156 research outputs found
Validity of abundances derived from spaxel spectra of the MaNGA survey
We measured the emission lines in the spaxel spectra of MaNGA galaxies in
order to determine the abundance distributions therein. It has been suggested
that the strength of the low-ionization lines, R_2, N_2, and S_2 may be
increased (relative to Balmer lines) in (some) spaxel spectra of the MaNGA
survey due to a contribution of the radiation of the diffuse ionized gas.
Consequently, the abundances derived from the spaxel spectra through
strong-line methods may suffer from large errors. We examined this expectation
by comparing the behaviour of the line intensities and the abundances estimated
through different calibrations for slit spectra of HII regions in nearby
galaxies, for fibre spectra from the SDSS, and for spaxel spectra of the MaNGA
survey. We found that the S_2 strength is increased significantly in the fibre
and spaxel spectra. The mean enhancement changes with metallicity and can be as
large as a factor of 2. The mean distortion of R_2 and N_2 is less than a
factor of 1.3. This suggests that Kaufmann et al.'s demarcation line between
AGNs and HII regions in the BPT diagram is a useful criterion to reject spectra
with significantly distorted strengths of the N_2 and R_2 lines. We find that
the three-dimensional R calibration, which uses the N_2 and R_2 lines, produces
reliable abundances in the MaNGA galaxies. The one-dimensional N2 calibration
produces either reliable or wrong abundances depending on whether excitation
and N/O abundance ratio in the target region (spaxel) are close to or differ
from those parameters in the calibrating points located close to the
calibration relation. We then determined abundance distributions within the
optical radii in the discs of 47 MaNGA galaxies. The optical radii of the
galaxies were estimated from the surface brightness profiles constructed based
on the MaNGA observations.Comment: 19 pages, 15 figures, accepted for publication in A&
Plastic Deformation of Polycrystalline Iridium at Room Temperature
Defect structure and its relationship with deformation behaviour at room temperature of iridium, the sole refractory face centred cubic (f.c.c.) metal, are discussed. Small angle boundaries and pile-ups of curvilinear dislocation segments are the main features of dislocation structure in polycrystalline iridium at room temperature, while homogeneously distributed rectilinear dislocation segments were the main element of defect structure of iridium single crystals at the same conditions. Small angle boundaries and pile-ups of curvilinear dislocation segments are formed in iridium single crystals under mechanical treatment at elevated temperatures (> 800°C) only. The evolution of defect structure in polycrystalline iridium and other f.c.c. metals under room temperature deformation occurs by the same process: accumulation of dislocations in the matrix leads to the appearance of both new sub-grains and new grains up to the fine grain (nanocrystalline) structure. Neither single straight dislocations nor their pile-ups are observed in iridium at room temperature if small angle boundaries have been formed. This feature may be considered as the reason why polycrystalline iridium demonstrates advanced necking (high localised plasticity) and small total elongation.The authors would like to thank Professor David Lupton (W. C. Heraeus GmbH, Hanau, Germany) and Professor Easo George (The University of Tennessee, Knoxville, Tennessee, U.S.A.) for helpful discussions. This research was partially supported by the JSC Ekaterinburg NonFerrous Metals Processing Plant, the Ministry of Education and Science of the Russian Federation (Grant No. 2.2.2.2/5579) and the U.S. Civilian Research and Development Foundation (CRDF) (Grant No. RUXO-005-EK-06/BG7305)
The First Galaxies: Clues from Element Abundances
It has recently become possible to measure directly the abundances of several
chemical elements in a variety of environments at redshifts up to z = 5. In
this review I summarise the latest observations of Lyman break galaxies, damped
Lyman alpha systems and the Lyman alpha forest with a view to uncovering any
clues which these data may offer to the first episodes of star formation. The
picture which is emerging is one where the universe at z = 3 already included
