2,035 research outputs found
Moyo Vol. IV N 1
Gilmore, Seth. A Note From Our Fearless Leader . 3.
Aufrance, Jeremy. Oral Sects: A Look at Denison\u27s Music Scene . 4.
Blake, Ben. Pay Attention! . 9.
Russell, Mark. Above & Below: Unearthing the Denison Underground . 10.
Gilmore, Seth. The Death of Cooties . 12.
Christie, Carey. Summer Whoroscopes: Something for Every Sinner . 19.
Mathews, Peter Edward. Sankofa: The Africa Inside Us All . 20.
Perry, Andrea. Taking it Off: Denison\u27s Hidden history De-robed . 22.
Clamurro, William H. Sexual Deviance: A Clamurrian Analysis . 24.
Trabert, Heather. Get Out! (But Kindly Leave Your Wallets Behind) . 26
Moyo Vol. III N 1
Boyden, John and Rich Vanderklok. Are You a $nob? . 2.
Herman, James. River Phoenix: A Final Conversation . 4.
Blake, Ben. Arbor Vitae Victories: Other Crafty Everyday Uses For Those Inconspicuous Little Trees . 9.
Fischesser, S. Separate But Unequal: A View of Denison\u27s Black Orientation . 10.
Gilmore, Seth. Evil Upheaval: The Reforming of Organized Religion... in Granville .; Boyden, John. “Reaching Out & Talking Dirty (When Touching Turns to Touch Tones)”. 20.
Vanderklok, Rich. Gen-X Angst . 24.
Driscoll, Julie. Bang! Thump (Getting A Taste For The Meat Processing Industry). 25.
Stillman, Lisa. The Bare Facts: An Exposé on Public Nudity . 26.
Endicott, Josh. Frames . 29.
Emmons, Alex. Frames . 29.
Emmons, Alex. Untitled. 11.
Bussan, Dave. Bull Session With a Former Editor On Denison\u27s Sacred Cow . 30.
Webb, Aaron. Color Blind: From Diversity Adversity to Racial Rapport . 33.
Archer, Troy Color Blind: From Diversity Adversity to Racial Rapport . 33
The two-phase formation history of spiral galaxies traced by the cosmic evolution of the bar fraction
We study the evolution of galactic bars and the link with disk and spheroid
formation in a sample of zoom-in cosmological simulations. Our simulation
sample focuses on galaxies with present-day stellar masses in the 10^10-10^11
Msun range, in field and loose group environments, with a broad variety of mass
growth histories. In our models, bars are almost absent from the progenitors of
present-day spirals at z>1.5, and they remain rare and generally too weak to be
observable down to z~1. After this characteristic epoch, the fractions of
observable and strong bars raise rapidly, bars being present in 80% of spiral
galaxies and easily observable in two thirds of these at z<0.5. This is
quantitatively consistent with the redshift evolution of the observed bar
fraction. Our models predict that the decrease in the bar fraction with
increasing redshift should continue with a fraction of observable bars <10-15%
in disk galaxies at z>1. Our models also predict later bar formation in
lower-mass galaxies, in agreement with existing data. We find that the
characteristic epoch of bar formation, namely redshift z~0.8-1, corresponds to
the epoch at which today's spirals acquire their disk-dominated morphology. At
higher redshift, disks tend to be rapidly destroyed by mergers and
gravitational instabilities and rarely develop significant bars. The bar
formation epoch corresponds to the transition between an early "violent" phase
of spiral galaxy formation at z>1 and a late "secular" phase at z<0.8. In the
secular phase, the presence of bars substantially contributes to the growth of
the bulge, but the bulge mass budget remains statistically dominated by the
contribution of mergers, interactions and disk instabilities at high redshift.
Early bars at z>1 are often short-lived, while most of the bars formed at z<1
persist down to z=0, late cosmological gas infall being necessary to maintain
some of them.Comment: 15 pages, 15 figures, ApJ accepte
Kinematical and chemical vertical structure of the Galactic thick disk I. Thick disk kinematics
The variation of the kinematical properties of the Galactic thick disk with
Galactic height Z are studied by means of 412 red giants observed in the
direction of the south Galactic pole up to 4.5 kpc from the plane. We confirm
the non-null mean radial motion toward the Galactic anticenter found by other
authors, but we find that it changes sign at |Z|=3 kpc, and the proposed inward
motion of the LSR alone cannot explain these observations. The rotational
velocity decreases with |Z| by -30 km/s/kpc, but the data are better
represented by a power-law with index 1.25, similar to that proposed from the
analysis of SDSS data. All the velocity dispersions increase with |Z|, but the
vertical gradients are small. The dispersions grow proportionally, with no
significant variation of the anisotropy. The ratio sigma_U/sigma_W=2 suggests
that the thick disk could have formed from a low-latitude merging event. The
vertex deviation increases with Galactic height, reaching ~20 degrees at
|Z|=3.5 kpc. The tilt angle also increases, and the orientation of the
ellipsoid in the radial-vertical plane is constantly intermediate between the
alignment with the cylindrical and the spherical coordinate systems. The tilt
angle at |Z|=2 kpc coincides with the expectations of MOND, but an extension of
the calculations to higher |Z| is required to perform a conclusive test.
