1,520 research outputs found
A view of the narrow-line region in the infrared: active galactic nuclei with resolved fine-structure lines in the Spitzer archive
We queried the Spitzer archive for high-resolution observations with the
Infrared Spectrograph of optically selected active galactic nuclei (AGN) for
the purpose of identifying sources with resolved fine-structure lines that
would enable studies of the narrow-line region (NLR) at mid-infrared
wavelengths. By combining 298 Spitzer spectra with 6 Infrared Space Observatory
spectra, we present kinematic information of the NLR for 81 z<=0.3 AGN. We used
the [NeV], [OIV], [NeIII], and [SIV] lines, whose fluxes correlate well with
each other, to probe gas photoionized by the AGN. We found that the widths of
the lines are, on average, increasing with the ionization potential of the
species that emit them. No correlation of the line width with the critical
density of the corresponding transition was found. The velocity dispersion of
the gas, sigma, is systematically higher than that of the stars, sigma_*, in
the AGN host galaxy, and it scales with the mass of the central black hole,
M_BH. Further correlations between the line widths and luminosities L, and
between L and M_BH, are suggestive of a three dimensional plane connecting
log(M_BH) to a linear combination of log(sigma) and log(L). Such a plane can be
understood within the context of gas motions that are driven by AGN feedback
mechanisms, or virialized gas motions with a power-law dependence of the NLR
radius on the AGN luminosity. The M_BH estimates obtained for 35 type 2 AGN
from this plane are consistent with those obtained from the M_BH-sigma_*
relation.Comment: ApJ, revised to match the print versio
Near Infrared Spectroscopy of High Redshift Active Galactic Nuclei. II. Disappearing Narrow Line Regions and the Role of Accretion
We present new near infrared spectroscopic measurements for 29 luminous
high-z quasars and use the data to discuss the size and other properties of the
NLRs in those sources. The high resolution spectra have been used to carefully
model the Fe II blends and to provide reliable [O III], Fe II and Hb
measurements. We find that about 2/3 of all high luminosity sources show strong
[O III] lines while the remaining objects show no or very weak such line. While
weak [O III] emitters are also found among lower luminosity AGN, we argue that
the implications for very high luminosity objects are different. In particular,
we suggest that the averaging of these two populations in other works gave rise
to claims of a Baldwin relationship in [O III] which is not confirmed by our
data. We also argue that earlier proposed relations of the type R_NLR \propto
L_[O III]^{1/2}, where R_NLR is the NLR radius, are theoretically sound yet
they must break down for R_NLR exceeding a few kpc. This suggests that the NLR
properties in luminous sources are different from those observed in nearby AGN.
In particular, we suggest that some sources lost their very large, dynamically
unbound NLR while others are in a phase of violent star-forming events that
produce a large quantity of high density gas in the central kpc. This gas is
ionized and excited by the central radiation source and its spectroscopic
properties may be different from those observed in nearby, lower luminosity
NLRs. We also discuss the dependence of EW(Hb) and Fe II/Hb on L, M_BH, and
accretion rate for a large sample of AGNs. The strongest dependence of the two
quantities is on the accretion rate and the Fe II/Hb correlation is probably
due to the EW(Hb) dependence on accretion rate. We show the most extreme values
measured so far of Fe II/Hb and address its correlation with EW([O III]).Comment: 10 pages (emulateapj), 9 figures. Accepted by Ap
High-ionization mid-infrared lines as black hole mass and bolometric luminosity indicators in active galactic nuclei
We present relations of the black hole mass and the optical luminosity with
the velocity dispersion and the luminosity of the [Ne V] and the [O IV]
high-ionization lines in the mid-infrared (MIR) for 28 reverberation-mapped
active galactic nuclei. We used high-resolution Spitzer Infrared Spectrograph
and Infrared Space Observatory Short Wavelength Spectrometer data to fit the
profiles of these MIR emission lines that originate from the narrow-line region
of the nucleus. We find that the lines are often resolved and that the velocity
