Physical Sciences and Mathematics | Open Access Articles

The Case For Optically Thick High-Velocity Broad-Line Region Gas In Active Galactic Nuclei, Stephanie A. Snedden, C. Martin Gaskell

C. Martin Gaskell Publications

A combined analysis of the profiles of the main broad quasar emission lines in both Hubble Space Telescope and optical spectra shows that while the profiles of the strong UV lines are quite similar, there is frequently a strong increase in the Lyα/Hα ratio in the high-velocity gas.We show that the suggestion that the high-velocity gas is optically thin presents many problems.We show that the relative strengths of the high-velocity wings arise naturally in an optically thick BLR component. An optically thick model successfully explains the equivalent widths of the lines, the Lyα/Hα ratios and flatter Balmer decrements in the …

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Agn Reddening And Ultraviolet Extinction Curves From Hubble Space Telescope Spectra, C. Martin Gaskell, C. Martin Gaskell

C. Martin Gaskell Publications

We present intrinsic extinction curves for 14 AGNs. The AGNs have reddenings, E(B-V), of up to 0.36 mag. The majority (13 out of 14) of the extinction curves are not steep in the UV. Of the seven best determined extinction curves, five have extinction curves that are as flat as the standard Galactic curve in the optical and near UV, but flatter in the far UV, and without the λ2175 feature. One AGN, B3 0754+394, has a steep SMC-like extinction curve, and another, Mrk 304, has an LMC-like extinction curve, including a probable λ2175 bump. The remaining seven, lower-quality, extinction …

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Discovery Of Polarization Reverberation In Ngc 4151, C. Martin Gaskell, René W. Goosmann, Nelly I. Merkulova, Nikolay M. Shakhovskoy, Masatoshi Shoji

C. Martin Gaskell Publications

Observations of the optical polarization of NGC 4151 in 1997–2003 show variations of an order of magnitude in the polarized flux while the polarization position angle remains constant. The amplitude of variability of the polarized flux is comparable to the amplitude of variability of the total U-band flux, except that the polarized flux follows the total flux with a lag of 8±3 days. The time lag and the constancy of the position angle strongly favor a scattering origin for the variable polarization rather than a non-thermal synchrotron origin. The orientation of the position angle of the polarized flux (parallel to …

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Ngc 5548: The Agn Energy Budget Problem And The Geometry Of The Broad-Line Region And Torus, C. Martin Gaskell, Elizabeth S. Klimek, Ludmila S. Nazarova

C. Martin Gaskell Publications

We consider in detail the spectral energy distribution (SED) and multi-wavelength variability of NGC 5548. Comparison with the SEDs of other AGNs implies that the internal reddening of NGC 5548 is E(B-V) = 0.17 mag. The extinction curve is consistent with the mean curve of other AGNs found by Gaskell & Benker, but inconsistent with an SMC-type reddening curve. Because most IR emission originates exterior to the broad-line region (BLR), the SED seen by the inner BLR is different from that seen by the outer BLR and from the earth. The most likely BLR covering factor is ~ 40% and …

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Transformations Between 2mass, Sdss And Bvri Photometric Systems: Bridging The Near Infrared And Optical, S. Bilir, S. Ak, S. Karaali, A. Cabrera-Lavers, T. S. Chonis, C. Martin Gaskell

C. Martin Gaskell Publications

We present color transformations for the conversion of the 2MASS photometric system to the Johnson-Cousins UBV RI system and further into the SDSS ugriz system. We have taken SDSS gri magnitudes of stars measured with the 2.5-m telescope from SDSS Data Release 5 (DR5), and BV RI and JHK_s magnitudes from Stetson’s catalogue and Cutri et al. (2003), respectively. We matched thousands of stars in the three photometric systems by their coordinates and obtained a homogeneous sample of 825 stars by the following constraints, which are not used in previous transformations: 1) the data are de-reddened, 2) giants are …

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Modeling Optical And Uv Polarization Of Agns I. Imprints Of Individual Scattering Regions, René W. Goosmann, C. Martin Gaskell

C. Martin Gaskell Publications

Context. Spectropolarimetry of AGNs is a powerful tool for studying the structure and kinematics of the inner regions of quasars. Aims. We wish to investigate the effects of various AGN scattering region geometries on the polarized flux. Methods. We introduce a new, publicly available Monte Carlo radiative transfer code, STOKES, which models polarization induced by scattering off free electrons and dust grains. We model a variety of regions in AGNs. Results. We find that the shape of the funnel of the dusty torus has a significant impact on the polarization efficiency. A compact torus with a steep inner surface scatters …

