117 research outputs found
A Multiwavelength Study on the Fate of Ionizing Radiation in Local Starbursts
The fate of ionizing radiation is vital for understanding cosmic ionization,
energy budgets in the interstellar and intergalactic medium, and star formation
rate indicators. The low observed escape fractions of ionizing radiation have
not been adequately explained, and there is evidence that some starbursts have
high escape fractions. We examine the spectral energy distributions of a sample
of local star-forming galaxies, containing thirteen local starburst galaxies
and ten of their ordinary star-forming counterparts, to determine if there
exist significant differences in the fate of ionizing radiation in these
galaxies. We find that the galaxy-to-galaxy variations in the SEDs is much
larger than any systematic differences between starbursts and non-starbursts.
For example, we find no significant differences in the total absorption of
ionizing radiation by dust, traced by the 24um, 70um, and 160um MIPS bands of
the Spitzer Space Telescope, although the dust in starburst galaxies appears to
be hotter than that of non-starburst galaxies. We also observe no excess
ultraviolet flux in the GALEX bands that could indicate a high escape fraction
of ionizing photons in starburst galaxies. The small H-alpha fractions of the
diffuse, warm ionized medium in starburst galaxies are apparently due to
temporarily boosted H-alpha luminosity within the star-forming regions
themselves, with an independent, constant WIM luminosity. This independence of
the WIM and starburst luminosities contrasts with WIM behavior in non-starburst
galaxies and underscores our poor understanding of radiation transfer in both
ordinary and starburst galaxies.Comment: 10 pages, 8 figures, accepted to ApJ 10/11/1
Spectral action for torsion with and without boundaries
We derive a commutative spectral triple and study the spectral action for a
rather general geometric setting which includes the (skew-symmetric) torsion
and the chiral bag conditions on the boundary. The spectral action splits into
bulk and boundary parts. In the bulk, we clarify certain issues of the previous
calculations, show that many terms in fact cancel out, and demonstrate that
this cancellation is a result of the chiral symmetry of spectral action. On the
boundary, we calculate several leading terms in the expansion of spectral
action in four dimensions for vanishing chiral parameter of the
boundary conditions, and show that is a critical point of the action
in any dimension and at all orders of the expansion.Comment: 16 pages, references adde
UVUDF: Ultraviolet Imaging of the Hubble Ultradeep Field with Wide-field Camera 3
We present an overview of a 90-orbit Hubble Space Telescope treasury program
to obtain near ultraviolet imaging of the Hubble Ultra Deep Field using the
Wide Field Camera 3 UVIS detector with the F225W, F275W, and F336W filters.
This survey is designed to: (i) Investigate the episode of peak star formation
activity in galaxies at 1<z<2.5; (ii) Probe the evolution of massive galaxies
by resolving sub-galactic units (clumps); (iii) Examine the escape fraction of
ionizing radiation from galaxies at z~2-3; (iv) Greatly improve the reliability
of photometric redshift estimates; and (v) Measure the star formation rate
efficiency of neutral atomic-dominated hydrogen gas at z~1-3. In this overview
paper, we describe the survey details and data reduction challenges, including
both the necessity of specialized calibrations and the effects of charge
transfer inefficiency. We provide a stark demonstration of the effects of
charge transfer inefficiency on resultant data products, which when
uncorrected, result in uncertain photometry, elongation of morphology in the
readout direction, and loss of faint sources far from the readout. We agree
with the STScI recommendation that future UVIS observations that require very
sensitive measurements use the instrument's capability to add background light
through a "post-flash". Preliminary results on number counts of UV-selected
galaxies and morphology of galaxies at z~1 are presented. We find that the
number density of UV dropouts at redshifts 1.7, 2.1, and 2.7 is largely
consistent with the number predicted by published luminosity functions. We also
confirm that the image mosaics have sufficient sensitivity and resolution to
support the analysis of the evolution of star-forming clumps, reaching 28-29th
magnitude depth at 5 sigma in a 0.2 arcsecond radius aperture depending on
filter and observing epoch.Comment: Accepted A
The Survey for Ionization in Neutral Gas Galaxies: I. Description and Initial Results