Finally, between 2.5 and 3.5 kpc we detect deviations from the linear trend of
many kinematical quantities, suggesting that some kinematical substructure
could be present.Comment: Accepted for publication in Ap
Dynamics of barred galaxies: effects of disk height
We study dynamics of bars in models of disk galaxies embeded in realistic
dark matter halos. We find that disk thickness plays an important, if not
dominant, role in the evolution and structure of the bars. We also make
extensive numerical tests of different N-body codes used to study bar dynamics.
Models with thick disks typically used in this type of modeling
(height-to-length ratio hz/Rd=0.2) produce slowly rotating, and very long,
bars. In contrast, more realistic thin disks with the same parameters as in our
Galaxy (hz/Rd= 0.1) produce bars with normal length Rbar approx R_d, which
rotate quickly with the ratio of the corotation radius to the bar radius
1.2-1.4 compatible with observations. Bars in these models do not show a
tendency to slow down, and may lose as little as 2-3 percent of their angular
momentum due to dynamical friction with the dark matter over cosmological time.
We attribute the differences between the models to a combined effect of high
phase-space density and smaller Jeans mass in the thin disk models, which
result in the formation of a dense central bulge. Special attention is paid to
numerical effects such as the accuracy of orbital integration, force and mass
resolution. Using three N-body codes -- Gadget, ART, and Pkdgrav -- we find
that numerical effects are very important and, if not carefully treated, may
produce incorrect and misleading results. Once the simulations are performed
with sufficiently small time-steps and with adequate force and mass resolution,
all the codes produce nearly the same results: we do not find any systematic
deviations between the results obtained with TREE codes (Gadget and Pkdgrav)
and with the Adaptive-Mesh-Refinement (ART) code.Comment: 15 pages, 14 plots, submitted to MNRA
The stellar population content of the thick disk and halo of the Milky Way analogue NGC 891
We present deep ACS images of 3 fields in the edge-on disk galaxy NGC 891,
which extend from the plane of the disk to 12 kpc, and out to 25 kpc along the
major axis. The photometry of individual stars reaches 2.5 magnitudes below the
tip of the RGB. We use the astrophotometric catalogue to probe the stellar
content and metallicity distribution across the thick disk and spheroid of NGC
891. The CMDs of thick disk and spheroid population are dominated by old RGB
stars with a wide range of metallicities, from a metal-poor tail at [Fe/H] ~
-2.4 dex, up to about half-solar metallicity. The peak of the MDF of the thick
disk is at -0.9 dex. The inner parts of the thick disk, within 14 kpc along the
major axis show no vertical colour/metallicity gradient. In the outer parts, a
mild vertical gradient of Delta(V-I)/Delta|Z| = 0.1 +/- 0.05 kpc^-1 is
detected. This gradient is however accounted for by the mixing with the metal
poor halo stars. No metallicity gradient along the major axis is present for
thick disk stars, but strong variations of about 0.35 dex around the mean of
[Fe/H] = -1.13 dex are found. The properties of the asymmetric MDFs of the
thick disk stars show no significant changes in both the radial and the
vertical directions. The stellar populations at solar cylinder-like distances
show strikingly different properties from those of the Galaxy, suggesting that
the accretion histories of both galaxies have been different. The spheroid
population shows remarkably uniform stellar population properties. The median
metallicity of the halo stellar population shows a shallow gradient from about
-1.15 dex in the inner parts to -1.27 dex at 24 kpc distance from the centre.
