100 research outputs found
Evidence for an outflow from the Seyfert galaxy NGC 4051
New observations using narrow band imaging, long-slit spectroscopy and MERLIN
observations of the nuclear region of the Seyfert galaxy NGC~4051 have been
made. An edge brightened, triangular region of ionized gas extending 420 pc
from the centre of the galaxy has been detected. Long-slit spectra of this
ionised gas, taken at 1.5\arcsec\ from the core, show the \oiii\ emission line
to consist of two velocity components, both blue-shifted from the systemic
radial velocity, with velocity widths of 140\kms\ and separated by 120\kms.
This region is co-spatial with weak extended radio emission and is suggestive
of a centrally driven outflow. The \oiii\ line spectrum and image of this
region have been modelled as an outflowing conical structure at 50\degr\ to the
line of sight with a half opening angle of 23\degr .
In addition to the extended structure, high resolution MERLIN observations of
the 18-cm nuclear radio emission reveal a compact (1\arcsec) radio triple
source in PA 73. This source is coincident with the HST-imaged
emission line structure. These high resolution observations are consistent with
a more compact origin of activity (i.e. a Seyfert nucleus) than a starburst
region.Comment: latex, epsf.sty, 8 pages, 8 figures. Also available at
http://axp2.ast.man.ac.uk:8000/Preprints.htm
H-alpha Kinematics of the SINGS Nearby Galaxies Survey. II
This is the second part of an H-alpha kinematics follow-up survey of the
Spitzer Infrared Nearby Galaxies Survey (SINGS) sample. The aim of this program
is to shed new light on the role of baryons and their kinematics and on the
dark/luminous matter relation in the star forming regions of galaxies, in
relation with studies at other wavelengths. The data for 37 galaxies are
presented. The observations were made using Fabry-Perot interferometry with the
photon-counting camera FaNTOmM on 4 different telescopes, namely the
Canada-France-Hawaii 3.6m, the ESO La Silla 3.6m, the William Herschel 4.2m,
and the Observatoire du mont Megantic 1.6m telescopes. The velocity fields are
computed using custom IDL routines designed for an optimal use of the data. The
kinematical parameters and rotation curves are derived using the GIPSY
software. It is shown that non-circular motions associated with galactic bars
affect the kinematical parameters fitting and the velocity gradient of the
rotation curves. This leads to incorrect determinations of the baryonic and
dark matter distributions in the mass models derived from those rotation
curves.Comment: 18 pages, 5 figures, 4 tables. Accepted for publication in MNRAS. All
high-res. figures are available at
http://www.astro.umontreal.ca/fantomm/singsII
The infrared supernova rate in starburst galaxies
We report the results of our ongoing search for extincted supernovae (SNe) at
near-infrared wavelengths. We have monitored at 2.2 micron a sample of 46
Luminous Infrared Galaxies and detected 4 SNe. The number of detections is
still small but sufficient to provide the first estimate of supernova rate at
near-infrared wavelengths. We measure a SN rate ofv 7.6+/-3.8 SNu which is an
order of magnitude larger than observed in quiescent galaxies. On the other
hand, the observed near-infrared rate is still a factor 3-10 smaller than that
estimated from the far-infrared luminosity of the galaxies. Among various
possibilities, the most likely scenario is that dust extinction is so high
(Av>30) to obscure most SNe even in the near-IR.
The role of type Ia SNe is also discussed within this context. We derive the
type Ia SN rate as a function of the stellar mass of the galaxy and find a
sharp increase toward galaxies with higher activity of star formation. This
suggests that a significant fraction of type Ia SNe are associated with young
stellar populations.
