Browsing by Subject "populations"
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Item Chemical Abundances Of The Leo II Dwarf Galaxy(2009-01) Shetrone, Matthew D.; Siegel, Michael H.; Cook, David O.; Bosler, Tammy; Shetrone, Matthew D.; Siegel, Michael H.We use previously published moderate-resolution spectra in combination with stellar atmosphere models to derive the first measured chemical abundance ratios in the Leo II dwarf Spheroidal (dSph) galaxy. We find that for spectra with signal-to-noise ratio greater than 24, we are able to measure abundances from weak Ti, Fe, and Mg lines located near the calcium infrared triplet (CaT). We also quantify and discuss discrepancies between the metallicities measured from Fe I lines and those estimated from the CaT features. We find that while the most metal-poor ([Fe/H] < - 2.0]) Leo II stars have Ca and Ti abundance ratios similar to those of Galactic globular clusters, the more metal-rich stars show a gradual decline of Ti, Mg, and Ca abundance ratio with increasing metallicity. Finding these trends in this distant and apparently dynamically stable dSph galaxy supports the hypothesis that the slow chemical enrichment histories of the dSph galaxies is universal, independent of any interaction with the Milky Way. Combining our spectroscopic abundances with published broadband photometry and updated isochrones, we are able to approximate stellar ages for our bright red giant branch stars to a relative precision of 2-3 Gyr. While the derived age-metallicity relationship of Leo II hints at some amount of slow enrichment, the data are still statistically consistent with no enrichment over the history of Leo II.Item Design of a Randomized Controlled Trial for Multiple Cancer Risk Behaviors Among Spanish-Speaking Mexican-Origin Smokers(2013-03) Castro, Yessenia; Basen-Engquist, Karen; Fernandez, Maria E.; Strong, Larkin L.; Eakin, Elizabeth G.; Resnicow, Ken; Li, Y. S.; Wetter, David W.; Castro, YesseniaSmoking, poor diet, and physical inactivity account for as much as 60% of cancer risk. Latinos experience profound disparities in health behaviors, as well as the cancers associated with them. Currently, there is a dearth of controlled trials addressing these health behaviors among Latinos. Further, to the best of our knowledge, no studies address all three behaviors simultaneously, are culturally sensitive, and are guided by formative work with the target population. Latinos represent 14% of the U. S. population and are the fastest growing minority group in the country. Efforts to intervene on these important lifestyle factors among Latinos may accelerate the elimination of cancer-related health disparities. Methods/design: The proposed study will evaluate the efficacy of an evidence-based and theoretically-driven Motivation And Problem Solving (MAPS) intervention, adapted and culturally-tailored for reducing cancer risk related to smoking, poor diet, and physical inactivity among high-risk Mexican-origin smokers who are overweight/ obese (n = 400). Participants will be randomly assigned to one of two groups: Health Education (HE) or MAPS (HE + up to 18 MAPS counseling calls over 18 months). Primary outcomes are smoking status, servings of fruits and vegetables, and both self-reported and objectively measured physical activity. Outcome assessments will occur at baseline, 6 months, 12 months, and 18 months. Discussion: The current study will contribute to a very limited evidence base on multiple risk factor intervention studies on Mexican-origin individuals and has the potential to inform both future research and practice related to reducing cancer risk disparities. An effective program targeting multiple cancer risk behaviors modeled after chronic care programs has the potential to make a large public health impact because of the dearth of evidence-based interventions for Latinos and the extended period of support that is provided in such a program. Trial registration: National Institutes of Health Clinical Trials Registry # NCT01504919Item Evolution In Metacommunities: On The Relative Importance Of Species Sorting And Monopolization In Structuring Communities(2008-06) Loeuille, Nicolas; Leibold, Mathew A.; Loeuille, Nicolas; Leibold, Mathew A.Adaptive evolution within species and community assembly involving multiple species are both affected by dispersal and spatiotemporal environmental variation and may thus interact with each other. We examined this interaction in a simple three-patch metacommunity and found that these two processes produce very different associations between species composition and local environment. In most conditions, we find a pattern we call >species sorting,> wherein local adaptation by resident species cannot prevent invasions by other preadapted species as environmental conditions change (strong association between local environmental conditions and local community composition). When dispersal rates are very low relative to the other two rates, local adaptation by resident species predominates, leading to strong priority effects that prevent successful colonization by other species that would have been well adapted, a pattern we call > local monopolization.