2,300 research outputs found
Understanding the redshift evolution of the luminosity functions of Lyman-alpha emitters
We present a semi-analytical model of star formation which explains
simultaneously the observed UV luminosity function of high redshift Lyman break
galaxies (LBGs) and luminosity functions of Lyman-alpha emitters. We consider
both models that use the Press-Schechter (PS) and Sheth-Tormen (ST) halo mass
functions to calculate the abundances of dark matter halos. The Lyman-alpha
luminosity functions at z < 4 are well reproduced with only <10% of the LBGs
emitting Lyman-alpha lines with rest equivalent width greater than the limiting
equivalent width of the narrow band surveys. However, the observed luminosity
function at z > 5 can be reproduced only when we assume that nearly all LBGs
are Lyman-alpha emitters. Thus it appears that 4 < z < 5 marks the epoch when a
clear change occurs in the physical properties of the high redshift galaxies.
As Lyman-alpha escape depends on dust and gas kinematics of the inter stellar
medium (ISM), this could mean that on an average the ISM at z > 5 could be less
dusty, more clumpy and having more complex velocity field. All of these will
enable easier escape of the Lyman-alpha photons. At z > 5 the observed
Lyman-alpha luminosity function are well reproduced with the evolution in the
halo mass function along with very minor evolution in the physical properties
of high redshift galaxies. In particular, upto z = 6.5, we do not see the
effect of evolving inter galactic medium (IGM) opacity on the Lyman-alpha
escape from these galaxies.Comment: 9 pages, 4 figures, 2 tables, Accepted for publication in MNRA
A Meta-narrative Review to Investigate Psychological Distress and Coping Mechanisms Among Healthcare Workers, Related to the COVID-19 Pandemic
Objective: Determining the factors that influence psychological distress of healthcare workers during the COVID-19 pandemic.
Background: Due to the sudden occurrence and high transmission rate of the virus that causes COVID-19, many hospitals became overwhelmed and had to respond quickly to the high patient demand. This caused increased burnout among healthcare workers, which we explored on this project.
Methodology: PubMed search of peer reviewed articles under topics of burnout, distress, and mental health of healthcare workers during the COVID-19 pandemic yielded 11 articles that we focused on for this meta-narrative review.
Discussion: Articles analyzed had a higher response from nurses and women. Burnout was evaluated by using modified versions of the Maslach Burnout Inventory-General Survey which measured emotional exhaustion, depersonalization, and personal accomplishment. Depression, anxiety, and insomnia were prevalent features discussed in the sources. Most of the articles highlighted that increasing psychological stress can lead to PTSD. Psychological distress was greatly influenced by job stress and high job demand. Coping mechanisms such as maintaining regular working hours, adequate supplies and protocols for safety, support, and encouraging resilience were seen to manage the increased psychological distress.
Conclusion: We observed that during the COVID-19 pandemic healthcare workers experienced significant psychological distress. We were able to identify coping mechanisms that could aid with stress management. We urge medical institutions to incorporate these measures to prevent a negative impact on the quality of patient care, and arm healthcare workers with tools to manage distress in times of drastic increases in patient caseload.https://openworks.mdanderson.org/rmps/1005/thumbnail.jp
Evidence for powerful AGN winds at high redshift: Dynamics of galactic outflows in radio galaxies during the "Quasar Era"
AGN feedback now appears as an attractive mechanism to resolve some of the
outstanding problems with the "standard" cosmological models, in particular
those related to massive galaxies. To directly constrain how this may influence
the formation of massive galaxies near the peak in the redshift distribution of
powerful quasars, z~2, we present an analysis of the emission-line kinematics
of 3 powerful radio galaxies at z~2-3 (HzRGs) based on rest-frame optical
integral-field spectroscopy obtained with SINFONI on the VLT. HzRGs are among
the most massive galaxies, so AGN feedback may have a particularly clear
signature. We find evidence for bipolar outflows in all HzRGs, with kinetic
energies that are equivalent to 0.2% of the rest-mass of the supermassive black
hole. Velocity offsets in the outflows are ~800-1000 km s^-1 between the
blueshifted and redshifted line emission, FWHMs ~1000 km s^-1 suggest strong
turbulence. Ionized gas masses estimated from the Ha luminosity are of order
10^10 M_s, similar to the molecular gas content of HzRGs, underlining that
these outflows may indicate a significant phase in the evolution of the host
galaxy. The total energy release of ~10^60 erg during a dynamical time of ~10^7
yrs corresponds to about the binding energy of a massive galaxy. Geometry,
timescales and energy injection rates of order 10% of the kinetic energy flux
of the jet suggest that the outflows are most likely driven by the radio
source. The global energy density release of ~10^57 erg s^-1 Mpc^-3 may also
influence the subsequent evolution of the HzRG by enhancing the entropy and
pressure in the surrounding halo and facilitating ram-pressure stripping of gas
in satellite galaxies that may contribute to the subsequent mass assembly of
the HzRG through low-dissipation "dry" mergers.Comment: A&A in press, minor edits & typo in table captions 2-
Coulomb corrections to production in ultra-relativistic nuclear collisions
The purpose of this paper is to explain the discrepancies existing in the
literature relative to pair production in peripheral heavy ion
collisions at ultra-relativistic energies. A controversial issue is the
possible cancellation of Coulomb corrections to the Born term in the pair
production cross-section. Such a cancellation has been observed in a recent
approach based on finding retarded solutions of the Dirac equation, but does
not seem to hold in a perturbative approach. We show in this paper that the two
approaches are in fact calculating different observables: the perturbative
approach gives the exclusive cross-section of single pair production, while the
other method gives the inclusive cross-section.
