Browsing by Author "Bautista, M. A."

Now showing 1 - 9 of 9
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    Galactic-scale absorption outflow in the low-luminosity quasar IRAS F04250-5718: Hubble Space Telescope/Cosmic Origins Spectrograph observations
    Edmonds, Douglas; Borguet, Benoit; Arav, Nahum; Dunn, Jay P.; Penton, S.; Kriss, G. A.; Korista, K. T.; Costantini, E.; Steenbrugge, K. C.; Gonzalez-Serrano, J. I.; Aoki, K.; Bautista, M. A.; Behar, E.; Benn, C.; Crenshaw, D. M.; Everett, J.; Gabel, J.; Kaastra, J.; Moe, M.; Scott, J. (IOP Publishing Ltd., 2011-09)
    We present absorption line analysis of the outflow in the quasar IRAS F04250-5718. Far-ultraviolet data from the Cosmic Origins Spectrograph on board the Hubble Space Telescope reveal intrinsic narrow absorption lines from high ionization ions (e. g., C IV, N V, and O VI) as well as low ionization ions (e. g., C II and Si III). We identify three kinematic components with central velocities ranging from similar to-50 to similar to-230 km s(-1). Velocity-dependent, non-black saturation is evident from the line profiles of the high ionization ions. From the non-detection of absorption from a metastable level of C II, we are able to determine that the electron number density in the main component of the outflow is less than or similar to 30 cm(-3). Photoionization analysis yields an ionization parameter log U-H similar to -1.6 +/- 0.2, which accounts for changes in the metallicity of the outflow and the shape of the incident spectrum. We also consider solutions with two ionization parameters. If the ionization structure of the outflow is due to photoionization by the active galactic nucleus, we determine that the distance to this component from the central source is greater than or similar to 3 kpc. Due to the large distance determined for the main kinematic component, we discuss the possibility that this outflow is part of a galactic wind.
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    Ionization-driven Fragmentation of Gas Outflows Responsible for FeLoBALs in Quasars
    Bautista, M. A.; Dunn, Jay P. (IOP PUBLISHING LTD, 2010-07)
    We show that time variations in the UV ionizing continuum of quasars, on scales of similar to 1 yr, affect the dynamic structure of the plasmas responsible for low-ionization broad absorption lines. Variations of the ionizing continuum produce non-equilibrium photoionization conditions over a significant fraction of the absorbing clouds and supersonically moving ionization fronts. When the flux drops, the contraction of the ionized region drives a supersonic cooling front toward the radiation source and a rarefaction wave in the opposite direction. The pressure imbalance is compensated by an increased speed of the cool gas relative to the front. When the flux recovers, the cool gas is re-ionized and re-heated by a supersonic ionization front traveling away from the radiation source and a forward shock is created. The re-heated clouds equilibrate to a temperature of similar to 10(4) K and are observed to have different radial velocities than the main cloud. Such fragmentation seems consistent with the multicomponent structure of troughs seen in some objects. The velocity differences measured among various components in the quasars QSO 2359-1241 and SDSS J0318-0600 can be reproduced by our model if strong magnetic fields (similar to 10 mG) are present within the clouds.
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    Nitrogen K-Shell Photoabsorption
    Garcia, J.; Kallman, T. R.; Witthoeft, M.; Behar, E.; Mendoza, C.; Palmeri, P.; Quinet, P.; Bautista, M. A.; Klapisch, M. (IOP PUBLISHING LTD, 2009-12)
    Reliable atomic data have been computed for the spectral modeling of the nitrogen K lines, which may lead to useful astrophysical diagnostics. Data sets comprise valence and K-vacancy level energies, wavelengths, Einstein A-coefficients, radiative and Auger widths, and K-edge photoionization cross sections. An important issue is the lack of measurements that are usually employed to fine-tune calculations so as to attain spectroscopic accuracy. In order to estimate data quality, several atomic structure codes are used and extensive comparisons with previous theoretical data have been carried out. In the calculation of K photoabsorption with the Breit-Pauli R-matrix method, both radiation and Auger dampings, which cause the smearing of the K edge, are taken into account. This work is part of a wider project to compute atomic data in the X-ray regime to be included in the database of the popular XSTAR modeling code.
