S. B. Kraemer

The Catholic University of America, Washington, Washington, D.C., United States

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Publications (234)605.87 Total impact

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    ABSTRACT: We report early observations with Space Telescope Imaging Spectrometer (STIS) of the nuclear region of NGC 4151. Direct images in [O II] and [O III] and slitless medium-dispersion spectral images of the Hβ to [O III] region were obtained. A slitless UV spectral image was taken of the C IV 1550 Å region. We present radial velocities and line ratios of ~40 clouds resolved in the narrow-line region (NLR). The kinematics suggest outflow within a biconical region about the nucleus, centered on the radio axis and viewed near the edge of the cones. A few high-velocity clouds are seen that do not fit this simple picture. Line ratios indicate that the NLR gas is photoionized by the central continuum source and that there may be a density gradient in the NLR. These observations are being followed by an extensive STIS program on NGC 4151.
    Full-text · Article · Jan 2009 · The Astrophysical Journal
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    ABSTRACT: Visual and ultraviolet spatially resolved (~01) spectra of SN 1987A obtained on days 3715 and 3743 with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope show that the high-velocity supernova debris is colliding with circumstellar gas. Very broad Lyα emission with velocities extending to ~±20,000 km s-1 originates inside the inner circumstellar ring and appears to fill most of the surface area within 067 ± 003 (0.14 pc at a distance of 50 kpc) of the ring's center. The observed Lyα flux from the shocked ejecta is (1.85±0.53) × 10−13 and (1.25±0.51) × 10−12 ergs cm-2 s-1 after correcting for extinction. A spatially unresolved blueshifted emission feature was discovered in Hα (and other lines) on the inner ring at position angle 31°±8°. The Hα emission extends to -250 km s-1 with no corresponding redshifted emission. This highly localized interaction appears to be the initial contact of the supernova blast wave with an inward protrusion of the inner ring. The broad Lyα emission and the "hot spot" are separate interaction phenomena associated with the reverse and forward shocks, respectively. We also find that the size of the inner ring in forbidden lines of oxygen has a dependence on ionization potential, in agreement with photoionization models of the ring.
    Full-text · Article · Jan 2009 · The Astrophysical Journal
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    ABSTRACT: We present optical long-slit spectroscopy of the nucleus of the nearby radio galaxy M84 (NGC 4374 = 3C 272.1) obtained with the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope. Our spectra reveal that the nuclear gas disk seen in the Wide Field Planetary Camera 2 imaging by Bower et al. is rotating rapidly. The velocity curve has an S-shape with a peak amplitude of 400 km s−1 at 01 = 8 pc from the nucleus. To model the observed gas kinematics, we construct a thin Keplerian disk model that fits the data well if the rotation axis of the gas disk is aligned with the radio jet axis. These models indicate that the gasdynamics are driven by a nuclear compact mass of 1.5 × 109 M☉ with an uncertainty range of (0.9-2.6) × 109 M☉, and that the inclination of the disk with respect to the plane of the sky is 75°-85°. Of this nuclear mass, only ≤2 × 107 M☉ can possibly be attributed to luminous mass. Thus, we conclude that a dark compact mass (most likely a supermassive black hole) resides in the nucleus of M84.
    Full-text · Article · Jan 2009 · The Astrophysical Journal
  • D. Michael Crenshaw · S. B. Kraemer
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    ABSTRACT: We present HST/STIS echelle observations of the Seyfert 1 galaxy NGC 5548 obtained in 2004, when the AGN was in an historically low state. We have identified emission lines in the spectra that have widths of 700 km/sec (FWHM), intermediate between those of the broad and narrow emission line regions. Photoionization models indicate that the ionic column densities from this intermediate-line region (ILR) are much greater than the observed columns from the outflowing UV absorbers. This suggests that we are viewing the AGN at a smaller polar angle than that in NGC 4151, where we see the ILR directly in absorption. We present a simple geometic model of the mass outflow in these two sources.
