2,483 research outputs found
New low surface brightness dwarf galaxies in the Centaurus group
We conducted an extensive CCD search for faint, unresolved dwarf galaxies of
very low surface brightness in the whole Centaurus group region encompassing
the Cen A and M 83 subgroups lying at a distance of roughly 4 and 5 Mpc,
respectively. The aim is to significantly increase the sample of known
Centaurus group members down to a fainter level of completeness, serving as a
basis for future studies of the 3D structure of the group. Following our
previous survey of 60 square degrees covering the M 83 subgroup, we extended
and completed our survey of the Centaurus group region by imaging another 500
square degrees area in the g and r bands with the wide-field Dark Energy Survey
Camera at the 4m Blanco telescope at CTIO. The limiting central surface
brightness reached for suspected Centaurus members is mag
arcsec, corresponding to an absolute magnitude . The
images were enhanced using different filtering techniques. We found 41 new
dwarf galaxy candidates, which together with the previously discovered 16 dwarf
candidates in the M 83 subgroup amounts to almost a doubling of the number of
known galaxies in the Centaurus complex, if the candidates are confirmed. We
carried out surface photometry in g and r, and report the photometric
parameters derived therefrom, for all new candidates as well as previously
known members in the surveyed area. The photometric properties of the
candidates, when compared to those of LG dwarfs and previously known Centaurus
dwarfs, suggest membership in the Centaurus group. The sky distribution of the
new objects is generally following a common envelope around the Cen A and M 83
subgroups. How the new dwarfs are connected to the intriguing double-planar
feature recently reported by Tully et al. (2015) must await distance
information for the candidates.Comment: 14 pages, 12 figures, accepted for publication in A&
Tip of the red giant branch distances to the dwarf galaxies dw1335-29 and dw1340-30 in the Centaurus group
The abundance and spatial distribution of dwarf galaxies are excellent
empirical benchmarks to test models of structure formation on small scales. The
nearby Centaurus group, with its two subgroups centered on CenA and M83, stands
out as an important alternative to the Local Group for scrutinizing
cosmological model predictions in a group of galaxies context. We have obtained
deep optical images of three recently discovered M83 satellite galaxy
candidates with the FORS2 instrument mounted on the Very Large Telescope. We
aim to confirm their group membership and study their stellar population. Deep
VI-band photometry is used to resolve the brightest stars in our targets.
Artificial star tests are performed to estimate the completeness and
uncertainties of the photometry. The color-magnitude diagrams reveal the red
giant branch (RGB) stars allowing to use the Sobel edge detection method to
measure the magnitude of the RGB tip and thus derive distances and group
membership for our targets. The mean metallicity of the dwarf galaxies are
further determined by fitting BASTI model isochrones to the mean RGB locus. We
confirm the two candidates, dw1335-29 and dw1340-30, to be dwarf satellites of
the M83 subgroup, with estimated distances of 5.03 +- 0.24 Mpc and 5.06 +- 0.24
Mpc, respectively. Their respective mean metallicities of = -1.79 +-
0.4 and = -2.27 +- 0.4 are consistent with the metallicity-luminosity
relation for dwarf galaxies. The third candidate, dw1325-33, could not be
resolved into stars due to insufficiently deep images, implying its distance
must be larger than 5.3 Mpc. Using the two newly derived distances we assess
the spatial distribution of the galaxies in the M83 subgroup and discuss a
potential plane-ofsatellites around M83.Comment: 10 pages, 9 figures, accepted for publication in A&
New dwarf galaxy candidates in the Centaurus group
Recent studies of the distribution and kinematics of the Milky Way and
Andromeda satellite galaxy systems have confirmed the existence of coplanar,
corotating structures of galaxies. In addition to the 'missing satellite
problem', these structures pose a major challenge to the standard CDM
scenario of structure formation. We complement the efforts made by the dwarf
galaxy community to extend these studies to other nearby galaxy groups by
systematically searching for faint, unresolved dwarf members with a low surface
brightness in the Southern Centaurus group of galaxies. The aim is to determine
whether these coplanar, corotating structures are a universal phenomenon. We
imaged an area of 60 square degrees (0.3 Mpc) around the M83 subgroup with
the wide-field Dark Energy Camera (DECam) at the CTIO 4 m Blanco telescope in
and down to a limiting surface brightness of mag
arcsec. Various image-filtering techniques were applied to the DECam
data to enhance the visibility of extremely low-surface brightness objects. We
report the discovery of 16 new dwarf galaxy candidates in the direction of the
M83 subgroup, roughly doubling the number of known dwarfs in that region. The
photometric properties of the candidates, when compared to those of the Local
Group, suggest membership in the M83 subgroup. The faintest objects have a
central star density of pc and a total magnitude of
, corresponding to at the nominal distance of 4.9 Mpc.
