678 research outputs found
Gas Accretion via Lyman Limit Systems
In cosmological simulations, a large fraction of the partial Lyman limit
systems (pLLSs; 16<log N(HI)<17.2) and LLSs (17.2log N(HI)<19) probes
large-scale flows in and out of galaxies through their circumgalactic medium
(CGM). The overall low metallicity of the cold gaseous streams feeding galaxies
seen in these simulations is the key to differentiating them from metal rich
gas that is either outflowing or being recycled. In recent years, several
groups have empirically determined an entirely new wealth of information on the
pLLSs and LLSs over a wide range of redshifts. A major focus of the recent
research has been to empirically determine the metallicity distribution of the
gas probed by pLLSs and LLSs in sizable and representative samples at both low
(z2) redshifts. Here I discuss unambiguous evidence for
metal-poor gas at all z probed by the pLLSs and LLSs. At z<1, all the pLLSs and
LLSs so far studied are located in the CGM of galaxies with projected distances
<100-200 kpc. Regardless of the exact origin of the low-metallicity pLLSs/LLSs,
there is a significant mass of cool, dense, low-metallicity gas in the CGM that
may be available as fuel for continuing star formation in galaxies over cosmic
time. As such, the metal-poor pLLSs and LLSs are currently among the best
observational evidence of cold, metal-poor gas accretion onto galaxies.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics
and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by
Springe
A translational framework for public health research
<p><b>Background</b></p>
<p>The paradigm of translational medicine that underpins frameworks such as the Cooksey report on the funding of health research does not adequately reflect the complex reality of the public health environment. We therefore outline a translational framework for public health research.</p>
<p><b>Discussion</b></p>
<p>Our framework redefines the objective of translation from that of institutionalising effective interventions to that of improving population health by influencing both individual and collective determinants of health. It incorporates epidemiological perspectives with those of the social sciences, recognising that many types of research may contribute to the shaping of policy, practice and future research. It also identifies a pivotal role for evidence synthesis and the importance of non-linear and intersectoral interfaces with the public realm.</p>
<p><b>Summary</b></p>
<p>We propose a research agenda to advance the field and argue that resources for 'applied' or 'translational' public health research should be deployed across the framework, not reserved for 'dissemination' or 'implementation'.</p>
The Cosmic Ultraviolet Baryon Survey (CUBS) I. Overview and the diverse environments of Lyman limit systems at z<1
We present initial results from the Cosmic Ultraviolet Baryon Survey (CUBS).
CUBS is designed to map diffuse baryonic structures at redshift z<~1 using
absorption-line spectroscopy of 15 UV-bright QSOs with matching deep galaxy
survey data. CUBS QSOs are selected based on their NUV brightness to avoid
biases against the presence of intervening Lyman Limit Systems (LLSs) at
zabs~ 17.2 over a total
redshift survey pathlength of dz=9.3, and a number density of n(z)=0.43 (-0.18,
+0.26). Considering all absorbers with log N(HI)/cm^-2 > 16.5 leads to
n(z)=1.08 (-0.25, +0.31) at z<1. All LLSs exhibit a multi-component structure
and associated metal transitions from multiple ionization states such as CII,
CIII, MgII, SiII, SiIII, and OVI absorption. Differential chemical enrichment
levels as well as ionization states are directly observed across individual
components in three LLSs. We present deep galaxy survey data obtained using the
VLT-MUSE integral field spectrograph and the Magellan Telescopes, reaching
sensitivities necessary for detecting galaxies fainter than 0.1L* at d<~300
physical kpc (pkpc) in all five fields. A diverse range of galaxy properties is
seen around these LLSs, from a low-mass dwarf galaxy pair, a co-rotating
gaseous halo/disk, a star-forming galaxy, a massive quiescent galaxy, to a
galaxy group. The closest galaxies have projected distances ranging from d=15
to 72 pkpc and intrinsic luminosities from ~0.01L* to ~3L*. Our study shows
that LLSs originate in a variety of galaxy environments and trace gaseous
structures with a broad range of metallicities.Comment: 26 pages, 14 figures, MNRAS in pres
Cosmic Origins Spectrograph and FUSE Observations of T ~ 10^5 K Gas In A Nearby Galaxy Filament
We present a detection of a broad Ly-alpha absorber (BLA) with a matching O
VI line in the nearby universe. The BLA is detected at z = 0.01028 in the high
S/N spectrum of Mrk 290 obtained using the Cosmic Origins Spectrograph. The
Ly-alpha absorption has two components, with b(HI) = 55 +/- 1 km/s and b(HI) =
33 +/- 1 km/s, separated in velocity by v ~ 115 km/s. The O VI, detected by
FUSE at z = 0.01027, has a b(OVI) = 29 +/- 3 km/s and is kinematically well
aligned with the broader HI component. The different line widths of the BLA and
OVI suggest a temperature of T = 1.4 x 10^5 K in the absorber. The observed
line strength ratios and line widths favor an ionization scenario in which both
ion-electron collisions and UV photons contribute to the ionization in the gas.
