23 research outputs found
On the Influence of Minor Mergers on the Radial Abundance Gradient in Disks of Milky Way-like Galaxies
We investigate the influence of stellar migration caused by minor mergers
(mass ratio from 1:70 to 1:8) on the radial distribution of chemical abundances
in the disks of Milky Way-like galaxies during the last four Gyr. A GPU-based
pure N-body tree-code model without hydrodynamics and star formation was used.
We computed a large set of mergers with different initial satellite masses,
positions, and orbital velocities. We find that there is no significant
metallicity change at any radius of the primary galaxy in the case of accretion
of a low-mass satellite of 10 M (mass ratio 1:70) except for the
special case of prograde satellite motion in the disk plane of the host galaxy.
The accretion of a satellite of a mass M (mass
ratio 1:23) results in an appreciable increase of the chemical abundances at
galactocentric distances larger than kpc. The radial abundance
gradient flattens in the range of galactocentric distances from 5 to 15 kpc in
the case of a merger with a satellite with a mass
M. There is no significant change in the abundance gradient slope in
the outer disk (from kpc up to 25 kpc) in any merger while the scatter
in metallicities at a given radius significantly increases for most of the
satellite's initial masses/positions compared to the case of an isolated
galaxy. This argues against attributing the break (flattening) of the abundance
gradient near the optical radius observed in the extended disks of Milky
Way-like galaxies only to merger-induced stellar migration.Comment: 17 pages, 15 figures, accepted for publication in Ap
Deuterated molecules in regions of high-mass star formation
We present the results of our studies of deuterated molecules (DCN, DNC,
DCO, ND and NHD) in regions of high-mass star formation, which
include a survey of such regions with the 20-m Onsala radio telescope and
mapping of several objects in various lines with the 30-m IRAM and 100-m MPIfR
radio telescopes. The deuteration degree reaches 10 in these
objects. We discuss its dependencies on the gas temperature and velocity
dispersion, as well as spatial distributions of deuterated molecules. We show
that the HCN/HNC intensity ratio may be a good indicator of the
gas kinetic temperature and estimate densities of the investigated objects.Comment: 8 pages, 4 figures, to be published in Proceedings of Science
(Proceedings of the conference "The Multifaceted Universe: Theory and
Observations - 2022", 23-27 May 2022, SAO RAS, Nizhny Arkhyz, Russia
Effective temperature of ionizing stars in extragalactic H II regions : II. Nebular parameter relationships based on CALIFA data
We calculate the effective temperature (Teff) of ionizing star(s), the oxygen abundance of the gas phase (O/H), and the ionization parameter U for a sample of H II regions located in the discs of 59 spiral galaxies in the redshift range 0.005 eff and U) and empirical (for O/H) calibrations based on strong emission lines. We consider the spatial distribution and radial gradients of these parameters in each galactic disc for the objects in our sample. Most of the galaxies in our sample (∼70 per cent) show positive Teff radial gradients, although some exhibit negative or flat ones. The median value of the Teff radial gradient is 0.762 kK/R25. We find that the radial gradients of both log U and Teff depend on the oxygen abundance gradient, in the sense that the gradient of log U increases as the log(O/H) gradient increases while there is an anti-correlation between the gradient of Teff and the oxygen abundance gradient. Moreover, galaxies with flat oxygen abundance gradients tend to have flat log U and Teff gradients as well. Although our results are in agreement with the idea of the existence of positive Teff gradients along the disc of the majority of spiral galaxies, it seems that this is not a universal property for these objects.Instituto de Astrofísica de La Plat
The massive relic galaxy NGC 1277 is dark matter deficient. From dynamical models of integral-field stellar kinematics out to five effective radii
According to the CDM cosmology, present-day galaxies with stellar
masses should contain a sizable fraction of
dark matter within their stellar body. Models indicate that in massive
early-type galaxies (ETGs) dark matter should account for of the
dynamical mass within five effective radii (). Most massive ETGs
have been shaped through a two-phase process: the rapid growth of a compact
core was followed by the accretion of an extended envelope through mergers. The
exceedingly rare galaxies that have avoided the second phase, the so-called
relic galaxies, are thought to be the frozen remains of the massive ETG
population at . The best relic galaxy candidate discovered to date