We introduce the Survey for Ionization in Neutral Gas Galaxies (SINGG), a
census of star formation in HI-selected galaxies. The survey consists of
H-alpha and R-band imaging of a sample of 468 galaxies selected from the HI
Parkes All Sky Survey (HIPASS). The sample spans three decades in HI mass and
is free of many of the biases that affect other star forming galaxy samples. We
present the criteria for sample selection, list the entire sample, discuss our
observational techniques, and describe the data reduction and calibration
methods. This paper focuses on 93 SINGG targets whose observations have been
fully reduced and analyzed to date. The majority of these show a single
Emission Line Galaxy (ELG). We see multiple ELGs in 13 fields, with up to four
ELGs in a single field. All of the targets in this sample are detected in
H-alpha indicating that dormant (non-star forming) galaxies with M(HI) > ~3e7
M_sun are very rare. A database of the measured global properties of the ELGs
is presented. The ELG sample spans four orders of magnitude in luminosity
(H-alpha and R-band), and H-alpha surface brightness, nearly three orders of
magnitude in R surface brightness and nearly two orders of magnitude in H-alpha
equivalent width (EW). The surface brightness distribution of our sample is
broader than that of the Sloan Digital Sky Survey spectroscopic sample, the
(EW) distribution is broader than prism-selected samples, and the morphologies
found include all common types of star forming galaxies (e.g. irregular,
spiral, blue compact dwarf, starbursts, merging and colliding systems, and even
residual star formation in S0 and Sa spirals). (abridged)Comment: 28 pages, ApJS, in press. Full resolution version with all panels of
Fig. 8 available at http://sungg.pha.jhu.edu/publications.html . On line data
available at http://sungg.pha.jhu.edu/PubData/ . Author list corrected. Wrong
value for f_ap used in eq. 7 now corrected; typos corrected, non-used
references replaced, others update
The GALEX Arecibo SDSS Survey II: The Star Formation Efficiency of Massive Galaxies
We use measurements of the HI content, stellar mass and star formation rates
in ~190 massive galaxies with stellar masses greater than 10^10 Msun, obtained
from the Galex Arecibo SDSS Survey (GASS) described in Paper I (Catinella et
al. 2010) to explore the global scaling relations associated with the
bin-averaged ratio of the star formation rate over the HI mass, which we call
the HI-based star formation efficiency (SFE). Unlike the mean specific star
formation rate, which decreases with stellar mass and stellar mass surface
density, the star formation efficiency remains relatively constant across the
sample with a value close to SFE = 10^-9.5 yr^-1 (or an equivalent gas
consumption timescale of ~3 Gyr). Specifically, we find little variation in SFE
with stellar mass, stellar mass surface density, NUV-r color and concentration.
We interpret these results as an indication that external processes or feedback
mechanisms that control the gas supply are important for regulating star
formation in massive galaxies. An investigation into the detailed distribution
of SFEs reveals that approximately 5% of the sample shows high efficiencies
with SFE > 10^-9 yr^-1, and we suggest that this is very likely due to a
deficiency of cold gas rather than an excess star formation rate. Conversely,
we also find a similar fraction of galaxies that appear to be gas-rich for
their given specific star-formation rate, although these galaxies show both a
higher than average gas fraction and lower than average specific star formation
rate. Both of these populations are plausible candidates for "transition"
galaxies, showing potential for a change (either decrease or increase) in their
specific star formation rate in the near future. We also find that 36+/-5% of
the total HI mass density and 47+/-5% of the total SFR density is found in
galaxies with stellar mass greater than 10^10 Msun. [abridged]Comment: 18 pages, 11 figures. Accepted for publication in MNRAS. GASS
publications and released data can be found at
http://www.mpa-garching.mpg.de/GASS/index.ph
The H alpha Galaxy Survey VII. The spatial distribution of star formation within disks and bulges
We analyse the current build-up of stellar mass within the disks and bulges
of nearby galaxies through a comparison of the spatial distributions of forming
and old stellar populations. H alpha and R-band imaging are used to determine
the distributions of young and old stellar populations in 313 S0a - Im field
galaxies out to 40 Mpc. Concentration indices and mean normalised light
profiles are calculated as a function of galaxy type and bar classification.
