483 research outputs found
A Candidate Brightest Proto-Cluster Galaxy at z = 3.03
We report the discovery of a very bright (m_R = 22.2) Lyman break galaxy at z
= 3.03 that appears to be a massive system in a late stage of merging. Deep
imaging reveals multiple peaks in the brightness profile with angular
separations of ~0.''8 (~25 h^-1 kpc comoving). In addition, high
signal-to-noise ratio rest-frame UV spectroscopy shows evidence for ~5
components based on stellar photospheric and ISM absorption lines with a
velocity dispersion of sigma ~460 km s^-1 for the three strongest components.
Both the dynamics and high luminosity, as well as our analysis of a LCDM
numerical simulation, suggest a very massive system with halo mass M ~ 10^13
M_solar. The simulation finds that all halos at z = 3 of this mass contain
sub-halos in agreement with the properties of these observed components and
that such systems typically evolve into M ~ 10^14 M_solar halos in groups and
clusters by z = 0. This discovery provides a rare opportunity to study the
properties and individual components of z ~ 3 systems that are likely to be the
progenitors to brightest cluster galaxies.Comment: 14 pages, 3 figures, submitted to ApJ Letter
Orbiting Circum-galactic Gas as a Signature of Cosmological Accretion
We use cosmological SPH simulations to study the kinematic signatures of cool
gas accretion onto a pair of well-resolved galaxy halos. Cold-flow streams and
gas-rich mergers produce a circum-galactic component of cool gas that generally
orbits with high angular momentum about the galaxy halo before falling in to
build the disk. This signature of cosmological accretion should be observable
using background-object absorption line studies as features that are offset
from the galaxy's systemic velocity by ~100 km/s. Accreted gas typically
co-rotates with the central disk in the form of a warped, extended cold flow
disk, such that the observed velocity offset is in the same direction as galaxy
rotation, appearing in sight lines that avoid the galactic poles. This
prediction provides a means to observationally distinguish accreted gas from
outflow gas: the accreted gas will show large one-sided velocity offsets in
absorption line studies while radial/bi-conical outflows will not (except
possibly in special polar projections). This rotation signature has already
been seen in studies of intermediate redshift galaxy-absorber pairs; we suggest
that these observations may be among the first to provide indirect
observational evidence for cold accretion onto galactic halos. Cold mode halo
gas typically has ~3-5 times more specific angular momentum than the dark
matter. The associated cold mode disk configurations are likely related to
extended HI/XUV disks seen around galaxies in the local universe. The fraction
of galaxies with extended cold flow disks and associated offset absorption-line
gas should decrease around bright galaxies at low redshift, as cold mode
accretion dies out.Comment: 15 pages, 9 figures, edited to match published version. Includes
expanded discussion, with primary results unchange
Stealth Galaxies in the Halo of the Milky Way
We predict that there is a population of low-luminosity dwarf galaxies
orbiting within the halo of the Milky Way that have surface brightnesses low
enough to have escaped detection in star-count surveys. The overall count of
stealth galaxies is sensitive to the presence (or lack) of a low-mass threshold
in galaxy formation. These systems have luminosities and stellar velocity
dispersions that are similar to those of known ultrafaint dwarf galaxies but
they have more extended stellar distributions (half light radii greater than
about 100 pc) because they inhabit dark subhalos that are slightly less massive
than their higher surface brightness counterparts. As a result, the typical
peak surface brightness is fainter than 30 mag per square arcsec. One
implication is that the inferred common mass scale for Milky Way dwarfs may be
an artifact of selection bias. If there is no sharp threshold in galaxy
formation at low halo mass, then ultrafaint galaxies like Segue 1 represent the
high-mass, early forming tail of a much larger population of objects that could
number in the hundreds and have typical peak circular velocities of about 8
km/s and masses within 300 pc of about 5 million solar masses. Alternatively,
if we impose a low-mass threshold in galaxy formation in order to explain the
