1,846 research outputs found
The DEEP2 Galaxy Redshift Survey: Clustering of Groups and Group Galaxies at z~1
We study the clustering properties of groups and of galaxies in groups in the
DEEP2 Galaxy Redshift Survey dataset at z~1. Four clustering measures are
presented: 1) the group correlation function for 460 groups with estimated
velocity dispersions of sigma>200 km/s, 2) the galaxy correlation for the full
galaxy sample, using a flux-limited sample of 9800 objects between 0.7<z<1.0,
3) the galaxy correlation for galaxies in groups, and 4) the group-galaxy
cross-correlation function. Using the observed number density and clustering
amplitude of the groups, the estimated minimum group dark matter halo mass is
M_min~6 10^12 h^-1 M_Sun for a flat LCDM cosmology. Groups are more clustered
than galaxies, with a relative bias of b=1.7 +/-0.04 on scales r_p=0.5-15
Mpc/h. Galaxies in groups are also more clustered than the full galaxy sample,
with a scale-dependent relative bias which falls from b~2.5 +/-0.3 at r_p=0.1
Mpc/h to b~1 +/-0.5 at r_p=10 Mpc/h. The correlation functions for all galaxies
and galaxies in groups can be fit by a power-law on scales r_p=0.05-20 Mpc/h.
We empirically measure the contribution to the projected correlation function
for galaxies in groups from a `one-halo' term and a `two-halo' term by counting
pairs of galaxies in the same or in different groups. The projected
cross-correlation between shows that red galaxies are more centrally
concentrated in groups than blue galaxies at z~1. DEEP2 galaxies in groups
appear to have a shallower radial distribution than that of mock galaxy
catalogs made from N-body simulations, which assume a central galaxy surrounded
by satellite galaxies with an NFW profile. We show that the clustering of
galaxies in groups can be used to place tighter constraints on the halo model
than can be gained from using the usual galaxy correlation function alone.Comment: 22 pages, 12 figures, in emulateapj format, accepted to ApJ, minor
changes made to match published versio
Quantum Confinement and Thickness-Dependent Electron Transport in Solution-Processed InâOâ Transistors
The dependence of charge carrier mobility on semiconductor channel thickness in field-effect transistors is a universal phenomenon that has been studied extensively for various families of materials. Surprisingly, analogous studies involving metal oxide semiconductors are relatively scarce. Here, spray-deposited In_{2}O_{3} layers are employed as the model semiconductor system to study the impact of layer thickness on quantum confinement and electron transport along the transistor channel. The results reveal an exponential increase of the in-plane electron mobility (”e) with increasing In2O3 thickness up to â10 nm, beyond which it plateaus at a maximum value of â35 cm^{2} V^{â1} s^{â1}. Optical spectroscopy measurements performed on In_{2}O_{3} layers reveal the emergence of quantum confinement for thickness <10 nm, which coincides with the thickness that ”e starts deteriorating. By combining two- and four-probe field-effect mobility measurements with high-resolution atomic force microscopy, it is shown that the reduction in ”e is attributed primarily to surface scattering. The study provides important guidelines for the design of next generation metal oxide thin-film transistors
The DEEP2 Galaxy Redshift Survey: The Voronoi-Delaunay Method Catalog of Galaxy Groups
We present a public catalog of galaxy groups constructed from the spectroscopic sample of galaxies in the fourth data release from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) Galaxy Redshift Survey, including the Extended Groth Strip (EGS). The catalog contains 1165 groups with two or more members in the EGS over the redshift range 0 0.6 in the rest of DEEP2. Twenty-five percent of EGS galaxies and fourteen percent of high-z DEEP2 galaxies are assigned to galaxy groups. The groups were detected using the Voronoi-Delaunay method (VDM) after it has been optimized on mock DEEP2 catalogs following similar methods to those employed in Gerke et al. In the optimization effort, we have taken particular care to ensure that the mock catalogs resemble the data as closely as possible, and we have fine-tuned our methods separately on mocks constructed for the EGS and the rest of DEEP2. We have also probed the effect of the assumed cosmology on our inferred group-finding efficiency by performing our optimization on three different mock catalogs with different background cosmologies, finding large differences in the group-finding success we can achieve for these different mocks. Using the mock catalog whose background cosmology is most consistent with current data, we estimate that the DEEP2 group catalog is 72% complete and 61% pure (74% and 67% for the EGS) and that the group finder correctly classifies 70% of galaxies that truly belong to groups, with an additional 46% of interloper galaxies contaminating the catalog (66% and 43% for the EGS). We also confirm that the VDM catalog reconstructs the abundance of galaxy groups with velocity dispersions above ~300 km s^(â1) to an accuracy better than the sample variance, and this successful reconstruction is not strongly dependent on cosmology. This makes the DEEP2 group catalog a promising probe of the growth of cosmic structure that can potentially be used for cosmological tests
Dissipationless Mergers of Elliptical Galaxies and the Evolution of the Fundamental Plane
We carry out numerical simulations of dissipationless major mergers of
elliptical galaxies using initial galaxy models that consist of a dark matter
halo and a stellar bulge with properties consistent with the observed
fundamental plane. By varying the density profile of the dark matter halo
(standard NFW versus adiabatically contracted NFW), the global stellar to dark
matter mass ratio, and the orbit of the merging galaxies, we are able to assess
the impact of each of these factors on the structure of the merger remnant. Our
results indicate that the properties of the remnant bulge depend primarily on
the angular momentum and energy of the orbit; for a cosmologically motivated
orbit, the effective radius and velocity dispersion of the remnant bulge remain
approximately on the fundamental plane. This indicates that the observed
properties of elliptical galaxies are consistent with significant growth via
late dissipationless mergers. We also find that the dark matter fraction within
the effective radius of our remnants increases after the merger, consistent
