Physics of Seyfert Galaxies (original) (raw)
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Probing the physics of Seyfert galaxies using their emission-line regions
Active galaxies have powerhouses of radiation in their nuclear regions that are driven by accreting supermassive black holes. The accretion system also generates outflows of ionized gas and synchrotron-emitting bipolar jets of plasma, which could have a significant impact on the host galaxy. We have initiated an investigation into the physics of nearby active galaxies by studying morphology, kinematics, excitation abundance structure, and radio structure of about 120 nearby targets. We present a few early results from this investigation.
Constraining the Active Galactic Nucleus Contribution in a Multiwavelength Study of Seyfert Galaxies
Astrophysical Journal, 2008
We have studied the relationship between the high- and low-ionization [O IV] λ25.89 μm, [Ne III] λ15.56 μm, and [Ne II] λ12.81 μm emission lines with the aim of constraining the active galactic nuclei (AGNs) and star formation contributions for a sample of 103 Seyfert galaxies. We use the [O IV] and [Ne II] emission as tracers for the AGN power and star formation to investigate the ionization state of the emission-line gas. We find that Seyfert 2 galaxies have, on average, lower [O IV]/[Ne II] ratios than Seyfert 1 galaxies. This result suggests two possible scenarios: (1) Seyfert 2 galaxies have intrinsically weaker AGNs, or (2) Seyfert 2 galaxies have relatively higher star formation rates than Seyfert 1 galaxies. We estimate the fraction of [Ne II] directly associated with the AGNs and find that Seyfert 2 galaxies have a larger contribution from star formation, by a factor of ~1.5 on average, than what is found in Seyfert 1 galaxies. Using the stellar component of [Ne II] as a tracer of the current star formation, we found similar star formation rates in Seyfert 1 and Seyfert 2 galaxies. We examined the mid- and far-infrared continua and found that [Ne II] is well correlated with the continuum luminosity at 60 μm and that both [Ne III] and [O IV] are better correlated with the 25 μm luminosities than with the continuum at longer wavelengths, suggesting that the mid-infrared continuum luminosity is dominated by the AGN, while the far-infrared luminosity is dominated by star formation. Overall, these results test the unified model of AGNs and suggest that the differences between Seyfert galaxies cannot be solely due to viewing angle dependence.
Emission Line Properties of Seyfert Galaxies in the 12 μm Sample
The Astrophysical Journal
We present optical and ultraviolet spectroscopic measurements of the emission lines of 81 Seyfert 1 and 104 Seyfert 2 galaxies which comprise nearly all of the IRAS 12µm AGN sample. We have analyzed the emission-line luminosity functions, reddening, and other diagnostics. For example, the narrow-line regions (NLR) of Seyfert 1 and 2 galaxies do not significantly differ from each other in most of these diagnostics. Combining the Hα/Hβ ratio with a new reddening indicator-the [SII]6720/[OII]3727 ratio, we find the average E(B − V) is 0.49 ± 0.35 for Seyfert 1's and 0.52 ± 0.26 for Seyfert 2's. The NLR of Sy 1 galaxies has only insignificantly higher ionization level than in the Sy 2's. For the broad-line region (BLR), we find that the C IV equivalent width correlates more strongly with [O III]/Hβ than with UV luminosity. Our bright sample of local active galaxies includes 22 Seyfert nuclei with extremely weak broad wings in Hα, known as Seyfert 1.9's and 1.8's, depending on whether or not broad Hβ wings are detected. Aside from these weak broad lines, our low-luminosity Seyferts are more similar to the Sy2's than to the Sy 1's. In a a BPT diagram we find that Sy 1.8's and Sy 1.9's overlap the region occupied by the Sy 2 galaxies. We compare our results on optical emission lines with those obtained by previous investigators using AGN subsamples from the Sloan Digital Sky Survey. The luminosity functions of forbidden emission lines [OII]λ3727Å, [OIII]λ5007Å, and [SII]λ6720Å in Seyfert 1's and 2's are indistinguishable. They all show strong downward curvature. Unlike the LF's of Seyfert galaxies measured by the Sloan Digital Sky Survey, ours are nearly flat at low luminosities. The larger number of faint Sloan "AGN" is attributable to their inclusion of weakly emitting LINERs
AIP Conference Proceedings, 1997
Observations with Compton Gamma Ray Observatory have provided key insights to the high energy emission mechanisms in Active Galactic Nuclei (AGN) and clearly separate them into a class of Blazars, with apparent non-thermal jet emissions often peaking in the EGRET energy band, and into the Seyfert class with emissions more closely related to the accretion disk presumably energizing the nuclear black hole. OSSE measurements indicate that the high energy emission from Seyfert AGN has a high energy cuto below 100 ? 200 keV and no Seyferts have been detected by COMPTEL or EGRET. Here, we review the X-ray and -ray observations of Seyferts and Radio Galaxies and the broad band emission models that describe the observed spectral characteristics. A comparision of Seyfert 1, Seyfert 2, and radio galaxies can be made in the context of the AGN uni cation models.
Optical Properties of Radio-selected Narrow-Line Seyfert 1 Galaxies
The Astronomical Journal, 2006
We present results from the analysis of the optical spectra of 47 radio-selected narrow-line Seyfert 1 galaxies (NLS1s). These objects are a subset of the First Bright Quasar Survey (FBQS) and were initially detected at 20 cm (flux density limit ∼ 1 mJy) in the VLA FIRST Survey. We run Spearman rank correlation tests on several sets of parameters and conclude that, except for their radio properties, radio-selected NLS1 galaxies do not exhibit significant differences from traditional NLS1 galaxies. Our results are also in agreement with previous studies suggesting that NLS1 galaxies have small black hole masses that are accreting very close to the Eddington rate. We have found 16 new radio-loud NLS1 galaxies, which increases the number of known radio-loud NLS1 galaxies by a factor of ∼ 5.
