15 research outputs found
The Star Formation Demographics of Galaxies in the Local Volume
We examine the connections between the current global star formation
activity, luminosity, dynamical mass and morphology of galaxies in the Local
Volume, using H-alpha data from the 11 Mpc H-alpha and Ultraviolet Galaxy
Survey (11HUGS). Taking the equivalent width (EW) of the H-alpha emission line
as a tracer of the specific star formation rate, we analyze the distribution of
galaxies in the M_B-EW and rotational velocity (V_{max})-EW planes.
Star-forming galaxies show two characteristic transitions in these planes. A
narrowing of the galaxy locus occurs at M_B~-15 and V_{max}~50 km/s, where the
scatter in the logarithmic EWs drops by a factor of two as the
luminosities/masses increase, and galaxy morphologies shift from predominately
irregular to late-type spiral. Another transition occurs at M_B~-19 and
V_{max}~120 km/s, above which the sequence turns off toward lower EWs and
becomes mostly populated by intermediate and early-type bulge-prominent
spirals. Between these two transitions, the mean logarithmic EW appears to
remain constant at 30 A. We comment on how these features reflect established
empirical relationships, and provide clues for identifying the large-scale
physical processes that both drive and regulate star formation, with emphasis
on the low-mass galaxies that dominate our approximately volume-limited sample.Comment: 5 pages, accepted for publication in ApJL pending editing for lengt
A GALEX Ultraviolet Imaging Survey of Galaxies in the Local Volume
We present results from a GALEX ultraviolet (UV) survey of a complete sample
of 390 galaxies within ~11 Mpc of the Milky Way. The UV data are a key
component of the composite Local Volume Legacy (LVL), an
ultraviolet-to-infrared imaging program designed to provide an inventory of
dust and star formation in nearby spiral and irregular galaxies. The ensemble
dataset is an especially valuable resource for studying star formation in dwarf
galaxies, which comprise over 80% of the sample. We describe the GALEX survey
programs which obtained the data and provide a catalog of far-UV (~1500
Angstroms) and near-UV (~2200 Angstroms) integrated photometry. General UV
properties of the sample are briefly discussed. We compute two measures of the
global star formation efficiency, the SFR per unit HI gas mass and the SFR per
unit stellar mass, to illustrate the significant differences that can arise in
our understanding of dwarf galaxies when the FUV is used to measure the SFR
instead of H-alpha. We find that dwarf galaxies may not be as drastically
inefficient in coverting gas into stars as suggested by prior H-alpha studies.
In this context, we also examine the UV properties of late-type dwarf galaxies
that appear to be devoid of star formation because they were not detected in
previous H-alpha narrowband observations. Nearly all such galaxies in our
sample are detected in the FUV, and have FUV SFRs that fall below the limit
where the H-alpha flux is robust to Poisson fluctuations in the formation of
massive stars. The UV colors and star formation efficiencies of
H-alpha-undetected, UV-bright dwarf irregulars appear to be relatively
unremarkable with respect to those exhibited by the general population of
star-forming galaxies.Comment: submitted to ApJS, revised per referee's comments; accepted Oct. 30
w/o further revision; 37 pages; figure 6 omitted due to size; figure
available from http://users.obs.carnegiescience.edu/jlee/paper
Comparison of H-alpha and UV Star Formation Rates in the Local Volume: Systematic Discrepancies for Dwarf Galaxies
(abridged) Using a complete sample of ~300 star-forming galaxies within 11
Mpc, we evaluate the consistency between star formation rates (SFRs) inferred
from the far ultraviolet (FUV) non-ionizing continuum and H-alpha nebular
emission, assuming standard conversion recipes in which the SFR scales linearly
with luminosity at a given wavelength. Our analysis probes SFRs over 5 orders
of magnitude, down to ultra-low activities on the order of ~0.0001 M_sun/yr.
