7,023 research outputs found
Dynamical analysis of the cluster pair: A3407 + A3408
We carried out a dynamical study of the galaxy cluster pair A3407 \& A3408
based on a spectroscopic survey obtained with the 4 meter Blanco telescope at
the CTIO, plus 6dF data, and ROSAT All-Sky-Survey. The sample consists of 122
member galaxies brighter than . Our main goal is to probe the galaxy
dynamics in this field and verify if the sample constitutes a single galaxy
system or corresponds to an ongoing merging process. Statistical tests were
applied to clusters members showing that both the composite system A3407 +
A3408 as well as each individual cluster have Gaussian velocity distribution. A
velocity gradient of was identified around
the principal axis of the projected distribution of galaxies, indicating that
the global field may be rotating. Applying the KMM algorithm to the
distribution of galaxies we found that the solution with two clusters is better
than the single unit solution at the 99\% c.l. This is consistent with the
X-ray distribution around this field, which shows no common X-ray halo
involving A3407 and A3408. We also estimated virial masses and applied a
two-body model to probe the dynamics of the pair. The more likely scenario is
that in which the pair is gravitationally bound and probably experiences a
collapse phase, with the cluster cores crossing in less than 1
Gyr, a pre-merger scenario. The complex X-ray morphology, the gas temperature,
and some signs of galaxy evolution in A3408 suggests a post-merger scenario,
with cores having crossed each other Gyr ago, as an
alternative solution.Comment: 17 pages, 12 figures, submitted to MNRAS, accepted 2016 May 9.
Received 2016 May 9; in original form 2016 April 1
Novel approaches to determine residual stresses by ultramicroindentation techniques: application to sand blasted austenitic stainless steel
This research addresses the determination of residual stresses in sandblasted austenitic steel by ultramicroindentation techniques using a sharp indenter, whose sensitivity to residual stress effects is said to be inferior to that for spherical ones. We propose the introduction of an angular correction in the model of Wang et al. that relates variations in the maximum load to the presence of residual stresses. Likewise, the contribution to hardness of grain size refinement and work hardening, developed as a consequence of the severe plastic deformation during blasting, is determined to avoid overestimation of the residual stresses. Measurements were performed on polished cross sections along a length of several microns, thus obtaining a profile of the residual stresses. Results show a good agreement with those obtained by synchrotron radiation on the same specimens, which validates the method and demonstrates that microindentation using sharp indenters may be sensitive to the residual stress effect.Peer Reviewe
Star formation in low density HI gas around the Elliptical Galaxy NGC2865
Interacting galaxies surrounded by HI tidal debris are ideal sites for the
study of young clusters and tidal galaxy formation. The process that triggers
star formation in the low-density environments outside galaxies is still an
open question. New clusters and galaxies of tidal origin are expected to have
high metallicities for their luminosities. Spectroscopy of such objects is,
however, at the limit of what can be done with existing 8-10m class telescopes,
which has prevented statistical studies of these objects. NGC2865 is an
UV-bright merging elliptical galaxy with shells and extended HI tails. The
regions observed in this work were previously detected using multi-slit imaging
spectroscopy. We obtain new multislit spectroscopy of six young star-forming
regions around NGC2865, to determine their redshifts and metallicities. The six
emission-line regions are located 16-40 kpc from NGC2865 and they have similar
redshifts. They have ages of ~10Myears and an average metallicity of
12+log(O/H) ~ 8.6, suggesting a tidal origin for the regions. It is noted that
they coincide with an extended HI tail, which has projected density of N
< 10 cm, and displays a low surface brightness counterpart. These
regions may represent the youngest of the three populations of star clusters
already identified in NGC2865. The high, nearly-solar, oxygen abundances found
for the six regions in the vicinity of NGC2865 suggest that they were formed by
pre-enriched material from the parent galaxy, from gas removed during the last
major merger. Given the mass and the location of the HII regions, we can
speculate that these young star-forming regions are potential precursors of
globular clusters that will be part of the halo of NGC2865 in the future. Our
result supports the use of the multi-slit imaging spectroscopy as a useful tool
for finding nearly-formed stellar systems around galaxies.Comment: 7 pages, 2 figures accepted in A&
Detection of the Ammonium Ion in Space
We report on the detection of a narrow feature at 262816.73 MHz towards Orion
and the cold prestellar core B1-bS, that we attribute to the 1(0)-0(0) line of
the deuterated Ammonium ion, NH3D+. The observations were performed with the
IRAM 30m radio telescope. The carrier has to be a light molecular species as it
is the only feature detected over 3.6 GHz of bandwidth. The hyperfine structure
is not resolved indicating a very low value for the electric quadrupolar
coupling constant of Nitrogen which is expected for NH3D+ as the electric field
over the N nucleus is practically zero. Moreover, the feature is right at the
predicted frequency for the 1(0)-0(0) transition of the Ammonium ion, 262817(6)
MHz (3sigma), using rotational constants derived from new infrared data
obtained in our laboratory in Madrid. The estimated column density is
1.1(0.2)e12 cm-2. Assuming a deuterium enhancement similar to that of NH2D, we
derive N(NH4+) sim 2.6e13 cm-2, i.e., an abundance for Ammonium of a few
1e(-11).Comment: Accepted for publication in the Astrophysical Journal Letters 04 June
201
Recommended from our members
Cutibacterium (formerly Propionibacterium) acnes clavicular infection.
Cutibacterium (formerly Propionibacterium) acnes13, 16 is a slow growing, gram-positive bacteria that is naturally found in higher concentrations as skin flora on the chest and back, as well as in other areas with greater numbers of hair follicles.25, 37 Most of the reported cases of C. acnes shoulder girdle infection follow arthroplasty surgery,18, 20, 26, 27, 32, 35 which then often requires debridement, administration of intravenous antibiotics, and surgical revision of the implanted device.12, 15, 21, 28-30 In a recent study, 56% of 193 shoulder revisions had a positive culture, 70% of which grew C. acnes.30 Despite the relatively common presumed association of C. acnes humeral osteomyelitis with prosthetic infection, infection of the scapula or clavicle secondary to C. acnes is rare.4, 23, 36 Osteomyelitis of the clavicle involving any organism is also an uncommon event that can arise spontaneously via presumed hematogenous spread, or secondary to open fractures or internal fixation.6, 33 The most commonly found organism in clavicular osteomyelitis is Staphylococcus aureus.9 We here report two cases of clavicular infection secondary to C. acnes that were not associated with implants
- …