The mean profiles and concentration indices show a strong and smooth dependence
on galaxy type. Apart from a central deficit due to bulge/bar light in some
galaxy types, mean H alpha and R-band profiles are very similar. Mean profiles
within a given type are remarkably constant even given wide ranges in galaxy
luminosity and size. SBc, SBbc and particularly SBb galaxies have profiles that
are markedly different from those of unbarred galaxies. H alpha emission from
SBb galaxies is studied in detail; virtually all show resolved central
components and concentrations of star formation at or just outside the bar-end
radius. In these galaxies, star formation has the same radial distribution as
R-band light, i.e. stellar mass is building at approximately constant
morphology, with no strong evidence for outer truncation or inside-out disk
formation. (Abridged.)Comment: 15 pages, accepted for publication by Astronomy and Astrophysics. See
also arXiv:0904.426
Особенности развития малого предпринимательства в Украине
В этой работе рассмотрена эволюция предпринимательства Украины на всех этапах ее общественной жизни, в том числе в период экономического кризиса в годы становления независимости. Отражены основные параметры отнесения предприятий к субъектам малого предпринимательства и их роль в развитии экономики государств.У цій роботі розглянута еволюція підприємництва України на всіх етапах її суспільного життя, зокрема в період економічної кризи в роки становлення незалежності. Відображені основні параметри віднесення підприємств до суб'єктів малого підприємництва і їх роль в розвитку економіки держав
The SINS survey: modeling the dynamics of z~2 galaxies and the high-z Tully-Fisher relation
We present the modeling of SINFONI integral field dynamics of 18 star forming
galaxies at z ~ 2 from Halpha line emission. The galaxies are selected from the
larger sample of the SINS survey, based on the prominence of ordered rotational
motions with respect to more complex merger induced dynamics. The quality of
the data allows us to carefully select systems with kinematics dominated by
rotation, and to model the gas dynamics across the whole galaxy using suitable
exponential disk models. We obtain a good correlation between the dynamical
mass and the stellar mass, finding that large gas fractions Mgas~M*) are
required to explain the difference between the two quantities. We use the
derived stellar mass and maximum rotational velocity Vmax from the modeling to
construct for the first time the stellar mass Tully-Fisher relation at z ~ 2.2.
The relation obtained shows a slope similar to what is observed at lower
redshift, but we detect an evolution of the zero point. We find that at z ~ 2.2
there is an offset in log(M*) for a given rotational velocity of 0.41+-0.11
with respect to the local Universe. This result is consistent with the
predictions of the latest N-body/hydrodynamical simulations of disk formation
and evolution, which invoke gas accretion onto the forming disk in filaments
and cooling flows. This scenario is in agreement with other dynamical evidence
from SINS, where gas accretion from the halo is required to reproduce the
observed properties of a large fraction of the z ~ 2 galaxies.Comment: 10 pages, 6 figures, submitted to Ap
Spectral energy distribution and radio halo of NGC253 at low radio frequencies
A. D. Kapinska, 'Spectral Energy Distribution and Radio Halo of NGC 253 at Low Radio Frequencies', The Astrophysical Journal, Vol. 838(68), 15 pp, March 2017. The version of record is available online at doi: https://doi.org/10.3847/1538-4357/aa5f5d. © 2017. The American Astronomical Society. All rights reserved.We present new radio continuum observations of NGC253 from the Murchison Widefield Array at frequencies between 76 and 227 MHz. We model the broadband radio spectral energy distribution for the total flux density of NGC253 between 76 MHz and 11 GHz. The spectrum is best described as a sum of central starburst and extended emission. The central component, corresponding to the inner 500pc of the starburst region of the galaxy, is best modelled as an internally free-free absorbed synchrotron plasma, with a turnover frequency around 230 MHz. The extended emission component of the NGC253 spectrum is best described as a synchrotron emission flattening at low radio frequencies. We find that 34% of the extended emission (outside the central starburst region) at 1 GHz becomes partially absorbed at low radio frequencies. Most of this flattening occurs in the western region of the SE halo, and may be indicative of synchrotron self-absorption of shock re-accelerated electrons or an intrinsic low-energy cut off of the electron distribution. Furthermore, we detect the large-scale synchrotron radio halo of NGC253 in our radio images. At 154 - 231 MHz the halo displays the well known X-shaped/horn-like structure, and extends out to ~8kpc in z-direction (from major axis).Peer reviewedFinal Published versio
Global, regional, and national comparative risk assessment of 84 behavioural, environmental and occupational, and metabolic risks or clusters of risks for 195 countries and territories, 1990-2017: a systematic analysis for the Global Burden of Disease Study 2017
Background
The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2017 comparative risk assessment (CRA) is a comprehensive approach to risk factor quantification that offers a useful tool for synthesising evidence on risks and risk–outcome associations. With each annual GBD study, we update the GBD CRA to incorporate improved methods, new risks and risk–outcome pairs, and new data on risk exposure levels and risk–outcome associations.