Such a model requires a low-metallicity of -1.7 dex, ionization parameter of
log U ~ -1.4, a large total hydrogen column density of N(H) ~ 4 x 10^19 cm^-2,
and a path length of 400 kpc. The line of sight to Mrk 290 intercepts at the
redshift of the absorber, a megaparsec scale filamentary structure extending
over 20 deg in the sky, with several luminous galaxies distributed within 1.5
Mpc projected distance from the absorber. The collisionally ionized gas in this
absorber is likely tracing a shock-heated gaseous structure, consistent with a
few different scenarios for the origin, including an over-dense region of the
WHIM in the galaxy filament or highly ionized gas in the extended halo of one
of the galaxies in the filament. In general, BLAs with metals provide an
efficient means to study T ~ 10^5 - 10^6 K gas in galaxy halos and in the
intergalactic medium. A substantial fraction of the baryons "missing" from the
present universe is predicted to be in such environments in the form of highly
ionized plasma.Comment: Astrophysical Journal Accepte
Patient perspectives of managing fatigue in ankylosing spondylitis, and views on potential interventions: a qualitative study
<p>Background: Fatigue is a major component of living with ankylosing spondylitis (AS), though it has been largely over-looked, and currently there are no specific agreed management strategies.</p>
<p>Methods: This qualitative exploratory study involved participants who are members of an existing population-based ankylosing spondylitis (PAS) cohort. Participants residing in South West Wales were invited to participate in a focus group to discuss; (1) effects of fatigue, (2) self-management strategies and (3) potential future interventions. The focus groups were audio-recorded and the transcripts were analysed using thematic analysis.</p>
<p>Results: Participants consisted of 3 males/4 females (group 1) and 4 males/3 females (group 2), aged between 35 and 73 years (mean age 53 years). Three main themes were identified: (1) The effects of fatigue were multi-dimensional with participants expressing feelings of being ‘drained’ (physical), ‘upset’ (emotional) and experiencing ‘low-mood’ (psychological); (2) The most commonly reported self-management strategy for fatigue was a balanced combination of activity (exercise) and rest. Medication was reluctantly taken due to side-effects and worries over dependency; (3) Participants expressed a preference for psychological therapies rather than pharmacological for managing fatigue. Information on Mindfulness-Based Stress Reduction (MBSR) was received with interest, with recommendations for delivery in a group format with the option of distance-based delivery for people who were not able to attend a group course.</p>
<p>Conclusions: Patients frequently try and manage their fatigue without any formal guidance or support. Our research indicates there is a need for future research to focus on psychological interventions to address the multi-faceted aspects of fatigue in AS.</p>
Barriers to Adopting and Implementing Local-Level Tobacco Control Policies
Although California communities have been relatively successful in adopting and implementing a wide range of local tobacco control policies, the process has not been without its setbacks and barriers. Little is known about local policy adoption, and this paper examines these processes related to adopting and implementing outdoor smoke-free policies, focusing on the major barriers faced by local-level tobacco control organizations in this process. Ninety-six projects funded by the California Tobacco Control Program submitted final evaluation reports pertaining to an outdoor smoking objective, and the reports from these projects were analyzed. The barriers were grouped in three primary areas: politically polarizing barriers, organizational barriers, and local political orientation. The barriers identified in this study underscore the need for an organized action plan in adopting local tobacco policy. The authors also suggest potential strategies to offset the barriers, including: (1) having a “champion” who helps to carry an objective forward; (2) tapping into a pool of youth volunteers; (3) collecting and using local data as a persuasive tool; (4) educating the community in smoke-free policy efforts; (5) working strategically within the local political climate; and (6) demonstrating to policymakers the constituent support for proposed policy
Applied public health research - falling through the cracks?