is NGC 1277, in the Perseus cluster. We used deep integral field GCMS data to
revisit NGC 1277 out to an unprecedented radius of 6 kpc (corresponding to ). By using Jeans anisotropic modelling we find a negligible dark
matter fraction within (; two-sigma
confidence level), which is in tension with the expectation. Since the lack of
an extended envelope would reduce dynamical friction and prevent the accretion
of an envelope, we propose that NGC 1277 lost its dark matter very early or
that it was dark matter deficient ab initio. We discuss our discovery in the
framework of recent proposals suggesting that some relic galaxies may result
from dark matter stripping as they fell in and interacted within galaxy
clusters. Alternatively, NGC 1277 might have been born in a high-velocity
collision of gas-rich proto-galactic fragments, where dark matter left behind a
disc of dissipative baryons. We speculate that the relative velocities of
required for the latter process to happen were
possible in the progenitors of the present-day rich galaxy clusters.Comment: Accepted for publication in A&
Molecular and Cellular Mechanisms of M. tuberculosis and SARS-CoV-2 Infections-Unexpected Similarities of Pathogenesis and What to Expect from Co-Infection
Tuberculosis is still an important medical and social problem. In recent years, great strides have been made in the fight against M. tuberculosis, especially in the Russian Federation. However, the emergence of a new coronavirus infection (COVID-19) has led to the long-term isolation of the population on the one hand and to the relevance of using personal protective equipment on the other. Our knowledge regarding SARS-CoV-2-induced inflammation and tissue destruction is rapidly expanding, while our understanding of the pathology of human pulmonary tuberculosis gained through more the 100 years of research is still limited. This paper reviews the main molecular and cellular differences and similarities caused by M. tuberculosis and SARS-CoV-2 infections, as well as their critical immunological and pathomorphological features. Immune suppression caused by the SARS-CoV-2 virus may result in certain difficulties in the diagnosis and treatment of tuberculosis. Furthermore, long-term lymphopenia, hyperinflammation, lung tissue injury and imbalance in CD4+ T cell subsets associated with COVID-19 could propagate M. tuberculosis infection and disease progression
The redshift evolution of oxygen and nitrogen abundances in emission-line SDSS galaxies
The oxygen and nitrogen abundance evolutions with redshift and galaxy stellar
mass in emission-line SDSS galaxies are investigated. This is the first such
study for nitrogen abundances, and it provides an additional constraint for the
study of the chemical evolution of galaxies. We have devised a criterion to
recognize and exclude from consideration AGNs and star-forming galaxies with
large errors in the line flux measurements. To select star-forming galaxies
with accurate line fluxes measurements, we require that, for each galaxy, the
nitrogen abundances derived with various calibrations based on different
emission lines agree. Using this selection criterion, subsamples of
star-forming galaxies have been extracted from catalogs of the MPA/JHU group.
We found that the galaxies of highest masses, those with masses > 10^11.2
M_sun, have not been enriched in both oxygen and nitrogen over the last 3 Gyr:
they have formed their stars in the so distant past that these have returned
their nucleosynthesis products to the interstellar medium before z=0.25. The
galaxies in the mass range from 10^11.0 M_sun to 10^11.2 M_sun do not show an
appreciable enrichment in oxygen, but do show some enrichment in nitrogen: they
also formed their stars before z=0.25 but later in comparison to the galaxies
of highest masses; these stars have not returned nitrogen to the interstellar
medium before z=0.25 because they have not had enough time to evolve. This
suggests that stars with lifetimes of 2-3 Gyr contribute to the nitrogen
production. Finally, galaxies with masses < 10^11 M_sun show enrichment in both
oxygen and nitrogen during the last 3 Gyr: they have undergone appreciable star
formation and have converted up to 20% of their mass into stars over this
period.Comment: 43 pages, 15 figures, accepted for publication in the Astrophysical
Journa
Chemical abundance of the LINER galaxy UGC 4805 with SDSS-IV MaNGA
