632 research outputs found
Longitudinal patterns in an Arkansas River Valley stream: an Application of the River Continuum Concept
The River Continuum Concept (RCC) provides the framework for studying how lotic ecosystems vary from headwater streams to large rivers. The RCC was developed in streams in eastern deciduous forests of North America, but watershed characteristics and land uses differ across ecoregions, presenting unique opportunities to study how predictions of the RCC may differ across regions. Additionally, RCC predictions may vary due to the influence of fishes, but few studies have used fish taxa as a metric for evaluating predictions of the RCC. Our goal was to determine if RCC predictions for stream orders 1 through 5 were supported by primary producer, macroinvertebrate, and fish communities in Cadron Creek of the Arkansas River Valley. We sampled chlorophyll a, macroinvertebrates, and fishes at five stream reaches across a gradient of watershed size. Contrary to RCC predictions, chlorophyll a did not increase in concentration with catchment size. As the RCC predicts, fish and macroinvertebrate diversity increased with catchment size. Shredding and collecting macroinvertebrate taxa supported RCC predictions, respectively decreasing and increasing in composition as catchment area increased. Herbivorous and predaceous fish did not follow RCC predictions; however, surface-water column feeding fish were abundant at all sites as predicted. We hypothesize some predictions of the RCC were not supported in headwater reaches of this system due to regional differences in watershed characteristics and altered resource availability due to land use surrounding sampling sites
Constraining the LRG Halo Occupation Distribution using Counts-in-Cylinders
The low number density of the Sloan Digital Sky Survey (SDSS) Luminous Red
Galaxies (LRGs) suggests that LRGs occupying the same dark matter halo can be
separated from pairs occupying distinct dark matter halos with high fidelity.
We present a new technique, Counts-in-Cylinders (CiC), to constrain the
parameters of the satellite contribution to the LRG Halo-Occupation
Distribution (HOD). For a fiber collision-corrected SDSS spectroscopic LRG
subsample at 0.16 < z < 0.36, we find the CiC multiplicity function is fit by a
halo model where the average number of satellites in a halo of mass M is
= ((M - Mcut)/M1)^alpha with Mcut = 5.0 +1.5/-1.3 (+2.9/-2.6) X 10^13
Msun, M1 = 4.95 +0.37/-0.26 (+0.79/-0.53) X 10^14 Msun, and alpha = 1.035
+0.10/-0.17 (+0.24/-0.31) at the 68% and 95% confidence levels using a WMAP3
cosmology and z=0.2 halo catalog.
Our method tightly constrains the fraction of LRGs that are satellite
galaxies, 6.36 +0.38/-0.39, and the combination Mcut/10^{14} Msun + alpha =
1.53 +0.08/-0.09 at the 95% confidence level. We also find that mocks based on
a halo catalog produced by a spherical overdensity (SO) finder reproduce both
the measured CiC multiplicity function and the projected correlation function,
while mocks based on a Friends-of-Friends (FoF) halo catalog has a deficit of
close pairs at ~1 Mpc/h separations. Because the CiC method relies on higher
order statistics of close pairs, it is robust to the choice of halo finder. In
a companion paper we will apply this technique to optimize Finger-of-God (FOG)
compression to eliminate the 1-halo contribution to the LRG power spectrum.Comment: 40 pages, 9 figures, submitted to Astrophysical Journa
The triggering probability of radio-loud AGN: A comparison of high and low excitation radio galaxies in hosts of different colors
Low luminosity radio-loud active galactic nuclei (AGN) are generally found in
massive red elliptical galaxies, where they are thought to be powered through
gas accretion from their surrounding hot halos in a radiatively inefficient
manner. These AGN are often referred to as "low-excitation" radio galaxies
(LERGs). When radio-loud AGN are found in galaxies with a young stellar
population and active star formation, they are usually high-power
radiatively-efficient radio AGN ("high-excitation", HERG). Using a sample of
low-redshift radio galaxies identified within the Sloan Digital Sky Survey
(SDSS), we determine the fraction of galaxies that host a radio-loud AGN,
, as a function of host galaxy stellar mass, , star formation
rate, color (defined by the 4000 \angstrom break strength), radio luminosity
and excitation state (HERG/LERG).
