642 research outputs found
Detection of high Lyman continuum leakage from four low-redshift compact star-forming galaxies
Following our first detection reported in Izotov et al. (2016), we present
the detection of Lyman continuum (LyC) radiation of four other compact
star-forming galaxies observed with the Cosmic Origins Spectrograph (COS)
onboard the Hubble Space Telescope (HST). These galaxies, at redshifts of
z~0.3, are characterized by high emission-line flux ratios [OIII]5007/[OII]3727
> 5. The escape fractions of the LyC radiation fesc(LyC) in these galaxies are
in the range of ~6%-13%, the highest values found so far in low-redshift
star-forming galaxies. Narrow double-peaked Lyalpha emission lines are detected
in the spectra of all four galaxies, compatible with predictions for Lyman
continuum leakers. We find escape fractions of Lyalpha, fesc(Lyalpha) ~20%-40%,
among the highest known for Lyalpha emitters (LAEs). Surface brightness
profiles produced from the COS acquisition images reveal bright star-forming
regions in the center and exponential discs in the outskirts with disc scale
lengths alpha in the range ~0.6-1.4 kpc. Our galaxies are characterized by low
metallicity, ~1/8-1/5 solar, low stellar mass ~(0.2 - 4)e9 Msun, high star
formation rates SFR~14-36 Msun/yr, and high SFR densities Sigma~2-35
Msun/yr/kpc^2. These properties are comparable to those of high-redshift
star-forming galaxies. Finally, our observations, combined with our first
detection reported in Izotov et al. (2016), reveal that a selection for compact
star-forming galaxies showing high [OIII]5007/[OII]3727 ratios appears to pick
up very efficiently sources with escaping Lyman continuum radiation: all five
of our selected galaxies are LyC leakers.Comment: 21 pages, 14 figures, accepted for publication in MNRAS; corrected
Lyalpha escape fraction
Lyman-alpha spectral properties of five newly discovered Lyman continuum emitters
We have recently reported the discovery of five low redshift Lyman continuum
(LyC) emitters (LCEs, hereafter) with absolute escape fractions fesc(LyC)
ranging from 6 to 13%, higher than previously found, and which more than
doubles the number of low redshift LCEs.We use these observations to test
theoretical predictions about a link between the characteristics of the
Lyman-alpha (Lya) line from galaxies and the escape of ionising photons. We
analyse the Lya spectra of eight LCEs of the local Universe observed with the
Cosmic Origins Spectrograph onboard the Hubble Space Telescope (our five
leakers and three galaxies from the litterature), and compare their strengths
and shapes to the theoretical criteria and comparison samples of local
galaxies: the Lyman Alpha Reference Survey, Lyman Break Analogs, Green Peas,
and the high-redshift strong LyC leaker Ion2. Our LCEs are found to be strong
Lya emitters, with high equivalent widths, EW(Lya)> 70 {\AA}, and large Lya
escape fractions, fesc(Lya) > 20%. The Lya profiles are all double-peaked with
a small peak separation, in agreement with our theoretical expectations. They
also have no underlying absorption at the Lya position. All these
characteristics are very different from the Lya properties of typical
star-forming galaxies of the local Universe. A subset of the comparison samples
(2-3 Green Pea galaxies) share these extreme values, indicating that they could
also be leaking. We also find a strong correlation between the star formation
rate surface density and the escape fraction of ionising photons, indicating
that the compactness of star-forming regions plays a role in shaping low column
density paths in the interstellar medium of LCEs. The Lya properties of LCEs
are peculiar: Lya can be used as a reliable tracer of LyC escape from galaxies,
in complement to other indirect diagnostics proposed in the literature.Comment: 11 pages, 10 figures, accepted for publication in A&
Do galaxies that leak ionizing photons have extreme outflows?