Similar to the thick disk stars, large variations around the mean relation are
present.Comment: 19 pages, 19 figures, accepted for publication in MNRA
Family Poverty Affects the Rate of Human Infant Brain Growth
Living in poverty places children at very high risk for problems across a variety of domains, including schooling, behavioral regulation, and health. Aspects of cognitive functioning, such as information processing, may underlie these kinds of problems. How might poverty affect the brain functions underlying these cognitive processes? Here, we address this question by observing and analyzing repeated measures of brain development of young children between five months and four years of age from economically diverse backgrounds (n = 77). In doing so, we have the opportunity to observe changes in brain growth as children begin to experience the effects of poverty. These children underwent MRI scanning, with subjects completing between 1 and 7 scans longitudinally. Two hundred and three MRI scans were divided into different tissue types using a novel image processing algorithm specifically designed to analyze brain data from young infants. Total gray, white, and cerebral (summation of total gray and white matter) volumes were examined along with volumes of the frontal, parietal, temporal, and occipital lobes. Infants from low-income families had lower volumes of gray matter, tissue critical for processing of information and execution of actions. These differences were found for both the frontal and parietal lobes. No differences were detected in white matter, temporal lobe volumes, or occipital lobe volumes. In addition, differences in brain growth were found to vary with socioeconomic status (SES), with children from lower-income households having slower trajectories of growth during infancy and early childhood. Volumetric differences were associated with the emergence of disruptive behavioral problems
Fermi Large Area Telescope Constraints on the Gamma-ray Opacity of the Universe
The Extragalactic Background Light (EBL) includes photons with wavelengths
from ultraviolet to infrared, which are effective at attenuating gamma rays
with energy above ~10 GeV during propagation from sources at cosmological
distances. This results in a redshift- and energy-dependent attenuation of the
gamma-ray flux of extragalactic sources such as blazars and Gamma-Ray Bursts
(GRBs). The Large Area Telescope onboard Fermi detects a sample of gamma-ray
blazars with redshift up to z~3, and GRBs with redshift up to z~4.3. Using
photons above 10 GeV collected by Fermi over more than one year of observations
for these sources, we investigate the effect of gamma-ray flux attenuation by
the EBL. We place upper limits on the gamma-ray opacity of the Universe at
various energies and redshifts, and compare this with predictions from
well-known EBL models. We find that an EBL intensity in the optical-ultraviolet
wavelengths as great as predicted by the "baseline" model of Stecker et al.
(2006) can be ruled out with high confidence.Comment: 42 pages, 12 figures, accepted version (24 Aug.2010) for publication
in ApJ; Contact authors: A. Bouvier, A. Chen, S. Raino, S. Razzaque, A.
Reimer, L.C. Reye
Formation of galaxies in {\Lambda}CDM cosmologies. I. The fine structure of disc galaxies
We present a detailed analysis of the global and fine structure of four
middle-mass disc galaxies obtained from simulations in a CDM scenario.
These objects have photometric D/T ratios in good agreement with those observed
for late-type spirals, as well as kinematic properties in agreement with the
observational Tully-Fisher relation. We identify the different dynamical
components at z=0 on the basis of both orbital parameters and the binding
energy of stars in the galaxy. In this way, we recognize a slowly rotating
centrally concentrated spheroid, and two disc components supported by rotation:
a thin disc with stars in nearly circular orbits, and a thick disc with orbital
parameters transitional between the thin disc and the spheroid. The spheroidal
component is composed mainly by old, metal-poor and {\alpha}-enhanced stars.
The distribution of metals in this component shows, however, a clear bimodality
with a low-metallicity peak, which could be related to a classical bulge, and a
high-metallicity peak, which could be related to a pseudo-bulge. The thin disc
appears in our simulations as the youngest and most metal-rich component. The
radial distribution of ages and colours in this component are U-shaped: the new
stars are forming in the inner regions, and then migrate through secular
processes. Finally, we also find a thick disc containing about 16% of the total
stellar mass and with properties that are intermediate between those of the
thin disc and the spheroid. Its low-metallicity stars are {\alpha}-enhanced
when compared to thin disc stars of the same metallicity. The structural
parameters (e.g., the scale height) of the simulated thick discs suggest that
such a component could result from the combination of different thickening
mechanisms that include merger-driven processes, but also long-lived internal
perturbations of the thin disc. [Abridged]Comment: 23 pages, 16 figures, accepted for publication in MNRAS, references
fixe
A review of elliptical and disc galaxy structure, and modern scaling laws
A century ago, in 1911 and 1913, Plummer and then Reynolds introduced their
models to describe the radial distribution of stars in `nebulae'. This article
reviews the progress since then, providing both an historical perspective and a
contemporary review of the stellar structure of bulges, discs and elliptical
galaxies. The quantification of galaxy nuclei, such as central mass deficits
and excess nuclear light, plus the structure of dark matter halos and cD galaxy
envelopes, are discussed. Issues pertaining to spiral galaxies including dust,
bulge-to-disc ratios, bulgeless galaxies, bars and the identification of
pseudobulges are also reviewed. An array of modern scaling relations involving
sizes, luminosities, surface brightnesses and stellar concentrations are
presented, many of which are shown to be curved. These 'redshift zero'
relations not only quantify the behavior and nature of galaxies in the Universe
today, but are the modern benchmark for evolutionary studies of galaxies,
whether based on observations, N-body-simulations or semi-analytical modelling.
For example, it is shown that some of the recently discovered compact
elliptical galaxies at 1.5 < z < 2.5 may be the bulges of modern disc galaxies.Comment: Condensed version (due to Contract) of an invited review article to
appear in "Planets, Stars and Stellar
Systems"(www.springer.com/astronomy/book/978-90-481-8818-5). 500+ references
incl. many somewhat forgotten, pioneer papers. Original submission to
Springer: 07-June-201
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