3,152 research outputs found
Gravitational lens magnification by Abell 1689: Distortion of the background galaxy luminosity function
Gravitational lensing magnifies the luminosity of galaxies behind the lens.
We use this effect to constrain the total mass in the cluster Abell 1689 by
comparing the lensed luminosities of background galaxies with the luminosity
function of an undistorted field. Since galaxies are assumed to be a random
sampling of luminosity space, this method is not limited by clustering noise.
We use photometric redshift information to estimate galaxy distance and
intrinsic luminosity. Knowing the redshift distribution of the background
population allows us to lift the mass/background degeneracy common to lensing
analysis. In this paper we use 9 filters observed over 12 hours with the Calar
Alto 3.5m telescope to determine the redshifts of 1000 galaxies in the field of
Abell 1689. Using a complete sample of 151 background galaxies we measure the
cluster mass profile. We find that the total projected mass interior to
0.25h^(-1)Mpc is (0.48 +/- 0.16) * 10^(15)h^(-1) solar masses, where our error
budget includes uncertainties from the photometric redshift determination, the
uncertainty in the off-set calibration and finite sampling. This result is in
good agreement with that found by number count and shear-based methods and
provides a new and independent method to determine cluster masses.Comment: 13 pages, 10 figures. Submitted to MNRAS (10/99); Replacement with 1
page extra text inc. new section, accepted by MNRA
Conical scan impact study. Volume 2: Small local user data processing facility
The impact of a conical scan versus a linear scan multispectral scanner (MSS) instrument on a small local-user data processing facility was studied. User data requirements were examined to determine the unique system rquirements for a low cost ground system (LCGS) compatible with the Earth Observatory Satellite (EOS) system. Candidate concepts were defined for the LCGS and preliminary designs were developed for selected concepts. The impact of a conical scan MSS versus a linear scan MSS was evaluated for the selected concepts. It was concluded that there are valid user requirements for the LCGS and, as a result of these requirements, the impact of the conical scanner is minimal, although some new hardware development for the LCGS is necessary to handle conical scan data
Lens magnification by CL0024+1654 in the U and R band
[ABRIDGED] We estimate the total mass distribution of the galaxy cluster
CL0024+1654 from the measured source depletion due to lens magnification in the
R band. Within a radius of 0.54Mpc/h, a total projected mass of
(8.1+/-3.2)*10^14 M_sol/h (EdS) is measured, which corresponds to a mass-
to-light ratio of M/L(B)=470+/-180. We compute the luminosity function of
CL0024+1654 in order to estimate contamination of the background source counts
from cluster galaxies. Three different magnification-based reconstruction
methods are employed using both local and non-local techniques. We have
modified the standard single power-law slope number count theory to incorporate
a break and applied this to our observations. Fitting analytical magnification
profiles of different cluster models to the observed number counts, we find
that the cluster is best described either by a NFW model with scale radius
r_s=334+/-191 kpc/h and normalisation kappa_s=0.23+/-0.08 or a power-law
profile with slope xi=0.61+/-0.11, central surface mass density
kappa_0=1.52+/-0.20 and assuming a core radius of r_core=35 kpc/h. The NFW
model predicts that the cumulative projected mass contained within a radius R
scales as M(<R)=2.9*10^14*(R/1')^[1.3-0.5lg (R/1')] M_sol/h. Finally, we have
exploited the fact that flux magnification effectively enables us to probe
deeper than the physical limiting magnitude of our observations in searching
for a change of slope in the U band number counts. We rule out both a total
flattening of the counts with a break up to U_AB<=26.6 and a change of slope,
reported by some studies, from dlog N/dm=0.4->0.15 up to U_AB<=26.4 with 95%
confidence.Comment: 19 pages, 12 figures, submitted to A&A. New version includes more
robust U band break analysis and contamination estimates, plus new plot
[NII] fine-structure emission at 122 and 205um in a galaxy at z=2.6: a globally dense star-forming interstellar medium
© 2020. The American Astronomical Society. All rights reserved.We present new observations with the Atacama Large Millimeter/sub-millimeter Array of the 122um and 205um fine-structure line emission of singly-ionised nitrogen in a strongly lensed starburst galaxy at z=2.6. The 122/205um [NII] line ratio is sensitive to electron density, n_e, in the ionised interstellar medium, and we use this to measure n_e~300cm^-3 averaged across the galaxy. This is over an order of magnitude higher than the Milky Way average, but comparable to localised Galactic star-forming regions. Combined with observations of the atomic carbon (CI(1-0)) and carbon monoxide (CO(4-3)) in the same system, we reveal the conditions in this intensely star-forming system. The majority of the molecular interstellar medium has been driven to high density, and the resultant conflagration of star formation produces a correspondingly dense ionised phase, presumably co-located with myriad HII regions that litter the gas-rich disk.Peer reviewedFinal Accepted Versio
Combining high conductivity with complete optical transparency: A band-structure approach