many of the components of today's galaxies--even at these early times we see
evidence for Populations I and II stars, while the `smoking gun' for Population
III objects may be hidden in the chemical composition of the lowest density
regions of the IGM, yet to be deciphered.Comment: 15 pages, LaTex, 8 Postscript Figures. To appear in the Philosophical
Transactions of The Royal Society, Series
Mechanical Behavior of Polycrystalline Rhenium under 3-Points Bending at a Low Homological Temperature
Mechanical behaviour of polycrystalline rhenium under 3-points bending at such low homological temperature as room is discussed. Two metallurgical technologies (electron beam melting and powder metallurgy) were used for the samples preparation. Fine-grained samples (PM metal) exhibit some plasticity prior the failure, while coarse-grained ones (EBM metal) behave like a brittle solid. The intergranular fracture is the fracture mode of rhenium in both cases. Basal slip and prismatic slip of dislocations are not active in rhenium at low homological temperature, but the grain boundary sliding occurs under these conditions. Therefore, polycrystalline rhenium cannot be machined at room temperature despite the growth of grain boundary cracks are braked in the samples due to grain boundary sliding. © Published under licence by IOP Publishing Ltd.Russian Science Foundation, RSF: 18-19-00217This work is supported by the Russian Science Foundation (#18-19-00217)
A study of HI-selected galaxies in the Hercules cluster
The present study is aimed at a sample of 22 galaxies detected in the blind
VLA HI survey of the Hercules cluster by Dickey (1997), 18 of which were
selected on an HI line width smaller than 270 km/s and 4 others with only
tentative optical counterparts on the Palomar Sky Survey. Sensitive single-dish
HI line spectra were obtained for 20 of them, and for one (47-154) the VLA
detection was not confirmed. Optical surface photometry was obtained of 10
objects, for 8 of which optical spectroscopy was obtained as well. Based on
various selection criteria, two (ce-143 and ne-204) can be classified as
dwarfs. The objects of which optical observations were made show star formation
properties similar to those of published samples of actively star forming
galaxies, and approximately half of them have properties intermediate between
those of dwarf galaxies and low-luminosity disc galaxies. No optical redshifts
could be obtained for two of the galaxies (sw-103 and sw-194) and their
physical association with the HI clouds detected at their positions therefore
remains uncertain. Unique among the objects is the Tidal Dwarf Galaxy ce-061 in
a tail of the IC 1182 merger system.Comment: 20 pages, 19 figures, accepted for publication in A&
Evaluation of the structural-phase characteristics of a supersaturated ultrafine-grained Au-Co solid solution by diffractometry in hard synchrotron radiation
A synchrotron radiation study of immiscible Au-Co alloys obtained by consolidating a heterogeneous mixture of components and subsequent severe plastic deformation was performed. Namely, the estimates of the crystal lattice parameter, the average size of the coherent scattering regions and lattice strains in mechanically alloyed supersaturated solid solutions were made using obtained diffraction patterns and diffraction spectra. The effect of the temperature regime of deformation processing on the listed characteristics is shown, when the transition from cold deformation to cryogenic is carried out. © 2020 American Institute of Physics Inc. All rights reserved.The work was done at the shared research center SSTRC on the basis of the VEPP-4 - VEPP-2000 complex at BINP SB RAS, using equipment supported by project RFMEFI62119X0022. The SR XRD performed at the station "Diffractometry in the "hard" X-ray range" of the 4th synchrotron radiation channel of the VEPP-3 accelerator of the Siberian Center of Synchrotron and Terahertz Radiation of the Budker Institute of Nuclear Physics by Alexey I. Ancharov. Obtaining and deformation processing of the investigated materials were carried out on the basis of M.N. Mikheev Institute of Metal Physics of the Ural Branch of the Russian Academy of Sciences, Yekaterinburg. The research was carried out within the state assignment of Ministry of Science and Higher Education of the Russian Federation (theme “Рressure” No. АААА-А18-118020190104-3), supported in part by RFBR (project No. 19-32-60039)
