75 research outputs found
The optically-powerful quasar E1821+643 is associated with a 300-kpc scale FRI radio structure
We present a deep image of the optically-powerful quasar E1821+643 at 18cm
made with the Very Large Array (VLA). This image reveals radio emission, over
280 kpc in extent, elongated way beyond the quasar's host galaxy. Its radio
structure has decreasing surface brightness with increasing distance from the
bright core, characteristic of FRI sources (Fanaroff & Riley 1974). Its radio
luminosity at 5GHz falls in the classification for `radio-quiet' quasars (it is
only 10^23.9 W/Hz/sr; see e.g. Kellermann et al 1994). Its radio luminosity at
151MHz (which is 10^25.3 W/Hz/sr) is at the transition luminosity observed to
separate FRIs and FRIIs. Hitherto, no optically-powerful quasar had been found
to have a conventional FRI radio structure. For searches at low-frequency this
is unsurprising given current sensitivity and plausible radio spectral indices
for radio-quiet quasars. We demonstrate the inevitability of the extent of any
FRqI radio structures being seriously under-estimated by existing targetted
follow-up observations of other optically-selected quasars, which are typically
short exposures of z > 0.3 objects, and discuss the implications for the
purported radio bimodality in quasars.
The nature of the inner arcsec-scale jet in E1821+643, together with its
large-scale radio structure, suggest that the jet-axis in this quasar is
precessing (cf. Galactic jet sources such as SS433). A possible explanation for
this is that its central engine is a binary whose black holes have yet to
coalesce. The ubiquity of precession in `radio-quiet' quasars, perhaps as a
means of reducing the observable radio luminosity expected in highly-accreting
systems, remains to be established.Comment: Accepted by ApJ Letters; higher quality versions of figures available
at http://www-astro.physics.ox.ac.uk/~km
Probing Cool and Warm Infrared Galaxies using Photometric and Structural Measures
We have analyzed a sample of nearby cool and warm infrared (IR) galaxies
using photometric and structural parameters. The set of measures include
far-infrared color (), total IR
luminosity (), radio surface brightness as well as radio,
near-infrared, and optical sizes. In a given luminosity range cool and warm
galaxies are considered as those sources that are found approximately below and above the mean color in the far-infrared
diagram. We find that galaxy radio surface brightness is well correlated with
color whereas size is less well correlated with color. Our analysis indicates
that IR galaxies that are dominated by cool dust are large, massive spirals
that are not strongly interacting or merging and presumably the ones with the
least active star formation. Dust in these cool objects is less centrally
concentrated than in the more typical luminous and ultra-luminous IR galaxies
that are dominated by warm dust. Our study also shows that low luminosity early
type unbarred and transitional spirals are responsible for the large scatter in
the diagram. Among highly luminous galaxies, late type unbarred
spirals are predominately warm, and early type unbarred and barred are
systematically cooler. We highlight the significance of diagram
in terms of local and high redshifts sub-millimeter galaxies.Comment: Accepted for publication in ApJ, 2006, 23 pages, 3 postscript
figures, 1 table. The table can be obtained on request from the author
A relativistic jet in the radio-quiet quasar PG1407+263
We present the results of a multi-epoch radio monitoring campaign measuring
the milliarcsecond structure of the jet in the radio-quiet quasar PG1407+263.
This is the highest-sensitivity, highest-resolution multi-year study of a
distant active galaxy. The observations are naturally explained in terms of a
beamed relativistic jet, some of whose fluctuations in flux density can be
ascribed to interaction with the narrow-line region of the quasar. The optical
properties of PG1407+263, in particular the low equivalent widths of the
emission lines, may be related to the fact that we are viewing this quasar
almost pole-on, giving us a direct view into its broad-line region.Comment: 4 pages, uses emulateapj5.sty; accepted by ApJ Letter
The Structure of IR Luminous Galaxies at 100 Microns
We have observed twenty two galaxies at 100 microns with the Kuiper Airborne
Observatory in order to determine the size of their FIR emitting regions. Most
of these galaxies are luminous far-infrared sources, with L_FIR > 10^11 L_sun.
