471 research outputs found
Far-infrared and accretion luminosities of the present-day active galactic nuclei
We investigate the relation between star formation (SF) and black hole
accretion luminosities, using a sample of 492 type-2 active galactic nuclei
(AGNs) at z < 0.22, which are detected in the far-infrared (FIR) surveys with
AKARI and Herschel. We adopt FIR luminosities at 90 and 100 um as SF
luminosities, assuming the proposed linear proportionality of star formation
rate with FIR luminosities. By estimating AGN luminosities from [OIII]5007 and
[OI]6300 emission lines, we find a positive linear trend between FIR and AGN
luminosities over a wide dynamical range. This result appears to be
inconsistent with the recent reports that low-luminosity AGNs show essentially
no correlation between FIR and X-ray luminosities, while the discrepancy is
likely due to the Malmquist and sample selection biases. By analyzing the
spectral energy distribution, we find that pure-AGN candidates, of which FIR
radiation is thought to be AGN-dominated, show significantly low-SF activities.
These AGNs hosted by low-SF galaxies are rare in our sample (~ 1%). However,
the low fraction of low-SF AGN is possibly due to observational limitations
since the recent FIR surveys are insufficient to examine the population of
high-luminosity AGNs hosted by low-SF galaxies.Comment: Accepted for publication in ApJ, 13 pages, 9 figure
The Prevalence of Gas Outflows in Type 2 AGNs. II. 3D Biconical Outflow Models
We present 3D models of biconical outflows combined with a thin dust plane
for investigating the physical properties of the ionized gas outflows and their
effect on the observed gas kinematics in type 2 active galactic nuclei (AGNs).
Using a set of input parameters, we construct a number of models in 3D and
calculate the spatially integrated velocity and velocity dispersion for each
model. We find that three primary parameters, i.e., intrinsic velocity, bicone
inclination, and the amount of dust extinction, mainly determine the simulated
velocity and velocity dispersion. Velocity dispersion increases as the
intrinsic velocity or the bicone inclination increases, while velocity (i.e.,
velocity shifts with respect to systemic velocity) increases as the amount of
dust extinction increases. Simulated emission-line profiles well reproduce the
observed [O III] line profiles, e.g., a narrow core and a broad wing
components. By comparing model grids and Monte Carlo simulations with the
observed [O III] velocity-velocity dispersion (VVD) distribution of ~39,000
type 2 AGNs, we constrain the intrinsic velocity of gas outflows ranging from
~500 km/s to ~1000 km/s for the majority of AGNs, and up to ~1500-2000 km/s for
extreme cases. The Monte Carlo simulations show that the number ratio of AGNs
with negative [O III] velocity to AGNs with positive [O III] velocity
correlates with the outflow opening angle, suggesting that outflows with higher
intrinsic velocity tend to have wider opening angles. These results demonstrate
the potential of our 3D models for studying the physical properties of gas
outflows, applicable to various observations, including spatially integrated
and resolved gas kinematics.Comment: 14 pages, 14 figures, 2 tables; matched with the ApJ published
versio
MgII Line Variability of High Luminosity Quasars
We monitored five high-luminosity quasars with lambda L_{3000A} > 10^45 erg
s^-1 at 0.4 < z < 0.6 to measure flux variability of the MgII 2798 line and
explore feasibility of reverberation mapping using MgII. Over the two year
monitoring program, imaging data were obtained with the A Noble Double-Imaging
Camera on the 1.3-m telescope at the Cerro Tololo Inter-American Observatory
(CTIO), while spectroscopic data were obtained at the same night with the R-C
spectrograph on the 1.5-m telescope at the CTIO. By performing differencial
photometry using available field stars in each quasar image, we measured
variability -- 10%-24% peak-to-peak changes and 3%-8% rms variations -- in the
B band, which includes flux changes in the rest-frame UV continuum (~2500A --
~3600A) as well as the MgII line. Utilizing photometric measurements for
spectroscopic flux calibration, we measured the MgII line flux and the
continuum flux at 3000\AA from each single-epoch spectrum. Four objects showed
MgII line flux variability with 23%-50% peak-to-peak changes and 8%-17% rms
variations over 1-1.5 year rest-frame time scales, while one object showed no
MgII flux variability within the measurement error (<5%). We also detected
4%-15% rms variations of the MgII line width for all five objects. With
synchronous observations for photometry and spectroscopy, we demonstrated the
feasibility of the MgII line reverberation mapping for high-luminosity quasars
at intermediate redshift.Comment: AJ in press, 8 pages, 8 figures edited versio
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