448 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
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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