Finally, as a by-product, we give the average K-band light curve of
core-collapse SNe based on all the existing data, and review the relation
between SN rate and far-infrared luminosity.Comment: A&A, in press, 13 page
Evolutionary dynamics of methicillin-resistant Staphylococcus aureus within a healthcare system
Background: In the past decade, several countries have seen gradual replacement of endemic multi-resistant healthcare-associated methicillin-resistant Staphylococcus aureus (MRSA) with clones that are more susceptible to antibiotic treatment. One example is Singapore, where MRSA ST239, the dominant clone since molecular profiling of MRSA began in the mid-1980s, has been replaced by ST22 isolates belonging to EMRSA-15, a recently emerged pandemic lineage originating from Europe.Results: We investigated the population structure of MRSA in Singaporean hospitals spanning three decades, using whole genome sequencing. Applying Bayesian phylogenetic methods we report that prior to the introduction of ST22, the ST239 MRSA population in Singapore originated from multiple introductions from the surrounding region; it was frequently transferred within the healthcare system resulting in a heterogeneous hospital population. Following the introduction of ST22 around the beginning of the millennium, this clone spread rapidly through Singaporean hospitals, supplanting the endemic ST239 population. Coalescent analysis revealed that although the genetic diversity of ST239 initially decreased as ST22 became more dominant, from 2007 onwards the genetic diversity of ST239 began to increase once more, which was not associated with the emergence of a sub-clone of ST239. Comparative genomic analysis of the accessory genome of the extant ST239 population identified that the Arginine Catabolic Mobile Element arose multiple times, thereby introducing genes associated with enhanced skin colonization into this population.Conclusions: Our results clearly demonstrate that, alongside clinical practice and antibiotic usage, competition between clones also has an important role in driving the evolution of nosocomial pathogen populations.</p
Milliarcsec-scale radio structure of a matched sample of Seyfert 1 and Seyfert 2 galaxies
We have obtained mas-scale resolution very long baseline interferometry
(VLBI) images of a sample of Seyfert 1 and Seyfert 2 galaxies at 5 GHz
(wavelength, = 6 cm). The Seyferts of the two types were chosen to be
matched in several orientation-independent properties, primarily in order to
rigorously test predictions of the unified scheme. We detected all the 15
objects that we observed. In this paper we describe the observations and data
reduction procedures, and present the VLBI radio images as well as simultaneous
Very Large Array images that we obtained for these 15 Seyferts.Comment: 14 pages, 2 figures (32 panels). Accepted for publication in
Astronomy & Astrophysic
Vertical Nanowire TFET Diameter Influence on Intrinsic Voltage Gain for Different Inversion Conditions
In this work, the impact of the nanowire TFET diameter on analog parameters in "weak" and "strong inversion" conditions is analyzed. Its relation with the current conduction mechanism is also studied. A comparison of the analog performance among TFETs doped with different source doping profile (abrupt and nonabrupt) and MOSFETs was experimentally realized for larger diameter nanowires. Additionally the TFET evaluation was extrapolated for smaller diameters by numerical simulation. The transistor efficiency and the Early voltage were considered in order to calculate the intrinsic voltage gain (AV). Both effects influence AV degradation for TFETs with smaller diameters biased in "weak inversion". While larger TFET nanowires show better AV than MOSFETs under "strong inversion" bias, narrower nanowires present potentialities for low power and low voltage applications, since their AV is better than the corresponding values for larger diameters TFET nanowires under "weak inversion" bias
The Hamburg/SAO Survey for Emission--Line Galaxies. V. The Fifth List of 161 Galaxies
We present the fifth list with results of the Hamburg/SAO Survey for
Emission-Line Galaxies (HSS therein, SAO -- Special Astrophysical Observatory,
Russia). The list is a result of follow-up spectroscopy conducted with the 2.2m
CAHA and 4m Kitt Peak telescopes in 1999. The data of this snap-shot
spectroscopy survey confirmed 166 emission-line objects out of 209 observed
candidates and allowed their quantitative spectral classification and redshift
determination. We could classify 98 emission-line objects as BCG/HII galaxies
or probable BCGs, 5 -- as QSOs, 3 - as Seyfert galaxies, 2 - as
super-associations in subluminous spiral galaxies. 25 low-excitation objects
were classified as starburst nuclei (SBN), 24 as dwarf amorphous nuclei
starburst galaxies (DANS) and 3 as LINERs. Due to low signal-to-noise ratio we
could not classify 6 ELGs. Furthermore, for another 4 galaxies we did not
detect any significant emission lines. For 131 emission-line galaxies, the
redshifts and/or line intensities are determined for the first time. For the
remaining 30 previously known ELGs we give either improved data of the line
intensities or some independent measurements.Comment: 18 pages, A&A in press. Figures A1-A17 (spectra) available in
GIF-format. PS-file with Figures A1-A17 available via
http://precise.sao.ru/Laboratory/Publications/2001/HSSV_figs.ps.g
The Relationship Between Gas Content and Star Formation in Molecule-Rich Spiral Galaxies
We investigate the relationship between HI, H_2, and the star formation rate
(SFR) using azimuthally averaged data for seven CO-bright spiral galaxies.