    No preview · Article · Jan 2009
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    ABSTRACT: We present our preliminary results of the analysis of Spitzer observations of the first unbiased AGN sample of the local universe. High column densities of absorbing material along our line of sight can significantly change the observed properties of AGNs. Thus, optical, infrared, and soft X-ray selected samples are hampered by extinction, star formation and absorption, respectively. Therefore an unbiased sample of AGNs is important to investigate the "hidden" nature of the nuclear source. The swift BAT survey in the 14-195 keV band represents a complete sample including Compton thin and previously unknown or non-famous AGNs that were missed from previous X-ray surveys in the 2-10 keV band. Our BAT AGN sample contains 130 objects (z < 0.05 and |b| >15 degrees) that have been observed with the Infrared Spectrograph (IRS) on board Spitzer (Spitzer observer proposal 30745 and 50588; PI: K.A. Weaver). This statistically significant unbiased AGN sample and the richness of the infrared spectrum provides a unique opportunity to test our understanding of AGN unification, classification and evolution in general. Strong polycyclic aromatic hydrocarbon (PAH) emission features at 6.2 and 11.25, and low ionization emission lines such as [Ne II] 12.81 are good indicators of stellar activity. On the other hand, high ionization emission lines such as [O IV] 25.89, [Ne III] 15.51 and [Ne V] 14.32,24.32 can be associated with the AGN. The line ratios between the high- and low-ionization emission lines can be used to measure the relative dominance of the AGN and to investigate the ionization state of the emission-line gas. We present the preliminary infrared spectra of our X-ray selected sample, different correlations and implication to the AGN classification and evolution.
    Preview · Article · Dec 2008
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    ABSTRACT: We present a study of available Hubble Space Telescope (HST) spectroscopic and imaging observations of the low-ionization nuclear emission-line region (LINER) galaxy NGC 1052. The WFPC2 imagery clearly differentiates extended nebular Hα emission from that of the compact core. Faint Object Spectrograph (FOS) observations provide a full set of optical and UV data (1200-6800 Å). These spectral data sample the innermost region (086 × 086 ~ 82 × 82 pc) and exclude the extended Hα emission seen in the WFPC2 image. The derived emission-line fluxes allow a detailed analysis of the physical conditions within the nucleus. The measured flux ratio for Hα/Hβ, FHα/FHβ = 4.53, indicates substantial intrinsic reddening, E(B-V) = 0.42, for the nuclear nebular emission. This is the first finding of a large extinction of the nuclear emission-line fluxes in NGC 1052. If the central ionizing continuum is assumed to be attenuated by a comparable amount, then the emission-line fluxes can be reproduced well by a simple photoionization model using a central power-law continuum source with a spectral index of α = -1.2 as deduced from the observed flux distribution. A multidensity, dusty gas gives the best fit to the observed emission-line spectrum. Our calculations show that the small contribution from a highly ionized gas observed in NGC 1052 can also be reproduced solely by photoionization modeling. The high gas covering factor determined from our model is consistent with the assumption that our line of sight to the central engine is obscured.
    Full-text · Article · Dec 2008 · The Astrophysical Journal
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    ABSTRACT: We use Hubble Space Telescope UV and optical spectra of the narrow-line Seyfert 1 (NLS1) galaxy Ark 564 to investigate its internal reddening and properties of its emission-line and intrinsic UV absorption gas. We find that the extinction curve of Ark 564, derived from a comparison of its UV/optical continuum to that of an unreddened NLS1, lacks a 2200 Å bump and turns up toward the UV at a longer wavelength (4000 Å) than the standard Galactic, LMC, and SMC curves. However, it does not show the extremely steep rise to 1200 Å that characterizes the extinction curve of the Seyfert 1 galaxy NGC 3227. The emission lines and continuum experience the same amount of reddening, indicating the presence of a dust screen that is external to the narrow-line region. Echelle spectra from the Space Telescope Imaging Spectrograph show intrinsic UV absorption lines due to Lyα, N V, C IV, Si IV, and Si III, centered at a radial velocity of -190 km s-1 (relative to the host galaxy). Photoionization models of the UV absorber indicate that it has a sufficient column (NH = 1.6 × 1021 cm-2) and is at a sufficient distance from the nucleus (D > 95 pc) to be the source of the dust screen. Thus, Ark 564 contains a dusty "lukewarm absorber" similar to that seen in NGC 3227.