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Setting Ubvri Photometric Zero-Points Using Sloan Digital Sky Survey Ugriz Magnitudes, Taylor S. Chonis, C. Martin Gaskell

C. Martin Gaskell Publications

We discuss the use of Sloan Digital Sky Survey (SDSS) ugriz point-spread function (PSF) photometry for setting the zero points of UBVRI CCD images. From a comparison with the Landolt (1992) standards and our own photometry we find that there is a fairly abrupt change in B, V, R, & I zero points around g, r, i ~ 14.5, and in the U zero point at u ~ 16. These changes correspond to where there is significant interpolation due to saturation in the SDSS PSF fluxes. There also seems to be another, much smaller systematic effect for stars with g,r …

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X-Ray/Ultraviolet Observing Campaign Of The Markarian 279 Active Galactic Nucleus Outflow: A Close Look At The Absorbing/Emitting Gas With Chandra-Letgs, E. Costantini, Jelle S. Kaastra, Nahum Arav, Gerard A. Kriss, K. C. Steenbrugge, Jack R. Gabel, F. Verbunt, Ehud Behar, C. Martin Gaskell, Kirk T. Korista, Daniel Proga, Jessica Kim-Quijano, J. E. Scott, Elizabeth S. Klimek, C. H. Hedrick

C. Martin Gaskell Publications

We present a Chandra-LETGS observation of the Seyfert 1 galaxy Mrk 279. This observation was carried out simultaneously with HST-STIS and FUSE, in the context of a multi-wavelength study of this source. The Chandra pointings were spread over ten days for a total exposure time of ~360 ks. The maximal continuum flux variation is of the order of 30%. The spectrum of Mrk 279 shows evidence of broad emission features, especially at the wavelength of the OVII triplet. We quantitatively explore the possibility that this emission is produced in the broad line region (BLR). We modeled the broad UV …

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Chemical Abundances In An Agn Environment: X-Ray/Uv Campaign On The Markarian 279 Outflow, Nahum Arav, Jack R. Gabel, Kirk T. Korrista, Jelle S. Kaastra, Gerard A. Kriss, Ehud Behar, Elisa Constantini, C. Martin Gaskell, Ari Laor, C. Nalaka Kodituwakku, Daniel Proga, Masao Sako, Jennifer E. Scott, Katrien C. Steenbrugge

C. Martin Gaskell Publications

We present the first reliable determination of chemical abundances in an active galactic nucleus (AGN) outflow. The abundances are extracted from the deep and simultaneous Far Ultraviolet Spectroscopic Explorer (FUSE) and Hubble Space Telescope (HST ) STIS observations of Mrk 279. This data set is exceptional for its high signal-to-noise ratio, unblended doublet troughs, and little Galactic absorption contamination. These attributes allow us to solve for the velocity-dependent covering fraction and therefore obtain reliable column densities for many ionic species. For the first time, we have enough such column densities to simultaneously determine the ionization equilibrium and abundances in the …

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Hubble Space Telescope Ultraviolet Spectroscopy Of 14 Low-Redshift Quasars, Rajib Ganguly, Michael S. Brotherton, Nahum Arav, Sara R. Heap, Lutz Wisotzki, Thomas L. Aldcroft, Danielle Alloin, Ehud Behar, Gabriela Canalizo, D. Michael Crenshaw, Martijn De Kool, Kenneth Chambers, Gerald Cecil, Eleni Chatzichristou, John Everett, Jack R. Gabel, C. Martin Gaskell, Emmanuel Galliano, Richard F. Green, Patrick B. Hall, Dean C. Hines, Vesa T. Junkkarinen, Jelle S. Kaastra, Mary Elizabeth Kaiser, Demosthenes Kazanas, Arieh Konigl, Kirk T. Korista, Gerard A. Kriss, Ari Laor, Karen M. Leighly, Smita Mathur, Patrick Ogle, Daniel Proga, Bassem Sabra, Ran Sivron, Stephanie A. Snedden, Randal Telfer, Marianne Vestergaard