<p>Abstract</p> <p>Background</p> <p>There is a degree of dissonance between the types of evaluative research required by organisations providing or commissioning health care, those recommended by organisations developing evidence-based guidance, and those which research funding bodies are prepared to support.</p> <p>Methods</p> <p>We present a case study of efforts to establish a pragmatic but robust evaluation of local exercise referral schemes. We considered the epidemiological, ethical and practical advantages and disadvantages of a number of study designs and applied for research funding based on an uncontrolled design, outlining the difficulties of carrying out a randomised controlled trial to evaluate an existing service.</p> <p>Results</p> <p>Our proposal was praised for its relevance and clear patient outcomes, but the application was twice rejected because both funders and reviewers insisted on a randomised controlled trial design, which we had found to be impractical, unacceptable to service users and potentially unethical.</p> <p>Conclusion</p> <p>The case study highlights continuing challenges for applied public health research in the current funding climate.</p
Gas Accretion in Star-Forming Galaxies
Cold-mode gas accretion onto galaxies is a direct prediction of LCDM
simulations and provides galaxies with fuel that allows them to continue to
form stars over the lifetime of the Universe. Given its dramatic influence on a
galaxy's gas reservoir, gas accretion has to be largely responsible for how
galaxies form and evolve. Therefore, given the importance of gas accretion, it
is necessary to observe and quantify how these gas flows affect galaxy
evolution. However, observational data have yet to conclusively show that gas
accretion ubiquitously occurs at any epoch. Directly detecting gas accretion is
a challenging endeavor and we now have obtained a significant amount of
observational evidence to support it. This chapter reviews the current
observational evidence of gas accretion onto star-forming galaxies.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics
and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by
Springer. This chapter includes 22 pages with 7 Figure
The Cosmic Ultraviolet Baryon Survey (CUBS) V: On the Thermodynamic Properties of the Cool Circumgalactic Medium at
This paper presents a systematic study of the photoionization and
thermodynamic properties of the cool circumgalactic medium (CGM) as traced by
rest-frame ultraviolet absorption lines around 26 galaxies at redshift
. The study utilizes both high-quality far-ultraviolet and optical
spectra of background QSOs and deep galaxy redshift surveys to characterize the
gas density, temperature, and pressure of individual absorbing components and
to resolve their internal non-thermal motions. The derived gas density spans
more than three decades, from to
, while the temperature of the gas is confined in a narrow range of . In addition, a weak anti-correlation between
gas density and temperature is observed, consistent with the expectation of the
gas being in photoionization equilibrium. Furthermore, decomposing the observed
line widths into thermal and non-thermal contributions reveals that more than
30% of the components at exhibit line widths driven by
non-thermal motions, in comparison to % found at -3.
Attributing the observed non-thermal line widths to intra-clump turbulence, we
find that massive quenched galaxies on average exhibit higher non-thermal
broadening/turbulent energy in their CGM compared to star-forming galaxies at
. Finally, strong absorption features from multiple ions covering
a wide range of ionization energy (e.g., from Mg II to O IV) can be present
simultaneously in a single absorption system with kinematically aligned
component structure, but the inferred pressure in different phases may differ
by a factor of .Comment: 16 pages, 4 figures, 1 table, accepted for publication in MNRA
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