Methods
We used the CRA framework developed for previous iterations of GBD to estimate levels and trends in exposure, attributable deaths, and attributable disability-adjusted life-years (DALYs), by age group, sex, year, and location for 84 behavioural, environmental and occupational, and metabolic risks or groups of risks from 1990 to 2017. This study included 476 risk–outcome pairs that met the GBD study criteria for convincing or probable evidence of causation. We extracted relative risk and exposure estimates from 46 749 randomised controlled trials, cohort studies, household surveys, census data, satellite data, and other sources. We used statistical models to pool data, adjust for bias, and incorporate covariates. Using the counterfactual scenario of theoretical minimum risk exposure level (TMREL), we estimated the portion of deaths and DALYs that could be attributed to a given risk. We explored the relationship between development and risk exposure by modelling the relationship between the Socio-demographic Index (SDI) and risk-weighted exposure prevalence and estimated expected levels of exposure and risk-attributable burden by SDI. Finally, we explored temporal changes in risk-attributable DALYs by decomposing those changes into six main component drivers of change as follows: (1) population growth; (2) changes in population age structures; (3) changes in exposure to environmental and occupational risks; (4) changes in exposure to behavioural risks; (5) changes in exposure to metabolic risks; and (6) changes due to all other factors, approximated as the risk-deleted death and DALY rates, where the risk-deleted rate is the rate that would be observed had we reduced the exposure levels to the TMREL for all risk factors included in GBD 2017.
Findings
In 2017, 34·1 million (95% uncertainty interval [UI] 33·3–35·0) deaths and 1·21 billion (1·14–1·28) DALYs were attributable to GBD risk factors. Globally, 61·0% (59·6–62·4) of deaths and 48·3% (46·3–50·2) of DALYs were attributed to the GBD 2017 risk factors. When ranked by risk-attributable DALYs, high systolic blood pressure (SBP) was the leading risk factor, accounting for 10·4 million (9·39–11·5) deaths and 218 million (198–237) DALYs, followed by smoking (7·10 million [6·83–7·37] deaths and 182 million [173–193] DALYs), high fasting plasma glucose (6·53 million [5·23–8·23] deaths and 171 million [144–201] DALYs), high body-mass index (BMI; 4·72 million [2·99–6·70] deaths and 148 million [98·6–202] DALYs), and short gestation for birthweight (1·43 million [1·36–1·51] deaths and 139 million [131–147] DALYs). In total, risk-attributable DALYs declined by 4·9% (3·3–6·5) between 2007 and 2017. In the absence of demographic changes (ie, population growth and ageing), changes in risk exposure and risk-deleted DALYs would have led to a 23·5% decline in DALYs during that period. Conversely, in the absence of changes in risk exposure and risk-deleted DALYs, demographic changes would have led to an 18·6% increase in DALYs during that period. The ratios of observed risk exposure levels to exposure levels expected based on SDI (O/E ratios) increased globally for unsafe drinking water and household air pollution between 1990 and 2017. This result suggests that development is occurring more rapidly than are changes in the underlying risk structure in a population. Conversely, nearly universal declines in O/E ratios for smoking and alcohol use indicate that, for a given SDI, exposure to these risks is declining. In 2017, the leading Level 4 risk factor for age-standardised DALY rates was high SBP in four super-regions: central Europe, eastern Europe, and central Asia; north Africa and Middle East; south Asia; and southeast Asia, east Asia, and Oceania. The leading risk factor in the high-income super-region was smoking, in Latin America and Caribbean was high BMI, and in sub-Saharan Africa was unsafe sex. O/E ratios for unsafe sex in sub-Saharan Africa were notably high, and those for alcohol use in north Africa and the Middle East were notably low.
Interpretation
By quantifying levels and trends in exposures to risk factors and the resulting disease burden, this assessment offers insight into where past policy and programme efforts might have been successful and highlights current priorities for public health action. Decreases in behavioural, environmental, and occupational risks have largely offset the effects of population growth and ageing, in relation to trends in absolute burden. Conversely, the combination of increasing metabolic risks and population ageing will probably continue to drive the increasing trends in non-communicable diseases at the global level, which presents both a public health challenge and opportunity. We see considerable spatiotemporal heterogeneity in levels of risk exposure and risk-attributable burden. Although levels of development underlie some of this heterogeneity, O/E ratios show risks for which countries are overperforming or underperforming relative to their level of development. As such, these ratios provide a benchmarking tool to help to focus local decision making. Our findings reinforce the importance of both risk exposure monitoring and epidemiological research to assess causal connections between risks and health outcomes, and they highlight the usefulness of the GBD study in synthesising data to draw comprehensive and robust conclusions that help to inform good policy and strategic health planning
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