1,654 research outputs found
Nearby Gas-Rich Low Surface Brightness Galaxies
We examine the Fisher-Tully cz<1000 km/s galaxy sample to determine whether
it is a complete and representative sample of all galaxy types, including low
surface brightness populations, as has been recently claimed. We find that the
sample is progressively more incomplete for galaxies with (1) smaller physical
diameters at a fixed isophote and (2) lower HI masses. This is likely to lead
to a significant undercounting of nearby gas-rich low surface brightness
galaxies. However, through comparisons to other samples we can understand how
the nearby galaxy counts need to be corrected, and we see some indications of
environmental effects that probably result from the local high density of
galaxies.Comment: 12 page, 2 figures, to appear in Ap
Galaxy-galaxy(-galaxy) lensing as a sensitive probe of galaxy evolution
The gravitational lensing effect provides various ways to study the mass
environment of galaxies. We investigate how galaxy-galaxy(-galaxy) lensing can
be used to test models of galaxy formation and evolution. We consider two
semi-analytic galaxy formation models based on the Millennium Run N-body
simulation: the Durham model by Bower et al. (2006) and the Garching model by
Guo et al. (2011). We generate mock lensing observations for the two models,
and then employ Fast Fourier Transform methods to compute second- and
third-order aperture statistics in the simulated fields for various galaxy
samples. We find that both models predict qualitatively similar aperture
signals, but there are large quantitative differences. The Durham model
predicts larger amplitudes in general. In both models, red galaxies exhibit
stronger aperture signals than blue galaxies. Using these aperture measurements
and assuming a linear deterministic bias model, we measure relative bias ratios
of red and blue galaxy samples. We find that a linear deterministic bias is
insufficient to describe the relative clustering of model galaxies below ten
arcmin angular scales. Dividing galaxies into luminosity bins, the aperture
signals decrease with decreasing luminosity for brighter galaxies, but increase
again for fainter galaxies. This increase is likely an artifact due to too many
faint satellite galaxies in massive group and cluster halos predicted by the
models. Our study shows that galaxy-galaxy(-galaxy) lensing is a sensitive
probe of galaxy evolution.Comment: 11 pages, 8 figures, accepted in A&
Relationship between and implications of the isotope and pressure effects on transition temperature, penetration depths and conductivities
It is shown that the empirical relations between transition temperature,
normal state conductivity linearly extrapolated to the value at the transition
temperature, zero temperature penetration depths, etc., as observed in a rich
variety of cuprate superconductors, are remarkably consistent with the
universal critical properties of anisotropic systems which fall into the 3D-XY
universality class and undergo a crossover to a quantum critical point in 2D.
The variety includes n- and p-type cuprates, comprises the underdoped and
overdoped regimes and the consistency extends up to six decades in the scaling
variables. The resulting scaling relations for the oxygen isotope and
hydrostatic pressure effects agree with the experimental data and reveal that
these effects originate from local lattice distortions preserving the volume of
the unit cell. These observations single out 3D and anisotropic microscopic
models which incorporate local lattice distortions, fall in the experimentally
accessible regime into the 3D-XY universality class, and incorporate the
crossover to 2D quantum criticality where superconductivity disappears.Comment: 19 pages, 17 figure
Aquilegia, Vol. 35 No. 4, Winter 2011: Newsletter of the Colorado Native Plant Society
https://epublications.regis.edu/aquilegia/1109/thumbnail.jp
An open and parallel multiresolution framework using block-based adaptive grids
A numerical approach for solving evolutionary partial differential equations
in two and three space dimensions on block-based adaptive grids is presented.
The numerical discretization is based on high-order, central finite-differences
and explicit time integration. Grid refinement and coarsening are triggered by
multiresolution analysis, i.e. thresholding of wavelet coefficients, which
allow controlling the precision of the adaptive approximation of the solution
with respect to uniform grid computations. The implementation of the scheme is
fully parallel using MPI with a hybrid data structure. Load balancing relies on
space filling curves techniques. Validation tests for 2D advection equations
allow to assess the precision and performance of the developed code.
