80 research outputs found
The age-redshift relation for Luminous Red Galaxies in the Sloan Digital Sky Survey
We present a detailed analysis of 17,852 quiescent, Luminous Red Galaxies
(LRGs) selected from Sloan Digital Sky Survey (SDSS) Data Release Seven (DR7)
spanning a redshift range of 0.0 < z < 0.4. These galaxies are co-added into
four equal bins of velocity dispersion and luminosity to produce high
signal-to-noise spectra (>100A^{-1}), thus facilitating accurate measurements
of the standard Lick absorption-line indices. In particular, we have carefully
corrected and calibrated these indices onto the commonly used Lick/IDS system,
thus allowing us to compare these data with other measurements in the
literature, and derive realistic ages, metallicities ([Z/H]) and alpha-element
abundance ratios ([alpha/Fe]) for these galaxies using Simple Stellar
Population (SSP) models. We use these data to study the relationship of these
galaxy parameters with redshift, and find little evidence for evolution in
metallicity or alpha-elements (especially for our intermediate mass samples).
This demonstrates that our subsamples are consistent with pure passive evolving
(i.e. no chemical evolution) and represent a homogeneous population over this
redshift range. We also present the age-redshift relation for these LRGs and
clearly see a decrease in their age with redshift (5 Gyrs over the redshift
range studied here) which is fully consistent with the cosmological lookback
times in a concordance Lambda CDM universe. We also see that our most massive
sample of LRGs is the youngest compared to the lower mass galaxies. We provide
these data now to help future cosmological and galaxy evolution studies of
LRGs, and provide in the appendices of this paper the required methodology and
information to calibrate SDSS spectra onto the Lick/IDS system.Comment: 26 pages, with several appendices containing data. Accepted for
publication in MNRA
Spectral modelling of the "Super-Chandra" Type Ia SN 2009dc - testing a 2 M_sun white dwarf explosion model and alternatives
Extremely luminous, super-Chandrasekhar (SC) Type Ia Supernovae (SNe Ia) are
as yet an unexplained phenomenon. We analyse a well-observed SN of this class,
SN 2009dc, by modelling its photospheric spectra with a spectral synthesis
code, using the technique of 'Abundance Tomography'. We present spectral models
based on different density profiles, corresponding to different explosion
scenarios, and discuss their consistency. First, we use a density structure of
a simulated explosion of a 2 M_sun rotating C-O white dwarf (WD), which is
often proposed as a possibility to explain SC SNe Ia. Then, we test a density
profile empirically inferred from the evolution of line velocities
(blueshifts). This model may be interpreted as a core-collapse SN with an
ejecta mass ~ 3 M_sun. Finally, we calculate spectra assuming an interaction
scenario. In such a scenario, SN 2009dc would be a standard WD explosion with a
normal intrinsic luminosity, and this luminosity would be augmented by
interaction of the ejecta with a H-/He-poor circumstellar medium. We find that
no model tested easily explains SN 2009dc. With the 2 M_sun WD model, our
abundance analysis predicts small amounts of burning products in the
intermediate-/high-velocity ejecta (v > 9000 km/s). However, in the original
explosion simulations, where the nuclear energy release per unit mass is large,
burned material is present at high v. This contradiction can only be resolved
if asymmetries strongly affect the radiative transfer or if C-O WDs with masses
significantly above 2 M_sun exist. In a core-collapse scenario, low velocities
of Fe-group elements are expected, but the abundance stratification in SN
2009dc seems 'SN Ia-like'. The interaction-based model looks promising, and we
have some speculations on possible progenitor configurations. However,
radiation-hydro simulations will be needed to judge whether this scenario is
realistic at all.Comment: 22 pages, 12 figures, published in MNRAS. V2: several small
corrections (typos, style
Galaxy Zoo: Passive Red Spirals
We study the spectroscopic properties and environments of red spiral galaxies
found by the Galaxy Zoo project. By carefully selecting face-on, disk dominated
spirals we construct a sample of truly passive disks (not dust reddened, nor
dominated by old stellar populations in a bulge). As such, our red spirals
represent an interesting set of possible transition objects between normal blue
spirals and red early types. We use SDSS data to investigate the physical
processes which could have turned these objects red without disturbing their
morphology. Red spirals prefer intermediate density regimes, however there are
no obvious correlations between red spiral properties and environment -
environment alone is not sufficient to determine if a spiral will become red.
