1,351 research outputs found
Gas and stellar kinematic misalignment in MaNGA galaxies: what is the origin of counter-rotating gas?
Kinematic misalignment between gas and stellar components observed in a
certain fraction of galaxies. It believed to be caused by acquisition of gas
from the external reservoir by major or minor mergers, accretion from
cosmological filaments or circumgalactic medium, etc. We aim to constrain
possible sources of the gas that forms counter-rotating component. We derived
the gas-phase oxygen abundance in 69 galaxies with kinematic misalignment
between gas and stellar components from MaNGA DR17 survey and compared it with
the metallicity expected according to the mass-metallicity relation. We found
that the oxygen abundance of the counter-rotating gas in our sample is higher
than 8.2 dex that excludes significant role of inflow of pristine gas.
Meanwhile, there is a significant difference in the oxygen abundance of the
counter-rotating gas between red and blue galaxies. In general, the oxygen
abundance is lower than expected for their stellar mass in red galaxies, but is
compatible with or even higher than typical values for their stellar mass in
blue galaxies. We showed that the exchange of enriched gas between galaxies is
the most plausible mechanism for explaining the metallicity of counter-rotating
gas components in galaxies of all masses and colors. Meanwhile, minor mergers
may play a significant role in the formation of counter-rotating gas components
in red and quenched galaxies.Comment: 5 pages, 3 figures, accepted for publication in A&A Letter
Characterizing the radial oxygen abundance distribution in disk galaxies
We examine the possible dependence of the radial oxygen abundance
distribution on non-axisymmetrical structures (bar/spirals) and other
macroscopic parameters such as the mass, the optical radius R25, the color g-r,
and the surface brightness of the galaxy. A sample of disk galaxies from the
CALIFA DR3 is considered. We adopted the Fourier amplitude A2 of the surface
brightness as a quantitative characteristic of the strength of non-axisymmetric
structures in a galactic disk, in addition to the commonly used morphologic
division for A, AB, and B types based on the Hubble classification. To
distinguish changes in local oxygen abundance caused by the non-axisymmetrical
structures, the multiparametric mass--metallicity relation was constructed as a
function of parameters such as the bar/spiral pattern strength, the disk size,
color index g-r in the SDSS bands, and central surface brightness of the disk.
The gas-phase oxygen abundance gradient is determined by using the R
calibration. We find that there is no significant impact of the
non-axisymmetric structures such as a bar and/or spiral patterns on the local
oxygen abundance and radial oxygen abundance gradient of disk galaxies.
Galaxies with higher mass, however, exhibit flatter oxygen abundance gradients
in units of dex/kpc, but this effect is significantly less prominent for the
oxygen abundance gradients in units of dex/R25 and almost disappears when the
inner parts are avoided. We show that the oxygen abundance in the central part
of the galaxy depends neither on the optical radius R25 nor on the color g-r or
the surface brightness of the galaxy. Instead, outside the central part of the
galaxy, the oxygen abundance increases with g-r value and central surface
brightness of the disk.Comment: 11 pages, 6 figures; accepted for publication in A&
Oxygen abundance distributions in six late-type galaxies based on SALT spectra of HII regions
Spectra of 34 H II regions in the late-type galaxies NGC1087, NGC2967,
NGC3023, NGC4030, NGC4123, and NGC4517A were observed with the South African
Large Telescope (SALT). In all 34 H II regions, oxygen abundances were
determined through the "counterpart" method (C method). Additionally, in two H
II regions in which the auroral lines were detected oxygen abundances were
measured through the classic Te method. We also estimated the abundances in our
H II regions using the O3N2 and N2 calibrations and compared those with the
C-based abundances. With these data we examined the radial abundance
distributions in the disks of our target galaxies. We derived
surface-brightness profiles and other characteristics of the disks (the surface
brightness at the disk center and the disk scale length) in three photometric
bands for each galaxy using publicly available photometric imaging data. The
radial distributions of the oxygen abundances predicted by the relation between