> When dispersal and evolutionary rates are both very high, we find that an evolving species outcompetes other species in all patches, a pattern we call > global monopolization.> When environmental oscillations are very frequent, local monopolization predominates. Our findings indicate that there can be strong modification of community assembly by local adaptive processes and that these depend strongly on the relative rates of evolution, dispersal, and environmental change.Item The Gentle Growth of Galaxies at High Redshifts in Overdense Environments(2014-08) Romano-Diaz, Emilio; Shlosman, Issac; Choi, Jun-Hwan; Sadoun, Raphael; Shlosman, IssacWe have explored prevailing modes of galaxy growth for redshifts z similar to 6-14, comparing substantially overdense and normal regions of the universe, using high-resolution zoom-in cosmological simulations. Such rare overdense regions have been projected to host high-z quasars. We demonstrate that galaxies in such environments grow predominantly by a smooth accretion from cosmological filaments which dominates the mass input from major, intermediate, and minor mergers. We find that by z similar to 6, the accumulated galaxy mass fraction from mergers falls short by a factor of 10 of the cumulative accretion mass for galaxies in the overdense regions, and by a factor of 5 in the normal environments. Moreover, the rate of the stellar mass input from mergers also lies below that of an in situ star Formation (SF) rate. The fraction of stellar masses in galaxies contributed by mergers in overdense regions is similar to 12%, and similar to 33% in the normal regions, at these redshifts. Our median SF rates for similar to few x 10(9) M-circle dot galaxies agrees well with the recently estimated rates for z similar to 7 galaxies from Spitzer's SURF-UP survey. Finally, we find that the main difference between the normal and overdense regions lies in the amplified growth of massive galaxies in massive dark matter halos. This leads to the Formation of similar to 10(10) M-circle dot galaxies due to the similar to 100 fold increase in mass during the above time period. Such galaxies are basically absent in the normal regions at these redshifts.Item How Do SNP Ascertainment Schemes and Population Demographics Affect Inferences about Population History?(2015-04) McTavish, Emily J.; Hillis, David M.; Hillis, David M.The selection of variable sites for inclusion in genomic analyses can influence results, especially when exemplar populations are used to determine polymorphic sites. We tested the impact of ascertainment bias on the inference of population genetic parameters using empirical and simulated data representing the three major continental groups of cattle: European, African, and Indian. We simulated data under three demographic models. Each simulated data set was subjected to three ascertainment schemes: (I) random selection; (II) geographically biased selection; and (III) selection biased toward loci polymorphic in multiple groups. Empirical data comprised samples of 25 individuals representing each continental group. These cattle were genotyped for 47,506 loci from the bovine 50 K SNP panel. We compared the inference of population histories for the empirical and simulated data sets across different ascertainment conditions using F-ST and principal components analysis (PCA). Results: Bias toward shared polymorphism across continental groups is apparent in the empirical SNP data. Bias toward uneven levels of within-group polymorphism decreases estimates of F-ST between groups. Subpopulation-biased selection of SNPs changes the weighting of principal component axes and can affect inferences about proportions of admixture and population histories using PCA. PCA-based inferences of population relationships are largely congruent across types of ascertainment bias, even when ascertainment bias is strong. Conclusions: Analyses of ascertainment bias in genomic data have