We find the following: 1. LERGs are predominantly found in red galaxies. 2.
The radio-loud AGN fraction of LERGs hosted by galaxies of any color follows a
power law. 3. The fraction of red galaxies
hosting a LERG decreases strongly for increasing radio luminosity. For massive
blue galaxies this is not the case. 4. The fraction of green galaxies hosting a
LERG is lower than that of either red or blue galaxies, at all radio
luminosities. 5. The radio-loud AGN fraction of HERGs hosted by galaxies of any
color follows a power law. 6. HERGs have a
strong preference to be hosted by green or blue galaxies. 7. The fraction of
galaxies hosting a HERG shows only a weak dependence on radio luminosity cut.
8. For both HERGs and LERGs, the hosting probability of blue galaxies shows a
strong dependence on star formation rate. This is not observed in galaxies of a
different color.[abridged]Comment: 7 pages, 6 figure
New Approaches To Photometric Redshift Prediction Via Gaussian Process Regression In The Sloan Digital Sky Survey
Expanding upon the work of Way and Srivastava 2006 we demonstrate how the use
of training sets of comparable size continue to make Gaussian process
regression (GPR) a competitive approach to that of neural networks and other
least-squares fitting methods. This is possible via new large size matrix
inversion techniques developed for Gaussian processes (GPs) that do not require
that the kernel matrix be sparse. This development, combined with a
neural-network kernel function appears to give superior results for this
problem. Our best fit results for the Sloan Digital Sky Survey (SDSS) Main
Galaxy Sample using u,g,r,i,z filters gives an rms error of 0.0201 while our
results for the same filters in the luminous red galaxy sample yield 0.0220. We
also demonstrate that there appears to be a minimum number of training-set
galaxies needed to obtain the optimal fit when using our GPR rank-reduction
methods. We find that morphological information included with many photometric
surveys appears, for the most part, to make the photometric redshift evaluation
slightly worse rather than better. This would indicate that most morphological
information simply adds noise from the GP point of view in the data used
herein. In addition, we show that cross-match catalog results involving
combinations of the Two Micron All Sky Survey, SDSS, and Galaxy Evolution
Explorer have to be evaluated in the context of the resulting cross-match
magnitude and redshift distribution. Otherwise one may be misled into overly
optimistic conclusions.Comment: 32 pages, ApJ in Press, 2 new figures, 1 new table of comparison
methods, updated discussion, references and typos to reflect version in Pres
Properties of Disks and Bulges of Spiral and Lenticular Galaxies in the Sloan Digital Sky Survey
A bulge-disk decomposition is made for 737 spiral and lenticular galaxies
drawn from a SDSS galaxy sample for which morphological types are estimated. We
carry out the bulge-disk decomposition using the growth curve fitting method.
It is found that bulge properties, effective radius, effective surface
brightness, and also absolute magnitude, change systematically with the
morphological sequence; from early to late types, the size becomes somewhat
larger, and surface brightness and luminosity fainter. In contrast disks are
nearly universal, their properties remaining similar among disk galaxies
irrespective of detailed morphologies from S0 to Sc. While these tendencies
were often discussed in previous studies, the present study confirms them based
on a large homogeneous magnitude-limited field galaxy sample with morphological
types estimated. The systematic change of bulge-to-total luminosity ratio,
, along the morphological sequence is therefore not caused by disks but
mostly by bulges. It is also shown that elliptical galaxies and bulges of
spiral galaxies are unlikely to be in a single sequence. We infer the stellar
mass density (in units of the critical mass density) to be 0.0021 for
spheroids, i.e., elliptical galaxies plus bulges of spiral galaxies, and
0.00081 for disks.Comment: 30 pages, 9 figure
Reducing Zero-point Systematics in Dark Energy Supernova Experiments
We study the effect of filter zero-point uncertainties on future supernova
dark energy missions. Fitting for calibration parameters using simultaneous
analysis of all Type Ia supernova standard candles achieves a significant
improvement over more traditional fit methods. This conclusion is robust under
diverse experimental configurations (number of observed supernovae, maximum
survey redshift, inclusion of additional systematics). This approach to
supernova fitting considerably eases otherwise stringent mission calibration
