92 research outputs found
Spatially Resolved Far-Ultraviolet Spectroscopy of the Nuclear Region of NGC 1068
We carry out high-resolution FUSE spectroscopy of the nuclear region of NGC
1068. The first set of spectra was obtained with a 30" square aperture that
collects all emission from the narrow-line region. The data reveal a strong
broad OVI component of FWHM ~3500 kms-1 and two narrow OVI 1031/1037 components
of ~350 kms-1. The CIII 977 and NIII 991 emission lines in this spectrum can be
fitted with a narrow component of FWHM ~1000 kms-1 and a broad one of ~2500
kms-1. Another set of seven spatially resolved spectra were made using a long
slit of 1.25" X 20", at steps of ~1" along the axis of the emission-line cone.
We find that (1) Major emission lines in the FUSE wavelength range consist of a
broad and a narrow component; (2) There is a gradient in the velocity field for
the narrow OVI component of ~200 kms-1 from ~2" southwest of the nucleus to ~4"
northeast. A similar pattern is also observed with the broad OVI component,
with a gradient of ~3000 kms-1. These are consistent with the HST/STIS findings
and suggest a biconical structure in which the velocity field is mainly radial
outflow; (3) A major portion of the CIII and NIII line flux is produced in the
compact core. They are therefore not effective temperature diagnostics for the
conical region; and (4) The best-fitted UV continuum suggests virtually no
reddening, and the HeII 1085/1640 ratio suggests a consistently low extinction
factor across the cone.Comment: To appear in the Astrophysical Journal. 37 pages with 12 figure
Updating quasar bolometric luminosity corrections. II. Infrared bolometric corrections
We present infrared bolometric luminosity corrections derived from the
detailed spectral energy distributions of 62 bright quasars of low- to
moderate-redshift (z=0.03-1.4). At 1.5, 2, 3, 7, 12, 15, and 24 microns we
provide bolometric corrections of the mathematical forms L_iso=\zeta \lambda
L_\lambda and log(L_iso)=A+B log(\lambda L_\lambda). Bolometric corrections for
radio-loud and radio-quiet objects are consistent within 95% confidence
intervals, so we do not separate them. Bolometric luminosities estimated using
these corrections are typically smaller than those derived from some commonly
used in the literature. We investigate the possibility of a luminosity
dependent bolometric correction and find that, while the data are consistent
with such a correction, the dispersion is too large and the luminosity range
too small to warrant such a detailed interpretation. Bolometric corrections at
1.5 m are appropriate for objects with properties that fall in the range
log(L_bol)=45.4-47.3 and bolometric corrections at all other wavelengths are
appropriate for objects with properties that fall in the range
log(L_bol)=45.1-47.0.Comment: 13 pages, 4 tables, 8 figures, accepted to MNRA
Intrinsic Absorption in the Spectrum of NGC 7469: Simultaneous Chandra, FUSE, and STIS Observations
We present simultaneous X-ray, far-ultraviolet, and near-ultraviolet spectra
of the Seyfert 1 galaxy NGC 7469 obtained with the Chandra X-Ray Observatory,
the Far Ultraviolet Spectroscopic Explorer, and the Space Telescope Imaging
Spectrograph on the Hubble Space Telescope. Previous non-simultaneous
observations of this galaxy found two distinct UV absorption components, at
-560 and -1900 km/s, with the former as the likely counterpart of the X-ray
absorber. We confirm these two absorption components in our new UV
observations, in which we detect prominent O VI, Ly alpha, N V, and C IV
absorption. In our Chandra spectrum we detect O VIII emission, but no
significant O VIII or O VII absorption. We also detect a prominent Fe K alpha
emission line in the Chandra spectrum, as well as absorption due to
hydrogen-like and helium-like neon, magnesium, and silicon at velocities
consistent with the -560 km/s UV absorber. The FUSE and STIS data reveal that
the H I and C IV column densities in this UV- and X-ray- absorbing component
have increased over time, as the UV continuum flux decreased. We use measured H
I, N V, C IV, and O VI column densities to model the photoionization state of
both absorbers self-consistently. We confirm the general physical picture of
the outflow in which the low velocity component is a highly ionized, high
density absorber with a total column density of 10^20 cm^-2, located near the
broad emission line region, although due to measurable columns of N V and C IV,
we assign it a somewhat smaller ionization parameter than found previously,
U~1. The high velocity UV component is of lower density, log N=18.6, and likely
resides farther from the central engine as we find its ionization parameter to
be U=0.08.Comment: Minor correction to abstract; STScI eprint #1683; 50 pages, incl. 19
figures, 4 tables; Accepted to Ap
Intrinsic Absorption in the Spectrum of Mrk 279: Simultaneous Chandra, FUSE, and STIS Observations
We present a study of the intrinsic X-ray and far-ultraviolet absorption in
the Seyfert 1.5 galaxy Markarian 279 using simultaneous observations from the
Chandra X-ray Observatory, the Space Telescope Imaging Spectrograph aboard the
Hubble Space Telescope, and the Far Ultraviolet Spectroscopic Explorer (FUSE).