dispersion of [Ne V] and [O IV] follows a relation similar to that between the
black hole mass and the bulge stellar velocity dispersion found for local
galaxies. The luminosity of the [Ne V] and the [O IV] lines in these sources is
correlated with that of the optical 5100A continuum and with the black hole
mass. Our results provide a means to derive black hole properties in various
types of active galactic nuclei, including highly obscured systems.Comment: accepted for publication in ApJ
Quasar Parallax: a Method for Determining Direct Geometrical Distances to Quasars
We describe a novel method to determine direct geometrical distances to
quasars that can measure the cosmological constant, Lambda, with minimal
assumptions. This method is equivalent to geometric parallax, with the
`standard length' being the size of the quasar broad emission line region
(BELR) as determined from the light travel time measurements of reverberation
mapping. The effect of non-zero Lambda on angular diameter is large, 40% at
z=2, so mapping angular diameter distances vs. redshift will give Lambda with
(relative) ease. In principle these measurements could be made in the UV,
optical, near infrared or even X-ray bands. Interferometers with a resolution
of 0.01mas are needed to measure the size of the BELR in z=2 quasars, which
appear plausible given reasonable short term extrapolations of current
technology.Comment: 13 pages, with 3 figures. ApJ Letters, in press (Dec 20, 2002
Detailed Analysis of Balmer Lines in a Sloan Digital Sky Survey Sample of 90 Broad Line Active Galactic Nuclei
In order to contribute to the general effort aiming at the improvement of our
knowledge about the physical conditions within the Broad Line Region (BLR) of
Active Galactic Nuclei (AGN), here we present the results achieved by our
analysis of the spectral properties of a sample of 90 broad line emitting
sources, collected at the Sloan Digital Sky Survey (SDSS) database. By focusing
our attention mainly onto the Balmer series of hydrogen emission lines, which
is the dominant feature in the optical wavelength range of many BLR spectra, we
extracted several flux and profile measurements, which we related to other
source properties, such as optical continuum luminosities, inferred black hole
masses, and accretion rates. Using the Boltzmann Plot method to investigate the
Balmer line flux ratios as a function of the line profiles, we found that
broader line emitting AGN typically have larger H_alpha / H_beta and smaller
H_gamma / H_beta and H_delta / H_beta line ratios. With the help of some recent
investigations, we model the structure of the BLR and we study the influence of
the accretion process on the properties of the BLR plasma.Comment: 14 pages, 11 figures, fixes the wrong names of 4 objects; published
on Ap
The Near-Infrared Broad Emission Line Region of Active Galactic Nuclei -- I. The Observations
We present high quality (high signal-to-noise ratio and moderate spectral
resolution) near-infrared (near-IR) spectroscopic observations of 23 well-known
broad-emission line active galactic nuclei (AGN). Additionally, we obtained
simultaneous (within two months) optical spectroscopy of similar quality. The
near-IR broad emission line spectrum of AGN is dominated by permitted
transitions of hydrogen, helium, oxygen, and calcium, and by the rich spectrum
of singly-ionized iron. In this paper we present the spectra, line
identifications and measurements, and address briefly some of the important
issues regarding the physics of AGN broad emission line regions. In particular,
we investigate the excitation mechanism of neutral oxygen and confront for the
first time theoretical predictions of the near-IR iron emission spectrum with
observations.Comment: 45 pages, 17 figures, accepted by ApJ
Predictors of Long-Term Visual Outcome in Intermediate Uveitis
PURPOSE: To describe factors that predict visual loss and complications in intermediate uveitis.
DESIGN:
Cross-sectional study.
PARTICIPANTS:
Subjects with intermediate uveitis were identified from a database of 1254 uveitis patients seen in the clinic of a single consultant (S.L.L.) between 2011 and 2013.
S
METHODS:
Information was gathered from the clinical notes of all subjects examined in clinic.
MAIN OUTCOME MEASURES:
Best-corrected visual acuity (BCVA), moderate visual loss (MVL; ≤20/50), severe visual loss (SVL; ≤20/200).