largely been conducted on human data. As genomic analyses are being applied to non-model organisms, and across taxa with deeper divergences, care must be taken to consider the potential for bias in ascertainment of variation to affect inferences. Estimates of F-ST, time of separation, and population divergence as estimated by principal components analysis can be misleading if this bias is not taken into account.Item Identifying Structural Variation in Haploid Microbial Genomes from Short-Read Resequencing Data Using Breseq(2014-11) Barrick, Jeffrey E.; Colburn, Geoffrey; Deatherage, Daniel E.; Traverse, Charles C.; Strand, Matthew D.; Borges, Jordan J.; Knoester, David B.; Reba, Aaron; Meyer, Austin G.; Barrick, Jeffrey E.; Colburn, Geoffrey; Deatherage, Daniel E.; Traverse, Charles C.; Strand, Matthew D.; Borges, Jordan J.; Reba, Aaron; Meyer, Austin G.Mutations that alter chromosomal structure play critical roles in evolution and disease, including in the origin of new lifestyles and pathogenic traits in microbes. Large-scale rearrangements in genomes are often mediated by recombination events involving new or existing copies of mobile genetic elements, recently duplicated genes, or other repetitive sequences. Most current software programs for predicting structural variation from short-read DNA resequencing data are intended primarily for use on human genomes. They typically disregard information in reads mapping to repeat sequences, and significant post-processing and manual examination of their output is often required to rule out false-positive predictions and precisely describe mutational events. Results: We have implemented an algorithm for identifying structural variation from DNA resequencing data as part of the breseq computational pipeline for predicting mutations in haploid microbial genomes. Our method evaluates the support for new sequence junctions present in a clonal sample from split-read alignments to a reference genome, including matches to repeat sequences. Then, it uses a statistical model of read coverage evenness to accept or reject these predictions. Finally, breseq combines predictions of new junctions and deleted chromosomal regions to output biologically relevant descriptions of mutations and their effects on genes. We demonstrate the performance of breseq on simulated Escherichia coli genomes with deletions generating unique breakpoint sequences, new insertions of mobile genetic elements, and deletions mediated by mobile elements. Then, we reanalyze data from an E. coli K-12 mutation accumulation evolution experiment in which structural variation was not previously identified. Transposon insertions and large-scale chromosomal changes detected by breseq account for similar to 25% of spontaneous mutations in this strain. In all cases, we find that breseq is able to reliably predict structural variation with modest read-depth coverage of the reference genome (>40-fold). Conclusions: Using breseq to predict structural variation should be useful for studies of microbial epidemiology, experimental evolution, synthetic biology, and genetics when a reference genome for a closely related strain is available. In these cases, breseq can discover mutations that may be responsible for important or unintended changes in genomes that might otherwise go undetected.Item Integral Field Unit Spectroscopy of the Stellar Disk Truncation Region of NGC 6155(2010-06) Yoachim, Peter; Roskar, Rok; Debattista, Victor P.; Roskar, RokLike the majority of spiral galaxies, NGC 6155 exhibits an exponential surface brightness profile that steepens significantly at large radii. Using the VIRUS-P integral field unit spectrograph, we have gathered spatially resolved spectra of the system. Modifying the GANDALF spectral fitting routine for use on the complex stellar populations found in spirals, we find that the average stellar ages increase significantly beyond the profile break radius. This result is in good agreement with recent simulations that predict the outskirts of disk galaxies are populated through stellar migration. With the ability to bin multiple fibers, we are able to measure stellar population ages down to mu(V) similar to 24 mag arcsec(-2).Item Inverting Color-Magnitude Diagrams To Access Precise Star Cluster Parameters: A New White Dwarf Age For The Hyades(2009-05) Degennaro, Steven; von Hippel, Ted; Jefferys, William H.; Stein, Nathan; van Dyk, David; Jeffery, Elizabeth; Degennaro, Steven; von Hippel, Ted; Jefferys, William H.; Stein, Nathan; Jeffery, ElizabethWe have extended our Bayesian modeling of stellar