C. Martin Gaskell Publications

We present low-resolution ultraviolet spectra of 14 low-redshift (z_em ≤ 0:8) quasars observed with the Hubble Space Telescope STIS as part of a Snapshot project to understand the relationship between quasar outflows and luminosity. By design, all observations cover the C iv emission line. Ten of the quasars are from the Hamburg-ESO catalog, three are from the Palomar-Green catalog, and one is from the Parkes catalog. The sample contains a few interesting quasars, including two broad absorption line (BAL) quasars (HE 0143-3535 and HE 0436-2614), one quasar with a mini-BAL (HE 1105-0746), and one quasar with associated narrow absorption …

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Agn Polarization Modeling With Stokes, René W. Goosmann, C. Martin Gaskell

C. Martin Gaskell Publications

We introduce a new, publicly available Monte Carlo radiative transfer code, STOKES, which has been developed to model polarization induced by scattering off free electrons and dust grains. It can be used in a wide range of astrophysical applications. Here, we apply it to model the polarization produced by the equatorial obscuring and scattering tori assumed to exist in active galactic nuclei (AGNs). We present optical/UV modeling of dusty tori with a curved inner shape and for two different dust types: one composition reproduces extinction properties of our Galaxy, and the other is derived from composite quasar spectra. The polarization …

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Modeling The Polarization Of Dusty Scattering Cones In Active Galactic Nuclei, René W. Goosmann, C. Martin Gaskell, Masatoshi Shoji

C. Martin Gaskell Publications

We have used the STOKES radiative transfer code, to model polarization induced by dust scattering in the polar regions of Active Galactic Nuclei (AGN). We discuss the wavelength-dependence of the spectral intensity and polarization over the optical/UV range at different viewing angles for two different types of dust: a Galactic dust model, and a dust model inferred from extinction properties of AGN.

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Modeling Optical And Uv Polarization Of Agnsi. Imprints Of Individual Scattering Regions, René W. Goosmann, C. Martin Gaskell

C. Martin Gaskell Publications

Context. Spectropolarimetry of AGNs is a powerful tool for studying the structure and kinematics of the inner regions of quasars. Aims. We wish to investigate the effects of various AGN scattering region geometries on the polarized flux. Methods. We introduce a new, publicly available Monte Carlo radiative transfer code, stokes, which models polarization induced by scattering off free electrons and dust grains. We model a variety of regions in AGNs. Results. We find that the shape of the funnel of the dusty torus has a significant impact on the polarization efficiency. A compact torus with a steep inner surface scatters …

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Full-Text Articles in Physical Sciences and Mathematics

The Case For Optically Thick High-Velocity Broad-Line Region Gas In Active Galactic Nuclei, Stephanie A. Snedden, C. Martin Gaskell

C. Martin Gaskell Publications

Agn Reddening And Ultraviolet Extinction Curves From Hubble Space Telescope Spectra, C. Martin Gaskell, C. Martin Gaskell

C. Martin Gaskell Publications

Discovery Of Polarization Reverberation In Ngc 4151, C. Martin Gaskell, René W. Goosmann, Nelly I. Merkulova, Nikolay M. Shakhovskoy, Masatoshi Shoji

C. Martin Gaskell Publications

Ngc 5548: The Agn Energy Budget Problem And The Geometry Of The Broad-Line Region And Torus, C. Martin Gaskell, Elizabeth S. Klimek, Ludmila S. Nazarova

C. Martin Gaskell Publications

Transformations Between 2mass, Sdss And Bvri Photometric Systems: Bridging The Near Infrared And Optical, S. Bilir, S. Ak, S. Karaali, A. Cabrera-Lavers, T. S. Chonis, C. Martin Gaskell

C. Martin Gaskell Publications

Modeling Optical And Uv Polarization Of Agns I. Imprints Of Individual Scattering Regions, René W. Goosmann, C. Martin Gaskell

C. Martin Gaskell Publications

Setting Ubvri Photometric Zero-Points Using Sloan Digital Sky Survey Ugriz Magnitudes, Taylor S. Chonis, C. Martin Gaskell

C. Martin Gaskell Publications

C. Martin Gaskell Publications

C. Martin Gaskell Publications

C. Martin Gaskell Publications

Agn Polarization Modeling With Stokes, René W. Goosmann, C. Martin Gaskell

C. Martin Gaskell Publications

Modeling The Polarization Of Dusty Scattering Cones In Active Galactic Nuclei, René W. Goosmann, C. Martin Gaskell, Masatoshi Shoji

C. Martin Gaskell Publications

Modeling Optical And Uv Polarization Of Agnsi. Imprints Of Individual Scattering Regions, René W. Goosmann, C. Martin Gaskell

C. Martin Gaskell Publications