36 research outputs found
Predicting Quiescence: The Dependence of Specific Star Formation Rate on Galaxy Size and Central Density at 0.5<z<2.5
In this paper, we investigate the relationship between star formation and
structure, using a mass-complete sample of 27,893 galaxies at
selected from 3D-HST. We confirm that star-forming galaxies are larger than
quiescent galaxies at fixed stellar mass (M). However, in contrast
with some simulations, there is only a weak relation between star formation
rate (SFR) and size within the star-forming population: when dividing into
quartiles based on residual offsets in SFR, we find that the sizes of
star-forming galaxies in the lowest quartile are 0.270.06 dex smaller than
the highest quartile. We show that 50% of star formation in galaxies at fixed
M takes place within a narrow range of sizes (0.26 dex). Taken
together, these results suggest that there is an abrupt cessation of star
formation after galaxies attain particular structural properties. Confirming
earlier results, we find that central stellar density within a 1 kpc fixed
physical radius is the key parameter connecting galaxy morphology and star
formation histories: galaxies with high central densities are red and have
increasingly lower SFR/M, whereas galaxies with low central densities
are blue and have a roughly constant (higher) SFR/M at a given
redshift. We find remarkably little scatter in the average trends and a strong
evolution of 0.5 dex in the central density threshold correlated with
quiescence from . Neither a compact size nor high- are
sufficient to assess the likelihood of quiescence for the average galaxy;
rather, the combination of these two parameters together with M
results in a unique quenching threshold in central density/velocity.Comment: 20 pages, 15 figures, and 2 tables; Accepted for publication in the
Astrophysical Journa
Direct measurements of dust attenuation in z~1.5 star-forming galaxies from 3D-HST: Implications for dust geometry and star formation rates
The nature of dust in distant galaxies is not well understood, and until
recently few direct dust measurements have been possible. We investigate dust
in distant star-forming galaxies using near-infrared grism spectra of the
3D-HST survey combined with archival multi-wavelength photometry. These data
allow us to make a direct comparison between dust around star-forming regions
() and the integrated dust content ().
We select a sample of 163 galaxies between with H
signal-to-noise ratio and measure Balmer decrements from stacked spectra
to calculate . First, we stack spectra in bins of
, and find that
, with a significance of
. Our result is consistent with the two-component dust model, in
which galaxies contain both diffuse and stellar birth cloud dust. Next, we
stack spectra in bins of specific star formation rate (),
star formation rate (), and stellar mass (). We
find that on average increases with SFR and mass, but
decreases with increasing SSFR. Interestingly, the data hint that the amount of
extra attenuation decreases with increasing SSFR. This trend is expected from
the two-component model, as the extra attenuation will increase once older
stars outside the star-forming regions become more dominant in the galaxy
spectrum. Finally, using Balmer decrements we derive dust-corrected H
SFRs, and find that stellar population modeling produces incorrect SFRs if
rapidly declining star formation histories are included in the explored
parameter space.Comment: Accepted for publication in the Astrophysical Journal (13 pages, 9
figures
Exploring the chemical link between local ellipticals and their high-redshift progenitors
We present Keck/MOSFIRE K-band spectroscopy of the first mass-selected sample
of galaxies at . Targets are selected from the 3D-HST Treasury
survey. The six detected galaxies have a mean [NII]6584/H
ratio of , with a small standard deviation of 0.05. This mean
value is similar to that of UV-selected galaxies of the same mass. The mean
gas-phase oxygen abundance inferred from the [NII]/H ratios depends on
the calibration method, and ranges from 12+log(O/H) for the
{Pettini} & {Pagel} (2004) calibration to 12+log(O/H) for the
{Maiolino} {et~al.} (2008) calibration. Measurements of the stellar oxygen
abundance in nearby quiescent galaxies with the same number density indicate
12+log(O/H), similar to the gas-phase abundances of the
galaxies if the {Maiolino} {et~al.} (2008) calibration is used. This
suggests that these high-redshift star forming galaxies may be progenitors of
today's massive early-type galaxies. The main uncertainties are the absolute
calibration of the gas-phase oxygen abundance and the incompleteness of the
sample: the galaxies with detected H tend to be larger and
have higher star formation rates than the galaxies without detected H,
and we may still be missing the most dust-obscured progenitors.Comment: 7 pages, 5 figures. Accepted for publication in ApJ
A CANDELS - 3D-HST Synergy: Resolved Star Formation Patterns at 0.7 < z < 1.5
We analyze the resolved stellar populations of 473 massive star-forming
galaxies at 0.7 < z < 1.5, with multi-wavelength broad-band imaging from
CANDELS and Halpha surface brightness profiles at the same kiloparsec
resolution from 3D-HST. Together, this unique data set sheds light on how the
assembled stellar mass is distributed within galaxies, and where new stars are
being formed. We find the Halpha morphologies to resemble more closely those
observed in the ACS I band than in the WFC3 H band, especially for the larger
systems. We next derive a novel prescription for Halpha dust corrections, which
accounts for extra extinction towards HII regions. The prescription leads to
