470 research outputs found
Intrinsic Axis Ratio Distribution of Early-type Galaxies From Sloan Digital Sky Survey
Using Sloan Digital Sky Survey Data Release 5, we have investigated the
intrinsic axis ratio distribution (ARD) for early-type galaxies. We have
constructed a volume-limited sample of 3,922 visually-inspected early-type
galaxies at carefully considering sampling biases
caused by the galaxy isophotal size and luminosity. We attempt to de-project
the observed ARD into three-dimensional types (oblate, prolate, and triaxial),
which are classified in terms of triaxiality. We confirm that no linear
combination of -distributed axis ratios of the three types can
reproduce the observed ARD. However, using Gaussian intrinsic distributions, we
have found reasonable fits to the data with preferred mean axis ratios for
oblate, prolate, and triaxial (triaxials in two axis ratios), where the fractions of
oblate, prolate and triaxial types are
\textrm{O:P:T}=0.29^{\pm0.09}:0.26^{\pm0.11}:0.45^{\pm0.13}-23.3 < M_r \leq -21.2-21.2 < M_r <-19.3$) sample does. Oblate is
relatively more abundant among the less luminous galaxies. Interestingly, the
preferences of axis ratios for triaxial types in the two luminosity classes are
remarkably similar. We have not found any significant influence of the local
galaxy number density on ARD. We show that the results can be seriously
affected by the details in the data selection and type classification scheme.
Caveats and implications on galaxy formation are discussed.Comment: 9 pages, 11 figures, Accepted for publication in Ap
On hydrogen bond correlations at high pressures
In situ high pressure neutron diffraction measured lengths of O H and H O
pairs in hydrogen bonds in substances are shown to follow the correlation
between them established from 0.1 MPa data on different chemical compounds. In
particular, the conclusion by Nelmes et al that their high pressure data on ice
VIII differ from it is not supported. For compounds in which the O H stretching
frequencies red shift under pressure, it is shown that wherever structural data
is available, they follow the stretching frequency versus H O (or O O) distance
correlation. For compounds displaying blue shifts with pressure an analogy
appears to exist with improper hydrogen bonds.Comment: 12 pages,4 figure
The impact of constructive operating lease capitalisation on key accounting ratios
Current UK lease accounting regulation does not require operating leases to be capitalised in the accounts of lessees, although this is likely to change with the publication of FRS 5. This study conducts a prospective analysis of the effects of such a change. The potential magnitude of the impact of lease capitalisation upon individual users' decisions, market valuations, company cash flows, and managers' behaviour can be indicated by the effect on key accounting ratios, which are employed in decision-making and in financial contracts. The capitalised value of operating leases is estimated using a method similar to that suggested by Imhoff, Lipe and Wright (1991), adapted for the UK accounting and tax environment, and developed to incorporate company-specific assumptions. Results for 1994 for a random sample of 300 listed UK companies show that, on average, the unrecorded long-term liability represented 39% of reported long-term debt, while the unrecorded asset represented 6% of total assets. Capitalisation had a significant impact (at the 1% level) on six of the nine selected ratios (profit margin, return on assets, asset turnover, and three measures of gearing). Moreover, the Spearman rank correlation between each ratio before and after capitalisation revealed that the ranking of companies changed markedly for gearing measures in particular. There were significant inter-industry variations, with the services sector experiencing the greatest impact. An analysis of the impact of capitalisation over the five-year period from 1990 to 1994 showed that capitalisation had the greatest impact during the trough of the recession. Results were shown to be robust with respect to key assumptions of the capitalisation method. These findings contribute to the assessment of the economic consequences of a policy change requiring operating lease capitalisation. Significant changes in the magnitude of key accounting ratios and a major shift in company performance rankings suggest that interested parties' decisions and company cash flows are likely to be affected
Red riding on hood: Exploring how galaxy colour depends on environment
Galaxy populations are known to exhibit a strong colour bimodality,
corresponding to blue star-forming and red quiescent subpopulations. The
relative abundance of the two populations has been found to vary with stellar
mass and environment. In this paper, we explore the effect of environment
considering different types of measurements. We choose a sample of
galaxies with from the Galaxy And Mass Assembly survey. We
study the dependence of the fraction of red galaxies on different measures of
the local environment as well as the large-scale "geometric" environment
defined by density gradients in the surround- ing cosmic web. We find that the
red galaxy fraction varies with the environment at fixed stellar mass. The red
fraction depends more strongly on local environmental measures than on
