Spectroscopical Confirmation of Variability-Selected Active Galactic Nuclei
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The cosmological evolution of active galactic nuclei (AGN) luminosity function is poorly known at the faint end, since active nuclei fainter than their host galaxies cannot be selected by color techniques. A sample of low luminosity AGN candidates has been selected on the basis of their variability. We carried out spectroscopic observations with the WYFFOS multi-fiber facility at the 4.2 m William Herschel Telescope. Preliminary results are presented, indicating the validity of the selection technique.Keywords:
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For investigating the statistical properties of X-ray selected Active Galactic Nuclei (AGNs), we have carried out a program of optical identification of a selection of X-ray sources from ROSAT All Sky Survey Bright Source Catalogue (RASS-BSC) using the 2.16 m telescope of Beijing Astronomical Observatory (BAO). In the preliminary observations, 23 new AGNs were discovered, of which 9 are quasars, and 14 are Seyfert galaxies.
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We present an analysis of X-ray variability in a flux-limited sample of quasi-stellar objects (QSOs). Selected from our deep ROSAT survey, these QSOs span a wide range in redshift (0.10.5) do not show the anticorrelation with luminosity seen in local AGN. We speculate on the implications of these results for physical models of AGN and their evolution. Finally, we find evidence for X-ray variability in an object classified as a narrow-emission-line galaxy, suggesting the presence of an AGN.
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view Abstract Citations (166) References (62) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Near-Infrared Imaging of CfA Seyfert Galaxies McLeod, K. K. ; Rieke, G. H. Abstract We present near-IR images of 43 Seyfert galaxies from the CfA Seyfert sample. The near-IR luminosity is a good tracer of luminous mass in these galaxies. Most of the Seyfert nuclei are found in hosts of mass similar to that of L^*^ galaxies and ranging in type from S0 to Sc. In addition, there is a population of low-mass host galaxies with very low luminosity Seyfert nuclei. We have examined our images for signs of perturbations that could drive fuel toward the galaxy nucleus, but there are none we can identify at a significant level. The critical element for fueling is evidently not reflected clearly in the large-scale distribution of luminous mass in the galaxy. The Seyfert hosts are compared with a sample of 50 low-redshift quasar host galaxies we have also imaged. The radio-quiet quasars and the Seyfert nuclei lie in similar kinds of galaxies spanning the same range of mass centered around L^*^. However, for the most luminous quasars, there is a correlation between the minimum host-galaxy mass and the luminosity of the active nucleus. Radio-loud quasars are generally found in hosts more massive than an L^*^ galaxy. The low-luminosity quasars and the Seyfert nuclei both tend to lie in host galaxies seen preferentially face-on, which suggests that there is a substantial amount of obscuration coplanar with the galaxian disk. The obscuration must be geometrically thick (thickness-to-radius ratio ~1) and must cover a significant fraction of the narrow-line region (r > 100 pc). Publication: The Astrophysical Journal Pub Date: March 1995 DOI: 10.1086/175339 Bibcode: 1995ApJ...441...96M Keywords: Active Galactic Nuclei; Infrared Imagery; Luminosity; Quasars; Seyfert Galaxies; Mass Distribution; Red Shift; Astronomy; GALAXIES: NUCLEI; GALAXIES: PHOTOMETRY; GALAXIES: QUASARS: GENERAL; GALAXIES: SEYFERT; INFRARED: GALAXIES full text sources ADS | data products SIMBAD (50) NED (48)
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Cherenkov Telescope Array
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I. Surveys of Active Galaxies and QSO's.- Lists of Active Galaxies, Problems of Detection and Statistics.- The First Byurakan Survey (FBS) and Search Problems for AGN.- The Second Byurakan Spectral Sky Survey.- A Survey and Related Observations of the KISO Ultraviolet-Excess Galaxies.- Observational Evidences for the Evolution of the Quasar-Luminosity Function.- A Deep Spectral Survey on the 6-Meter Telescope.- An Emission-Line Galaxy Survey with the UK Schmidt Telescope.- Search for Variable Extragalactic Objects.- II. Ultraviolet Excess Galaxies.- UV-Galaxies.- Several Statistical Properties of Galaxies with UV Excess.- Markarian Galaxies and Zwicky Clusters.- The Byurakan Classification and the Colours of the Central Parts of Spiral Galaxies.- Morphology of Galaxies with UV-Continuum.- Morphology of Isolated and Grouped Galaxies.- Blue Objects Near M 31 and Optical Identifications of 5C3 Sources.- III. Seyfert Galaxies.- Seyfert Galaxies: Classification, Morphology, Observations at Optical Wavelengths, Environmental Factors.- The 0.3 to 100 Micron Continua of Type 1 Seyferts.- Extended Infrared Emission in Seyfert Galaxies.- Extended Line Emitting Regions in the Seyfert Galaxy NGC 2992.