RESULTS:
Three hundred and five subjects (550 eyes) were included in the study, comprising 24.3% of subjects seen in clinic. Mean (± standard deviation) age at diagnosis was 40.9±16.9 years, and 64.6% of subjects were female. Median follow-up was 8.2 years (mean, 9.7 years, 5452 eye-years). Systemic diagnosis was made in 36.1% of patients, with sarcoidosis (22.6%) and multiple sclerosis (4.6%) the most frequent systemic associations. Median BCVA was 20/30 (mean logarithm of the minimum angle of resolution [logMAR] 0.26±0.38, n = 550 eyes) at presentation, 20/30 (mean logMAR 0.22±0.42, n = 430) at 5 years, and 20/30 (mean logMAR 0.23±0.46, n = 260) at 10 years. Macular edema was observed in 224 eyes (40.7%) and was associated with idiopathic disease (P = 0.001) and diabetes (P = 0.001). Topical therapy was used in 82.7%, and 34.2% received local injections of corticosteroids. A total of 50.5% required oral steroids and 13.8% required second-line immunosuppression. Subjects with a diagnosis of sarcoidosis were less likely to require a second-line agent (4.3% vs. 16.2%, P = 0.011). On multivariate analysis, visual acuity at referral, retinal pigment epithelial atrophy, and macular scarring were associated with increased risk of MVL; and visual acuity at referral, local therapy, macular scarring, retinal detachment, and hypotony and phthisis were associated with increased risk of SVL.
CONCLUSIONS:
Intermediate uveitis has a long disease course with frequent complications and often requires systemic treatment. Despite this, most subjects are still able to achieve good long-term visual outcomes
Enhanced Star Formation in Narrow Line Seyfert 1 AGN revealed by Spitzer
We present new low resolution Spitzer mid-infrared spectroscopy of a sample
of 20 ROSAT selected local Narrow Line Seyfert 1 galaxies (NLS1s). We detect
strong AGN continuum in all and clear PAH emission in 70% of the sources. The
6.2 micron PAH luminosity spans three orders of magnitudes, from ~10^(39) erg/s
to ~10^(42) erg/s providing strong evidence for intense ongoing star formation
in the circumnuclear regions of these sources. Using the IRS/Spitzer archive we
gather a large number of additional NLS1s and their broad line counterparts
(BLS1s) and constructed NLS1 and BLS1 sub-samples to compare them in various
ways. The comparison shows a clear separation according to FWHM(H_beta) such
that objects with narrower broad H_beta lines are the strongest PAH emitters.
We test this division in various ways trying to remove biases due to luminosity
and aperture size. Specifically, we find that star formation activity around
NLS1 AGN is larger than around BLS1 of the same AGN luminosity. The above
result seems to hold over the entire range of distance and luminosity. Moreover
the star formation rate is higher in low black hole mass and high L/L_Edd
systems indicating that black hole growth and star formation are occurring
simultaneously.Comment: 30 pages, 11 figures, 4 tables. Now accepted in MNRA
X-ray Characteristics of NGC 3516: A View through the Complex Absorber
We consider new Suzaku data for NGC 3516 taken during 2009, along with other
recent X-ray observations of the source. The cumulative characteristics of NGC
3516 cannot be explained without invoking changes in the line-of-sight
absorption. Contrary to many other well-studied Seyfert galaxies, NGC 3516 does
not show a positive lag of hard X-ray photons relative to soft photons over the
timescales sampled. In the context of reverberation models for the X-ray lags,
the lack of such a signal in NGC 3516 is consistent with flux variations being
dominated by absorption changes. The lack of any reverberation signal in such a
highly variable source disfavors intrinsic continuum variability in this case.
Instead, the colorless flux variations observed at high flux states for NGC
3516 are suggested to be a consequence of Compton-thick clumps of gas crossing
the line-of-sight.Comment: 12 pages, 6 figures, accepted for publication in The Astrophysical
Journa
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