unexpectedly high densities of the ultrafaint dwarfs, then we expect only a
handful of stealth galaxies in the halo of the Milky Way. A complete census of
these objects will require deeper sky surveys, 30m-class follow-up telescopes,
and more refined methods to identify extended, self-bound groupings of stars in
the halo.Comment: 12 pages, 7 figures, accepted by ApJ. Several crucial references
added and the discussion has been expanded. Conclusions are unchanged
Exposure-Response Estimates for Diesel Engine Exhaust and Lung Cancer Mortality Based on Data from Three Occupational Cohorts
Background: Diesel engine exhaust (DEE) has recently been classified as a known human carcinogen. Objective: We derived a meta-exposure–response curve (ERC) for DEE and lung cancer mortality and estimated lifetime excess risks (ELRs) of lung cancer mortality based on assumed occupational and environmental exposure scenarios. Methods: We conducted a meta-regression of lung cancer mortality and cumulative exposure to elemental carbon (EC), a proxy measure of DEE, based on relative risk (RR) estimates reported by three large occupational cohort studies (including two studies of workers in the trucking industry and one study of miners). Based on the derived risk function, we calculated ELRs for several lifetime occupational and environmental exposure scenarios and also calculated the fractions of annual lung cancer deaths attributable to DEE. Results: We estimated a lnRR of 0.00098 (95% CI: 0.00055, 0.0014) for lung cancer mortality with each 1-μg/m3-year increase in cumulative EC based on a linear meta-regression model. Corresponding lnRRs for the individual studies ranged from 0.00061 to 0.0012. Estimated numbers of excess lung cancer deaths through 80 years of age for lifetime occupational exposures of 1, 10, and 25 μg/m3 EC were 17, 200, and 689 per 10,000, respectively. For lifetime environmental exposure to 0.8 μg/m3 EC, we estimated 21 excess lung cancer deaths per 10,000. Based on broad assumptions regarding past occupational and environmental exposures, we estimated that approximately 6% of annual lung cancer deaths may be due to DEE exposure. Conclusions: Combined data from three U.S. occupational cohort studies suggest that DEE at levels common in the workplace and in outdoor air appear to pose substantial excess lifetime risks of lung cancer, above the usually acceptable limits in the United States and Europe, which are generally set at 1/1,000 and 1/100,000 based on lifetime exposure for the occupational and general population, respectively. Citation: Vermeulen R, Silverman DT, Garshick E, Vlaanderen J, Portengen L, Steenland K. 2014. Exposure-response estimates for diesel engine exhaust and lung cancer mortality based on data from three occupational cohorts. Environ Health Perspect 122:172–177; http://dx.doi.org/10.1289/ehp.130688
A central role for dityrosine crosslinking of Amyloid-β in Alzheimer’s disease
Background
Alzheimer’s disease (AD) is characterized by the deposition of insoluble amyloid plaques in the neuropil composed of highly stable, self-assembled Amyloid-beta (Aβ) fibrils. Copper has been implicated to play a role in Alzheimer’s disease. Dimers of Aβ have been isolated from AD brain and have been shown to be neurotoxic.
Results
We have investigated the formation of dityrosine cross-links in Aβ42 formed by covalent ortho-ortho coupling of two tyrosine residues under conditions of oxidative stress with elevated copper and shown that dityrosine can be formed in vitro in Aβ oligomers and fibrils and that these links further stabilize the fibrils. Dityrosine crosslinking was present in internalized Aβ in cell cultures treated with oligomeric Aβ42 using a specific antibody for dityrosine by immunogold labeling transmission electron microscopy. Results also revealed the prevalence of dityrosine crosslinks in amyloid plaques in brain tissue and in cerebrospinal fluid from AD patients.
Conclusions
Aβ dimers may be stabilized by dityrosine crosslinking. These results indicate that dityrosine cross-links may play an important role in the pathogenesis of Alzheimer’s disease and can be generated by reactive oxygen species catalyzed by Cu2+ ions. The observation of increased Aβ and dityrosine in CSF from AD patients suggests that this could be used as a potential biomarker of oxidative stress in AD
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