471 research outputs found

    Far-infrared and accretion luminosities of the present-day active galactic nuclei

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    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

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    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

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    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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