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    Physical Conditions in Quasar Outflows: Very Large Telescope Observations of QSO 2359-1241
    Korista, K. T.; Bautista, M. A.; Arav, Nahum; Moe, Maxwell; Costantini, E.; Benn, C. (IOP PUBLISHING LTD, 2008-11)
    We analyze the physical conditions of the outflow seen in QSO 2359-1241 (NVSS J235953-124148), based on high-resolution spectroscopic VLT observations. This object was previously studied using Keck HIRES data. The main improvement over the HIRES results is our ability to accurately determine the number density of the outflow. For the major absorption component, the populations from five different Fe II excited levels yield a gas density n(H) = 10(4.4) cm(-3) with less than 20% scatter. We find that the Fe II absorption arises from a region with roughly constant conditions and temperature greater than 9000 K, before the ionization front where temperature and electron density drop. Further, we model the observed spectra and investigate the effects of varying gas metallicities and the spectral energy distribution of the incident ionizing radiation field. The accurately measured column densities allow us to determine the ionization parameter (log U-H approximate to -2.4) and total column density of the outflow [log N-H(cm(-2)) approximate to 20.6]. Combined with the number density finding, these are stepping stones toward determining the mass flux and kinetic luminosity of the outflow, and therefore its importance to AGN feedback processes.
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    Quasar Outflow Contribution to AGN Feedback: Observations of QSO SDSS J0838+2955
    Moe, Maxwell; Arav, Nahum; Bautista, M. A.; Korista, K. T. (IOP PUBLISHING LTD, 2009-11)
    We present a detailed analysis of the Astrophysical Research Consortium 3.5 m telescope spectrum of QSO SDSS J0838+2955. The object shows three broad absorption line (BAL) systems at 22,000, 13,000, and 4900 km s(-1) blueshifted from the systemic redshift of z = 2.043. Of particular interest is the lowest velocity system that displays absorption from low-ionization species such as MgII, Al II, Si II, Si II*, Fe II, and Fe II*. Accurate column densities were measured for all transitions in this lowest velocity BAL using an inhomogeneous absorber model. The ratio of column densities of Si II* and Fe II* with respect to their ground states gave an electron number density of log n(e) (cm(-3)) = 3.75 +/- 0.22 for the outflow. Photoionization modeling with careful regards to chemical abundances and the incident spectral energy distribution predicts an ionization parameter of log U(H) = -1.93 +/- 0.21 and a hydrogen column density of log N(H) (cm(-2)) = 20.80 +/- 0.28. This places the outflow at 3.3(-1.0)(+1.5) kpc from the central active galactic nucleus (AGN). Assuming that the fraction of solid angle subtended by the outflow is 0.2, these values yield a kinetic luminosity of (4.5(-1.8)(+3.1)) x 10(45) erg s(-1), which is (1.4(-0.6))% the bolometric luminosity of the QSO itself. Such large kinetic luminosity suggests that QSO outflows are a major contributor to AGN feedback mechanisms.
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    The quasar outflow contribution to AGN feedback: VLT measurements of SDSS J0318-0600
    Dunn, Jay P.; Bautista, M. A.; Arav, Nahum; Moe, Maxwell; Korista, K. T.; Costantini, E.; Benn, C.; Ellison, S.; Edmonds, Douglas (IOP Publishing Ltd., 2010-02)
    We present high spectral resolution Very Large Telescope observations of the broad absorption line quasar SDSS J0318-0600. This high-quality data set allows us to extract accurate ionic column densities and determine an electron number density of n(e) = 10(3.3 +/- 0.2) cm(-3) for the main outflow absorption component. The heavily reddened spectrum of SDSS J0318-0600 requires purely silicate dust with a reddening curve characteristic of predominately large grains, from which we estimate the bolometric luminosity. We carry out photoionization modeling to determine the total column density, ionization parameter, and distance of the gas and find that the photoionization models suggest abundances greater than solar. Due to the uncertainty in the location of the dust extinction, we arrive at two viable distances for the main ouflow component from the central source, 6 and 17 kpc, where we consider the 6 kpc location as somewhat more physically plausible. Assuming the canonical global covering of 20% for the outflow and a distance of 6 kpc, our analysis yields a mass flux of 120 M(circle dot) yr(-1) and a kinetic luminosity that is similar to 0.1% of the bolometric luminosity of the object. Should the dust be part of the outflow, then these values are similar to 4x larger. The large mass flux and kinetic luminosity make this outflow a significant contributor to active galactic nucleus feedback processes.
