating that these lines appeared sometime after 1980. Thus NGC 3065 joins the set of LINERs with broad, variable Balmer lines, which includes such well-known galaxies as NGC 1097 and M81. Inspired by the sometimes double-peaked profiles of the variable Balmer lines in other LINERs, we speculate that the broad Balmer lines of NGC 3065 also come from an accretion disk. We illustrate the plausibility of this hypothesis by fitting a disk model to the observed Hα profile. We also estimate the mass of the central black hole to be (9 ± 4) × 107 M☉ from the properties of the host galaxy, which leads to the conclusion that the accretion rate is only ~2 × 10-4 times the Eddington value, a property that appears to be common among LINERs. At such a low relative accretion rate, the inner accretion disk can turn into a vertically extended ion torus, which can illuminate the outer thin disk and power the broad-line emission. The reason for the sudden appearance of broad Balmer lines is an open question, although we suggest two possible explanations: (1) tidal disruption of a star or (2) a sudden transition in the structure of the accretion disk.

Balmer‐dominated Spectra of Nonradiative Shocks in the Cygnus Loop, RCW 86, and Tycho Supernova Remnants

We present an observational and theoretical study of the optical emission from nonradiative shocks in three supernova remnants: the Cygnus Loop, RCW 86 and Tycho. The spectra of these shocks are dominated by collisionally excited hydrogen Balmer lines which have both a broad component caused by proton-neutral charge exchange and a narrow component caused by excitation of cold neutrals entering the shock. In each remnant we have obtained the broad to narrow flux ratios of the Halpha and Hbeta lines and measured the Halpha broad component width. A new numerical shock code computes the broad and narrow Balmer line emission from nonradiative shocks in partially neutral gas. The Balmer line fluxes are sensitive to Lyman line trapping and the degree of electron-proton temperature equilibration. The code calculates the density, temperature and size of the postshock ionization layer and uses a Monte Carlo simulation to compute narrow Balmer line enhancement from Lyman line trapping. The initial fraction of the shock energy allocated to the electrons and protons (the equilibration) is a free parameter. Our models show that variations in electron-proton temperature equilibration and Lyman line trapping can reproduce the observed range of broad to narrow ratios. The results give 80%-100% equilibration in nonradiative portions of the NE Cygnus Loop (v_shock ~ 300 km/s), 40%-50% equilibration in nonradiative portions of RCW 86 (v_shock ~ 600 km/s) and <~ 20% equilibration in Tycho (v_shock ~ 2000 km/s). Our results suggst an inverse correlation between magnetosonic Mach number and equilibration in the observed remnants.

Compton-thick X-ray absorption in the Seyfert galaxies Tololo 0109-383 and ESO 138-G1

We present analyses of the ASCA X-ray spectra of two Seyfert galaxies, Tololo 0109-383 and ESO 138-G1. In both cases, spectral fitting reveals two statistically acceptable continuum models: Compton reflection and partial covering. Both spectra have strong iron Kα lines, with equivalent widths greater than 1.5 keV. These large equivalent widths are suggestive of heavier obscuration than that directly indicated by the partial-covering models (≈2×1023 cm−2), with the actual column densities being ‘Compton-thick’ (i.e. NH≳1.5×1024 cm−2). We use the hard X-ray/[O iii] flux correlation for Seyferts and data from the literature to provide additional support for this hypothesis. Since Tololo 0109-383 is known to have optical type 1 characteristics such as broad Balmer line components and Fe ii emission, this result marks it as a notable object.

High-Ionization Nuclear Emission-Line Region of Seyfert Galaxies

Recently, Murayama & Taniguchi proposed that a significant part of the high-ionization nuclear emission-line region (HINER) in Seyfert nuclei arises from the inner wall of dusty tori because type 1 Seyfert nuclei (S1s) show excess HINER emission with respect to type 2 Seyfert nuclei (S2s). This means that the radiation from the HINER is anisotropic, and thus statistical properties of the HINER emission can be used to investigate the viewing angle toward dusty tori for various types of Seyfert nuclei. In order to investigate viewing angles toward narrow-line Seyfert 1 galaxies (NLS1s) and intermediate types of Seyfert galaxies (i.e., type 1.5, 1.8, and 1.9 Seyfert galaxies, hereafter S1.5, S1.8, and S1.9, respectively), we apply this HINER test to them. We also apply the same test for S2s with and without the hidden broad-line region. The sample of Seyfert nuclei analyzed here consists of 124 Seyfert nuclei compiled from the literature. Our main results and suggestions are as follows: (1) The NLS1s are viewed more face-on toward dusty tori than the S2s. However, the HINER properties of the NLS1s are indistinguishable from those of the S1s. (2) The S1.5s appear to compose heterogeneous populations; e.g., (a) some of them may be seen from an intermediate viewing angle between S1s and S2s, (b) some S1.5s are basically S1s but a significant part of the broad-line region (BLR) emission is accidentally obscured by dense, clumpy gas clouds, or (c) some S1.5s are basically S2s, but a part of the BLR emission can be seen from some optically thin regions of the dusty torus. (3) The S1.8s, the S1.9s, and the objects showing either a broad Paβ line or polarized broad Balmer lines are seen from a large inclination angle, and the emission from the BLRs of such objects reaches us through optically thin parts of dusty tori. These three results support strongly the current unified model of Seyfert nuclei. Finally, (4) the line ratios of [Fe X] λ6374 to the low-ionization emission lines are rather more isotropic than those of [Fe VII] λ6087. Therefore, it is suggested that the [Fe X] λ6374 emission is not useful for investigating the viewing angle toward the dusty torus in Seyfert nuclei. The most plausible reason seems to be that the [Fe X] λ6374 emission is spatially extended, and thus its strength tends to show less viewing-angle dependence.

