Jack Raymond Gabel

Simultaneous Ultraviolet and X-Ray Observations of Seyfert Galaxy NGC 4151. I. Physical Conditions in the X-Ray Absorbers

We present a detailed analysis of the intrinsic X-ray absorption in the Seyfert 1 galaxy NGC 4151 using Chandra High Energy Transmission Grating Spectrometer data obtained in 2002 May as part of a program that included simultaneous ultraviolet (UV) spectra using the Hubble Space Telescope Space Telescope Imaging Spectrograph and the Far Ultraviolet Spectrographic Explorer. Previous studies, most recently using Advanced Satellite for Cosmology and Astrophysics (ASCA) spectra, revealed a large (>1022 cm-2) column of intervening gas, which has varied both in ionization state and total column density. NGC 4151 was in a relatively low flux state during the observations reported here (~25% of its historic maximum), although roughly 2.5 times as bright in the 2-10 keV band as during a Chandra observation in 2000. At both epochs, the soft X-ray band was dominated by emission lines, which show no discernible variation in flux between the two observations. The 2002 Chandra data show the presence of a very highly ionized absorber, in the form of H-like and He-like Mg, Si, and S lines, as well as lower ionization gas via the presence of inner-shell absorption lines from lower ionization species of these elements. The latter accounts for both the bulk of the soft X-ray absorption and the high covering factor UV absorption lines of O VI, C IV, and N V with outflow velocities ≈500 km s-1. The presence of high-ionization gas, which is not easily detected at low resolution (e.g., with ASCA), appears common among Seyfert galaxies. Since this gas is too highly ionized to be radiatively accelerated in sources such as NGC 4151, which is radiating at a small fraction of its Eddington Luminosity, it may be key to understanding the dynamics of mass outflow. We find that the deeper broadband absorption detected in the 2000 Chandra data is the result of both (1) lower ionization of the intervening gas due to the lower ionizing flux and (2) a factor of ~3 higher column density of the lower ionization component. To account for this bulk motion, we estimate that this component must have a velocity 1250 km s-1 transverse to our line of sight. This is consistent with the rotational velocity of gas arising from the putative accretion disk. While both thermal wind and magnetohydrodynamic models predict large nonradial motions, we suggest that the latter mechanism is more consistent with the results of the photoionization models of the absorbers

The host galaxies of narrow-line Seyfert 1 galaxies: Evidence for bar-driven fueling

We present a study of the host galaxy morphologies of narrow- and broad-line Seyfert 1 galaxies (NLS1s and BLS1s) based on broadband optical images from the Hubble Space Telescope archives. We find that large-scale stellar bars, starting at ~1 kpc from the nucleus, are much more common in NLS1s than BLS1s. Furthermore, the fraction of NLS1 spirals that have bars increases with decreasing full width at half-maximum of the broad component of Hβ. These results suggest a link between the large-scale bars, which can support high fueling rates to the inner kiloparsecs, and the high mass accretion rates associated with the supermassive black holes in NLS1s.

X-RAY/ULTRAVIOLET OBSERVING CAMPAIGN OF THE MARKARIAN 279 ACTIVE GALACTIC NUCLEUS OUTFLOW: A GLOBAL-FITTING ANALYSIS OF THE ULTRAVIOLET ABSORPTION