We have also performed a thorough study of the electron propagator in the
non-static background field of the two nuclei, the conclusion of which is that
the retarded propagator is in the ultra-relativistic limit a much simpler
object than the Feynman propagator, and can be calculated exactly.Comment: 31 pages LaTeX document, 10 postscript figures (expanded 3rd section,
version to be published in Nucl. Phys. A
Field characterization of three-dimensional lee-side airflow patterns under offshore winds at a beach-dune system
Characterization of three-dimensional (3D) airflow remains elusive within a variety of environments and is particularly challenging over complex dune topography. Previous work examining airflow over and in the lee of dunes has been restricted to two-dimensional studies and has concentrated on dune shapes containing angle of repose lee sides only. However, the presence of vegetation in coastal dunes creates topographic differences and irregular shapes that interfere with flow separation at the crest and significantly modify lee-side airflow patterns and potential transport. This paper presents the first 3D field characterization of airflow patterns at the lee side of a subaerial dune. Flow information was obtained using an array of 3D ultrasonic anemometers deployed over a beach surface during seven offshore wind events. Data were used to measure cross-shore and alongshore lee-side airflow patterns using the three dimensions of the wind vector. Distances to re-attachment were similar to previous studies, but the range of transverse incident wind directions resulting in flow separation (0+/-35 degrees) was almost twice that previously reported (0+/-20 degrees). Airflow reversal took place with winds as slow as 1m s(-1). Transverse offshore winds generated areas of opposing wind directions both within the reversed zone and beyond re-attachment, contrary to consistent deflection in only one direction found in transverse desert dunes. Patterns of flow convergence-divergence have been reported in fluvial studies. However, while convergence was associated with weak reversal in fluvial settings, it appeared to be related to strong flow reversal here and could be produced by pressure differentials at the dune crest
Mergers as triggers for nuclear activity : A near-IR study of the close environment of AGN in the VISTA-VIDEO survey
copyright 2014 The Authors; Published by Oxford University Press on behalf of the Royal Astronomical SocietyThere is an ongoing debate concerning the driver of nuclear activity in galaxies, with active galactic nuclei (AGN) either being triggered by major or minor galactic mergers or, alternatively, through secular processes like cold gas accretion and/or formation of bars. We investigate the close environment of active galaxies selected in the X-ray, the radio and the mid-IR. We utilize the first data release of the new near-IR VISTA Deep Extragalactic Observations (VIDEO) survey of the XMM-Large Scale Structure field. We use two measures of environment density, namely counts within a given aperture and a finite redshift slice (pseudo- 3D density) and closest neighbour density measures â2 and â5. We select both AGN and control samples, matching them in redshift and apparent Ks-band magnitude. We find that AGN are found in a range of environments, with a subset of the AGN samples residing in overdense environments. Seyfert-like X-ray AGN and flat-spectrum radio-AGN are found to inhabit significantly overdense environments compared to their control sample. The relation between overdensities and AGN luminosity does not however reveal any positive correlation. Given the absence of an environment density-AGN luminosity relation, we find no support for a scheme where high-luminosity AGN are preferentially triggered by mergers. On the contrary, we find that AGN likely trace over dense environments at high redshift due to the fact that they inhabit the most massive galaxies, rather than being an AGN.Peer reviewe
A Sample of Ultra Steep Spectrum Sources Selected from the Westerbork In the Southern Hemisphere (WISH) survey
The 352 MHz Westerbork In the Southern Hemisphere (WISH) survey is the
southern extension of the WENSS, covering 1.60 sr between -9 < DEC < -26 to a
limiting flux density of ~18 mJy (5sigma). Due to the very low elevation of the
observations, the survey has a much lower resolution in declination than in
right ascension (54" x 54"cosec(DEC)). A correlation with the 1.4 GHz NVSS
shows that the positional accuracy is less constrained in declination than in
right ascension, but there is no significant systematic error. We present a
source list containing 73570 sources.