Chemical abundance determinations in Low-Ionization Nuclear Line Regions (LINERs) are especially complex and uncertain because the nature of the ionizing source of this kind of object is unknown. In this work, we study the oxygen abundance in relation to the hydrogen abundance (O/H) of the gas phase of the UGC 4805 LINER nucleus. Optical spectroscopic data from the Mapping Nearby Galaxies (MaNGA) survey was employed to derive the O/H abundance of the UGC 4805 nucleus based on the extrapolation of the disk abundance gradient, on calibrations between O/H abundance and strong emission-lines for Active Galactic Nuclei (AGNs) as well as on photoionization models built with the Cloudy code, assuming gas accretion into a black hole (AGN) and post-Asymptotic Giant Branch (p-AGB) stars with different effective temperatures. We found that abundance gradient extrapolations, AGN calibrations, AGN and p-AGB photoionization models produce similar O/H values for the UGC 4805 nucleus and similar ionization parameter values. The study demonstrated that the methods used to estimate the O/H abundance using nuclear emission-line ratios produce reliable results, which are in agreement with the O/H values obtained from the independent method of galactic metallicity gradient extrapolation. Finally, the results from the WHAN diagram combined with the fact that the high excitation level of the gas has to be maintained at kpc scales, we suggest that the main ionizing source of the UGC 4805 nucleus probably has a stellar origin rather than an AGN.Instituto de Astrofísica de La Plat
Metal-THINGS: On the metallicity and ionization of ULX sources in NGC 925
We present an analysis of the optical properties of three Ultra Luminous
X-ray (ULX) sources identified in NGC 925. We use Integral field unit data from
the George Mitchel spectrograph in the context of the Metal-THINGS survey. The
optical properties for ULX-1 and ULX-3 are presented, while the spaxel
associated with ULX-2 had a low S/N, which prevented its analysis. We also
report the kinematics and dimensions of the optical nebula associated with each
ULX using ancillary data from the PUMA Fabry-Perot spectrograph. A BPT analysis
demonstrates that most spaxels in NGC 925 are dominated by star-forming
regions, including those associated with ULX-1 and ULX-3. Using the resolved
gas-phase metallicities, a negative metallicity gradient is found, consistent
with previous results for spiral galaxies, while the ionization parameter tends
to increase radially throughout the galaxy. Interestingly, ULX-1 shows a very
low gas metallicity for its galactocentric distance, identified by two
independent methods, while exhibiting a typical ionization. We find that such
low gas metallicity is best explained in the context of the high-mass X-ray
binary population, where the low-metallicity environment favours active Roche
lobe overflows that can drive much higher accretion rates. An alternative
scenario invoking accretion of a low-mass galaxy is not supported by the data
in this region. Finally, ULX-3 shows both a high metallicity and ionization
parameter, which is consistent with the progenitor being a highly-accreting
neutron star within an evolved stellar population region.Comment: Accepted by Ap
The metrological aspects of converters based on operational amplifiers used to measure the electrical parameters of oxide coatings
Background. The study is devoted to the issue of improving the accuracy of automated measuring instruments for the electrical parameters of oxide coatings. In measuring instruments, integrating circuits based on an operational amplifier, which is a universal amplifying device, are used to perform linear mathematical operations on analog signals. The disadvantage of the integrating circuit is the use of an operational amplifier, when using which it is necessary to take into account many parameters and factors that can affect the output signal, and hence the accuracy of the measured value. Materials and methods. Methods of indirect measurement of voltage and current on the studied sample with an oxide coating using the proposed structures of measuring channels are presented. It is shown that the parameters of operational amplifiers have a significant influence on the additive and multiplicative errors of measurement results, for the analysis of which a linear model of an operational amplifier is considered. Results. Based on the metrological analysis of the voltage measurement channel on the test sample, formulas for estimating additive, multiplicative and nonlinear error components are obtained. The contribution of multiplicative and additive parameters of the operational amplifier to the error of measurement results is analyzed in detail. Conclusions. Metrological analysis of the equivalent circuit of an operational amplifier with feedback has been performed, which can be used to estimate additive and multiplicative errors of circuits based on operational amplifiers widely used in instruments and measuring systems. It is shown that the total relative error of the developed channels for measuring current and voltage does not exceed 0.5%, which makes it possible to measure these values of the studied oxide coatings with guaranteed accuracy