clusters-which uses main-sequence stellar evolution models, a mapping between initial masses and white dwarf (WD) masses, WD cooling models, and WD atmospheres-to include binary stars, field stars, and two additional main-sequence stellar evolution models. As a critical test of our Bayesian modeling technique, we apply it to Hyades UBV photometry, with membership priors based on proper motions and radial velocities, where available. Under the assumption of a particular set of WD cooling models and atmosphere models, we estimate the age of the Hyades based on cooling WDs to be 648 +/- 45 Myr, consistent with the best prior analysis of the cluster main-sequence turnoff (MSTO) age by Perryman et al. Since the faintest WDs have most likely evaporated from the Hyades, prior work provided only a lower limit to the cluster's WD age. Our result demonstrates the power of the bright WD technique for deriving ages and further demonstrates complete age consistency between WD cooling and MSTO ages for seven out of seven clusters analyzed to date, ranging from 150 Myr to 4 Gyr.Item Orbit-Based Dynamical Models Of The Sombrero Galaxy (NGC 4594)(2011-09) Jardel, John R.; Gebhardt, Karl; Shen, Juntai T.; Fisher, David B.; Kormendy, John; Kinzler, Jeffry; Lauer, Tod R.; Richstone, Douglas; Gultekin, Kayhan; Jardel, John R.; Gebhardt, Karl; Kinzler, JeffryWe present axisymmetric, orbit-based models to study the central black hole (BH), stellarmass-to-light ratio (M/L), and dark matter (DM) halo of NGC 4594 (M104, the Sombrero Galaxy). For stellar kinematics, we use published high-resolution kinematics of the central region taken with the Hubble Space Telescope, newly obtained Gemini long-slit spectra of the major axis, and integral field kinematics from the Spectroscopic Areal Unit for Research on Optical Nebulae instrument. At large radii, we use globular cluster kinematics to trace the mass profile and apply extra leverage to recovering the DM halo parameters. We find a BH of mass M-center dot = (6.6 +/- 0.4) x 10(8) M-circle dot and determine the stellar M/L-I = 3.4 +/- 0.05 (uncertainties are the 68% confidence band marginalized over the other parameters). Our best-fit DM halo is a cored logarithmic model with asymptotic circular speed V-c = 376 +/- 12 km s(-1) and core radius r(c) = 4.7 +/- 0.6 kpc. The fraction of dark to total mass contained within the half-light radius is 0.52. Taking the bulge and disk components into account in our calculation of sigma(e) puts NGC 4594 squarely on the M-sigma relation. We also determine that NGC 4594 lies directly on the M-L relation.Item Testing the Asteroseismic Mass Scale Using Metal-Poor Stars Characterized With APOGEE and Kepler(2014-04) Epstein, Courtney R.; Elsworth, Yvonne P.; Johnson, Jennifer A.; Shetrone, Matthew; Mosser, Benoit; Hekker, Saskia; Tayar, Jamie; Harding, Paul; Pinsonneault, Marc; Aguirre, Victor Silva; Basu, Sarbani; Beers, Timothy C.; Bizyaev, Dmitry; Bedding, Timothy R.; Chaplin, William J.; Frinchaboy, Peter M.; Garcia, Rafael A.; Perez, Ana E. Garcia; Hearty, Fred R.; Huber, Daniel; Ivans, Inese I.; Majewski, Steven R.; Mathur, Savita; Nidever, David; Serenelli, Aldo; Schiavon, Ricardo P.; Schneider, Donald P.; Schoenrichi, Ralph; Sobeck, Jennifer S.; Stassun, Keivan G.; Stello, Dennis; Zasowski, Gail; Shetrone, MatthewFundamental stellar properties, such as mass, radius, and age, can be inferred using asteroseismology. Cool stars with convective envelopes have turbulent motions that can stochastically drive and damp pulsations. The properties of the oscillation frequency power spectrum can be tied to mass and radius through solar-scaled asteroseismic relations. Stellar properties derived using these scaling relations need verification over a range of metallicities. Because the age and mass of halo stars are well-constrained by astrophysical priors, they provide an independent, empirical check on asteroseismic mass estimates in the low-metallicity regime. We identify nine metal-poor red giants (including six stars that are kinematically associated with the halo) from a sample observed by both the Kepler space telescope and the Sloan Digital Sky Survey-III APOGEE spectroscopic survey. We compare masses inferred using asteroseismology to those expected for halo and thick-disk stars. Although our sample is small, standard scaling relations, combined with asteroseismic parameters from the APOKASC Catalog, produce masses that are systematically higher ((Delta M) = 0.17 +/- 0.05 M-circle dot) than astrophysical expectations. The magnitude of the mass discrepancy