We correlate this WISH catalogue with the NVSS to construct a sample of faint
Ultra Steep Spectrum (USS) sources, which is accessible for follow-up studies
with large optical telescopes in the southern hemisphere. This sample is aimed
at increasing the number of known high redshift radio galaxies to allow
detailed follow-up studies of these massive galaxies and their environments in
the early Universe.Comment: 12 Pages, including 5 PostScript figures. Accepted for publication in
Astronomy & Astrophysics. The full WISH catalog with 73570 sources is
available from http://www.strw.leidenuniv.nl/wenss
Radiogalaxies in the Sloan Digital Sky Survey: spectral index-environment correlations
We analyze optical and radio properties of radiogalaxies detected in the
Sloan Digital Sky Survey (SDSS). The sample of radio sources are selected from
the catalogue of Kimball & Ivezi\'c (2008) with flux densities at 325, 1400 and
4850 MHz, using WENSS, NVSS and GB6 radio surveys and from flux measurements at
74 MHz taken from VLA Low-frequency Sky Survey \citep{cohen}. We study
radiogalaxy spectral properties using radio colour-colour diagrams and find
that our sample follows a single power law from 74 to 4850 MHz. The spectral
index vs. spectroscopic redshift relation () is not significant for
our sample of radio sources. We analyze a subsample of radio sources associated
with clusters of galaxies identified from the maxBCG catalogue and find that
about 40% of radio sources with ultra steep spectra (USS, , where
) are associated with galaxy clusters or groups of
galaxies. We construct a Hubble diagram of USS radio sources in the optical
band up to .8 and compare our results with those for normal galaxies
selected from different optical surveys and find that USS radio sources are
around as luminous as the central galaxies in the maxBCG cluster sample and
typically more than 4 magnitudes brighter than normal galaxies at .3.
We study correlations between spectral index, richness and luminosity of
clusters associated with radio sources. We find that USS at low redshift are
rare, most of them reside in regions of unusually high ambient density, such of
those found in rich cluster of galaxies. Our results also suggest that clusters
of galaxies associated with steeper than the average spectra have higher
richness counts and are populated by luminous galaxies in comparison with those
environments associated to radio sources with flatter than the average spectra.
A plausible explanation for our results is that radio emission is more pressure
confined in higher gas density environments such as those found in rich
clusters of galaxies and as a consequence radio lobes in rich galaxy clusters
will expand adiabatically and lose energy via synchrotron and inverse Compton
losses, resulting in a steeper radio spectra.Comment: 13 pages, 14 figures; accepted for publication in Monthly Notices of
the Royal Astronomical Society Main Journal
Radio imaging of the Subaru/XMM-Newton Deep Field - III. Evolution of the radio luminosity function beyond z=1
We present spectroscopic and eleven-band photometric redshifts for galaxies
in the 100-uJy Subaru/XMM-Newton Deep Field radio source sample. We find good
agreement between our redshift distribution and that predicted by the SKA
Simulated Skies project. We find no correlation between K-band magnitude and
radio flux, but show that sources with 1.4-GHz flux densities below ~1mJy are
fainter in the near-infrared than brighter radio sources at the same redshift,
and we discuss the implications of this result for spectroscopically-incomplete
samples where the K-z relation has been used to estimate redshifts. We use the
infrared--radio correlation to separate our sample into radio-loud and
radio-quiet objects and show that only radio-loud hosts have spectral energy
distributions consistent with predominantly old stellar populations, although
the fraction of objects displaying such properties is a decreasing function of
radio luminosity. We calculate the 1.4-GHz radio luminosity function (RLF) in
redshift bins to z=4 and find that the space density of radio sources increases
with lookback time to z~2, with a more rapid increase for more powerful
sources. We demonstrate that radio-loud and radio-quiet sources of the same
radio luminosity evolve very differently. Radio-quiet sources display strong
evolution to z~2 while radio-loud AGNs below the break in the radio luminosity
function evolve more modestly and show hints of a decline in their space
density at z>1, with this decline occurring later for lower-luminosity objects.
If the radio luminosities of these sources are a function of their black hole
spins then slowly-rotating black holes must have a plentiful fuel supply for
longer, perhaps because they have yet to encounter the major merger that will
spin them up and use the remaining gas in a major burst of star formation.Comment: Accepted for publication in MNRAS: 36 pages, including 13 pages of
figures to appear online only. In memory of Stev
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