abundance and disk surface brightness in the W1 band obtained for spiral
galaxies in our previous study are close to the radial distributions of the
oxygen abundances determined from the analysis of the emission line spectra for
four galaxies where this relation is applicable. Hence, when the
surface-brightness profile of a late-type galaxy is known, this parametric
relation can be used to estimate the likely present-day oxygen abundance in its
disk.Comment: 15 pages, 11 figures; Accepted for publication in Astronomy &
Astrophysic
A Search for Small-Scale Clumpiness in Dense Cores of Molecular Clouds
We have analyzed HCN(1-0) and CS(2-1) line profiles obtained with high
signal-to-noise ratios toward distinct positions in three selected objects in
order to search for small-scale structure in molecular cloud cores associated
with regions of high-mass star formation. In some cases, ripples were detected
in the line profiles, which could be due to the presence of a large number of
unresolved small clumps in the telescope beam. The number of clumps for regions
with linear scales of ~0.2-0.5 pc is determined using an analytical model and
detailed calculations for a clumpy cloud model; this number varies in the
range: ~2 10^4-3 10^5, depending on the source. The clump densities range from
~3 10^5-10^6 cm^{-3}, and the sizes and volume filling factors of the clumps
are ~(1-3) 10^{-3} pc and ~0.03-0.12. The clumps are surrounded by inter-clump
gas with densities not lower than ~(2-7) 10^4 cm^{-3}. The internal thermal
energy of the gas in the model clumps is much higher than their gravitational
energy. Their mean lifetimes can depend on the inter-clump collisional rates,
and vary in the range ~10^4-10^5 yr. These structures are probably connected
with density fluctuations due to turbulence in high-mass star-forming regions.Comment: 23 pages including 4 figures and 4 table
Detection of a new methanol maser line with ALMA
Aims. We aimed at investigating the structure and kinematics of the gaseous
disk and outflows around the massive YSO S255 NIRS3 in the S255IR-SMA1 dense
clump. Methods. Observations of the S255IR region were carried out with ALMA at
two epochs in the compact and extended configurations. Results. We
serendipitously detected a new, never predicted, bright maser line at about
349.1 GHz, which most probably represents the CHOH A transition. The emission covers most of the 6.7 GHz methanol maser emission
area of almost 1 in size and shows a velocity gradient in the
same sense as the disk rotation. No variability was found on the time interval
of several months. It is classified as Class II maser and probably originates
in a ring at a distance of several hundreds AU from the central star.Comment: 4 pages, 4 figures, accepted by Astronomy and Astrophysic
Multi-wavelength study of the star-formation in the S237 H II region
We present a detailed multi-wavelength study of observations from X-ray,
near-infrared to centimeter wavelengths to probe the star formation processes
in the S237 region. Multi-wavelength images trace an almost sphere-like shell
morphology of the region, which is filled with the 0.5--2 keV X-ray emission.
The region contains two distinct environments - a bell-shaped cavity-like
structure containing the peak of 1.4 GHz emission at center, and elongated
filamentary features without any radio detection at edges of the sphere-like
shell - where {\it Herschel} clumps are detected. Using the 1.4 GHz continuum
and CO line data, the S237 region is found to be excited by a radio
spectral type of B0.5V star and is associated with an expanding H{\sc ii}
region. The photoionized gas appears to be responsible for the origin of the
bell-shaped structure. The majority of molecular gas is distributed toward a
massive {\it Herschel} clump (M 260 M), which
contains the filamentary features and has a noticeable velocity gradient. The
photometric analysis traces the clusters of young stellar objects (YSOs) mainly
toward the bell-shaped structure and the filamentary features. Considering the
lower dynamical age of the H\,{\sc ii} region (i.e. 0.2-0.8 Myr), these
clusters are unlikely to be formed by the expansion of the H\,{\sc ii} region.
Our results also show the existence of a cluster of YSOs and a massive clump at
the intersection of filamentary features, indicating that the collisions of
these features may have triggered cluster formation, similar to those found in
Serpens South region.Comment: 21 pages, 14 figures, 1 table, Accepted for publication in The
Astrophysical Journa
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