The data are drawn from the 11 Mpc H-alpha and Ultraviolet Galaxy Survey
(11HUGS), which has obtained H-alpha fluxes from ground-based narrowband
imaging, and UV fluxes from imaging with GALEX. For normal spiral galaxies
(SFR~1 M_sun/yr), our results are consistent with previous work which has shown
that FUV SFRs tend to be lower than H-alpha SFRs before accounting for internal
dust attenuation, but that there is relative consistency between the two
tracers after proper corrections are applied. However, a puzzle is encountered
at the faint end of the luminosity function. As lower luminosity dwarf
galaxies, roughly less active than the Small Magellanic Cloud, are examined,
H-alpha tends to increasingly under-predict the SFR relative to the FUV.
Although past studies have suggested similar trends, this is the first time
this effect is probed with a statistical sample for galaxies with SFR~<0.1
M_sun/yr. A range of standard explanations does not appear to be able to
account for the magnitude of the systematic. Some recent work has argued for an
IMF which is deficient in high mass stars in dwarf and low surface brightness
galaxies, and we also consider this scenario.Comment: 29 pages, 10 figures, 2 tables, accepted for publication in Ap
Interfaces entre a histĂłria da violĂȘncia e a constituição do territĂłrio no CearĂĄ: um esforço de sĂntese e periodização
Mortality and complications in patients with portal hypertension who underwent transjugular intrahepatic portosystemic shunt (TIPS) - 12 years experience
Dementia in Latin America : paving the way towards a regional action plan
Regional challenges faced by Latin American and Caribbean countries (LACs) to fight dementia, such as heterogeneity, diversity, political instabilities, and socioeconomic disparities, can be addressed more effectively grounded in a collaborative setting based on the open exchange of knowledge. In this work, the Latin American and Caribbean Consortium on Dementia (LAC-CD) proposes an agenda for integration to deliver a Knowledge to Action Framework (KtAF). First, we summarize evidence-based strategies (epidemiology, genetics, biomarkers, clinical trials, nonpharmacological interventions, networking and translational research) and align them to current global strategies to translate regional knowledge into actions with transformative power. Then, by characterizing genetic isolates, admixture in populations, environmental factors, and barriers to effective interventions and mapping these to the above challenges, we provide the basic mosaics of knowledge that will pave the way towards a KtAF. We describe strategies supporting the knowledge creation stage that underpins the translational impact of KtAF
Association of vitamin d with mild cognitive impairment and alzheimer's dementia in older mexican adults
Background: It has been proposed that Vitamin D helps reduce the accumulation of cerebral beta-amyloid-42 by innate immune stimulation and phagocytosis activation. An association between low Vitamin D levels and Alzheimer's dementia (AD) has been established. We determined the association between Vitamin D, mild cognitive impairment (MCI), and AD in older Mexican adults (> 65 years). Methods: Cross-sectional study conducted at the memory clinic in a tertiary-level hospital in Mexico City. We evaluated subjects with MCI, AD, and normal cognition (NC) with available serum Vitamin D [25(OH)D] levels (past 6 months). Three categories were assigned according to 25(OH)D levels: sufficiency (> 30 ng/mL), insufficiency (21-29 ng/mL), and deficiency (</= 20 ng/mL). Descriptive statistics, means and standard deviations were used. Logistic regression analyses adjusted by age, sex, and educational level were performed. Results: We evaluated 208 patients. Mean age was 79 +/- 1 year, 65% (n = 136) were female; and mean educational level was 6.7 +/- 2.3 years. Thirty-one subjects (14%) had NC; 42% (n = 88) had MCI; and 43% (n = 89) had AD. Prevalence of Vitamin D deficiency was 54%, more frequent in the AD group (64%) followed by the MCI (59%) and NC (13%) (p < 0.001) groups. In the multivariate logistic regression analysis, Vitamin D deficiency was associated with MCI (HR 25.02 [confidence interval 95% 4.48-139]; p < 0.001) and AD (HR 41.7 [5.76-301]; p < 0.001) after adjusting for confounders. Conclusions: Serum Vitamin D deficiency was associated with MCI and dementia; low levels produced a greater effect over executive functions