2,314 research outputs found
HST Observations of the Double-Peaked Emission Lines in the Seyfert Galaxy Markarian 78: Mass Outflows from a Single AGN
Previous ground based observations of the Seyfert 2 galaxy Mrk 78 revealed a
double set of emission lines, similar to those seen in several AGN from recent
surveys. Are the double lines due to two AGN with different radial velocities
in the same galaxy, or are they due to mass outflows from a single AGN?We
present a study of the outflowing ionized gas in the resolved narrow-line
region (NLR) of Mrk 78 using observations from Space Telescope Imaging
Spectrograph (STIS) and Faint Object Camera (FOC) aboard the Hubble Space
Telescope(HST) as part of an ongoing project to determine the kinematics and
geometries of active galactic nuclei (AGN) outflows. From the spectroscopic
information, we deter- mined the fundamental geometry of the outflow via our
kinematics modeling program by recreating radial velocities to fit those seen
in four different STIS slit positions. We determined that the double emission
lines seen in ground-based spectra are due to an asymmetric distribution of
outflowing gas in the NLR. By successfully fitting a model for a single AGN to
Mrk 78, we show that it is possible to explain double emission lines with
radial velocity offsets seen in AGN similar to Mrk 78 without requiring dual
supermassive black holes.Comment: 22 pages, 7 figures (2 color), accepted for publication in The
Astrophysical Journa
Physical Conditions in the Inner Narrow-Line Region of the Seyfert 2 Galaxy NGC 1068
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 are Hubble Space Telescope (HST) Harchive
data obtained with the Faint Object Spectrograph (FOS). We selected spectra of
four regions, taken through the 0.3" FOS aperture, covering the full FOS 1200A
to 6800A waveband. Each region is approximately 20 pc in extent, and all are
within 100 pc of the apparent nucleus of NGC 1068. The spectra show similar
emission-line ratios from wide range of ionization states for the most abundant
elements. After extensive photoionization modeling, we interpret this result as
an indication that each region includes a range of gas densities, which we
included in the models as separate components. Supersolar abundances were
required for several elements to fit the observed emission line ratios. Dust
was included in the models but apparently dust to gas fraction varies within
these regions. The low ionization lines in these spectra can be best explained
as arising in gas that is partially shielded from the ionizing continuum.
Although the predicted line ratios from the photoionization models provide a
good fit to the observed ratios, it is apparent that the model predictions of
electron temperatures in the ionized gas are too low. We interpret this as an
indication of additional collisional heating due to shocks and/or energetic
particles associated with the radio jet that traverses the NLR of NGC 1068. The
density structure within each region may also be the result of compression by
the jet.Comment: 38 pages, Latex, includes 5 figures (postscript), to appear in Ap
Resolved Spectroscopy of the Narrow-Line Region in NGC 1068. I. The Nature of the Continuum Emission
We present the first long-slit spectra of the Seyfert 2 galaxy NGC 1068
obtained by the Space Telescope Imaging Spectrograph (STIS); the spectra cover
the wavelength range 1150 - 10,270 Angstroms at a spatial resolution of 0.05 -
0.1 arcsec and a spectral resolving power of 1000. In this first paper, we
concentrate on the far-UV to near-IR continuum emission from the continuum
``hot spot'' and surrounding regions extending out to +/- 6 arcsec (+/-432 pc)
at a position angle of 202 degrees In addition to the broad emission lines
detected by spectropolarimetry, the hot spot shows the ``little blue bump'' in
the 2000 - 4000 Ang. range, which is due to Fe II and Balmer continuum
emission. The continuum shape of the hot spot is indistinguishable from that of
NGC 4151 and other Seyfert 1 galaxies. Thus, the hot spot is reflected emission
from the hidden nucleus, due to electron scattering (as opposed to
wavelength-dependent dust scattering). The hot spot is ~0.3 arcsec in extent
and accounts for 20% of the scattered light in the inner 500 pc. We are able to
deconvolve the extended continuum emission in this region into two components:
electron-scattered light from the hidden nucleus (which dominates in the UV)
and stellar light (which dominates in the optical and near-IR). The scattered
light is heavily concentrated towards the hot spot, is stronger in the
northeast, and is enhanced in regions of strong narrow-line emission. The
stellar component is more extended, concentrated southwest of the hot spot,
dominated by an old (> 2 x 10 Gyr) stellar population, and includes a nuclear
stellar cluster which is ~200 pc in extent.Comment: 32 pages, Latex, includes 11 figures (postscript), to appear in the
Astrophysical Journa
Significant X-ray Line Emission in the 5-6 keV band of NGC 4051
A Suzaku X-ray observation of NGC 4051 taken during 2005 Nov reveals line
emission at 5.44 keV in the rest-frame of the galaxy which does not have an
obvious origin in known rest-frame atomic transitions. The improvement to the
fit statistic when this line is accounted for establishes its reality at >99.9%
confidence: we have also verified that the line is detected in the three XIS
units independently. Comparison between the data and Monte Carlo simulations
shows that the probability of the line being a statistical fluctuation is p <
3.3 x 10^-4. Consideration of three independent line detections in Suzaku data
taken at different epochs yields a probability p< 3 x 10^-11 and thus
conclusively demonstrates that it cannot be a statistical fluctuation in the
data. The new line and a strong component of Fe Ka emission from neutral
material are prominent when the source flux is low, during 2005. Spectra from
2008 show evidence for a line consistent with having the same flux and energy
as that observed during 2005, but inconsistent with having a constant
equivalent width against the observed continuum. The stability of the line flux
and energy suggests that it may not arise in transient hotspots, as has been
suggested for similar lines in other sources, but could arise from a special
location in the reprocessor, such as the inner edge of the accretion disk.
Alternatively, the line energy may be explained by spallation of Fe into Cr, as
discussed in a companion paper.Comment: 18 pages, accepted for publication by Ap
Simultaneous X-ray and Ultraviolet spectroscopy of the Seyfert galaxy NGC 5548. III. X-ray time variability
The Seyfert 1 galaxy NGC 5548 was observed for a week by Chandra using both
the HETGS and LETGS spectrometers. In this paper we study the time variability
of the continuum radiation. During our observation, the source showed a gradual
increase in flux over four days, followed by a rapid decrease and flattening of
the light curve afterwards. Superimposed upon these relatively slow variations
several short duration bursts or quasi-periodic oscillations occured with a
typical duration of several hours and separation between 0.6-0.9 days. The
bursts show a delay of the hard X-rays with respect to the soft X-rays of a few
hours. We interprete these bursts as due to a rotating, fluctuating hot spot at
approximately 10 gravitational radii; the time delay of the hard X-rays from
the bursts agree with the canonical picture of Inverse Compton scattering of
the soft accretion disk photons on a hot medium that is relatively close to the
central black hole.Comment: 6 pages, 7 figures, accepted for publication in Astronomy and
Astrophysic
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