To reionize the early universe, high-energy photons must escape the galaxies
that produce them. It has been suggested that stellar feedback drives galactic
outflows out of star-forming regions, creating low density channels through
which ionizing photons escape into the inter-galactic medium. We compare the
galactic outflow properties of confirmed Lyman continuum (LyC) leaking galaxies
to a control sample of nearby star-forming galaxies to explore whether the
outflows from leakers are extreme as compared to the control sample. We use
data from the Cosmic Origins Spectrograph on the Hubble Space Telescope to
measure the equivalent widths and velocities of Si II and Si III absorption
lines, tracing neutral and ionized galactic outflows. We find that the Si II
and Si III equivalent widths of the LyC leakers reside on the low-end of the
trend established by the control sample. The leakers' velocities are not
statistically different than the control sample, but their absorption line
profiles have a different asymmetry: their central velocities are closer to
their maximum velocities. The outflow kinematics and equivalent widths are
consistent with the scaling relations between outflow properties and host
galaxy properties -- most notably metallicity -- defined by the control sample.
Additionally, we use the Ly\alpha\ profiles to show that the Si II equivalent
width scales with the Ly\alpha\ peak velocity separation. We determine that the
low equivalent widths of the leakers are likely driven by low metallicities and
low H I column densities, consistent with a density-bounded ionization region,
although we cannot rule out significant variations in covering fraction. While
we do not find that the LyC leakers have extreme outflow velocities, the low
maximum-to-central velocity ratios demonstrate the importance of the
acceleration and density profiles for LyC and Ly\alpha\ escape. [abridged]Comment: 17 pages, 8 Figures. Accepted for publication in Astronomy &
Astrophysic
SBS 0335-052W: The Lowest-Metallicity Star-Forming Galaxy Known
We present 4-meter Kitt Peak telescope and 6.5-meter MMT spectrophotometry of
the extremely low-metallicity galaxy SBS 0335-052W, the western companion of
the blue compact dwarf galaxy SBS 0335-052E. These observations have been
combined with published 10-meter Keck data to derive for the brightest region
of SBS 0335-052W an oxygen abundance 12+logO/H=7.12+/-0.03. This makes SBS
0335-052W the lowest metallicity star-forming galaxy known in the local
universe. Using a Monte Carlo technique, we fit the spectral energy
distribution of SBS 0335-052W to derive the age of the oldest stars
contributing to its optical light. We find that star formation in SBS 0335-052W
began less than 500 Myr ago, making it a likely nearby young dwarf galaxy.Comment: 13 pages, 3 figures, accepted for publication in the Astrophysical
Journa
J1154+2443: a low-redshift compact star-forming galaxy with a 46 per cent leakage of Lyman continuum photons
We report the detection of the Lyman continuum (LyC) radiation of the compact
star-forming galaxy (SFG) J1154+2443 observed with the Cosmic Origins
Spectrograph (COS) onboard the Hubble Space Telescope. This galaxy, at a
redshift of z=0.3690, is characterized by a high emission-line flux ratio
O32=[OIII]5007/[OII]3727=11.5. The escape fraction of the LyC radiation
fesc(LyC) in this galaxy is 46 per cent, the highest value found so far in
low-redshift SFGs and one of the highest values found in galaxies at any
redshift. The narrow double-peaked Lya emission line is detected in the
spectrum of J1154+2443 with a separation between the peaks Vsep of 199 km/s,
one of the lowest known for Lya-emitting galaxies, implying a high fesc(Lya).