We present an analysis of the intrinsic UV absorption in the Seyfert 1 galaxy Mrk 279 based on simultaneous long observations with the Hubble Space Telescope (41 ks) and the Far Ultraviolet Spectroscopic Explorer (91 ks). To extract the line-of-sight covering factors and ionic column densities, we separately fit two groups of absorption lines: the Lyman series and the CNO lithium-like doublets. For the CNO doublets we assume that all three ions share the same covering factors. The fitting method applied here overcomes some limitations of the traditional method using individual doublet pairs; it allows for the treatment of more complex, physically realistic scenarios for the absorption-emission geometry and eliminates systematic errors that we show are introduced by spectral noise. We derive velocity-dependent solutions based on two models of geometrical covering: a single covering factor for all background emission sources, and separate covering factors for the continuum and emission lines. Although both models give good statistical fits to the observed absorption, we favor the model with two covering factors because (1) the best-fit covering factors for both emission sources are similar for the independent Lyman series and CNO doublet fits; (2) the fits are consistent with full coverage of the continuum source and partial coverage of the emission lines by the absorbers, as expected from the relative sizes of the nuclear emission components; and (3) it provides a natural explanation for variability in the Lyα absorption detected in an earlier epoch. We also explore physical and geometrical constraints on the outflow from these results.We present an analysis of the intrinsic UV absorption in the Seyfert 1 galaxy Mrk 279 based on simultaneous long observations with the Hubble Space Telescope (41 ks) and the Far Ultraviolet Spectroscopic Explorer (91 ks). To extract the line-of-sight covering factors and ionic column densities, we separately fit two groups of absorption lines: the Lyman series and the CNO lithium-like doublets. For the CNO doublets we assume that all three ions share the same covering factors. The fitting method applied here overcomes some limitations of the traditional method using individual doublet pairs; it allows for the treatment of more complex, physically realistic scenarios for the absorption-emission geometry and eliminates systematic errors that we show are introduced by spectral noise. We derive velocity-dependent solutions based on two models of geometrical covering – a single covering factor for all background emission sources, and separate covering factors for the continuum and emission lines. Although both models give good statistical fits to the observed absorption, we favor the model with two covering factors because: (a) the best-fit covering factors for both emission sources are similar for the independent Lyman series and CNO doublet fits; (b) the fits are consistent with full coverage of the continuum source and partial coverage of the emission lines by the absorbers, as expected from the relative sizes of the nuclear emission components; and (c) it provides a natural explanation for variability in the Lyα absorption detected in an earlier epoch. We also explore physical and geometrical constraints on the outflow from these results. Subject headings: galaxies: individual (Mrk 279) — galaxies: active — galaxies: Seyfert — ultraviolet: galaxies

Chemical Abundances in an AGN Environment: X-Ray/UV Campaign on the Markarian 279 Outflow*

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 flow. Our analysis uses the full spectral information embedded in these high-resolution data. Slicing a given trough into many independent outflow elements yields the extra constraints needed for a physically meaningful abundance determination. We find that relative to solar, the abundances in the Mrk 279 outflow are (linear scaling) carbon 2.2 ± 0.7, nitrogen 3.5 ± 1.1, and oxygen 1.6 ± 0.8. Our UV-based photoionization and abundance results are in good agreement with the independent analysis of the simultaneous Mrk 279 X-ray spectra. This is the best agreement between the UV and X-ray analyses of the same outflow to date.

The Ionized Gas and Nuclear Environment in NGC 3783. II. Averaged Hubble Space Telescope/STIS and Far Ultraviolet Spectroscopic Explorer Spectra

We present observations of the intrinsic absorption in the Seyfert 1 galaxy NGC 3783 obtained with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope and the Far Ultraviolet Spectroscopic Explorer (FUSE). We have combined 18 STIS and five FUSE observations to obtain a high signal-to-noise ratio averaged spectrum spanning 905-1730 A. The averaged spectrum reveals absorption in O VI, N V, C IV, N III, C III, and the Lyman lines up to Ly in the three blueshifted kinematic components previously detected in the STIS spectrum (at radial velocities of -1320, -724, and -548 km s-1). The highest velocity component exhibits absorption in Si IV. We also detect metastable C III in this component, indicating a high density in this absorber. No lower ionization lines, i.e., C II and Si II, are detected. A weak, fourth absorption component is tentatively detected in the high-ionization lines and Lyα and Lyβ at a radial velocity of -1027 km s-1. The Lyman lines reveal a complex absorption geometry. The strength of the higher order lines indicates that Lyα and Lyβ are saturated over much of the resolved profiles in the three strongest absorption components and that, therefore, their observed profiles are determined by the covering factor. We separate the individual covering factors of the continuum and emission-line sources as a function of velocity in each kinematic component using the Lyα and Lyβ lines. The covering factor of the broad-line region is found to vary dramatically between the cores of the individual kinematic components, ranging from 0 to 0.84. In addition, we find that the continuum covering factor varies with velocity within the individual kinematic components, decreasing smoothly in the wings of the absorption by at least 60%. Comparison of the effective covering factors derived from the H I results with those determined directly from the doublets reveals that the covering factor of Si IV is less than half that of H I and N V in the high-velocity component. In addition, the FWHMs of N III and Si IV are narrower than those of the higher ionization lines in this component. These results indicate there is substructure within this absorber. We also find evidence for structure in the column density profiles of the high-ionization lines in this component. We derive a lower limit on the total column (NH ≥ 1019 cm-2) and ionization parameter (U ≥ 0.005) in the low-ionization subcomponent of this absorber. The metastable-to-total C III column density ratio implies ne ≈ 109 cm-3 and an upper limit on the distance of the absorber from the ionizing continuum of R ≤ 8 × 1017 cm. The decreasing covering factor found in the wings of the absorption and the extreme compactness of the C III* absorber are suggestive of a clumpy absorption gas with a low volume filling factor.We present observations of the intrinsic absorption in the Seyfert 1 galaxy NGC 3783 obtained with the STIS/HST and FUSE. We have coadded multiple STIS and FUSE observations to obtain a high S/N averaged spectrum spanning 905-1730 A. The averaged spectrum reveals absorption in O VI, N V, C IV, N III, C III and the Lyman lines up to LyE in the three blueshifted kinematic components previously detected in the STIS spectrum (at radial velocities of -1320, -724, and -548 km/s). The highest velocity component exhibits absorption in Si IV. We also detect metastable C III* in this component, indicating a high density in this absorber. We separate the individual covering factors of the continuum and emission-line sources as a function of velocity in each kinematic component using the LyA and LyB lines. Additionally, we find that the continuum covering factor varies with velocity within the individual kinematic components, decreasing smoothly in the wings of the absorption by at least 60%. The covering factor of Si IV is found to be less than half that of H I and N V in the high velocity component. Additionally, the FWHM of N III and Si IV are narrower than the higher ionization lines in this component. These results indicate there is substructure within this absorber. We derive a lower limit on the total column (N_H>=10^{19}cm^{-2}) and ionization parameter (U>=0.005) in the low ionization subcomponent of this absorber. The metastable-to-total C III column density ratio implies n_e~10^9 cm^{-3} and an upper limit on the distance of the absorber from the ionizing continuum of R<=8x10^{17} cm.