2016
A radio study of a carefully selected sample of 20 Seyfert galaxies that are matched in orientationindependent parameters, which are measures of intrinsic active galactic nuclei (AGN) power and host galaxy properties is presented to test the predictions of the unified scheme hypothesis. Our sample sources have core flux densities greater than 8 mJy at 5 GHz on arcsec-scales due to the feasibility requirements. These simultaneous pc-scale and kpc-scale radio observations reveal (i) that Seyfert 1 and Seyfert 2 galaxies have equal tendency to show compact radio structures on mas-scales, (ii) the distributions of pc-scale and kpc-scale radio luminosities are similar for both Seyfert 1 and Seyfert 2 galaxies, (iii) no evidence for relativistic beaming in Seyfert galaxies, (iv) similar distributions of source spectral indices in spite of the fact that Seyferts show nuclear radio flux density variations, and (v) the distributions of projected linear size for Seyfert 1 and Seyfert 2 galaxies are not significantly different as would be expected in the unified scheme. The latter could be mainly due to a relatively large spread in the intrinsic sizes. We also find that a starburst alone cannot power these radio sources. Finally, an analysis of the kpc-scale radio properties of the CfA Seyfert galaxy sample shows results consistent with the predictions of the unified scheme.
Parsec‐Scale Radio Structures in the Nuclei of Four Seyfert Galaxies
The Astrophysical Journal, 1999
We present 18-cm radio maps of four Seyfert nuclei, Mrk 1, Mrk 3, Mrk 231 and Mrk 463E, made with the European VLBI Network (EVN). Linear radio structures are present in three out of four sources on scales of ∼100 pc to ∼1 kpc, and the 20-mas beam of the EVN enables us to resolve details within the radio structures on scales of < 10 pc. Mrk 3 was also imaged using MERLIN and the data combined with the EVN data to improve the sensitivity to extended emission. We find an unresolved flat-spectrum core in Mrk 3, which we identify with the hidden Seyfert 1 nucleus in this object, and we also see marked differences between the two highly-collimated radio jets emanating from the core. The western jet terminates in a bright hotspot and resembles an FRII radio structure, whilst the eastern jet has more in common with an FRI source. In Mrk 463E, we use the radio and optical structure of the source to argue that the true nucleus lies approximately 1 arcsec south of the position of the radio and optical brightness peaks, which probably represent a hotspot at the working surface of a radio jet. The EVN data also provide new evidence for a 100-pc radio jet powering the radio source in the Type 1 nucleus of Mrk 231. However, the Seyfert 2 galaxy Mrk 1 shows no evidence for radio jets down to the limits of resolution (∼ 10 pc). We discuss the range of radio source size and morphology which can occur in the nuclei of Seyfert galaxies and the implications for Seyfert unification schemes and for radio surveys of large samples of objects.
Multiwavelength survey of a sample of flat-spectrum radio-loud narrow-line Seyfert 1 galaxies
2015
We report on a multiwavelength survey of a sample of 42 flat-spectrum radio-loud narrow-line Seyfert 1 galaxies (RLNLS1s). This is the largest known sample of this type of active galactic nucleus (AGN) to date. We found that 17% of sources were detected at high-energy gamma rays (E>100 MeV), and 90% at X-rays (0.3-10 keV). The masses of the central black holes are in the range sim106−8Modot\sim 10^{6-8}M_{\odot}sim106−8Modot, smaller than the values of blazars. The disk luminosities are about 1-49% of the Eddington value, with one outlier at 0.3%, comparable with the luminosities observed in flat-spectrum radio quasars (FSRQs). The jet powers are sim1042−46\sim 10^{42-46}sim1042−46 erg s$^{-1}$, comparable with BL Lac Objects, yet relatively smaller than FSRQs. However, once renormalized by the mass of the central black hole, the jet powers of RLNLS1s, BL Lacs, and FSRQs are consistent each other, indicating the scalability of the jets. We found episodes of extreme variability at high energies on time scales of hours. In...
Statistical multifrequency study of narrow-line Seyfert 1 galaxies
Astronomy & Astrophysics, 2014
Context. High-energy γ-rays, which are produced by powerful relativistic jets, are usually associated with blazars and radio galaxies. In the current active galactic nuclei (AGN) paradigm, such jets are almost exclusively launched from massive elliptical galaxies. Recently, however, Fermi/LAT detected γ-rays from a few narrow-line Seyfert 1 galaxies and thus confirmed the presence of relativistic jets in them. Since NLS1 galaxies are assumed to be young evolving AGN, they offer a unique opportunity to study the production of relativistic jets in late-type galaxies. Aims. Our aim is to estimate by which processes the emission of various kinds is produced in NLS1 galaxies and to study how emission properties are connected to other intrinsic AGN properties. Methods. We have compiled the so far largest multiwavelength database of NLS1 sources. This allowed us to explore correlations between different wavebands and source properties using, for example, Pearson and Spearman correlations and principal component analysis. We did this separately for radio-loud and radio-quiet sources. Results. Multiwavelength correlations suggest that radio-loud sources host relativistic jets that are the predominant sources of radio, optical, and X-ray emission. The origin of infrared emission remains unclear. Radio-quiet sources do not host a jet, or the jet is very weak. In them, radio and infrared emission is more likely generated via star formation processes, and the optical and X-ray emission originate in the inner parts of the AGN. We also find that the black hole mass correlates significantly with radio loudness, which suggests that NLS1 galaxies with more massive black holes are more likely to be able to launch powerful relativistic jets.