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This paper describes observations of seven narrow-lined Seyfert 1 (NLS1) galaxies and one high-ionization Seyfert 2 galaxy with the very large array (VLA). Also, these observations are combined with published data, and summarized here are the radio properties of the NLS1 galaxies for which spectopolarimetry was reported in 1989 by Goodrich.
ABSTRACT Narrow-line Seyfert 1 (NLSy1) galaxies are an enigmatic class of active galactic nuclei (AGN) that exhibit peculiar multiwavelength properties across the electromagnetic spectrum. For example, these sources have allowed us to explore the innermost regions of the central engine of AGN using X-ray observations and have also provided clues about the origin of relativistic jets considering radio and gamma-ray bands. Keeping in mind the ongoing and upcoming wide-field, multifrequency sky surveys, we present a new catalogue of NLSy1 galaxies. This was done by carrying out a detailed decomposition of >2 million optical spectra of quasars and galaxies from the Sloan Digital Sky Survey Data Release 17 (SDSS-DR17) using the publicly available software ‘Bayesian AGN Decomposition Analysis for SDSS Spectra’. The catalogue contains 22656 NLSy1 galaxies which is more than twice the size of the previously identified NLSy1s based on SDSS-DR12. As a corollary, we also release a new catalogue of 52273 broad-line Seyfert 1 (BLSy1) galaxies. The estimated optical spectral parameters and derived quantities confirm the previously known finding of NLSy1 galaxies being AGN powered by highly accreting, low-mass black holes. We conclude that this enlarged sample of NLSy1 and BLSy1 galaxies will enable us to explore the low-luminosity end of the AGN population by effectively utilizing the sensitive, high-quality observations delivered by ongoing/upcoming wide-field sky surveys. The catalogue has been made public at https://www.ucm.es/blazars/seyfert.
The physical conditions in a high density hydrogen gas heated and ionized by suprathermal protons were investigated, with application to the gas in the nuclear region of Seyfert galaxies. The gas is assumed optically thick to Lyman and Balmer line radiation. Mechanisms by which the radiation from the gas can balance the heating by the fast protons were investigated, and minimum values for the mass of gas were estimated. Under certain conditions, the suprathermal atoms themselves can cool the ambient gas by rescattering the line radiation into the optically thin region in the wings of the line. This mechanism, called optical reverberation, can enhance the broad component of the hydrogen lines produced by inelastic atomic collisions and yield line widths consistent with those observed in Seyfert and quasar spectra. Also discussed is the possibility of achieving dynamic equilibrium of the ambient gas by balancing the momentum transfer from the suprathermals with gravitational attraction of a massive central source.
The radially-streaming particle model for broad quasar and Seyfert galaxy emission features is modified to include sources of time dependence. The results are suggestive of reported observations of multiple components, variability, and transient features in the wings of Seyfert and quasi-stellar emission lines.
Radial velocity observations and red shift determinations of some galaxies east of the Seyfert Sextet are discussed. It is suggested that the Sextet may be a condensation in an extended group of galaxies. The velocities of galaxies in this region are segregated into three main groups, corresponding to the redshifts of the Hercules cluster, the group including the Seyfert Sextet, and a third group as indicated by the velocities of NGC 6035 and Mark 294.
Physical conditions in a high-density hydrogen gas heated and ionized by suprathermal protons are investigated, and the results are applied to the gas in the nuclear region of Seyfert galaxies. The gas is assumed to be optically thick to Lyman and Balmer line radiation. Mechanisms by which the radiation from the gas can balance the heating by the fast protons are investigated, and minimum values for the mass of gas are estimated. Under certain conditions, the suprathermal atoms themselves can cool the ambient gas by rescattering the line radiation into the optically thin region in the wings of the line. This mechanism, optical reverberation, can enhance the broad component of the hydrogen lines produced by inelastic atomic collisions and yield line widths consistent with those observed in Seyfert and quasar spectra. If this mechanism is important, the Lyman decrement can depend strongly on the temperature and density of the ambient hydrogen. The possibility is discussed of achieving dynamic equilibrium of the ambient gas by balancing the momentum transfer from the suprathermals with gravitational attraction of a massive central source.
