Low-luminosity Active Galaxies Research Articles

A New Technique for Measuring Polycyclic Aromatic Hydrocarbon Emission in Different Environments

Abstract We present a new method to decompose the emission features of polycyclic aromatic hydrocarbons (PAHs) from mid-infrared spectra using theoretical PAH templates in conjunction with modified blackbody components for the dust continuum and an extinction term. The primary goal is to obtain robust measurements of the PAH features, which are sensitive to the star formation rate, in a variety of extragalactic environments. We demonstrate the effectiveness of our technique, starting with the simplest Galactic high-latitude clouds to extragalactic systems of ever-increasing complexity, from normal star-forming galaxies to low-luminosity active galaxies, quasars, and heavily obscured infrared-luminous galaxies. In addition to providing accurate measurements of the PAH emission, including the upper limits thereof, our fits can reproduce reasonably well the overall continuum shape and constrain the line-of-sight extinction. Our new PAH line flux measurements differ systematically and significantly from those of previous methods by ∼15% to as much as a factor of ∼6. The decomposed PAH spectra show remarkable similarity among different systems, suggesting a uniform set of conditions responsible for their excitation.

Dusty spirals versus gas kinematics in the inner kiloparsec of four low-luminosity active galactic nuclei

We used the Gemini Multi-Object Spectrograph Integral Field Unit to map the gas distribution, excitation and kinematics within the inner kiloparsec of four nearby low-luminosity active galaxies: NGC3982, NGC4501, NGC2787 and NGC4450. The observations cover the spectral range 5600-7000{\AA} at a velocity resolution of 120km/s and spatial resolution ranging from 50 to 70pc at the galaxies. Extended emission in H{\alpha}, [NII]{\lambda}{\lambda}6548,6583, [SII]{\lambda}{\lambda}6716,6730 over most of the field-of-view is observed for all galaxies, while only NGC3982 shows [OI]{\lambda}6300 extended emission. The H{\alpha} equivalent widths combined with the [NII]/H{\alpha} line ratios reveal that NGC3982 and NGC4450 harbor Seyfert nuclei surrounded by regions with LINER excitation, while NGC2787 and NGC4501 harbor LINER nuclei. NGC3982 shows a partial ring of recent star-formation at 500pc from the nucleus, while in NGC4501 a region at 500pc west of the nucleus shows LINER excitation but has been interpreted as an aging HII region with the gas excitation dominated by shocks from supernovae. The line-of-sight velocity field of the gas shows a rotation pattern for all galaxies, with deviations from pure disk rotation observed in NGC3982, NGC4501 and NGC4450. For NGC4501 and NGC4450, many of these deviations are spatially coincident with dust structures seen in optical continuum images, leading to the interpretation that the deviations are due to shocks in the gas traced by the dust. A speculation is that these shocks lead to loss of angular momentum, allowing the gas to be transferred inwards to feed the AGN. In the case of NGC2787, instead of deviations in the rotation field, we see a misalignment of 40{^\circ} between the orientation of the line of nodes of the gas rotation and the photometric major axis of the galaxy. Evidence of compact nuclear outflows are seen in NGC4501 and NGC4450.

The dust origin of the Broad Line Region and the model consequences for AGN unification scheme

We propose a very simple physical mechanism responsible for the formation of the Low Ionization Line part of the Broad Line Region in Active Galactic Nuclei. It explains the scaling of the Broad Line Region size with the monochromatic luminosity, including the exact slope and the proportionality constant, seen in the reverberation studies of nearby sources. The scaling is independent from the mass and accretion rate of an active nucleus. The mechanism predicts the formation of a dust-driven wind in the disk region where the local effective temperature of a non-illuminated accretion disk drops below 1000K and allows for dust formation. We explore now the predictive power of the model with the aim to differentiate between this model and the previously proposed mechanisms of the formation of the Broad Line Region. We discuss the expected departures from the universal scaling at long wavelength, and the role of the inclination angle of the accretion disk in the source. We compare the expected line profiles with Mg II line profiles in the quasars observed by us with the SALT telescope. We also discuss the tests based on the presence or absence of the broad emission lines in low luminosity active galaxies. Finally, we discuss the future tests of the model to be done with expected ground-based observations and satellite missions.