    Full-text · Article · Dec 2008 · The Astrophysical Journal
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    ABSTRACT: We present echelle observations of the intrinsic UV absorption lines in the Seyfert galaxy NGC 4151; these observations were obtained with the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope on 1999 July 19. The UV-continuum flux at 1450 Å decreased by factor of about 4 over the previous 2 years, and there was a corresponding dramatic increase in the column densities of the low-ionization absorption lines (e.g., Si II, Fe II, and Al II), presumably as a result of a decrease in the ionizing continuum. In addition to the absorption lines seen in previous low states, we identify a large number of Fe II absorption lines that arise from metastable levels as high as 4.1 eV above the ground state, indicating high densities (>106 cm-3). We find that the transient absorption feature in the blue wing of the broad C IV emission, seen in a Goddard High Resolution Spectrograph spectrum and thought to be a high-velocity C IV component, is actually a Si II fine-structure absorption line at a radial velocity of -560 km s-1 (relative to systemic). We also demonstrate that the "satellite" emission lines of C IV found in IUE spectra are actually regions of unabsorbed continuum plus broad emission that become prominent when the UV continuum of NGC 4151 is in a low state.
    Full-text · Article · Dec 2008 · The Astrophysical Journal
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    ABSTRACT: We have examined the physical conditions in intrinsic UV-absorbing gas in the Seyfert galaxy NGC 4151, using echelle spectra obtained with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope on 1999 July 19. We confirm the presence of the kinematic components detected in earlier Goddard High Resolution Spectrograph (GHRS) observations, all of which appear to be outflowing from the nucleus, as well as a new broad absorption feature at a radial velocity of -1680 km s-1. The UV continuum of NGC 4151 was a factor of about 4 lower than in observations taken over the previous 2 yr, and we argue that the changes in the column density of the low-ionization absorption lines associated with the broad component at -490 km s-1 reflect the decrease in the ionizing flux. Most of the strong absorption lines (e.g., N V, C IV, Si IV, etc.) from this component are saturated but show substantial residual flux in their cores, indicating that the absorber does not fully cover the source of emission. Our interpretation is that the unocculted light is due to scattering by free electrons from an extended region, which reflects continuum, emission lines, and absorption lines. For the first time in such a study, we have been able to constrain the densities for this kinematic component and several others based on the strength of absorption lines from metastable states of C III and Fe II and/or the ratios of ground and fine structure lines of O I, C II, and Si II. We have generated a set of photoionization models that successfully match not only the ionic column densities for each component during the present low-flux state but also those seen in previous high-flux states with the GHRS and STIS, confirming that the absorbers are photoionized and respond to the changes in the continuum flux. Based on the model parameters (ionization parameter and density), we have been able to map the relative radial positions of the absorbers. We find that the absorbing gas decreases in density with distance. Finally, none of the UV absorbers is of sufficiently large column density or high enough ionization state to account for the observed X-ray absorption, while the scatterer is too highly ionized. Hence, the X-ray absorption must arise in a separate component of circumnuclear gas.
    Full-text · Article · Dec 2008 · The Astrophysical Journal
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    ABSTRACT: We present new UV spectra of the nucleus of the Seyfert 1 galaxy NGC 5548, which we obtained with the Space Telescope Imaging Spectrograph at high spectral resolution, in conjunction with simultaneous Chandra X-Ray Observatory spectra. Taking advantage of the low UV continuum and broad emission-line fluxes, we have determined that the deepest UV absorption component covers at least a portion of the inner, high-ionization narrow-line region (NLR). We find nonunity covering factors in the cores of several kinematic components, which increase the column density measurements of N V and C IV by factors of 1.2-1.9 over the full-covering case; however, the revised columns have only a minor effect on the parameters derived from our photoionization models. For the first time, we have simultaneous N V and C IV columns for component 1 (at -1040 km s-1) and find that this component cannot be an X-ray warm absorber, contrary to our previous claim based on nonsimultaneous observations. We find that models of the absorbers based on solar abundances severely overpredict the O VI columns previously obtained with the Far Ultraviolet Spectroscopic Explorer and present arguments that this is not likely due to variability. However, models that include either enhanced nitrogen (twice solar) or dust, with strong depletion of carbon in either case, are successful in matching all of the observed ionic columns. These models result in substantially lower ionization parameters and total column densities compared to dust-free solar-abundance models and produce little O VII or O VIII, indicating that none of the UV absorbers are X-ray warm absorbers.