Computations of the compressible Navier-Stokes equations for a temporally
developing 2D mixing layer illustrate the properties of the code for nonlinear
multi-scale problems. The code is open source
Mapping dark matter with cosmic magnification
We develop a new tool to generate statistically precise dark matter maps from
the cosmic magnification of galaxies with distance estimates. We show how to
overcome the intrinsic clustering problem using the slope of the luminosity
function, because magnificability changes strongly over the luminosity
function, while intrinsic clustering only changes weakly. This may allow
precision cosmology beyond most current systematic limitations. SKA is able to
reconstruct projected matter density map at smoothing scale with
S/N, at the rate of 200-4000 deg per year, depending on the
abundance and evolution of 21cm emitting galaxies. This power of mapping dark
matter is comparable to, or even better than that of cosmic shear from deep
optical surveys or 21cm surveys.Comment: 4 pages, 1 figures. Discussions added. PRL accepte
The clustering of Luminous Red Galaxies around MgII absorbers
We study the cross-correlation between 212 MgII quasar absorption systems and
\~20,000 Luminous Red Galaxies (LRGs) selected from the Sloan Digital Sky
Survey Data Release 1 in the redshift range 0.4<z<0.8. The MgII systems were
selected to have 2796 & 2803 rest-frame equivalent widths >=1.0 Angstrom and
identifications confirmed by the FeII 2600 or MgI 2852 lines. Over comoving
scales 0.05--13 h^-1 Mpc, the MgII--LRG cross-correlation has an amplitude
0.69+/-0.09 times that of the LRG--LRG auto-correlation. Since LRGs have
halo-masses greater than 3.5 x 10^12 solar masses for M_R<-21, this relative
amplitude implies that the absorber host-galaxies have halo-masses greater than
2--8 x 10^11 Msun. For 10^13 Msun LRGs, the absorber host-galaxies have
halo-masses 0.5--2.5 x 10^12 Msun. Our results appear consistent with those of
Steidel et al. (1994) who found that MgII absorbers with W_r>=0.3 Angstrom are
associated with ~0.7 L^*_B galaxies.Comment: 7 pages, 3 figs; Accepted for publication in MNRAS Letters; Extended
version with Appendix; Text version of MgII absorber catalogue (Table 1) can
be found at http://www.ast.cam.ac.uk/~mim/pub.html. Minor changes to match
the published tex
Noisy weak-lensing convergence peak statistics near clusters of galaxies and beyond
Taking into account noise from intrinsic ellipticities of source galaxies, in
this paper, we study the peak statistics in weak-lensing convergence maps
around clusters of galaxies and beyond. We emphasize how the noise peak
statistics is affected by the density distribution of nearby clusters, and also
how cluster-peak signals are changed by the existence of noise. These are the
important aspects to be understood thoroughly in weak-lensing analyses for
individual clusters as well as in cosmological applications of weak-lensing
cluster statistics. We adopt Gaussian smoothing with the smoothing scale
in our analyses. It is found that the noise peak
distribution near a cluster of galaxies depends sensitively on the density
profile of the cluster. For a cored isothermal cluster with the core radius
, the inner region with appears noisy containing on average
peaks with for and the true peak
height of the cluster , where denotes the convergence signal to
noise ratio. For a NFW cluster of the same mass and the same central , the
average number of peaks with within is . Thus a
high peak corresponding to the main cluster can be identified more cleanly in
the NFW case. In the outer region with , the number of high
noise peaks is considerably enhanced in comparison with that of the pure noise
case without the nearby cluster. (abridged)Comment: 10 figures, ApJ in pres
GaBoDS: The Garching-Bonn Deep Survey: VII. Probing galaxy bias using weak gravitational lensing
[ABRIDGED] The weak gravitational lensing effect is used to infer matter
density fluctuations within the field-of-view of the Garching-Bonn Deep Survey
(GaBoDS). This information is employed for a statistical comparison of the
galaxy distribution to the total matter distribution. The result of this
comparison is expressed by means of the linear bias factor, b, the ratio of
density fluctuations, and the correlation factor between density
fluctuations. The total galaxy sample is divided into three sub-samples using
R-band magnitudes and the weak lensing analysis is applied separately for each
sub-sample. Together with the photometric redshifts from the related COMBO-17
survey we estimate the typical mean redshifts of these samples with
, respectively. For all three samples, a slight
galaxy anti-bias, b~0.8+-0.1, on scales of a few Mpc/h is found; the bias
factor shows evidence for a slight scale-dependence. The correlation between
galaxy and (dark) matter distribution is high, r~0.6+-0.2, indicating a
non-linear or/and stochastic biasing relation between matter and galaxies.
Between the three samples no significant evolution with redshift is found.Comment: 22 pages, 11 figures, LaTeX, accepted by A&A; estimates for the
uncertainties in the galaxy redshift distribution were added, new Section 4.4
on statistical errors in the galaxy bias calibration factor
The overdensities of galaxy environments as a function of luminosity and color
We study the mean environments of galaxies in the Sloan Digital Sky Survey as
a function of rest-frame luminosity and color. Overdensities in galaxy number
are estimated in and spheres
centered on galaxies taken from the SDSS spectroscopic sample. We
find that, at constant color, overdensity is independent of luminosity for
galaxies with the blue colors of spirals. This suggests that, at fixed
star-formation history, spiral-galaxy mass is a very weak function of
environment. Overdensity does depend on luminosity for galaxies with the red
colors of early types; both low-luminosity and high-luminosity red galaxies are
found to be in highly overdense regions.Comment: submitted to ApJ
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