537 research outputs found
Long term Arecibo monitoring of the water megamaser in MG J0414+0534
We monitored the 22 GHz maser line in the lensed quasar MG J0414+0534 at
z=2.64 with the 300-m Arecibo telescope for almost two years to detect possible
additional maser components and to measure a potential velocity drift of the
lines. The main maser line profile is complex and can be resolved into a number
of broad features with line widths of 30-160 km/s. A new maser component was
tentatively detected in October 2008 at a velocity of +470 km/s. After
correcting for the estimated lens magnification, we find that the H2O isotropic
luminosity of the maser in MG J0414+0534 is about 26,000 solar luminosities,
making this source the most luminous ever discovered. Both the main line peak
and continuum flux densities are surprisingly stable throughout the period of
the observations. An upper limit on the velocity drift of the main peak of the
line has been estimated from our observations and is of the order of 2 km/s per
year. We discuss the results of the monitoring in terms of the possible nature
of the maser emission, associated with an accretion disk or a radio jet. This
is the first time that such a study is performed in a water maser source at
high redshift, potentially allowing us to study the parsec-scale environment
around a powerful radio source at cosmological distances.Comment: 5 pages, 2 figures, to appear in the Proceedings of the IAU Symposium
287, 2012, "Cosmic masers: from OH to H0
Current status of laboratory and imaging diagnosis of neonatal necrotizing enterocolitis
Necrotizing enterocolitis continues to be a devastating disease process for very low birth weight infants in Neonatal Intensive Care Units. The aetiology and pathogenesis of necrotizing enterocolitis are not definitively understood. It is known that necrotizing enterocolitis is secondary to a complex interaction of multiple factors that results in mucosal damage, which leads to intestinal ischemia and necrosis. Advances in neonatal care, including resuscitation and ventilation support technology, have seen increased survival rates among premature neonates and a concomitant detection in the incidence of this intestinal disease.Diagnosis can be difficult, and identifying infants at the onset of disease remains a challenge. Early diagnosis, which relies on imaging findings, and initiation of prompt therapy are essential to limit morbidity and mortality. Moreover, early management is critical and life-saving.This review summarizes what is known on the laboratory and instrumental diagnostic strategies needed to improve neonatal outcomes and, possibily, to prevent the onset of an overt necrotizing enterocolitis
Water vapour at high redshift: Arecibo monitoring of the megamaser in MG J0414+0534
The study of water masers at cosmological distances would allow us to
investigate the parsec-scale environment around powerful radio sources, to
probe the physical conditions of the molecular gas in the inner parsecs of
quasars, and to estimate their nuclear engine masses in the early universe. To
derive this information, the nature of the maser source, jet or disk-maser,
needs to be assessed through a detailed investigation of the observational
characteristics of the line emission. We monitored the maser line in the lensed
quasar MGJ0414+0534 at z = 2.64 with the 300-m Arecibo telescope for ~15 months
to detect possible additional maser components and to measure a potential
velocity drift of the lines. In addition, we follow the maser and continuum
emissions to reveal significant variations in their flux density and to
determine correlation or time-lag, if any, between them. The main maser line
profile is complex and can be resolved into a number of broad features with
line widths of 30-160 km/s. A new maser component was tentatively detected in
October 2008 that is redshifted by 470 km/s w.r.t the systemic velocity of the
quasar. The line width of the main maser feature increased by a factor of two
between the Effelsberg and EVLA observations reported by Impellizzeri et al.
(2008) and the first epoch of the Arecibo monitoring campaign. After correcting
for the lens magnification, we find that the total H2O isotropic luminosity of
the maser in MGJ0414+0534 is now ~30,000 Lsun, making this source the most
luminous ever discovered.[Abridged]Comment: 8 pages, 6 figures, accepted for publication in A&
On carbon and oxygen isotope ratios in starburst galaxies: New data from NGC253 and Mrk231 and their implications
Using the IRAM 30-m telescope, CN and CO isotopologues have been measured
toward the central regions of the nearby starburst galaxy NGC253 and the
prototypical ultraluminous infrared galaxy Mrk231. In NGC253, the 12C/13C ratio
is 40+-10. Assuming that the ratio also holds for the CO emitting gas, this
yields 16O/18O = 145+-36 and 16O/17O = 1290+-365 and a 32S/34S ratio close to
that measured for the local interstellar medium (20-25). No indication for
vibrationally excited CN is found. Peak line intensity ratios between NGC253
and Mrk231 are ~100 for 12C16O and 12C18O J=1-0, while the ratio for 13C16O
J=1-0 is ~250. This and similar 13CO and C18O line intensities in the J=1-0 and
2-1 transitions of Mrk231 suggest 12C/13C ~ 100 and 16O/18O ~ 100, in agreement
with values obtained for the less evolved ultraluminous merger Arp220. Also
accounting for other extragalactic data, 12C/13C ratios appear to vary over a
full order of magnitude, from >100 in ultraluminous high redshift galaxies to
~100 in more local such galaxies to ~40 in weaker starbursts not undergoing a
large scale merger to 25 in the Central Molecular Zone of the Milky Way. With
12C being predominantly synthesized in massive stars, while 13C is mostly
ejected by longer lived lower mass stars at later times, this is qualitatively
consistent with our results of decreasing carbon isotope ratios with time and
rising metallicity. It is emphasized, however, that both infall of poorly
processed material, initiating a nuclear starburst, as well as the ejecta from
newly formed massive stars (in particular in case of a top-heavy stellar
initial mass function) can raise the carbon isotope ratio for a limited amount
of time.Comment: Accepted by Astronomy & Astrophysics, 6 figures, 4 table
ALLSMOG: an APEX Low-redshift Legacy Survey for MOlecular Gas. I - molecular gas scaling relations, and the effect of the CO/H2 conversion factor
We present ALLSMOG, the APEX Low-redshift Legacy Survey for MOlecular Gas.