consistent SFR estimates and reproduces the observed relation between the
Halpha/UV luminosity ratio and visual extinction, both on a pixel-by-pixel and
on a galaxy-integrated level. We find the surface density of star formation to
correlate with the surface density of assembled stellar mass for spatially
resolved regions within galaxies, akin to the so-called 'main sequence of star
formation' established on a galaxy-integrated level. Deviations from this
relation towards lower equivalent widths are found in the inner regions of
galaxies. Clumps and spiral features, on the other hand, are associated with
enhanced Halpha equivalent widths, bluer colors, and higher specific star
formation rates compared to the underlying disk. Their Halpha/UV luminosity
ratio is lower than that of the underlying disk, suggesting the ACS clump
selection preferentially picks up those regions of elevated star formation
activity that are the least obscured by dust. Our analysis emphasizes that
monochromatic studies of galaxy structure can be severely limited by
mass-to-light ratio variations due to dust and spatially inhomogeneous star
formation histories.Comment: Accepted by The Astrophysical Journal, 18 pages, 1 table, 10 figure
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Barriers and facilitators to adherence to group exercise in institutionalized older people living with dementia: a systematic review
Objectives
Research suggests targeted exercise is important for people living with dementia, especially those living in residential care. The aim of this review was to collect and synthesize evidence on the known barriers and facilitators to adherence to group exercise of institutionalized older people living with dementia.
Methods
We searched all available electronic databases. Additionally, we searched trial registries (clinicaltrial.gov, and WHO ICTRP) for ongoing studies. We searched for and included papers from January 1990 until September 2017 in any language. We included randomized, non-randomized trials. Studies were not eligible if participants were either healthy older people or people suffering from dementia but not living in an institution. Studies were also excluded if they were not focused on barriers and facilitators to adherence to group exercise.
Results
Using narrative analysis, we identified the following themes for barriers: bio-medical reasons and mental wellbeing and physical ability, relationships dynamics, and socioeconomic reasons. The facilitators were grouped under the following thematic frames: bio-medical benefits and benefits related to physical ability, feelings and emotions and confidence improvements, therapist and group relationships dynamics and activity related reasons.
Conclusions
We conclude that institutionalized older people living with dementia, even those who are physically frail, incontinent and/or have mild dementia can demonstrate certain level of exercise adherence, and therefore can respond positively to exercise programs. Tailored, individually-adjusted and supported physical activity, led by a knowledgeable, engaging and well communicating therapist/facilitator improves the adherence to group exercise interventions of institutionalized older people living with dementia
The Assembly of Milky Way-like Galaxies Since z~2.5
Galaxies with the mass of the Milky Way dominate the stellar mass density of
the Universe but it is uncertain how and when they were assembled. Here we
study progenitors of these galaxies out to z=2.5, using data from the 3D-HST
and CANDELS Treasury surveys. We find that galaxies with present-day stellar
masses of log(M)~10.7 built ~90% of their stellar mass since z=2.5, with most
of the star formation occurring before z=1. In marked contrast to the assembly
history of massive elliptical galaxies, mass growth is not limited to large
radii: the mass in the central 2 kpc of the galaxies increased by a factor of
3.2+-0.8 between z=2.5 and z=1. We therefore rule out simple models in which
bulges were fully assembled at high redshift and disks gradually formed around
them. Instead, bulges (and black holes) likely formed in lockstep with disks,
through bar instabilities, migration, or other processes. We find that after
z=1 the growth in the central regions gradually stopped and the disk continued
to build, consistent with recent studies of the gas distributions in z~1
galaxies and the properties of many spiral galaxies today.Comment: Accepted for publication in ApJ Letters. 7 pages, 5 figure
The Radial Distribution of Star Formation in Galaxies at z~1 From The 3D-HST Survey
The assembly of galaxies can be described by the distribution of their star formation as a function of cosmic time.Thanks to the WFC3 grism on the Hubble Space Telescope (HST) it is now possible to measure this beyond thelocal Universe. Here we present the spatial distribution of H emission for a sample of 54 strongly star-forming-galaxies at z~1 in the 3D-HST Treasury survey. By stacking the Halpha emission, we find that star formation occurredin approximately exponential distributions at z~1, with a median Sersic index of n=1.0 plus or minus 0.2. The stacks areelongated with median axis ratios of b/a 0.58 plus or minus 0.09 in Halpha consistent with (possibly thick) disks at randomorientation angles. Keck spectra obtained for a subset of eight of the galaxies show clear evidence for rotation, withinclination corrected velocities of 90-330 km per second. The most straightforward interpretation of our results is that starformation in strongly star-forming galaxies at z~1 generally occurred in disks. The disks appear to be scaled-upversions of nearby spiral galaxies: they have EW(Halpha)~100 Angstroms out to the solar orbit and they have star formation surface densities above the threshold for driving galactic scale winds