Comparing the extinction-corrected Lya/Hb flux ratio with the case B value we
find fesc(Lya) = 98 per cent. Our observations, combined with previous
detections in the literature, reveal an increase of O32 with increasing
fesc(LyC). We also find a tight anticorrelation between fesc(LyC) and Vsep. The
surface brightness profile derived from the COS acquisition image reveals a
bright star-forming region in the centre and an exponential disc in the
outskirts with a disc scale length alpha=1.09 kpc. J1154+2443, compared to
other known low-redshift LyC leakers, is characterized by the lowest
metallicity, 12+logO/H=7.65+/-0.01, the lowest stellar mass M*=10^8.20 Msun, a
similar star formation rate SFR=18.9 Msun/yr and a high specific SFR of
1.2x10^-7 yr^-1.Comment: 16 pages, 8 figures, accepted for publication in MNRAS. arXiv admin
note: text overlap with arXiv:1605.0516
Physical education and health
Each person 's health - it's great value. Taking part in sports and physical education prepare society for life, quenched the body and improve health, promote physical development, raise the necessary personality traits, moral and physical qualities. Physical culture - is a phenomenon that carries significant actions society in the field of ethics, morality and education. Currently, high interest that young people have grown physical development and health. Therefore, this topic is relevant to the present dayУ каждого человека здоровье – это большая ценность. Занятия спортом и физической культурой подготавливают человека к общественной жизни - укрепляют здоровье, способствуют физическому развитию, воспитывают необходимые черты личности, моральные и физические качества. Физическая культура – это явление, которое выполняет значимые действия общества в области этики, морали и воспитания. В настоящее время высока заинтересованность в том, что бы молодежь росла физически развитой и здоровой. Поэтому данная тема актуальна и по сей ден
An Exploratory Assessment of Applying Risk Management Practices to Engineered Nanomaterials
The widespread industrial application of nanotechnology has increased the number of workers exposed to engineered nanomaterials (ENMs), but it is not clear to what extent prevention guidance is practiced. Our aim was to explore the extent that companies manufacturing and/or using ENMs apply risk assessment and management measures. Thirty-four companies were surveyed with an international 35-item questionnaire investigating company and workforce features, types of ENM handled, and risk evaluation and preventive measures adopted. Among participating companies, 62% had a maximum of 10 employees. Metal-based nanomaterials were most frequently identified (73%). Environmental monitoring was performed by 41% of the companies, while engineering exposure controls were approximately reported by 50%. Information and training programs were indicated by 85% of the sample, only 9% performed specific health surveillance for ENM workers. Personal protective equipment primarily included gloves (100%) and eye/face protection (94%). This small-scale assessment can contribute to the limited amount of published literature on the topic. Future investigations should include a greater number of companies to better represent ENM workplaces and a direct access to industrial settings to collect information on site. Finally, deeper attention should be paid to define standardized frameworks for ENM risk assessment that may guide nano-specific preventive actions
Helium Porosity Formation in Vanadium Alloys of V-Ti-Cr, V-W-Zr and V-W-Ta Systems in Comparison with Binary Alloys
Vanadium alloys are considered candidates for use as structural materials of fusion reactors. A large amount of helium will be accumulated in such materials. The presence of helium in the materials may result in gas swelling. This paper presents the results on helium porosity formation researches in V–Ti–Cr, V–W–Zr and V–W–Ta alloys obtained by means of TEM. Samples were irradiated by 40 keV Не+ ions up to dose of 5 ⋅ 1020m−2 at 923 K. Alloy V–4%Ti–4%Cr has a smallest helium swelling among the ternary alloys and its swelling is significantly lower than swelling of dual V–Ti and V–Cr alloys. The swelling of the ternary V–2%W–1%Zr alloy is more than 3 times less than the swelling of vanadium, several times less than that of V–W alloys and slightly lower than the swelling of V– Zr alloys. Swelling increases by a factor of 1.5 with increasing of Zr content to 2% in the ternary V–2%W–1%Zr alloy. Similarly, gas swelling of ternary V–2%W–1%Ta alloy is significantly lower than that for binary V–W and V–Ta alloys. Assumptions are made about the possible mechanisms of the effect of alloying elements in vanadium on helium porosity formation.
Keywords: vanadium alloys, swelling, helium, radiation resistance
Functional Improvement of Non-State Pension Funds as Mechanism of Investment in Russian Economy
The article is dedicated to the search of investments in the domestic financial market that is a relevant problem for the Russian economy. The authors believe that pension funds attracted by non-state pension institutions are an essential resource for the Russian economy; practices of foreign pension institutions need to be examined and implemented to tap this resource more efficiently.The proposed measures specified in the article following the study of foreign pension funds' functioning include: changes in the criteria for balancing portfolios of Russian pension funds' securities; development of new instruments for pension funds' investment; enhancing activities of non-state pension funds' shares market; activation of pension funds' investments in shares of innovative enterprises, etc. Practical proposals on the improvement of Russian non-state pension funds' activities have been made
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