172 research outputs found
Variability in Low Ionization Broad Absorption Line outflows
We present results of our time variability studies of Mgâii and Alâiii absorption lines in a sample of 22 Low Ionization Broad Absorption Line QSOs (LoBAL QSOs) at 0.2 †z_(em) †2.1 using the 2-m telescope at IUCAA Girawali Observatory over a time-scale of 10âd to 7.69âyears in the QSO's rest frame. Spectra are analysed in conjunction with photometric light curves from Catalina Real-Time Transient Survey. Long time-scale (i.e. â„1 year) absorption line variability is seen in eight cases (36 per cent systems) while only four of them (i.e. 18 per cent systems) show variability over short time-scales (i.e. <1 year). We notice a tendency of highly variable LoBAL QSOs to have high ejection velocity, low equivalent width and low redshift. The detection rate of variability in LoBAL QSOs showing Fe fine-structure lines (FeLoBAL QSOs) is less than that seen in non-Fe LoBAL QSOs. Absorption line variability is more frequently detected in QSOs having continuum dominated by Fe emission lines compared to rest of the QSOs. Confirming these trends with a bigger sample will give vital clues for understanding the physical distinction between different BAL QSO sub-classes. We correlate the absorption line variability with various parameters derived from continuum light curves and find no clear correlation between continuum flux and absorption line variabilities. However, sources with large absorption line variability also show large variability in their light curves. We also see appearance/disappearance of absorption components in two cases and clear indications for profile variations in four cases. The observed variability can be best explained by a combination of process driven by continuum variations and clouds transiting across the line of sight
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
A novel hybrid swarm optimized multilayer neural network for spatial prediction of flash floods in tropical areas using sentinel-1 SAR imagery and geospatial data
© 2018 by the authors. Licensee MDPI, Basel, Switzerland. Flash floods are widely recognized as one of the most devastating natural hazards in the world, therefore prediction of flash flood-prone areas is crucial for public safety and emergency management. This research proposes a new methodology for spatial prediction of flash floods based on Sentinel-1 SAR imagery and a new hybrid machine learning technique. The SAR imagery is used to detect flash flood inundation areas, whereas the new machine learning technique, which is a hybrid of the firefly algorithm (FA), LevenbergâMarquardt (LM) backpropagation, and an artificial neural network (named as FA-LM-ANN), was used to construct the prediction model. The Bac Ha Bao Yen (BHBY) area in the northwestern region of Vietnam was used as a case study. Accordingly, a Geographical Information System (GIS) database was constructed using 12 input variables (elevation, slope, aspect, curvature, topographic wetness index, stream power index, toposhade, stream density, rainfall, normalized difference vegetation index, soil type, and lithology) and subsequently the output of flood inundation areas was mapped. Using the database and FA-LM-ANN, the flash flood model was trained and verified. The model performance was validated via various performance metrics including the classification accuracy rate, the area under the curve, precision, and recall. Then, the flash flood model that produced the highest performance was compared with benchmarks, indicating that the combination of FA and LM backpropagation is proven to be very effective and the proposed FA-LM-ANN is a new and useful tool for predicting flash flood susceptibility
Herschel-ATLAS: The angular correlation function of submillimetre galaxies at high and low redshift
Original article can be found at: http://www.aanda.org/ Copyright The European Southern ObservatoryWe present measurements of the angular correlation function of galaxies selected from the first field of the H-ATLAS survey. Careful removal of the background from galactic cirrus is essential, and currently dominates the uncertainty in our measurements. For our 250 ÎŒm-selected sample we detect no significant clustering, consistent with the expectation that the 250 ÎŒm-selected sources are mostly normal galaxies at z 1. For our 350 ÎŒm and 500 ÎŒm-selected samples we detect relatively strong clustering with correlation amplitudes A of 0.2 and 1.2 at 1', but with relatively large uncertainties. For samples which preferentially select high redshift galaxies at z~2â3 we detect significant strong clustering, leading to an estimate of r0 ~ 7â11 h-1 Mpc. The slope of our clustering measurements is very steep, ÎŽ ~ 2. The measurements are consistent with the idea that sub-mm sources consist of a low redshift population of normal galaxies and a high redshift population of highly clustered star-bursting galaxies.Peer reviewe
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
Discovery of a compact gas-rich DLA galaxy at z = 2.2: evidences for a starburst-driven outflow
We present the detection of Ly-alpha, [OIII] and H-alpha emission associated
with an extremely strong DLA system (N(HI) = 10^22.10 cm^-2) at z=2.207 towards
the quasar SDSS J113520-001053. This is the largest HI column density ever
measured along a QSO line of sight, though typical of what is seen in GRB-DLAs.