This data constitutes the highest spatial resolution ever achieved on luminous
galaxies in the far infrared. Our data includes direct measurements of the
spatial structure of the sources, in which we look for departures from point
source profiles. Additionally, comparison of our small beam 100 micron fluxes
with the large beam IRAS fluxes shows how much flux falls beyond our detectors
but within the IRAS beam. Several sources with point- like cores show evidence
for such a net flux deficit. We clearly resolved six of these galaxies at 100
microns and have some evidence for extension in seven others. Those galaxies
which we have resolved can have little of their 100 micron flux directly
emitted by a point-like active galactic nucleus (AGN). Dust heated to ~40 K by
recent bursts of non-nuclear star formation provides the best explanation for
their extreme FIR luminosity. In a few cases, heating of an extended region by
a compact central source is also a plausible option. Assuming the FIR emission
we see is from dust, we also use the sizes we derive to find the dust
temperatures and optical depths at 100 microns which we translate into an
effective visual extinction through the galaxy. Our work shows that studies of
the far infrared structure of luminous infrared galaxies is clearly within the
capabilities of new generation far infrared instrumentation, such as SOFIA and
SIRTF.Comment: 8 tables, 23 figure
The Sunyaev-Zel'dovich Effect by Cocoons of Radio Galaxies
We estimate the deformation of the cosmic microwave background radiation by
the hot region (``cocoon'') around a radio galaxy. A simple model is adopted
for cocoon evolution while the jet is on, and a model of evolution is
constructed after the jet is off. It is found that at low redshift the phase
after the jet is off is longer than the lifetime of the jets. The Compton
y-parameter generated by cocoons is calculated with a Press-Schechter number
density evolution. The resultant value of y is of the same order as the COBE
constraint. The Sunyaev-Zeldovich effect due to cocoons could therefore be a
significant foreground source of small angular scale anisotropies in the cosmic
microwave background radiation.Comment: Published version, 23 pages with 5 figure
Investigation of early night sleep effects on subsequent fear extinction learning and recall
Extinction learning is considered an important underlying process of successful treatment of posttraumatic stress disorder (PTSD). However, sleep disturbances may impede this learning process: Current accounts postulate that sleep facilitates encoding by promoting neural plasticity during slow wave sleep (SWS). Based on this hypothesis, we tested whether early night sleep, with high amounts of SWS, facilitates subsequent extinction learning and recall. Sixty-three participants took part in a trauma-adapted fear conditioning experiment. One group received a three-hour sleep opportunity in the early night half, whereas the other group stayed awake. Thereafter, both groups underwent extinction training and a return-of-fear test. Retention was assessed after another sleep opportunity in both groups. Linear mixed-effects models and Bayesian inference did not support the hypothesis of strengthened fear extinction by prior early night sleep. Subsequent exploratory analyses, in contrast, point to a role of rapid eye movement sleep in promoting successful fear extinction learning. Further confirmatory research should re-investigate these effects and their implications for the treatment of PTSD
The Prospective Influence of Trait Alexithymia on Intrusive Memories: What Is the Role of Emotional Recognition Memory?
Posttraumatic stress disorder (PTSD) is often considered to be a disorder of memory as patients suffer from fragmented uncontrollable memories (intrusions) whilst experiencing difficulties in intentionally retrieving details of the traumatic event. Recent research suggests that trait-related deficits in the identification of emotional states (alexithymia) may impact emotional memory processes in a way that promotes intrusion formation in PTSD. Therefore, we investigated the influence of alexithymia on intrusive re-experiencing and emotional recognition memory in a prospective analog study. Twenty-six healthy participants took part in a laboratory experiment, which combined two independent paradigms. Participants were exposed to a traumatic film (first session) and completed an episodic memory task comprising neutral and emotional stimuli (second session). In between sessions, participants recorded intrusive memories of the film. Individuals with higher trait alexithymia (HTA) reported an increased number of intrusions on the day of film presentation. Moreover, analyses of memory performance revealed a negative correlation between alexithymia and emotional recognition memory. Further analyses suggest that reduced emotional recognition memory, as evident in individuals with HTA, may, in turn, be associated with enhanced intrusive re-experiencing. As such, the current findings provide first indications regarding the role of alexithymia in emotional learning and PTSD. Future studies should further investigate these associations as well as potential implications for the treatment of PTSD
APM 08279+5255: an ultraluminous BAL quasar at a redshift z=3.87
We report on the discovery of a highly luminous, broad absorption line quasar
at a redshift of which is positionally coincident, within one
arcsecond, with the IRAS FSC source F08279+5255. A chance alignment of the
quasar and the IRAS source is extremely unlikely and we argue that the optical
and FIR flux are different manifestations of the same object. With an R-band
magnitude of 15.2, and an IRAS 60\mum flux of 0.51\jy, APM 08279+5255 is
(apparently) easily the most intrinsically luminous object known, with
L_{Bol}\sim5\times10^{15}L_{\odot}}. Imaging suggests that gravitational
lensing may play a role in amplifying the intrinsic properties of the system.
