Steven B. Kraemer

The Space Telescope Imaging Spectrograph Design

ABSTRACT The Space Telescope Imaging Spectrograph (STIS) instrument was installed on the Hubble Space Telescope (HST) during the second servicing mission, in 1997 February. Four bands cover the wavelength range of 115–1000 nm, with spectral resolving powers between 26 and 200,000. Camera modes are used for target acquisition and deep imaging. Correction for HSTs spherical aberration and astigmatism is included. The 115–170 nm range is covered by a CsI MAMA (Multianode Microchannel Array) detector and the 165–310 nm range by a Cs2Te MAMA, each with a format of \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cy...

High‐Resolution X‐Ray and Ultraviolet Spectroscopy of the Complex Intrinsic Absorption in NGC 4051 with Chandra and the Hubble Space Telescope

We present the results from simultaneous observations of the narrow-line Seyfert 1 galaxy NGC 4051 with the Chandra High Energy Transmission Grating Spectrometer and the Hubble Space Telescope Space Telescope Imaging Spectrograph. The X-ray grating spectrum reveals absorption and emission lines from hydrogen-like and helium-like ions of O, Ne, Mg, and Si. We resolve two distinct X-ray absorption systems: a high-velocity blueshifted system at -2340 ± 130 km s-1 and a low-velocity blueshifted system at -600 ± 130 km s-1. In the UV spectrum we detect strong absorption, mainly from C IV, N V, and Si IV, that is resolved into as many as nine different intrinsic absorption systems with velocities between -650 and 30 km s-1. Although the low-velocity X-ray absorption is consistent in velocity with many of the UV absorption systems, the high-velocity X-ray absorption seems to have no UV counterpart. In addition to the absorption and emission lines, we also observe rapid X-ray variability and a state of low X-ray flux during the last ≈15 ks of the observation. NGC 4051 has a soft X-ray excess that we fit in both the high and low X-ray flux states. The high-resolution X-ray spectrum directly reveals that the soft excess is not composed of narrow emission lines and that it has significant spectral curvature. A power-law model fails to fit it, while a blackbody produces a nearly acceptable fit. We compare the observed spectral variability with the results of previous studies of NGC 4051.

Resolved Spectroscopy of the Narrow-Line Region in NGC 1068: Kinematics of the Ionized Gas

We have determined the radial velocities of the [O iii]-emitting gas in the inner narrow-line region of the Seyfert 2 galaxy NGC 1068, along a slit at position angle 202 degrees, from STIS observations at a spatial resolution of 0&farcs;1 and a spectral resolving power of lambda&solm0;Deltalambda approximately 1000. We use these data to investigate the kinematics of the narrow-line region within 6&arcsec; ( approximately 430 pc) of the nucleus. The emission-line knots show evidence for radial acceleration to a projected angular distance of 1&farcs;7 in most cases, followed by deceleration that approaches the systemic velocity at a projected distance of approximately 4&arcsec;. We find that a simple kinematic model of biconical radial outflow can match the general trend of observed radial velocities. In this model, the emitting material is evacuated along the bicone axis, and the axis is inclined 5 degrees out of the plane of the sky. The acceleration of the emission-line clouds provides support for dynamical models that invoke radiation and/or wind pressure. We suggest that the deceleration of the clouds is due to their collision with a patchy and anistropically distributed ambient medium.

A Kinematic Model for the Narrow-Line Region in NGC 4151*

We present a simple kinematic model for the narrow-line region (NLR) of the Seyfert 1 galaxy NGC 4151, based on our previous observations of extended [O III] emission with the Space Telescope Imaging Spectrograph. The model is similar to a biconical radial outflow model developed for the Seyfert 2 galaxy NGC 1068, except that the bicone axis is tilted much more into our line of sight (40? out of the plane of the sky instead of 5?), and the maximum space velocities are lower (750 km s-1 instead of 1300 km s-1). We find evidence for radial acceleration of the emission-line knots to a distance of 160 pc, followed by deceleration that approaches the systemic velocity at a distance of 290 pc (for a distance to NGC 4151 of 13.3 Mpc). Other similarities to the kinematics of NGC 1068 are (1) there are a number of high-velocity clouds that are not decelerated, suggesting that the medium responsible for the deceleration is patchy, and (2) the bicone in NGC 4151 is at least partially evacuated along its axis. Together, these two Seyfert galaxies provide strong evidence for radial outflow (e.g., due to radiation and/or wind pressure) and against gravitational motion or expansion away from the radio jets as the principal kinematic component in the NLR.