We also present FUSE observations made at three additional epochs. We detect
the Fe K-alpha emission line in the Chandra spectrum, and its flux is
consistent with the low X-ray continuum flux level of Mrk 279 at the time of
the observation. Due to low signal-to-noise ratios in the Chandra spectrum, no
O VII or O VIII absorption features are observable in the Chandra data, but the
UV spectra reveal strong and complex absorption from HI and high-ionization
species such as O VI, N V, and C IV, as well as from low-ionization species
such as C III, N III, C II, and N II in some velocity components. The far-UV
spectral coverage of the FUSE data provides information on high-order Lyman
series absorption, which we use to calculate the optical depths and line and
continuum covering fractions in the intrinsic HI absorbing gas in a
self-consistent fashion. The UV continuum flux of Mrk 279 decreases by a factor
of ~7.5 over the time spanning these observations and we discuss the
implications of the response of the absorption features to this change. From
arguments based on the velocities, profile shapes, covering fractions and
variability of the UV absorption, we conclude that some of the absorption
components, particularly those showing prominent low-ionization lines, are
likely associated with the host galaxy of Mrk 279, and possibly with its
interaction with a close companion galaxy, while the remainder arises in a
nuclear outflow.Comment: To appear in 2004 May ApJS; double-column format; 58 pages, incl. 29
figures, 9 tables; minor changes to tex
M87: A Misaligned BL LAC?
The nuclear region of M87 was observed with the Faint Object Spectrograph
(FOS) on the Hubble Space Telescope (HST) at 6 epochs, spanning 18 months,
after the HST image quality was improved with the deployment of the corrective
optics (COSTAR) in December 1993. From the FOS target acquisition data, we have
established that the flux from the optical nucleus of M87 varies by a factor ~2
on time scales of ~2.5 months and by as much as 25% over 3 weeks, and remains
unchanged (<= 2.5%) on time scales of ~1 day. The changes occur in an
unresolved central region <= 5 pc in diameter, with the physical size of the
emitting region limited by the observed time scales to a few hundred
gravitational radii. The featureless continuum spectrum becomes bluer as it
brightens while emission lines remain unchanged. This variability combined with
the observations of the continuum spectral shape, strong relativistic boosting
and the detection of significant superluminal motions in the jet, strongly
suggest that M87 belongs to the class of BL Lac objects but is viewed at an
angle too large to reveal the classical BL Lac properties.Comment: 12 pages, 3 Postscript figure
Quasars and the Big Blue Bump
We investigate the ultraviolet-to-optical spectral energy distributions
(SEDs) of 17 active galactic nuclei (AGNs) using quasi-simultaneous
spectrophotometry spanning 900-9000 Angstrom (rest frame). We employ data from
the Far Ultraviolet Spectroscopic Explorer (FUSE), the Hubble Space Telescope
(HST), and the 2.1-meter telescope at Kitt Peak National Observatory (KPNO).
Taking advantage of the short-wavelength coverage, we are able to study the
so-called "big blue bump," the region where the energy output peaks, in detail.
Most objects exhibit a spectral break around 1100 Angstrom. Although this
result is formally associated with large uncertainty for some objects, there is
strong evidence in the data that the far-ultraviolet spectral region is below
the extrapolation of the near-ultraviolet-optical slope, indicating a spectral
break around 1100 Angstrom. We compare the behavior of our sample to those of
non-LTE thin-disk models covering a range in black-hole mass, Eddington ratio,
disk inclination, and other parameters. The distribution of ultraviolet-optical
spectral indices redward of the break, and far-ultraviolet indices shortward of
the break, are in rough agreement with the models. However, we do not see a
correlation between the far-ultraviolet spectral index and the black hole mass,
as seen in some accretion disk models. We argue that the observed spectral
break is intrinsic to AGNs, although intrinsic reddening as well as
Comptonization can strongly affect the far-ultraviolet spectral index. We make
our data available online in digital format.Comment: 32 pages (10pt), 12 figures. Accepted for publication in Ap
The Ionized Gas and Nuclear Environment in NGC 3783. I. Time-Averaged 900 ks Chandra Grating Spectroscopy
We present results from a 900 ks exposure of NGC 3783 with the High-Energy
Transmission Grating Spectrometer on board the Chandra X-ray Observatory. The
resulting X-ray spectrum has the best combination of signal-to-noise and
resolution ever obtained for an AGN. This spectrum reveals absorption lines
from H-like and He-like ions of N, O, Ne, Mg, Al, Si, and S. There are also
possible absorption lines from H-like and He-like Ar and Ca. We also identify
inner-shell absorption from lower-ionization ions such as Si_VII-Si_XII and
S_XII-S_XIV. The iron absorption spectrum is very rich; L-shell lines of
Fe_XVII-Fe_XXIV are detected, strong complex of M-shell lines, and probable
resonance lines from Fe_XXV. The absorption lines are blueshifted relative to
the systemic velocity by a mean velocity of -590+-150 km/s. We resolve many of
the absorption lines, and their mean FWHM is 820+-280 km/s. We do not find
correlations between the velocity shifts or the FWHMs with the ionization
potentials of the ions. Most absorption lines show asymmetry, having more
extended blue wings than red wings. In O_VII we have resolved this asymmetry to
be from an additional absorption system at ~ -1300 km/s. The two X-ray
absorption systems are consistent in velocity shift and FWHM with the ones
identified in the UV lines of C IV, N V, and H I. Equivalent width measurements
for all lines are given and column densities are calculated for several ions.