Peculiar motions of the gas at the centre of the barred galaxy UGC 4056
We derive the circular velocity curves of the gaseous and stellar discs of
UGC 4056, a giant barred galaxy with an active galactic nucleus (AGN). We
analyse UGC 4056 using the 2D spectroscopy obtained within the framework of the
Mapping Nearby Galaxies at APO (MaNGA) survey. Using images and the colour
index g-r from the Sloan Digital Sky Survey (SDSS), we determined the tilt of
the galaxy, which allows us to conclude that the galaxy rotates clockwise with
trailing spiral arms. We found that the gas motion at the central part of the
UGC 4056 shows peculiar features. The rotation velocity of the gaseous disc
shows a bump within around three kiloparsecs while the rotation velocity of the
stellar disc falls smoothly to zero with decreasing galactocentric distance. We
demonstrate that the peculiar radial velocities in the central part of the
galaxy may be caused by the inflow of the gas towards the nucleus of the
galaxy. The unusual motion of the gas takes place at the region with the
AGN-like radiation and can be explained by the gas response to the bar
potential.Comment: 11 pages, 10 figures, 1 table, accepted for publication in A&
Evolution of Microstructure and Properties of Ni–Mn–In Alloys after Torsional Deformation under High Pressure
Исследованы сплавы Гейслера системы Ni–Mn–In после деформации методом кручения под давлением 8 ГПа. Обсуждаются структурно-фазовые превращения и свойства после деформации сплавов Ni–Mn–In с разным соотношением Ni/Mn.Heusler alloys of the Ni–Mn–In system were investigated after torsional deformation under a pressure of 8 GPa. Structural-phase transformations and properties after deformation of Ni–Mn–In alloys with different Ni/Mn ratios are discussed.Исследование выполнено в рамках государственного задания Минобрнауки России (темы «Структура» г. р. № ААААА18-118020190116-6, «Давление» г. р. № АААА-А18-118020190104-3) при частичной поддержке РФФИ (проект № 20–03–00056).The study was carried out within the framework of the state task of the Ministry of Education and Science of Russia (topics „Structure“ of the year no. AAAA18-118020190116-6, „Pressure“ of the year no. AAAA18-118020190104-3) with partial support of the RFBR (project no. 20-03-00056)
Tidal Dwarf Candidates in a Sample of Interacting Galaxies. II. Properties and Kinematics of the Ionized Gas
We present low-resolution spectroscopy of the ionized gas in a sample of
optical knots located along the tidal features of 14 interacting galaxies and
previously selected as candidates of Tidal Dwarf Galaxies (TDGs). From redshift
measurements, we are able to confirm their physical association with the
interacting system in almost all cases. For most knots, the oxygen abundance
does not depend on the blue luminosity. The average, 12+log(O/H)=8.34+-0.20, is
typical of TDGs and comparable to that measured in the outer stellar disk of
spirals from which they were formed. A few knots showing low metallicities are
probably pre-existing low-mass companions. The estimated Ha luminosity of the
TDG candidates is higher than the one of typical individual HII regions in
spiral disks and comparable to the global Ha luminosity of dwarf galaxies. We
find several instances of velocity gradients with amplitudes apparently larger
than 100 km/s in the ionized gas in the tidal knots and discuss various
possible origins for the large velocity amplitudes. While we can exclude tidal
streaming motions and outflows, we cannot rule out projection effects with the
current resolution. The velocity gradients could be indicative of the internal
kinematics characteristic of self-gravitating objects. Higher resolution
spectra are required to confirm whether the tidal knots in our sample have
already acquired their dynamical independence and are therefore genuine Tidal
Dwarf Galaxies.Comment: 12 pages, 7 figures, partly color (but printable in greyscale without
loss of information). Paper is accepted by A&A. The appendix with images of
the galaxies can be downloaded from
http://www.uni-sw.gwdg.de/~weilbach/pubs/pub.htm
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