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On The Unified Scheme Of y- Ray Emitting Jetted Active Galactic Nuclei

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Abstract

The discovery of  - ray emitting Seyfert galaxies has opened a new unified scheme of active galactic nuclei (AGN) in which jetted Seyfert galaxies are viewed as young counterparts of radio loud AGN. Открытие сейфертовских галактик с гамма-излучением позволило представить новую унифицированную схему активных ядер галактик (АЯГ), в которой сейфертовские галактики со струями (джеты) рассматриваются как молодые аналоги радиогромких АЯГ.

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We summarize what large surveys of the contemporary universe have taught us about the physics and phenomenology of the processes that link the formation and evolution of galaxies and their central supermassive black holes. We present a picture in which the population of AGN can be divided into two distinct populations. The Radiative-Mode AGN are associated with black holes that produce radiant energy powered by accretion at rates in excess of ~1% of the Eddington Limit. They are primarily associated with less massive black holes growing in high-density pseudo-bulges at a rate sufficient to produce the total mass budget in these black holes in ~10 Gyr. The circum-nuclear environment contains high density cold gas and associated star-formation. Major mergers are not the primary mechanism for transporting this gas inward; secular processes appear dominant. Stellar feedback will be generic in these objects and strong AGN feedback is seen only in the most powerful AGN. In Jet-Mode AGN the bulk of energetic output takes the form of collimated outflows (jets). These AGN are associated with the more massive black holes in more massive (classical) bulges and elliptical galaxies. Neither the accretion onto these black holes nor star-formation in their host bulge is significant today. These AGN are probably fueled by the accretion of slowly cooling hot gas that is limited by the feedback/heating provided by AGN radio sources. Surveys of the high-redshift universe are painting a similar picture. (Abridged).
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We have presented an alternative interpretation for the absence of correlation in the relationship between the core radio power (P C) and core-dominance parameter (R) for a sample of BL Lacs and radio galaxies found in Fan & Zhang (Astron. Astrophys. 407, 899 (2003)). This is contrary to the predictions of the relativistic beaming and radio source orientation models in which the core luminosity is expected to be Doppler-boosted relative to the extended luminosity which is generally assumed to be isotropic. Our analysis of the P C − R data indicates a strong luminosity selection effect (reminiscent of bright source samples due to Malmquist bias) in the sample. In particular, we showed that a strong P C − R correlation exists above some redshift cut-off which may correspond to the flux limit of the sample used.
Article
We use the correlation between the core-to-lobe radio luminosity ratio (R) and the linear size (D) of a sample of BL Lacertae objects to investigate the relativistic beaming and radio source orientation paradigm for high peaked and low-peaked BL Lacs (X-ray and radio selected BL Lacs respectively) and to constrain relativistic beaming model for this extreme class of active galactic nuclei. We show that the R − D distributions of the BL Lac populations contradict blazar orientation sequence, with the X-ray selected BL Lacs (XBLs) being more consistent with the beaming and orientation model. On the premise that Fanaroff-Riley Type I radio galaxies are the unbeamed parent population of these objects, we derive the bulk Lorentz factor of the jets, γ~7 − 20 corresponding to a critical cone angle for optimum boosting, φ c of ~ 1° − 4°, while on average, these objects are inclined at 5° − 12° to the line-of-sight. The implications of these results for the blazar unification sequence are discussed.