Variability in the 2MASS calibration fields: a search for transient obscuration events

We searched the light curves of over 40 000 stars in the Two Micron All Sky Survey (2MASS) calibration data base, spanning approximately 4 yr, for objects that have significant day-long dimming events. We also searched the multi-colour light curves for red-dimming events that could be due to transient extinction. In the colour-independent sigma-limited search, we found 46 previously unrecognized eclipsing binaries, 6 previously unrecognized periodic variable stars likely to be intrinsic pulsators and 21 young stellar objects in the ρ Ophiuchus star formation region previously studied by Parks et al. An additional 11 objects exhibited dimming events, and most of these are unclassified. The search for red-dimming events primarily reveals a population of low-luminosity active galaxies that become bluer when they are brighter, and variable young stellar objects exhibiting high cross-correlation coefficients between colour and brightness. The young stellar objects primarily exhibit brightness and colour variations in the direction of interstellar extinction whereas the active galaxies can have a bowed distribution in colour and magnitude with reduced variation in colour when the object is brightest. Among the objects that are usually quiescent (not strongly variable), we failed to find any dimming events deeper than 0.2 mag and lasting longer than a day. Two of the young stellar objects, however, dimmed by 0.2 mag for longer than a day without strong colour variation.

A DEEPCHANDRAVIEW OF THE NGC 404 CENTRAL ENGINE

We present the results of a 100 ks Chandra observation of the NGC 404 nuclear region. The long exposure and excellent spatial resolution of Chandra have enabled us to critically examine the nuclear environment of NGC 404, which is known to host a nuclear star cluster and potentially an intermediate-mass black hole (IMBH; on the order of a few times 105 M☉). We find two distinct X-ray sources: a hard, central point source coincident with the optical and radio centers of the galaxy, and a soft extended region that is coincident with areas of high Hα emission and likely recent star formation. When we fit the 0.3–8 keV spectra of each region separately, we find the hard nuclear point source to be dominated by a power law (Γ = 1.88), while the soft off-nuclear region is best fit by a thermal plasma model (kT = 0.67 keV). We therefore find evidence for both a power-law component and hot gas in the nuclear region of NGC 404. We estimate the 2–10 keV luminosity to be 1.3+0.8−0.5 × 1037 erg s−1. A low level of diffuse X-ray emission was detected out to ∼15'' (∼0.2 kpc) from the nucleus. We compare our results to the observed relationships between power-law photon index and Eddington ratio for both X-ray binaries and low-luminosity active galaxies and find NGC 404 to be consistent with other low-luminosity active galaxies. We therefore favor the conclusion that NGC 404 harbors an IMBH accreting at a very low level.

The connection between radio loudness and central surface brightness profiles in optically selected low-luminosity active galaxies

Recent results indicate a correlation between nuclear radio-loudness of active galaxies and their central stellar surface-brightness profiles, in that `core' galaxies (with inner logarithmic slope {\gamma}<0.3) are significantly more radio loud than `power-law' galaxies ({\gamma}>0.5). This connection, which indicates possible links between radio-loudness and galaxy formation history (e.g. through black hole spin) has so far only been confirmed for a radio-selected sample of galaxies. Furthermore, it has since been shown that the Nuker law, which was used to parameterise the brightness profiles in these studies, gives a poor description of the brightness profile. Here, we present an analysis of the central surface brightness profiles of the active galaxies of Hubble Type T<3, that were identified by the optically-selected Palomar spectroscopic survey of nearby galaxies. We fit the brightness profiles using Sersic, Core-Sersic and, where necessary, Double-Sersic models, which we fit to the semi-major axis brightness profiles extracted from high resolution images of the galaxies from the Hubble Space Telescope (HST). We use these fits to classify the galaxies as `Core', `Sersic' or `Double-Sersic' and compare this classification with the properties of the Active Galactic Nuclei (AGNs). We find that AGN hosted in Core galaxies are generally more radio-loud than those hosted in Sersic galaxies, although there is a large overlap between the two subsamples. The correlation between radio-loudness and brightness profile can partly be explained by a correlation between radio-loudness and black hole mass. Additionally, there is a significant (99 per cent confidence) partial correlation between radio-loudness and the Core/Sersic classification of the host galaxy, which lends support to the previous results based on the radio-selected sample.