Ultraviolet photometry of Seyfert galaxies is analyzed for variations in nuclear magnitude. Using multiple apertures permits the estimation of stellar concentration; four Seyfert and two normal spiral galaxies are compared.
Measurements are reported for the spectral energy distributions of the Seyfert galaxies Zw 2130+09 and Zw 0051+12 as well as the quasar 3C 273 over the wavelength range from 3300 to 10,760 A. Absolute emission-line intensities are derived for numerous Fe II blends and the O I line at 8446 A. Several new Fe II emission features are identified, the absence of Fe III emission is noted, and interesting properties of the individual spectra are described. Constraints on the ionizing continuum and on the geometry and velocity field of the emission-line regions are discussed. The observations show that Seyfert galaxies with strong Fe II emission also have strong O I 8446-A emission and that a flat continuum in the near-UV appears to be common in such objects. Assuming photoionization, it is suggested that both the Fe II and the O I emission could result from continuum fluorescence in an outer, optically thick H I zone in an emission-line region about 1 pc in radius and consisting of many small high-velocity filaments.
Photometric observations of the Seyfert Sextet (VV 115) are analyzed. Apparent integrated magnitudes are derived relative to the sky brightness, and isophotal maps are given for the field. No evidence for interaction between NGC 6027 and d is found. Luminosity profiles are given for NGC 6027, a, b, and d, with the d profile having been corrected for seeing effects in one dimension. The corrected profile parameters favor the interpretation of d as a highly luminous background galaxy at its cosmological distance. The nearby anonymous galaxy 1558.2 + 2100 is similarly studied, with no clear evidence of photometric peculiarities detected. Its interaction with the Seyfert Sextet appears to be excluded.
The A-2 experiment on HEAO-1 determined spectral parameters for seven Seyfert 1 galaxies: NGC3783, NGC4151, NGC5548, NGC6814, MK509, MCG8-11-11, and ES0141-G55. The X-ray spectra above 5 keV can be well fit by power laws of energy index alpha between .3 and 1.0 and, with the exception of MK509, by a high temperature (kt 15 keV) thermal bremsstrahlung spectrum. The column densities, with the exception of NGC4151, are less than 5 x 10 to the 22nd power at/sq cm with only the low luminosity objects having measurable columns. Galaxy ES0141-G55 showed a strong soft X-ray excess in March 1978 similar to that seen in the BL lac object MK421. Variability on a six month time scale was exhibited by MCG8-11-11, NGC3783, and possibly NGC6814. Various correlations between optical and X-ray properties are discussed. Using the typical Seyfert 1 spectrum their contribution to the diffuse X-ray background above five keV is computed.
The spectrum of the Seyfert 1 galaxy Mrk 79 is studied, and the results are compared with a similar study of the Seyfert 1 galaxy I Zw 1. It is found that: (1) both galaxies have broad permitted lines and narrower forbidden lines; (2) the broad lines in Mrk 79 are 3 to 4 times as broad as those in I Zw 1; (3) both galaxies have very strong Fe II lines; (4) the stronger forbidden lines, such as those of O III, O II, and Ne III, are present in both spectra; (5) I Zw 1 is 12 times as luminous as Mrk 79; and (6) the relative continuum spectral energy distributions of the two galaxies are similar, with a modest slope in the visual and red and flat in the violet.
Precise positions of four X-ray sources associated with Type 1 Seyfert galaxies are reported which were measured with the HEAO 1 scanning modulation collimator. The Seyferts are confirmed as the X-ray emitters in each case. The sources (and corresponding galaxies) studied include 2A 0551+466 (NGC 4151), 2A 1207+397 (MCG 8-11-11), 2A 1914-589 (ESO 141-G55), and A 1021+198 (NGC 3227). It is found that the X-ray source is located in the nucleus or the nuclear region for NGC 4151 and that the galaxy is unresolved by the present instrument in the other cases.
