86 research outputs found
Weighing neutrinos using high redshift galaxy luminosity functions
Laboratory experiments measuring neutrino oscillations, indicate small mass
differences between different mass eigenstates of neutrinos. The absolute mass
scale is however not determined, with at present the strongest upper limits
coming from astronomical observations rather than terrestrial experiments. The
presence of massive neutrinos suppresses the growth of perturbations below a
characteristic mass scale, thereby leading to a decreased abundance of
collapsed dark matter halos. Here we show that this effect can significantly
alter the predicted luminosity function (LF) of high redshift galaxies. In
particular we demonstrate that a stringent constraint on the neutrino mass can
be obtained using the well measured galaxy LF and our semi-analytic structure
formation models. Combining the constraints from the Wilkinson Microwave
Anisotropy Probe 7 year (WMAP7) data with the LF data at z = 4, we get a limit
on the sum of the masses of 3 degenerate neutrinos \Sigma m_\nu < 0.52 eV at
the 95 % CL. The additional constraints using the prior on Hubble constant
strengthens this limit to \Sigma m_\nu < 0.29 eV at the 95 % CL. This neutrino
mass limit is a factor of order 4 improvement compared to the constraint based
on the WMAP7 data alone, and as stringent as known limits based on other
astronomical observations. As different astronomical measurements may suffer
from different set of biases, the method presented here provides a
complementary probe of \Sigma m_\nu . We suggest that repeating this exercise
on well measured luminosity functions over different redshift ranges can
provide independent and tighter constraints on \Sigma m_\nu .Comment: 14 pages, 7 figures, submitted to PR
Constrained semi-analytical models of Galactic outflows
We present semi-analytic models of galactic outflows, constrained by
available observations on high redshift star formation and reionization.
Galactic outflows are modeled in a manner akin to models of stellar wind blown
bubbles. Large scale outflows can generically escape from low mass halos
(M<10^9 M_sun) for a wide range of model parameters but not from high mass
halos (M> 10^{11} M_sun). The gas phase metallicity of the outflow and within
the galaxy are computed. Ionization states of different metal species are
calculated and used to examine the detectability of metal lines from the
outflows. The global influence of galactic outflows is also investigated.
Models with only atomic cooled halos significantly fill the IGM at z~3 with
metals (with -2.5>[Z/Z_sun]>-3.7), the actual extent depending on the
efficiency of winds, the IMF, the fractional mass that goes through star
formation and the reionization history of the universe. In these models, a
large fraction of outflows at z~3 are supersonic, hot (T> 10^5 K) and have low
density, making metal lines difficult to detect. They may also result in
significant perturbations in the IGM gas on scales probed by the Lyman-alpha
forest. On the contrary, models including molecular cooled halos with a normal
mode of star formation can potentially volume fill the universe at z> 8 without
drastic dynamic effects on the IGM, thereby setting up a possible metallicity
floor (-4.0<[Z/Z_sun]<-3.6). Interestingly, molecular cooled halos with a
``top-heavy'' mode of star formation are not very successful in establishing
the metallicity floor because of the additional radiative feedback, that they
induce. (Abridged)Comment: 27 pages, 31 figures, 2 tables, pdflatex. Accepted for publication in
MNRA
SITE CHARACTERIZATION OF (IGCAR) KALPAKKAM USING SOFT COMPUTING TECHNICES
Abstract This study employ
Reionization and feedback in overdense regions at high redshift
Observations of galaxy luminosity function at high redshifts typically focus
on fields of view of limited sizes preferentially containing bright sources.
These regions possibly are overdense and hence biased with respect to the
globally averaged regions. Using a semi-analytic model based on Choudhury &
Ferrara (2006) which is calibrated to match a wide range of observations, we
study the reionization and thermal history of the universe in overdense
regions. The main results of our calculation are: (i) Reionization and thermal
histories in the biased regions are markedly different from the average ones
because of enhanced number of sources and higher radiative feedback. (ii) The
galaxy luminosity function for biased regions is markedly different from those
corresponding to average ones. In particular, the effect of radiative feedback
arising from cosmic reionization is visible at much brighter luminosities.
(iii) Because of the enhanced radiative feedback within overdense locations,
the luminosity function in such regions is more sensitive to reionization
history than in average regions. The effect of feedback is visible for absolute
AB magnitude at , almost within the reach of present
day observations and surely to be probed by JWST. This could possibly serve as
an additional probe of radiative feedback and hence reionization at high
redshifts.Comment: 10 pages, 5 figures. Added Section 2.5, Figure 5, and an Appendix.