THE LICK AGN MONITORING PROJECT: ALTERNATE ROUTES TO A BROAD-LINE REGION RADIUS

It is now possible to estimate black hole masses across cosmic time, using broad emission lines in active galaxies. This technique informs our views of how galaxies and their central black holes coevolve. Unfortunately, there are many outstanding uncertainties associated with these "virial" mass estimates. One of these comes from using the accretion luminosity to infer a size for the broad-line region. Incorporating the new sample of low-luminosity active galaxies from our recent monitoring campaign at Lick Observatory, we recalibrate the radius-luminosity relation with tracers of the accretion luminosity other than the optical continuum. We find that the radius of the broad-line region scales as the square root of the X-ray and Hbeta luminosities, in agreement with recent optical studies. On the other hand, the scaling appears to be marginally steeper with narrow-line luminosities. This is consistent with a previously observed decrease in the ratio of narrow-line to X-ray luminosity with increasing total luminosity. The radius of the broad-line region correlates most tightly with Hbeta luminosity, while the X-ray and narrow-line relations both have comparable scatter of a factor of two. These correlations provide useful alternative virial BH masses in objects with no detectable optical/UV continuum emission, such as high-redshift galaxies with broad emission lines, radio-loud objects, or local active galaxies with galaxy-dominated continua.

SOURCE MATCHING IN THE SDSS AND RASS: WHICH GALAXIES ARE REALLY X-RAY SOURCES?

The current view of galaxy formation holds that all massive galaxies harbor a massive black hole at their center, but that these black holes are not always in an actively accreting phase. X-ray emission is often used to identify accreting sources, but for galaxies that are not harboring quasars (low-luminosity active galaxies), the X-ray flux may be weak, or obscured by dust. To aid in the understanding of weakly accreting black holes in the local universe, a large sample of galaxies with X-ray detections is needed. We cross-match the ROSAT All Sky Survey (RASS) with galaxies from the Sloan Digital Sky Survey Data Release 4 (SDSS DR4) to create such a sample. Because of the high SDSS source density and large RASS positional errors, the cross-matched catalog is highly contaminated by random associations. We investigate the overlap of these surveys and provide a statistical test of the validity of RASS–SDSS galaxy cross-matches. The SDSS quasars provide a test of our cross-match validation scheme, as they have a very high fraction of true RASS matches. We find that the number of true matches between the SDSS main galaxy sample and the RASS is highly dependent on the optical spectral classification of the galaxy; essentially no star-forming galaxies are detected, while more than 0.6% of narrow-line Seyferts are detected in the RASS. Also, galaxies with ambiguous optical classification have a surprisingly high RASS detection fraction. This allows us to further constrain the SEDs of low-luminosity active galaxies. Our technique is quite general, and can be applied to any cross-matching between surveys with well-understood positional errors.

NUclei of GAlaxies

We present high angular resolution radio snap-shot observations of seven nearby low-luminosity active galaxies (LLAGN) from the NUclei of GAlaxies (NUGA) survey. The observations were conducted with MERLIN and EVN/VLBI at 18cm and 6cm. At all observed angular resolutions and frequencies, we find indications for extended emission in about ~40% of the sources, consistent with the decrease of flux with increasing angular resolution. The extended components resemble jet emission in a majority of cases, consistent with the optically thin synchrotron emission implied by their steep spectra. We consider the compact 6cm EVN/VLBI radio emission of our sources in the context of the ``fundamental plane'' that previous LLAGN studies identified within the three-dimensional parameter space of radio luminosity, X-ray luminosity, and black hole mass. We demonstrate, using NGC7217 and NGC1068 as particular examples, that high-resolution, multi-epoch radio observations offer useful information about the origin of offsets from the fundamental plane.

Search for dense molecular gas in two QSO host galaxies

Context. The HCN(1-0) rotational line transition traces the dense (n H2 > 10 4 cm -3 ) fraction of the molecular gas typically located in starforming (SF) regions. In addition, an abnormally high HCN/CO line ratio close to AGNs may indicate then conditions of an X-ray-dominated region. Observed correlations between the CO-, HCN-, and FIR luminosities in nearby non-active, starburst, and low-luminosity active galaxies represent the physical connection between star formation and molecular gas as its fuel. HCN(1-0) has hardly been investigated in nearby high-luminosity AGN within this context. Aims. The aim of this study is to compare the HCN luminosity with published CO and IR luminosities to investigate the role of SF in the observed QSO host galaxies. Methods. We used the IRAM 30 m for the first time to search for the HCN(1-0) transition in two standard QSO host galaxies at z ∼ 0.1. Results. Our upper limits on L HCN agree with the known correlations and do not show strong excess abundance or excitation of the HCN due to the luminous active quasar nucleus. The starburst origin of the far-infrared luminosity in the observed QSO hosts cannot be proven unambiguously by the upper limits. We found that the IR/FIR ratio indicates independently of L IR if a significant amount of AGN heated dust is present.

