150 research outputs found
Galaxy Quenching from Cosmic Web Detachment
We propose the Cosmic Web Detachment (CWD) model, a framework to interpret
the star-formation history of galaxies in a cosmological context. The CWD model
unifies several starvation mechanisms known to disrupt or stop star formation
into one single physical framework. Galaxies begin accreting star-forming gas
at early times via a network of primordial filaments, simply related to the
pattern of density fluctuations in the initial conditions. But when
shell-crossing occurs on intergalactic scales, this pattern is disrupted, and
the galaxy detaches from its primordial filaments, ending the accretion of cold
gas. We argue that CWD encompasses known external processes halting star
formation, such as harassment, strangulation and starvation. On top of these
external processes, internal feedback processes such as AGN contribute to stop
in star formation as well.
By explicitly pointing out the non-linear nature of CWD events we introduce a
simple formalism to identify CWD events in N-body simulations. With it we
reproduce and explain, in the context of CWD, several observations including
downsizing, the cosmic star formation rate history, the galaxy mass-color
diagram and the dependence of the fraction of red galaxies with mass and local
density.Comment: 20 pages, accepted for publication in OJA. High-res version:
http://skysrv.pha.jhu.edu/~miguel/Papers/CWD/ms.pd
A halo bias function measured deeply into voids without stochasticity
We study the relationship between dark-matter haloes and matter in the MIP
-body simulation ensemble, which allows precision measurements of this
relationship, even deeply into voids. What enables this is a lack of
discreteness, stochasticity, and exclusion, achieved by averaging over hundreds
of possible sets of initial small-scale modes, while holding fixed large-scale
modes that give the cosmic web. We find (i) that dark-matter-halo formation is
greatly suppressed in voids; there is an exponential downturn at low densities
in the otherwise power-law matter-to-halo density bias function. Thus, the
rarity of haloes in voids is akin to the rarity of the largest clusters, and
their abundance is quite sensitive to cosmological parameters. The exponential
downturn appears both in an excursion-set model, and in a model in which
fluctuations evolve in voids as in an open universe with an effective
proportional to a large-scale density. We also find that (ii) haloes
typically populate the average halo-density field in a super-Poisson way, i.e.
with a variance exceeding the mean; and (iii) the rank-order-Gaussianized halo
and dark-matter fields are impressively similar in Fourier space. We compare
both their power spectra and cross-correlation, supporting the conclusion that
one is roughly a strictly-increasing mapping of the other. The MIP ensemble
especially reveals how halo abundance varies with `environmental' quantities
beyond the local matter density; (iv) we find a visual suggestion that at fixed
matter density, filaments are more populated by haloes than clusters.Comment: Changed to version accepted by MNRA
Extremely Red Objects in the Field of QSO 1213-0017: A Galaxy Concentration at z=1.31
We have discovered a concentration of extremely red objects (EROs; R-K>6) in
the field of the z=2.69 quasar QSO 1213-0017 (UM 485), which is significantly
overabundant compared to the field ERO surface density. The optical/near-IR
colors of the EROs and numerous other red galaxies in this field are consistent
with elliptical galaxies at z=1-2. HST optical images for a subset of galaxies
show regular morphologies, most of them being disky or diffuse and without any
obvious evidence for interactions. Ground-based IR images show similar
morphologies, indicating any dust reddening in these objects is spatially
uniform. Optical spectroscopy with the W. M. Keck Telescope has found that four
of the red galaxies lie at =1.31, and a fifth lies in the foreground at
z=1.20. Of the =1.31 galaxies, one is a reddened AGN while the remaining
three have rest-frame UV absorption-line spectra characteristic of old (few
Gyr) stellar populations, similar to the old red galaxy LBDS 53W091 at z=1.55.
