3,513 research outputs found
Large amounts of optically-obscured star formation in the host galaxies of some type-2 quasars
We present Hubble Space Telescope images, and spectral energy distributions
from optical to infrared wavelengths for a sample of six 0.3<z<0.8 type-2
quasars selected in the mid-infrared using data from the Spitzer Space
Telescope. All the host galaxies show some signs of disturbance. Most seem to
possess dusty, star-forming disks. The disk inclination, estimated from the
axial ratio of the hosts, correlates with the depth of the silicate feature in
the mid-infrared spectra, implying that at least some of the reddening towards
the AGN arises in the host galaxy. The star formation rates in these objects,
as inferred from the strengths of the PAH features and far-infrared continuum,
range from 3-90 Msun/yr, but are mostly much larger than those inferred from
the [OII]3727 emission line luminosity, due to obscuration. Taken together with
studies of type-2 quasar hosts from samples selected in the optical and X-ray,
this is consistent with previous suggestions that two types of extinction
processes operate within the type-2 quasar population, namely a component due
to the dusty torus in the immediate environment of the AGN, and a more extended
component due to a dusty, star forming disk.Comment: 5 pages, 3 figures. Accepted by ApJ Letter
Radio Galaxy Clustering at z~0.3
Radio galaxies are uniquely useful as probes of large-scale structure as
their uniform identification with giant elliptical galaxies out to high
redshift means that the evolution of their bias factor can be predicted. As the
initial stage in a project to study large-scale structure with radio galaxies
we have performed a small redshift survey, selecting 29 radio galaxies in the
range 0.19<z<0.45 from a contiguous 40 square degree area of sky. We detect
significant clustering within this sample. The amplitude of the two-point
correlation function we measure is consistent with no evolution from the local
(z<0.1) value. This is as expected in a model in which radio galaxy hosts form
at high redshift and thereafter obey a continuity equation, although the
signal:noise of the detection is too low to rule out other models. Larger
surveys out to z~1 should reveal the structures of superclusters at
intermediate redshifts and strongly constrain models for the evolution of
large-scale structure.Comment: 7 pages, 3 figures, accepted by ApJ Letter
Analysis of progeny from interallelic crosses
Analysis of progeny from interallelic crosse
[Su-2\u3csub\u3ea\u3c/sub\u3e, one of the genes which suppress the td-2]
[Su-2a, one of the genes which suppress the td-2
Neurospora in the freshman biology course.
Neurospora in the freshman biology course
Attempts to increase fertility in interallelic crosses
Attempts to increase fertility in interallelic crosse
Tryptophan synthetase levels in hist-1 mutants
Trypophan synthetase levels in hist-1 mutant
Radio and near-infrared observations of the steep spectrum Galactic plane radio source WKB 0314+57.8
Radio and near-infared observations towards the steep spectrum Galactic plane
radio source WKB 0314+57.8 are presented, in order to clarify the nature of
this source. The radio observations include archival and survey data, together
with new Giant Metrewave Radio Telescope observations at 617 MHz. The
near-infrared observations are in the J and K bands, from the Gemini instrument
on the Shane 3-m telescope. The radio observations show that WKB 0314+57.8 is
extended, with an very steep spectrum (with flux density proportional to
frequency to -2.5 power between 40 MHz and 1.5 GHz). The colour--magnitude
diagram constructed from near-infrared observations of the field suggests the
presence of a z approx 0.08 galaxy cluster behind the Galactic plane, reddened
by about 6 magnitudes of visual extinction. Although the steep spectrum source
has no obvious identification, two other radio sources in the field covered by
the near-infrared observations have tentative identifications with galaxies.
These observations indicate that WKB 0314+57.8 is a relic source in a cluster
of galaxies, not a pulsar.Comment: 6 pages, to appear in MNRAS, typos correcte
Mid-infrared selection of quasar-2s in Spitzer's First Look Survey
We present early results from the spectroscopic follow-up of a sample of
candidate obscured AGN selected in the mid-infrared from the Spitzer First Look
Survey. Our selection allows a direct comparison of the numbers of obscured and
unobscured AGN at a given luminosity for the first time, and shows that the
ratio of obscured to unobscured AGN at infrared luminosities corresponding to
low luminosity quasars is ~1:1 at z~0.5. Most of our optically-faint candidate
obscured AGN have the high-ionization, narrow-line spectra expected from type-2
AGN. A composite spectrum shows evidence for Balmer absorption lines,
indicating recent star-formation activity in the host galaxies. There is
tentative evidence for a decrease in the obscured AGN fraction with increasing
AGN luminosity.Comment: To appear in the proceedings of the workshop "Multiband approach to
AGN" Bonn October 2004 in Memorie della Societa Astronomica Italian
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