ALLSMOG is a survey designed to observe the CO(2-1) emission line with the APEX
telescope, in a sample of local galaxies (0.01 < z < 0.03), with stellar masses
in the range 8.5 < log(M*/Msun) < 10. This paper is a data release and initial
analysis of the first two semesters of observations, consisting of 42 galaxies
observed in CO(2-1). By combining these new CO(2-1) emission line data with
archival HI data and SDSS optical spectroscopy, we compile a sample of low-mass
galaxies with well defined molecular gas masses, atomic gas masses, and
gas-phase metallicities. We explore scaling relations of gas fraction and gas
consumption timescale, and test the extent to which our findings are dependent
on a varying CO/H2 conversion factor. We find an increase in the H2/HI mass
ratio with stellar mass which closely matches semi-analytic predictions. We
find a mean molecular gas fraction for ALLSMOG galaxies of MH2/M* = (0.09 -
0.13), which decreases with stellar mass. We measure a mean molecular gas
consumption timescale for ALLSMOG galaxies of 0.4 - 0.7 Gyr. We also confirm
the non-universality of the molecular gas consumption timescale, which varies
(with stellar mass) from ~100 Myr to ~2 Gyr. Importantly, we find that the
trends in the H2/HI mass ratio, gas fraction, and the non-universal molecular
gas consumption timescale are all robust to a range of recent
metallicity-dependent CO/H2 conversion factors.Comment: 25 pages, 15 figures. Accepted for publication in MNRA
ALMA Observations of the Physical and Chemical Conditions in Centaurus A
Centaurus A, with its gas-rich elliptical host galaxy, NGC 5128, is the
nearest radio galaxy at a distance of 3.8 Mpc. Its proximity allows us to study
the interaction between an active galactic nucleus, radio jets, and molecular
gas in great detail. We present ALMA observations of low J transitions of three
CO isotopologues, HCN, HCO, HNC, CN, and CCH toward the inner projected
500 pc of NGC 5128. Our observations resolve physical sizes down to 40 pc. By
observing multiple chemical probes, we determine the physical and chemical
conditions of the nuclear interstellar medium of NGC 5128. This region contains
molecular arms associated with the dust lanes and a circumnuclear disk (CND)
interior to the molecular arms. The CND is approximately 400 pc by 200 pc and
appears to be chemically distinct from the molecular arms. It is dominated by
dense gas tracers while the molecular arms are dominated by CO and its
rare isotopologues. The CND has a higher temperature, elevated CN/HCN and
HCN/HNC intensity ratios, and much weaker CO and CO emission than
the molecular arms. This suggests an influence from the AGN on the CND
molecular gas. There is also absorption against the AGN with a low velocity
complex near the systemic velocity and a high velocity complex shifted by about
60 km s. We find similar chemical properties between the CND in emission
and both the low and high velocity absorption complexes implying that both
likely originate from the CND. If the HV complex does originate in the CND,
then that gas would correspond to gas falling toward the supermassive black
hole
Fluorine effect on As diffusion in Ge
The enhanced diffusion of donor atoms, via a vacancy (V)-mechanism, severely affects the realization of ultrahigh doped regions in miniaturized germanium (Ge) based devices. In this work, we report a study about the effect of fluorine (F) on the diffusion of arsenic (As) in Ge and give insights on the physical mechanisms involved. With these aims we employed experiments in Ge co-implanted with F and As and density functional theory calculations. We demonstrate that the implantation of F enriches the Ge matrix in V, causing an enhanced diffusion of As within the layer amorphized by F and As implantation and subsequently regrown by solid phase epitaxy. Next to the end-of-range damaged region F forms complexes with Ge interstitials, that act as sinks for V and induce an abrupt suppression of As diffusion. The interaction of Ge interstitials with fluorine interstitials is confirmed by theoretical calculations. Finally, we prove that a possible F-As chemical interaction does not play any significant role on dopant diffusion. These results can be applied to realize abrupt ultra-shallow n-type doped regions in future generation of Ge-based devices
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