Article
We present the results of an optical spectroscopic survey designed to search for low-luminosity "dwarf" Seyfert nuclei in a magnitude-limited (BT ≤ 12.5 mag) sample of 486 bright, northern galaxies. Moderate-resolution spectra of exceptionally high quality were obtained, in part to detect broad Hα emission similar in character to, but much weaker than, the broad permitted lines that define type 1 Seyfert nuclei. One of the primary goals of the survey is to better quantify the faint end of the luminosity function of active galactic nuclei. This paper describes the subset of nuclei showing definite or probable evidence of broad Hα emission. We outline the procedures for determining the presence of this elusive spectral feature, steps for its quantitative measurement, and the associated systematic errors. Of the 211 emission-line galaxies classified as having Seyfert or LINER (low-ionization nuclear emission-line region) nuclei in our survey, the broad Hα line was detected with confidence in 34 objects and with less certainty in another 12. Most of the detections are reported for the first time, and the detection rate represents a lower limit to the true incidence of active nuclei harboring a broad emission-line region. These statistics imply that broad-lined active nuclei are much more common than previously believed: they exist in at least 20% of all galaxies spectroscopically classified as "active" and in more than 10% of all luminous galaxies at the current epoch. Excluding nine well-known Seyfert 1 nuclei, the broad Hα lines of the remaining "dwarf" nuclei have median luminosity of ~1 × 1039 ergs s-1 and median FWHM of ~2200 km s-1. The broad lines constitute approximately 30% of the total emission of the Hα + [N II] λλ6548, 6583 blend. Several objects have broad Hα luminosities as low as (1-3) × 1038 ergs s-1.
Article
The statistical predictions of a unified scheme for the radio emission from quasars are explored. This scheme attributes the observed differences between flat- and steep-spectrum quasars to projection and the effects of relativistic beaming of the emission from the nuclear components. A simple quasar model consisting of a compact relativistically beamed core with spectral index zero and unbeamed lobes, spectral index - 1, is used to predict the proportion of flat-spectrum sources in flux-limited samples selected at different frequencies. In this model this fraction depends on the core Lorentz factor, gamma, and it is found that a value of approximately 5 gives satisfactory agreement with observation. In a similar way the model is used to construct the expected number/flux density counts for flat-spectrum quasars from the observed steep-spectrum counts. Again, good agreement with the observations is obtained if the average core Lorentz factor is about 5. It is concluded that the statistical properties of quasars are entirely consistent with the predictions of simple relativistic-beam models.
Article
The relativistic formula for the observed angular sizes of cosmological objects is shown to be expressible as a power law function of (1 + redshift), providing a better framework for the interpretation of angular diameter-redshift diagrams for extragalactic radio sources. In the case of an assumed homogeneous Friedman world model, it is shown that the variation of angular diameter as the inverse of redshift in extended radio sources is consistent with the angular diameter-redshift relation for rigid rods, as modified by source linear size evolution, and perhaps luminosity-linear size correlation, but not by the latter alone. These results are shown to be consistent with a linear size evolution law of the form: l varies as the inverse of (1 + redshift) to the inverse of (1 + redshift-squared), over the density parameter range zero-0.2.
Article
A redshift dependence of the maximum distance out to which active galactic nuclei (AGN) can transport their relativistic particles was first found for radio quasars by Miley1. He demonstrated that this distance was, on average, smaller in the past than it is at present, Analysing the run of median angular size with flux density for the entire extragalactic radio source population, Kapahi2 concluded that the radio galaxy population probably shares this property with the extended radio quasars. By using samples of radio ellipticals complete to vastly different flux limits, we can, for the first time, separate redshift- and luminosity-dependences of their linear sizes. Ram pressure in a medium with cosmologically varying density will naturally cause a dependence on redshift3, but this cannot explain so steep a dependence as that implied here. It may be expected if galaxy haloes influence the outward energy transport4.
Article
The relativistic beaming model has been successfully used to explain many of the observational properties of active galactic nuclei. In this model the total emission is formed by two components, one beamed, one unbeamed. However, the exact contribution from each component in unresolved sources is still not clear. In the radio band, the core and extended emissions are clearly separated. We adopt the method proposed by Kembhavi to separate the two contributions in the X-ray emissions in a sample of 19 gamma-ray loud blazars. It is clearly shown that the beamed emission dominates the X-ray flux and the unbeamed X-ray emission is correlated with the extended radio emission of the considered objects. We also find that the ratio of the beamed to the unbeamed X-ray luminosity is correlated with the X-ray spectral index, an effect that should be a consequence of the underlying X-ray emission mechanism.
