1,642 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
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
The asymmetric radio structure and record jet of giant quasar 4C 34.47
Giant double-lobed radio source 4C34.47 displays a straight one-sided jet,
measuring a record length of 380kpc, in its double-lobed radio structure.
Assuming an intrinsically symmetric two-sided jet structure the radio source
jet axis must be at least 33 degrees away from the sky plane, that is within 57
degrees from the line of sight. The radio polarization properties indicate that
this giant source has largely outgrown the depolarizing halo generally
associated with the host galaxies of powerful radio sources. The measured small
depolarization asymmetry is nevertheless in accordance with its inferred
orientation. All data for this giant radio source are in agreement with its
preferred orientation as predicted within the unification scheme for powerful
radio sources. Seen under a small aspect angle the radio source is large but
not excessively large. The global properties of 4C34.47 do not differ from
other giant (old) FR2 radio sources: it is a slowly expanding low-luminosity
radio source.Comment: Accepted for publication in Astronomy and Astrophysic
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
On the evolutionary behaviour of BL Lac objects
We present a new well defined sample of BL Lac objects selected from the
ROSAT All-Sky Survey (RASS). The sample consists of 39 objects with 35 forming
a flux limited sample down to f_X = 8 x 10^{-13} cgs, redshifts are known for
33 objects (and 31 of the complete sample). X-ray spectral properties were
determined for each object individually with the RASS data. The luminosity
function of RASS selected BL Lac objects is compatible with results provided by
objects selected with the Einstein observatory, but the RASS selected sample
contains objects with luminosities at least tenfold higher. Our analysis
confirms the negative evolution for X-ray selected BL Lac objects found in a
sample by the Einstein observatory, the parameterization provides similar
results. A subdivision of the sample into halves according to the X-ray to
optical flux ratio yielded unexpected results. The extremely X-ray dominated
objects have higher redshifts and X-ray luminosities and only this subgroup
shows clear signs of strong negative evolution. The evolutionary behaviour of
objects with an intermediate spectral energy distribution between X-ray and
radio dominated is compatible with no evolution at all. Consequences for
unified schemes of X-ray and radio selected BL Lac objects are discussed.We
suggest that the intermediate BL Lac objects are the basic BL Lac population.
The distinction between the two subgroups can be explained if extreme X-ray
dominated BL Lac objects are observed in a state of enhanced X-ray activity.Comment: 14 pages incl. 8 figures, accepted by A&
Rapid Single-Shot Measurement of a Singlet-Triplet Qubit
We report repeated single-shot measurements of the two-electron spin state in
a GaAs double quantum dot. The readout scheme allows measurement with fidelity
above 90% with a 7 microsecond cycle time. Hyperfine-induced precession between
singlet and triplet states of the two-electron system are directly observed, as
nuclear Overhauser fields are quasi-static on the time scale of the measurement
cycle. Repeated measurements on millisecond to second time scales reveal
evolution of the nuclear environment.Comment: supplemental material at
http://marcuslab.harvard.edu/papers/single_shot_sup.pd
Probing the BLR in AGNs using time variability of associated absorption line
It is know that most of the clouds producing associated absorption in the
spectra of AGNs and quasars do not completely cover the background source
(continuum + broad emission line region, BLR). We note that the covering factor
derived for the absorption is the fraction of photons occulted by the absorbing
clouds, and is not necessarily the same as the fractional area covered. We show
that the variability in absorption lines can be produced by the changes in the
covering factor caused by the variation in the continuum and the finite light
travel time across the BLR. We discuss how such a variability can be
distinguished from the variability caused by other effects and how one can use
the variability in the covering factor to probe the BLR.Comment: 12 pages, latex(aaspp4.sty), 2 figures, (To appear in ApJ
The Kast Ground Based UV Spectral Survey of 79 QSOs at Redshift 2 for Lyman Alpha Forest and Metal Absorption
We present a moderate resolution (~1.15 Angstroms/pixel) survey of 79 quasars
obtained using the Kast spectrograph on the Shane 3m telescope at Lick
observatory. The spectra span the wavelength range of 3175-5880 Angstroms, and
have typical signal to noise of 6-20 in the regions of the spectra showing
Lyman alpha forest absorption. The quasars have a mean emission redshift of
z=2.17, and nearly all cover the entire Lyman alpha forest between Lyman alpha
and Lyman beta. Although the quasars were selected to avoid BAL, two quasars in
the survey are BAL, one of which is a new discovery. We list the HI and metal
ions observed in a total of 140 absorption systems. We also identify 526
emission lines, and list their observed wavelengths, along with new redshifts
of the quasars. We determine the rest wavelengths of 3 emission lines or line
blends in the forest to be 1070.95 +/- 1.00, 1123.13 +/- 0.51, and 1175.88 +/-
0.30 Angstroms.Comment: Submitted to the Astronomical Journa
Occurrence and Global Properties of Narrow CIV lambda 1549 Absorption Lines in Moderate-Redshift Quasars
A statistical study is presented of (a) the frequency of narrow CIV lambda
1549 absorption lines in 1.5 <~ z <~ 3.6 radio-quiet and radio-loud quasars,
and of (b) the UV and radio properties of the absorbed quasars. The quasar
sample is unbiased with respect to absorption properties and the radio-quiet
and radio-loud subsamples are well matched in redshift and luminosity. A
similarly high incidence (>~50%) of narrow CIV absorbers is detected for the
radio-quiet and radio-loud quasars, and a constant ~25% of all the quasars,
irrespective of radio type display associated CIV absorbers stronger than a
rest equivalent width of 0.5A. Both radio-quiet and radio-loud quasars with
narrow absorption lines have systematically redder continua, especially
strongly absorbed objects. There is evidence of inclination dependent dust
reddening and absorption for the radio quasars. An additional key result is
that the most strongly absorbed radio quasars have the largest radio source
extent. This result is in stark contrast to a recent study of the low-frequency
selected Molonglo survey in which a connection between the strength of the
narrow absorbers and the (young) age of the radio source has been proposed. The
possible origin of these discrepant results is discussed and may be related to
the higher source luminosity for the quasars studied here.Comment: 28 pages, including 10 figures and 8 tables. To appear in ApJ, 599,
December 200
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