large-scale geometric environment measures. By comparing the different
environmental densities, we show that no density measurement fully explains the
observed environmental red fraction variation, suggesting the different
measures of environmental density contain different information. We test
whether the local environmental measures, when combined together, can explain
all the observed environmental red fraction variation. The geometric
environment has a small residual effect, and this effect is larger for voids
than any other type of geometric environment. This could provide a test of the
physics applied to cosmological-scale galaxy evolution simulations as it
combines large-scale effects with local environmental impact.Comment: Accepted for publication in MNRAS; 16 pages; 10 figures; 2 tables
The Clustering of Colour Selected Galaxies
We present measurements of the angular correlation function of galaxies
selected from a B_J=23.5 multicolour survey of two 5 degree by 5 degree fields
located at high galactic latitudes. The galaxy catalogue of approximately
400,000 galaxies is comparable in size to catalogues used to determine the
galaxy correlation function at low-redshift. Measurements of the z=0.4
correlation function at large angular scales show no evidence for a break from
a power law though our results are not inconsistent with a break at >15 Mpc.
Despite the large fields-of-view, there are large discrepancies between the
measurements of the correlation function in each field, possibly due to dwarf
galaxies within z=0.11 clusters near the South Galactic Pole.
Colour selection is used to study the clustering of galaxies z=0 to z=0.4.
The galaxy correlation function is found to strongly depend on colour with red
galaxies more strongly clustered than blue galaxies by a factor of 5 at small
scales. The slope of the correlation function is also found to vary with colour
with gamma=1.8 for red galaxies while gamma=1.5 for blue galaxies. The
clustering of red galaxies is consistently strong over the entire magnitude
range studied though there are large variations between the two fields. The
clustering of blue galaxies is extremely weak over the observed magnitude range
with clustering consistent with r_0=2 Mpc. This is weaker than the clustering
of late-type galaxies in the local Universe and suggests galaxy clustering is
more strongly correlated with colour than morphology. This may also be the
first detection of a substantial low redshift galaxy population with clustering
properties similar to faint blue galaxies.Comment: Accepted for publication in MNRAS. 13 pages, 20 figure
The Optical, Infrared and Radio Properties of Extragalactic Sources Observed by SDSS, 2MASS and FIRST Surveys
We positionally match sources observed by the Sloan Digital Sky Survey
(SDSS), the Two Micron All Sky Survey (2MASS), and the Faint Images of the
Radio Sky at Twenty-cm (FIRST) survey. Practically all 2MASS sources are
matched to an SDSS source within 2 arcsec; ~11% of them are optically resolved
galaxies and the rest are dominated by stars. About 1/3 of FIRST sources are
matched to an SDSS source within 2 arcsec; ~80% of these are galaxies and the
rest are dominated by quasars. Based on these results, we project that by the
completion of these surveys the matched samples will include about 10^7 stars
and 10^6 galaxies observed by both SDSS and 2MASS, and about 250,000 galaxies
and 50,000 quasars observed by both SDSS and FIRST. Here we present a
preliminary analysis of the optical, infrared and radio properties for the
extragalactic sources from the matched samples. In particular, we find that the
fraction of quasars with stellar colors missed by the SDSS spectroscopic survey
is probably not larger than ~10%, and that the optical colors of radio-loud
quasars are ~0.05 mag. redder (with 4-sigma significance) than the colors of
radio-quiet quasars.Comment: 10 pages, 6 color figures, presented at IAU Colloquium 184. AGN
Survey
Constructing Dirac linear fermions in terms of non-linear Heisenberg spinors
We show that the massive (or massless) neutrinos can be described as special
states of Heisenberg nonlinear spinors. As a by-product of this decomposition a
particularly attractive consequence appears: the possibility of relating the
existence of only three species of mass-less neutrinos to such internal
non-linear structure. At the same time it allows the possibility that neutrino
oscillation can occurs even for massless neutrinos
Locally Biased Galaxy Formation and Large Scale Structure
We examine the influence of the morphology-density(MD) relation and a wide
range of simple models for biased galaxy formation on statistical measures of
large scale structure. We contrast the behavior of local biasing models, in
which the efficiency of galaxy formation is determined by density, geometry, or
velocity dispersion of the local mass distribution, with that of non-local
biasing models, in which galaxy formation is modulated coherently over scales
larger than the galaxy correlation length. If morphological segregation of
galaxies is governed by a local MD relation, then the correlation function of
E/S0 galaxies should be steeper and stronger than that of spiral galaxies on
small scales, as observed, while on large scales the correlation functions of
E/S0 and spiral galaxies should have the same shape but different amplitudes.