Article
Analytical and numerical methods have been used to develop a dynamical model for the evolution of the linear size, D, of compact steep spectrum (CSS) sources through the ambient medium of density, ne, within a characteristic time, T. This shows that the empirical relation between spectral turnover, νp, and D implies that νp∼n0.35e, suggesting that the spectral turnover constitutes a characteristic signature of dense gases around CSS sources.
Article
We develop a new method to constrain the star formation histories, dust attenuation and stellar masses of galaxies. It is based on two stellar absorption-line indices, the 4000-Å break strength and the Balmer absorption-line index HδA. Together, these indices allow us to constrain the mean stellar ages of galaxies and the fractional stellar mass formed in bursts over the past few Gyr. A comparison with broad-band photometry then yields estimates of dust attenuation and of stellar mass. We generate a large library of Monte Carlo realizations of different star formation histories, including starbursts of varying strength and a range of metallicities. We use this library to generate median likelihood estimates of burst mass fractions, dust attenuation strengths, stellar masses and stellar mass-to-light ratios for a sample of 122 808 galaxies drawn from the Sloan Digital Sky Survey. The typical 95 per cent confidence range in our estimated stellar masses is ±40 per cent. We study how the stellar mass-to-light ratios of galaxies vary as a function of absolute magnitude, concentration index and photometric passband and how dust attenuation varies as a function of absolute magnitude and 4000- Å break strength. We also calculate how the total stellar mass of the present Universe is distributed over galaxies as a function of their mass, size, concentration, colour, burst mass fraction and surface mass density. We find that most of the stellar mass in the local Universe resides in galaxies that have, to within a factor of approximately 2, stellar masses ∼5× 1010 M⊙, half-light radii ∼3 kpc and half-light surface mass densities ∼109 M⊙ kpc−2. The distribution of Dn(4000) is strongly bimodal, showing a clear division between galaxies dominated by old stellar populations and galaxies with more recent star formation.
Article
A sample of 18286 radio-loud AGN is presented, constructed by combining the SDSS DR7 with the NVSS and FIRST radio surveys. Using this sample, the differences between `high-excitation' (or `quasar-mode'; HERG) and `low-excitation' (`radio-mode'; LERG) radio galaxies are investigated. A primary difference is the distinct nature of the Eddington-scaled accretion rate onto their central black holes: HERGs typically have accretion rates between 1 and 10% of Eddington, whereas LERGs predominatly accrete at a rate below 1% Eddington. This is consistent with models where the population dichotomy is caused by a switch between radiatively efficient and inefficient accretion modes at low accretion rates. Local radio luminosity functions are derived separately for the two populations, showing that although LERGs dominate at low luminosity and HERGs above 1e26 W/Hz, examples of both classes are found at all radio luminosities. Using the V/Vmax test it is shown that the populations show differential cosmic evolution at fixed radio luminosity: HERGs evolve strongly at all luminosities, while LERGs show weak or no evolution. This suggests that the luminosity-dependent evolution of the radio luminosity function is driven, at least in part, by the changing relative contributions of these two populations with luminosity. The host galaxies of the sources are also distinct: HERGs are typically of lower stellar mass, with lower black hole masses, bluer colours and weaker 4000-Ang breaks indicating younger stellar populations. These results offer strong support to the picture in which HERGs are fuelled at high rates through radiative accretion disks by cold gas, perhaps from mergers and interactions, while LERGs are fuelled via radiatively inefficient flows at low accretion rates, often by gas associated with the hot X-ray haloes of their host galaxy/cluster, as part of a radio-AGN feedback loop (abridged).