Polarimetry and Unification of Low-Redshift Radio Galaxies

We have made high-quality measurements of the polarization spectra of 13 FR II radio galaxies and taken polarization images for 11 of these with the Keck telescopes. Seven of the eight narrow-line radio galaxies (NLRGs) are polarized, and six of the seven show prominent broad Balmer lines in polarized light. The broad lines are also weakly visible in total flux. Some of the NLRGs show bipolar regions with roughly circumferential polarization vectors, revealing a large reflection nebula illuminated by a central source. Our observations powerfully support the hidden quasar hypothesis for some NLRGs. According to this hypothesis, the continuum and broad lines are blocked by a dusty molecular torus, but can be seen by reflected, hence polarized, light. Classification as a NLRG, a broad-line radio galaxy (BLRG), or a quasar therefore depends on orientation. However, not all objects fit into this unification scheme. Our sample is biased toward objects known in advance to be polarized, but the combination of our results with the 1996 findings of Hill, Goodrich, and DePoy show that at least six out of a complete, volume and flux-limited sample of nine FR II NLRGs have broad lines, seen either in polarization or P{alpha}.The BLRGs in ourmore » sample range from 3C 382, which has a quasar-like spectrum, to the highly reddened IRAS source FSC 2217+259. This reddening sequence suggests a continuous transition from unobscured quasar to reddened BLRG to NLRG. Apparently the obscuring torus does not have a distinct edge. The BLRGs have polarization images that are consistent with a point source broadened by seeing and diluted by starlight. We do not detect extended nebular or scattered emission, perhaps because it is swamped by the nuclear source. Our starlight-corrected BLRG spectra can be explained with a two-component model: a quasar viewed through dust and quasar light scattered by dust. The direct flux is more reddened than the scattered flux, causing the polarization to rise steeply to the blue. Strong rotations of the electric vector position angle across H{alpha} in 3C 227 and 3C 445 may be explained by systematic orbital motions in an equatorial broad-line region. (c) (c) 1999. The American Astronomical Society.« less

Are there any Type 2 QSOs? The case of AXJ0341.4-4453

The X-ray source AXJ0341.4-4453 was described by Boyle et al. as a Type 2 AGN at z = 0.672 based on the absence of broad emission lines in the observed wavelength range 4000-7000 Angstroms. We obtained a new spectrum of AXJ0341.4-4453 extending to 9600 Angstroms which reveals broad Balmer lines and other characteristics of Seyfert 1 galaxies. The FWHM of broad H-beta is at least 1600 km/s, while [O III]5007 has FWHM = 730 km/s. The flux ratio [O III]5007/H-beta = 1. Thus, AXJ0341.4-4453 is by definition a narrow-line Seyfert 1 galaxy, or perhaps a moderately reddened Seyfert 1 galaxy, but it is not a Type 2 QSO. Although examples of the latter have long been sought, particularly in connection with the problem of the X-ray background, there is still virtually no evidence for the existence of any Type 2 QSO among X-ray selected samples.

Spectropolarimetry of the Luminous Narrow‐Line Seyfert Galaxies IRAS 20181−2244 and IRAS 13224−3809

We observed the narrow-line Seyfert 1 galaxies IRAS 20181-2244 and IRAS 13224-3809 with a new spectropolarimeter on the Ritchey-Chretien spectrograph at the CTIO 4 m telescope. Previously it had been suggested that IRAS 20181-2244 was a type 2 QSO and thus might contain an obscured broad-line region that could be detected by the presence of broad Balmer lines in the polarized flux. We found the object to be polarized at about 2% and constant with wavelength (unlike most narrow-line Seyfert 1 galaxies), but with no evidence of broad Balmer lines in polarized flux. The spectropolarimetry indicates that the scattering material is inside the broad-line region. IRAS 13224-3809, notable for its high variability in X-ray and UV wavelengths, has a low polarization consistent with a Galactic interstellar origin.