13,352 research outputs found
Weak lensing evidence for a filament between A222/A223
We present a weak lensing analysis and comparison to optical and X-ray maps
of the close pair of massive clusters A222/223. Indications for a filamentary
connection between the clusters are found and discussed.Comment: 6 pages, 1 figure. To appear in Proc. IAU Colloquium 195: Outskirts
of Galaxy Clusters - Intense Life in the Suburbs. Version with higher
resolution available at
http://www.astro.uni-bonn.de/~dietrich/torino_proc.ps.g
GaBoDS: The Garching-Bonn Deep Survey VIII. Lyman-break galaxies in the ESO Deep Public Survey
Aims. The clustering properties of a large sample of U-dropouts are
investigated and compared to very precise results for B-dropouts from other
studies to identify a possible evolution from z=4 to z=3. Methods. A population
of ~8800 candidates for star-forming galaxies at z=3 is selected via the
well-known Lyman-break technique from a large optical multicolour survey (the
ESO Deep Public Survey). The selection efficiency, contamination rate, and
redshift distribution of this population are investigated by means of extensive
simulations. Photometric redshifts are estimated for every Lyman-break galaxy
(LBG) candidate from its UBVRI photometry yielding an empirical redshift
distribution. The measured angular correlation function is deprojected and the
resulting spatial correlation lengths and slopes of the correlation function of
different subsamples are compared to previous studies. Results. By fitting a
simple power law to the correlation function we do not see an evolution in the
correlation length and the slope from other studies at z=4 to our study at z=3.
In particular, the dependence of the slope on UV-luminosity similar to that
recently detected for a sample of B-dropouts is confirmed also for our
U-dropouts. For the first time number statistics for U-dropouts are sufficient
to clearly detect a departure from a pure power law on small scales down to ~2"
reported by other groups for B-dropouts.Comment: 10 pages, 11 figures, accepted by A&A, full resolution version
available at http://www.astro.uni-bonn.de/~hendrik/5880.pd
First-order layering and critical wetting transitions in non-additive hard sphere mixtures
Using fundamental-measure density functional theory we investigate entropic
wetting in an asymmetric binary mixture of hard spheres with positive
non-additivity. We consider a general planar hard wall, where preferential
adsorption is induced by a difference in closest approach of the different
species and the wall. Close to bulk fluid-fluid coexistence the phase rich in
the minority component adsorbs either through a series of first-order layering
transitions, where an increasing number of liquid layers adsorbs sequentially,
or via a critical wetting transition, where a thick film grows continuously.Comment: 4 pages, 4 figure
Quantifying Tensions between CMB and Distance Datasets in Models with Free Curvature or Lensing Amplitude
Recent measurements of the Cosmic Microwave Background (CMB) by the Planck
Collaboration have produced arguably the most powerful observational evidence
in support of the standard model of cosmology, i.e. the spatially flat
CDM paradigm. In this work, we perform model selection tests to
examine whether the base CMB temperature and large scale polarization
anisotropy data from Planck 2015 (P15) prefer any of eight commonly used
one-parameter model extensions with respect to flat CDM. We find a
clear preference for models with free curvature, , or free
amplitude of the CMB lensing potential, . We also further develop
statistical tools to measure tension between datasets. We use a Gaussianization
scheme to compute tensions directly from the posterior samples using an
entropy-based method, the surprise, as well as a calibrated evidence ratio
presented here for the first time. We then proceed to investigate the
consistency between the base P15~CMB data and six other CMB and distance
datasets. In flat CDM we find a tension between the base
P15~CMB data and a distance ladder measurement, whereas the former are
consistent with the other datasets. In the curved CDM model we find
significant tensions in most of the cases, arising from the well-known low
power of the low- multipoles of the CMB data. In the flat CDM
model, however, all datasets are consistent with the base
P15~CMB observations except for the CMB lensing measurement, which remains in
significant tension. This tension is driven by the increased power of the CMB
lensing potential derived from the base P15~CMB constraints in both models,
pointing at either potentially unresolved systematic effects or the need for
new physics beyond the standard flat CDM model.Comment: 16 pages, 8 figures, 6 table
Effects of boundary conditions on the critical spanning probability
The fractions of samples spanning a lattice at its percolation threshold are
found by computer simulation of random site-percolation in two- and
three-dimensional hypercubic lattices using different boundary conditions. As a
byproduct we find in the cubic lattice.Comment: 8 pages Latex, To appear in Int. J. Mod. Phys.