    Full-text · Article · Dec 2008 · The Astrophysical Journal
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    ABSTRACT: We have studied the relationship between the high- and low-ionization [O IV] λ25.89 μm, [Ne III] λ15.56 μm, and [Ne II] λ12.81 μm emission lines with the aim of constraining the active galactic nuclei (AGNs) and star formation contributions for a sample of 103 Seyfert galaxies. We use the [O IV] and [Ne II] emission as tracers for the AGN power and star formation to investigate the ionization state of the emission-line gas. We find that Seyfert 2 galaxies have, on average, lower [O IV]/[Ne II] ratios than Seyfert 1 galaxies. This result suggests two possible scenarios: (1) Seyfert 2 galaxies have intrinsically weaker AGNs, or (2) Seyfert 2 galaxies have relatively higher star formation rates than Seyfert 1 galaxies. We estimate the fraction of [Ne II] directly associated with the AGNs and find that Seyfert 2 galaxies have a larger contribution from star formation, by a factor of ~1.5 on average, than what is found in Seyfert 1 galaxies. Using the stellar component of [Ne II] as a tracer of the current star formation, we found similar star formation rates in Seyfert 1 and Seyfert 2 galaxies. We examined the mid- and far-infrared continua and found that [Ne II] is well correlated with the continuum luminosity at 60 μm and that both [Ne III] and [O IV] are better correlated with the 25 μm luminosities than with the continuum at longer wavelengths, suggesting that the mid-infrared continuum luminosity is dominated by the AGN, while the far-infrared luminosity is dominated by star formation. Overall, these results test the unified model of AGNs and suggest that the differences between Seyfert galaxies cannot be solely due to viewing angle dependence.
    Full-text · Article · Dec 2008 · The Astrophysical Journal
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    ABSTRACT: We have examined the physical conditions in the narrow-line region of the well-studied Seyfert galaxy NGC 4151, using long-slit spectra obtained with the Hubble Space Telescope Space Telescope Imaging Spectrograph. The data were taken along a position angle of 221°, centered on the optical nucleus. We have generated photoionization models for a contiguous set of radial zones, out to 23 in projected position to the southwest of the nucleus and 27 to the northeast. Given the uncertainties in the reddening correction, the calculated line ratios successfully matched nearly all the dereddened ratios. We find that the narrow-line region consists of dusty atomic gas photoionized by a power-law continuum that has been modified by transmission through a mix of low- and high-ionization gas, specifically, UV-absorbing and X-ray-absorbing components. The physical characteristics of the absorbers resemble those observed along our line of sight to the nucleus, although the column density of the X-ray absorber is a factor of 10 less than observed. The large inferred covering factor of the absorbing gas is in agreement with the results of our previous study of UV absorption in Seyfert 1 galaxies. We find evidence, specifically the suppression of Lyα, that we are observing the back end of dusty ionized clouds in the region southwest of the nucleus. Since these clouds are blueshifted, this supports the interpretation of the cloud kinematics as being due to radial outflow from the nucleus. We find that the narrow-line gas at each radial position is inhomogeneous and can be modeled as consisting of a radiation-bounded component and a more tenuous, matter-bounded component. The density of the narrow-line gas drops with increasing radial distance, which confirms our earlier results and may be a result of the expansion of radially outflowing emission-line clouds.