Article
We propose a scenario where blazars are classified as flat-spectrum radio quasars (FSRQs), BL Lacs, low synchrotron, or high synchrotron peaked objects according to a varying mix of the Doppler boosted radiation from the jet, the emission from the accretion disk, the broad line region, and the light from the host galaxy. In this framework the peak energy of the synchrotron power (nu_peak) in blazars is independent of source type and of radio luminosity. We test this new approach, which builds upon unified schemes, using extensive Monte Carlo simulations and show that it can provide simple answers to a number of long-standing issues including, amongst others, the different cosmological evolution of BL Lacs selected in the radio and X-ray bands, the larger nu_peak values observed in BL Lacs, the fact that high synchrotron peaked blazars are always of the BL Lac type, and the existence of FSRQ/BL Lac transition objects. Objects so far classified as BL Lacs on the basis of their observed weak, or undetectable, emission lines are of two physically different classes: intrinsically weak lined objects, more common in X-ray selected samples, and heavily diluted broad lined sources, more frequent in radio selected samples, which explains some of the confusion in the literature. We also show that strong selection effects are the main cause of the diversity observed in radio and X-ray samples, and that the correlation between luminosity and nu_peak, that led to the proposal of the "blazar sequence", is also a selection effect arising from the comparison of shallow radio and X-ray surveys, and to the fact that high nu_peak-high radio power objects have never been considered because their redshift is not measurable.
Article
In this paper, based on a paper by Liu and Zhang (2002), we have chosen a sample of 542 extragalactic sources (27 BL Lac objects, 300 galaxies (radio galaxies and Seyfert galaxies), and 215 quasars), for which we have calculated the core-dominance parameters and investigated the relation between core-dominance parameter and the core and extended luminosities. The core-dominance parameter of galaxies is smaller than that in quasars, which is smaller than that in BL Lac objects. log R=1.40±0.74R = -1.40 \pm0.74 for galaxies, log R=0.53±0.92R = -0.53 \pm0.92 for quasars, and log R=0.01±0.65R = 0.01 \pm0.65 for BL Lac objects on average respectively. For quasars, there is clear correlation between the core-luminosity and core-dominance parameter and an anti-correlation between the extended luminosity and the core-dominance parameter, which is explained by the beaming effect.
Article
Spectral and morphological data for 282 Seyfert and emission-line galaxies spanning radio to X-ray wavelengths are compiled. The data include a large number of optical emission-line measurements which have not been reported previously. These data are intended to provide a convenient summary of the relevant properties of these galaxies, as well as a data base to search for correlations among the various parameters in order to obtain a better understanding of the active galaxy phenomenon. The paper presents the data and analyzes the distributions of various properties of Seyfert 1 and Seyfert 2 galaxies and starburst galaxies. It is found that Seyferts 2s have a higher 60 micron/forbidden O III 5007 A flux ratio than Seyfert 1s. This result, combined with the fact that Seyfert 2s are more heavily reddened, indicate that they have a higher dust content. It is also found that starburst nuclei are comparable to Seyfert 2s in far-infrared and 20 cm luminosities, although their optical spectra are markedly different.
Article
The redshift and luminosity dependence of the linear sizes of powerful radio galaxies on epoch is investigated using samples of similar radio luminosity extending to z larger than about one. It is found that a strong evolution in linear sizes with epoch of a given form is required for q0 = 1/2. Fairly strong evolution is required even if the steep-spectrum compact sources which make an increasing contribution with redshift are excluded from the analysis. When linear size distributions of samples of radio galaxies of different luminosities are compared at similar redshifts, it is found that, at constant redshift, linear sizes increase with luminosity in a given way. Strong evidence is found that, for radio galaxies, the epoch and luminosity dependence of linear sizes can be factorized over the entire range of luminosity and redshift space.
