1,832 research outputs found
Star formation in the warped outer pseudoring of the spiral galaxy NGC 3642
NGC 3642 was classified as a spiral galaxy with three rings and no bar. We
have performed an HI and optical study of this nearly face-on galaxy. We find
that the nuclear ring might in fact be part of an inner one-armed spiral, that
could be driving nuclear accretion and feeding the central activity in the
inner kpc. The inner ring is faint, and the outer ring is a rather ill-defined
pseudoring. Furthermore, the size ratio of the rings is such that they cannot
be due to a single pattern speed linking them together.
The outer pseudoring is peculiar, since it lies in the faint outer parts of
the disk, where star formation is still going on at 1.4 times the optical
radius. Higher HI column densities are associated with these regions and the
atomic gas layer is warped. These perturbations affect only the outer disk,
since the kinematics within the main body conforms well to an ordinary
differentially rotating disk.
We propose here that both nuclear activity and star formation in the warped
outer parts might be linked to the fact that NGC 3642 is located in a rich
environment, where its close neighbors show clear signs of merging. Our
suggestion is that NGC 3642 has captured recently a low-mass, gas-rich dwarf,
and star formation was triggered in this infalling external gas that produced
also a pronounced warp in the gaseous disk.Comment: Accepted for publication in A&A. Full resolution version available at
http://www.iaa.es/~lourdes/3642/H3551.tar.g
The relationship between star formation rates and mid-infrared emission in galactic disks
International audienceThe Hα and mid-infrared mean disk surface brightnesses are compared in a sample of nearby spirals observed by ISOCAM. This shows that, in spiral disks, dust emission at 7 and 15 µm provides a reasonable star formation tracer. The fact that the 15 to 7 µm flux ratio is nearly constant in various global exciting conditions indicates a common origin, namely the aromatic infrared band carriers, and implies that at these wavelengths, dust emission from the disks of normal galaxies is dominated by photodissociation regions and not by HII regions themselves. We use this newly-found correlation between the mid-infrared and the Hα line to investigate the nature of the link between the far-infrared (60 and 100 µm) and Hα. Although the separation of the central regions from the disk is impossible to achieve in the far-infrared, we show that a circumnuclear contribution to the dust emission, having no equivalent counterpart in Hα, is most likely responsible for the well-known non-linearity between far-infrared and Hα fluxes in spiral galaxies. We derive a calibration of 7 and 15 µm fluxes in terms of star formation rates from a primary calibration of Hα in the literature, and also outline the applicability limits of the proposed conversion, which should not be blindly extrapolated to objects whose nature is unknown
L4Fe2As2Te1-xO4-yFy (L = Pr, Sm, Gd): a layered oxypnictide superconductor with Tc up to 45 K
The synthesis, structural and physical properties of iron lanthanide
oxypnictide superconductors, L4Fe2As2Te1-xO4 (L = Pr, Sm, Gd), with transition
temperature at ~ 25 K are reported. Single crystals have been grown at high
pressure using cubic anvil technique. The crystal structure consists of layers
of L2O2 tetrahedra separated by alternating layers of chains of Te and of
Fe2As2 tetrahedra: -L2O2-Te-L2O2-Fe2As2-L2O2-Te-L2O2- (space group: I4/mmm, a ~
4.0, c ~ 29.6 {\AA}). Substitution of oxygen by fluorine increases the critical
temperature, e.g. in Gd4Fe2As2Te1-xOyF4-y up to 45 K. Magnetic torque
measurements reveal an anisotropy of the penetration depths of ~31.Comment: 8 figures, 4 table
Forming first-ranked early-type galaxies through hierarchical dissipationless merging
We have developed a computationally competitive N-body model of a
previrialized aggregation of galaxies in a flat LambdaCDM universe to assess
the role of the multiple mergers that take place during the formation stage of
such systems in the configuration of the remnants assembled at their centres.