Including the MgII absorber seen in the QSO spectrum, we find five galaxies at
=1.31 spread over 1.5 h_50^{-1} Mpc on the sky. These results suggest we
have discovered a coherent structure of old galaxies at high-redshift, possibly
associated with a massive galaxy cluster.Comment: 37 pages including 11 Postscript figures. To appear in the June 2000
issue of the Astronomical Journa
The Evolution of Early-Type Galaxies in Distant Clusters
We present results from an optical-IR photometric study of early-type
galaxies in 19 galaxy clusters out to z=0.9. The galaxy sample is selected on
the basis of morphologies determined from HST WFPC2 images, and is
photometrically defined in the K-band to minimize redshift-dependent selection
biases. The optical-IR colors of the early-type cluster galaxies become bluer
with increasing redshift in a manner consistent with the passive evolution of
an old stellar population formed at an early cosmic epoch. The degree of color
evolution is similar for clusters at similar redshift, and does not depend
strongly on the optical richness or X-ray luminosity of the cluster, suggesting
that the history of early-type galaxies is relatively insensitive to
environment. The slope of the color-magnitude relationship shows no significant
change out to z=0.9, providing evidence that it arises from a correlation
between galaxy mass and metallicity, not age. Finally, the intrinsic scatter in
the optical-IR colors is small and nearly constant with redshift, indicating
that the majority of giant, early-type galaxies in clusters share a common star
formation history, with little perturbation due to uncorrelated episodes of
later star formation. Taken together, our results are consistent with models in
which most early-type galaxies in rich clusters are old, formed the majority of
their stars at high redshift in a well-synchronized fashion, and evolved
quiescently thereafter.Comment: 55 pages, 24 figures, uses AASTeX. Accepted for publication in The
Astrophysical Journa
Optical and Near-Infrared Photometry of Distant Galaxy Clusters
We present optical and near-infrared photometry of 45 clusters of galaxies at
0.1 < z < 1.3. Galaxy catalogs in each cluster were defined at the longest
wavelenth available, generally the K-band, down to approximately two magnitudes
below M*. We include finding chart images of the band used for catalog
definition. The photometry has been used in previously published papers to
examine the origin and evolution of galaxies in distant clusters.Comment: Accepted for publication in The Astrophysical Journal Supplement. 232
pages including 43 figures. Tables in ascii format to be electronically
available from the Ap
Serine / threonine protein phosphatase 5 (PP5) participates in the regulation of glucocorticoid receptor nucleocytoplasmic shuttling
BACKGROUND: In most cells glucocorticoid receptors (GR) reside predominately in the cytoplasm. Upon hormone binding, the GR translocates into the nucleus, where the hormone-activated GR-complex regulates the transcription of GR-responsive genes. Serine/threonine protein phosphatase type 5 (PP5) associates with the GR-heat-shock protein-90 complex, and the suppression of PP5 expression with ISIS 15534 stimulates the activity of GR-responsive reporter plasmids, without affecting the binding of hormone to the GR. RESULTS: To further characterize the mechanism by which PP5 affects GR-induced gene expression, we employed immunofluorescence microscopy to track the movement of a GR-green fluorescent fusion protein (GR-GFP) that retained hormone binding, nuclear translocation activity and specific DNA binding activity, but is incapable of transactivation. In the absence of glucocorticoids, GR-GFP localized mainly in the cytoplasm. Treatment with dexamethasone results in the efficient translocation of GR-GFPs into the nucleus. The nuclear accumulation of GR-GFP, without the addition of glucocorticoids, was also observed when the expression of PP5 was suppressed by treatment with ISIS 15534. In contrast, ISIS 15534 treatment had no apparent effect on calcium induced nuclear translocation of NFAT-GFP. CONCLUSION: These studies suggest that PP5 participates in the regulation of glucocorticoid receptor nucleocytoplasmic shuttling, and that the GR-induced transcriptional activity observed when the expression of PP5 is suppressed by treatment with ISIS 15534 results from the nuclear accumulation of GR in a form that is capable of binding DNA yet still requires agonist to elicit maximal transcriptional activation
Update on Streptococcus suis Research and Prevention in the Era of Antimicrobial Restriction: 4th International Workshop on S. suis.
Streptococcus suis is a swine pathogen and a zoonotic agent afflicting people in close contact with infected pigs or pork meat. Sporadic cases of human infections have been reported worldwide. In addition, S. suis outbreaks emerged in Asia, making this bacterium a primary health concern in this part of the globe. In pigs, S. suis disease results in decreased performance and increased mortality, which have a significant economic impact on swine production worldwide. Facing the new regulations in preventive use of antimicrobials in livestock and lack of effective vaccines, control of S. suis infections is worrisome. Increasing and sharing of knowledge on this pathogen is of utmost importance. As such, the pathogenesis and epidemiology of the infection, antimicrobial resistance, progress on diagnosis, prevention, and control were among the topics discussed during the 4th International Workshop on Streptococcus suis (held in Montreal, Canada, June 2019). This review gathers together recent findings on this important pathogen from lectures performed by lead researchers from several countries including Australia, Canada, France, Germany, Japan, Spain, Thailand, The Netherlands, UK, and USA. Finally, policies and recommendations for the manufacture, quality control, and use of inactivated autogenous vaccines are addressed to advance this important field in veterinary medicine
Straightening the Density-Displacement Relation with a Logarithmic Transform
We investigate the use of a logarithmic density variable in estimating the
Lagrangian displacement field, motivated by the success of a logarithmic
transformation in restoring information to the matter power spectrum. The
logarithmic relation is an extension of the linear relation, motivated by the
continuity equation, in which the density field is assumed to be proportional
to the divergence of the displacement field; we compare the linear and
logarithmic relations by measuring both of these fields directly in a
cosmological N-body simulation. The relative success of the logarithmic and
linear relations depends on the scale at which the density field is smoothed.
Thus we explore several ways of measuring the density field, including
Cloud-In-Cell smoothing, adaptive smoothing, and the (scale-independent)
Delaunay tessellation, and we use both a Fourier space and a geometrical
tessellation approach to measuring the divergence. We find that the relation
between the divergence of the displacement field and the density is
significantly tighter with a logarithmic density variable, especially at low
redshifts and for very small (~2 Mpc/h) smoothing scales. We find that the
grid-based methods are more reliable than the tessellation-based method of
calculating both the density and the divergence fields, though in both cases
the logarithmic relation works better in the appropriate regime, which
corresponds to nonlinear scales for the grid-based methods and low densities
for the tessellation-based method.Comment: 6 pages, 3 figures, accepted to Ap
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