Complex X-Ray Absorption and the Fe Kα Profile in NGC 3516

We present data from simultaneous Chandra, XMM-Newton and BeppoSAX observations of the Seyfert 1 galaxy NGC 3516, taken during 2001 April and Nov. We have investigated the nature of the very flat observed X-ray spectrum. Chandra grating data show the presence of X-ray absorption lines, revealing two distinct components of the absorbing gas, one which is consistent with our previous model of the UV/X-ray absorber while the other, which is outflowing at a velocity of ~1100 km/s has a larger column density and is much more highly ionized. The broad-band spectral characteristics of the X-ray continuum observed with XMM during 2001 April, reveal the presence of a third layer of absorption consisting of a very large column (~2.5 x 10E23 cm^-2) of highly ionized gas with a covering fraction ~50%. This low covering fraction suggests that the absorber lies within a few lt-days of the X-ray source and/or is filamentary in structure. Interestingly, these absorbers are not in thermal equilibrium with one another. The two new components are too highly ionized to be radiatively accelerated, which we suggest is evidence for a hydromagnetic origin for the outflow. Applying our model to the Nov dataset, we can account for the spectral variability primarily by a drop in the ionization states of the absorbers, as expected by the change in the continuum flux. When this complex absorption is accounted for we find the underlying continuum to be typical of Seyfert 1 galaxies. The spectral curvature attributed to the high column absorber, in turn, reduces estimates of the flux and extent of any broad Fe emission line from the accretion disk.We present data from simultaneous Chandra, XMM-Newton, and BeppoSAX observations of the Seyfert 1 galaxy NGC 3516, taken during 2001 April and November. We have investigated the nature of the very flat observed X-ray spectrum. Chandra grating data show the presence of X-ray absorption lines, revealing two distinct components of the absorbing gas, one that is consistent with our previous model of a UV/X-ray absorber while the other, which is outflowing at a velocity of ~1100 km s-1, has a larger column density and is much more highly ionized. The broadband spectral characteristics of the X-ray continuum observed with XMM-Newton during 2001 April reveal the presence of a third layer of absorption consisting of a very large column (≈2.5 × 1023 cm-2) of highly ionized gas with a covering fraction ~50%. This low covering fraction suggests that the absorber lies within a few light days of the X-ray source and/or is filamentary in structure. Interestingly, these absorbers are not in thermal equilibrium with one another. The two new components are too highly ionized to be radiatively accelerated, which we suggest is evidence for a hydromagnetic origin for the outflow. Applying our model to the November data set, we can account for the spectral variability primarily by a drop in the ionization states of the absorbers, as expected by the change in the continuum flux. When this complex absorption is accounted for, we find the underlying continuum to be typical of Seyfert 1 galaxies. The spectral curvature attributed to the high column absorber in turn reduces estimates of the flux and the extent of any broad Fe emission line from the accretion disk.