X-ray spectral survey with XMM–Newton of a complete sample of nearby Seyfert galaxies

Results obtained from an X-ray spectral survey of nearby Seyfert galaxies using XMM–Newton are reported. The sample was optically selected, well defined, complete in B magnitude, and distance limited: it consists of the nearest ($D \la22$ Mpc) 27 Seyfert galaxies (9 of type 1, 18 of type 2) taken from the Ho et al. (1997a, ApJS, 112, 315) sample. This is one of the largest atlases of hard X-ray spectra of low-luminosity active galaxies ever assembled. All nuclear sources except two Seyfert 2s are detected between 2 and 10 keV, half for the first time ever, and average spectra are obtained for all of them. Nuclear luminosities reach values down to 10 38 erg s -1 . The shape of the distribution of X-ray parameters is affected by the presence of Compton-thick objects ($\ga$30% among type 2s). The latter have been identified either directly from their intense FeK line and flat X-ray spectra, or indirectly with flux diagnostic diagrams which use isotropic indicators. After taking into account these highly absorbed sources, we find that (i) the intrinsic X-ray spectral properties (i.e., spectral shapes and luminosities above 2 keV) are consistent between type 1 and type 2 Seyferts, as expected from “unified models”; (ii) Seyfert galaxies as a whole are distributed fairly continuously over the entire range of N H , between 10 20 and 10 25 cm -2 ; and (iii) while Seyfert 1s tend to have lower N H and Seyfert 2s tend to have the highest, we find 30% and 10% exceptions, respectively. Overall the sample is of sufficient quality to well represent the average intrinsic X-ray spectral properties of nearby active galactic nuclei, including a proper estimate of the distribution of their absorbing columns. Finally, we conclude that, with the exception of a few cases, the present study agrees with predictions of unified models of Seyfert galaxies, and extends their validity down to very low luminosities.

Iron Kα Emission from the Low‐Luminosity Active Galaxies M81 and NGC 4579

We report on the XMM-Newton spectroscopy of the low-luminosity active galaxies (LLAGNs) M81 and NGC 4579, both of which have known black hole masses and well-sampled spectral energy distributions (SEDs). The iron Kα line profiles from both LLAGNs can be described in terms of two components: a narrow line at 6.4 keV, and a moderately broad line (FWHM ~ 2 × 104 km s -1) arising from highly ionized, He-like or H-like species (E ~ 6.8 keV). We interpret the broad lines arising from an accretion disk, the inner edge of which is restricted to large radii (rin ~ 100rg). However, the Eddington ratio, L/LEdd, of these sources is 3-4 orders of magnitude lower than that required to photoionize a cold disk to He-like iron. We suggest that the lines can be explained as collisionally ionized X-ray lines arising from the transition region between a hot (radiatively inefficient) flow in the inner regions and a cold disk outside r ~ 100rg. The accretion flow geometry probed by our XMM-Newton observations is consistent with the truncated disk models proposed to explain the SED of LLAGNs.