This version accepted for publication in MNRA
Modelling high redshift Lyman-alpha Emitters
We present a new model for high redshift Lyman-Alpha Emitters (LAEs) in the
cosmological context which takes into account the resonant scattering of Ly-a
photons through expanding gas. The GALICS semi-analytic model provides us with
the physical properties of a large sample of high redshift galaxies. We
implement a gas outflow model for each galaxy based on simple scaling
arguments. The coupling with a library of numerical experiments of Ly-a
transfer through expanding or static dusty shells of gas allows us to derive
the Ly-a escape fractions and profiles. The predicted distribution of Ly-a
photons escape fraction shows that galaxies with a low star formation rate have
a f_esc of the order of unity, suggesting that, for those objects, Ly-a may be
used to trace the star formation rate assuming a given conversion law. In
galaxies forming stars intensely, the escape fraction spans the whole range
from 0 to 1. The model is able to get a good match to the UV and Ly-a
luminosity function (LF) data at 3 < z < 5. We find that we are in good
agreement with both the bright Ly-a data and the faint population observed by
Rauch et al. (2008) at z=3. Most of the Ly-a profiles of our LAEs are
redshifted by the diffusion in the outflow which suppresses IGM absorption. The
bulk of the observed Ly-a equivalent width (EW) distribution is recovered by
our model, but we fail to obtain the very large values sometimes detected.
Predictions for stellar masses and UV LFs of LAEs show a satisfactory agreement
with observational estimates. The UV-brightest galaxies are found to show only
low Ly-a EWs in our model, as it is reported by many observations of high
redshift LAEs. We interpret this effect as the joint consequence of old stellar
populations hosted by UV-bright galaxies, and high HI column densities that we
predict for these objects, which quench preferentially resonant Ly-a photons
via dust extinction.Comment: 17 pages, 12 figures, 3 tables, accepted for publication in MNRA
Early prediction of COVID-19 outcome using artificial intelligence techniques and only five laboratory indices
We aimed to develop a prediction model for intensive care unit (ICU) hospitalization of Coronavirus disease-19 (COVID-19) patients using artificial neural networks (ANN). We assessed 25 laboratory parameters at first from 248 consecutive adult COVID-19 patients for database creation, training, and development of ANN models. We developed a new alpha-index to assess association of each parameter with outcome. We used 166 records for training of computational simulations (training), 41 for documentation of computational simulations (validation), and 41 for reliability check of computational simulations (testing). The first five laboratory indices ranked by importance were Neutrophil-to-lymphocyte ratio, Lactate Dehydrogenase, Fibrinogen, Albumin, and D-Dimers. The best ANN based on these indices achieved accuracy 95.97%, precision 90.63%, sensitivity 93.55%. and F1-score 92.06%, verified in the validation cohort. Our preliminary findings reveal for the first time an ANN to predict ICU hospitalization accurately and early, using only 5 easily accessible laboratory indices
Galactic winds driven by cosmic-ray streaming
Galactic winds are observed in many spiral galaxies with sizes from dwarfs up
to the Milky Way, and they sometimes carry a mass in excess of that of newly
formed stars by up to a factor of ten. Multiple driving processes of such winds
have been proposed, including thermal pressure due to supernova-heating, UV
radiation pressure on dust grains, or cosmic ray (CR) pressure. We here study
wind formation due to CR physics using a numerical model that accounts for CR
acceleration by supernovae, CR thermalization, and advective CR transport. In
addition, we introduce a novel implementation of CR streaming relative to the
rest frame of the gas. We find that CR streaming drives powerful and sustained
winds in galaxies with virial masses M_200 < 10^{11} Msun. In dwarf galaxies
(M_200 ~ 10^9 Msun) the winds reach a mass loading factor of ~5, expel ~60 per
cent of the initial baryonic mass contained inside the halo's virial radius and
suppress the star formation rate by a factor of ~5. In dwarfs, the winds are
spherically symmetric while in larger galaxies the outflows transition to
bi-conical morphologies that are aligned with the disc's angular momentum axis.