is reduced by known theoretical corrections to the measured large frequency separation scaling relationship. Using alternative methods for measuring asteroseismic parameters induces systematic shifts at the 0.04 M-circle dot level. We also compare published asteroseismic analyses with scaling relationship masses to examine the impact of using the frequency of maximum power as a constraint. Upcoming APOKASC observations will provide a larger sample of similar to 100 metal-poor stars, important for detailed asteroseismic characterization of Galactic stellar populations.Item To Stack Or Not To Stack: Spectral Energy Distribution Properties Of Ly Alpha-Emitting Galaxies At Z=2.1(2014-03) Vargas, Carlos J.; Bish, Hannah; Acquaviva, Viviana; Gawiser, Eric; Finkelstein, Steven L.; Ciardullo, Robin; Ashby, Matthew L. N.; Feldmeier, John; Ferguson, Henry; Gronwall, Caryl; Guaita, Lucia; Hagen, Alex; Koekemoer, Anton; Kurczynski, Peter; Newman, Jeffrey A.; Padilla, Nelson; Finkelstein, Steven L.We use the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS) GOODS-S multi-wavelength catalog to identify counterparts for 20 Ly alpha emitting (LAE) galaxies at z = 2.1. We build several types of stacked spectral energy distributions (SEDs) of these objects. We combine photometry to form average and median flux-stacked SEDs, and postage-stamp images to form average and median image-stacked SEDs. We also introduce scaled flux stacks that eliminate the influence of variation in overall brightness. We use the SED fitting code SpeedyMC to constrain the physical properties of individual objects and stacks. Our LAEs at z = 2.1 have stellar masses ranging from 2 x 10(7) M-circle dot to 8 x 10(9) M-circle dot (median = 3 x 10(8) M-circle dot), ages ranging from 4 Myr to 500 Myr (median = 100 Myr), and E(B - V) between 0.02 and 0.24 (median = 0.12). Although still low, this represents significantly more dust reddening than has been reported for LAEs at higher redshifts. We do not observe strong correlations between Ly alpha equivalent width (EW) and age or E(B - V). The Ly alpha radiative transfer (q) factors of our sample are predominantly close to one and do not correlate strongly with EW or E(B - V). The absence of strong correlations with EW or q implies that Ly alpha radiative transfer is highly anisotropic and/or prevents Ly alpha photons from scattering in dusty regions. The SED parameters of the flux stacks match the average and median values of the individual objects, with the flux-scaled median SED performing best with uncertainties reduced by a factor of two. Median image-stacked SEDs provide a poor representation of the median individual object, and none of the stacking methods capture the large dispersion of LAE properties.Item the UV Continuum of Z > 1 Star-forming Galaxies in the Hubble Ultraviolet Ultradeep Field(2014-09) Kurczynski, Peter; Gawiser, Eric; Rafelski, Marc; Teplitz, Harry I.; Acquaviva, Viviana; Brown, Thomas M.; Coe, Dan; de Mello, Duilia F.; Finkelstein, Steven L.; Grogin, Norman A.; Koekemoer, Anton M.; Lee, Kyoung-Soo; Scarlata, Claudia; Siana, Brian D.; Finkelstein, Steven L.We estimate the UV continuum slope, beta, for 923 galaxies in the range 1 < z < 8 in the Hubble Ultradeep Field (HUDF). These data include 460 galaxies at 1 < z < 2 down to an absolute magnitude M-UV = -14(similar to 0.006L(z=1)(*); 0.02L(z=0)(*)), comparable to dwarf galaxies in the local universe. We combine deep HST/UVIS photometry in F225W, F275W, F336W wavebands (UVUDF) with recent data from HST/WFC3/IR (HUDF12). Galaxies in the range 1 < z < 2 are significantly bluer than local dwarf galaxies. We find theirmean (median) values (beta)= -1.382(-1.830)+/- 0.002 (random)+/- 0.1 (systematic). We find comparable scatter in beta (standard deviation = 0.43) to local dwarf galaxies and 30% larger scatter than z > 2 galaxies. We study the trends of beta with redshift and absolute magnitude for binned sub-samples and find a modest color-magnitude relation, d beta/dM= -0.11 +/- 0.01, and no evolution in d beta/dM with redshift. A modest increase in dust reddening with redshift and luminosity, Delta E(B -V) similar to 0.1, and a comparable increase in the dispersion of dust reddening atz < 2, appears likely to explain the observed trends. At z > 2, we find trends that are consistent with previous works; combining our data with the literature in the range 1 < z < 8, we find a color evolution with redshift, d beta/dz=-0.09 +/- 0.01 for low luminosity (0.05 L*z=3), and d beta/dz = -0.06 +/- 0.01 for medium luminosity (0.25 L-z=3(*)) galaxies.