The Ionized Gas and Nuclear Environment in NGC 3783. V. Variability and Modeling of the Intrinsic Ultraviolet Absorption

We present results on the location, physical conditions, and geometry of the outflow in the Seyfert 1 galaxy NGC 3783 from a study of the variable intrinsic UV absorption. Based on analysis of 18 observations with the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope and 6 observations with the Far Ultraviolet Spectroscopic Explorer obtained between 2000 February and 2002 January, we obtain the following results: 1) The lowest-ionization species detected in each of the three strong kinematic components (components 1 – 3 at radial velocities −1350, −550, and −725 km s −1 , respectively) varied, with equivalent widths inversely correlated with the continuum flux. This indicates the ionization structure in the absorbers responded to changes in the photoionizing flux, with variations occurring over the weekly timescales sampled by our observations. 2) A multi-component model of the line-of-sight absorption covering factors, which includes an unocculted narrow emission-line region (NLR) and separate covering factors derived for the broad line region and continuum emission sources, predicts saturation in several lines, consistent with the lack of observed variability in these lines. Differences in covering factors and kinematic structure imply component 1 is comprised of two physically distinct regions (1a and 1b). 3) We obtain column densities for the individual metastable levels from the resolved C III* λ1175 absorption complex in component 1a. Based on our computed metastable level populations, the electron density of this absorber is ∼ 3×10 4 cm −3 . Combined with photoionization modeling results, this places component 1a at ∼ 25 pc from the central source. 5) Using time-dependent calculations, we are able to reproduce the detailed variability observed in component 1 and derive upper limits on the distances for components 2 and 3 of ≤ 25 and ≤ 50 pc, respectively. 6) The ionization parameters derived for the higher ionization UV absorbers (components 1b, 2, and 3 with log(U)≈ −0.5) are consistent with the modeling results for the lowest-ionization X-ray component, but with smaller total column density. The high-ionization UV components are found to have similar pressures as the three X-ray ionization components. These results are consistent with an inhomogeneous wind model for the outflow in NGC 3783, with denser, colder, lower-ionization regions embedded in more highly-ionized gas. 7) Based on the predicted emission-line luminosities, global covering factor constraints, and distances derived for the UV absorbers, they may be identified with emission-line gas observed in the inner NLR of AGNs. We explore constraints for dynamical models of AGN outflows implied by these results. Subject headings: galaxies: individual (NGC 3783) — galaxies: active — galaxies: Seyfert — ultraviolet: galaxies

X-ray/ultraviolet observing campaign of the Markarian 279 active galactic nucleus outflow: a close look at the absorbing/emitting gas with Chandra-LETGS

We present a Chandra-LETGS observation of the Seyfert 1 galaxy Mrk 279. This observation was simultaneous with HST-STIS and FUSE observations, in the context of a multiwavelength study of this source. The data also allow for the presence of intermediate ionization components. The distribution of the column densities of such extra components as a function of the ionization parameter is not consistent with a continuous, power-law like, absorber, suggesting a complex structure for the gas outflow for Mrk 279.