We show that damping of Alfven waves excited by streaming CRs provides a means
of heating the outflows to temperatures that scale with the square of the
escape speed. In larger haloes (M_200 > 10^{11} Msun), CR streaming is able to
drive fountain flows that excite turbulence. For halo masses M_200 > 10^{10}
Msun, we predict an observable level of H-alpha and X-ray emission from the
heated halo gas. We conclude that CR-driven winds should be crucial in
suppressing and regulating the first epoch of galaxy formation, expelling a
large fraction of baryons, and - by extension - aid in shaping the faint end of
the galaxy luminosity function. They should then also be responsible for much
of the metal enrichment of the intergalactic medium.Comment: 25 pages, 14 figures, accepted by MNRA
Evidence of Yersinia pestis DNA from fleas in an endemic plague area of Zambia
BACKGROUND: Yersinia pestis is a bacterium that causes plague which infects a variety of mammals throughout the world. The disease is usually transmitted among wild rodents through a flea vector. The sources and routes of transmission of plague are poorly researched in Africa, yet remains a concern in several sub-Saharan countries. In Zambia, the disease has been reported on annual basis with up to 20 cases per year, without investigating animal reservoirs or vectors that may be responsible in the maintenance and propagation of the bacterium. In this study, we undertook plague surveillance by using PCR amplification of the plasminogen activator gene in fleas. FINDINGS: Xenopsylla species of fleas were collected from 83 rodents trapped in a plague endemic area of Zambia. Of these rodents 5 had fleas positive (6.02%) for Y. pestis plasminogen activator gene. All the Y. pestis positive rodents were gerbils. CONCLUSIONS: We conclude that fleas may be responsible in the transmission of Y. pestis and that PCR may provide means of plague surveillance in the endemic areas of Zambia
Magnetic fields in cosmic particle acceleration sources
We review here some magnetic phenomena in astrophysical particle accelerators
associated with collisionless shocks in supernova remnants, radio galaxies and
clusters of galaxies. A specific feature is that the accelerated particles can
play an important role in magnetic field evolution in the objects. We discuss a
number of CR-driven, magnetic field amplification processes that are likely to
operate when diffusive shock acceleration (DSA) becomes efficient and
nonlinear. The turbulent magnetic fields produced by these processes determine
the maximum energies of accelerated particles and result in specific features
in the observed photon radiation of the sources. Equally important, magnetic
field amplification by the CR currents and pressure anisotropies may affect the
shocked gas temperatures and compression, both in the shock precursor and in
the downstream flow, if the shock is an efficient CR accelerator. Strong
fluctuations of the magnetic field on scales above the radiation formation
length in the shock vicinity result in intermittent structures observable in
synchrotron emission images. Resonant and non-resonant CR streaming
instabilities in the shock precursor can generate mesoscale magnetic fields
with scale-sizes comparable to supernova remnants and even superbubbles. This
opens the possibility that magnetic fields in the earliest galaxies were
produced by the first generation Population III supernova remnants and by
clustered supernovae in star forming regions.Comment: 30 pages, Space Science Review
Magnetic fields in Local Group dwarf irregulars
We wish to clarify whether strong magnetic fields can be effectively
generated in typically low-mass dwarf galaxies and to assess the role of dwarf
galaxies in the magnetization of the Universe. We performed a search for radio
emission and magnetic fields in an unbiased sample of 12 Local Group (LG)
irregular and dwarf irregular galaxies with the 100m Effelsberg telescope at
2.64 and 4.85GHz. Magnetic fields in LG dwarfs are three times weaker than in
the normal spirals (<4.2+-1.8muG). The production of total magnetic fields
appears to be regulated mainly by the star-formation surface density, with the
power-law exponent of 0.30+-0.04, or by the gas surface density (with the
exponent 0.47+-0.09). In addition, we find systematically stronger fields in
objects of higher global star-formation rate. The dwarf galaxies follow a
similar far-infrared relationship (with a slope of 0.91+-0.08) to that
determined for high surface brightness spiral galaxies. The magnetic field
strength in dwarf galaxies does not correlate with their maximum rotational
velocity, indicating a small-scale rather than a large-scale dynamo process. If
magnetization of the Universe by galactic outflows is coeval with its metal
enrichment, we show that more massive objects (such as Lyman Break Galaxies)
can efficiently magnetize the intergalactic medium with a magnetic field
strength of about 0.8nG out to a distance of 160-530kpc at redshifts 5-3,
respectively. Several times weaker fields and shorter magnetization distances
are expected from primordial dwarf galaxies. We also predict that most
star-forming local dwarfs might have magnetized their surroundings up to about
0.1muG within about 5kpc distance. Strong magnetic fields (>6muG) are observed
only in dwarfs of extreme characteristics while typical LG dwarfs are
unsuitable objects for the efficient supply of magnetic fields to the
intergalactic medium.Comment: Published in Astronomy and Astrophysics, 15 pages, 11 figures, minor
changes to version 1, Fig. 6 changed, discussion of interactions enlarge
- …