X-ray absorption and rapid variability of the dwarf Seyfert nucleus of NGC 4395

ABSTRA C T We report the detection of an absorbed central X-ray source and its strong, rapid, variability in NGC 4395, the least luminous Seyfert nucleus known. The X-ray source exhibits a number of flares with factors of 3‐4 flux changes during a half-day ASCA observation. The shortest doubling time observed is about 100 s. Such X-ray variability is in contrast to the behaviour of other low-luminosity active galaxies and resembles that of higher luminosity Seyfert 1 galaxies. It provides further support for an accreting black hole model rather than an extreme stellar process in accounting for the nuclear activity of NGC 4395. The ASCA spectrum shows a power-law continuum of photon index Ga 1:7 ^ 0:3 with a Fe K line marginally detected at ,6.4 keV. The soft-X-ray emission below 3 keV is strongly attenuated by absorption. The energy spectrum in this absorption band shows a dramatic change in response to the variation in continuum luminosity. A variable warm absorber appears to be the most likely explanation to account for the spectral change. The absorption-corrected 2‐ 10 keV luminosity is 4 10 39 erg s 21 for a source distance of 2.6 Mpc, and at 1 keV is one order of magnitude above previous ROSAT estimates, which affects the appearance of the wide-band spectral energy distribution and photoionization calculations. The rapid X-ray variation is consistent with a black hole of a few times 10 4 M(, as suggested by the optical results and the small bulge of this dwarf galaxy. Such a light black hole is also favoured in order for the Eddington ratio (LBol/LEdd) to be above the range of advection-dominated accretion flows, which would clearly fail to explain the observed X-ray variability. The nuclear source of NGC 4395 is therefore consistent with a scaled-down version of higherluminosity Seyfert nuclei, with an intermediate-mass (10 4 ‐10 5 M() black hole, unlike the

Lyα/Hα Ratio of Singly Ionized Helium in Quasars

He II Lyα λ304/Hα λ1640 emission lines are mainly produced by recombination, and their canonical ratio of ~10 may be a sensitive reddening indicator. We obtain the high signal-to-noise ratio optical spectra of two quasars and combine them with the far-ultraviolet spectra that show the He II λ304 emission. For HS 1700+64, the He II λ1640 emission is not detected, and an upper limit to it sets the ratio greater than 20. This may not be inconsistent with the theoretical value when all observational uncertainties are taken into consideration. For Q0302-003, the ratio is very low and on the order of unity. The most plausible cause for such a low ratio is extinction in the EUV band by very fine grains of dust. Q0302-003 has a prominent narrow component of FWHM ~ 2000 km s-1 in its major emission lines, and it appears that reddening is associated only with the line-emitting region. We suggest that the geometry of the line-emitting region in high-z quasars resembles that in low-luminosity active galaxies, with the presence of dust mostly in the outer part.

A Note on the Viability of Gaseous Ionization in Active Galaxies by Fast Shocks

Morphological and spectroscopic evidence suggests that may affect the spatial and velocity distributions of gas in the narrow-line region (NLR) and the extended NLR of some active galaxies. It thus seemed plausible that may energize the NLR also. The observed emission-line ratios strongly favor photoionization as the heating source for this gas, but it is not clear whether the ionizing radiation is generated in the NLR by shocks or whether the ionizing radiation originates at the central continuum source. Here I point out that are highly inefficient in producing line emission. Shocks in the NLR can convert at most ~10-6 of the rest mass to ionizing radiation, compared with a maximum conversion efficiency of ~10-1 for the central continuum source. The required mass flow rate through shocks in the NLR is thus a few orders of magnitude higher than the mass accretion rate required to power the NLR by the central continuum source. Since gravity appears to dominate the NLR cloud dynamics, must lead to an inflow, and the implied high inflow rates can be ruled out in most active galaxies. NLR dynamics driven by a thermal wind or by some jet configurations may produce the mass flux through required for photoionizing to be viable, but the mass flux inward from the NLR must be kept ~100-1000 times smaller. Photoionizing are a viable mechanism in very low luminosity active galaxies if they are highly sub-Eddington (10-4) and if they convert mass to radiation with a very low efficiency (10-4).

Fluctuations in the diffuse X-ray background observed with Ginga

We present Ginga measurements of the spatial fluctuations in the diffuse X-ray background. When combined with earlier results, the new data constrain the extragalactic log N - log S relation in the 2-10 keV energy band to a form close to the Euclidean prediction over the flux range 1E-10 - 5E-13 erg/cm2/s. The normalisation of the 2-10 keV source counts is a factor 2-3 above that derived in the softer 0.3-3.5 keV band from the Einstein Extended Medium Sensitivity Survey if a spectral conversion is assumed which ignores X-ray absorption intrinsic to the sources. Both this result and the spectral characteristics of the spatial fluctuations are consistent with relatively low-luminosity active galaxies (i.e. L_X < 1E44 erg/s) dominating the 2-10 keV source counts at intermediate flux levels. We also use the `excess variance' of the fluctuations to constrain possible clustering of the underlying discrete sources.

Low-luminosity active galaxies: Are they similar to Seyfert galaxies?