The kinematics and physical conditions of the ionized gas in markarian 509. I. Chandra high energy grating spectroscopy

We observed the Seyfert 1 galaxy Mrk 509 for ~59 ks with the Chandra high-energy transmission gratings, simultaneously with HST/STIS and RXTE. Here we present a detailed analysis of the soft X-ray spectrum observed with Chandra. We measure strong absorption lines from He-like Ne and Mg and from H-like N, O, and Ne. Weaker absorption lines may also be present. The lines are unresolved except for Ne X Lyα (λ12.134) and Ne IX 1s2-1s2p (λ13.447), which appear to be marginally resolved. The profiles are blueshifted with respect to the systemic velocity of Mrk 509, indicating an outflow of ~-200 km s-1. There is also a hint that the profiles may have a velocity component near systemic. The soft X-ray spectrum can be described in remarkable detail with a simple, single-zone photoionized absorber having an equivalent neutral hydrogen column density of 2.06 × 1021cm-2 and an ionization parameter of log ξ = 1.76 (or log U = 0.27). Although the photoionized gas almost certainly is comprised of matter in more than one ionization state and may consist of several kinematic components, data with better spectral resolution and signal-to-noise ratio would be required to justify a more complex model. The UV data, on the other hand, have a velocity resolution of ~10 km s-1 and can easily detect eight kinematic components, covering roughly the same velocities as the X-ray absorption profiles. Even though the X-ray and UV absorbers share the same velocity space, the UV absorbers have a much smaller column density and ionization state. We show that models of the X-ray data do not predict significant UV absorption and are therefore consistent with the UV data. Finally, we do not detect any soft X-ray emission lines.

X-Ray/Ultraviolet Campaign on the Mrk 279 AGN Outflow: Constraining Inhomogeneous Absorber Models

We investigate the applicability of inhomogeneous absorber models in the formation of active galactic nucleus outflow absorption troughs. The models we explore are limited to monotonic gradients of absorbing column densities in front of a finite emission source. Our main finding is that simple power-law and Gaussian distributions are hard-pressed to fit the Mrk 279 high-quality UV outflow data. An acceptable fit for the O VI troughs can only be obtained by assuming unrealistic optical depth values (upward of 100). The strongest constraints arise from the attempt to fit the Lyman series troughs. In this case it is evident that even allowing for complete freedom of both the power-law exponent and the optical depth as a function of velocity cannot yield an acceptable fit. In contrast, partial covering models do yield good fits for the Lyman series troughs. We conclude that monotonic inhomogeneous absorber models that do not include a sharp edge in the optical depth distribution across the source are not an adequate physical model to explain the trough formation mechanism for the outflow observed in Mrk 279.

The AGN Outflow in the HDF-S Target QSO J2233–606 from a High-Resolution VLT UVES Spectrum*

We present a detailed analysis of the intrinsic UV absorption in the central HDF-S target QSO J2233-606, based on a high-resolution, high-S/N (~25-50) spectrum obtained with VLT UVES. This spectrum samples the cluster of intrinsic absorption systems outflowing from the AGN at radial velocities v ≈ -5000 to -3800 km s-1 in the key far-UV diagnostic lines: the lithium-like CNO doublets and H I Lyman series. We fit the absorption troughs using a global model of all detected lines to solve for the independent velocity-dependent covering factors of the continuum and emission-line sources and ionic column densities. This reveals increasing covering factors in components with greater outflow velocity. Narrow substructure is revealed in the optical depth profiles, suggesting that the relatively broad absorption is comprised of a series of multiple components. We perform velocity-dependent photoionization modeling, which allows a full solution to the C, N, and O abundances, as well as the velocity-resolved ionization parameter and total column density. The absorbers are found to have supersolar abundances, with [C/H] and [O/H] ≈ 0.5-0.9, and [N/H] ≈ 1.1-1.3, consistent with enhanced nitrogen production expected from secondary nucleosynthesis processes. Independent fits to each kinematic component give consistent results for the abundances. The lowest ionization material in each of the strong absorbers is modeled with similar ionization parameters. Components of higher ionization (indicated by stronger O VI relative to C IV and N V) are present at velocities just redward of each low-ionization absorber. We explore the implications of these results for the kinematic-geometric-ionization structure of the outflow.