2,529 research outputs found
Clues to Quasar Broad Line Region Geometry and Kinematics
We present evidence that the high-velocity CIV lambda 1549 emission line gas
of radio-loud quasars may originate in a disk-like configuration, in close
proximity to the accretion disk often assumed to emit the low-ionization lines.
For a sample of 36 radio-loud z~2 quasars we find the 20--30% peak width to
show significant inverse correlations with the fractional radio core-flux
density, R, the radio axis inclination indicator. Highly inclined systems have
broader line wings, consistent with a high-velocity field perpendicular to the
radio axis. By contrast, the narrow line-core shows no such relation with R, so
the lowest velocity CIV-emitting gas has an inclination independent velocity
field. We propose that this low-velocity gas is located at higher
disk-altitudes than the high-velocity gas. A planar origin of the high-velocity
CIV-emission is consistent with the current results and with an accretion
disk-wind emitting the broad lines. A spherical distribution of randomly
orbiting broad-line clouds and a polar high-ionization outflow are ruled out.Comment: 5 Latex pages, 1 figure, accepted for publication in ApJ Letter
Radio imaging of core-dominated high redshift quasars
VLA imaging at kiloparsec-scale resolution of sixteen core-dominated
radio-loud QSOs is presented. Many objects appear to display variable radio
emission and their radio morphologies are significantly smaller than those of
steep-spectrum quasars, consistent with these objects being observed at sight
lines close to their (relativistic, 4-7) jet axes. The
usefulness of the radio source orientation indicator R_V, being defined as
ratio of radio core and rest frame optical V-band luminosity, is confirmed.Comment: 11 pages, 11 postscript figures, uses aa.cls 4.03 for LaTeX2e To
appear in Astronomy and Astrophysic
Star-forming QSO host galaxies
The recent finding of substantial masses of cold molecular gas as well as
young stellar populations in the host galaxies of quasars is at odds with
results of Hubble Space Telescope imaging studies, since the latter appear to
yield mature, quiescent early type hosts. It is demonstrated here that the
characterization as `quiescent' is incorrect. Radio and far-infrared properties
of both the HST sample and a larger comparison sample of uv-excess selected
radio-quiet QSOs are consistent with substantial recent star-formation
activity.Comment: Accepted for publication by Astronomy & Astrophysic
Environment of compact extragalactic radio sources
We have studied the interrelation of young AGN with their hosts. The objects
of study are the young and powerful GPS and CSS radio sources. Due to their
small size, GPS and CSS sources are excellent probes of this relation.
Furhthermore, their young age allows us to compare them to the larger, old
radio sources and establish a time-line evolution of this relation. Combining
imaging and spectroscopy at UV, optical and radio wavelengths we find evidence
of strong interaction between the host and the radio source. The presence and
expansion of the radio source clearly affects the properties and evolution of
the host. Furthermore, the radio source and host significantly affect each
other's evolution. We describe our results and how these interactions take
place.Comment: 6 pages. To appear in "Highlights of Spanisg astrophysics IV.
Proceedings of the VII scientific meeting of the Spanish Astronomical
Society". Editors: F. Figueras, J.M. Girart, M.Hernanz, C. Jordi. Springe
Early Growth and Efficient Accretion of Massive Black Holes at High Redshift
Black-hole masses of the highest redshift quasars (4 <~ z <~ 6) are estimated
using a previously presented scaling relationship, derived from reverberation
mapping of nearby quasars, and compared to quasars at lower redshift. It is
shown that the central black holes in luminous z >~ 4 quasars are very massive
(>~ 10^9 solar masses). It is argued that the mass estimates of the high-z
quasars are not subject to larger uncertainties than those for nearby quasars.
Specifically, the large masses are not overestimates and the lack of similarly
large black-hole masses in the nearby Universe does not rule out their
existence at high-z. However, AGN host galaxies do not typically appear fully
formed or evolved at these early epochs. This supports scenarios in which black
holes build up mass very fast in a radiatively inefficient (or obscured) phase
relative to the stars in their galaxies. Additionally, upper envelopes of
black-hole mass of approximately 10^{10} solar masses and bolometric luminosity
of ~ 10^{48} erg/s are observed at all redshifts.Comment: 17 pages including 7 figures (5 in color) and 1 table. To appear in
ApJ, v600, January 1, 200
1245+676 - a CSO/GPS source being an extreme case of a double-double structure
AGN with the so-called `double-double' radio structure have been interpreted
as restarted AGN where the inner structure is a manifestation of a new phase of
activity which happened to begin before the outer radio lobes resulting from
the previous one had faded completely. The radio galaxy 1245+676 is an extreme
example of such a double-double object - its outer structure, measuring 970
h^{-1} kpc, is five orders of magnitude larger than the 9.6 h^{-1} pc inner
one. We present a series of VLBI observations of the core of 1245+676 which
appears to be a compact symmetric object (CSO). We have detected the motion of
the CSO's lobes, measured its velocity, and inferred the kinematic age of that
structure.Comment: A contribution to The Third Workshop on Compact Steep Spectrum and
GHz-Peaked Spectrum Radio Sources, Kerastari, Greece May 28-31, 2002.
Refereed and accepted by Publications of the Astronomical Society of
Australia. 4 pages. Final version copyedited by PASA Edito
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Enhancing Terminal Deoxynucleotidyl Transferase Activity on Substrates with 3' Terminal Structures for Enzymatic De Novo DNA Synthesis.
Enzymatic oligonucleotide synthesis methods based on the template-independent polymerase terminal deoxynucleotidyl transferase (TdT) promise to enable the de novo synthesis of long oligonucleotides under mild, aqueous conditions. Intermediates with a 3' terminal structure (hairpins) will inevitably arise during synthesis, but TdT has poor activity on these structured substrates, limiting its usefulness for oligonucleotide synthesis. Here, we described two parallel efforts to improve the activity of TdT on hairpins: (1) optimization of the concentrations of the divalent cation cofactors and (2) engineering TdT for enhanced thermostability, enabling reactions at elevated temperatures. By combining both of these improvements, we obtained a ~10-fold increase in the elongation rate of a guanine-cytosine hairpin
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