Article
We have used the Very Large Array (VLA) to conduct a survey for radio continuum emission in the sample of 52 Seyfert nuclei selected from the optical spectroscopic galaxy catalog of Ho, Filippenko, and Sargent. This Seyfert sample is the most complete and least biased available, and, as such, it will be useful for a variety of statistical analyses. Here we present the observations, measurements, and an atlas of radio maps. The observations were made at 6 cm in the B-array and at 20 cm in the A-array, yielding matched angular resolutions of approximately 1". We detected 44 objects (85%) at 6 cm and 37 objects (71%) at 20 cm above a 3-sigma threshold of 0.12 mJy/beam. The sources have a wide range of radio powers (10^{18}-10^{25} W/Hz), spectral indices (+0.5 to -1 between 20 and 6 cm), and linear sizes (from a few tens pc to 15 kpc). The morphology of the radio emission is predominantly that of a compact core, either unresolved or slightly resolved, occasionally accompanied by elongated, jet-like features. Linearly polarized emission was detected at 6 cm in 12 sources, 9 of which were also detected at 20 cm. Comment: To appear in The Astrophysical Journal Supplements. Latex, 48 pages, plus and additional 14 figures as JPEG images
Article
Narrow Line Seyfert 1 galaxies (NLS1s) are intriguing owing to their continuum as well as emission-line properties. The observed peculiar properties of the NLS1s are believed to be as a result of an accretion rate close to the Eddington limit. As a consequence of this, for a given luminosity, NLS1s have smaller black hole (BH) masses compared with normal Seyfert galaxies. Here we argue that NLS1s might be Seyfert galaxies in their early stage of evolution and as such may be low-redshift, low-luminosity analogues of high-redshift quasars. We propose that NLS1s may reside in rejuvenated, gas-rich galaxies. We also argue in favour of collisional ionization for production of Fe ii in active galactic nuclei.
Article
We derive the non-linear relation between the core flux Fν of accretion-powered jets at a given frequency and the mass M of the central compact object. For scale-invariant jet models, the mathematical structure of the equations describing the synchrotron emission from jets enables us to cancel out the model-dependent complications of jet dynamics, retaining only a simple, model-independent algebraic relation between Fν and M. This approach allows us to derive the Fν–M relation for any accretion disc scenario that provides a set of input boundary conditions for the magnetic field and the relativistic particle pressure in the jet, such as standard and advection-dominated accretion flow (ADAF) disc solutions. Surprisingly, the mass dependence of Fν is very similar in different accretion scenarios. For typical flat-spectrum core-dominated radio jets and standard accretion scenarios, we find Fν∼M17/12. The 7–9 orders of magnitude difference in black hole mass between microquasars and active galactic nuclei (AGN) jets imply that AGN jets must be about 3–4 orders of magnitude more radio-loud than microquasars, i.e. the ratio of radio to bolometric luminosity is much smaller in microquasars than in AGN jets. Because of the generality of these results, measurements of this Fν–M dependence are a powerful probe of jet and accretion physics. We show how our analysis can be extended to derive a similar scaling relation between the accretion rate ṁ and Fν for different accretion disc models. For radiatively inefficient accretion modes, we find that the flat-spectrum emission follows Fν ∝ (M ṁ)17/12.
Article
A catalogue of extra-galactic jets is very useful both in observational and theoretical studies of active galaxies. With the use of new powerful radio instruments, the detailed structures of very compact or weak radio sources are investigated observationally and many new radio jets are detected. In this paper, we give a list of 661 radio sources with detected radio jets known to us prior to the end of December 2000. All references are collected for the observations of jets in radio, IR, optical, UV and X-ray wave-bands. Comment: 43 pages, 1 figure
Article
The appearance of active galactic nuclei (AGN) depends so strongly on orientation that our current classification schemes are dominated by random pointing directions instead of more interesting physical properties. Light from the centers of many AGN is obscured by optically thick circumnuclear matter and in radio-loud AGN, bipolar jets emanating from the nucleus emit light that is relativistically beamed along the jet axes. Understanding the origin and magnitude of radiation anisotropies in AGN allows us to unify different classes of AGN; that is, to identify each single, underlying AGN type that gives rise to different classes through different orientations. This review describes the unification of radio-loud AGN, which include radio galaxies, quasars, and blazars. We describe the classification and properties of AGN and summarize the evidence for anisotropic emission. We outline the two most plausible unified schemes for radio-loud AGN, one linking quasars and luminous radio galaxies and another linking BL~Lac objects and less luminous radio galaxies. Using the formalism appropriate to samples biased by relativistic beaming, we show the population statistics for two schemes are in accordance with available data. We analyze the possible connections between low- and high-luminosity radio-loud AGN. We review potential difficulties with unification and conclude that none currently constitutes a serious problem. We discuss likely complications to unified schemes that are suggested by realistic physical considerations; these will be important to consider when more comprehensive data for larger complete samples become available. We conclude with a list of the ten questions we believe are the most pressing in this field.