This absorption system also classifies as ultrastrong MgII system with
W2796_r=3.6 A. The mean metallicity of the gas ([Zn/H]=-1.1) and dust depletion
factors ([Zn/Fe]=0.72, [Zn/Cr]=0.49) are consistent with (and only marginally
larger than) the mean values found in the general QSO-DLA population. The
[OIII]-Ha emitting region has a very small impact parameter with respect to the
QSO line of sight, b=0.1", and is unresolved. From the Ha line, we measure
SFR=25 Msun/yr. The Ly-a line is double-peaked and is spatially extended. More
strikingly, the blue and red Ly-a peaks arise from distinct regions extended
over a few kpc on either side of the star-forming region. We propose that this
is the consequence of Ly-a transfer in outflowing gas. The presence of
starburst-driven outflows is also in agreement with the large SFR together with
a small size and low mass of the galaxy (Mvir~10^10 Msun). From the stellar UV
continuum luminosity of the galaxy, we estimate an age of at most a few 10^7
yr, again consistent with a recent starburst scenario. We interpret the data as
the observation of a young, gas rich, compact starburst galaxy, from which
material is expelled through collimated winds powered by the vigorous star
formation activity. We substantiate this picture by modelling the radiative
transfer of Ly-a photons in the galactic counterpart. Though our model (a
spherical galaxy with bipolar outflowing jets) is a simplistic representation
of the true gas distribution and velocity field, the agreement between the
observed and simulated properties is particularly good. [abridged]Comment: 15 pages, 18 figures, 4 tables, accepted for publication in Astronomy
and Astrophysic
A search for debris disks in the Herschel-ATLAS
Original article can be found at: http://www.aanda.org/ Copyright The European Southern Observatory (ESO)Aims. We aim to demonstrate that the Herschel-ATLAS (H-ATLAS) is suitable for a blind and unbiased survey for debris disks by identifying candidate debris disks associated with main sequence stars in the initial science demonstration field of the survey. We show that H-ATLAS reveals a population of far-infrared/sub-mm sources that are associated with stars or star-like objects on the SDSS main-sequence locus. We validate our approach by comparing the properties of the most likely candidate disks to those of the known population. Methods. We use a photometric selection technique to identify main sequence stars in the SDSS DR7 catalogue and a Bayesian Likelihood Ratio method to identify H-ATLAS catalogue sources associated with these main sequence stars. Following this photometric selection we apply distance cuts to identify the most likely candidate debris disks and rule out the presence of contaminating galaxies using UKIDSS LAS K-band images. Results. We identify 78 H-ATLAS sources associated with SDSS point sources on the main-sequence locus, of which two are the most likely debris disk candidates: H-ATLAS J090315.8 and H-ATLAS J090240.2. We show that they are plausible candidates by comparing their properties to the known population of debris disks. Our initial results indicate that bright debris disks are rare, with only 2 candidates identified in a search sample of 851 stars. We also show that H-ATLAS can derive useful upper limits for debris disks associated with Hipparcos stars in the field and outline the future prospects for our debris disk search programme.Peer reviewe
High-Ion Absorption in Seven GRB Host Galaxies at z=2-4: Evidence for both Circumburst Plasma and Outflowing Interstellar Gas
(Abridged) We use VLT/UVES high-resolution optical spectroscopy of seven GRB
afterglows at z_GRB>2 to investigate circumburst and interstellar plasma in the
host galaxies. Our sample consists of GRBs 021004, 050730, 050820, 050922C,
060607, 071031, and 080310. Four of these spectra were taken in rapid-response
mode, within 30 minutes of the Swift GRB detection. We identify several
distinct categories of high-ion absorption at velocities close to z_GRB: (i)
Strong high-ion components at z_GRB itself are always seen in OVI, CIV, and
SiIV, and usually (in 6 of 7 cases) in NV. We discuss circumburst and
interstellar models for the origin of this absorption. Using the non-detection
of SIV* toward GRB 050730 together with a UV photo-excitation model, we place a
lower limit of 400 pc on the distance of the SIV-bearing gas from the GRB. (ii)
Complex, multi-component CIV and SiIV profiles extending over 100-400 km/s
around z_GRB are observed in each spectrum; these velocity fields are similar
to those measured in damped Lyman-alpha systems at similar redshifts,
suggesting a galactic origin. (iii) Asymmetric, blueshifted, absorption-line
wings covering 65-140 km/s are seen in the CIV, SiIV, and OVI profiles in 4 of
the 7 spectra. The wing kinematics together with the observation that two wings
show "Galactic" CIV/SiIV ratios suggest these features trace outflowing ISM gas
in the GRB host galaxies. (iv) High-velocity (HV; 500-5000 km/s) components are
detected in 6 of the 7 spectra. The HV components show diverse properties. In
the cases of GRBs 071031 and 080310, both the ionization level (very high
CIV/SiIV ratios and absence of neutral-phase absorption) and the kinematics of
the HV components can be explained by Wolf-Rayet winds from the GRB
progenitors.Comment: 20 pages, 9 figures (7 in color), accepted by A&A, updated with proof
corrections including changes to Table
The Lyman-alpha emission of high-z damped Lyman-alpha systems
Using a spectral stacking technique we searched for the average \lya emission
from high-z Damped \lya (DLA) galaxies detected in the Sloan Digital Sky Survey
QSO spectra. We used a sample of 341 DLAs of mean redshift = 2.86 and log
N(HI) > 20.62 to place a 3 upper limit of 3.0 \times 10^{-18} erg
s^{-1} cm^{-2} on the \lya flux emitted within 1.5 arcsec (or 12 kpc)
from the QSO line of sight. This corresponds to an average \lya luminosity of <
2 \times 10^{41} erg s^{-1} or 0.03 (\lya). This limit is deeper than
the limit of most surveys for faint \lya emitters. The lack of \lya emission in
DLAs is consistent with the in situ star formation, for a given N(HI), being
less efficient than what is seen in local galaxies. Thus, the overall DLA
population seems to originate from the low luminosity end of the high redshift
\lya emitting galaxies and/or to be located far away from the star forming
regions. The latter may well be true since we detect strong OVI absorption in
the stacked spectrum, indicating that DLAs are associated with a highly ionized
phase possibly the relics of galactic winds and/or originating from cold
accretion flows. We find the contribution of DLA galaxies to the global star
formation rate density to be comparatively lower than that of Lyman Break
Galaxies.Comment: 5 pages, 3 figures; Accepted for publication in MNRA
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