- Low Frequency Cutoffs in the Spectra of Radioquiet Quasars.- The Structure of Galaxies and their Nuclear Activity.- Statistical Studies of AGN and QSOs.- On the Hydrodynamical Conception of the Spiral Structure in Galaxies with a Velocity Kink on the Rotation Curve.- IV. Variability.- Spectral Variability in Seyfert Galaxies.- Emission Lines Variations in the Spectra of Seyfert Galaxies Nuclei. Observational Data.- A Search for Periodicities in the Light Variation of Some Seyfert Galaxies.- Kinematical and Spectral Evidences of Complex Structure of NGC 1275 Nucleus.- Photoelectric Observations of Continuous and Emission Lines Variability in Spectra of Seyfert Galaxy NGC 1275 Nucleus.- Investigation of the Spectra of some Seyfert Galaxies.- Hss Profile Variations in the Spectrum of Seyfert Galaxy NGC 5548 Nucleus.- Variable Objects in a Complete Sample of Faint Radio Sources.- The Low Frequency Variability of Extragalactic Radio Sources.- Multifrequency Observations of the Seyfert Galaxy 3C 120 in 1983-1986.- 1-3-Day Variations of the Broad Emission Lines of Seyfert Nuclei.- A Possible Mechanism to Explain the Narrow Line Variability of Seyfert Galaxies on Timescales of Months.- The Excitation Mechanism of Metastable Levels and Variability of Oxygen Forbidden Lines 4959+5007 A [OIII] in the Seyfert Nuclei.- V. Jets, Motions and Blazars.- Ionization and Kinematics of the Narrow Line Region in Seyfert Galaxies.- Unity and Diversity Among Jets in Active Galaxies.- VLBI Observations of NGC4151 at 6 CM Wavelength.- Radio Emission from Active Galactic Nuclei.- Bulk Relativistic Motion in a Complete Sample of Radio Selected AGN.- 3C454.3: A New Kind of Source?.- Studies of the 3C 345 Quasar Structure at DM-Wavelengths.- Connection between Optical Outbursts and Motion in the Milliarcsecond Radio Structure of the Extragalactic Objects.- A Probable Model of Compact Variable Radio Sources with a Superluminal Motion Of VLBI-Components.- On the Nature of Processes Occurring in Active Nuclei of Galaxies.- Multifrequency Observations of Blazars.- Polarimetric and Photometric Investigations of Lacertids.- Active Galactic Nuclei from the Extended Einstein Medium Survey.- The Forest of Absorption Lines in QSO Spectra - A Key to the Large Scale Structure Development?.- The Primeval Hadron: Origin of Rotation and Magnetic Fields in the Universe.- VI. Environmental Aspects of Nuclear Activity.- Relationships between Seyfert Galaxies, QSOs, and BL LACs.- Imaging of Low Redshift PG Quasars and their Companions.- Nuclear Activity of Galaxies within Groups.- Multi-Frequency Observations of Multiple Nucleus Markarian Galaxies.- High Spatial Resolution Observations of the Quasar MR2251-178.- 1411+442: Optical Imaging of a BAL QSO.- Morphology and Spectroscopy of Markarian 231.- Seyfert 2 Galaxies with Double Nuclei.- The Role of Environment in the Origin of Radio Emission from Galaxies.- On the Radio Emission from Interacting Spiral Galaxies.- VII. Low Level Activity and Intermediate Objects.- The Nature of Liners.- Low-Luminosity Active Nuclei in Elliptical Galaxies.- A Search for Low-Level Seyfert Activity in the 500 Brightest Northern Galaxies.- Activity in Near-Normal Galaxies.- X-Ray Emission as Evidence of Activity in otherwise Galaxies.- Tight Nuclear Spirals: Observational Evidence of Nuclear Activity.- Evidence for Activity in the Spiral Galaxy NGC4319.- On the Radio Emission of Barred Spirals.- Radio Continuum Emission and Optical Emission-Line Activity in the Nuclei of Spirals.- VIII. Starburst Activity.- Starburst Models for AGNs.- VLBI Observations of the M81-M82 Pair of Galaxies.- Optical Evidence for a Dust Ring in the Centre of M 82 and (OR?) a Flat Star Burst Region.- Star Formation in Galactic Nuclei.- The Thermal Component of the Seyfert Galaxy NGC1275.- Spectra of Nucleus of NGC 6240.- Superassociations in the Arms of Normal and Active Galaxies.- Activity in Blue Compact Galaxies.- Nests of Interacting Galaxies: What is it?.- A Spectral Study of Markarian 297.- Concluding Remarks.- List Of Authors.
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Peculiar galaxy
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We observed four active galactic nuclei (AGNs) (the type 1 Seyfert systems 3C 249.1, NGC 6814, and Mrk 205, and the BL Lac object 3C 371) using the High Speed Photometer on the Hubble Space Telescope (HST) to search for short-timescale microvariability in the UV. Continuous observations of ~3000 s duration were obtained for each system on several consecutive HST orbits using a 1 s sample time in a 1400-3000 Å bandpass. No photometric variability greater than 0.3% (0.003 mag) was detected in any AGN on timescales shorter than 1500 s. The distribution of photon arrival times observed from each source was consistent with Poisson statistics. Because of HST optical problems, the limit on photometric variability at longer timescales is less precise. These results restrict the masses of black holes as the central engines of AGNs and the diskoseismic oscillations of any accretion disk around such a black hole.
BL Lac object
Black hole (networking)
Photometer
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