The Kinematics of Massive Quiescent Galaxies at 1.4 < z < 2.1: Dark Matter Fractions, IMF Variation, and the Relation to Local Early-type Galaxies
We study the dynamical properties of massive quiescent galaxies at 1.4 <z <2.1 using deep Hubble Space Telescope WFC3/F160W imaging and a combination of literature stellar velocity dispersion measurements and new near-infrared spectra obtained using the K-band Multi Object Spectrograph(KMOS) on the ESO Very Large Telescope. We use these data to show that the typical dynamical-to-stellar mass ratio has increased by∼0.2 dex from z = 2 to the present day, and we investigate this evolution in the context of possible changes in the stellar initial mass function(IMF) and/or fraction of dark matter contained within the galaxy effective radius,fDM[<re]. Comparing our high-redshift sample to their likely descendants at low redshift, we find that fDM[<re] has increased by a factor of more than 4 since z ≈ 1.8, from fDM[<re] = 6.6% +-1.0% to∼24%. The observed increase appears robust to changes in the methods used to estimate dynamical masses or match progenitors and descendants. We quantify possible variation of the stellar IMF through the offset parameter α, defined as the ratio of dynamical mass in stars to the stellar mass estimated using a Chabrier IMF. We demonstrate that the correlation between stellar velocity dispersion and α reported among quiescent galaxies at low redshift is already in place atz = 2, and we argue that subsequent evolution through (mostly minor) merging should act to preserve this relation while contributing significantly to galaxies'overall growth in size and stellar mass.J.T.M. acknowledges the support of the Australian Research Council Centre of
Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO
3D), through project No. CE170100013. D.J.W. and M.F.
acknowledge the support of the Deutsche Forschungsgemeinschaft via Project IDs 3871/1-1 and 3871/1-2. M.F. has
received funding from the European Research Council (ERC)
under the European Union’s Horizon 2020 research and
innovation program (grant agreement No. 757535)
Quality standards for the management of alcohol-related liver disease: consensus recommendations from the British Association for the Study of the Liver and British Society of Gastroenterology ARLD special interest group
Objective Alcohol-related liver disease (ALD) is the most common cause of liver-related ill health and liver-related deaths in the UK, and deaths from ALD have doubled in the last decade. The management of ALD requires treatment of both liver disease and alcohol use; this necessitates effective and constructive multidisciplinary working. To support this, we have developed quality standard recommendations for the management of ALD, based on evidence and consensus expert opinion, with the aim of improving patient care.Design A multidisciplinary group of experts from the British Association for the Study of the Liver and British Society of Gastroenterology ALD Special Interest Group developed the quality standards, with input from the British Liver Trust and patient representatives.Results The standards cover three broad themes: the recognition and diagnosis of people with ALD in primary care and the liver outpatient clinic; the management of acutely decompensated ALD including acute alcohol-related hepatitis and the posthospital care of people with advanced liver disease due to ALD. Draft quality standards were initially developed by smaller working groups and then an anonymous modified Delphi voting process was conducted by the entire group to assess the level of agreement with each statement. Statements were included when agreement was 85% or greater. Twenty-four quality standards were produced from this process which support best practice. From the final list of statements, a smaller number of auditable key performance indicators were selected to allow services to benchmark their practice and an audit tool provided.Conclusion It is hoped that services will review their practice against these recommendations and key performance indicators and institute service development where needed to improve the care of patients with ALD
The JWST UNCOVER Treasury survey: Ultradeep NIRSpec and NIRCam ObserVations before the Epoch of Reionization
In this paper we describe the survey design for the Ultradeep NIRSpec and
NIRCam ObserVations before the Epoch of Reionization (UNCOVER) Cycle 1 JWST
Treasury program, which executed its early imaging component in November 2022.
The UNCOVER survey includes ultradeep () imaging of
45 arcmin on and around the well-studied Abell 2744 galaxy cluster at
and will follow-up galaxies with extremely deep
low-resolution spectroscopy with the NIRSpec/PRISM during the summer of 2023.
We describe the science goals, survey design, target selection, and planned
data releases. We also present and characterize the depths of the first NIRCam
imaging mosaic, highlighting previously unparalleled resolved and ultradeep 2-4
micron imaging of known objects in the field. The UNCOVER primary NIRCam mosaic
spans 28.8 arcmin in seven filters (F115W, F150W, F200W, F277W, F356W,
F410M, F444W) and 16.8 arcmin in our NIRISS parallel (F115W, F150W, F200W,
F356W, and F444W). To maximize early community use of the Treasury data set, we
publicly release full reduced mosaics of public JWST imaging including 45
arcmin NIRCam and 17 arcmin NIRISS mosaics on and around the Abell 2744
cluster, including the Hubble Frontier Field primary and parallel footprints.Comment: 17 pages, 8 figures, 4 tables, submitted to ApJ, comments welcome (v2
with full author list in metadata