    Full-text · Article · Dec 2008 · The Astrophysical Journal
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    ABSTRACT: A new Chandra observation and archival observations by ASCA are used to investigate spectral variations in the Seyfert 1 galaxy NGC 3516 over a period of 7 yr. A large change in flux (factor of ~50 at 1 keV) is observed between an ASCA observation in 1994 and the Chandra observation in 2000, with the source close to the all-time maximum and minimum X-ray flux states, respectively. We find the variations in the observed flux and spectra at these epochs to be consistent with a constant column density of line-of-sight material reacting to changes in the ionizing continuum. The data from the two epochs are consistent with a simple decrease (by a factor of 8-10) in the luminosity of a constant 0.5-50 keV slope source and a line-of-sight absorber with an equivalent hydrogen column density of 1021.9 cm-2. Intermediate luminosities, sampled during other ASCA observations, are all fitted by the same model with a very small change in spectral index (well below ΔΓ = 0.2). In addition, analysis of the long (360 ks) ASCA observation in 1998 shows clear color variations that are entirely consistent with this model and are interpreted as due to changes in the opacity of the absorbing gas. The data allow us to put a conservative upper limit of 60 ks on the recombination time, which translates to a lower limit of about 2.4 × 106 cm-3 on the density of the recombining gas and an upper limit of about 6 × 1017 h cm on its distance from the central source. These are the best limits obtained so far on the density and location of the X-ray-absorbing gas in a type 1 active galactic nucleus (AGN). They indicate that the absorbing gas is different in terms of its density and location from the ionized gas commonly observed in type II AGNs. The Chandra ACIS/LETGS data also reveals a strong (EW = 290 eV), unresolved 6.4 keV iron line, a strong O VII 0.561 keV line, and a marginally detected N VI 0.419 keV line. The former is interpreted as originating in a large column of gas of a lower state of ionization seen in reflection and is consistent with the spectrum at high energies at all epochs. The two other emission lines are probably emitted by the gas also responsible for the line-of-sight absorption.
    Full-text · Article · Dec 2008 · The Astrophysical Journal
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    ABSTRACT: We present slitless spectra of the narrow-line region (NLR) in NGC 4151 from the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope and investigate the kinematics and physical conditions of the emission-line clouds in this region. Using medium resolution (~0.5 Å) slitless spectra at two roll angles and narrow-band undispersed images, we have mapped the NLR velocity field from 1.2 kpc to within 13 pc (H0 = 75 km s-1 Mpc-1) of the nucleus. The inner biconical cloud distribution exhibits recessional velocities relative to the nucleus to the NE and approaching velocities to the SW of the nucleus. We find evidence for at least two kinematic components in the NLR. One kinematic component is characterized by low velocities and low velocity dispersions (LVLVD clouds: v < 400 km s-1, and Δv < 130 km s-1). This population extends through the NLR, and their observed kinematics may be gravitationally associated with the host galaxy. Another component is characterized by high velocities and high velocity dispersions (HVHVD clouds: 400 < v 1700 km s-1, Δv ≥ 130 km s-1). This set of clouds is located within 11 (~70 pc) of the nucleus and has radial velocities that are too high to be gravitational in origin but show no strong correlation between velocity or velocity dispersion and the position of the radio knots. Outflow scenarios will be discussed as the driving mechanism for these HVHVD clouds. We also find clouds characterized by low velocities and high velocity dispersions (LVHVD clouds: v < 400 km s-1, Δv ≥ 130 km s-1). These clouds are located within 32 (~200 pc) of the nucleus. It is not clear if the LVHVD clouds are HVHVD clouds whose low velocities are the result of projection effects. Within 32 (~200 pc) of the nucleus, the [O III]/Hβ ratio declines roughly linearly for both the high-velocity-dispersion (HVD) and LVLVD clouds. Since the ionization parameter is proportional to r-2n-1, it appears that the density, n, must decrease as ~r-1 for the clouds within the inner ~32. At distances further from the nucleus, the [O III]/Hβ ratio is roughly constant.
    Full-text · Article · Dec 2008 · The Astrophysical Journal
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    T. J. Turner · S. B. Kraemer
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    ABSTRACT: We present results from a 20 ks XMM-Newton observation of Mrk 231. The European Photon Imaging Camera (EPIC) spectral data reveal strong line emission due to Fe Kα, which has rarely been detected in this class, as broad absorption line quasars (BAL QSOs) are very faint in the X-ray band. The line energy is consistent with an origin in neutral Fe. The width of the line is equivalent to a velocity dispersion ~18,000 km s-1, and thus the line may be attributed to transmission and/or reflection from a distribution of emitting clouds. If, instead, the line originates in the accretion disk, then the line strength and flat X-ray continuum support some contribution from a reflected component, although the data disfavor a model in which the hard X-ray band is purely reflected X-rays from a disk. The line parameters are similar to those obtained for the Fe Kα line detected in another BAL QSO, H1413+117.