A comparison of the structural, optical and electronic properties of the
recently discovered transparent conducting oxide (TCO), nanoporous Ca12Al14O33,
with those of the conventional TCO's (such as Sc-doped CdO) indicates that this
material belongs conceptually to a new class of transparent conductors. For
this class of materials, we formulate criteria for the successful combination
of high electrical conductivity with complete transparency in the visible
range. Our analysis suggests that this set of requirements can be met for a
group of novel materials called electrides.Comment: 3 pages, 3 figures, submitted for publicatio
Finite Projective Spaces, Geometric Spreads of Lines and Multi-Qubits
Given a (2N - 1)-dimensional projective space over GF(2), PG(2N - 1, 2), and
its geometric spread of lines, there exists a remarkable mapping of this space
onto PG(N - 1, 4) where the lines of the spread correspond to the points and
subspaces spanned by pairs of lines to the lines of PG(N - 1, 4). Under such
mapping, a non-degenerate quadric surface of the former space has for its image
a non-singular Hermitian variety in the latter space, this quadric being {\it
hyperbolic} or {\it elliptic} in dependence on N being {\it even} or {\it odd},
respectively. We employ this property to show that generalized Pauli groups of
N-qubits also form two distinct families according to the parity of N and to
put the role of symmetric operators into a new perspective. The N=4 case is
taken to illustrate the issue.Comment: 3 pages, no figures/tables; V2 - short introductory paragraph added;
V3 - to appear in Int. J. Mod. Phys.
Evolution of the Dark Matter Distribution with 3-D Weak Lensing
We present a direct detection of the growth of large-scale structure, using
weak gravitational lensing and photometric redshift data from the COMBO-17
survey. We use deep R-band imaging of two 0.25 square degree fields, affording
shear estimates for over 52000 galaxies; we combine these with photometric
redshift estimates from our 17 band survey, in order to obtain a 3-D shear
field. We find theoretical models for evolving matter power spectra and
correlation functions, and fit the corresponding shear correlation functions to
the data as a function of redshift. We detect the evolution of the power at the
7.7 sigma level given minimal priors, and measure the rate of evolution for
0<z<1. We also fit correlation functions to our 3-D data as a function of
cosmological parameters sigma_8 and Omega_Lambda. We find joint constraints on
Omega_Lambda and sigma_8, demonstrating an improvement in accuracy by a factor
of 2 over that available from 2D weak lensing for the same area.Comment: 11 pages, 4 figures; submitted to MNRA
On the consistency of scale among experiments, theory, and simulation
As a tool for addressing problems of scale, we consider an evolving approach
known as the thermodynamically constrained averaging theory (TCAT), which has
broad applicability to hydrology. We consider the case of modeling of two-fluid-phase flow in porous media, and we focus on issues of scale as they
relate to various measures of pressure, capillary pressure, and state
equations needed to produce solvable models. We apply TCAT to perform
physics-based data assimilation to understand how the internal behavior
influences the macroscale state of two-fluid porous medium systems. A
microfluidic experimental method and a lattice Boltzmann simulation method
are used to examine a key deficiency associated with standard approaches. In
a hydrologic process such as evaporation, the water content will ultimately
be reduced below the irreducible wetting-phase saturation
determined from experiments. This is problematic since the derived closure
relationships cannot predict the associated capillary pressures for these
states. We demonstrate that the irreducible wetting-phase saturation is an
artifact of the experimental design, caused by the fact that the boundary
pressure difference does not approximate the true capillary pressure. Using
averaging methods, we compute the true capillary pressure for fluid
configurations at and below the irreducible wetting-phase saturation. Results
of our analysis include a state function for the capillary pressure expressed
as a function of fluid saturation and interfacial area
Polarized thermal emission from dust in a galaxy at redshift 2.6
Magnetic fields are fundamental to the evolution of galaxies, playing a key
role in the astrophysics of the interstellar medium and star formation.
Large-scale ordered magnetic fields have been mapped in the Milky Way and
nearby galaxies, but it is not known how early in the Universe such structures
form. Here we report the detection of linearly polarized thermal emission from
dust grains in a strongly lensed, intrinsically luminous galaxy that is forming
stars at a rate more than a thousand times that of the Milky Way at redshift
2.6, within 2.5 Gyr of the Big Bang. The polarized emission arises from the
alignment of dust grains with the local magnetic field. The median polarization
fraction is of order one per cent, similar to nearby spiral galaxies. Our
observations support the presence of a 5 kiloparsec-scale ordered magnetic
field with a strength of around 500uG or lower, orientated parallel to the
molecular gas disk. This confirms that such structures can be rapidly formed in
galaxies, early in cosmic history.Comment: Published in Nature. Online version available at
https://www.nature.com/articles/s41586-023-06346-
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