An analysis of a suite of 48 simulations of low-mass forming groups (of about
1E13 solar masses) demonstrates that the gravitational dynamics involved in
their hierarchical collapse is capable of creating realistic first-ranked
galaxies without the aid of dissipative processes. Our simulations indicate
that the brightest group galaxies (BGGs) constitute a distinct population from
other group members, sketching a scenario in which the assembly path of these
objects is dictated largely by the formation of their host system. We detect
significant differences in the distribution of Sersic indices and total
magnitudes, as well as a luminosity gap between BGGs and the next brightest
galaxy that is positively correlated with the total luminosity of the parent
group. Such gaps arise from both the grow of BGGs at the expense of lesser
companions and the decrease in the relevance of second-ranked objects in equal
measure. This results in a dearth of intermediate-mass galaxies which explains
the characteristic central dip detected in their luminosity functions in
dynamically young galaxy aggregations. The fact that the basic global
properties of our BGGs define a thin mass fundamental plane strikingly similar
to that followed giant early-type galaxies in the local universe reinforces
confidence in the results obtained.Comment: 25 pages, 14 figures, 3 tables. Accepted to MNRA
A ~ 12 kpc HI extension and other HI asymmetries in the isolated galaxy CIG 340 (IC 2487)
HI kinematic asymmetries are common in late-type galaxies irrespective of
environment, although the amplitudes are strikingly low in isolated galaxies.
As part of our studies of the HI morphology and kinematics in isolated
late-type galaxies we have chosen several very isolated galaxies from the AMIGA
sample for HI mapping. Here we present GMRT 21-cm HI line mapping of CIG 340
which was selected because its integrated HI spectrum has a very symmetric
profile, Aflux = 1.03. Optical images of the galaxy hinted at a warped disk in
contrast to the symmetric integrated HI spectrum profile. Our aim is to
determine the extent to which the optical asymmetry is reflected in the
resolved HI morphology and kinematics. GMRT observations reveal significant HI
morphological asymmetries in CIG 340 despite it's overall symmetric optical
form and highly symmetric HI spectrum. The most notable HI features are: 1) a
warp in the HI disk (with an optical counterpart), 2) the HI north/south flux
ratio = 1.32 is much larger than expected from the integrated HI spectrum
profile and 3) a ~ 45" (12 kpc) HI extension, containing ~ 6% of the detected
HI mass on the northern side of the disk. We conclude that in isolated galaxies
a highly symmetric HI spectrum can mask significant HI morphological
asymmetries. The northern HI extension appears to be the result of a recent
perturbation (10^8 yr), possibly by a satellite which is now disrupted or
projected within the disk. This study provides an important step in our ongoing
program to determine the predominant source of HI asymmetries in isolated
galaxies. For CIG 340 the isolation from major companions, symmetric HI
spectrum, optical morphology and interaction timescales have allowed us to
narrow the possible causes the HI asymmetries and identify tests to further
constrain the source of the asymmetries.Comment: 10 page
Mass Models for Spiral Galaxies from 2-D Velocity Maps
We model the mass distributions of 40 high surface brightness spiral galaxies
inside their optical radii, deriving parameters of mass models by matching the
predicted velocities to observed velocity maps. We use constant mass-to-light
disk and bulge models, and we have tried fits with no halo and with three
different halo density profiles. The data require a halo in most, but not all,
cases, while in others the best fit occurs with negligible mass in the luminous
component, which we regard as unphysical. All three adopted halo profiles lead
to fits of about the same quality, and our data therefore do not constrain the
functional form of the halo profile. The halo parameters display large
degeneracies for two of the three adopted halo functions, but the separate
luminous and dark masses are better constrained. However, the fitted disk and
halo masses vary substantially between the adopted halo models, indicating that
even high quality 2-D optical velocity maps do not provide significant
constraints on the dark matter content of a galaxy. We demonstrate that data
from longslit observations are likely to provide still weaker constraints. We
conclude that additional information is needed in order to constrain the