The optical spectrum of the quasar clearly reveals the presence of three
potential lensing galaxies, \mg absorption systems at and ,
and a \ly absorption system at . We estimate the total amplification of
the optical component to be , but, due to the larger scale of the
emitting region, would expect the infrared amplification to be significantly
less. Even making the conservative assumption that all wavelengths are
amplified by a factor 40, APM 08279+5255 still possesses a phenomenal
luminosity of \simgt 10^{14L_{\odot}}, indicating that it belongs to a small,
but significant population of high--redshift, hyperluminous objects with
copious infrared emission.Comment: 15 Pages with Four figures. Accepted for publication in the
Astrophysical Journa
Radio Variability of Radio Quiet and Radio Loud Quasars
The majority of quasars are weak in their radio emission, with flux densities
comparable to those in the optical, and energies far lower. A small fraction,
about 10%, are hundreds to thousands of times stronger in the radio.
Conventional wisdom holds that there are two classes of quasars, the radio
quiets and radio louds, with a deficit of sources having intermediate power.
Are there really two separate populations, and if so, is the physics of the
radio emission fundamentally different between them? This paper addresses the
second question, through a study of radio variability across the full range of
radio power, from quiet to loud. The basic findings are that the root mean
square amplitude of variability is independent of radio luminosity or
radio-to-optical flux density ratio, and that fractionally large variations can
occur on timescales of months or less in both radio quiet and radio loud
quasars. Combining this with similarities in other indicators, such as radio
spectral index and the presence of VLBI-scale components, leads to the
suggestion that the physics of radio emission in the inner regions of all
quasars is essentially the same, involving a compact, partially opaque core
together with a beamed jet.Comment: 32 pages, 9 figures. Astrophysical Journal, in pres
Interferometric Observations of the Nuclear Region of Arp220 at Submillimeter Wavelengths
We report the first submillimeter interferometric observations of an
ultraluminous infrared galaxy. We observed Arp220 in the CO J=3-2 line and
342GHz continuum with the single baseline CSO-JCMT interferometer consisting of
the Caltech Submillimeter Observatory (CSO) and the James Clerk Maxwell
Telescope (JCMT). Models were fit to the measured visibilities to constrain the
structure of the source. The morphologies of the CO J=3-2 line and 342GHz
continuum emission are similar to those seen in published maps at 230 and
110GHz. We clearly detect a binary source separated by about 1 arcsec in the
east-west direction in the 342GHz continuum. The CO J=3-2 visibility
amplitudes, however, indicate a more complicated structure, with evidence for a
compact binary at some velocities and rather more extended structure at others.
Less than 30% of the total CO J=3-2 emission is detected by the interferometer,
which implies the presence of significant quantities of extended gas. We also
obtained single-dish CO J=2-1, CO J=3-2 and HCN J=4-3 spectra. The HCN J=4-3
spectrum, unlike the CO spectra, is dominated by a single redshifted peak. The
HCN J=4-3/CO J=3-2, HCN J=4-3/HCN J=1-0 and CO J=3-2/2-1 line ratios are larger
in the redshifted (eastern) source, which suggests that the two sources may
have different physical conditions. This result might be explained by the
presence of an intense starburst that has begun to deplete or disperse the
densest gas in the western source, while the eastern source harbors undispersed
high density gas.Comment: 17 pages, 9 figures, 4 Tables. accepted by Ap
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