The sky distribution of the new objects is significantly prolonged toward Cen
A, suggesting that many of them belong to the Cen A subgroup or a common halo.
We also provide updated surface photometry for the brighter, known dwarf
members in the surveyed area
The time-dependent von Kármán plate equation as a limit of 3D nonlinear elasticity
The asymptotic behaviour of the solutions of three-dimensional
nonlinear elastodynamics in a thin plate is studied, as the thickness h of the
plate tends to zero. Under appropriate scalings of the applied force and of the
initial values in terms of h, it is shown that three-dimensional solutions of the
nonlinear elastodynamic equation converge to solutions of the time-dependent
von Kármán plate equation
The M101 group complex: new dwarf galaxy candidates and spatial structure
The fine details of the large-scale structure in the local universe provide
important empirical benchmarks for testing cosmological models of structure
formation. Dwarf galaxies are key object for such studies. Enlarge the sample
of known dwarf galaxies in the local universe. We performed a search for faint,
unresolved low-surface brightness dwarf galaxies in the M101 group complex,
including the region around the major spiral galaxies M101, M51, and M63 lying
at a distance 7.0, 8.6, and 9.0 Mpc, respectively. The new dwarf galaxy sample
can be used in a first step to test for significant substructure in the
2D-distribution and in a second step to study the spatial distribution of the
galaxy complex. Using filtering algorithms we surveyed 330 square degrees of
imaging data obtained from the Sloan Digital Sky Survey. The images were
visually inspected. The spatial distribution of known galaxies and candidates
was analyzed transforming the system into a M101 eigenframe, using the
geometrical alignment of the group. We discovered 15 new dwarf galaxies and
carried out surface photometry in the g and r bands. The similarity of the
photometric properties of these dwarfs to those of Local Group dwarfs suggest
membership to the M101 group complex. The sky distribution of the candidates
follows the thin planar structure outlined by the known members of the three
subgroups. The ~3Mpc long filamentary structure has a rms thickness of 67 kpc.
The planar structure of the embedded M101 subgroup is even thinner, with rms=46
kpc. The formation of this structure might be due to the expansion of the Local
Void to which it borders. Other implications are discussed as well. We show the
viability of SDSS data to extend the sample of dwarfs in the local universe and
test cosmological models on small scales.Comment: 12 pages, 8 figures, accepted for publication in A&
Efficient Prediction Designs for Random Fields
For estimation and predictions of random fields it is increasingly
acknowledged that the kriging variance may be a poor representative of true
uncertainty. Experimental designs based on more elaborate criteria that are
appropriate for empirical kriging are then often non-space-filling and very
costly to determine. In this paper, we investigate the possibility of using a
compound criterion inspired by an equivalence theorem type relation to build
designs quasi-optimal for the empirical kriging variance, when space-filling
designs become unsuitable. Two algorithms are proposed, one relying on
stochastic optimization to explicitly identify the Pareto front, while the
second uses the surrogate criteria as local heuristic to chose the points at
which the (costly) true Empirical Kriging variance is effectively computed. We
illustrate the performance of the algorithms presented on both a simple
simulated example and a real oceanographic dataset
Influence of Sterilization Procedures on Thermoplastics, with Special Regard to Modified Surfaces
