192 research outputs found
Realization of GHZ States and the GHZ Test via Cavity QED
In this article we discuss the realization of atomic GHZ states involving
three-level atoms and we show explicitly how to use this state to perform the
GHZ test in which it is possible to decide between local realism theories and
quantum mechanics. The experimental realizations proposed makes use of the
interaction of Rydberg atoms with a cavity prepared in a coherent state.Comment: 16 pages and 3 figures. submitted to J. Mod. Op
Imaging the molecular gas in a submm galaxy at z = 4.05: cold mode accretion or a major merger?
We present a high resolution (down to 0.18"), multi-transition imaging study
of the molecular gas in the z = 4.05 submillimeter galaxy GN20. GN20 is one of
the most luminous starburst galaxy known at z > 4, and is a member of a rich
proto-cluster of galaxies at z = 4.05 in GOODS-North. We have observed the CO
1-0 and 2-1 emission with the VLA, the CO 6-5 emission with the PdBI
Interferometer, and the 5-4 emission with CARMA. The H_2 mass derived from the
CO 1-0 emission is 1.3 \times 10^{11} (\alpha/0.8) Mo. High resolution imaging
of CO 2-1 shows emission distributed over a large area, appearing as partial
ring, or disk, of ~ 10kpc diameter. The integrated CO excitation is higher than
found in the inner disk of the Milky Way, but lower than that seen in high
redshift quasar host galaxies and low redshift starburst nuclei. The VLA CO 2-1
image at 0.2" resolution shows resolved, clumpy structure, with a few brighter
clumps with intrinsic sizes ~ 2 kpc. The velocity field determined from the CO
6-5 emission is consistent with a rotating disk with a rotation velocity of ~
570 km s^{-1} (using an inclination angle of 45^o), from which we derive a
dynamical mass of 3 \times 10^{11} \msun within about 4 kpc radius. The star
formation distribution, as derived from imaging of the radio synchrotron and
dust continuum, is on a similar scale as the molecular gas distribution. The
molecular gas and star formation are offset by ~ 1" from the HST I-band
emission, implying that the regions of most intense star formation are highly
dust-obscured on a scale of ~ 10 kpc. The large spatial extent and ordered
rotation of this object suggests that this is not a major merger, but rather a
clumpy disk accreting gas rapidly in minor mergers or smoothly from the
proto-intracluster medium. ABSTRACT TRUNCATEDComment: 33 pages, 8 figures, submitted to the ApJ, aas latex forma
Does a "Level I Evidence" rating imply high quality of reporting in orthopaedic randomised controlled trials?
BACKGROUND: The Levels of Evidence Rating System is widely believed to categorize studies by quality, with Level I studies representing the highest quality evidence. We aimed to determine the reporting quality of Randomised Controlled Trials (RCTs) published in the most frequently cited general orthopaedic journals. METHODS: Two assessors identified orthopaedic journals that reported a level of evidence rating in their abstracts from January 2003 to December 2004 by searching the instructions for authors of the highest impact general orthopaedic journals. Based upon a priori eligibility criteria, two assessors hand searched all issues of the eligible journal from 2003–2004 for RCTs. The assessors extracted the demographic information and the evidence rating from each included RCT and scored the quality of reporting using the reporting quality assessment tool, which was developed by the Cochrane Bone, Joint and Muscle Trauma Group. Scores were conducted in duplicate, and we reached a consensus for any disagreements. We examined the correlation between the level of evidence rating and the Cochrane reporting quality score. RESULTS: We found that only the Journal of Bone and Joint Surgery – American Volume (JBJS-A) used a level of evidence rating from 2003 to 2004. We identified 938 publications in the JBJS-A from January 2003 to December 2004. Of these publications, 32 (3.4%) were RCTs that fit the inclusion criteria. The 32 RCTs included a total of 3543 patients, with sample sizes ranging from 17 to 514 patients. Despite being labelled as the highest level of evidence (Level 1 and Level II evidence), these studies had low Cochrane reporting quality scores among individual methodological safeguards. The Cochrane reporting quality scores did not differ significantly between Level I and Level II studies. Correlations varied from 0.0 to 0.2 across the 12 items of the Cochrane reporting quality assessment tool (p > 0.05). Among items closely corresponding to the Levels of Evidence Rating System criteria assessors achieved substantial agreement (ICC = 0.80, 95%CI:0.60 to 0.90). CONCLUSION: Our findings suggest that readers should not assume that 1) studies labelled as Level I have high reporting quality and 2) Level I studies have better reporting quality than Level II studies. One should address methodological safeguards individually
