2,634 research outputs found
Mean Occupation Function of High Redshift Quasars from the Planck Cluster Catalog
We characterise the distribution of quasars within dark matter halos using a
direct measurement technique for the first time at redshifts as high as . Using the Planck Sunyaev-Zeldovich (SZ) catalogue for galaxy groups and the
Sloan Digital Sky Survey (SDSS) DR12 quasar dataset, we assign host
clusters/groups to the quasars and make a measurement of the mean number of
quasars within dark matter halos as a function of halo mass. We find that a
simple power-law fit of \log\left = (2.11 \pm 0.01) \log (M) -(32.77
\pm 0.11) can be used to model the quasar fraction in dark matter halos. This
suggests that the quasar fraction increases monotonically as a function of halo
mass even to redshifts as high as .Comment: Accepted for publication in PAS
SALT Long-slit Spectroscopy of Luminous Obscured Quasars: An Upper Limit on the Size of the Narrow-Line Region?
We present spatially resolved long-slit spectroscopy from the Southern
African Large Telescope (SALT) to examine the spatial extent of the narrow-line
regions (NLRs) of a sample of 8 luminous obscured quasars at 0.10 < z < 0.43.
Our results are consistent with an observed shallow slope in the relationship
between NLR size and L_[OIII], which has been interpreted to indicate that NLR
size is limited by the density and ionization state of the NLR gas rather than
the availability of ionizing photons. We also explore how the NLR size scales
with a more direct measure of instantaneous AGN power using mid-IR photometry
from WISE, which probes warm to hot dust near the central black hole and so,
unlike [OIII], does not depend on the properties of the NLR. Using our results
as well as samples from the literature, we obtain a power-law relationship
between NLR size and L_8micron that is significantly steeper than that observed
for NLR size and L_[OIII]. We find that the size of the NLR goes approximately
as L^(1/2)_8micron, as expected from the simple scenario of constant-density
clouds illuminated by a central ionizing source. We further see tentative
evidence for a flattening of the relationship between NLR size and L_8micron at
the high luminosity end, and propose that we are seeing a limiting NLR size of
10 - 20 kpc, beyond which the availability of gas to ionize becomes too low. We
find that L_[OIII] ~ L_8micron^(1.4), consistent with a picture in which the
L_[OIII] is dependent on the volume of the NLR. These results indicate that
high-luminosity quasars have a strong effect in ionizing the available gas in a
galaxy.Comment: 9 Pages, 5 figures, accepted to Ap
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