Pearling instability of nanoscale fluid flow confined to a chemical channel
We investigate the flow of a nano-scale incompressible ridge of
low-volatility liquid along a "chemical channel": a long, straight, and
completely wetting stripe embedded in a planar substrate, and sandwiched
between two extended less wetting solid regions. Molecular dynamics
simulations, a simple long-wavelength approximation, and a full stability
analysis based on the Stokes equations are used, and give qualitatively
consistent results. While thin liquid ridges are stable both statically and
during flow, a (linear) pearling instability develops if the thickness of the
ridge exceeds half of the width of the channel. In the flowing case periodic
bulges propagate along the channel and subsequently merge due to nonlinear
effects. However, the ridge does not break up even when the flow is unstable,
and the qualitative behavior is unchanged even when the fluid can spill over
onto a partially wetting exterior solid region.Comment: 17 pages, 12 figures, submitted to Physics of Fluids, fixed equation
numbering after Eq. (17
High Redshift Quasars and Star Formation in the Early Universe
In order to derive information on the star formation history in the early
universe we observed 6 high-redshift (z=3.4) quasars in the near-infrared to
measure the relative iron and \mgii emission strengths. A detailed comparison
of the resulting spectra with those of low-redshift quasars show essentially
the same FeII/MgII emission ratios and very similar continuum and line spectral
properties, indicating a lack of evolution of the relative iron to magnesium
abundance of the gas since z=3.4 in bright quasars. On the basis of current
chemical evolution scenarios of galaxies, where magnesium is produced in
massive stars ending in type II SNe, while iron is formed predominantly in SNe
of type Ia with a delay of ~1 Gyr and assuming as cosmological parameters H_o =
72 km/s Mpc, Omega_M = 0.3, and Omega_Lambda = 0.7$, we conclude that major
star formation activity in the host galaxies of our z=3.4 quasars must have
started already at an epoch corresponding to z_f ~= 10, when the age of the
universe was less than 0.5 Gyrs.Comment: 29 pages, 5 figures, ApJ in pres
Implications of Quasar Black Hole Masses at High Redshifts
We investigated a sample of 15 luminous high-redshift quasars (3.3 < z < 5.1)
to measure the mass of their super-massive black holes (SMBH) and compare, for
the first time, results based on CIV, MgII, and Hbeta emission lines at
high-redshifts. Assuming gravitationally bound orbits as dominant broad-line
region gas motion, we determine black hole masses in the range of M_bh = 2
times 10^8 M_sun up to M_bh = 4 times 10^10 M_sun. While the black hole mass
estimates based on CIV and Hbeta agree well, MgII typically indicates a factor
of lower SMBH masses. A flatter slope of the Hbeta radius -
luminosity relation, a possibly steeper slope of the MgII radius - luminosity
relation, and a slightly larger radius of the MgII BLR than for Hbeta could
relax the discrepancy. In spite of these uncertainties, the CIV, MgII, and
Hbeta emission lines consistently indicate super-massive black hole masses of
several times 10^9 M_sun at redshifts up to z = 5.1. Assuming logarithmic
growth by spherical accretion with a mass to energy conversion efficiency of
epsilon = 0.1 and an Eddington ratio L_bol / L_edd calculated for each quasar
individually, we estimate black hole growth-times of the order of several ~100
Myr which are smaller than the age of the universe at the corresponding
redshift. Assuming high-mass seed black holes (M_bh^seed = 10^3 to 10^5 M_sun)
the SMBHs in the z = 3.5 quasars began to grow at redshifts z > 4, while for
the quasars with z > 4.5 they started at z = 6 to 10. These estimated time
scales for forming SMBHs at high redshifts, together with previous studies
indicating high quasar metallicities, suggest that the main SMBH growth phase
occurs roughly contemporaneously with a period of violent and extensive star
formation in proto-galactic nuclei.Comment: 26 pages, 4 figures. ApJ, accepted, Vol.611 (Aug20
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