250 research outputs found
Very metal-poor galaxies: ionized gas kinematics in nine objects
The study of ionized gas morphology and kinematics in nine eXtremely
Metal-Deficient (XMD) galaxies with the scanning Fabry-Perot interferometer on
the SAO 6-m telescope is presented. Some of these very rare objects (with
currently known range of O/H of 7.12 < 12+log(O/H) < 7.65, or Zo/35 < Z <
Zo/10) are believed to be the best proxies of `young' low-mass galaxies in the
high-redshift Universe. One of the main goals of this study is to look for
possible evidence of star formation (SF) activity induced by external
perturbations. Recent results from HI mapping of a small subsample of XMD
star-forming galaxies provided confident evidence for the important role of
interaction-induced SF. Our observations provide complementary or new
information that the great majority of the studied XMD dwarfs have strongly
disturbed gas morphology and kinematics or the presence of detached components.
We approximate the observed velocity fields by simple models of a rotating
tilted thin disc, which allow us the robust detection of non-circular gas
motions. These data, in turn, indicate the important role of current/recent
interactions and mergers in the observed enhanced star formation. As a
by-product of our observations, we obtained data for two LSB dwarf galaxies:
Anon J012544+075957 that is a companion of the merger system UGC 993, and SAO
0822+3545 which shows off-centre, asymmetric, low SFR star-forming regions,
likely induced by the interaction with the companion XMD dwarf HS 0822+3542.Comment: Accepted to MNRAS, 20 pages, 3 tables, 7 figure
Study of galaxies in the Lynx-Cancer void. -- III. New extreme LSB dwarf galaxies
(Abridged) We present the results of the complex study of the low surface
brightness dwarf (LSBD) gas-rich galaxies J0723+3621, J0737+4724 and
J0852+1350, which reside in the nearby Lynx-Cancer void. Their ratios
M(HI)/L_B, according to HI data obtained with the NRT, are respectively ~3.9,
~2, ~2.6. For the two latter galaxies, we derived oxygen abundance
corresponding to the value of 12+log(O/H) <~7.3, using spectra from the Russian
6m telescope and from the SDSS database. We found two additional blue LSB
dwarfs, J0723+3622 and J0852+1351, which appear to be physical companions of
J0723+3621 and J0852+1350 situated at the projected distances of ~12--13 kpc.
The companion relative velocities, derived from the BTA spectra, are dV = +89
km/s and +30 km/s respectively. The geometry and the relative orientation of
orbits and spins in these pairs indicate, respectively, prograde and polar
encounters for J0723+3621 and J0852+1350. The NRT HI profiles of J0723+3621 and
J0723+3622 indicate a sizable gas flow in this system. The SDSS u,g,r,i images
of the five dwarfs are used to derive the photometric parameters and the
exponential or Sersic disc model fits. For three of them, the (u-g),(g-r),(r-i)
colours of the outer parts, being compared with the PEGASE evolutionary tracks,
evidence for the dominance of the old stellar populations with ages of T
~(8-10)+-3 Gyr. For J0723+3622 and J0737+4724, the outer region colours appear
rather blue, implying the ages of the oldest visible stars of T <~1-3 Gyr. The
new LSB galaxies complement the list of the known most metal-poor and
`unevolved' dwarfs in this void, including DDO 68, SDSS J0926+3343 and others.
This unique concentration of 'unevolved' dwarf galaxies in a small cell of the
nearby Universe implies a physical relationship between the slow galaxy
evolution and the void-type global environment.Comment: 16 pages, 5 tables, 9 figures. MNRAS, in pres
Search for and study of extremely metal-deficient galaxies
We summarize the progress in identifying and observational study of extremely
metal-deficient (XMD) gas-rich galaxies (BCGs, dIr and LSBDs). Due to volume
limitations only following issues are addressed: sample creation, some
statistical data, Colour-Magnitude Diagrams (CMD) and ages, the case of SBS
0335--052 system, and probable evolution paths of various XMD objects.Comment: 4 pages, 3 figures. To appear in the proceedings of Euroconference
"The evolution of galaxies. III. From simple approaches to self-consistent
models" Kiel, Germany, July 200
HI study of extremely metal-deficient dwarf galaxies. I. The Nancay Radio Telescope observations of twenty-two objects
The goal of this study is to measure parameters of the integrated HI emission
for twenty-two dwarf galaxies with oxygen abundance 12+log(O/H) in the range of
7.42 to 7.65, which are representatives of the eXtremely Metal-Deficient (XMD)
galaxy group. Some of them are expected to be similar to the well-known
candidates for local young galaxies, IZw18 and SBS 0335-052 that have most of
their baryon mass in the form of neutral gas. Therefore, the HI 21-cm line
observations are crucial to understanding their group and individual
properties. The Nancay Radio Telescope (NRT) with the upgraded focal receiver
was used for observations of the 21-cm HI-line. This permitted the detection of
the faintest sources with rms of ~1 mJy per 10.5 km/s resolution element. For
eighteen detected galaxies we present the parameters of their integrated HI
line emission and describe the data on individual objects in more detail. For
four undetected XMD galaxies, we give upper limits on their M$(HI). For 70% of
the twenty studied non low surface brightness XMD galaxies, we find evidence
(both from HI and optical data) for their interaction with neighboring objects.
In the brief discussion of the group HI properties of the observed subsample
(the total O/H range is of 0.23 dex, or a factor of 1.7), we underline the
broad distributions of the HI mass (range is of 2 orders of magnitude), of the
ratio M(HI)/L_B (of 1 order of magnitude), and of the blue luminosity (range is
of 2 orders of magnitude). We also obtained HI parameters of six galaxies that
do not belong to the XMD sample. These data increase the number of XMD galaxies
with known integrated HI parameters (or upper limits) by a factor of two. This
allows us to address statistical properties of this group, which will be
presented in a forthcoming paper. (Abridged).Comment: 11 pages, including 2 tables and 2 postscript figures. Accepted to
Astronomy and Astrophysic
Observational physics of mirror world
The existence of the whole world of shadow particles, interacting with each other and having no mutual interactions with ordinary particles except gravity is a specific feature of modern superstring models, being considered as models of the theory of everything. The presence of shadow particles is the necessary condition in the superstring models, providing compensation of the asymmetry of left and right chirality states of ordinary particles. If compactification of additional dimensions retains the symmetry of left and right states, shadow world turns to be the mirror one, with particles and fields having properties strictly symmetrical to the ones of corresponding ordinary particles and fields. Owing to the strict symmetry of physical laws for ordinary and mirror particles, the analysis of cosmological evolution of mirror matter provides rather definite conclusions on possible effects of mirror particles in the universe. A general qualitative discussion of possible astronomical impact of mirror matter is given, in order to make as wide as possible astronomical observational searches for the effects of mirror world, being the unique way to test the existence of mirror partners of ordinary particles in the Nature
Singlet-triplet transition in a lateral quantum dot
We study transport through a lateral quantum dot in the vicinity of the
singlet-triplet transition in its ground state. This transition, being sharp in
an isolated dot, is broadened to a crossover by the exchange interaction of the
dot electrons with the conduction electrons in the leads. For a generic set of
system's parameters, the linear conductance has a maximum in the crossover
region. At zero temperature and magnetic field, the maximum is the strongest.
It becomes less pronounced at finite Zeeman splitting, which leads to an
increase of the background conductance and a decrease of the conductance in the
maximum
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