A CO emission line from the optical and near-IR undetected submillimeter galaxy GN10
We report the detection of a CO emission line from the submillimiter galaxy
(SMG) GN10 in the GOODS-N field. GN10 lacks any counterpart in extremely deep
optical and near-IR imaging obtained with the Hubble Space Telescope and
ground-based facilities. This is a prototypical case of a source that is
extremely obscured by dust, for which it is practically impossible to derive a
spectroscopic redshift in the optical/near-IR. Under the hypothesis that GN10
is part of a proto-cluster structure previously identified at z~4.05 in the
same field, we searched for CO[4-3] at 91.4 GHz with the IRAM Plateau de Bure
Interferometer, and successfully detected a line. We find that the most likely
redshift identification is z=4.0424+-0.0013, based on: 1) the very low chance
that the CO line is actually serendipitous from a different redshift; 2) a
radio-IR photometric redshift analysis; 3) the identical radio-IR SED, within a
scaling factor, of two other SMGs at the same redshift. The faintness at
optical/near-IR wavelengths requires an attenuation of A_V~5-7.5 mag. This
result supports the case that a substantial population of very high-z SMGs
exists that had been missed by previous spectroscopic surveys. This is the
first time that a CO emission line has been detected for a galaxy that is
invisible in the optical and near-IR. Our work demonstrates the power of
existing and planned facilities for completing the census of star formation and
stellar mass in the distant Universe by measuring redshifts of the most
obscured galaxies through millimeter spectroscopy.Comment: 5 pages, 4 figures. ApJ Letters in pres
The influence of cosmic rays in the circumnuclear molecular gas of NGC1068
We surveyed the circumnuclear disk of the Seyfert galaxy NGC1068 between the
frequencies 86.2 GHz and 115.6 GHz, and identified 17 different molecules.
Using a time and depth dependent chemical model we reproduced the observational
results, and show that the column densities of most of the species are better
reproduced if the molecular gas is heavily pervaded by a high cosmic ray
ionization rate of about 1000 times that of the Milky Way. We discuss how
molecules in the NGC1068 nucleus may be influenced by this external radiation,
as well as by UV radiation fields.Comment: 6 pages. Conference proceeding for the workshop on "Cosmic-ray
induced phenomenology in star-forming environments" held in Sant Cugat,
Spain, on April 16-19, 201
Stellar feedback as the origin of an extended molecular outflow in a starburst galaxy
Recent observations have revealed that starburst galaxies can drive molecular gas outflows through stellar radiation pressure. Molecular gas is the phase of the interstellar medium from which stars form, so these outflows curtail stellar mass growth in galaxies. Previously known outflows, however, involve small fractions of the total molecular gas content and have typical scales of less than a kiloparsec. In at least some cases, input from active galactic nuclei is dynamically important, so pure stellar feedback (the momentum return into the interstellar medium) has been considered incapable of rapidly terminating star formation on galactic scales. Molecular gas has been detected outside the galactic plane of the archetypal starburst galaxy M82 (refs 4 and 5), but so far there has been no evidence that starbursts can propel substantial quantities of cold molecular gas to the same galactocentric radius (about 10 kiloparsecs) as the warmer gas that has been traced by metal ion absorbers in the circumgalactic medium. Here we report observations of molecular gas in a compact (effective radius 100 parsecs) massive starburst galaxy at redshift 0.7, which is known to drive a fast outflow of ionized gas. We find that 35 per cent of the total molecular gas extends approximately 10 kiloparsecs, and one-third of this extended gas has a velocity of up to 1,000 kilometres per second. The kinetic energy associated with this high-velocity component is consistent with the momentum flux available from stellar radiation pressure. This demonstrates that nuclear bursts of star formation are capable of ejecting large amounts of cold gas from the central regions of galaxies, thereby strongly affecting their evolution by truncating star formation and redistributing matter.Peer reviewedFinal Accepted Versio
A multi-transition HCN and HCO+ study of 12 nearby active galaxies: AGN versus SB environments
Recent studies have indicated that the HCN-to-CO(J=1-0) and
HCO+-to-HCN(J=1-0) ratios are significantly different between galaxies with AGN
(active galactic nucleus) and SB (starburst) signatures. In order to study the
molecular gas properties in active galaxies and search for differences between
AGN and SB environments, we observed the HCN(J=1-0), (J=2-1), (J=3-2),
HCO+(J=1-0) and HCO+(J=3-2), emission with the IRAM 30m in the centre of 12
nearby active galaxies which either exhibit nuclear SB and/or AGN signatures.