A careful X-ray study of five low-luminosity active galactic nuclei (LLAGNs) was conducted to address specifically the issue of whether the dominant X-ray production mechanism is the same at all luminosities in AGNs. The sample consists of three Seyfert 1 galaxies (NGC 4639, NGC 5033, and NGC 5273), and two low-ionization nuclear emission-line regions (NGC 3642 and NGC 4278) having a weak broad component of H-alpha emission. We find that the X-ray emission (ROSAT High Resolution Interferometer (HRI)) is mostly or entirely nuclear (less than or approximately = 500 pc) despite the low X-ray luminosities (approximately 9 x 10(exp 40) ergs/s) of the sample. The correlation between X-ray luminosity and the broad H-alpha emission-line luminosity observed in high-luminosity active galaxies continues down to the low-luminosity range; the mean L(sub X)/L(sub H-alpha) ratio of LLAGNs is approximately 14, while that of AGNs is approximately 29. ROSAT Position Sensitive Proportional Counter (PSPC) observations of three LLAGNs in our sample indicate that the 0.2-2.2 keV X-ray spectral energy distributions are similar to those seen in Seyfert nuclei but do not have high intrinsic absorbing columns. Using existing ultraviolet data for four LLAGNs, we find that the 'optical' (2500 A) to X-ray spectral index (alpha(sub OX)) has an average upper limit of 1.6; for comparison, the measured value in AGNs is typically 1.4, while that in M81 (the prototypical LLAGN) is 1.0.

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 'Seyfert 1' optical spectra of the type II supernovae 1987F and 1988I

view Abstract Citations (122) References (74) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The ``Seyfert 1'' Optical Spectra of the Type II Supernovae 1987F and 1988I Filippenko, Alexei V. Abstract Optical spectra of the Type II supernova 1987F, obtained shortly after discovery and at late times, are atypical of SNe II. When first observed, broad Hα was superposed on a nearly featureless continuum, but its profile did not have the characteristic P Cygni shape, and its centroid was blueshifted by >~1500 km s^-1^ with respect to the systemic velocity. Many months later, the object was dominated by broad permitted emission lines of hydrogen, with Fe II and Ca II emission detected as well; forbidden lines, normally quite strong at this phase, were very weak. The derived electron density in the ejected envelope at this time was >~10^9^ cm^-3^. Together with the observed expansion velocities, this leads to an estimate of M>~5-30 M_sun_ for the envelope, implying that the progenitor was very massive. The light curve, which declined very slowly at both early and late times, supports this conclusion. With a few small but possibly significant exceptions, the overall optical spectroscopic properties of SN 1987F closely resemble those of Type I Seyfert nuclei and QSOs; in particular, a comparison is made with the spectrum of 3C 48. The same can be said for the much less extensively observed Type II SN 1988I, although in this object there is no direct evidence for Fe II emission. Even the optical luminosities of the SNe are comparable to those of moderately active galactic nuclei. Had either of these SNe occurred in the nucleus of a normal galaxy, the nucleus would probably have been classified as a Type I Seyfert the only data available were low-resolution optical spectra. It is possible that certain environment conditions, such as the presence of a dense interstellar medium, may increase the rate at which object such as SN 1987F and SN 1988I are produced. Following the work of Terlevich and Melnick, I suggest that the observed properties of some low-luminosity active galaxies might actually be due to violent bursts of star formation rather than accretion onto a supermassive black hole. Publication: The Astronomical Journal Pub Date: March 1989 DOI: 10.1086/115018 Bibcode: 1989AJ.....97..726F Keywords: Quasars; Seyfert Galaxies; Spiral Galaxies; Supernovae; Active Galactic Nuclei; Balmer Series; Emission Spectra; H Alpha Line; Light Curve; Star Formation; Stellar Evolution; Astrophysics; GALAXIES: SEYFERT; STARS: SUPERNOVAE full text sources ADS | data products SIMBAD (5) NED (5)

The statistics of radio galaxies &amp; quasars at high redshift

Evidence is now accumulating that the most powerful extragalactic radio sources display a cutoff in comoving density at relatively low redshift. For both radio galaxies and quasars, the luminosity function falls by a factor ≥ 3 between z = 2 and 4. We describe the data which lead to this conclusion, and discuss the prospects for studying the behaviour of low-luminosity active galaxies at high redshift. The strong evolution of highly luminous radio-quiet quasars at z &gt; 2 may be an artifact of gravitational lensing.