Browsing by Author "Moe, Maxwell"

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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.