Resolved Spectroscopy of the Narrow-Line Region in NGC 1068. III. Physical Conditions in the Emission-Line Gas*

The physical conditions in the inner narrow-line region (NLR) of the Seyfert 2 galaxy NGC 1068 are examined using ultraviolet and optical spectra and photoionization models. The spectra were taken with the Hubble Space Telescope Space Telescope Imaging Spectrograph (STIS), through the 01 ? 520 slit, covering the full STIS 1200-10000 ? waveband. The slit was centered on a position 014 north of the optical continuum peak (or hot spot) at a position angle of 202?, bisecting the brighter part of the biconical emission-line region. We have measured the emission-line fluxes for a region extending 38 northeast (~270 pc) to 18 southwest (~130 pc) of this point. The emission lines on each side show evidence of two principal kinematic components, one blueshifted with respect to the systemic velocity and the other redshifted (the kinematics were discussed in a separate paper). Based on the photoionization modeling results, we find that the physical conditions vary among these four quadrants. (1) The emission-line gas in the blueshifted northeast quadrant is photoionized by the hidden central source out to ~100 pc, at which point we find evidence of another source of ionizing radiation, which may be due to fast (~1000 km s-1) shocks resulting from the interaction of the emission-line knots and the interstellar medium. Interestingly, this occurs at approximately the location where the knots begin to show signs of deceleration. (2) The gas in the redshifted northeast quadrant is photoionized by continuum radiation that has been heavily absorbed by gas within ~30 pc of the central source. We find no strong evidence of the effects of shocks in this component. (3) The redshifted emission-line gas in the southwest quadrant is photoionized by unabsorbed continuum from the central source, similar to that in the inner ~100 pc of the blueshifted northeast quadrant. Finally, (4) the emission-line spectrum of the blueshifted southwest quadrant appears to be the superposition of highly ionized, tenuous component within the ionization cone and gas outside the cone, the latter photoionized by scattered continuum radiation. There are several implications of this complicated physical scenario. First, the hidden active nucleus is the dominant source of ionizing radiation in the inner NLR. The absorption of continuum radiation along the line of sight to the redshifted northeast quadrant may result from the intersection of the ionization cone and the plane of the host galaxy. Finally, the evidence for shock-induced continuum radiation at the point where the emission-line knots begin to decelerate indicates that the deceleration is due to the interaction of emission-line knots with slower moving gas, such as the interstellar medium of NGC 1068.

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.

Spitzer IRS Observations of Seyfert 1.8 and 1.9 Galaxies: A Comparison with Seyfert 1 and Seyfert 2

We present Spitzer mid-infrared spectra of 12 Seyfert 1.8 and 1.9 galaxies over the 5-38 μm region. We compare the spectral characteristics of this sample to those of 58 Seyfert 1 and 2 galaxies from the Spitzer archives. An analysis of the spectral shapes, the silicate 10 μm feature and the emission-line fluxes have enabled us to characterize the mid-IR properties of Seyfert 1.8/1.9s. We find that the EWs of the 10 μm silicate feature are generally weak in all Seyfert galaxies, as previously reported by several studies. The few Seyfert galaxies in this sample that show deep 10 μm silicate absorption features are highly inclined and/or merging galaxies. It is likely that these absorption features originate primarily in the dusty interstellar medium of the host galaxy rather than in a dusty torus on parsec scales close to the central engine. We find that the EW of the PAH band at 6.2 μm correlates strongly with the 20-30 μm spectral index. Either of these quantities is a good indicator of the amount of starburst contribution to the mid-IR spectra. The spectra of Seyfert 1.8s and 1.9s are dominated by these starburst features, similar to most Seyfert 2s. They show strong PAH bands and a strong red continuum toward 30 μm. The strengths of the high-ionization forbidden narrow emission lines [O IV] 25.89 μm, [Ne III] 15.56 μm, and [Ne V] 14.32 μm relative to [Ne II] 12.81 μm are weaker in Seyfert 1.8/1.9s and Seyfert 2s than in Seyfert 1s. The weakness of high-ionization lines in Seyfert 1.8-1.9s is suggestive of intrinsically weak AGN continua and/or stronger star formation activity leading to enhanced [Ne II]. We discuss the implications of these observational results in the context of the unified model of AGNs.

The Resolved Narrow-Line Region in NGC 4151*

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 A) 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.

Space Telescope Imaging Spectrograph Long-Slit Spectroscopy of the Narrow-Line Region of NGC 4151. II. Physical Conditions along Position Angle 221° *

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.