We resolve the narrow Fe_K\alpha line at 6398.2+-3.3 eV to have a FWHM of
1720+-360 km/s, which suggests that this narrow line may be emitted from the
outer part of the broad line region or the inner part of the torus. We also
detect a `Compton shoulder' redward of the narrow Fe_K\alpha line which
indicates that it arises in cold, Compton-thick gas.Comment: 19 pages, 12 figures (2 in color), emulateapj5, accepted for
publication in The Astrophysical Journal Supplement
The New Generation Atlas of Quasar Spectral Energy Distributions from Radio to X-rays
We have produced the next generation of quasar spectral energy distributions
(SEDs), essentially updating the work of Elvis et al. (1994) by using
high-quality data obtained with several space and ground-based telescopes,
including NASA's Great Observatories. We present an atlas of SEDs of 85
optically bright, non-blazar quasars over the electromagnetic spectrum from
radio to X-rays. The heterogeneous sample includes 27 radio-quiet and 58
radio-loud quasars. Most objects have quasi-simultaneous ultraviolet-optical
spectroscopic data, supplemented with some far-ultraviolet spectra, and more
than half also have Spitzer mid-infrared IRS spectra. The X-ray spectral
parameters are collected from the literature where available. The radio,
far-infrared, and near-infrared photometric data are also obtained from either
the literature or new observations. We construct composite spectral energy
distributions for radio-loud and radio-quiet objects and compare these to those
of Elvis et al., finding that ours have similar overall shapes, but our
improved spectral resolution reveals more detailed features, especially in the
mid and near-infrared.Comment: 46 pages, 10 figures, 10 tables, Accepted by ApJS. Composite SED data
files for radio-loud and radio-quiet quasars (rlmsedMR.txt, rqmsedMR.txt) are
included in the source (Other formats -> Source). Supplemental figures are
not include
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 18 observations with HST/STIS and 6 observations with
FUSE, we find: 1) The absorption from the lowest-ionization species in each of
the three strong kinematic components varied inversely with the continuum flux,
indicating the ionization structure responded to changes in the photoionizing
flux over the weekly timescales sampled by our observations. 2) A multi-
component model with an unocculted NLR and separate BLR and continuum
line-of-sight covering factors predicts saturation in several lines, consistent
with the lack of observed variability. 3) Column densities for the individual
metastable levels are measured from the resolved C III *1175 absorption complex
observed in one component. Based on our computed metastable level populations,
the electron density of this absorber is ~3x10^4 cm^-3. Photoionization
modeling results place it at ~25 pc from the central source. 4) Using
time-dependent calculations, we are able to reproduce the detailed variability
observed in this absorber, and derive upper limits on the distances for the
other components of 25-50 pc. 5) The ionization parameters derived for the
higher ionization UV absorbers are consistent with the modeling results for the
lowest-ionization X-ray component, but with smaller total column density. They
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. 6)
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. (abridged)Comment: 30 pages, 18 figures (7 color), emulateapj, accepted for publication
in The Astrophysical Journa
Hubble Space Telescope Ultraviolet Spectroscopy of Fourteen Low-Redshift Quasars
We present low-resolution ultraviolet spectra of 14 low redshift (z<0.8)
quasars observed with HST/STIS as part of a Snap project to understand the
relationship between quasar outflows and luminosity. By design, all
observations cover the CIV emission line. Nine of the quasars are from the
Hamburg-ESO catalog, three are from the Palomar-Green catalog, and one is from
the Parkes catalog. The sample contains a few interesting quasars including two
broad absorption line (BAL) quasars (HE0143-3535, HE0436-2614), one quasar with
a mini-BAL (HE1105-0746), and one quasar with associated narrow absorption
(HE0409-5004). These BAL quasars are among the brightest known (though not the
most luminous) since they lie at z<0.8. We compare the properties of these BAL
quasars to the z1.4 Large Bright Quasar samples. By
design, our objects sample luminosities in between these two surveys, and our
four absorbed objects are consistent with the v ~ L^0.62 relation derived by
Laor & Brandt (2002). Another quasar, HE0441-2826, contains extremely weak
emission lines and our spectrum is consistent with a simple power-law
continuum. The quasar is radio-loud, but has a steep spectral index and a
lobe-dominated morphology, which argues against it being a blazar. The unusual
spectrum of this quasar resembles the spectra of the quasars PG1407+265,
SDSSJ1136+0242, and PKS1004+13 for which several possible explanations have
been entertained.Comment: Uses aastex.cls, 21 pages in preprint mode, including 6 figures and 2
tables; accepted for publication in The Astronomical Journal (projected vol
133
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