Similarly, all of our local bias models produce scale-independent amplification
of the correlation function and power spectrum in the linear and mildly
non-linear regimes; only a non-local biasing mechanism can alter the shape of
the power spectrum on large scales. Moments of the biased galaxy distribution
retain the hierarchical pattern of the mass moments, but biasing alters the
values and scale-dependence of the hierarchical amplitudes S3 and S4.
Pair-weighted moments of the galaxy velocity distribution are sensitive to the
details of the biasing prescription. The non-linearity of the relation between
galaxy density and mass density depends on the biasing prescription and the
smoothing scale, and the scatter in this relation is a useful diagnostic of the
physical parameters that determine the bias. Although the sensitivity of galaxy
clustering statistics to the details of biasing is an obstacle to testing
cosmological models, it is an asset for testing galaxy formation theories.Comment: 47 pages including 17 Figures, submitted to Ap
The Luminosity Function Of Field Galaxies And Its Evolution Since z=1
We present the B-band luminosity function and comoving space and luminosity
densities for a sample of 2779 I-band selected field galaxies based on
multi-color data from the CADIS survey. The sample is complete down to I_815 =
22 without correction and with completeness correction extends to I_815=23.0.
By means of a new multi-color analysis the objects are classified according to
their spectral energy distributions (SEDs) and their redshifts are determined
with typical errors of delta z <= 0.03. We have split our sample into four
redshift bins between z=0.1 and z=1.04 and into three SED bins E-Sa,Sa-Sc and
starbursting (emission line) galaxies. The evolution of the luminosity function
is clearly differential with SED. The normalization phi* of luminosity function
for the E-Sa galaxies decreases towards higher redshift, and we find evidence
that the comoving galaxy space density decreases with redshift as well. In
contrast, we find phi* and the comoving space density increasing with redshift
for the Sa-Sc galaxies. For the starburst galaxies we find a steepening of the
luminosity function at the faint end and their comoving space density increases
with redshift.Comment: 15 pages, 14 figures, accepted by Astronomy&Astrophysic
Galaxy And Mass Assembly (GAMA) : galaxy close pairs, mergers and the future fate of stellar mass
ASGR acknowledges STFC and SUPA funding that were used to do this work. GAMA is funded by the STFC (UK), the ARC (Australia), the AAO and the participating institutions.We use a highly complete subset of the Galaxy And Mass Assembly II (GAMA-II) redshift sample to fully describe the stellar mass dependence of close pairs and mergers between 10(8) and 10(12)M(circle dot). Using the analytic form of this fit we investigate the total stellar mass accreting on to more massive galaxies across all mass ratios. Depending on how conservatively we select our robust merging systems, the fraction of mass merging on to more massive companions is 2.0-5.6 per cent. Using the GAMA-II data we see no significant evidence for a change in the close pair fraction between redshift z = 0.05 and 0.2. However, we find a systematically higher fraction of galaxies in similar mass close pairs compared to published results over a similar redshift baseline. Using a compendium of data and the function gamma(M) = A(1 + z)(m) to predict the major close pair fraction, we find fitting parameters of A = 0.021 +/- 0.001 and m = 1.53 +/- 0.08, which represents a higher low-redshift normalization and shallower power-law slope than recent literature values. We find that the relative importance of in situ star formation versus galaxy merging is inversely correlated, with star formation dominating the addition of stellar material below M* and merger accretion events dominating beyond M*. We find mergers have a measurable impact on the whole extent of the galaxy stellar mass function (GSMF), manifest as a deepening of the 'dip' in the GSMF over the next similar to Gyr and an increase in M* by as much as 0.01-0.05 dex.Publisher PDFPeer reviewe
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