    Full-text · Article · Dec 2008 · The Astrophysical Journal
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    ABSTRACT: We present the intrinsic spectral energy distribution (SED) of the narrow-line Seyfert 1 galaxy (NLS1) Ark 564, constructed with contemporaneous data obtained during a multiwavelength, multisatellite observing campaign in 2000 and 2001. We compare this SED with that of the NLS1 Ton S180 and with those obtained for broad-line Seyfert 1 galaxies to infer how the relative accretion rates vary among the Seyfert 1 population. Although the peak of the SED is not well constrained, in our parameterization most of the energy of this object is emitted in the 10-100 eV regime, constituting roughly half of the emitted energy in the optical/X-ray ranges. This is consistent with a primary spectral component peaking in the extreme-UV/soft X-ray band and with disk-corona models, hence high accretion rates. Indeed, we estimate that ≈ 1. We also address the issue of the energy budget in this source by examining the emission lines observed in its spectrum, and we constrain the physical properties of the line-emitting gas through photoionization modeling. The available data suggest that the line-emitting gas is characterized by log n ≈ 11 and log U ≈ 0 and is stratified around log U ≈ 0. Our estimate of the radius of the Hβ-emitting region R ≈ 10 ± 2 lt-days is consistent with the R-luminosity relationships found for Seyfert 1 galaxies, which indicates that the narrowness of the emission lines in this NLS1 is not due to the broad-line region being relatively farther away from the central mass than in broad-line Seyfert 1 galaxies of comparable luminosity. We also find evidence for supersolar metallicity in this NLS1. We show that the emission lines are not good diagnostics for the underlying SEDs and that the absorption line studies offer a far more powerful tool to determine the ionizing continuum of active galactic nuclei, especially if one is comparing the lower and higher ionization lines.
    Full-text · Article · Dec 2008 · The Astrophysical Journal
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    ABSTRACT: Long-slit spectra of the Seyfert galaxy NGC 4151 from the UV to the near-infrared have been obtained with the Space Telescope Imaging Spectrograph (STIS) to study the kinematics and physical conditions in the narrow-line region (NLR). The kinematics shows evidence for three components, a low-velocity system in normal disk rotation, a high-velocity system in radial outflow at a few hundred kilometers per second relative to the systemic velocity, and an additional high-velocity system also in outflow with velocities up to 1400 km s-1, in agreement with results from STIS slitless spectroscopy. We have explored two simple kinematic models and suggest that radial outflow in the form of a wind is the most likely explanation. We also present evidence indicating that the wind may be decelerating with distance from the nucleus. We find that the emission-line ratios along our slits are all entirely consistent with photoionization from the nuclear continuum source. A decrease in the ratios [O III] λ5007/Hβ and [O III] λ5007/[O II] λ3727 suggests that the density decreases with distance from the nucleus. This trend is borne out by the [S II] ratios as well. We find no strong evidence for interaction between the radio jet and the NLR gas in either the kinematics or the emission-line ratios, in agreement with the recent results of Kaiser et al., who found no spatial coincidence of NLR clouds and knots in the radio jet. These results are in contrast to other recent studies of nearby active galactic nuclei that find evidence for significant interaction between the radio source and the NLR gas.
    Full-text · Article · Dec 2008 · The Astrophysical Journal
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    ABSTRACT: We have studied the relationship between the [O iv] 25.89 mu m emission- line luminosities, obtained from Spitzer spectra, the X- ray continua in the 2Y10 keV band, primarily from ASCA, and the 14Y195 keV band obtained with the SWIFT Burst Alert Telescope ( BAT), for a sample of nearby ( z < 0: 08) Seyfert galaxies. For comparison, we have examined the relationship between the [ O iii] k5007, the 2Y10 keV, and the 14Y195 keV luminosities for the same set of objects. We find that both the [ O iv] and [ O iii] luminosities are well correlated with the BAT luminosities. When comparing [ O iv] and [ O iii] luminosities for the different types of galaxies, we find that the Seyfert 2s have significantly lower [ O iii] to [ Oiv] ratios than the Seyfert 1s. We suggest that this is due to more reddening of the narrowline region ( NLR) of the Seyfert 2s, since the [ O iv] 25.89 mu m emission line is much less affected by extinction. The combined effects of reddening and the X- ray absorption is the probable reason why the [ O iii] versus 2Y10 keV correlation is better than the [ O iv] versus 2Y10 kev correlation. Based on photoionization models, we find that the [ O iv] comes from higher ionization states and lower density regions than previous studies had determined for [ O iii]. Overall, we find the [ O iv] to be an accurate indicator of the power of the AGN.