with the hypothesis that the tilt of the fundamental plane from the virial
theorem is due to a varying dark matter fraction as a function of galaxy mass.Comment: 14 pages, 6 figures; MNRAS, in press. Minor revisions, results from
an additional simulation adde
Betacyanins, major components in Opuntia red-purple fruits, protect against acetaminophen-induced acute liver failure
Acetaminophen (APAP) misuse or overdose is the most important cause of drug-induced acute liver failure. Overdoses of acetaminophen induce oxidative stress and liver injury by the electrophilic metabolite N-acetyl-pbenzoquinone imine (NAPQI). Plant-based medicine has been used for centuries against diseases or intoxications due to their biological activities. The aim of this study was to evaluate the therapeutic value of Opuntia robusta and Opuntia streptacantha fruit extracts against acetaminophen-induced liver damage and to identify the major biocomponents on them. Opuntia fruit extracts were obtained by peeling and squeezing each specie, followed by lyophilization. HPLC was used to characterize the extracts. The effect of the extracts against acetaminophen induced acute liver injury was evaluated both in vivo and in vitro using biochemical, molecular and histological determinations. The results showed that betacyanins are the main components in the analyzed Opuntia fruit extracts, with betanin as the highest concentration. Therapeutic treatments with Opuntia extracts reduced biochemical, molecular and histological markers of liver (in vivo) and hepatocyte (in vitro) injury. Opuntia extracts reduced the APAP-increased expression of the stress-related gene Gadd45b. Furthermore, Opuntia extracts exerted diverse effects on the antioxidant related genes Sod2, Gclc and Hmox1, independent of their ROSscavenging ability. Therefore, betacyanins as betanin from Opuntia robusta and Opuntia streptacantha fruits are promising nutraceutical compounds against oxidative liver damage
Machine-learning of atomic-scale properties based on physical principles
We briefly summarize the kernel regression approach, as used recently in
materials modelling, to fitting functions, particularly potential energy
surfaces, and highlight how the linear algebra framework can be used to both
predict and train from linear functionals of the potential energy, such as the
total energy and atomic forces. We then give a detailed account of the Smooth
Overlap of Atomic Positions (SOAP) representation and kernel, showing how it
arises from an abstract representation of smooth atomic densities, and how it
is related to several popular density-based representations of atomic
structure. We also discuss recent generalisations that allow fine control of
correlations between different atomic species, prediction and fitting of
tensorial properties, and also how to construct structural kernels---applicable
to comparing entire molecules or periodic systems---that go beyond an additive
combination of local environments
Galaxy clustering and projected density profiles as traced by satellites in photometric surveys: Methodology and luminosity dependence
We develop a new method which measures the projected density distribution
w_p(r_p)n of photometric galaxies surrounding a set of
spectroscopically-identified galaxies, and simultaneously the projected
correlation function w_p(r_p) between the two populations. In this method we
are able to divide the photometric galaxies into subsamples in luminosity
intervals when redshift information is unavailable, enabling us to measure
w_p(r_p)n and w_p(r_p) as a function of not only the luminosity of the
spectroscopic galaxy, but also that of the photometric galaxy. Extensive tests
show that our method can measure w_p(r_p) in a statistically unbiased way. The
accuracy of the measurement depends on the validity of the assumption in the
method that the foreground/background galaxies are randomly distributed and
thus uncorrelated with those galaxies of interest. Therefore, our method can be
applied to the cases where foreground/background galaxies are distributed in
large volumes, which is usually valid in real observations. We applied our
method to data from SDSS including a sample of 10^5 LRGs at z~0.4 and a sample
of about half a million galaxies at z~0.1, both of which are cross-correlated
with a deep photometric sample drawn from the SDSS. On large scales, the
relative bias factor of galaxies measured from w_p(r_p) at z~0.4 depends on
luminosity in a manner similar to what is found at z~0.1, which are usually
probed by autocorrelations of spectroscopic samples. On scales smaller than a
few Mpc and at both z~0.4 and z~0.1, the photometric galaxies of different
luminosities exhibit similar density profiles around spectroscopic galaxies at
fixed luminosity and redshift. This provides clear support for the assumption
commonly-adopted in HOD models that satellite galaxies of different
luminosities are distributed in a similar way, following the dark matter
distribution within their host halos.Comment: 38 pages, 12 figures, published in Ap
Reconstructing galaxy fundamental distributions and scaling relations from photometric redshift surveys. Applications to the SDSS early-type sample
Noisy distance estimates associated with photometric rather than
spectroscopic redshifts lead to a mis-estimate of the luminosities, and produce
a correlated mis-estimate of the sizes. We consider a sample of early-type
galaxies from the SDSS DR6 for which both spectroscopic and photometric
information is available, and apply the generalization of the V_max method to
correct for these biases. We show that our technique recovers the true
redshift, magnitude and size distributions, as well as the true size-luminosity
relation. We find that using only 10% of the spectroscopic information randomly
spaced in our catalog is sufficient for the reconstructions to be accurate
within about 3%, when the photometric redshift error is dz = 0.038. We then
address the problem of extending our method to deep redshift catalogs, where
only photometric information is available. In addition to the specific
applications outlined here, our technique impacts a broader range of studies,
when at least one distance-dependent quantity is involved. It is particularly
relevant for the next generation of surveys, some of which will only have
photometric information.Comment: 14 pages, 12 figures, 1 table, new section 3.1 and appendix added,
MNRAS in pres
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