Calculations of the anisotropy of line emission from photoionized clouds, and the resulting asymmetry in the line profiles are discussed. The permitted emission-line profiles of Seyfert galaxies and QSO's often contain more light in the red than in the violet wing, and this asymmetry can arise from self-absorption of the line radiation in an expanding system of optically thick clouds. It is shown that the Balmer line optical depths are large enough to give strongly asymmetric line profiles for pure expansion, but the observed lack of strong asymmetry in the Balmer lines of most Seyfert galaxies suggests that the broad-line widths may result from random motions, or that clouds radiate isotropically. It is concluded that the frequently observed absorption of the violet wing of Lyman-alpha must occur in a surrounding region undergoing systematic outflow, or that the weakness of the Balmer line asymmetries is explained by the Balmer line emission resulting from collisional excitation from n=2.
A consistent theoretical interpretation is given for the suggestion that a steepening of the spectrum between X-ray and gamma ray energies may be a general, gamma-ray characteristic of Seyfert galaxies, if the diffuse gamma ray spectrum is considered to be a superposition of unresolved contributions, from one or more classes of extragalactic objects. In the case of NGC 4151, the dominant process is shown to be Penrose Compton scattering in the ergosphere of a Kerr black hole, assumed to exist in the Seyfert's active galactic nucleus.
Spectrophotometry of the nucleus of the X-ray galaxy NGC2110 shows a typical Seyfert Type 2 spectrum with a strong galactic continuum. The widths of the forbidden lines are about 360 km/s (FWHM), H-beta being somewhat broader. The moderate Balmer decrement implies that the interstellar reddening is approximately 2.1 mag. The average electron density and temperature in the line-emitting region are approximately 300 per cu cm and 35,000 K, respectively. From measurements of the nebulium line, it is found that the extent of the nucleus measured along the major axis of the galaxy is about 10 arcsec (2100 pc) and the full range of gas velocities is about 700 km/s. A direct plate is discussed which shows faint spirallike features in NGC2110, a galaxy currently classified as elliptical. NGC2110 is a member of a new class (about 5 members) of very nearby (cz less than 2500 km/s) X-ray galaxies. Bradt et al. (1978) tentatively concluded that they are Seyfert Type 2 galaxies. This conclusion is supported, and it is shown that this is not inconsistent with the narrowness (less than 500 km/s FWHM) of their emission line.
The paper presents the 2-50-keV X-ray spectra and time variability information on seven Seyfert 1 galaxies NGC 3783, NGC 4151, NGC 5548, NGC 6814, MK 509, MCG 8-11-11, and ESO 141-G55, obtained with the A2(2) experiment on HEAO 1. It is concluded that the spectra of Seyfert 1 galaxies can be well represented by flat power laws of high-temperature thermal breamsstrahlung models with relatively low column densities.
Spectrophotometry of the bright class 1 Seyfert galaxy NGC 4593 is presented. The emission-line characteristics are briefly discussed and compared with those of other Seyfert galaxies. The measured hydrogen Balmer-line ratios are reasonably consistent with expected recombination values, and the emission intensities of Fe II, He I 5876, and forbidden O III 4363 relative to other lines are stronger than average in NGC 4593.
Spectrophotometry in the range 2.1-4.0 microns is presented for the Seyfert galaxies NGC 1068, NGC 4151 and Mrk 231 and the quasar 3C 273, together with broadband and narrowband observations of the Seyfert galaxies in the range 8-13 microns. The spectra of NGC 1068 and NGC 4151 are found to contain a significant component due to starlight, especially at shorter wavelengths. The nonstellar component in NGC 1068 is observed to fall off rapidly at wavelengths shorter than 4 microns, consistent with the interpretation of the excess beyond 5 microns as thermal reradiation by dust. Observations confirm the variability of NGC 4151, and indicate the presence of two components of the flux other than starlight: a nonthermal variable component predominant at shorter wavelengths and a constant, probably thermal component at wavelengths greater than 3 microns. Mrk 231 and 3C 273 exhibit no discernable stellar component and were not observed to vary by more than 10%. Evidence is obtained for a broad minimum in the 8 to 13 micron spectrum of Mrk 231, as well as possible structure between rest wavelengths of 2.8 and 2.9 microns, and the spectrum is not a power law. The spectrum of 3C 273 is consistent with a power law from 1.2 to 10 microns, with small but significant deviations.