Browsing by Author "Korista, K. T."

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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    Mass Outflow in the Seyfert 1 Galaxy NGC 5548
    Crenshaw, D. M.; Kraemer, S. B.; Schmitt, H. R.; Kaastra, J. S.; Arav, Nahum; Gabel, J. R.; Korista, K. T. (IOP PUBLISHING LTD, 2009-06)
    We present a study of the intrinsic UV absorption and emission lines in an historically low-state spectrum of the Seyfert 1 galaxy NGC 5548, which we obtained in 2004 February at high spatial and spectral resolution with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. We isolate a component of emission with a width of 680 km s(-1) that arises from an "intermediate-line region" (ILR), similar to that we discovered in NGC 4151, at a distance of similar to 1 pc from the central continuum source. From a detailed analysis of the five intrinsic absorption components in NGC 5548 and their behavior over a span of eight years, we present evidence that most of the UV absorbers only partially cover the ILR and do not cover an extended region of UV continuum emission, most likely from hot stars in the circumnuclear region. We also find that four of the UV absorbers are at much greater distances (greater than 70 pc) than the ILR, and none have sufficient N V or C IV column densities to be the ILR in absorption. At least a portion of the UV absorption component 3, at a radial velocity of -530 km s(-1), is likely responsible for most of the X-ray absorption, at a distance less than 7 pc from the central source. The fact that we see the ILR in absorption in NGC 4151 and not in NGC 5548 suggests that the ILR is located at a relatively large polar angle (similar to 45 degrees) with respect to the narrow-line region outflow axis.
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    Measuring column densities in quasar outflows: VLT observations of QSO 2359-1241
    Arav, Nahum; Moe, Maxwell; Costantini, E.; Korista, K. T.; Benn, C.; Ellison, S. (IOP Publishing Ltd., 2008-07)
    We present high-resolution spectroscopic VLT observations of the outflow seen in QSO 2359-1241. These data contain absorption troughs from five resonance Fe II lines with a resolution of similar to 7 km s(-1) and a signal-to-noise ratio per resolution element of order 100. We use this unprecedented high-quality data set to investigate the physical distribution of the material in front of the source and by that to determine the column densities of the absorbed troughs. We find that the apparent optical depth model gives a very poor fit to the data and greatly underestimates the column density measurements. Power-law distributions and partial covering models give much better fits, with some advantage to power-law models, while both models yield similar column density estimates. The better fit of the power-law model solves a long-standing problem plaguing the partial covering model when applied to large distance scale outflow: how to obtain a velocity-dependent covering factor for an outflow situated at distances thousands of time greater than the size of the AGN emission source. This problem does not affect power-law models. Therefore, based on the better fit and plausibility of the physical model, we conclude that in QSO 2359-1241, the outflow covers the full extent of the emission source but in a nonhomogeneous way.
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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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    Space Telescope and Optical Reverberation Mapping Project. X. Understanding the Absorption-line Holiday in NGC 5548
    Dehghanian, M.; Ferland, G. J.; Kriss, G. A.; Peterson, B. M.; Mathur, S.; Mehdipour, M.; Guzman, F.; Chatzikos, M.; van Hoof, P. A. M.; Williams, R. J. R.; Arav, Nahum; Barth, A. J.; Bentz, M. C.; Bisogni, S.; Brandt, W. N.; Crenshaw, D. M.; Dalla Bonta, E.; De Rosa, G.; Fausnaugh, M. M.; Gelbord, J. M.; Goad, M. R.; Gupta, A.; Horne, Keith; Kaastra, J.; Knigge, C.; Korista, K. T.; McHardy, I. M.; Pogge, R. W.; Starkey, D. A.; Vestergaard, M. (2019-06-01)
    The Space Telescope and Optical Reverberation Mapping Project (AGN STORM) on NGC 5548 in 2014 is one of the most intensive multiwavelength AGN monitoring campaigns ever. For most of the campaign, the emission-line variations followed changes in the continuum with a time lag, as expected. However, the lines varied independently of the observed UV-optical continuum during a 60-70 day "holiday," suggesting that unobserved changes to the ionizing continuum were present. To understand this remarkable phenomenon and to obtain an independent assessment of the ionizing continuum variations, we study the intrinsic absorption lines present in NGC 5548. We identify a novel cycle that reproduces the absorption line variability and thus identify the physics that allows the holiday to occur. In this cycle, variations in this obscurer's line-of-sight covering factor modify the soft X-ray continuum, changing the ionization of helium Ionizing radiation produced by recombining helium then affects the level of ionization of some ions seen by the Hubble Space Telescope. In particular, high-ionization species are affected by changes in the obscurer covering factor, which does not affect the optical or UV continuum, and thus appear as uncorrelated changes, a "holiday." It is likely that any other model that selectively changes the soft X-ray part of the continuum during the holiday can also explain the anomalous emission-line behavior observed.