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    Radiative and Auger Decay Data for Modeling Nickel K Lines
    Palmeri, P.; Quinet, P.; Mendoza, C.; Bautista, M. A.; Garcia, J.; Witthoeft, M. C.; Kallman, T. R. (IOP PUBLISHING LTD, 2008-12)
    Radiative and Auger decay data have been calculated for modeling the K lines in ions of the nickel isonuclear sequence, from Ni(+) up to Ni(27+). Level energies, transition wavelengths, radiative transition probabilities, and radiative and Auger widths have been determined using Cowan's Hartree-Fock with relativistic corrections (HFR) method. Auger widths for the third-row ions (Ni(+)-Ni(10+)) have been computed using single-configuration average (SCA) compact formulae. Results are compared with data sets computed with the AUTOSTRUCTURE and MCDF atomic structure codes and with available experimental and theoretical values, mainly in highly ionized ions and in the solid state.
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    Radiative transition rates and collision strengths for Si II
    Bautista, M. A.; Quinet, P.; Palmeri, P.; Badnell, N. R.; Dunn, J.; Arav, Nahum (EDP SCIENCES, 2009-12)
    Aims. This work reports on radiative transition rates and electron impact excitation collision strengths for levels of the 3s(2)3p, 3s3p(2), 3s(2)4s, and 3s(2)3d configurations of Si II. Methods. The radiative data were computed using the Thomas-Fermi-Dirac-Amaldi central potential, but with the modifications introduced by Bautista (2008) that account for the effects of electron-electron interactions. We also introduce new schemes for the optimization of the variational parameters of the potential. Additional calculations were carried out with the Relativistic Hartree-Fock and the multiconfiguration Dirac-Fock methods. Collision strengths in LS-coupling were calculated in the close coupling approximation with the R-matrix method. Then, fine structure collision strengths were obtained by means of the intermediate-coupling frame transformation (ICFT) method which accounts for spin-orbit coupling effects. Results. We present extensive comparisons between the results of different approximations and with the most recent calculations and experiments available in the literature. From these comparisons we derive a recommended set of g f-values and radiative transition rates with their corresponding estimated uncertainties. We also study the effects of different approximations in the representation of the target ion on the electron-impact collision strengths. Our most accurate set of collision strengths were integrated over a Maxwellian distribution of electron energies and the resulting effective collision strengths are given for a wide range of temperatures. Our results present significant differences from recent calculations with the B-spline non-orthogonal R-matrix method. We discuss the sources of the differences.
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    Spectrum Synthesis Modeling of the X-Ray Spectrum of GRO J1655-40 Taken During the 2005 Outburst
    Kallman, T. R.; Bautista, M. A.; Goriely, S.; Mendoza, C.; Miller, J. M.; Palmeri, P.; Quinet, P.; Raymond, J. (IOP PUBLISHING LTD, 2009-08)
    The spectrum from the black hole X-ray transient GRO J1655-40 obtained using the Chandra High Energy Transmission Grating in 2005 is notable as a laboratory for the study of warm absorbers, and for the presence of many lines from odd-Z elements between Na and Co ( and Ti and Cr) not previously observed in X-rays. We present synthetic spectral models which can be used to constrain these element abundances and other parameters describing the outflow from the warm absorber in this object. We present results of fitting to the spectrum using various tools and techniques, including automated line fitting, phenomenological models, and photoionization modeling. We show that the behavior of the curves of growth of lines from H-like and Li-like ions indicate that the lines are either saturated or affected by filling-in from scattered or a partially covered continuum source. We confirm the conclusion of previous work by Miller et al., which shows that the ionization conditions are not consistent with wind driving due to thermal expansion. The spectrum provides the opportunity to measure abundances for several elements not typically observable in the X-ray band. These show a pattern of enhancement for iron peak elements, and solar or subsolar values for elements lighter than calcium. Models show that this is consistent with enrichment by a core-collapse supernova. We discuss the implications of these values for the evolutionary history of this system.