Contrary to some earlier studies based on global fluxes, we find that the SFR
surface density exhibits a much stronger correlation with the H_2 than with the
HI, as the HI surface density saturates at a value of 10 Msol pc^{-2} or
even declines at large SFR surface densities. Hence the good correlation
between the SFR surface density and the total (HI+H_2) gas surface density is
driven by the molecular component in these galaxies. We find no clear evidence
for a link between the gravitational instability parameter for the gas disk
(Q_g) and the SFR, and suggest that Q_g be considered a measure of the gas
fraction. This implies that for a state of marginal gravitational stability to
exist in galaxies with low gas fractions, it must be due to instability of the
stellar disk. In regions where we have both HI and CO measurements, the ratio
of HI to H_2 surface density scales with radius R as roughly R^{1.5}, and we
suggest that the balance between HI and H_2 is determined primarily by the
midplane interstellar pressure. These results favor a "law" of star formation
in quiescent disks in which the ambient pressure and metallicity control the
formation of molecular clouds from HI, with star formation then occurring at a
roughly constant rate per unit H_2 mass. (abstract abridged)Comment: To appear in ApJ. 28 pages with 16 figures (emulateapj5). Full
resolution figures available at
http://www.atnf.csiro.au/people/twong/preprints
Risk Factors, Molecular Epidemiology and Outcomes of Ertapenem-Resistant, Carbapenem-Susceptible Enterobacteriaceae: A Case-Case-Control Study
Background: Increasing prevalence of ertapenem-resistant, carbapenem-susceptible Enterobacteriaceae (ERE) in Singapore presents a major therapeutic problem. Our objective was to determine risk factors associated with the acquisition of ERE in hospitalized patients; to assess associated patient outcomes; and to describe the molecular characteristics of ERE. Methods: A retrospective case-case-control study was conducted in 2009 at a tertiary care hospital. Hospitalized patients with ERE and those with ertapenem-sensitive Enterobacteriaceae (ESE) were compared with a common control group consisting of patients with no prior gram-negative infections. Risk factors analyzed included demographics; co-morbidities; instrumentation and antibiotic exposures. Two parallel multivariate logistic regression models were performed to identify independent variables associated with ERE and ESE acquisition respectively. Clinical outcomes were compared between ERE and ESE patients. Results: Twenty-nine ERE cases, 29 ESE cases and 87 controls were analyzed. Multivariate logistic regression showed that previous hospitalization (Odds ratio [OR], 10.40; 95 % confidence interval [CI], 2.19–49.20) and duration of fluoroquinolones exposure (OR, 1.18 per day increase; 95 % CI, 1.05–1.34) were unique independent predictors for acquiring ERE. Duration of 4 th-generation cephalosporin exposure was found to predict for ESE acquisition (OR, 1.63 per day increase; 95 % CI, 1.05– 2.54). In-hospital mortality rates and clinical response rates were significantly different between ERE and ESE groups
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