Consistent with previous results, we find a significant difference of the
HCN(J=2-1)-to-HCN(J=1-0), HCN(J=3-2)-to-HCN(J=1-0), HCO+(J=3-2)-to-HCO+(J=3-2),
and HCO+-to-HCN intensity ratios between the sources dominated by an AGN and
those with an additional or pure central SB: the HCN, HCO+ and HCO+-to-HCN
intensity ratios tend to be higher in the galaxies of our sample with a central
SB as opposed to the pure AGN cases which show rather low intensity ratios.
Based on an LVG analysis of these data, i.e., assuming purely collisional
excitation, the (average) molecular gas densities in the SB dominated sources
of our sample seem to be systematically higher than in the AGN sources. The LVG
analysis seems to further support systematically higher HCN and/or lower HCO+
abundances as well as similar or higher gas temperatures in AGN compared to the
SB sources of our sample. Also, we find that the HCN-to-CO ratios decrease with
increasing rotational number J for the AGN while they stay mostly constant for
the SB sources.Comment: accepted for publication in ApJ; 20 pages, 7 figures; in emulateApJ
forma
Planck's Dusty GEMS: Gravitationally lensed high-redshift galaxies discovered with the Planck survey
We present an analysis of 11 bright far-IR/submm sources discovered through a
combination of the Planck survey and follow-up Herschel-SPIRE imaging. Each
source has a redshift z=2.2-3.6 obtained through a blind redshift search with
EMIR at the IRAM 30-m telescope. Interferometry obtained at IRAM and the SMA,
and optical/near-infrared imaging obtained at the CFHT and the VLT reveal
morphologies consistent with strongly gravitationally lensed sources.
Additional photometry was obtained with JCMT/SCUBA-2 and IRAM/GISMO at 850 um
and 2 mm, respectively. All objects are bright, isolated point sources in the
18 arcsec beam of SPIRE at 250 um, with spectral energy distributions peaking
either near the 350 um or the 500 um bands of SPIRE, and with apparent
far-infrared luminosities of up to 3x10^14 L_sun. Their morphologies and sizes,
CO line widths and luminosities, dust temperatures, and far-infrared
luminosities provide additional empirical evidence that these are strongly
gravitationally lensed high-redshift galaxies. We discuss their dust masses and
temperatures, and use additional WISE 22-um photometry and template fitting to
rule out a significant contribution of AGN heating to the total infrared
luminosity. Six sources are detected in FIRST at 1.4 GHz. Four have flux
densities brighter than expected from the local far-infrared-radio correlation,
but in the range previously found for high-z submm galaxies, one has a deficit
of FIR emission, and 6 are consistent with the local correlation. The global
dust-to-gas ratios and star-formation efficiencies of our sources are
predominantly in the range expected from massive, metal-rich, intense,
high-redshift starbursts. An extensive multi-wavelength follow-up programme is
being carried out to further characterize these sources and the intense
star-formation within them.Comment: A&A accepte
Dense molecular gas toward W49A: A template for extragalactic starbursts?
The HCN, HCO+, and HNC molecules are commonly used as tracers of dense
star-forming gas in external galaxies, but such observations are spatially
unresolved. Reliably inferring the properties of galactic nuclei and disks
requires detailed studies of sources whose structure is spatially resolved. We
compare the spatial distributions and abundance ratios of HCN, HCO+, and HNC in
W49A, the most massive and luminous star-forming region in the Galactic disk,
based on maps of a 2' (6.6 pc) field at 14" (0.83 pc) resolution of the J=4-3
transitions of HCN, H13CN, HC15N, HCO+, H13CO+, HC18O+ and HNC. The kinematics
of the molecular gas in W49A appears complex, with a mixture of infall and
outflow motions. Both the line profiles and comparison of the main and rarer
species show that the main species are optically thick. Two 'clumps' of
infalling gas appear to be at ~40 K, compared to ~100 K at the source centre,
and may be ~10x denser than the rest of the outer cloud. Chemical modelling
suggests that the HCN/HNC ratio probes the current gas temperature, while the
HCN/HCO+ ratio and the deuterium fractionation were set during an earlier,
colder phase of evolution. The data suggest that W49A is an appropriate
analogue of an extragalactic star forming region. Our data show that the use of
HCN/HNC/HCO+ line ratios as proxies for the abundance ratios is incorrect for
W49A, suggesting the same for galactic nuclei. Our observed isotopic line
ratios such as H13CN/H13CO+ approach our modeled abundance ratios quite well in
W49A. The 4-3 lines of HCN and HCO+ are much better tracers of the dense
star-forming gas in W49A than the 1-0 lines. Our observed HCN/HNC and HCN/HCO+
ratios in W49A are inconsistent with homogeneous PDR or XDR models, indicating
that irradiation hardly affects the gas chemistry in W49A. Overall, the W49A
region appears to be a useful template for starburst galaxies.Comment: Accepted by A&A; 17 pages, 15 figure
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