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    XMM-Newton RGS observation of the warm absorber in Mrk 279
    Ebrero, J.; Constantini, E.; Kaastra, J. S.; Detmers, R. G.; Arav, Nahum; Kriss, G. A.; Korista, K. T.; Steenbrugge, K. C. (EDP Sciences, 2010-09-10)
    Context. The Seyfert 1 galaxy Mrk 279 was observed by XMM-Newton in November 2005 on three consecutive orbits, showing significant short-scale variability (average soft band variation in flux ~20%). The source is known to host a two-component warm absorber with distinct ionisation states from a previous Chandra observation. Aims. We study the warm absorber in Mrk 279 and investigate any possible response to the short-term variations in the ionising flux and assess whether it has varied on a long-term timescale with respect to the Chandra observation. Methods. The XMM-Newton-RGS spectra of Mrk 279 were analysed in both the high- and low-flux states using the SPEX fitting package. Results. We find no significant changes in the warm absorber on either short timescales (~2 days) or longer ones (two and a half years), as the variations in the ionic column densities of the most relevant elements are below the 90% confidence level. The variations could still be present but are statistically undetected given the signal-to-noise ratio of the data. Starting from reasonable standard assumptions, we estimate the location of the absorbing gas, which is likely to be associated with the putative dusty torus rather than with the broad line region if the outflowing gas is moving at the escape velocity or greater.
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    XMM-Newton unveils the complex iron K alpha region of Mrk 279
    Costantini, E.; Kaastra, J. S.; Korista, K. T.; Ebrero, J.; Arav, Nahum; Kriss, G. A.; Steenbrugge, K. C. (EDP Sciences, 2010-03-04)
    We present the results of a similar to 160 ks-long XMM-Newton observation of the Seyfert 1 galaxy Mrk 279. The spectrum shows evidence of both broad and narrow emission features. The FeK alpha line may be equally well explained by a single broad Gaussian (FWHM similar to 10 000 km s(-1)) or by two components: an unresolved core plus a very broad profile (FWHM similar to 14 000 km s(-1)). For the first time we quantified, via the "locally optimally emitting cloud" model, the contribution of the broad line region (BLR) to the absolute luminosity of the broad component of the FeK alpha at 6.4 keV. We find that the contribution of the BLR is only similar to 3%. In the two-line component scenario, we also evaluated the contribution of the highly ionized gas component, which produces the Fe XXVI line in the iron K region. This contribution to the narrow core of the FeK alpha line is marginal <0.1%. Most of the luminosity of the unresolved, component of FeK alpha may come from the obscuring torus, while the very-broad associated component may come from the accretion disk. However, models of reflection by cold gas are difficult to test because of the limited energy band. The Fe XXVI line at 6.9 keV is consistent to be produced in a high column density (N(H) similar to 10(23) cm(-2)), extremely ionized (log xi similar to 5.5-7) gas. This gas may be a highly ionized outer layer of the torus.