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Für Werkstoffe für den Einsatz im Medikalbereich ist die Sterilisationsfähigkeit unabdingbare Voraussetzung. Die gängigen Sterilisationsmethoden rufen bei den meisten polymeren Werkstoffen Veränderungen hervor, die bis hin zur Spaltung der Polymerketten führen können. Speziell die in dieser Arbeit untersuchten, zur Verbesserung der Biokompatibilität modifizierten Oberflächen, die durch ihre stark vergrößerte Oberfläche eine besonders große Angriffsfläche bieten, stellen hier ein Problem dar. Aus diesem Grund wurden mögliche Veränderungen an drei verschiedenen thermoplastischen, im Medikalbereich gängigen Kunststoffen (Polyethylen, thermoplastisches Polyurethan, Polycarbonat) untersucht. Als Sterilisationsmethoden wurden Wasserdampf-, Gas- und Strahlensterilisation eingesetzt. Durch Zugversuche wurden Veränderungen mechanischer Kennwerte aufgrund verschiedener Sterilisationsverfahren unabhängig von der Oberflächenmodifizierung ermittelt. Mit dem Rasterelektronenmikroskop (REM) wurden sterilisationsbedingte Veränderungen in der Struktur der modifizierten Oberflächen dargestellt. Mit Hilfe der Differential-Thermo-Analyse (DTA) wurden sterilisationsbedingte Veränderungen der thermischen Eigenschaften der Kunststoffe ermittelt. Es konnten eindeutige Tendenzen über das Verhalten von Kunststoffen nach der Sterilisation mit verschiedenen Verfahren gezeigt werden. Eine globale Aussage über die Kompatibilität von Kunststoffen mit einem bestimmten Sterilisationsverfahren kann aufgrund der Untersuchungen nicht getroffen werden. Für jedes neue Kunststoffprodukt im Medikalbereich müssen also die nötigen Eigenschaften definiert und die zulässigen Veränderungen dieser Eigenschaften mit den verschiedenen möglichen Sterilisationsverfahren auf Erhalt überprüft werden.For materials intended for use in the medical setting their sterilizability is an indispensable prerequisite. In the case of most polymers the usual Sterilization methods result in changes that even extend to cleavage of the polymer chains. A particular problem in this respect are the surfaces modified for improved biocompatibility investigated in the present study, which are characterised by enlarged contact areas. For this reason, possible changes to three different thermoplastics commonly used for medical applications (polyethylene, thermoplastic polyurethane, polycarbonate) were investigated. Steam, gas and radiation were used for Sterilization. Tensile tests were employed to identify changes in mucosal characteristics caused by different Sterilization techniques irrespective of the surface modification. Sterilization-related changes to the structure of the modified surfaces were investigated with the scanning electron microscope (SEM). Differential thermo analysis (DTA) was used to determine changes in the thermal characteristics of the plastics. Clear tendencies with regard to the behaviour of the plastics after Sterilization with various techniques were found. A general Statement about the compatibility of plastic materials with a specific Sterilization method is not possible on the basis of this study. For every new polymeric product used for medical purposes, the characteristics required must first be defined and compliance with the permissible variations of these characteristics investigated for each of the various Sterilization techniques available
The abundance of dwarf galaxies around low-mass giants in the Local Volume
The abundance of satellite dwarf galaxies has long been considered a crucial
test for the current model of cosmology leading to the well-known missing
satellite problem. Recent advances in both simulations and observations have
allowed to study dwarf galaxies around host galaxies in more detail. We have
surveyed a 72 deg2 area of the nearby Sculptor group using the Dark Energy
Camera - also encompassing the two low-mass Local Volume galaxies NGC24 and
NGC45 residing behind the group - to search for hitherto undetected dwarf
galaxies. Apart from the previously known dwarf galaxies we have found only two
new candidates down to a 3 sigma surface brightness detection limit of 27.4 r
mag arcsec-2. Both systems are in projection close to NGC24. However, one of
these candidates could be an ultra-diffuse galaxy associated to a background
galaxy. We compared the number of known dwarf galaxy candidates around NGC24,
NGC45, and five other well-studied low-mass giant galaxies (NGC 1156, NGC2403,
NGC5023, M33, and the LMC) with predictions from cosmological simulations and
found that for the stellar-to-halo mass models considered, the observed
satellite numbers tend to be on the lower end of the expected range. This could
either mean that there is an over-prediction of luminous subhalos in LambdaCDM
or - and more likely - that we are missing some of the satellite members due to
observational biases.Comment: 7 pages, 2 tables, 4 figures, re-submitted to A&A after the referee
repor
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