Red spirals are a small fraction of spirals at low masses, but are a
significant fraction at large stellar masses - massive galaxies are red
independent of morphology. We confirm that red spirals have older stellar popns
and less recent star formation than the main spiral population. While the
presence of spiral arms suggests that major star formation cannot have ceased
long ago, we show that these are not recent post-starbursts, so star formation
must have ceased gradually. Intriguingly, red spirals are ~4 times more likely
than normal spirals to host optically identified Seyfert or LINER, with most of
the difference coming from LINERs. We find a curiously large bar fraction in
the red spirals suggesting that the cessation of star formation and bar
instabilities are strongly correlated. We conclude by discussing the possible
origins. We suggest they may represent the very oldest spiral galaxies which
have already used up their reserves of gas - probably aided by strangulation,
and perhaps bar instabilities moving material around in the disk.Comment: MNRAS in press, 20 pages, 15 figures (v3
Galaxy Zoo: the dependence of morphology and colour on environment
We analyse the relationships between galaxy morphology, colour, environment
and stellar mass using data for over 100,000 objects from Galaxy Zoo, the
largest sample of visually classified morphologies yet compiled. We
conclusively show that colour and morphology fractions are very different
functions of environment. Both are sensitive to stellar mass; however, at fixed
stellar mass, while colour is also highly sensitive to environment, morphology
displays much weaker environmental trends. Only a small part of both relations
can be attributed to variation in the stellar mass function with environment.
Galaxies with high stellar masses are mostly red, in all environments and
irrespective of their morphology. Low stellar-mass galaxies are mostly blue in
low-density environments, but mostly red in high-density environments, again
irrespective of their morphology. The colour-density relation is primarily
driven by variations in colour fractions at fixed morphology, in particular the
fraction of spiral galaxies that have red colours, and especially at low
stellar masses. We demonstrate that our red spirals primarily include galaxies
with true spiral morphology. We clearly show there is an environmental
dependence for colour beyond that for morphology. Before using the Galaxy Zoo
morphologies to produce the above results, we first quantify a luminosity-,
size- and redshift-dependent classification bias that affects this dataset, and
probably most other studies of galaxy population morphology. A correction for
this bias is derived and applied to produce a sample of galaxies with reliable
morphological type likelihoods, on which we base our analysis.Comment: 25 pages, 20 figures (+ 6 pages, 11 figures in appendices);
moderately revised following referee's comments; accepted by MNRA
Use of selected complementary and alternative medicine (CAM) treatments in veterans with cancer or chronic pain: a cross-sectional survey
BACKGROUND: Complementary and alternative medicine (CAM) is emerging as an important form of care in the United States. We sought to measure the prevalence of selected CAM use among veterans attending oncology and chronic pain clinics and to describe the characteristics of CAM use in this population. METHODS: The self-administered, mail-in survey included questions on demographics, health beliefs, medical problems and 6 common CAM treatments (herbs, dietary supplements, chiropractic care, massage therapy, acupuncture and homeopathy) use. We used the chi-square test to examine bivariate associations between our predictor variables and CAM use. RESULTS: Seventy-two patients (27.3%) reported CAM use within the past 12 months. CAM use was associated with more education (p = 0.02), higher income (p = 0.006), non-VA insurance (p = 0.003), additional care outside the VA (p = 0.01) and the belief that lifestyle contributes to illness (p = 0.015). The diagnosis of chronic pain versus cancer was not associated with differential CAM use (p = 0.15). Seventy-six percent of CAM non-users reported that they would use it if offered at the VA. CONCLUSION: Use of 6 common CAM treatments among these veterans is lower than among the general population, but still substantial. A large majority of veterans reported interest in using CAM modalities if they were offered at the VA. A national assessment of veteran interest in CAM may assist VA leaders to respond to patients' needs
Goal Reasoning: Papers from the ACS Workshop
This technical report contains the 14 accepted papers presented at the Workshop on Goal Reasoning,
which was held as part of the 2015 Conference on Advances in Cognitive Systems (ACS-15) in Atlanta,
Georgia on 28 May 2015. This is the fourth in a series of workshops related to this topic, the first of
which was the AAAI-10 Workshop on Goal-Directed Autonomy; the second was the Self-Motivated
Agents (SeMoA) Workshop, held at Lehigh University in November 2012; and the third was the Goal
Reasoning Workshop at ACS-13 in Baltimore, Maryland in December 2013
Mapping exclusive breastfeeding in Africa between 2000 and 2017.
Exclusive breastfeeding (EBF)-giving infants only breast-milk (and medications, oral rehydration salts and vitamins as needed) with no additional food or drink for their first six months of life-is one of the most effective strategies for preventing child mortality1-4. Despite these advantages, only 37% of infants under 6 months of age in Africa were exclusively breastfed in 20175, and the practice of EBF varies by population. Here, we present a fine-scale geospatial analysis of EBF prevalence and trends in 49 African countries from 2000-2017, providing policy-relevant administrative- and national-level estimates. Previous national-level analyses found that most countries will not meet the World Health Organization's Global Nutrition Target of 50% EBF prevalence by 20256. Our analyses show that even fewer will achieve this ambition in all subnational areas. Our estimates provide the ability to visualize subnational EBF variability and identify populations in need of additional breastfeeding support
THE SECRET OF MARY MAGDALENE (RAHASIA-RAHASIA MARIA MAGDALENA)
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