    Preview · Article · Jul 2008 · The Astrophysical Journal
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    ABSTRACT: In a continuing survey of active galactic nuclei observed by the Far Ultraviolet Spectroscopic Explorer, we provide a deeper analysis of intrinsic absorption features found in 35 objects. Our survey is for low-redshift and moderate-luminosity objects, mostly Seyfert galaxies. We find a strong correlation between maximum radial velocity and luminosity. We also examine the relationships between equivalent width (EW), full width at half maximum, velocity: and continuum flux. The correlation between velocity and luminosity has been explored previously by Laor & Brandt, but at a significantly higher redshift and heavily weighted by broad absorption line quasars. We also have examined each object with multiple observations for variability in each of the aforementioned quantities, and have characterized the variation of EW with the continuum flux. In our survey, we find that variability of O VI lambda1032, lambda1038 is less common than of the UV doublets of CIV and N V seen at longer wavelengths, because the O VI absorption is usually saturated. Lyman beta absorption variability is more frequent. In a target-by-target examination we find that broad absorption line absorption and narrow absorption line absorbers are related in terms of maximum outflow velocity and luminosity, and both can be exhibited in similar luminosity objects. We also find one object that shows radial velocity change, seven objects that show equivalent width variability, and two objects that show either transverse velocity changes or a change in ionization. Comment: 56 pages, 23 figures, Accepted for AJ, 2008 May 19
    Preview · Article · Jul 2008 · The Astronomical Journal
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    T. J. Turner · J. N. Reeves · S. B. Kraemer · L Miller
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    ABSTRACT: X-ray spectra of AGN often contain signatures indicative of absorption in multiple layers of gas whose ionization-state and covering fraction may vary with time. It has been unclear to date how much of the observed X-ray spectral and timing behavior in AGN can be attributed to variations in absorption, versus variations in the strengths of emission or reflection components. Diagnostics of the inner regions of AGN cannot be reliably performed until the origin of observed effects is understood. We investigate the role of the X-ray absorbers in the Seyfert 1 galaxy NGC 3516. Time-averaged and flux-selected spectroscopy is used to examine the behavior of NGC 3516 observed in Chandra HETG and XMM data from Oct 2006. New H-like and He-like emission and absorption features discovered in the Fe K regime reveal a previously unknown zone of circumnuclear gas in NGC 3516 with log xi ~ 4.3 and column density 1E23 cm^-2. A lower-ionization layer with log xi ~2 and of similar column density is confirmed from previous observations, this layer has a covering fraction around 50%, and changes in covering provide a simple explanation of a deep dip in the light curve that we interpret as an eclipse of the continuum due to passage of a cloud across the sight line within half a day. These inner zones of absorbing gas are detected to have outflow velocities in the range 1000-2000 km/s, this, and constraints on radial location are consistent with an origin as part of a disk wind in NGC 3516. Comment: 10 pages, 8 figures, accepted by A&A Feb 26 2008 Version 2: Figs 1 & 2 were corrected for a problem with ACIS section of the data. Little impact on text of the paper
    Full-text · Article · Mar 2008 · Astronomy and Astrophysics

Publication Stats

4k Citations
605.87 Total Impact Points

Institutions

  • 1997-2015
    • The Catholic University of America
      • Department of Physics
      Washington, Washington, D.C., United States
    • Rutgers, The State University of New Jersey
      • Department Physics and Astronomy
      New Brunswick, New Jersey, United States
  • 2002-2013
    • Georgia State University
      • Department of Physics and Astronomy
      Atlanta, Georgia, United States
  • 1998-2011
    • Johns Hopkins University
      • Department of Physics and Astronomy
      Baltimore, Maryland, United States
  • 2010
    • NASA
      Вашингтон, West Virginia, United States
  • 2009
    • University of Oxford
      • Department of Physics
      Oxford, England, United Kingdom
  • 2004
    • University of Maryland, Baltimore County
      • Department of Physics
      Baltimore, Maryland, United States
  • 2001
    • The Ohio State University
      • Department of Astronomy
      Columbus, Ohio, United States