separate disk and halo masses in a galaxy.Comment: 41 pages, 13 figures, accepted for publication in A
Setting the normalcy level of HI properties in isolated galaxies
Studying the atomic gas (HI) properties of the most isolated galaxies is
essential to quantify the effect that the environment exerts on this sensitive
component of the interstellar medium. We observed and compiled HI data for a
well defined sample of ~ 800 galaxies in the Catalog of Isolated Galaxies, as
part of the AMIGA project (Analysis of the ISM in Isolated GAlaxies,
http://amiga.iaa.es), which enlarges considerably previous samples used to
quantify the HI deficiency in galaxies located in denser environments. By
studying the shape of 182 HI profiles, we revisited the usually accepted result
that, independently of the environment, more than half of the galaxies present
a perturbed HI disk. In isolated galaxies this would certainly be a striking
result if these are supposed to be the most relaxed systems, and has
implications in the relaxation time scales of HI disks and the nature of the
most frequent perturbing mechanisms in galaxies. Our sample likely exhibits the
lowest HI asymmetry level in the local Universe. We found that other field
samples present an excess of ~ 20% more asymmetric HI profiles than that in
CIG. Still a small percentage of galaxies in our sample present large
asymmetries. Follow-up high resolution VLA maps give insight into the origin of
such asymmetries.Comment: 4 pages, 2 figures, Conference 'Galaxies in Isolation: Exploring
Nature vs. Nurture', Granada, 12-15 May 2009. To be published in the ASP
Conference Serie
Validation and verification of the GeneFinder (TM) COVID-19 Plus RealAmp kit on the ELITe InGenius (R) instrument
Background: Throughout the SARS-CoV-2 pandemic, a rapid identification of the virus was essential to quickly recognize positive cases and limit further spread by applying appropriate infection prevention. Many diagnostic laboratories use a multiplex Real-Time PCR assay, as they are not only highly sensitive but also specific. Currently, there are several assays and platforms in the market available which target different SARS-CoV-2 genes. The aim of this study was to validate and verify the GeneFinder (TM) COVID-19 PLUS RealAmp kit on the ELITe InGenius (R) instrument and compare to the national reference method. Methods: GeneFinder (TM) COVID-19 PLUS RealAmp kit was evaluated against the routine WHO in- house RealTime PCR assay, which is also the national reference method in the Netherlands and used in our laboratory. The sensitivity was tested using the analytical panel from Qnostics (Glasgow, United Kingdom) and the specificity was tested with patient material comprising of other seasonal respiratory viruses. In addition, 96 clinical samples initially analyzed by routine Real-Time PCR were tested using the GeneFinder (TM) COVID-19 PLUS RealAmp kit on the ELITe InGenius (R) instrument. Results: The GeneFinder (TM) COVID-19 PLUS RealAmp kit had a similar performance compared to routine in-house testing, with a limit of detection of 500 dC/mL for the RdRp-gene and E gene. Meanwhile, the N gene showed a limit of detection of 50 dC/mL. The SARS-CoV-2 test was highly specific and detected no other respiratory viruses. The results of the clinical samples were comparable between both assays with similar Ct values observed for the in-house Real-Time-PCR and the GeneFinder (TM) COVID-19 PLUS RealAmp kit for the N gene. Conclusion: The GeneFinder (TM) COVID-19 PLUS RealAmp kit on the ELITe InGenius (R) instrument had an appropriate sensitivity and specificity that could be used in small scale laboratories or during night shifts where accurate diagnostics are crucial
Magnetic torque study of the temperature dependent anisotropy parameter in overdoped superconducting single-crystal YBa_2Cu_3O_7
An overdoped YBa2Cu3O7 single crystal was studied by SQUID and torque
magnetometry in order to investigate the temperature dependence of the
anisotropy parameter close to the transition temperature T_c (0.87 T_c < T <
T_c). Angle dependent torque measurements were performed and analyzed with the
widely used Kogan model [Phys. Rev. B 38, 7049 (1988)] as well as with an
extended model by Hao and Clem [Phys. Rev. Lett. 67, 2371 (1991)], taking into
account the influence of the vortex cores on the magnetization. Both approaches
yield similar results, with an out-of-plane anisotropy parameter around 6.5
which slightly increases with decreasing temperature, and a temperature
independent in-plane anisotropy parameter gamma_ab}= 1.12(5).Comment: 7 pages, 6 figures, version2 - accepted for publication in PR
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