requirements. As an example we simulate a space-based mission based on the
proposed JDEM satellite; however the method and conclusions are general and
valid for any future supernova dark energy mission, ground or space-based.Comment: 30 pages,8 figures, 5 table, one reference added, submitted to
Astroparticle Physic
Two novel approaches for photometric redshift estimation based on SDSS and 2MASS databases
We investigate two training-set methods: support vector machines (SVMs) and
Kernel Regression (KR) for photometric redshift estimation with the data from
the Sloan Digital Sky Survey Data Release 5 and Two Micron All Sky Survey
databases. We probe the performances of SVMs and KR for different input
patterns. Our experiments show that the more parameters considered, the
accuracy doesn't always increase, and only when appropriate parameters chosen,
the accuracy can improve. Moreover for different approaches, the best input
pattern is different. With different parameters as input, the optimal bandwidth
is dissimilar for KR. The rms errors of photometric redshifts based on SVM and
KR methods are less than 0.03 and 0.02, respectively. Finally the strengths and
weaknesses of the two approaches are summarized. Compared to other methods of
estimating photometric redshifts, they show their superiorities, especially KR,
in terms of accuracy.Comment: accepted for publication in ChJA
Distant field BHB stars and the mass of the Galaxy II: Photometry and spectroscopy of UKST candidates 16<B<19.5, 11<R<52 kpc
This is the second in a series of papers presenting a new calculation of the
mass of the Galaxy based on radial velocities and distances for a sample of
faint 16 < B < 21.3 field blue horizontal-branch (BHB) stars. We present
accurate BV CCD photometry and spectra for 142 candidate A-type stars selected
from ub_jr photometry of UK Schmidt telescope plates in six
high-Galactic-latitude fields. Classification of these candidates produces a
sample of 60 BHB stars at distances of 11-52 kpc from the Sun (mean 28 kpc),
with heliocentric line-of-sight velocities accurate to 15 km/s, and distance
errors < 10%. We provide a summary table listing coordinates and velocities of
these stars. The measured dispersion of the radial component of the
Galactocentric velocity for this sample is 108+-10 km/s, in agreement with a
recent study of the distant halo by Sirko and coworkers. Measurements of the Ca
II K line indicate that nearly all the stars are metal-poor with a mean [Fe/H]
= -1.8 with dispersion 0.5. Subsequent papers will describe a second survey of
BHBs to heliocentric distances 70 < R < 125 kpc and present a new estimate of
the mass of the Galaxy.Comment: 16 pages, 15 figures. Accepted for publication in MNRA
Faint NUV/FUV Standards from Swift/UVOT, GALEX and SDSS Photometry
At present, the precision of deep ultraviolet photometry is somewhat limited
by the dearth of faint ultraviolet standard stars. In an effort to improve this
situation, we present a uniform catalog of eleven new faint (u sim17)
ultraviolet standard stars. High-precision photometry of these stars has been
taken from the Sloan Digital Sky Survey and Galaxy Evolution Explorer and
combined with new data from the Swift Ultraviolet Optical Telescope to provide
precise photometric measures extending from the Near Infrared to the Far
Ultraviolet. These stars were chosen because they are known to be hot (20,000 <
T_eff < 50,000 K) DA white dwarfs with published Sloan spectra that should be
photometrically stable. This careful selection allows us to compare the
combined photometry and Sloan spectroscopy to models of pure hydrogen
atmospheres to both constrain the underlying properties of the white dwarfs and
test the ability of white dwarf models to predict the photometric measures. We
find that the photometry provides good constraint on white dwarf temperatures,
which demonstrates the ability of Swift/UVOT to investigate the properties of
hot luminous stars. We further find that the models reproduce the photometric
measures in all eleven passbands to within their systematic uncertainties.
Within the limits of our photometry, we find the standard stars to be
photometrically stable. This success indicates that the models can be used to
calibrate additional filters to our standard system, permitting easier
comparison of photometry from heterogeneous sources. The largest source of
uncertainty in the model fitting is the uncertainty in the foreground reddening
curve, a problem that is especially acute in the UV.Comment: Accepted for publication in Astrophysical Journal. 31 pages, 13
figures, electronic tables available from ApJ or on reques
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